Supplemental Digital Content is Available in the Text. The aim of this study was to explore video-graded intraoperative risk factors for graft detachment (GD) and rebubbling in Descemet membrane endothelial keratoplasty surgery.Advanced Visualization In Corneal Surgery Evaluation trial. All surgical recordings were assessed by 2 graders using a structured assessment form. A multinominal regression was performed to estimate the independent effect of video-graded intraoperative factors on the incidence of GD and rebubbling. Secondary outcomes are corrected distance visual acuity and endothelial cell density.A post hoc analysis of 65 eyes of 65 pseudophakic subjects with Fuchs endothelial dystrophy that underwent Descemet membrane endothelial keratoplasty surgery as part of the In total, 33 GDs were recorded, of which 17 required rebubbling. No significant predictors for GD or rebubbling were identified. However, the results revealed 2 clinically relevant patterns. An unfavorable graft configuration  and a gas-bubble size smaller than the graft diameter were associated with an increased risk of GD  and rebubbling . Inversely, a larger gas-bubble size was associated with a reduced risk of GD (OR 0.37) and rebubbling (OR 0.36). At 3 and 6 months postoperatively, corrected distance visual acuity was poorer in subjects requiring a rebubbling and endothelial cell density loss was higher in subjects with a partial GD.Our analysis revealed that the gas-bubble size and graft shape/geometry seem to be relevant clinical factors for GD and rebubbling, whereas descemetorhexis difficulty, degree of graft manipulation, graft overlap, and surgical iridectomy were not associated with an increased risk. Only a handful of studies investigated the effect of surgical manipulation during graft unfolding or the effect of variations in intraoperative tissue handling on outcomes, although both are deemed important by surgeons.The underlying cause of GD is multifactorial. A wide range of risk factors have been proposed related to donor and patient characteristics and surgery.Advanced Visualization In Corneal Surgery Evaluation (ADVISE) trial to identify risk factors for GD and rebubbling. The aim of this explorative study was to obtain a better understanding of the impact of surgical factors on the incidence of GD and rebubbling and subsequently offer insights to improve the safety of our surgeries.In this study, we qualitatively and quantitatively analyzed surgical videos from the prospective 27 The study was approved by the Ethics Review Boards in the Netherlands  and Belgium . The details of this trial are previously reported and registered at clinicaltrials.gov (no° NCT03763721).28This article is a post hoc observational analysis of surgical recordings to identify risk factors for GDs and rebubbling procedures of the prospective ADVISE trial, an international noninferiority single-blinded RCT to investigate the utility of intraoperative optical coherence tomography (iOCT) in DMEK surgery. All procedures were performed in accordance with the Declaration of Helsinki, local and national laws regarding research, European directives with respect to privacy, and 2010 CONSORT standards for reporting RCTs.Subjects underwent surgery between December 2018 and April 2021 at the University Medical Center Utrecht (n = 39), University Hospital Leuven (n = 14), or Maastricht University Medical Center (n= 14). Inclusion criteria were pseudophakic adult patients with irreversible corneal endothelial dysfunction resulting from Fuchs endothelial corneal dystrophy, eligible for DMEK surgery. Subjects were excluded if they would undergo human leukocyte antigen-matched keratoplasty, underwent previous keratoplasty, were scheduled for combined phacoemulsification procedures, and had ocular comorbidities other than ocular surface disease, stable open-angle glaucoma, and mild age-related macular degeneration/changes. Only 1 eye per subject was enrolled.28 An optometrist measured the corrected distance visual acuity (CDVA) using an Early Treatment Diabetic Retinopathy Study letter chart at a distance of 4 m, and endothelial cell counts were assessed with specular microscopy .Each patient underwent a comprehensive ophthalmic examination preoperatively and 1 day, 1 week, 1 month, 3 months, and 6 months after surgery. Here, we report the baseline, 3 months, and 6 months measurements in detail. The ophthalmic examination was previously reported.2 and a diameter of 8.5 mm. No graft markings were used. Before surgery, 27 subjects underwent Nd:YAG laser iridotomy at the 6-o'clock position. In the other 38 subjects, surgical iridectomy was performed using a 27-gauge needle and Price hook at the 6-o'clock position after the descemetorhexis during surgery.Donor grafts were allocated by the Dutch Transplant Foundation . The grafts were cultured and provided prepeeled by the ETB-Bislife , with a minimum endothelial cell density (ECD) of 2300 cells/mm28 In short, the procedure consisted of a 9-mm descemetorhexis, and subsequently, the graft was stained and inserted in the anterior chamber using a glass injector through a 2.8-mm incision. A no-touch technique was used to unfold and position the graft. As per randomization of the ADVISE trial, iOCT was not available in half of the cases  and the intraocular pressure was raised above physiological limits  for 8 minutes at the end of surgery. In the other half of the cases , a brief AC fill was performed to adhere the graft and the iOCT was used to check for complete adherence of the graft without overpressurizing the eye. In all cases, air was replaced by sulfur hexafluoride 20% gas, and the size of the gas bubble was reduced to cover the graft . After surgery, patients remained strictly supine for 2 hours at the hospital and were instructed to remain supine for the following 24 hours.All surgical procedures were performed by experienced corneal surgeons . The surgical procedure was standardized because all included cases were part of the ADVISE trial. The study protocol has been reported in detail before; both arms of the trial were combined in this report on video grading.double scroll, loose roll, and unscrolled were coded favorable graft shapes to unfold, whereas the shapes tight roll, taco, and wrinkled were coded unfavorable. Ease of graft unfolding was classified in 4 mutually exclusive ordinal groups depending on the required manipulation and time to unfold/position the graft, as described by Maier et al.14 All manual manipulations of the graft  were recorded and coded in 3 nominal groups: the category external manipulation indicates only corneal swiping/tapping was used to unfold the graft, regardless of the time spent. Indirect internal manipulation refers to bubble bumping or fluid–air exchange to unfold the graft in addition to external manipulation. Direct internal manipulation was scored if the graft was manually unfolded or positioned using surgical instruments in addition to external and indirect internal manipulation. After fixation of the graft with gas, the size of the gas bubble was assessed, compared with the graft size, and coded in 3 nominal groups: a gas-bubble size equal to the graft diameter, larger than the graft diameter, and smaller than the graft diameter. Centering of the graft was determined in relationship to the descemetorhexis area and coded dichotomously; a graft was considered centered if it was completely within the descemetorhexis and decentered if the graft overlapped with the descemetorhexis edge.All surgical video recordings were analyzed by 2 graders (M.B.M. and H.J.) using a standardized assessment form. One grader was masked regarding the clinical outcomes of the surgery. The overall skin-to-skin surgical time and duration of surgical steps  were meticulously recorded. The difficulty of the descemetorhexis was coded in 3 groups based on time . Directly after insertion of the graft into the AC, graft configuration was determined based on geometry and number of folds. As such, 6 distinct shapes were distinguished: double scroll, tight roll, loose roll, taco, unscrolled, and wrinkled . Secondary outcomes are postoperative ECD and CDVA. The Early Treatment Diabetic Retinopathy Study letter score of the CDVA was converted to logarithm of the minimum angle of resolution units by multiplying the number of letters read by −0.02 log units and adding 1.7 log units.30The outcome variables of this study are the incidence of GDs and rebubbling procedures. A GD was defined as any nonadherence of the graft noticeable on slit-lamp examination and AS-OCT imaging  at any time point within 3 months after surgery.Missing observations of CDVA and ECD were considered missing at random and imputed using multiple imputation. Missing measurements of subjects who developed a graft failure were considered missing not at random and not imputed. The number of imputations was equal to the maximum percentage of missing data plus 1. Two surgical recordings were missing, and the results were not imputed.P value <0.05 was considered statistically significant. Internal consistency of the video grading between the 2 graders was assessed using the Cohen kappa.31Here, all cases were video analyzed irrespective of the randomization in the ADVISE trial. Consequences of the randomization  were entered as factors in the multivariable model. Subjects were post hoc assigned in 3 groups: completely attached graft, GD that did not require rebubbling, and GD that required rebubbling. Group differences were analyzed using a one-way ANOVA or Kruskal–Wallis test, as appropriate. Correction for multiple comparisons was performed using the Bonferroni correction. A 2-sided 32 The analysis was not adjusted for randomization used in the trial because no differences between the treatment arms regarding graft unfolding and manipulation were observed in the primary analysis of the trial. All statistical analyses were performed using R statistical software version 4.0.3 .A multivariate multinomial regression analysis was performed to analyze the independent effect of intraoperative factors on the incidence of GD and rebubbling. Predictors included graft manipulation, graft shape, graft centering, gas-bubble size, method of peripheral iridectomy , and overpressure duration. The regression analysis was adjusted for center, to account for differences between surgeons and number of surgeries, and donor age because this may influence scroll tightness.29 One repeated rebubbling was performed during the course of the study. No significant differences regarding the incidence of adverse events were found between the treatment arms nor between centers. Additional details of the ADVISE trial are previously reported, including the rate of adverse events between treatment arms and centers.28A total of 65 eyes of 65 patients were included for analysis. In total, 33 (51%) GDs were recorded over the study period, of which 17 (26%) required rebubbling. Of these 33 detachments, 3 cases underwent retransplantation for primary graft failure, and all 3 cases were preceded by a rebubbling. The average time between surgery and detection of detachment measured 7.54 days , and the average detached area measured 31% of the surface of the graft (range: 8%–100%) as previously reported.31 Baseline patient and donor characteristics are displayed in Table The internal consistency between the 2 graders (M.M. and H.J.) regarding video grading was considered strong .P values contribute little additional value. Although at first glance, analysis of the videos revealed considerable relative differences between the groups regarding the gas-bubble size at the end of surgery and postoperative adverse events, a smaller bubble was more prevalent in cases which subsequently developed a detachment . Inversely, a gas-bubble size greater than the graft diameter was more prevalent in completely attached grafts . The prevalence of an unfavorable graft shape  was higher in cases that developed a GD .The various categories of tissue handling and surgical manipulation did not show significant differences between the 3 post hoc groups. In other words, intraoperative factors of detached grafts and detached grafts requiring rebubbling on average did not differ from uneventful postoperative courses Table . It shouhttp://links.lww.com/ICO/B459). A larger gas bubble at the end of surgery had a lower risk of GD and rebubbling . Inversely, a smaller gas bubble had an increased risk of GD and rebubbling . Second, an unfavorable graft shape was associated with an increased risk of GD and rebubbling , independent of donor age. Other interesting outcomes are that surgical iridectomy was not related to an increased risk of GD and rebubbling . In decentered grafts, there is an apparent overlap between graft and host Descemet–endothelium, by some considered a risk factor for GDs.26 Our analysis did not show a consistent effect of graft decentering on the GD and rebubbling (OR: 1 and 0.77). Direct internal graft manipulation indicated a marginal increased risk of GD and rebubbling (OR: 1.14 and 1.09). Direct internal manipulation can be considered an iatrogenic trauma to the graft, which by some is considered related to unfavorable surgical outcomes, although a relation between ECD loss and internal manipulation was not found (data not shown).16To investigate independent effects and identify potential patterns that predict treatment outcomes, we conceptualized a multinomial regression model including surgical risk factors and confounding factors. No statistically significant predictors were identified in the analysis, although again the same 2 clinically relevant trends were identified: gas-bubble size at the end of surgery and graft shape after insertion  compared with cases with a completely attached graft and the detached grafts requiring a rebubbling. After adjustment for multiple comparisons and correction for baseline donor ECD, the difference between the groups was not significant. Furthermore, at 3 and 6 months postoperatively, subjects who underwent a rebubbling achieved a poorer CDVA compared with the other 2 groups, although this difference was not statistically significant after adjustment for multiple comparisons. A complete overview of postoperative clinical outcomes is shown in Table At 3 and 6 months postoperatively, a significant difference was observed regarding the ECD in cases with a GD  practice pattern variations to identify risk factors for GD and rebubbling. GDs have a notorious multifactorial origin, and several strategies to investigate this are reported, for example, case–control,28 the length of overpressuring did not relate to the incidence of GDs or rebubbling procedures. Another relevant factor in our model was graft configuration, a tissue characteristic that cannot be influenced by the surgeon; an unfavorable graft shape was associated with an increased risk of GD and rebubbling. One could hypothesize that the graft shape is a proxy for overall graft unfolding difficulty, including the associated intraoperative challenges. Still, we found no correlation between the coding of graft shape and the metrics of graft unfolding difficulty  and duration  as suggested by Quilendrino et al and Maier et al.33 Apparently, there is still an unexplained variation in our statistical model that predicts postoperative adverse events.The main findings of this study are that direct manipulation of the graft  is not associated with poor surgical outcome nor was overlap of the graft with host Descemet membrane. The gas-bubble size at the end of surgery did seem clinically relevant: bigger is better in maintaining an attached graft. Commensurate to the primary outcomes of the ADVISE trial,37 However, the causality between direct manual manipulation and detachment of the graft is unclear and evidence limited. Maier et al and Leon et al reported that manual manipulation was associated with a higher incidence of GD, although no significant associations were found.14 In our study, we did not find a higher incidence of adverse events in cases with direct graft manipulation, rather it seemed to have a reduced risk. The direct tissue effects of direct manual manipulation on ECD were not investigated in this study, only the effects on clinically relevant end points of graft adherence.There is limited evidence regarding the causality of surgical decision making and detachment/rebubbling rates. Our results underlines that it is very difficult to predict GD or rebubbling, based on how the surgery faired. Several recommended practices were not supported by our results, such as not directly manipulating the graft and preventing overlap with host Descemet membrane. One of those recommended practices is avoidance of direct manual manipulation of the graft, which may lead to endothelial damage and GD.12 and Tourtas et al.25 Furthermore, Muller et al reported that incomplete removal of Descemet membrane  and ultrastructural changes were related to GD. However, they reported that overlap with full-thickness Descemet membrane did not result in GD on histological images.26 In our study, we did not account for the extent of overlap, and actual complete removal of Descemet membrane layers or other ultrastructural changes were not investigated.In our study, we did not find an association between graft overlap with recipient Descemet membrane and GD or rebubbling contradicting the findings of Rock et al 20 Leon et al10 found that an air fill <75% of the anterior chamber height was associated with an increased risk of GD . Similarly, Cirkovic et al20 reported that an 80% fill of the anterior chamber was significantly associated with a decreased incidence of rebubbling (P = 0.032). Pralits et al21 showed that graft support is dependent on the gas-bubble coverage of the graft. They demonstrated that a 63% fill already leads to incomplete coverage of the graft in different gaze directions independent of the type of gas filling. A larger gas bubble may mitigate the decrease of air-bubble size by leakage and half-life time of the tamponade agent.38On the other hand, our results support that a larger gas-bubble size may be protective for a GD as previously reported by Leon et al and Cirkovic et al.39 . This may indicate that a partial GD compromises long-term graft viability and could form an argument for early rebubbling. Mechanical loss of endothelial cells as result of tissue manipulation during surgery seems unlikely as this did not differ from the other groups in our analysis. As a result, we can only speculate on the cause of this endothelial cell loss, which may be the result of a larger area to be repopulated or unrecorded mechanical causes or trauma inhibiting cellular processes.Endothelial decay at 3 months and 6 months was higher in eyes with a partial GD compared with eyes with an attached graft and eyes that required a rebubbling. A similar association between partial detachments and endothelial cell loss was found by Baydoun et alFurthermore, several limitations should be addressed. This study was a post hoc analysis of a trial that was not powered to determine associations between intraoperative factors and GD/rebubbling. Notwithstanding, the data were derived from a well-controlled sample of corneal transplant procedures and the video analysis enables an objective in-depth observation of the surgical course. In this study, we focused on intraoperative factors affecting graft disadherence. However, an analysis including recipient and additional donor factors may reveal additional insights, including graft quality or posterior stromal scarring. Several factors were assessed in the video analysis , although not included in the analysis because the incidence of these factors either was low or could not reliably be estimated in the video analysis. Similarly, some factors that were scored are inherently subjective, for example, the surgeons' assessment of how loose/tight the DMEK rolls were. What is considered tight or loose DMEK roll by 1 surgeon can be different for another surgeon. In this study, we cross-checked the video feed with the surgeons assessment; however, as this process is subjective, we chose not to report on the scroll tightness. During determining the graft shape, grafts were only classified as a tight roll if the graders' assessment on the video image matched the surgeons' assessment. Information on noncompliance of the patient and resorption time of the gas bubble was not collected and could not retrospectively be retrieved.In conclusion, using a structured video analysis, we explored intraoperative determinants for GD and rebubbling after DMEK. Our analysis revealed that the gas-bubble size and graft shape/geometry seem to be relevant clinical factors. GD and rebubbling were not associated with the degree of graft manipulation, graft positioning, surgical iridectomy, or overpressuring the eye.


In managing arterial rupture, stent-graft implantation may cause limb ischemia by crossing a major branch for hemostasis. The ViaHole technique could circumvent a major branch occlusion.The process involved advancing retrograde devices into an occluded major branch by the stent-graft implantation to reach the outer surface of the stent-graft, puncturing the stent-graft with a 20-gauge needle to touch the retrograde device, manipulating the guidewire through the needle hole and externalizing it, advancing the microcatheter into the proximal lumen, catching the microcatheter using an antegrade 4-Fr catheter, inserting an antegrade guidewire into the retrograde microcatheter to cross the stent-graft hole, dilating the lesion and stent-graft hole using a 3.0-mm balloon, and ensuring hemostasis at the puncture site.A 72-year-old male with a history of stent-grafted treatment for right popliteal aneurysm presented with acute limb ischemia (ALI). The occlusion spanned distal superficial femoral artery to the below-the-knee arteries. Hemostasis was achieved after an unintentional rupture of the proximal posterior tibial artery during surgical thrombectomy by implanting endoluminal stent-grafts instead of surgical bypass due to no distal anastomosis site. However, recurrent ALI occurred three months later. Surgical bypass was again deemed unfeasible due to no run-off. Unsuccessful recanalization attempts of the bilateral tibial arteries led us to perform the ViaHole technique to recanalize the peroneal artery occlusion. Finally. successful revascularization was achieved, and 1-year patency was confirmed.The ViaHole technique may be valuable for revascularizing a major side branch occluded by stent-graft implantation.The online version contains supplementary material available at 10.1186/s42155-023-00385-8. Heparin-bonded endoluminal stent-graft  with expanded polytetrafluoroethylene (ePTFE) covering has been reported as valuable in managing arterial rupture . HoweverFirstly, retrograde devices are advanced into a major branch occluded by stent-graft implantation. The retrograde devices reach the outer surface of the stent-graft, and a 20-gauge needle is used to puncture the stent-graft and access the retrograde device. The next step is to advance the guidewire through the needle hole to out of the body. After externalizing the guidewire, the retrograde microcatheter is advanced into the proximal lumen. An antegrade 4-Fr catheter is used to catch the retrograde microcatheter, and an antegrade guidewire is then inserted into the retrograde microcatheter to cross the stent-graft hole. The lesion and stent-graft hole are dilated using a balloon. Finally, it is crucial to ensure hemostasis at the puncture site.To verify the reproducibility of the ViaHole technique, in vitro experiments were performed using the same 5.0 × 100-mm Viabahn used in this case to determine whether its ePTFE could be punctured with puncture devices, whether all parts of the ePTFE could be punctured, and whether the ePTFE could be opened after balloon dilatation of the puncture hole. As a result, a 20-gauge needle successfully penetrated all parts of the ePTFE, including the edges, whereas the hardest 0.014-inch tapered type guidewire, guidewire tail, and Wingman , with a needle at the tip of the catheter, did not penetrate it . Computed tomography angiogram (CTA) and angiography revealed occlusion from the distal superficial femoral artery (SFA) to the below-the-knee arteries. During attempts to remove the thrombus using surgical thrombectomy, an unintentional rupture occurred in the proximal posterior tibial artery (PTA). A surgical bypass was not employed due to no run-off in the below-the-knee arteries. Therefore, an endoluminal stent-graft was emergently inserted to achieve hemostasis in the proximal PTA without covering the peroneal artery; however, bleeding persisted. Consequently, another 5.0 × 100-mm stent-graft was placed up to the tibioperoneal trunk, resulting in the occlusion of the peroneal artery. To prevent ALI reoccurrence, anticoagulation (Warfarin) and dual antiplatelet drugs were prescribed. Nevertheless, the patient experienced recurrent ALI three months later  the technique is applicable to infrainguinal arteries but not suprainguinal arteries; 2) this method is infeasible without a retrograde guidewire and microcatheter in the target lumen to be punctured with a needle; 3) while the current report showed revascularization of the peroneal artery, this technique should be used to specifically recanalize the profunda artery in cases where a stent-graft is placed from the common femoral artery to the SFA; and 4) the long-term clinical impact of this technique on restenosis remains uncertain.The ViaHole technique may be valuable for revascularizing a major side branch occluded by Viabahn stent-graft implantation for vessel perforation. Additional research is warranted to assess the success and long-term outcomes of this technique in various clinical scenarios.Additional file 1. In vitro experiments assessing the performance of various devices in penetrating the ePTFE of Viabahn stent-graftAdditional file 2. The process of the ViaHole technique


Polylactide (PLA)/thermoplastic starch/SiO2 composites were obtained through melt-blending of PLA with thermoplastic starch/SiO2 in a twin-screw extruder. The nonisothermal crystallization behavior of PLA in the composites was investigated by differential scanning calorimetry. An interface of PLA with thermoplastic starch was proven to exist in the composites, and its interfacial bonding characteristics were analyzed. The interfacial binding energy stemming from PLA with thermoplastic starch exerts a significant influence on the segmental mobility of PLA at the interface. The segmental mobility of PLA is gradually improved by increasing interfacial binding energy, and consequently, the relative crystallinity on the interface exhibits progressive promotion. The Jeziorny model could well describe the primary crystallization of PLA in the composites. The extracted Avrami exponents based on the Jeziorny model indicate that the primary crystallization of PLA follows heterogeneous nucleation and three-dimensional growth. This study has revealed the intrinsic effect of the interfacial segmental mobility on the nonisothermal crystallization behavior of PLA in composites, which is of technological significance for its blow molding.Corn starch was plasticized by glycerol suspension in a twin-screw extruder, in which the glycerol suspension was the pre-dispersion mixture of glycerol with nano-SiO PLA is an eco-friendly material due to its renewability and biodegradability. Disposable film prepared by PLA is suitable as a sustainable alternative to petrochemical-based film, which is beneficial for the alleviation of the consumption of oil, as well as the eradication of the environmental pollution induced by the petrochemical-based film ,2,3,4,5.2 composites were prepared in our previous work [2 encapsulated by thermoplastic starch and the interfacial characteristics of PLA with thermoplastic starch could account for its enhanced rheological properties and tensile strength [2 composites. Generally, the processing of polymers is commonly carried out under nonisothermal conditions. For crystalline polymers, the nonisothermal crystallization behavior of polymers has a crucial effect on their tensile strength and microstructures [To produce PLA-based composites with a lower cost and high melt strength, PLA/starch/SiOous work ,12. Starous work ,14,15. Tstrength . Howeverructures ,18,19,20The crystallization kinetics of polymers is a widely accepted means to evaluate their crystallization behavior. Many mathematical models are proposed to clarify the macroscopic evolution of crystallinity for polymers during their crystallization process ,23,24,25In this study, the nonisothermal crystallization behavior of PLA in the composites was investigated by differential scanning calorimetry (DSC). The interfacial bonding energy of PLA with thermoplastic starch was calculated by Materials Studio. The effect of the interface of PLA with thermoplastic starch on the nonisothermal crystallization behavior of PLA in the composites is discussed.2 with a specific surface area of 200 ± 25 m2·g−1 was purchased from Shanghai Yizhu Industrial Co., Ltd. . PLA with 4 g/mol and polydispersity of 2.1 was purchased from Shanghai Macklin Biochemical Co., Ltd. . Corn starch of reagent grade was purchased from Shanghai Aladdin Bio-Chem Technology Co., Ltd. . Nano-SiO2, PLA, and corn starch were dried under a vacuum at 50 °C for 12 h before use. Glycerol of analytical grade was purchased from Tianjin Fuyu Chemical Co., Ltd.  and used as received.Nano-SiO2 were first mixed and sonicated for 15 min and 100 parts of corn starch were mixed into the suspension of nano-SiO2 with glycerol and strongly stirred for 1 h at a speed of 2000 rpm. The obtained mixtures were kept for 3 h at room temperature, and subsequently, the thermoplastic starch/SiO2 composites were prepared through melt plasticization using a twin-screw extruder ). The temperature profile from zone 1 to zone 6 was as follows: 115 °C, 120 °C, 130 °C, 125 °C, 120 °C, and 120 °C in the extruder barrel, and 120 °C in the extruder head die. The screw speed was 150 rpm. The obtained thermoplastic starch/SiO2 composites were granules.The process was conducted as follows: 40 parts of glycerol and 2 parts of nano-SiO2 was 4, 6, and 8 parts, respectively.The same procedure was performed except that the mass fraction of nano-SiO2 were mixed and then extruded using a twin-screw extruder. The mass fraction of nano-SiO2 in thermoplastic starch/SiO2 varied from 2 to 8 parts. The temperature profile from zone 1 to zone 6 was as follows: 155 °C, 165 °C, 160 °C, 150 °C, 145 °C, and 140 °C in the extruder barrel, and 140 °C in the extruder head die. The screw speed was 150 rpm. The obtained PLA/thermoplastic starch/SiO2 composites were granules.One hundred parts of PLA and fifteen parts of thermoplastic starch/SiO2 was 10, 15, 20, 25, and 30 parts, respectively. Here, the mass fraction of nano-SiO2 in thermoplastic starch/SiO2 was six parts.The same procedure was performed except that the mass fraction of thermoplastic starch/SiOAll of the tested samples were dried under a vacuum at 50 °C for 12 h before the test.2 atmosphere and involved two heating processes. About 6 mg of the sample was first heated from −50 to 200 °C at a heating rate of 10 °C·min−1 and kept at 200 °C for 3 min, then cooled to −50 °C at a cooling rate of −100 °C·min−1 and kept at −50 °C for 20 min. The second heating was from −50 to 200 °C at a heating rate of 10 °C·min−1. The information on the thermal history obtained from the first heating process mainly involved thermoplastic processing and was eliminated after thermostatic control at 200 °C. There was no obvious exothermic peak observed during the cooling process at the cooling rate of 100 °C·min−1, which suggested that the tested sample could not crystallize under this cooling condition. The rapid cooling process allowed us to analyze the thermal behavior of the tested sample from the amorphous state during the second heating process. The second heating process could provide information about the behavior of the chain segment. The nonisothermal crystallization kinetics were analyzed according to DSC curves obtained from the second heating process.All of the DSC measurements were conducted on a Perkin-Elmer DSC system under N−1 [The crystallinity of the composites was calculated according to Equation (1).93 J·g−1 ,37.The relative crystallinity The molecular dynamics simulation of the interface of PLA with thermoplastic starch was conducted by Materials Studio 2020. The thermoplastic starch model and the PLA model were established with MS visualizer. The interfacial model of PLA with thermoplastic starch was constructed by an amorphous cell according to the mass fraction of PLA, AM, and Gly. The geometric optimization and calculation of these models, as well as the results analysis and output, were carried out by Forcite. In the molecular dynamics simulations and the model optimization, the compass II force field was used for all force fields. The molecular dynamics simulation of the geometrically optimized interface model was carried out at 298 K and 1 fs of the time step in the NVT ensemble. The simulation involved two stages of equilibrium and data collection. In the equilibrium stage, the initial velocity met the Maxwell–Boltzmann distribution, and an Andersen thermostat was used for the control of temperature. Subsequently, to achieve complete equilibrium, the cumulative calculation was 500 ps. In the data collection stage, another 500 PS was calculated on the basis of the last frame configuration of the equilibrium stage, in which a Nose thermostat was used, and a frame configuration was output every 5 PS. A total of 101 frame configurations (including the frame at time 0) were collected for the data analysis.2 in starch, nano-SiO2 was dispersed in glycerol by ultrasonic dispersion. Then, the plasticization process of starch with glycerol was conducted by melt extrusion. Subsequently, PLA/thermoplastic starch/SiO2 composites were obtained by melt extrusion of PLA with thermoplastic starch/SiO2.Amorphous thermoplastic starch could be obtained through the incorporation of native starch with polyol plasticizers under a thermomechanical process, in which the hydrogen bonds in native starch are partially substituted by the hydrogen bonds of polyol ,14,15. I2 on the segmental mobility of PLA, the mass fraction of PLA and thermoplastic starch/SiO2 is in 100 parts and 15 parts, respectively, while the mass fraction of SiO2 in thermoplastic starch/SiO2 varies from 2 to 8 parts. DSC curves of these composites obtained from the second heating process are shown in g of neat thermoplastic starch plasticized by glycerol, its value is about 28 °C [g in the DSC curve, which indirectly indicates that PLA has good compatibility with thermoplastic starch. The thermal transition temperatures mainly reflect the segmental mobility of PLA. When the mass fraction of PLA and thermoplastic starch are the same in the composites, the Tg, Tc, Tm1, and Tm2 of the composites do not change significantly with the mass fraction of SiO2 in thermoplastic starch. It is inferred that SiO2 is mainly wrapped in starch, and thus fails to form an effective interface of PLA/SiO2. SiO2 wrapped in starch has no obvious effect on the segmental mobility of PLA.To evaluate the effect of SiOut 28 °C ,16. Ther2, an interface of PLA with thermoplastic starch could probably be formed in the composites. The Tg, Tc, Tm1, and Tm2 of the composites sharply decreased as compared with those of neat PLA, suggesting that thermoplastic starch might exert an influence on the segmental mobility of PLA. When the mass fraction of PLA and thermoplastic starch are the same, the composites exhibit similar thermal transition temperatures and crystallization temperatures due to their similar interface of PLA with thermoplastic starch. This is consistent with the rheology and mechanical properties of the composites reported earlier. Nano-SiO2, mainly wrapped by thermoplastic starch, forms a “sandbag” microstructure [Quite contrary to SiOtructure . It is d2, it is 10, 15, 20, 25 and 30 parts, respectively. In this part, the thermoplastic starch comprises 100 parts of starch, 40 parts of glycerol, and 6 parts of SiO2.To evaluate the effect of the interface of PLA with thermoplastic starch on the crystallization of PLA in the composites, the mass fraction of components of the composites is 100 parts of PLA, and for thermoplastic starch/SiOg for the composite with a thermal history. Thus, for the same mass fraction of thermoplastic starch in the composite, the Tg of the composites with a thermal history is higher than that without a thermal history, as shown in g, the hydrogen bonds between thermoplastic starch and PLA also exert an effect on the segmental mobility of PLA. The Tg of the composite with a thermal history increased slightly with the increasing mass fraction of thermoplastic starch due to its increasing number of hydrogen bonds, and for the composites without a thermal history, the Tg varied obviously. It is well accepted that interchain hydrogen bonds could improve the Tg of the polymer [The interchain free volume of PLA is decreased due to the pressure in the barrel during the melt extrusion process. The segmental mobility of PLA needs a higher temperature, which leads to a higher T polymer ,38.g of the composite is much lower than that of neat PLA because of the plasticizing effect of thermoplastic starch on PLA. Compared with neat PLA, the Tm of the composites decreased significantly. The main melting peak (Tm2) is accompanied by a shoulder peak (Tm1), suggesting that thermoplastic starch could act as the crystallization nucleator during the heating process of the composites and stimulate PLA to crystallize on the interface of PLA with thermoplastic starch at a lower temperature. The shoulder peak is ascribed to the contribution of the melting of the interfacial crystal, and the main peak is ascribed to the contribution of the melting of the crystal in the PLA matrix. Tm1 increases with the increasing mass fraction of thermoplastic starch due to the increasing interfacial area. Unlike Tm1, Tm2 undergoes almost no change with the mass fraction of thermoplastic starch, suggesting that the crystal in the matrix exhibits similar crystalline perfection.As shown in 2 with 10, 15, 20 25, and 30 parts, in which the thermoplastic starch is 100 parts of starch, 40 parts of glycerol, and 6 parts of SiO2. Compared with neat PLA, the crystallization of PLA in the composites during its second heating process happens at a lower temperature. Just as shown in c,onset and Tc of the composites are obviously lower than that of the PLA. At the same time, the crystallinity is significantly improved with the increasing mass fraction of thermoplastic starch. This suggests that the heterogeneous nucleation exerted by thermoplastic starch has an appreciable effect on the crystallization of PLA in the composites.The considered composites are also composed of 100 parts of PLA and variable thermoplastic starch/SiOPLA would crystallize at its interface with thermoplastic starch and in its matrix, in which heterogeneous nucleation and growth of PLA occur on the interface at a lower temperature. This crystallization behavior could be furtherly clarified by the main melting peak and the shoulder peak derived from the melting endotherms on the DSC curves. The curve-fitting of the melting endotherms is shown in With the increasing mass fraction of thermoplastic starch, The Jeziorny model extended directly the Avrami equation from the isothermal crystallization to the nonisothermal crystallization in the following form:Considering the nonisothermal character of the crystallization in a constant heating rate, the crystallization rate constant is adjusted by introducing a constant heating rate, and the corrected crystallization rate constant  for each mass fraction of thermoplastic starch in the composites, as shown in 2 formed in the PLA/thermoplastic starch/SiO2 composites. Nano-SiO2 wrapped by thermoplastic starch has little effect on the nonisothermal crystallization of PLA. The interface of PLA with thermoplastic starch is effective in the composites, and its interfacial area increases with the increasing mass fraction of thermoplastic starch. The interface of PLA with thermoplastic starch exerted a remarkable effect on the segmental mobility of PLA on the interface. The Tg and Tm of the composites are much lower than those of pure PLA. The relative proportion of crystallization on the interface increases with the mass fraction of thermoplastic starch. Still, the varied trend for the crystallization of PLA in the matrix is on the contrary. The Jeziorny model could describe well the primary crystallization of PLA in the composites. The extracted Avrami exponents based on the Jeziorny model indicate that the crystallization of PLA on the interface follows heterogeneous nucleation and three-dimensional growth. The relative proportion of crystallinity on the interface increases with the increasing the fraction of thermoplastic starch, which could be well explained by the interfacial binding energy of PLA with thermoplastic starch. The composite with a higher mass fraction of thermoplastic starch would have a higher interfacial area of interaction and, consequently, have a higher relative proportion of crystallinity on the interface.There is almost no interface of PLA/SiO


The effect of 10 × 30 m repeated sprints on passive and active stiffness of semitendinosus (ST) and biceps femoris long head (BFlh), and knee flexor maximal voluntary isometric contraction (MVIC) and rate of force development (RFD), and whether athletes with previous hamstring injury have a different response, is unknown.Repeated sprints would (1) increase BFlh stiffness and decrease ST stiffness and knee flexors MVIC and RFD in healthy participants; and (2) greater magnitude of response would be seen in athletes with previous hamstring injury.Case series (experiment I) and case control (experiment II) study designs.Level 3.Healthy nonathletes attended 2 replicated sessions , while soccer players with (n = 38) and without (n = 67) previous hamstring injury attended 1 testing session (experiment II).P < 0.05). In experiment I, the ST and BFlh passive stiffness reduced after the sprints (P < 0.02), while a small BFlh active stiffness increase was noted (P = 0.02); however, no correlation was observed between the 2 testing sessions for the postsprint muscle stiffness responses . In experiment II, only an ST passive stiffness reduction was observed after the sprints (P < 0.01). No differences were noted between injured and noninjured lower limbs for any variable (P > 0.10).In both experiments, the knee flexors MVIC and RFD decreased after the sprints (Repeated sprints are likely to decrease the knee flexor’s maximal and rapid strength, and to alter the hamstring stiffness in the nonathlete population. Previous hamstring injury does not apparently affect the footballer’s hamstring functional and mechanical responses to repeated sprints.The responses of hamstring stiffness and knee flexor strength to repeated sprints are unlikely to be associated with hamstring injury. This type of injury affects mainly the biceps femoris long head (BFlh) and, to a lesser extent, the semitendinosus (ST), and occurs mostly during actions that require rapid muscle activation such as sprinting.11 However, inconsistent findings have been reported concerning the sprinting performance and knee flexors strength capacity of athletes with versus without previous hamstring injury.31 For instance, some studies have reported that previously injured athletes are faster, more susceptible to fatigue during the repeated sprints, but with lower knee flexors rate of force development (RFD)30; other studies have obtained different conclusions.29 Although previous investigations have shown that performing repeated sprints reduces sprint ability,12 these investigations have not examined the effects on knee flexor strength. In particular, the RFD of the knee flexors is an area of interest given the suggestions of relevance to the prevention of hamstring injuries.30 Thus, this topic needs to be further explored.The incidence of hamstring injuries in team athletes that involve repeated running sprints is commonly reported as high,27 has also been suggested by some studies as potentially relevant for understanding hamstring injuries. However, surprisingly, little has been investigated at this level, including the response of muscle stiffness after performing fatigue-inducing tasks such as repeated sprints. Interestingly, based on functional MRI measurements, it was previously proposed that an altered load distribution between hamstring muscles, in particular between BFlh and ST, could underlie the occurrence of hamstring injuries.33 Considering that active muscle stiffness represents in a way the load that the muscle develops in contraction, and based on the previous premise,33 it was recently observed that the responses of active stiffness of the BFlh and ST are distinct during submaximal knee flexors contractions , change over the course of fatigue , and are apparently different in elite soccer players with a history of hamstring injury. Specifically, soccer players with previous hamstring injury appear to have less active BFlh stiffness in a nonfatigue state, and tend to develop a greater increase in BFlh/ST active stiffness ratio during the course of fatigue onset. However, the active stiffness response of these hamstring muscles over the fatigue after repeated sprints has not yet been investigated, and could potentially provide relevant information.The stiffness of hamstring muscles, whether passive or active,29; and that under the absence of changes in muscles passive stiffness, ST active stiffness would be reduced and BFlh active stiffness would be increased. In (2) muscle stiffness responses would be similar between sessions. The second experiment examined whether soccer players with and without previous hamstring injury would present differences in repeated sprints performance, and verified whether previously injured and noninjured lower limbs would present differences in ST and BFlh stiffness and knee flexors MVIC and RFD before and after repeated sprints. It was hypothesized that previously injured athletes would present similar sprint performance, and previously injured limbs would have a greater active stiffness response in terms of BFlh increase and ST decrease after the sprints in the absence of changes in muscle passive stiffness, but with similar knee flexor MVIC and RFD responses.29The present study aimed to further explore the immediate effects of repeated sprinting on hamstring stiffness and knee flexors strength capacity in both healthy nonathletes and soccer players with and without previous hamstring injury in the last 2 years. Thus, 2 experiments were conducted. The first experiment focus was 2-fold: (1) to examine whether BFlh and ST passive and active stiffness, as well as the knee flexors maximal voluntary isometric contraction (MVIC) and RFD, would be altered by a repeated sprinting task in healthy participants; and (2) to determine whether muscle stiffness responses to the repeated sprinting task between the 2 replicated sessions would be associated. It was hypothesized that after the sprint task the knee flexor MVIC and RFD would reduce Healthy and physically active male adults  participated in experiment I, and none reported having previous hamstring injury. Semiprofessional (n = 60) and professional (n = 45) soccer players  from 10 Portuguese teams competing in the first (n = 2), second (n = 19), third (n = 24), and fourth (n = 60) divisions agreed to participate in experiment II. At the time of testing, athletes reported to be free of clinical injuries. This study was approved by the local ethics committee .Descriptive (experiment I) and a controlled (experiment II) laboratory study designs were implemented. Experiment I replicated the testing session with 7.3 ± 2.0 days between sessions, whereas experiment II consisted of only 1 session performed at the 2021/2022 preseason . The experiments had a similar protocol, consisting of muscle stiffness and knee flexors strength pretesting, standardized warm-up, sprint testing, and post testing (described in the “Protocol” section). For experiment I, participants were instructed to avoid the practice of vigorous physical activity but to maintain normal daily living, whereas in experiment II soccer players were coming from a vacation period, or from the beginning of the season. Based on preliminary statistical testing using G*Power software , 18 and 100 participants were estimated as necessary for experiments I and II, respectively, assuming statistical power of 90% in the main outcomes  and that at least 20% of footballers would present with previous hamstring injury. Participants were positioned in a prone position, with the hips in neutral position, and the tested knee flexed at 30º (0º = full extension). With the ankle at 90º, the foot of the tested limb was fixed in a foot holder, which contained a force transducer  near heel level to collect the linear force perpendicular to leg orientation. The force collected was amplified , converted digitally , recorded using DAQami software , and multiplied by the perpendicular distance between the force transducer center and the femoral lateral condyle to estimate knee torque.Knee flexor torque was measured with a sampling rate of 1 kHz using a piece of custom-built equipment as shown in a previous study.Knee flexor MVIC and RFD were obtained during unilateral testing in experiment I, and bilateral testing in experiment II. In a previous pilot testing (not published) we observed no differences in knee flexor MVIC and RFD between unilateral and bilateral testing. For each testing moment , athletes performed 2 trials with 60 seconds between trials. In experiment II, testing was randomized between limbs. For each trial, participants were instructed to relax as much as possible, and after the command “3, 2, 1, and go” to contract the knee flexors “as fast and strong” as possible, without performing a countermovement. Visual feedback was provided to the athletes. When visually verified that countermovement had occurred, an additional trial was performed. with the use of plastic casts fixed to the skin using double-sided adhesive tape, to ensure the measurement site was the same across repeated trials. Casts were oriented according to the fascicle direction of the muscle. Measurements were conducted by examiners trained by the principal investigator of this study, with a minimal ultrasound training time of 50 hours. Minimum pressures were applied by examiners during the stiffness measurements. Active stiffness measurements were obtained during a knee flexor isometric contraction at 20% of MVIC. This contraction intensity was chosen since it has been proven to be reliable, is acceptable to athletes, because ST displays greater active stiffness than BFlh, and previous research has indicated the injured limbs of footballers have different responses compared with controls. Videos were recorded with both B-mode and elastogram windows, with a minimum of 30 seconds for both passive and active measurements, with 30 seconds rest between trials. For further details of data acquisition and processing, please refer to earlier works.25BFlh and ST passive and active stiffness were assessed using 2 similar ultrasound scanners  in shear wave elastography mode . Each scanner was coupled with a linear transducer array . The push frequency that generated the elastogram window was set automatically by the ultrasound equipment to approximately 1 Hz , depending on the elastogram window size and position. The region of interest was defined at ~45% of the proximal-to-distal femur length for both muscles, the time to perform the 10 sprints of 30 m each was assessed using wired timing gates provided by Chronojump-Boscosystem (Velleman PEM10D photocell), connected to the Chronojump software . Photocells were placed at a distance of 30 m, at a height of 1.3 m. Sprints were performed on an indoor tartan floor, whereas participants positioned 1 m before each pair of photocells, and initiated each sprint upon a “3, 2, 1, and go” command by a local instructor. Participants rested 30 seconds between sprints.Using a previous published approach,Demographic, anthropometric, and injury history information was obtained upon arrival. With the participant lying in a prone position and the knees flexed at ~30°, the ST and BFlh region of interest were determined, and the muscle passive stiffness assessment performed. After a brief familiarization with the knee flexors strength equipment, athletes performed the MVIC/RFD testing followed by the ST and BFlh active stiffness assessment (in random order). Before the sprinting task, participants performed a standardized warm-up . Immediately after the sprints, muscle active stiffness, knee flexor MVIC and RFD, and the muscle passive stiffness were assessed. In experiment I, only 1 lower limb (randomized between athletes) was tested for muscle stiffness and for knee flexor strength, whereas in experiment II the 2 lower limbs were assessed in random order.Knee flexor MVIC and RFD were processed using a customized Matlab routine (Mathworks Inc). For MVIC, the highest value observed in pre- and postsprints trials was considered for analysis. For RFD, the torque slope at the 0 to 50, 50 to 100, 100 to 150, and 150 to 200 ms time intervals after the onset of muscle contraction , as well as the maximum RFD  and its moment of occurrence after the onset of muscle contraction were determined. and the average between the 2 repeated trials of each testing moment was considered for analysis.Shear modulus data were processed using custom Matlab routines (Mathworks Inc). Briefly, each clip exported from Aixplorer software was sequenced into .jpeg images. The largest rectangular region of interest in the elastogram window in each image was selected manually by avoiding aponeuroses and tissue artifacts . Grayscale pixels were excluded, and colored pixels were converted into elastic moduli values based on the recorded scale. The elastic moduli values were then averaged to obtain a representative muscle value. In each knee flexor isometric contraction trial, the average value observed during the most stable period of 15 seconds was determined,Concerning the repeated sprint performance, in addition to the sprint velocity in each repetition, the percentage of drop in velocity between the first and the last sprint repetitions was considered for analysis.SPSS software  was used to conduct statistical analysis. Data normal distribution was checked using Shapiro-Wilk test.t test. The effects of sprinting in both sessions on the BFlh and ST passive and active stiffness and knee flexor MVIC and RFD were examined using a 2-way repeated measures ANOVA  × moment ). Based on pretesting values, interday reliability outcomes  were also quantified. Pearson correlation coefficient was used to examine whether the active stiffness responses of BFlh and ST after the sprint task were consistent between sessions.In experiment I, a 2-way repeated measures analysis of variance (ANOVA)  with simple contrast against the first sprint repetition was performed to examine whether the velocity decreased along the repeated sprint task in both sessions, whereas the maximal sprint velocity and the percentage drop of velocity during the sprint task between sessions were compared using a paired t test was performed to compare age, height, body mass, and body mass index between athletes with versus without previous injury. To examine whether the repeated sprint task performance were different between previously injured and noninjured athletes, a 2-way repeated measures ANOVA  × repetition ) with simple contrast against the first sprint repetition was conducted, and a unpaired t test was used to compare the maximal sprint velocity and the percentage drop of velocity during the sprint task between groups. To compare the effects of sprinting on the BFlh and ST passive and active stiffness and the knee flexor MVIC and RFD between previously injured and noninjured lower limbs, a 2-way repeated measures ANOVA  × moment ) was conducted.In experiment II, an unpaired P > 0.05.In all ANOVAs, post hoc testing consisted of the Bonferroni test. Statistical significance was set at P < 0.01), but not for the session factor (P = 0.24) nor the session × repetition interaction (P = 0.86). Participants showed similar maximal sprint velocity  and percentage drop of velocity . Thus, suggesting that participants had similar sprint performance between the 2 testing sessions.In the repeated sprint task, the sprint velocity decreased from the second repetition in both testing sessions (P < 0.05) for BFlh active stiffness, RFD , and time when the maximum RFD occurred.r = 0.12, P = 0.64; passive, r = 0.26, P = 0.30) and ST  stiffness responses between testing sessions, suggesting that stiffness responses to repeated sprinting are inconsistent between days.No relation was found in BFlh  nor the group × repetition interaction (P = 0.26), but an effect was noted for the repetition factor . In addition, similar maximal sprint velocity  and percentage drop of velocity  was observed between groups.Regarding the repeated sprint performance, no effect was observed for the group factor  and in the initial stage of late RFD , as well as the maximum RFD . A previous review indicated that both early and maximum RFD have a greater magnitude of responses to a fatigue state compared with MVIC. Such a statement is in accordance with findings observed with the nonathletes denoted by normalized average changes, but also revealed by the greater partial eta square found for knee flexors early (ηp2 = 0.685-0.741) and maximum (ηp2 = 0.691) RFD compared with MVIC (ηp2 = 0.441). However, surprisingly, such a response was not observed with soccer players in experiment II, as a greater magnitude of response was observed for MVIC (ηp2 = 0.307) than early (ηp2 = 0.024-0.110) and maximum (ηp2 = 0.204) RFD. Interestingly, a previous study also reported that amateur soccer players did not change RFD after an effort similar to that of a football match, even in the presence of a considerable decrease in MVIC. This might be attributed to the greater knee flexors strength endurance of this population, due to the fact that they have greater exposure to repeated sprints compared with nonathletes. This aspect is worthy of further investigation.While previous research has clearly demonstrated that sprint velocity decreases along the repeated running sprinting trials,34 whereas an increase in muscle active stiffness  is an indicator of muscle overloading.24 However, the results found in the present study were somehow intriguing. For instance, while a reduction of passive stiffness in both ST and BFlh was found, a small increase in BFlh active stiffness was noted. Note, however, that the change in BFlh active stiffness was small, and lower than the interday methodological error; so whether this can be interpreted as a random result is questionable. Nevertheless, the increase in BFlh active stiffness might mean that the fatigue induced by the repeated sprinting may have induced a higher BFlh neural overdemand to execute submaximal knee flexor contraction to compensate for the decrease in passive stiffness, but possibly also to generate a compensation mechanism in relation to the load responses of other agonist muscles. Although this possibility cannot be confirmed as only 2 hamstring muscles were measured, it can be said that the potential BFlh compensation is not due to alterations in ST loading. Note that repeated sprints have been reported to decrease knee flexor strength capacity with greater magnitude compared with hip extensors, and that the production of horizontal force during repeated sprints is largely explained by the decrease in hip extensor strength capacity. Based on the findings of previous studies on single-joint  fatiguing tasks,24 repeated sprints would be expected to induce a decrease in ST active stiffness, which was not observed. This fact may have occurred due to many possibilities. One possibility could be due to the redundant number of kinematic strategies that athletes may have adopted during sprints to reduce the ST load. On the other hand, it may be related to the nature of the applied sprinting task , which involves a greater component of acceleration and hip extension force production dependence, thus inducing specific hip extension fatigue. Future research is wanted to further explore this topic.To our knowledge, this is the first study to report the effects of repeated sprinting on hamstring muscle passive and active stiffness, through the use of ultrasound-based shear wave elastography. Previous studies using shear wave elastography have interpreted the decrease in passive and active stiffness after fatiguing tasks as a indicators of localized muscle fatigue,4 and reinforces the premise that, due to the high number of body postures that participants can adopt during sprints, the load responses between hamstring heads may be highly variable. Future research may want to explore whether hamstring responses after repeated sprinting are related to the kinematic postures adopted during sprinting.Moreover, another important finding of this study is that muscle stiffness responses to repeated sprinting were not consistent between testing sessions, which suggests that intra-athlete muscle stiffness responses are highly variable between similar sprinting-induced fatigue tasks. This finding is in accordance with the suggestions of previous research, but also the most common mechanism of hamstring injuries,11 knee flexor strength capacity and the mechanical properties of hamstrings in response to repeated sprinting were also examined in soccer players. In accordance with previous research,19 soccer players reporting previous hamstring injury were slightly older and had higher body mass index. Concerning repeated sprinting performance, soccer players with previous hamstring injury did not differ from noninjured athletes as they had similar maximal sprint velocity and drop in velocity along the repeated sprint task. This result opposes the findings of previous research reporting that soccer players with previous hamstring injury are faster,31 and have a higher drop in velocity along the repeated sprints compared with noninjured soccer players. Note, however, that soccer players participating in the present study belonged to third (23%) and fourth (57%) division teams; thus, their competitive level (as well sprint performance level) might be lower than soccer players who participated in the study by Røksund et al. Also, the maximal sprint velocity was similar between soccer players (experiment II) and nonathletes (experiment I). Thus, the repeated sprinting performance difference between soccer players with versus without previous hamstring injury might be detected only at higher performance/competitive levels.Since sprinting is a key aspect of the football game,Similar to the findings of experiment I, the repeated sprinting was also shown to induce knee flexor fatigue, by decreasing MVIC and the RFD . However, the magnitude of the responses was generally lower in athletes compared with nonathletes, as denoted by the partial eta square values . On the other hand, muscle stiffness responses after repeated sprinting did not alter as observed in experiment I, with the exception of ST passive stiffness, which exhibited a reduction. We are unaware of the reason for this discordance of results between experiments; however, it may be explained by the degree of fatigue induced by repeated sprints. As mentioned, the magnitude of knee flexor fatigue was higher in soccer players. Also, note that soccer players decreased the sprint velocity only from the fourth trial compared with the first sprint trial, while nonathletes demonstrated a decrease in velocity immediately on the second trial. Perhaps, due to greater exposure to repeated sprints of soccer players (compared with nonathletes), they have developed greater hamstring strength endurance. Consequently, we may speculate that hamstring stiffness changes are evident only with higher levels of fatigue, and 10 repeated sprints with 30 seconds rest between attempts may not be enough to induce such stiffness alterations. Therefore, it is desirable that future research apply protocols that induce greater degrees of fatigue, to verify whether the stiffness of hamstring muscles in football players remains unaltered. and Buhmann et al, who assessed knee flexor RFD under dynamic conditions , but agree with the results of Nara et al, who assessed knee flexor RFD under isometric conditions. The findings for knee flexor MVIC also agree with those from previous studies, whereas no differences were found between athletes with versus without previous hamstring injury. Thus, it is possible that knee flexor strength differences between previously injured and noninjured hamstring athletes can be found only in a dynamic contraction regime, in particular in eccentric contractions. Regarding hamstring muscle stiffness, no differences were observed between groups for both fatigue and nonfatigue states; thus, the initial hypotheses of this study was not supported. To the best of our knowledge, using ultrasound shear wave elastography, only 1 previous study has assessed the active stiffness of ST and BFlh during a knee flexor fatiguing task with elite soccer players and reported that BFlh active stiffness in a nonfatigue state was lower in previously injured limbs. Although, in the present study, the mean BFlh active stiffness values of previously injured limbs were lower compared with those of noninjured limbs, such differences did not reach statistical significance (P = 0.13). We speculate that the reason for this discrepancy might be related to the competitive level of soccer players between studies, and the method of injury diagnosis . In terms of passive stiffness, our results are in accordance with those of Kawai et al, who did not find stiffness differences between injured and noninjured limbs in athletes who suffered injury >6 weeks before testing. Therefore, in nonsevere situations, it is possible that passive stiffness of injured muscles is restored in <6 weeks.With respect to the differences between limbs with versus without previous hamstring injury, surprisingly, we found no difference for any knee flexor strength or hamstring stiffness variable. Regarding knee flexor RFD, the present results opposes somewhat the findings of Opar et al Second, active stiffness assessment was performed only at 20% of MVIC. However, it should be noted that the changes in the vastus lateralis active stiffness with fatigue tend to occur over a wide band of contraction intensities; thus, it is unknown whether this is the case for the hamstring muscles. Finally, active stiffness analysis (between participants and limbs) was performed for a relative contraction intensity , instead of an absolute torque. The stiffness comparison for a given knee flexion torque is a possible methodological approach; however, it does not prove that the individual muscle force between participants/limbs is the same. It is necessary to consider other factors, such as muscle moment arm, physiological cross-sectional area, and degree of muscle activation. However, no differences were found in the knee flexors MVIC (or body mass) between footballers with and without a previous injury, which gives some degree of confidence for the approach taken.There are 3 main study limitations. First, hamstring injury screening was based on athlete self-report, instead of clinical imaging . This fact did not allow access to the exact muscle injury location and classification, but allowed access to the body region , time of injury occurrence, and injury time loss .Repeated sprints are likely to induce fatigue in the knee flexors by decreasing their MVIC and RFD in both athlete and nonathlete populations. However, the magnitude of this effect appears to be smaller in those with greater exposure to repeated sprints, namely football  players. In nonathletes, repeated sprinting seems to alter hamstring stiffness by decreasing both ST and BFlh passive stiffness, and slightly increasing the BFlh active stiffness. In soccer players, only a passive decrease in ST stiffness was noted. However, in nonathletes, the stiffness responses to repeated sprinting appear to not be consistent between days, suggesting high intraperson variability. Soccer players with previous hamstring injury in the last 2 years appear to have similar repeated sprinting performance compared with noninjured athletes; repeated sprints also appear not to induce different responses in knee flexor strength and hamstring stiffness between lower limbs with and without a history of hamstring injury.


In recent years, there has been an increasing interest in open-hole and filled-hole laminate failure analysis. The open and filled-hole laminate failure analysis is used in several important areas, especially in designing mechanically fastened composite joints. Various analytical, empirical, and numerical methods are available for the design of mechanically fastened composite joints. The large number of material and geometrical design variables at the preliminary design stage makes the empirical and numerical methods effortful, expensive, and time-consuming. Therefore, analytical methods are recommended over numerical and empirical methods at the preliminary design stage merely because of their simplification in calculations, making them computationally efficient. Taking this into consideration, current research presents an improvement to the analysis capabilities of the previously introduced analytical method, i.e., the coupled approach of Classical laminate theory (CLT) and Lekhnitskii solutions. These improvements include the development of failure envelops for the open-hole and filled-hole laminates, estimation of optimized filling material for attaining maximum load-bearing capacity of filled-hole laminates, and optimization of stacking sequence for maximum load-bearing capacity of open-hole and filled-hole laminates. From the failure envelop results, it was found that failure envelopes of filled-hole laminates are bigger than open-hole laminates. Furthermore, it was found that the stiffness of the filling material should be equal to the stiffness of the laminate to achieve maximum bearing strength of the filled-hole laminate. It was also demonstrated that the coupled approach of CLT and Lekhnitskii solutions may provide carpet plots that can be utilized to optimize the stacking sequence for open-hole and filled-hole laminates. A simplified analytical procedure was presented for the preliminary design of composite structures with open and filled holes.Filling material stiffness plays a crucial role in enhancing the bearing performance of filled-hole laminates.The CLT-Lekhnitskii coupled theory can generate carpet plots, which is useful for the stacking sequence optimization of open-hole and filled-hole composite structures during the preliminary design stage.Fiber-reinforced polymer (FRP) composites are widely used in the fields of aerospace, automobiles, energy, and civil engineering owing to their lightweight, high strength, superior fatigue, and durability ,2,3,4,5.In addition to OHT and OHC studies, it is important to predict the failure strength of filled-hole laminates under tensile loading because fasteners are extensively used for joining composite structures ,26,27,28Empirical methods are difficult and expensive at the preliminary design stage due to a large number of geometrical and material design factors. Therefore, numerical and analytical tools are considered feasible methods for the preliminary designing of open-hole and filled-hole composite structures. However, FEA has the disadvantage of being computationally inefficient. In addition, progressive damage modeling has been used for the analysis of composite structures. Progressive damage models encompass complex failure criteria and material degradation models. On the other hand, analytical approaches use simplified methods, unlike numerical methods. Therefore, analytical methods are recommended over numerical methods at the preliminary design stage, merely because of their simplifications and time efficiency. By keeping this in consideration, an analytical approach was chosen in this paper to study the response of open and filled-hole laminates working under various scenarios.Analytical solutions to predict the stress distribution around the circular hole is complex due to the presence of stress singularity. Therefore, several analytical models have been proposed to predict stress and strain distribution along the periphery of the circular and elliptical holes. Most of the contributions to the development of these models are from Muschelisvili , Savin , and LekThe analytical model developed by Lekhnitskii for isotropic plates was further improved and extended to orthotropic plates by Theocaris and Philippidis . In addiMost of the analytical solutions used to study the effect of inclusions are based on coupled theories. These theories use classical laminate theory (CLT) and complex potential functions. Hence, it can predict the coupling effect of multilayered unsymmetrical composites. A few authors coupled CLT and Lekhnitskii solutions to predict failure in FRC with open inclusions. Bradshaw and Pang  used CLTAll of these investigations have demonstrated that CLT can be coupled with the Lekhnitskii solution to predict the strength of open-hole laminates. Therefore, this research expands the analysis capabilities of this coupled theory, which would be very helpful for the designing of open-hole and filled-hole structures at the preliminary design stages. All previous research on CLT and the Lekhnitskii solution examined only the strength prediction capability of open-hole laminates. However, this research work presents the strength prediction of filled-hole laminates by using CLT-Lekhnitskii coupled theory. In addition, the current research revealed the capability of coupled theory to produce the failure envelopes of open-hole and filled-hole laminates, as well as its capability to generate carpet plots for the optimization of stacking sequence. These improvements in CLT-Lekhnitskii coupled theory have not been reported in the literature.Recently, most industries have started implementing end-of-life management in their products. Two factors need to be considered to achieve end-of-life management, namely recyclability and environmental friendliness of the product. Therefore, the material must have these two characteristics . ConsideHuang and Xin  proposedEquation (2) shows the relations used for the calculation of the longitudinal strength of laminates .(2)σ11uFor the calculation of transverse strength, Equation (3) was used .(3)σ22uT, XC, YT, and YC are longitudinal strength in tension, longitudinal strength in compression, transverse strength in tension, and transverse strength in compression, respectively. Similarly, E11, E22, G12, G23, v12, and v23 are longitudinal stiffness, transverse stiffness, in-plane shear stiffness, out-of-plane shear stiffness, in-plane Poisson’s ratio, and out-of-plane Poisson’s ratio, respectively. Constituent properties of basalt fiber and matrix [Based on this micromechanical approach (Equation (1) to Equation (3)), the strength and stiffness properties of the basalt laminate were estimated and tabulated in d matrix  are listDifferent laminate sequences were considered in this study. In the aerospace industry, only 0°, 45°, and 90° plies are used. Furthermore, composite products used in the aerospace industry must follow the 10% rule . Accordiis plies , whereasis plies .This section aims to describe the methodology used in this study. CLT  is consir, t, and rt. Equation (10) was utilized to estimate the value of The next step was to calculate constants k, n,r, t, and rt were calculated for each angle Laminate stresses are described in b = After calculating the laminate stresses, the transformation matrix was used to get the global loads, as given in Equation (14).Once the global loads were evaluated, CLT was implemented to assess the failure index along the periphery of the hole. Hashin failure criteria  were empThe proposed analytical model was validated with the finite element model in Abaqus. Stacking sequence The primary purpose of the current research is to extend further the capability of the CLT-Lekhnitskii coupled theory by adding three modules, i.e., strength prediction of open-hole and filled-hole laminates, failure envelopes of open-hole and filled-hole laminates and carpet plots for prediction of stacking sequence. The results of these three modules are discussed below.Failure of laminates depends on many factors, and a few of them are focused on in this study. These factors were the stiffness of the filling material, laminate sequence, and loading conditions. To evaluate the factors mentioned above in a broader aspect, a failure envelope was developed for a better representation of failure boundaries under various loading conditions. Therefore, the current section describes the effect of laminate sequences and different filling materials on the failure envelop of the open-hole and filled-hole laminates.As shown in As far as filled-hole laminates are concerned, a further change in the shape of failure envelopes was recorded. By examining 1 and E2, of the QI base laminate are also 24.1 Gpa. Therefore, it can be concluded that if the stiffness of the filling material is close to the equivalent stiffness of the base laminates, then the filling material can perform as a load-transferring agent. Whereas, if the stiffness of the filling material is higher than the equivalent stiffness of the base laminates, then the filling material imparts load on the wall of the hole which causes a reduction in the load-bearing capability.As discussed earlier, open-hole laminates have smaller failure envelopes than filled-hole laminates. Therefore, it can be said that open-hole laminates have the lowest load-bearing capacity. This low capacity was because of high-stress concentrations along the periphery of the hole. This high-stress concentration could be due to the free edge stresses. This stress concentration could be decreased by introducing filling material into the hole. The most prominent observation to emerge from the data comparison was the correlation between load-bearing capacity and stiffness of the filling material. The variation of load-bearing capacity with respect to the stiffness of the filling material is shown in E1 and E2 of the laminate. It was found that for hard laminates under uniaxial loadings, the stiffness of the filling material should be close to the E1 of the laminate. In addition, the stiffness of the filling material should be close to the E2 of the laminate if the hard laminates are subjected to multiaxial loadings. This is contrary to the case of the soft laminate, where the stiffness of the filling material should be close to the E1 of the base laminate when subjected to either uniaxial loadings or multiaxial loadings. It is important to note that the data points of multiaxial (hard) overlap the multiaxial (soft) data points, as shown in This behavior remained the same for different laminate sequences under various loading conditions. However, the values of the maximum load-bearing capacity and their respective stiffnesses of the filling materials were different for different loading conditions and laminate sequences. As shown in The study of the failure envelopes revealed that the percentage usage of 0°, 45°, and 90° plies in a laminate is of paramount importance. By setting the amount of 0°, 45°, and 90° plies in a laminate, the maximum load-bearing capacity of open and filled-hole laminates can be achieved under different loading scenarios. On the other hand, the percentages of plies were different for multiaxial loading. As shown in The CLT-Lekhnikstii coupled approach can generate failure envelops for open-hole and filled-hole composite structures, which is a very beneficial finding for the preliminary design stage of these structures.To achieve maximum bearing strength, the stiffness of the filler material for joining two composite laminates should be equal to or close to the stiffness of the joining composite laminates. For uniaxial loading conditions, the stiffness of the filler material should be close to the longitudinal equivalent stiffness of the base laminate. Meanwhile, for multiaxial loading conditions, it should be close to the transverse-equivalent stiffness of the base laminate.Carpet plots produced by CLT-Lekhnikstii coupled method can be very effective for deciding the stacking sequence of open-hole and filled-hole composite structures at the preliminary design stage.The current research work aims to propose an analytical method for the preliminary design stage of open-hole and filled-hole composite structures that is capable of finalizing the choice of stacking sequence and filling material. For that purpose, a CLT-Lekhnikstii coupled approach was used to generate failure envelops and carpet plots, and this theory was also used to select the filler material. The proposed analytical tool was found to be very useful during the preliminary design stage, and the following key conclusions were reached using the CLT-Lekhnikstii coupled approach:


A high malondialdehyde-oxidized low-density lipoprotein (MDA-oxLDL) level is associated with atherosclerotic cardiovascular diseases and major adverse cardiovascular events. A higher cardio-ankle vascular index (CAVI) is independently associated with an increased risk of cardiovascular events, cardiovascular mortality, myocardial infarction, and stroke in patients with cardiovascular risk. Thus, this study aimed to evaluate the relationship between serum MDA-oxLDL levels and CAVI in patients with triple-vessel coronary artery disease who underwent coronary artery bypass graft (CABG) surgery. Fasting blood samples and baseline characteristics were obtained from 88 patients who had undergone CABG. A commercialized enzyme-linked immunosorbent assay was used to measure MDA-oxLDL levels. An automatic pulse wave analyzer was used to measure CAVI values, and each side of CAVI values of ≥9 was designated as arterial stiffness. In total, 47 participants were assigned to the arterial stiffness group. More patients had diabetes mellitus, were older, and had higher serum MDA-oxLDL levels in the arterial stiffness group than in the control group. A multivariate logistic regression analysis disclosed that MDA-oxLDL and diabetes mellitus were independent predictors of arterial stiffness. Moreover, according to the Spearman’s correlation analysis, the serum MDA-oxLDL level was positively associated with both left and right CAVI. Serum MDA-oxLDL levels were positively associated with arterial stiffness in patients who had undergone CABG. Arterial stiffness is an aging process of the human body that results from combined mechanisms, including endothelial dysfunction, oxidative stress, elastin degradation, collagen deposition, calcium, advanced glycation end-product, and altered vascular smooth muscle tone . ArteriaThe oxidized low-density lipoprotein (ox-LDL), a product of the oxidative process in humans, is related to atherosclerotic plaque formation and thrombotic event ,9. The sPatients with coronary artery diseases who need surgical revascularization are those who have relatively higher plaque burden, oxidative stress, and CV risks. Comorbidities, such as diabetes mellitus (DM), hypertension, chronic kidney diseases, and arterial stiffness, affect the long-term prognosis of patients who had undergone coronary artery bypass graft (CABG) surgery . Thus, tn = 3), acute infection (n = 1), heart failure (n = 1), amputation (n = 3), acute myocardial infarction (n = 1), or an ABI < 0.9 (n = 15), at the time of enrollment. Patients were regarded as having DM if the fasting plasma glucose was ≥126 mg/dL or were using oral hypoglycemic medications or insulin. Blood pressure (BP) was measured in the morning using standard electronic sphygmomanometers with appropriate cuff sizes after resting for at least 10 min. Systolic BP (SBP) and diastolic BP (DBP) were taken three times at 5 min intervals, and the average values were recorded for the analysis. Hypertension was defined as SBP ≥ 140 mmHg and/or DBP ≥ 90 mmHg in patients who had received antihypertensive medication in the previous two weeks.This was a cross-sectional observational study, and participants were recruited from the cardiovascular surgery outpatient department in a single center of Hualien Tzu Chi Hospital, Hualien, Taiwan, between September 2018 and May 2019. There were 88 patients with a history of triple-vessel coronary artery disease who had undergone CABG enrolled in this study. All participants provided written informed consent. Blood samples were taken for laboratory analysis. CAVI and ankle–brachial index (ABI) were measured. Participants were excluded from the study if they had certain medical illnesses, such as malignancies (2).Anthropometric variables were measured in the morning after overnight fasting. Body weight and height were measured to the nearest 0.5 kg and 0.5 cm, respectively. Body mass index was calculated as weight (kg) divided by height squared , high-density lipoprotein cholesterol (HDL-C), and low-density lipoprotein cholesterol (LDL-C) were measured using an autoanalyzer . Serum cystatin C levels were measured using a nephelometric Siemens immunoassay . The estimated glomerular filtration rates (eGFRs) were determined using a Chronic Kidney Disease Epidemiology Collaboration equation (CKD-EPI Creatinine 2021). Serum MDA-oxLDL levels were measured using a commercially available enzyme-linked immunosorbent assay . The intra- and inter-assay coefficients of variation were 6.8% and 5.5%, respectively.Fasting blood samples (approximately 5 mL) were immediately centrifuged at 3000× Measurements were performed in a quiet, temperature-controlled room. After 10 min at rest in the supine position, CAVI was measured using the VaSera VS-1000 . Briefly, cuffs were applied to both arms and ankles, with the patient supine and the head held in the midline position. Then, the phonocardiography microphone and electrocardiography electrodes were set up at the designated location. The VaSera VS-1000 measured the brachial and ankle blood pressures, and the ABI and CAVI were automatically calculated. On the basis of an expert consensus from the Vascular Failure Committee in the Japan Society for Vascular Failure, CAVI of ≥9 was a statistically adequate value to indicate individuals with significant arterial stiffness and a high risk of cardiovascular disease . In thist-test or the Mann–Whitney U test was applied according to the Kolmogorov–Smirnov test, as appropriate. Categorical variables were presented as numbers along with percentages and compared using the chi-squared test. By using multivariable logistic regression analysis, we further assessed variables significantly associated with arterial stiffness, which was defined as CAVI ≥ 9. Factors that showed association with arterial stiffness were used in multivariable logistic regression analysis. A receiver operating characteristic (ROC) curve analysis was used to determine the optimal serum MDA-oxLDL levels indicative of arterial stiffness. Spearman’s rank correlation coefficient was used to analyze the correlation between the clinical variables and CAVI (left and right) and the MDA-oxLDL. IBM SPSS for Windows version 19.0  was used for all statistical analyses. A p < 0.05 was indicative of statistical significance.The Kolmogorov–Smirnov test was used to examine the normality of continuous variables. According to the results, these continuous data were expressed as the mean ± standard deviation or median with interquartile ranges. To compare the difference in continuous variables between the control and arterial stiffness groups, Student’s independent p = 0.004), had a higher percentage of DM (p = 0.029), and higher serum MDA-oxLDL levels (p < 0.001). Arterial stiffness did not differ significantly by sex or hypertension in this patient group. No significant difference in lipid profiles, fasting glucose, or renal function was found between the groups.In this study, 47 (53.4%) and 41 (46.6%) patients comprised the arterial stiffness and control groups, respectively . Comparep < 0.2, female, DM, age, triglyceride, height, BMI, Cystatin C, and MDA-oxLDL from p = 0.023) and DM  were independent predictors of arterial stiffness in patients with triple-vessel coronary artery disease who had undergone CABG .The results of this study revealed that older age, DM, and higher levels of serum MDA-oxLDL were associated with arterial stiffness in patients with triple-vessel coronary artery disease who had undergone CABG. After adjusting for confounding factors, the multivariable logistic regression analysis revealed that MDA-oxLDL levels and DM were independent predictors of arterial stiffness in these patients.Arterial stiffness increases with age, habits (smoking), and comorbidities, such as hypertension, DM, dyslipidemia, obesity, and sleep apnea ,7. SeverSince CAVI’s proposal in 2004, many studies have examined its utility as a relatively new method for evaluating arteriosclerotic disease and vascular stiffness ,4. CAVI One observational study demonstrated the positive correlation of arterial stiffness and the severity of coronary artery disease using arterial stiffness index, an index of vascular elasticity measured by oscillography . AnotherThe mechanism of arterial stiffness is composed mainly of endothelial dysfunction, change in extracellular matrix composition, calcification, impaired vascular smooth muscle cell relaxation, impaired nitric oxide bioactivity, inflammation, and multiple hormonals signaling pathways . Ox-LDL The purpose of this study was to demonstrate the relationship between oxidative stress and arterial stiffness, and the result implies that there is a positive correlation. We believe that CAVI is a simple and effective tool to evaluate arterial stiffness, and the process of measurement would not be too troublesome for most patients. Thus, CAVI could be used to evaluate the treatment response or identify the patients at high risk and to adjust the treatment strategy accordingly. MDA-LDL is a helpful laboratory marker of oxidative stress; however, it might not be a convenient tool for use in a clinical scenario at present. Currently, we use MDA-LDL only for study purposes, and we do not suggest it should be measured in every post-CABG patient.In this study, we used MDA-oxLDL as a marker of oxidative stress in our patients, and we found that MDA-oxLDL showed a significantly positive correlation with CAVI and was an independent predictor of arterial stiffness.The relationship that we found between MDA-oxLDL and arterial stiffness might have some clinical significance. First, CAVI is a simple and effective tool to evaluate the extent of the arterial stiffness and to predict the risk of a cardiovascular event in patients with high CV risks. In addition, it could be used as a measurable goal for evaluating the effect of the treatment targeting the reduction of the arterial stiffness risk, including both pharmaceutical and lifestyle modification.However, our study had several limitations. First, it was a cross-sectional observational study that analyzed a small sample size and was conducted in single center. Second, CAVI has been demonstrated to be positively correlated with the severity of coronary atherosclerosis ,32. In tIn a small cohort of patients with triple-vessel CAD who had undergone CABG, older age, DM, and MDA-oxLDL were found to be independent risk factors for arterial stiffness.