To distinguish clinical factors that have time-varying (as opposed to constant) impact upon patient and graft survival among pediatric liver transplant recipients.Using national data from 2002 through 2013, we examined potential clinical and demographic covariates using Gray’s piecewise constant time-varying coefficients (TVC) models. For both patient and graft survival, we estimated univariable and multivariable Gray’s TVC, retaining significant covariates based on backward selection. We then estimated the same specification using traditional Cox proportional hazards (PH) models and compared our findings.For patient survival, covariates included recipient diagnosis, age, race/ethnicity, ventilator support, encephalopathy, creatinine levels, use of living donor, and donor age. Only the effects of recipient diagnosis and donor age were constant; effects of other covariates varied over time. We retained identical covariates in the graft survival model but found several differences in their impact.The flexibility afforded by Gray’s TVC estimation methods identify several covariates that do not satisfy constant proportionality assumptions of the Cox PH model. Incorporating better survival estimates is critical for improving risk prediction tools used by the transplant community to inform organ allocation decisions. Liver allocation and transplantation policies in the US must balance the problems of donor organ scarcity with mandates for fair and effective allocation. In response, oversight of the allocation process has evolved to include development and maintenance of national registry data for patients who are listed and/or transplanted ; developThe Pediatric Acute Liver Failure (PALF) study funded by the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) is a multicenter study focused on children diagnosed with PALF. Diagnoses associated with PALF differ significantly from those seen in adults; in particular, specific diagnoses are not established in up to 50% of pediatric cases . ReliablAs collaborators with the PALF study, we are expanding prior work with a simulation model of liver transplant candidates originally calibrated for adults only . ExtendiIntegral to developing a liver transplant decision model for PALF, the focus of this report is to demonstrate optimal methods for predicting post-transplant outcomes in pediatric transplant recipients, including children with PALF, by comparing conventional estimation methods with those that are more flexible but also more challenging to employ.Separate but analogous analyses were conducted for two primary outcomes—post-transplant patient survival and graft survival—and survival curves were generated to illustrate effects over time for transplant recipients with a representative set of covariates. The University of Pittsburgh Institutional Review Board approved this study.without transplantation for liver transplant candidates has been estimated using severity of illness calculations, specifically Pediatric End-Stage Liver Disease (PELD) scores for children less than 12 years old [after transplantation. Researchers are divided, with some studies reporting associations between pre-transplant MELD scores and post-transplant survival[Since February 2002, risk of death ears old  and Mode survival, 14 and  survival, 16. In  survival.Instead, post-transplant outcomes rely on survival models, including our earlier work , 19. Theseries of Cox PH models—as the name suggests, it is “piecewise constant” within a given time interval that may be adjusted up or down in subsequent intervals. Gray’s TVC model captures important changes in covariate effects and is an extension of Cox, but estimation is more complicated and not easily available in software.Gray’s piecewise-constant time-varying coefficients (TVC) model  is one sWe obtained a standard de-identified data file of transplant candidates from United Network for Organ Sharing (UNOS), based on Organ Procurement and Transplantation Network (OPTN) data. The main file contains patient diagnoses  and demoFor transplant recipients, the database additionally provides demographic and clinical information about the donor organ; post-transplant follow-up information and lab values; and re-listing and re-transplantation information, if applicable.post-transplant patient survival (number of days between primary liver transplant and death) and graft survival (number of days between primary liver transplant and death or re-transplantation).We considered two outcome variables, without transplantation. For both outcomes, we considered the same initial covariates related to the recipient, the donated organ, and the transplant procedure , growth failure , ventilaDonor characteristics. Donor-specific covariates include demographics, blood type, whether the donor was deceased or living, and CMV and EBV status.Transplant information. Information describing the transplant itself included year of transplant (a proxy for secular changes), transplant center region (defined by OPTN/UNOS), a binary indicator for use of partial/split organs, cold ischemia time, and transport distance of the donor organ. Except for geographic region, information about transplant centers was not available.We summarized cohort characteristics using descriptive statistics, first for the entire sample and then separately for patients who remained alive (without re-transplant) for the study duration, died (without re-transplant), or were re-transplanted during the study period.P-value < 0.15. This subset was combined into a multivariable Gray TVC model, using a backward stepwise procedure for variable selection to gain more power.We followed the same analytical procedure for both patient and graft survival, initially testing proportionality assumptions for each covariate and estimating univariable models using Gray’s TVC model. Importantly, the Cox PH model is a special case of Gray’s; when covariates satisfy proportionality assumptions, estimates for the two models are identical. Using univariable results, we retained covariates with a We encountered two types of missing data: dichotomous variables  that are often overlooked when absent; and values where data were not captured. In the first case, we treated missing data as “absence” of a condition and tested this in sensitivity analyses; in the second case, data were treated as truly missing and observations were dropped from the estimation.After finalizing our specification using Gray’s TVC, we estimated the corresponding Cox PH model. The findings are summarized graphically, and we superimposed both hazard plots onto a common coordinate axis.The OPTN data file contained 5,718 children less than 18 years old who were listed for liver transplantation between February 2002 (when MELD/PELD was implemented) and June 2010. We excluded 1,183 children who were removed from the waiting list for myriad reasons, including death (n = 448), too sick (n = 172), too healthy (n = 445), refused transplant (n = 14), missing transplantation data (n = 3), and other/unknown reasons (n = 101). We also removed children still awaiting transplantation (n = 498). Finally, we excluded 574 children receiving multiple simultaneous organ transplants  and 288 recipients with liver cancer, who were evaluated separately [p < 0.001). An analogous figure for graft survival appears in supporting information  at transplant, black, and publicly insured. They were more likely to have acute liver failure or miscellaneous other diagnoses ; they apFactors related to the donor or procedure itself did not vary greatly, although recipients who remained alive enlisted living donors more often than those who died or were re-transplanted, and re-transplanted recipients had higher rates of partial/split donor organs for their primary transplant . DecedenIn estimating univariable Gray’s TVC models, serum sodium was excluded because of missing values (n = 883). Of the remaining covariates, 13 were significantly associated with overall survival: recipient age, race/ethnicity, primary source of payment, liver disease, total bilirubin, creatinine, encephalopathy, ventilator support, donor age, use of a living donor, use of partial/split organs, type of organ procurement , and cold ischemia time.Covariates were considered jointly for multivariable estimation using backward stepwise selection. The final Gray TVC model  and served as the referent category. In comparison, survival of recipients with acute liver failure, autoimmune diseases, and metabolic disorders experience was similar to that of biliary atresia . Only recipients with miscellaneous other  have significantly poorer survival outcomes after transplant.Recipient age. Recipient age at time of transplant has no effect initially; after 3 years, children who were older at time of transplant have a higher risk of death than those transplanted at younger ages. “Higher risk” is a relative statement: between any two age groups, older recipients have higher risk of death 3 years after transplantation. Although this statement appears self-evident, it bears mention because the cohort consists exclusively of children.Creatinine at transplant. In contrast to the Cox PH model, the estimated hazards from the Gray TVC model show that elevated creatinine levels increase the recipient’s risk of post-transplant death during the first 90 days. This risk declines afterwards and later becomes nonsignificant.Encephalopathy/Ventilator support. If encephalopathy is present and/or use of ventilation is required at transplant, patients experience a higher risk of death, particularly in the first 6–12 months.Race (black vs. nonblack). The Cox PH model indicates poorer post-transplant survival for black recipients at all time points, whereas the time-varying estimates show no differences initially but increased risk for black race over the long term.Use of living donors. The Cox PH model shows immediate benefit to use of living donors. In the Gray TVC model, the initial survival benefit is not statistically significant; however, the advantages become apparent after 6 months and remain significant.Donor age. Both models show that older donor organs increase risk of death and the risk is constant over time.Our findings reveal additional insights from time-varying methods, but clinical significance is harder to interpret. This section describes a pediatric transplant recipient with a typical combination of covariates (prototype) and generates survival curves to highlight covariate effects over time.We defined a prototype using median values for continuous covariates and modal outcomes for categorical variables. Only covariates for the final model  were conWe generated new survival curves and varied each covariate in turn, holding everything else at baseline values Figs , 5 and 6Tables and figures for graft survival are provided in supporting information.When these steps were repeated to evaluate graft survival, the same covariates were significant in univariable models, except for primary source of payment, use of partial/split organs, and cold ischemia time. We also retained the original race/ethnicity categories because the model converged without recoding. Covariates were combined for multivariable estimation, and non-significant covariates were excluded. The final graft survival model included the same covariates retained in the patient survival model .Graft survival for recipients with metabolic disease and acute liver failure was similar to biliary atresia, but autoimmune disorders and the miscellaneous other category both showed increasing risk of graft failure. The increased risk is observed late (after 4 years post-transplant) with autoimmune disorders but occurs early (after 6 months post-transplant) in miscellaneous other. The effect of creatinine is also different: higher creatinine levels at transplant increase the risk of graft failure, and the risk does not dissipate over time. Recipient age and race have the same effects on graft survival as they did with patient survival. Use of living donors is uniformly better and use of older donor organs increases risk for graft failure. As with patient survival, ventilator support dramatically increases risk of early graft failure, and risks associated with encephalopathy are immediate and persist over time.The series of graft survival curves for a prototypical recipient are provided in The figures show that older children experience better graft survival than younger patients; black recipients have worse graft survival than other recipients. There are slight differences based on liver disease and no variation across creatinine levels. The greatest risks for graft failure occur with encephalopathy or ventilator support, or with the use of deceased donors. Risk also increases with the age of the donor.The transplant community grapples with demand for services that far exceeds donor organ availability, and more than 2,200 individuals die on the waiting list annually . The simDefining goals and the best use of resources is part of the conversation. In renal transplantation, researchers have advocated for shifting organ allocation priorities from the sickest to those who will benefit the most , 27. SimWhen considering these or other potential policy changes, accurate and robust predictions of survival (with and without transplant) are needed. Decision models and risk prediction equations are increasingly important for anticipating the impact of potential changes a priori. The current paper demonstrates advantages of time-varying approaches for estimating risk of death/graft failure in children after transplant. Overall survival was related to recipient characteristics , severity of illness , and donor attributes . Beyond their importance in constructing post-transplant outcome models, these findings identify opportunities to improve pre-transplant management and highlight the challenges associated with outcome disparities related to age and race. Pre-transplant management that includes judicious use of blood products and colloid infusions and avoidance of nephrotoxic medications in settings of acute or acute-on-chronic liver failure may impact the frequency of ventilator support and renal insufficiency . Racial The Gray’s TVC model provided insights that were, in some cases, surprising. Though we might expect ventilator support and creatinine levels to have waning effects on survival after the initial peri-transplant period due to survivor bias , it is surprising that the effect of encephalopathy, another measure of illness severity, persists for much longer. Cross-sectional neurocognitive outcomes among children with acute liver failure identified lasting impairment of motor skills, attention, and executive function associated with clinical encephalopathy . The impThe same covariates matter in graft survival. Using older donor organs appears to increase the risk of graft failure later, but many other putative donor characteristics were not significant.Once adjusting for these covariates, structural characteristics of the transplantation network mattered less than historically believed. Specifically, differences in organ procurement  and cold ischemia time did not affect graft survival significantly, somewhat surprising given previous findings. Year of transplant was not significant either, suggesting that overall survival in children has been relatively stable. Where disease etiology matters , the effect is not apparent in the short term but becomes important over longer periods of time. The combined effect of these covariates was illustrated through the patient prototype rather than looking at each covariate in isolation.We encountered several limitations in our analysis, largely related to the covariates that were considered and the retrospective nature of the analysis. First, we had to exclude several covariates that had a high proportion of missingness, especially serum sodium which was not collected in OPTN data until November 2004. Data collection has expanded and these variables should be considered in the future. Second, using a stepwise procedure with backwards selection excluded several surprising variables from the final model, particularly cold ischemia time, transplant center location, and laboratory values measured at time of transplant. However, backwards selection also guards against highly correlated covariates, which may explain why variables were excluded. We therefore tested these exclusions in sensitivity analyses before finalizing the model specification. Third, our estimates relied upon retrospective information and should be validated prospectively. We also do not know yet how using more flexible prediction equations will affect the overall simulation or whether the predicted outcomes for pediatric recipients will be substantially different. Survival estimates are only one part of a larger model that needs to be considered in combination with simulation, cytokine networks and growth mixture models described previously , as a waThe strengths of the paper include use of comprehensive, national data for pediatric liver transplant recipients, suggesting that the findings here are generalizable. One group of recipients was systematically excluded (those with a primary diagnosis of cancer) because unadjusted survival differed substantially from other diagnoses and was examined separately . Using tFor both patient survival and graft survival, the effect of several variables varied over time, which is consistent with our understanding of pathophysiology. However, the Cox PH model must “average” these changing effects over time, which misrepresents the impact of covariates on survival and potentially results in faulty decision making.Our analysis demonstrated that standard Cox PH models are not appropriate statistical methods for predicting post-transplant survival. Effects of several important patient characteristics are not constant over time, and time-varying effects cannot be captured by the Cox PH model. Whatever transplant outcomes policymakers hope to optimize in the face of limited resources, good risk prediction tools are important for demonstrating the policies that will achieve those goals.S1 Fig(TIF)Click here for additional data file.S2 FigIn each graph, the effect of the covariate is graphed over time based on the Cox proportional hazards model (red line) and Gray’s time-varying model . The model estimates can be compared to a log hazard of 0 .(TIF)Click here for additional data file.S3 FigIn each of the graphs, the “prototypical pediatric transplant recipient” uses median values for continuous variables and modal values for categorical variables. The graft survival curve for the prototype appears in all graphs and is represented by solid circles.(TIF)Click here for additional data file.S4 FigIn each of the graphs, the “prototypical pediatric transplant recipient” uses median values for continuous variables and modal values for categorical variables. The graft survival curve for the prototype appears in all graphs and is represented by solid circles.(TIF)Click here for additional data file.S5 FigIn each of the graphs, the “prototypical pediatric transplant recipient” uses median values for continuous variables and modal values for categorical variables. The graft survival curve for the prototype appears in all graphs and is represented by solid circles.(TIF)Click here for additional data file.S1 Table(DOCX)Click here for additional data file.


Crystallography has influenced many of the traditional science disciplines and has opened a number of cross-disciplinary activities often bringing physicists, chemists, biologists and medical scientists together. Whether it is something as simple as table salt or as complex as the ribosome, crystallography has provided an insight that no other approach could provide. The first diffraction experiment on a single crystal of copper sulfate by Max von Laue in 1912  in 1948, the year in which the IUCr started its first journal, Acta Crystallographica, which aimed to provide a home for all aspects of crystallographic research. It is worth noting that the structure of jack bean urease was determined only in 2010 . In 1926, he succeeded in crystallizing the first enzyme with high activity  ‘for the development of multiscale models for complex chemical systems’, to Robert Lefkowitz and Brian Kobilka ‘for studies of G-protein-coupled receptors’, and to Danny Shechtman ‘for the discovery of quasicrystals’, respectively. In 2010, Andre Geim and Kostya Novoselov received the Physics Nobel Prize‘for groundbreaking experiments regarding the two-dimensional material graphene’, opening a whole new field of two-dimensional materials chemistry. We congratulate the 2016 Nobel Prize winners in Physiology and Medicine (Yoshinori Ohsumi ‘for his discoveries of mechanisms for autophagy’) and Chemistry . We are pleased to note that Ohsumi, Stoddart and Feringa have published some 40 papers in IUCr journals during the period 1986–2014.In the current decade, the ultimate recognition of a Nobel Prize has been acheived across a whole range of sciences, demonstrating the outreach of crystallography. The 2013, 2012 and 2011 Chemistry awards went to Martin Karplus and Michael Levitt IUCrJ. The journal received its first impact factor of 5.3 this year. This starting impact factor is pleasing and results from our authors having the trust and confidence to submit some of their best work to the journal. We encourage you all to consider the journal alongside other notable journals such as PNAS, JACS, Nature Communications and Nature Materials. The top ten countries contributing to the journal were the USA, the UK, Germany, France, India, Japan, Denmark, Switzerland, Australia and China/Russia/Spain; eight of these are common with Nature, Science and PNAS. The five top contributing countries of the 30 most cited papers  were Germany, the USA, the UK, France, India and Switzerland.One hundred years after the first Nobel Prize to crystallography to Laue in 1914, the IUCr celebrated the impact and influence of crystallography by launching a comprehensive, all inclusive open-access journal, et al., 2014et al., 2014et al., 2005These highly cited papers represent the full range of science, methods and instrumentation. The broad area of science covered was from halogen bonds , where as well as the keynote speakers of the IUCr Gjonnes Medal (Richard Henderson and Nigel Unwin), there will be an additional keynote (Sriram Subramanian) and three microsymposia each with six talks. Like the Congress, IUCrJ aims to be a leading journal for reporting important advances in cryo-EM methods as well as significant science results from the application of cryo-EM, which is proving to be the method of the decade.Like the FEL community, we wish to encourage the cryo-EM community to make http://www.ascb.org/dora/). The Declaration calls on the world scientific community to stop using journal-based metrics, particularly journal impact factors, as a surrogate measure of the quality of individual research articles, or in the assessment of individual scientists’ contributions. It is clear from a citation analysis of PNAS, IUCrJ and Nature that a large proportion of papers in these journals receive much lower numbers of citations than the journal’s impact factor, making use of such metrics for hiring, promotion or funding decisions irrational. The policy of IUCr Journals is to present impact factors within the context of a broader range of journal-based metrics such as five-year impact factors, Eigenfactors, publication times etc. We also publish journal citation distributions for each of our journals. We emphasize that even these extended metrics are merely indicators of the performance of a journal and must not be used for assessing an individual scientist’s performance for recruitment, promotion, or funding decisions.We are pleased to announce that the IUCr has signed the San Francisco Declaration on Research Assessment (DORA,


Journal of Health, Population and Nutrition (JHPN) into an open access, peer-reviewed online journal under the sponsorship of BioMed Central. While celebrating the start of an exciting new phase, it seems appropriate to reflect on the journal’s impressive history and to present some initial plans for the future of this new phase of the journal. Journal of Health, Population and Nutrition (JHPN) indeed has a rich and illustrious history. The International Centre for Diarrhoeal Diseases Research, Bangladesh , a world‐class public health research organization in a developing country, first launched the Journal of Diarrhoeal Diseases Research in 1983 and the journal took its current name in 2000. During the period 2000–2015, under the management of icddr,b, and with an eminent international editorial board, the journal became internationally renowned for its rigorous standards and its special focus on research of relevance to developing countries.We are pleased to announce a new phase of the The new incarnation of the journal will keep this special focus on the developing world. Under BioMed Central, we aim to offer an open access forum for scientifically sound and innovative articles across the broad areas of health, population and nutrition. Topic areas will include traditional areas of global health, such as maternal, newborn and child health, under-nutrition, common illnesses and injuries and determinants of population health. Global burden of disease studies demonstrate that the epidemiological transition is already well advanced and the poorest in developing countries face a triple burden that includes communicable diseases, non-communicable diseases and illnesses linked to socio-behavioural factors. The facts suggest that public health research, policy, and programs in resource poor countries need to adjust. JHPN, therefore, is adapting to address this shift in disease burden occurring in developing countries.Although the journal is entering a new phase, we decided to keep the name to make us mindful of the journal’s rich history. We hope, however, that as open access, international journal with broad focus on health, population and nutrition, streamlined review, and renewed emphasis on the quality and relevance of the papers, we can attract wider readership. With more downloads and more citations, we should be able to earn a higher impact factor. We hope our transformation will contribute to improvements of health, reduction of health disparities, and protection against global threats to health through sharing of innovations and by promoting exchange of information.The articles will be published as soon as they are accepted and will be archived in BioMed Central which will also allow the access by readership. Authors will continue to hold copyright for their work and will be able grant anyone the right to reproduce and disseminate the article, provided that it is correctly cited and no errors are introduced. We hope that the open access nature of JHPN will promote exchange of ideas internationally.Manuscripts submitted to JHPN will be reviewed independently by at least two experts in the field. We are interested in publishing articles of the highest quality and originality. Our goal is to make JHPN an important journal by providing opportunities for communication among the scientists in the field of health, population and nutrition. We look forward to your submission.


The stickiness of cooked rice is important for eating quality and consumer acceptance. The first molecular understanding of stickiness is obtained from leaching and molecular structural characteristics during cooking. Starch is a highly branched glucose polymer. We find (i) the molecular size of leached amylopectin is 30 times smaller than that of native amylopectin while (ii) that of leached amylose is 5 times smaller than that of native amylose, (iii) the chain-length distribution (CLD: the number of monomer units in a chain on the branched polymer) of leached amylopectin is similar to native amylopectin while (iv) the CLD of leached amylose is much narrower than that of the native amylose, and (v) mainly amylopectin, not amylose, leaches out of the granule and rice kernel during cooking. Stickiness is found to increase with decreasing amylose content in the whole grain, and, in the leachate, with increasing total amount of amylopectin, the proportion of short amylopectin chains, and amylopectin molecular size. Molecular adhesion mechanisms are put forward to explain this result. This molecular structural mechanism provides a new tool for rice breeders to select cultivars with desirable palatability by quantifying the components and molecular structure of leached starch. Rice is a major staple food world-wide. Consumer preferences are shifting towards better-quality rice, particularly towards varieties with good eating quality24Cooked rice texture is affected by a wide range of factors, such as the amylose content97–8, whereas Am has a smaller molecular weight (~105–6) and a few long branches11Starch structure has an important role in rice texture4511et al.et al.In contrast to hardness, stickiness between rice grains is less commonly investigated, and the mechanism of rice stickiness is unclear, even though stickiness between rice grains is the key requirement for sushi, which is a very popular food. Stickiness has previously been related to grain length, with short grains being usually thought of as sticky and the long grains as not234Rh) of the leached starch; and 2) to devise mechanistic reasons for any differences in terms of leaching characteristics and molecular structural features of leached starch.Using a set of rice cultivars differing in terms of amylose content, the objectives of this study are: 1) to identify and characterize the amounts and molecular structural features (both chain-length distribution (CLD) and molecular size, measured by size-exclusion chromatography  and amylopectin (Rh > 100 nm). The elution pattern of the two waxy varieties indicates that there is some co-elution of small amylopectin molecules and large amylose molecules. Another small peak at Rh ~1 nm may be residual proteins, due to the incomplete hydrolysis by protease during the starch extraction procedure. For the leached starches  varies significantly, especially for high-amylose rices, for which hAP2 of both grain and leached starches are much higher than that of other rice samples. et al.X = 6–12, 13–24, 25–36, and 37–100, described as short, medium, long, and very long chains respectively. Waxy rices (KN and HMN) have more short branches and fewer very long chains, whereas high-amylose rices show an opposite distribution with less short chains but more very long chains. For the Ap CLD comparing grain and leached starch, most rice cultivars, except high-amylose rices, do not display large variations. Compared to the Ap CLD of grain starch for high-amylose rices, the leached starch of high-amylose rices contains significantly less medium and long chains but more very long chains. Even though the average DP of amylopectin ifferent , the AM ifferent , whereasifferent . Even th samples .As shown in As displayed in As shown in 34Starch is the main component of the rice grain. When rice is cooked, the main physical change is starch gelatinization. When starch granules swell as a result of the loss of the crystalline order and the absorption of water2627293031Rh 10–100 nm is where amylose molecules elute  to long AP (X > 37) chains), together with larger molecular size of leached amylopectin, produces a higher viscous resistance, i.e. a higher stickiness.It is shown here and elsewhereIn this study, the way that TPA measures the property termed “stickiness” (which follows the same principle as that of measuring tack in adhesion) is as follows. A single layer of cooked rice grains is placed on a baseplate. A two-cycle force/distance compression test is conducted with a probe which descends slowly (step 1: bond formation) and then is moved back (step 2: bond separation)Since TPA stickiness is the resistance offered by the cooked rice grains to detachment from the probe, the higher the stickiness value, the more force is needed to make the grains and probe come apart. As presented in section 3.4, in the leachate, the stickiness increases with increasing total amount of amylopectin, the proportion of short amylopectin chains with DP ≤ 36, and amylopectin molecular size. A significant effect of amylose content (arising from cultivar differences) on leaching characteristics is also seen, which could be an underlying cause of the stickiness difference between rice varieties. As shown in Previous studies showed that the amount of leached amylose depends on the total amylose content223This study reveals that stickiness between cooked rice grains is determined by the total amount, molecular size and chain structure (CLD) of leached amylopectin. We present the first unified molecular-based mechanistic description of the causes of these important sensory properties, using the results in this study and previous findings by ourselves324An underlying origin of the stickiness differences between rice cultivars is the amylose content in the whole grain starch. With increasing amylose content, the total amount of leached materials, the amylopectin content in the leachate, and the molecular size and the proportion of short branches of leached amylopectin, all decrease, leading to a lower stickiness. However, amylose content is not the sole determinant. In some cases, amylose content is similar but the hardness425By quantifying the components and the molecular structure of leached starch, rice breeders could choose lines which optimize the texture of cultivars. For example, a cultivar which leaches more amylopectin with more short amylopectin chains and bigger molecular size would be sticky after cooking, which could be desirable for sushi. On the other hand, a cultivar which leaches more amylose should be less sticky but have a harder texture. This molecular structural mechanism provides a new tool for rice breeders to select cultivars with desirable palatability.Twelve varieties of rice were selected with a wide range with known phenotypes and genotypes for quality traits . After hStreptomyces griseus (type XIV), and LiBr (ReagentPlus) were purchased from Sigma-Aldrich Pty. Ltd. . Isoamylase (from Pseudomonas sp.) and a D-glucose  assay kit were purchased from Megazyme International, Ltd. . A series of pullulan standards with peak molecular weights ranging from 342 to 2.35 × 106 were from Polymer Standards Service (PSS) GmbH . Dimethyl sulfoxide  was from Merck Co. Inc. . All other chemicals were reagent-grade and used as received.Protease from Before cooking, residual bran and other adhering powders were removed from white rice kernels with an aspirating device. A 10-g sample of white rice was placed in a 100 mL beaker, and distilled water was added to the rice to give a rice-to-water weight ratio of 1:1.6. Thereafter, the beaker was sealed with aluminium foil, placed on a steaming tray, and cooked in a household rice cooker  for 30 min.After cooking and cooling to room temperature, a 1-g subsample of cooked rice grains was weighed and placed as a single layer of grains on the base plate. A two-cycle, force-versus-distance compression program was used for measurements with a TA.XT-Plus Texture analyser with a 35 mm cylindrical probe attachment . The probe descended at a speed of 1 mm/s, returned, and then the compression cycle was repeated. Compression was set to 40% strain to avoid destroying the rice grain. For each of 3 cooking replicates, texture measurements were conducted 6 times on the 1-g subsample of cooked rice grains. Stickiness between grains was recorded as the area of the negative force curve.μm sieve. The rinsing procedure was repeated again with 50 mL of hot deionized water. Both the washed kernels and the rinsing water were retained. The rinsed rice kernels were cooled and used to measure stickiness again by TPA. The water was frozen immediately using liquid nitrogen, and then freeze-dried for storage and further analysis. The total weight of the leached materials was recorded after freeze-drying.A sample of white rice (10 g) was cooked as described above. The leached materials on the surface of the cooked rice were extracted by rinsing with 100 mL of hot deionized water (~95 °C) with very gentle stirring using a glass rod for 5–10 s before filtering through a 250 Total starch content of leached materials was measured using a Megazyme total starch (AA/AMG) assay kit following a method described elsewherewbr(logRh). For branched starch molecules, as for any branched polymer, there is no unique relation between size and the molecular weight. For the debranched samples, which are linear, the relation between Rh and molecular weight M was obtained as follows. The assumption of universal calibration for SEC is that the elution time of the analyte depends only on its Rh and not on its structure, whence one has for two linear polymers, a sample and a standard, the relation:The structure of extracted whole starch and leached starch molecules was characterized by SEC using an Agilent 1100 Series SEC system  equipped with GRAM 30 and 3000 analytical columns (PSS) and a refractive index (RI) detector , following a method described elsewhere46K and α are the Mark-Houwink parameters for the polymer, solvent and temperature being used. Pullulan standards with known peak molecular weights were used for calibration to obtain a relationship between SEC elution volume and Rh of starch molecules following the Mark-Houwink equation:where NA is Avogadro’s constant. The Mark-Houwink parameters K and α of pullulan in DMSO/LiBr solution at 80 °C are 2.424 × 10−4 dL g−1 and 0.68, respectivelyHere μL isoamylase (1000 U mL−1), 0.1 mL acetate buffer solution , and 5 μL sodium azide solution (0.04 g mL−1). The mixture was incubated at 37 °C for 3 h. The debranched starch suspension was then heated in a water bath at 80 °C for 2 h after being neutralized with 0.1 M NaOH solution, and then freeze-dried overnight. The dried debranched starch was dissolved in DMSO/LiBr (0.5%) solution for SEC analysis.The extracted starch (~4 mg) was dissolved in 0.9 mL of deionized water and then mixed with 2.5 w(logX), obtained from the DRI signal was plotted against X (degree of polymerization DP), with X being determined using the Mark-Houwink relationship (see M = 162.2(X–1) + 18.0 ; K and α for linear starch chains in the eluent of DMSO/LiBr at 80 °C are 1.5 × 10–4 dL g–1 and 0.743, respectivelyNde(X), is related to the corresponding weight distribution byTo obtain SEC distributions of debranched starch, GRAM 100 and GRAM 1000 columns (PSS) were used, with the same pullulan standards and procedure as that used to calibrate the SEC for whole branched molecules. The SEC weight distribution, ship see  and withet al.The amylose content of all rices was determined from the SEC weight distributions of debranched starch following the procedure described by Syahariza p < 0.05. The textural measurements were analyzed in duplicate for each sample. One-way analysis of variance (ANOVA) and both Pearson and Spearman rank correlation methods were carried out using SPSS V. 16.0 software . The means of duplicated measurements were used for the correlation analysis.For each structural measurement, duplicate analyses were performed for each sample. All data were reported as mean ± standard deviation (SD) using analysis of variance (ANOVA) with Tukey’s pairwise comparisons. Significant differences of the mean values were determined at How to cite this article: Li, H. et al. The molecular structural features controlling stickiness in cooked rice, a major palatability determinant. Sci. Rep.7, 43713; doi: 10.1038/srep43713 (2017).Publisher's note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.


This study was performed to evaluate the effect of a lithium-disilicate spray-liner application on both the bond strength between zirconia cores and heat-pressed lithium-disilicate glass-ceramic veneers, and the fracture strength of all-ceramic zirconia crowns. A lithium-disilicate reinforced liner was applied on the surface of a zirconia core and lithium-disilicate glass-ceramic was veneered on zirconia through heat press forming. Microtensile and crown fracture tests were conducted in order to evaluate, respectively, the bonding strength between the zirconia cores and heat pressed lithium-disilicate glass-ceramic veneers, and the fracture strength of bilayered zirconia all-ceramic crowns. The role of lithium-disilicate spray-liner at the interface between zirconia and lithium-disilicate glass-ceramic veneers was investigated through surface and cross-sectional analyses. We confirmed that both the mean bonding strength between the zirconia ceramics and lithium-disilicate glass-ceramic veneers and the fracture strength of the liner-treated groups were significantly higher than those of the untreated groups, which resulted, on the one hand, from the chemical bonding at the interface of the zirconia and lithium-disilicate liner, and, on the other, from the existence of a microgap in the group not treated with liner. With the increase in patients’ demands for esthetic restoration, a variety of types of ceramic materials have been introduced to improve the esthetics of dental prostheses. Porcelain has several advantages, such as excellent esthetics, chemical durability, and a high compressive strength. Due to these advantages, it has been used in dental clinics as a form of porcelain jacket crown since 1887. However, it has not been widely employed due to fracture problems during mastication. Since then, a metal-ceramic restoration method, where a metal framework with superior mechanical properties reinforces fragile porcelain, has been adopted for the production of esthetic prostheses. However, since opaque prostheses resulting from both the metal framework’s interference of light and the exposure of the margin of metal have been pointed out as the main factor in the degradation of dental esthetics, much attention has been paid to the all-ceramics restoration method, which solely uses ceramic materials with sufficient strength, superior biocompatibility, and penetrability of light . Due to 2O3, which are rare-earth metal oxides, is added to pure zirconia sintered at a cubic section, and if this is then followed by heat treatment at a section where the cubic and tetragonal phases coexist, tetragonal crystals are precipitated within the cubic matrix and the transition to the monoclinic phase does not occur, even if the temperature is decreased [2O3, have widely been used to manufacture zirconia blocks for CAD/CAM processing.Zirconia refers to a zirconium (Zr) oxide that has excellent mechanical properties, even being comparable with those of metal. Thus, Garvie et al. claimed that zirconia was a “ceramic steel” and proposed a theoretical model around its superior mechanical properties . Pure ziecreased ,7. Thus,Zirconia has a high refractive index, which is not suitable for dental esthetics, as it can cause color mismatch with adjacent natural teeth. Because of this drawback, when zirconia has been employed in anterior esthetic restoration, porcelain or glass ceramic veneers have been used in the lower part of the zirconia, in traditional all-ceramic crowns for example. Although this two-layer structure is esthetic, there has been a problem with restoration failure due to veneers getting chipped or delaminated unless a strong bond is guaranteed between the two materials ,9.There has been much research on the causes of fractures at the interface between the zirconia core and veneer ceramics . It has In lately reported studies, lots of surface treatments have been conducted to enhance the adhesion between zirconia and veneering ceramic ,20,21,22This study therefore investigated the effect of a liner treatment on the bonding strength between zirconia cores and lithium-disilicate glass-ceramic veneers, as well as on the fracture strength of bilayered zirconia all-ceramic crown. The null hypothesis that is proposed in the present study is that liner treatment has no effect on either the bonding strength between zirconia cores and veneer ceramics or the fracture strength of bilayered zirconia all-ceramic crown.2Si2O5), zirconia (ZrO2), and silica (SiO2) peaks, we observed peaks for lithium metasilicate (Li2SiO3) and zirconium silicate (ZrSiO4).p < 0.01).2 > 0.86). The Weibull coefficient of the liner-treated group was higher than that of the untreated group. Additionally, the liner-treated group’s mean fracture strength was, statistically speaking, significantly higher than that of the untreated group (p < 0.01).We conducted this study in order to investigate what the effect of a lithium-disilicate liner treatment applied to a 3Y-TZP zirconia core would be on the bonding strength of lithium-disilicate glass-ceramic veneers and on the fracture strength of an bilayered zirconia all-ceramic crown. It was confirmed that the micro-gap dissipated after the linear treatment due to the chemical reaction at the interface between zirconia core and veneering ceramic during the heat press forming of the veneering ceramics, as shown in The strength of the material is an important factor in the chipping of veneer ceramics in zirconia all-ceramic crowns that were made of a zirconia core and upper veneer ceramics. However, both bonding and a matching thermal-expansion coefficient between the core and the veneer hold the highest importance, following the rationale that tensile stress occurring inside veneer ceramic may have a strong influence on chipping. Besides, structural improvements—such as a thickening of the vulnerable areas in veneers where high-tensile stress occurs, a structural design where the core can act as the support, and the prevention of pore-formation inside the sintered body and microgap-formation at the interfaces—are required in order to prevent the formation, via tensile stress, of chipping fractures in veneers .The mismatch of the thermal-expansion coefficient between the core and veneer induces residual tensile stress, which can lead to chipping creation . Since t4) was generated in a layer adjacent to the zirconia, while lithium metasilicate (Li2SiO3) was generated in a layer adjacent to the lithium-disilicate liner, as confirmed in Since zirconia is chemically stable at a high temperature, its bonding strength with veneer ceramics is low . To overAdditionally, the tensile bonding strength of the group treated with the lithium-disilicate reinforced spray-type liner was higher than that of the untreated group, and this was because of the formation of an acicular structure of lithium disilicate in the liner layer during the heat press forming of the veneer ceramics, as confirmed in After the fracture test of the all-ceramic zirconia crown, an interfacial fracture was revealed between the veneer and zirconia core for the untreated all-ceramic zirconia crown. For the liner-treated all-ceramic zirconia crown, a cohesive fracture was revealed in the reaction layer between the liner and core, resulting from strong bonding between the core and veneer materials. The fracture strength of the single crown was significantly higher for the liner-treated crown than for the untreated crown, as was the Weibull coefficient, and this was also confirmed by the figuration of the fracture. This can be explained by the fact that, when external force was applied to the crown, like To prepare the specimens of the zirconia-sintered body, a calcined 3Y-TZP disc block was prepared for CAD/CAM processing : it was sintered at 1450 °C for 2 h and then cut so as to measure 12 mm × 12 mm× 7 mm. 50 μm alumina abrasives  were sprayed with a pressure of 3 atm from a distance of 10 mm in order to increase surface roughness in the coupling portion. The specimens were put into an electric furnace and the temperature was increased at a heating rate of 50 °C/min to 1000 °C, and then maintained for 10 min in order to recover a phase-transition layer generated on the surface during the spray-treatment process. Finally, the specimens were then subjected to furnace cooling.2 < 82 wt %, Li2O > 10 wt %, P2O5 < 7 wt %, and other oxides and colorant < 6 wt %, was coated once on the surface of the 3Y-TZP, and the temperature was increased at a heating rate of 60 °C/min to 940 °C and then maintained for 90 s. Following this, a wax pattern that was the same size as the zirconia-sintered body was attached to both the untreated and the liner-treated group, and the investment material  was used to make a mold. After burning out the wax at 850 °C for 50 min, we conducted heat pressing at 925 °C using lithium-disilicate glass-ceramic ingot , as shown in The prepared specimens were randomly divided into the untreated and liner-treated group. For the liner-treated group, a lithium-disilicate reinforced spray-type liner , composed of SiO50 μm glass beads  were blasted at a pressure of 2 atm to remove the investment material that was attached to the specimen’s surface. Then, ultrasonic cleaning was conducted in deionized water for 5 min. The specimens were then fixed to a low-speed diamond cutter and cut into 1.1 mm × 1.1 mm sizes. Four of these cut samples were taken from the center of each specimen. A metal holder was attached to both sides of the specimen for microtensile bond testing. The prepared specimens were mounted to a universal testing machine , and tensile force was applied at a crosshead speed of 0.5 mm/min in order to measure a load at the moment of an interface fracture. The tensile-bond strength was calculated by dividing a load by a cross-section in the coupling portion. Twelve specimens from each of the untreated and liner-treated groups were used for the microtensile bond testing.A model of the mandibular first molars of permanent teeth was scanned. Thirty metal abutments were prepared following a customized cutback design. After designing the zirconia coping with a 0.5 mm thickness, a 3Y-TZP disc block  was processed with the milling machine M1  in order to prepare a total of 30 copings, which were then put into a zirconia sintering furnace  where the temperature was increased at a heating rate of 3 °C/min up to 1450 °C, and then maintained for two hours.All of the zirconia copings were treated by blasting with 50 μm alumina abrasives  at a pressure of 3 atm from a distance 10 mm in order to increase surface roughness in the coupling portion. Specimens were divided into the untreated and liner-treated groups, each with 15 randomly allocated specimens: the liner-treated group was obtained by increasing the temperature to 940 °C and maintaining it there for 90 s after applying one coating of spray-type liner.A crown wax pattern designed and prepared with CAD/CAM was bound to the copings of both the untreated and liner-treated groups, and their molds were made using investment  mixed with water at a ratio of 0.25 and then left at room temperature for 30 min. The molds were heated at 850 °C for 50 min, after which they were coupled to a disilicate glass-ceramic ingot  and put into the electric furnace  where they were maintained at 915 °C for 15 min, before being subjected to heat press molding.® Classic No. 5001, Dedeco International Inc., Long Eddy, NY, USA). For finishing, we used Kohinoor L . After molding was completed, the mold was taken out from the electric furnace and then cooled until it became a room temperature. Blasting with 50 μm glass beads was performed at a pressure of 2 atm to remove the investment material attached to the crown’s surface. In order to make it uniform, the surface was then sequentially polished using Carborundum Wheel , Carborundum Point , Silicone Wheel , and Rubber Wheel  for 30 min and then cleansed with water before being dried. Following this, 10-methacryloyloxydecyl dihydrogen phosphate (MDP)-containing primer  was coated and lightly dried with a drier. We took and evenly mixed a suitable amount of double-polymerized resin cement , a base agent, and accelerator, which we then filled inside the crown. After this, we applied a compressive force of 49 N using a static-load device to cement the crown to the metal abutment. It was then stored in distilled water at 37 °C for 24 h for an aging treatment.The prepared crown was fixed vertically on the retainer and then mounted to the universal testing machine . A steel ball measuring 3 mm in diameter was placed at the crown’s center and then arranged so as to be placed at the center of the load rod, as shown in Using a high-resolution field emission scanning electron microscope , we observed the morphological microstructure of the surface and bond interface after the liner treatment on 3Y-TZP and the fractured surface after the microtensile test, after acid-etching the specimen in a 9% HF aqueous solution for 30 s. Additionally, the surface of the liner-treated 3Y-TZP was acid-etched in a 5% HF aqueous solution for 30 min in order to remove a layer of liner, so as to identify the effect of the liner treatment on the structural change of zirconia grains. We analyzed the concentration change of elements in the reaction layer at the bond interface using energy-dispersive X-ray spectroscopy . We analyzed the crystal structure of the bond interface after the liner treatment on 3Y-TZP using an X-ray diffractometer .p-value of <0.01 as an indication of statistically significant differences.Data were statistically analyzed using the statistical software SPSS ver12.0 . A one-way analysis of variance (ANOVA) with the Tukey test was performed in order to compare the bonding strength between the zirconia core and ceramic veneer and the single crown’s fracture strength between the untreated and liner-treated group. We considered a The present study aimed to evaluate the effect of liner treatments of 3Y-TZP ceramic cores on the bonding strength of lithium-disilicate glass-ceramic veneers and on the fracture strength of bilayered zirconia all-ceramic crowns. To achieve this, we conducted microtensile bond tests and fracture tests on a bilayered zirconia all-ceramic crown and identified the following results. A chemical bond occurs via the reaction layer in the coupling portion between the zirconia and lithium-disilicate liner. Statistically speaking, both the mean bonding strength between the ceramic zirconia and lithium-disilicate glass-ceramic veneer, and the fracture strength of the liner-treated group were significantly higher than those of the untreated groups. We confirmed that for the untreated group, the resistance to fractures dropped due to the stress concentration at the interface, which resulted from the generation of a microgap between the core and veneer. For the liner-treated group, on the other hand, the resistance to fractures rose due to the stress relaxation at the interface, which resulted from the elimination of microgap between the core and veneer through the binding of the veneer and liner.In conclusion, given that the chemical bonding occurs at the interface, the application of a lithium-disilicate liner to zirconia and lithium-disilicate glass-ceramic veneering can greatly contribute to improvements in the fracture strength of crowns.


The Supporting Information files are incorrectly labeled and described. Please see the correct labels and descriptions for the Supporting Information files here:The proper caption for The proper caption for The proper caption for The proper caption for S1 TableThe equations indicate prosthetic displacement in meters (h) used to calculate the applied force in kN. Stiffness equals applied force divided by displacement. a and b are constants. All prostheses were tested with the manufacturer supplied sole, with the exception of stiffness category 7 No Sole.(DOCX)Click here for additional data file.S2 TableThe equations indicate prosthetic displacement in meters (h) used to calculate the applied force in kN. Stiffness equals applied force divided by displacement. a and b are constants. All prostheses were tested with the manufacturer supplied sole, with the exception of stiffness category 7 High No Sole.(DOCX)Click here for additional data file.S3 TableThe equations indicate prosthetic displacement in meters (h) used to calculate the applied force in kN. Stiffness equals applied force divided by displacement. a and b are constants. All RSPs were tested with the supplied sole from the Össur Flex-Run prostheses, with the exception of stiffness category 7 No Sole.(DOCX)Click here for additional data file.S4 TableThe equations indicate prosthetic displacement in meters (h) used to calculate the applied force in kN. Stiffness equals applied force divided by displacement. a and b are constants. All prostheses were tested with the manufacturer supplied sole, with the exception of stiffness category 5 No Sole.(DOCX)Click here for additional data file.


One of the disadvantages of the zirconia implants is the lack of elasticity, which is increased with the use of ceramic or zirconia crowns. The consequences that could result from this lack of elasticity have led to the search for new materials with improved mechanical properties.A patient who is a 45-year-old woman, non-smoker and has no medical record of interest with a longitudinal fracture in the palatal root of molar tooth 1.7 and absence of tooth 1.6 was selected in order to receive a zirconia implant with a PEEK-based restoration and a composite coating. The following case report describes and analyses treatment with zirconia implants in molars following a flapless surgical technique. Zirconia implants are an alternative to titanium implants in patients with allergies or who are sensitive to metal alloys. However, one of the disadvantages that they have is their lack of elasticity, which increases with the use of ceramic or zirconia crowns. The consequences that can arise from this lack of elasticity have led to the search for new materials with better mechanical properties to cushion occlusal loads. PEEK-based restoration in implant prosthetics can compensate these occlusal forces, facilitating cushioning while chewing.This procedure provides excellent elasticity and resembles natural tooth structure. This clinical case suggests that PEEK restorations can be used in zirconia implants in dentistry. In the field of implant dentistry, the most widely used implants over the past 40 years are those manufactured from titanium , which aThe recent demands for materials without metal alloys in dentistry, together with the increased sensitivity and allergies of some patients, have promoted the development of new materials.An example of this is zirconia-based dental implants, known as zirconia or zirconium oxide implants. Its biocompatibility and its extraordinary mechanical properties make it suitable for numerous situations. Its main advantage lies in its elasticity which is greater than that of titanium and much greater than that of cortical bone. To avoid overload of the underlying bone from the direct transmission of biting impacts, several materials that can absorb part of this excess force have developed.One of the prosthetic options lies in the combined use of PEEK restorations with composite coating on zirconia implants due to their physical and mechanical properties and their biocompatibility.A patient who is a 45-year-old woman and non-smoker has no medical record of interest. The patient complained of pain in the right second upper molar. She said that she felt intense pain while chewing. The pain was accentuated with occlusion and while chewing, making normal functioning impossible. The patient mentioned the absence of piece 16, which had been extracted 8 years previously.Clinical examination showed a longitudinal fracture in the palatal root of molar tooth 17, which was confirmed by a radiographic examination  zirconia implants of 10 mm length × 4.5 mm diameter in positions 17 and 16 (8 mm length × 4 mm diameter) Fig. .Fig. 2FlFifteen days after surgery, the appearance of the soft tissue was excellent, with no signs of inflammation in the mucosa. The patient mentioned the absence of bleeding and pain during the post-operation period. At the same time, we made a clinical and radiological evaluation. Three months after surgery, the stumps of the implants were carved to improve their parallelism with a special diamond drill (Kit Bredent®). Finally, we took impressions for the final restoration with polyether  without using retraction threads.The final restorations were produced using CAD/CAM System Juvora® for the PEEK structure with composite coating (Anaxdent®). For cementation ionomer glass cement reinforced with resin was used  Figs.  and 4.FiA clinical and radiographic review carried out a year after the initial surgery showed the complete success of the procedure according to Albrektsson’s criteria and the natural aspect of the soft tissue around the restorations Fig. .Fig. 5PeIntraoral conditions  interact with metals, increasing corrosion, a phenomenon that also affects titanium implants , 5. AmonIn recent years, several implant manufacturers have investigated the behaviour of zirconia implants on hard and soft tissues. The characteristics of their biocompatibility, together with good osseointegration, make them clear candidates for clinical use in dentistry , 8. One Several studies have shown that zirconia implants present a similar healing pattern to titanium implants, both as regards the healing time and marginal bone stability –13. HoweIn terms of the load-cushioning capacity of the prosthetic elements, the use of PEEK as a prosthetic structure on implants has increased in recent years . PEEK isPEEK has a modulus of elasticity (E-modulus 4 GPa) great overdenture implants compared to other conventional materials such as titanium (E-module 110 GPa) or zirconium dioxide (E-modulus 210 GPa).In addition, the bending resistance of metal-ceramic restorations stands at around 400 to 600 Mpa. , in contAs a whole, all of these features mean that the use of materials of high rigidity will result in direct transmission of chewing forces to the zirconia implant. This potential overload could cause bone reabsorption around the implants . Some auTo avoid exceeding the adaptive limits of the bone and maintain the proper stimulation of mechanical stress that will keep the bone vital , PEEK coFinite element analysis suggests that maximum contact pressure at the bone-titanium implant interface can be significantly reduced by using a PEEK crown rather than a ceramic crown .In addition to PEEK, new coatings based on PMMA or composite materials  which incorporate ceramic fillings have been developed. Due to their molecular structure, these materials have excellent density and homogeneity . The micNone of the authors have any competing interests in the manuscript. All authors have performed important contribution and have read and approved the final version to be published.Zirconia implants with PEEK restorations can be considered a good alternative for replacing natural teeth. Their biocompatibility and biostability make them a promising material for those patients who suffer from allergies and sensitivity to metal alloys.PEEK restorations are a valid and alternative recommendation when using zirconia implants because of their cushioning effect and elastic modulus, which absorb occlusal forces and wear like a natural tooth, which could optimise and preserve osseointegration with time.Within the limitations of this study, we recommend the combined use of zirconia implants, PEEK structures and PMMA coatings in patients with intolerance to or rejection of metal alloys.


Adiabatic shear banding (ASB) is a unique dynamic failure mechanism that results in an unpredicted catastrophic failure due to a concentrated shear deformation mode. It is universally considered as a material or structural instability and as such, ASB is hardly controllable or predictable to some extent. ASB is modeled on the premise of stability analyses. The leading paradigm is that a competition between strain (rate) hardening and thermal softening determines the onset of the failure. It was recently shown that microstructural softening transformations, such as dynamic recrystallization, are responsible for adiabatic shear failure. These are dictated by the stored energy of cold work, so that energy considerations can be used to macroscopically model the failure mechanism. The initial mechanisms that lead to final failure are still unknown, as well as the ASB formation mechanism(s). Most of all - is ASB an abrupt instability or rather a gradual transition as would be dictated by microstructural evolutions? This paper reports thorough microstructural characterizations that clearly show the gradual character of the phenomenon, best described as a nucleation and growth failure mechanism, and not as an abrupt instability as previously thought. These observations are coupled to a simple numerical model that illustrates them. Adiabatic shear banding (ASB) is a synonym for a unique dynamic uncontrolled failure mechanism1The leading paradigm is that a competition between strain (rate) hardening and thermal softening determines the onset of the failure34However, contrary to the current paradigm, it was recently shown that instead of thermal softening mechanisms, microstructural softening transformations such as dynamic recrystallization (DRX) are responsible for adiabatic shear failureYet, one question persists, namely, what brings to the formation of a shear band? What are the initial mechanisms that will later lead to final failure? And most of all, is adiabatic shear failure an abrupt instability or rather a gradual transition as would be dictated by microstructural evolutions?This paper reports fine scale microstructural characterizations that clearly show the gradual character of the phenomenon, best described as a nucleation and growth failure mechanism, as opposed to an abrupt instability, as thought until now. These observations are coupled to a simple numerical model that illustrates them.εf, εf being the strain to failure under given loading conditions. This value was chosen, knowing that DRX’ed grains were observed to form solely from this strain level and beyond in this materialAnnealed, commercially pure α-titanium was used as a model system in this study. Previous work has shown that the fillet of dynamic shear specimens is a preferential locus for ASB formation and subsequent failure2), no more than two DRX’ed islands were observed. Given that each island occupies ~0.5 μm2, this barely represents 2% (area density) of the whole area. The presence of sparse DRX’ed grains is supported by the ring diffraction patterns inserted in Here, the microstructure consists essentially of heavily deformed large grains (HDLG) with occasional twins and dislocation cells/subgrains . Within This region is characterized by heavily deformed large grains (HDLG), subgrains, twins and sparse DRX’ed (DRX) islands, as shown in discontinuous cracks along the fillet, spaced several tens of micrometers apart. In both the uncracked ligaments and roughly 5 μm away from the crack tips, the microstructure consists of heavily deformed large grains with typical features such as dislocations, dislocation cells, subgrains and twins. Within these regions DRX’ed islands are seldom observed, and they appear to nucleate as irregular low-density clusters. The area density of DRXed nanograins at the crack tip is almost 2 orders of magnitude larger than that that of the sparse DRXed islands, some 5 μm away from the crack-tip.To summarize the main findings of this microstructural characterization, the immediate vicinity of the crack tip is characterized by densely-packed DRXed nano-grains, whose concentration drops dramatically in the un-cracked ligaments. Those observations reveal that failure (specimen fracture) occurs by the formation of gradually from sparse DRX islands within a deformed matrix, to massive DRX areas in the immediate vicinity of the (future) crack-tip. Rittel et al.Those observations reveal that the microstructure evolves et al.In this work, we show that regions with a local high density of DRX are associated with cracking, while other regions in which DRX density is small or not developed, simply don’t crack. This not only strengthens the earlier claim that DRX precedes shear localization, but also indicates that the phenomenon is likely of a percolative nature in terms of density  strain hardening, as opposed to the surrounding matrix, and thus localize the deformation within them. The arising incompatibility between the high density DRX region and its surroundings serves as a source for void (crack) nucleation. The mechanism presented here is of a cascading nature. When micro cracks are formed in high density DRX regions, the connecting ligament experiences intense plastic deformation, thus accelerating the DRX process, leading in turn to additional local damage. Final fracture is achieved due to the coalescence of the observed micro cracks (damage).simply another form of ductile failure, controlled by the nucleation, growth and coalescence of voids and micro cracks. Here, the initiation of the failure process is driven by DRX’ed nanograins. The evolution of the DRX’ed nanograins is initially controlled by the heterogeneity in energy storage capability of the material  stress. The function ω(σ) represents the stress state in the system and is a function of the third invariant J3 and the Mises stress as shown in Equation (2). kw is a fitting parameter.Here Here, with A being a fitting parameter.the same critical value of stored energy (UDRX). In case B, the heterogeneous nature of the material is captured by choosing the value of UDRX from the left half of a Gaussian distribution centered around the value chosen for the uniform case. The damage evolution for the two cases is presented in Finite elements calculations were carried using the commercial finite element package ABAQUS/ExplicitThe results of our numerical exercise clearly show the progressive discontinuous character of fracture within the localization band for the more realistic case B, as opposed to spatially continuous damage for case A. Furthermore, it appears from case B that fracture can take place in spurious locations along the potential localization band, as dictated by the materials propensity to nucleate DRX nanograins, just like observed experimentally.The present experimental and numerical results suggest that for successful prediction and control of the adiabatic shear process, microstructural concepts must be taken into account. Furthermore, the framework of ductile fracture, which has shown great success in correlating microstructures with failure mechanisms should be used to further study the role of different material heterogeneities on the formation of adiabatic shear localization. We propose that a combined mechanical and microstructural effort should be taken to design microstructures and textures in such a way that a materials’ tendency to fail by adiabatic shear failure could be controlled.To conclude, this work has uncovered the very early stages of the shear localization, which consist of the nucleation, multiplication and growth of discontinuous islands of dynamic recrystallization. At a certain stage, those islands develop microcracks which are bridged by additional islands of DRX, whose formation is accelerated by the local intense strains. This discontinuous evolving damage mechanism cannot be considered as an abrupt instability as previously thought, and belongs instead to the damage nucleation and growth type of fracture.As a general final remark, it can be noted that now that the microstructurally related damage mechanisms are well defined, one can think of new strategies for impact toughening of new materials.−1. The specimens were deformed to 0.9εf, εf being the strain to failure, using stop rings. Specimen preparation was done by standard lift-out procedure in a Dual-beam Focused Ion Beam (FIB) which allowed for the careful extraction of samples from specific regions of interest in the fillet area.Dynamic shear experiments were performed on Ti shear-compression specimens (SCS)1919TM transmission electron microscope.Thorough microstructural characterization was performed using diffraction contrast in a Tecnai TF20How to cite this article: Landau, P. et al. The genesis of adiabatic shear bands. Sci. Rep.6, 37226; doi: 10.1038/srep37226 (2016).Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.


A lateral approach with open reduction and internal fixation with a plate is a very effective technique for the majority of distal fibular fractures. However, this open approach for ankle fixation may be complicated by wound dehiscence and infection, especially in high-risk patients. An alternative to plating is an intramedullary implant, which allows maintenance of length, alignment, and rotation and which allows for decreased soft tissue dissection. While there has been clinical data suggesting favorable short-term outcomes with these implants, there is no current biomechanical literature investigating this technology in this particular fracture pattern. This study sought to biomechanically compare an emerging technology with an established method of fixation for distal fibular fractures that traditionally require an extensive exposure.Ten matched cadaveric pairs from the proximal tibia to the foot were prepared to simulate an Arbeitsgemeinschaft für Osteosynthesefragen/Orthopaedic Trauma Association (AO/OTA) 44C2 ankle fracture and randomized to fixation with a distal fibular locking plate or intramedullary fibular rod. A constant 700-N axial load was applied, and all specimens underwent testing for external rotation stiffness, external rotation cyclic loading, and torque to failure. The syndesmotic diastasis, stiffness, torque to failure, angle at failure, and mode of failure were obtained from each specimen.There was no significant difference in syndesmotic diastasis during cyclic loading or at maximal external rotation between the rod and plate groups. Post-cycle external rotation stiffness across the syndesmosis was significantly higher for the locking plate than the fibular rod. There was no significant difference between the rod and plate in torque at failure or external rotation angle. The majority of specimens had failure at the syndesmotic screw.In the present cadaveric study of an AO/OTA 44C2 ankle fracture, a modern fibular rod demonstrated less external rotation stiffness while maintaining the syndesmotic diastasis to within acceptable tolerances and having similar failure characteristics. Ankle fractures comprise 9 % of all fractures , 2. SurgAn alternative to plating of fibular fractures is the use of an intramedullary implant. This technique allows re-establishment of length, alignment, and rotation of the distal segment while allowing a smaller incision with decreased soft tissue dissection. This is desirable in high-energy injuries with possible soft tissue compromise and older, diabetic, nicotine-using patients at high risk for wound complications. Additionally, patients with Arbeitsgemeinschaft für Osteosynthesefragen/Orthopaedic Trauma Association (AO/OTA) 44C-type fractures   in comminuted AO/OTA 44C-type fibular fractures. We hypothesize that a fibular rod will provide a biomechanically equivalent construct when compared to a lateral locking plate when evaluating external rotation stiffness, syndesmotic diastasis, and external rotation torque to failure. Evidence of biomechanical superiority or non-inferiority of the fibular rod in AO/OTA 44C fractures may lead to increased clinical investigation and more widespread use for this particular fracture pattern.Twenty-four fresh-frozen cadaveric ankle specimens  were obtained from the proximal tibia to the foot from the Biological Resource Center of Illinois . Ten matched pairs were placed into two groups. One group received a traditional 13-hole distal fibular locking plate while the second group was instrumented with a locking fibular rod (3.6 mm × 180 mm). Prior to dissection and experimentation, the specimens were examined grossly and radiographically to exclude any specimens with prior ankle surgery or deformity. Given the variability in mechanical properties between cadaveric specimens, this study was designed to use matched pairs with statistical comparisons made between the left and right limbs to reduce the effect of specimen variation on statistical inferences.For the first five matched pairs, the left limb received a fibular rod and the right limb received a 13-hole distal fibular locking plate. The fibular rod and locking plate were placed in the right and left limbs, respectively, of the last five matched pairs. Prior to testing, we removed the skin proximal to the ankle and exposed the fibula, interosseous membrane (IO), interosseous ligament (IL), anterior-inferior tibiofibular ligament (AITFL), posterior-inferior tibiofibular ligament (PITFL), and transverse ligament (TL).Multiple biomechanical studies have been performed on AO/OTA 44C-type fractures in regard to syndesmotic stability with an intact fibula –34. TherFor the fibular rod group, we then placed the rod with the targeting device externally rotated 30° . We drilWe inserted 3.5-mm non-locking cortical screws in the anterior-to-posterior interlocking holes. Once these screws were in place, we detached the interosseous membrane and interosseous ligament from fibula insertion using sharp dissection. We then inserted a 3.5-mm diameter syndesmotic screw in the previously drilled hole to gain tri-cortical purchase. After all the implants had been placed, we then detached the AITFL, PITFL, and TL from fibular insertion and lastly transected the deltoid ligament Fig. . A repeaIn the distal fibular locking plate group, we utilized a 13-hole low-profile lateral fibula locking plate. Prior to making the fibular osteotomy, the plate was appropriately positioned on the distal fibula. Using the locking drill guide, four unicortical holes were drilled in the distal cluster and four bicortical holes proximally. We drilled one tri-cortical hole for syndesmotic fixation parallel to the tibiotalar joint and externally rotated 30°. We then made our osteotomy as detailed above. The plate was re-positioned on the fibula, making sure that the predrilled holes were aligned such that the fibula was restored to the appropriate physiologic length. We inserted 3.5-mm locking screws into the predrilled holes both proximally and distally and a 3.5-mm diameter syndesmotic screw. Lastly, we detached the syndesmotic and deltoid ligaments and repeated the radiographs Figs.  and 2b.Lastly, two matched pairs  were used to quantify the biomechanics of the syndesmosis and intact fibula. For these four specimens, the deltoid ligament was transected but the syndesmotic complex of ligaments and fibula remained intact in order to determine the biomechanics in the native syndesmosis. This provided a standard for comparison for the rod and the plate fixation models.The tibias of the specimens were fixed in custom cups using polymethylmethacrylate (PMMA) bone cement. A custom jig was used to ensure that the tibia was centered in the cup and that the mechanical loading axis of the tibia and the base of the cup were perpendicular. The cup was then attached to the actuator of a biaxial servohydraulic material testing machine . The feet were placed onto a custom testing apparatus, and an individual heel cup and midfoot support was molded using PMMA for each specimen to stabilize the foot on the plate Fig. . Pins anInfrared light-emitting targets were rigidly fixed to the calcaneus, tibia, distal fibula, and proximal fibula. The three-dimensional position of these four targets was tracked during testing by an optoelectronic motion measurement system . Prior to testing, an optoelectronic three-dimensional digitizing probe was used to trace a series of points on the perimeter of the tibia at the level of the fibular osteotomy and on the distal fibula at the level of the syndesmotic screw. These points were digitized in relation to the optoelectronic target attached to the individual bones.All the specimens underwent testing for pre-cycle external rotation stiffness, external rotation cyclic loading, post-cycle external rotation stiffness, and torque to failure. All testing was conducted with a 700-N constant compressive axial load applied to the leg.The specimen was first tested to determine pre-cycle stiffness. After axial loading to 700 N, an external rotation torque was applied at 1°/s to a torque limit of 5 Nm. The specimen was cyclically loaded in external rotation while under the constant 700-N axial load 2000 times to a torque limit of 5 Nm under load control at a rate of 5 Nm/s. The post-cycle external rotation stiffness was then determined using the same protocol used for pre-cycle stiffness. Lastly, a torque to failure test was done for each specimen. An external rotation torque was applied to achieve rotation at a rate of 5°/s up to an actuator rotational displacement of 100° or an applied external rotation torque of 38 Nm. Axial load, external rotation torque, actuator rotation, actuator displacement, and the positions of the four infrared-emitting targets were recorded during the tests.The pre- and post-cycle external rotation stiffness of the constructs was calculated from the applied external rotation torque and target rotation data. The stiffness was the slope of the line fit to the torque versus rotation data for an applied torque between 25 and 90 % of maximum (between 1.25 and 4.5 Nm). Fibular stiffness was calculated using the difference in rotation across the fracture site . This stiffness  gives an indication of how well the distal and proximal fibula are kinematically tied together by the construct and therefore, the amount of load transmitted across the osteotomy site. Syndesmosis stiffness was calculated using the difference in rotation across the syndesmosis . This stiffness gives an indication of the quality of reduction of the syndesmosis.Lastly, the maximum lateral translation of the distal fibula with respect to the tibia, termed the syndesmotic diastasis, was calculated for all the tests , 39, 40.Statistical analyses were performed in specialized software . A repeated measures ANOVA was used to analyze differences between the two operative groups. On examination of the data, we found that three specimens had failed before any of the cyclical testing . These were deemed to be outliers and were excluded from our final data evaluation. Thus, our total number of specimens was 17.A post hoc power analysis was performed using 2-mm diastasis as a clinically relevant change. Utilizing eight pairs, the power was 42.5 % to detect a 2-mm gap. In order to achieve 80 % power to detect an effect size (difference in gap) of 2 mm, we would have needed to test 16 pairs of specimens.The maximum pre-cycle and post-cycle syndesmotic diastases were 1.4 ± 0.3 and 1.7 ± 0.4 mm, respectively. Thirty-eight Newton-meters of applied external rotation torque was achieved in all four intact state specimens during the external rotation torque to failure test.Both measurements of external rotation stiffness increased from pre- to post-cycle. The distal fibula to proximal fibular stiffness increased from 1.2 ± 0.3 to 1.7 ± 0.2 Nm/degree, while distal fibula to tibia stiffness increased from 1.5 ± 0.5 to 2.0 ± 0.3 Nm/degree.p = 0.02) as well as external rotation stiffness across the syndesmosis  , but not across the fracture site .The external rotation stiffness post-cycle was significantly higher for the locking plate than the fibular rod in regard to stiffness across the syndesmosis . During external rotation testing to failure, there was no significant difference in the diastasis   and post-cycle (2.4 versus 1.4 mm) using repeated measures ANOVA  or external rotation angle .There was no significant difference between the rod and plate in torque at failure . Fibular fracture occurred in 4 of the 17 specimens (one locking plate and three fibular rods). There was soft tissue damage in 2 of the 17 specimens (one locking plate and one fibular rod).Ankle fractures are a common orthopedic injury that occur at a rate of 187 per 100,000 person-years. They are the fourth most common fracture to require operative repair, which is recommended for unstable ankle fractures –46. WounThe use of intramedullary implants, such as screws, smooth rods, and the Kirschner wires, allows for decreased soft tissue dissection and has been a potential alternative to plating of fibular fractures –22, 25. Despite the increased interest in intramedullary fibular fixation, there have been no published biomechanical studies investigating the biomechanical properties of the modern fibular rod at present. While most of the existing literature examines the use of the fibular rod in Weber B fibular fractures, we feel that a potentially beneficial fracture pattern to utilize this fixation would be in AO/OTA 44C2 ankle fractures, which typically requires a large dissection and syndesmotic fixation , 50.Several investigations suggest that increased syndesmosis width can lead to poor outcomes , 52. LeeIt is important to define the normal functional anatomy of the distal tibiofibular joint when examining biomechanical literature. Beumer et al. showed that application of a 75-Nm external rotation moment on the foot of 11 healthy volunteers caused coronal plane translation between 0 and 2.5 mm and stated that these data can be used as normal reference values for studies of patients with suspected syndesmotic injuries . Other sUnfortunately, since there is no published biomechanical data on the modern fibular rod, we are unable to directly compare our results with those of other investigators. However, when inspecting the previous biomechanical literature in fracture models, Nousiainen et al. used a Weber C model and a similar biomechanical setup as the current study and showed that the change in syndesmosis width was between 0.5 and 1.25 mm in pre-cyclic loading when using rigid screw fixation of either three or four cortices, but did not utilize post-cyclic testing . When exIn the present study, when excluding outliers, both the fibular rod and locked plate demonstrated values in this range under pre-cyclic loading . The post-cyclic loading data shows that the fibular rod had a mean of 2.4 ± 1.9 mm of diastasis, which is only 0.7 mm greater than the native syndesmosis in the study and still within normal variation shown by Beumer et al. . The locIn regard to external rotation stiffness, in our study, the fibular rod was found to have less external rotation stiffness than the locking plate. This was true when measuring stiffness across the fracture site and across the syndesmosis. It is not surprising that the plate group demonstrated this increased external rotation stiffness, since the distal locking plate has multiple points of fixation both proximal and distal to the fracture site. The fibular rod has no proximal interlocking fixation to provide enhanced rotational control at the fracture site, but does provide stability to the distal segment through the syndesmotic interlocking screw. In this fracture pattern where the fracture occurs above the level of the syndesmosis, the main focus would be on the rotational control of the distal segment which includes the tibiofibular articulation. The clinical significance of this increased external rotation stiffness is unclear but again would suggest the importance of proper postoperative weightbearing precautions in the nail groupIn the present study, there was no significant difference in the failure properties between the two groups in either torque to failure or angle at failure. The values obtained for both groups were consistent with prior data examining syndesmotic fixation with both dynamic fixation and screw fixation by Ebramzadeh et al. and provided failure torques well above 20 Nm, exceeding likely torques applied in casts during healing . LooseniThere are several important limitations to note in the current study. Importantly, we excluded three specimens from our data analysis because their values fell far outside the mean values of the remaining specimens and demonstrated early catastrophic failure under pre-cyclic loads. This could be indicative of the potential surgeon-related difficulties with new technologies. However, statistical analysis was performed both including and excluding the outliers, and the comparative results were not changed substantially. Our post hoc power analysis revealed that we would have needed 32 specimens in order to achieve 80 % power to detect a 2-mm difference. Given financial constraints, this unfortunately was not attainable. Additionally, we did not examine the biomechanical properties of a non-locking plate and screw construct in this study, which is an acceptable form of fixation in this fracture pattern.In the present cadaveric study of an AO/OTA 44C2 ankle fracture, a modern fibular rod demonstrated inferior external rotation stiffness while maintaining the syndesmotic diastasis to within acceptable tolerances and having similar failure characteristics. We believe that the fibular rod can be utilized in select patient populations given that proper postoperative restrictions are placed.