A new method for fast diameter measurement of coaxial holes is studied. The paper describes a multi-layer measuring rod that installs a single laser displacement sensor (LDS) on each layer. This method is easy to implement by rotating the measuring rod, and immune from detecting the measuring rod’s rotation angles, so all diameters of coaxial holes can be calculated by sensors’ values. While revolving, the changing angles of each sensor’s laser beams are approximately equal in the rod’s radial direction so that the over-determined nonlinear equations of multi-layer holes for fitting circles can be established. The mathematical model of the measuring rod is established, all parameters that affect the accuracy of measurement are analyzed and simulated. In the experiment, the validity of the method is verified, the inner diameter measuring precision of 28 μm is achieved by 20 μm linearity LDS. The measuring rod has advantages of convenient operation and easy manufacture, according to the actual diameters of coaxial holes, and also the varying number of holes, LDS’s mounting location can be adjusted for different parts. It is convenient for rapid diameter measurement in industrial use. Coaxial holes refer to circular holes widely distributed along the same axis. The most common of these parts are aircraft wing hinges, internal combustion engine crankshaft holes, etc. . For theThere are many diameter measuring methods for coaxial holes, such as inside micrometer, contact probe, and pneumatic gauging, etc. The inside micrometer is the most widely used tool in the industrial production field, nimble handling but easy to be influenced by individuals , the minAs a non-contact probe, laser displacement sensors (LDS) are widely used in geometric measurement ,9, they With the decrease in volume and reference distance, LDSs are widely used in the measurement of small diameters. The usual procedure is installing multiple LDSs in the same cross-section of the hole. The corresponding point coordinates of the hole can be obtained by only one measurement ,12. For With regard to the diameter measurement of coaxial holes of internal combustion engines, based on a small coaxial error (0.03 mm) of holes, and ignoring holes’ roundness error (3 μm), we propose a measuring rod which contains single LDS to measure the diameter for each layer’s hole . In the For this method, the minimum hole size that can be measured would only be limited by the single LDS’s volume and reference distance. It significantly improves measuring range for coaxial hole parts, and expands LDS’s application for diameter measurement in industrial use.In this measuring method, the system is composed of: measuring rod, LDS, vee blocks, baffle, platform, and the coaxial hole part, as shown in Before measuring, put the coaxial hole part on the platform, and ensure its centerline is parallel to the platform. Place the two vee blocks outside the two ends of the coaxial holes, the baffle is installed on the end of a vee block’s V groove. Get the measuring rod through the coaxial holes, and the two ends of the rod arranged on the vee blocks, respectively. Press the measuring rod’s end against the baffle, which can limit the movement of the rod during rotation in the axial direction. Adjust the position of that vee blocks, so that the rod’s rotary axis can be parallel with the part’s centerline as much as possible.During the measurement operation, we can rotate the measuring rod randomly, and read all LDSs’ measuring values. All diameters of the part can be calculated from the measured values.Ow-xyz based on the coaxial hole part, as shown in Ow-Z axis, and the horizontal direction of the measuring platform is set as Ow-X axis.In the ideal circumstance, while the measuring rod is revolving to measure diameters, its spinning axis is stationary relative to the part’s centerline. We set up a global coordinate system F and B as the front and rear end of the measuring rod’s rotary axis. Line FB is paralleled with Ow-Z axis in the ideal measurement model. For the m-th layer’s hole, when the measuring rod has rotated in the n-th time, the LDS’s laser emission point Kmn is relative stationary to the part. The laser beam gets a laser spot Kmn’ on the hole wall. LDS measures the length of KmnKmn’, which is the distance between the point on the hole wall and the rotary axis of the measuring rod.Set Ow-xyz, we can get the three-dimensional coordinate point of the laser spot Kmn’ for each sensor’ laser beam, which can be written as:The measuring rod is rotated randomly during the measurement. As the two vee blocks and baffle have restricted the rod’s movement in both axial and radial directions. In global coordinate m-th hole, αn is variable angle of rod’s rotation in radial direction. lmn is the distance between laser emission point Kmn and the laser spot Kmn’, which is measured by LDS. Hm is the distance between Kmn and B.For the FB is perpendicular to the cross section of the hole. We can get a laser beam KmnKmn’ by rotating the measuring beam every time. Several laser beams KmnKmn’ can constitute a swept surface T is the transfer matrix from Ow-xyz to Os-xyz. λ is the scale factor.In the space coordinate system conversion , the BurKmnKmn’ around the Os-Z axis. While calculating the flatness error and roundness error of the spot trajectory {Kmn’}, the rotation angle zε can be any value. The baffle limits the movement of the measuring rod in the Os-Z axis, so the translation parameter Δz = 0. As the measuring rod is a rigid body, the scale factor λ = 1.In this measurement system, the curved surface is formed by revolving x, Δy, xε, and yε. We only need to calculate the roundness error and flatness error of the curve {Kmn’}, so the conversation can be simplified into the position relationship between the Os-Z axis and the Ow-Z axis, and it is expressed by eccentricity distance dΔ and deflection angle ωΔ, as shown in In the transition matrix, the unknowns are ΔdΔ, Δx, Δy, ωΔ, xε, and yε are as follows:The relationship between dΔ and deflection angle ωΔ, we can get the conversion matrix by Equation 13, and the point coordinate of the spot trajectory’s {Kmn’} can be calculated in the global coordinate system Ow-xyz. For calculating the flatness error and roundness error of the spot trajectory, the least square face trajP is obtained by the spot trajectory {Kmn’}. trajθ is the angle between trajP and the Ow-xy plane, trajL is the crossing line between trajP and the Ow-xy plane, respectively. We converse trajP to the Ow-xy plane by the use of Rodrigues' rotation formula [trajL as the rotation axis, and trajθ is the rotation angle, as shown in In the simulation, with difference of eccentricity distance  formula , take thKmn’} is transferred to near the Ow-xy plane, and the new 3-D points are denoted as {Kmn’}’. The flatness error (Δflat) of the laser spot trajectory is the maximum difference of {Kmn’}’ in the Ow-Z axis. By calculating the least square fitting circle of {Kmn’}’ on the Ow-xy plane, the roundness error (Δround) is calculated by the fitting circle and hole’s real radius. The final radius error Δrm of the laser spot trajectory {Kmn’} is given as:Finally, the 3-D points coordinate of {rm is different. Where dΔ and ωΔ are constant, the hole’s radius error Δrm is proportional to Hm. When analyzing the maximum measuring error of the radius, the hole near the front end of the rod should be chosen to calculate.For different holes in the part, the radius error Δrm of the curve {Kmn’}, we assume the rod’s manufacturing error as: dm = 0.5 mm and γm = 0.5°. The length of the measuring rod is 500 mm. The number of coaxial holes in the part is two, and all diameters are 150 mm. Based on these, the maximum radius error is simulated under different of dΔ and ωΔ. The simulate results are showed in In calculating the radius errors ΔωΔ < 1.5° and dΔ < 3 mm, the radius error is less than 10 μm. While installing the measuring rod, for the distance between the rod’s two ends and the part’s centerline, it is to be a small range of no more than 2.5 mm. Through this operation, the radius error of the spot trajectory formed by the laser beam does not exceed 10 μm. If we can achieve a higher installation accuracy, more precision radiuses can be calculated for the coaxial holes.rm of laser spot trajectory has been controlled in a small range on the diameters measurement result. Thus Δsen, which is caused by the measurement error of LDS, is the main factor that influence the diameter measurement accuracy. While the coaxial holes are considered ideal circles, the tolerance of roundness should be taken as the source of measuring uncertainty, and we set is as ΔHole. The total diameter measurement error is approximately calculated by:According to the above analyses, the accuracy of this measurement method depends on several factors. By evaluating the error caused by installation of the measuring rod, the radius error Δdm < 0.5 mm and γm < 0.5°, by using LDSs with measurement linearity of 20 μm, so the radius error Δrm caused by the installation position of the measuring rod is limited in the range of 10 μm. While the roundness of holes ΔHole is 3 μm, the measurement error Δsum is less than 24.8 μm. For a general machining workshop, it can achieve diameter measurement error of no more than 30 μm.From the Equation (15), as the installation of LDSs fulfills: dm and γm in To verify the measuring method for the diameters of coaxial holes, in this paper, two 150 mm ring gauges are chosen as the coaxial hole part, and they are clamped on the platform. The length of the hollow shaft for the measuring rod is 500 mm. For mounting LDS on the hollow shaft, two square holes were machined on the shaft by a CNC, it can satisfy the precision requirement of On the platform, a rectangular groove with 90 mm in width and 5 mm in depth was machined by an NC milling machine. The widths of vee blocks and clamps of the ring gauge are both 90 mm, and they were embedded in the rectangular groove, and the edge of the rectangular groove was the benchmark for the installation. Two vee blocks were formed by longitudinal cutting of an old vee block, which ensured that they had the same groove depth, so the altitude difference between the middle axis of the measuring rod and the centerline of part was not more than 1 mm. With regard to locating the coaxial hole part on the measurement platform, it is necessary to make the baseline of part to coincide with the rectangular groove of the platform. The baseline is the reference datum line for auxiliary machining the coaxial holes on the outer surface of the part. With the help of vee blocks on the rectangular groove, coaxial holes are approximately parallel to the measuring rod’s rotation axis. Through the high-precision rectangular groove, the deviation and inclination of the measuring rod achieved the accuracy requirement in The final experimental equipment is shown in n, and the number of coaxial holes is m, which determines the number of equations in Equation (3), being mn. In radial direction of the measuring rod, xm, ym) and is independent of the radius result. In order to simplify the calibration process, we set In the experiment, the measuring rod’s rotation count is m-th hole,  is the coordinate difference between the laser emission point Kmn and the centerline of coaxial holes. As LDS’s original angle xm, ym) is not credible. For Equation (16), the unknowns in the over-determined equations are: coaxial holes’ radius rm, coordinate difference , and the rotation angle of rod αn.For the m + n, only when the number of equations is mn ≥ 3m + n, the over-determined equations can converge. For the two holes in the experiment, the time of the rod’s rotation should be 6. While rotating the measuring rod manually, in order to reduce the operational errors and improve calculating precision, the rod’s rotation count is much more than 6, and the last result is the average of the multiple measurements. The number of unknowns in Equation (15) is 3The comparison between the measurement result and rotation counts of the measuring rod is shown in For coaxial holes with low roundness error—such as the crankshaft hole of an internal combustion engine—this paper proposes a simple inner diameter measurement method for coaxial holes. A multi-layer diameter measurement rod is designed, which has a single sensor on each layer. In the measurement process, we adjusted the machining datum line of coaxial hole part, so that it is collinear with the axis of measuring rod. By revolving the measuring rod and immune from detecting the measuring rod’s rotation angle, all diameters of coaxial holes can be calculated by sensors' values. For the measurement process, the influence of the installation posture of the measuring rod to the measurement results is analyzed by numerical analysis, and the tolerance range of measuring rod installation error is obtained by simulation. Two 150 mm ring gauges are used to verify the measuring method in the experiment, by the comparison between the measurement results and indicating value of the ring gauge, it is proven that the measurement precision of this method has achieved 30 μm by the use of the 20 μm linearity LDS. For coaxial holes with different sizes and number of holes, this method is simple to implement the diameter measurement. The retrofit of the measuring rod is inexpensive and simple, which can be easily applied in industrial use for rapid measurement.


Off-pump coronary artery bypass grafting (OPCAB) is one of the standardtreatments for coronary artery disease (CAD) while hybrid coronaryrevascularization (HCR) represents an evolving revascularization strategy.However, the difference in outcomes between them remains unclear.We performed a meta-analysis to compare the short-term and mid-term outcomesof HCR versus OPCAB for the treatment of multivessel or left main CAD.We searched the PubMed, EMBASE, Web of Science and Cochrane databases toidentify related studies and a routine meta-analysis was conducted.Nine studies with 6121 patients were included in the analysis. There was nosignificant difference in short-term major adverse cardiac andcerebrovascular event (MACCE) rate or mortality . HCR required lessventilator time , ICU stay, hospital stay  and blood transfusion rate , but needed more operation time  and hospitalization costs . The HCR group had lower mid-term MACCE rate  but higher rate in mid-term targetvessel revascularization .HCR had similar short-term mortality and morbidity comparing to OPCAB. HCRdecreased the ventilator time, ICU stay, hospital stay, blood transfusionrate and increased operation time and hospitalization costs. HCR has a lowermid-term MACCE rate while OPCAB shows better in mid-term TVR. Recent years, more andmore cardiac centers in the world have adopted OPCAB and HCR.3Surgical revascularization still plays an essential role in the treatment of coronaryartery disease (CAD) even in the era of widely prevalent percutaneous coronaryintervention (PCI). As the most classical and widespread procedure forrevascularization, coronary artery bypass grafting (CABG) has been considered thegold standard therapy in the past decades.4 Another research investigated 3445patents with a 13-year follow-up and drew conclusions that both OPCAB and on-pumpCABG were safe and effective, and no significant difference was observed betweenthem.5 However, ameta-analysis including 12 studies detected a lower rate of death and adverseeffects after OPCAB compared with conventional CABG.6 Generally speaking, OPCAB is considered as lowerincidence of neurological complications ,7 in addition to acomparable less mortality and morbidity, particularly in high-risk groups andelderly patients.9It has been intensively discussed whether OPCAB is superior for CAD compared withon-pump CABG, but it remains uncertain. A recent randomized controlled trial (RCT)including 4752 patients found that the outcomes of death, stroke, myocardialinfarction, renal failure or repeat revascularization at 5-year follow-up weresimilar among patients who underwent OPCAB or on-pump CABG.10 A study inFrance confirmed the feasibility and safety of HCR and also detected that HCRcompared favorably to those with traditional CABG alone.11 In addition, both of simultaneous and staged HCRwere indicated to be efficient and feasible with favorable outcomes at more than12-month follow-up.13 However, a 1-year clinicalfollow-up study angiographically showed a high rate of repeat revascularizationafter HCR.14 In addition, atransient reduction in the antiplatelet effect of aspirin and clopidogrel wasobserved after HCR despite limited surgical trauma and off-pump technique.15 Neither baseline plateletaggregation nor postoperatively increased platelet turnover and acute-phase responsecould explain it. Therefore, further research is badly needed.HCR combines minimally invasive CABG and PCI, offering a relatively atraumatictherapy for multivessel CAD. HCR utilizes a left internal mammary artery (LIMA)graft to the left anterior descending (LAD) coronary artery with drug-eluting stents(DES) to non-LAD target coronary arteries. Several studies have proved the excellentpostoperative survival (higher than 99%) and LIMA patency rates (higher than 95%) ofHCR, suggesting HCR should be considered as an alternative approach for patientswith multivessel CAD.Currently, several comparative studies about the clinical outcomes of OPCAB and HCRare available. Nonetheless, the optimal surgical strategy remains disputable. In thepresent analysis, we sought to compare the short-term and mid-term clinical outcomesof HCR versus OPCAB for the treatment of multivessel or left main CAD with a pooleddata.We searched four electronic bibliographic databases including PubMed, EMBASE, Webof Science and Cochrane by using following keywords with different combinations:“coronary artery disease”, “multivessel coronary artery disease”, “left maincoronary artery disease”, “no-touch coronary artery bypass”, “off-pump coronaryartery bypass”, “hybrid coronary revascularization”, “minimally invasivecoronary artery bypass” and “percutaneous coronary intervention”. The searcheswere limited to human studies and English-language literatures only. The lastsearch date was March 1, 2017.Inclusion criteria were: (1) RCTs, cohort studies or case-control trials (CCT)comparing the outcomes of HCR and OPCAB; (2) at least 15 participants in eachgroup; (3) available to get complete data. In addition, exclusion criteria were:(1) duplicated papers that fail to provide supplementary information; (2)unfinished studies or unavailable data (3) studies with obvious defects indesign or data statistics. Two researchers selected literatures and anydisagreements were resolved through consensus.16 and STROBEstatement17 were usedto measure the quality of RCTs and observational studies, respectively.Low-quality studies should be excluded and any disagreements were resolved byconsensus or judged by the senior author.For articles approved in the primary selection, two reviewers assessed thequality of studies and extract data independently. The CONSORTstatementExtracted information included: (1) characteristics of studies and patients; (2)basic management of HCR and OPCAB; (3) short-term  andmid-term (3 months to 36 months) mortality, stroke and major adverse cardiac andcerebrovascular event (MACCE) which was defined as the incidence of all-causedeath, stroke, myocardial infarction (MI) and target vessel revascularization(TVR); (4) in-hospital outcomes: operation time, ventilator time, ICU stay,hospital stay, blood transfusion rate, incidence of atrial fibrillation (AF) andhospitalization costs.Forestplots were presented graphically for all clinical outcomes.Statistical heterogeneity between studies was calculated using chi-squared testand the I-squared measure on a scale of 0-100% . Fix-effect model wasused in analysis with heterogeneity < 50% while random-effect model wasconducted with heterogeneity ≥ 50%. In addition, publication bias ofshort-term  MACCE rate was also assessed using funnelplot. Two-sided p value < 0.05 was considered statistically significant.We performed the analyses using RevMan 5.3 software . Relative risk (RR) with 95% confidence interval (CI) wascalculated for dichotomous variables and standardized mean difference (SMD) with95% CI was calculated for continuous variables. Then 26The process of literature selection for potentially eligible studies andexclusion reasons is illustrated using a flow diagram in The basic characteristics of these studies are presented in 2 = 0%) or mortality  or stroke  between thetwo groups. HCR required less ventilator time (standardized mean difference(SMD): -0.36, 95% CI: -0.55- -0.16, p < 0.001), ICU stay , hospital stay  and blood transfusion rate (relative risk (RR): 0.57, 95% CI:0.49-0.67, p < 0.001), but needed more operation time  and hospitalization costs .As illustrated in P value in bothsubgroups > 0.05).2 = 25%) but had higher rate in TVR  inmid-term follow. No significant difference in mid-term mortality was detectedbetween the two groups .The studies that contained mid-term outcomes were included in the analysis. Asshown in 2< 50%). And subgroup analysis showed no heterogeneity .In the current analysis, no obvious heterogeneity was found between studies ineither short-term or mid-term MACCE rate and mortality , outdated surgical procedures (8-10cm thoracotomy incisions), different kinds of DES (cypher or taxus), uncertainty ofbaseline LVEF (not reported) and high heterogeneity in analysis. We also put threerecent high-quality studies into pooled data so that all outcomes are updated. Inaddition, in the present study, we focus on postoperative complications and takestroke as a primary endpoint. Therefore, the present analysis is needed for a betterelucidation of HCR and OPCAB.The present meta-analysis shows that HCR, compared with OPCAB, seems not tosignificantly improve short-term mortality and morbidity of postoperativecomplications for patients with CAD. These results are similar to previews research.Hu26.It has been widely recognized that the dislodgement or rupture of atheroscleroticplaques during surgical aortic manipulation results in a major cause ofstroke.29 Since the aortais more or less affected in the surgical procedure, it is still unclear whetherOPCAB can decrease postoperative stroke rate compared with on-pump CABG. Incontrast, grafting in HCR only involves LAD artery while other coronary arteries aretreated by PCI. As a result, low rate of neurological complications becomes one ofthe main advantages of HCR. Although, in the present analysis we detect nosignificant difference of stroke rate between OPCAB and HCR in a short-termfollow-up, which seems to be contradictory to some previous analyses.To our knowledge, this is the first meta-analysis comparing the mid-term clinicaloutcomes between HCR and OPCAB so far. Our data shows that HCR has a lower mid-termMACCE rate while OPCAB shows a better result in mid-term TVR. Moreover, nosignificant difference in mid-term mortality was detected between the two groups.Patients undergoing the hybrid procedure have relatively better mid-term clinicaloutcomes probably owing to reduced myocardial manipulation and activation ofcoagulation26 reportedthat more patients in OPCAB group suffer from stroke than HCR group in a 30-monthfollow-up, which indicates that the differences may be well recognized in along-term follow-up. In recent years, technical advances in OPCAB utilize a no-touchtechnique to avoid aortic manipulation during grafting. A retrospective study showedthat the OPCAB with no-touch technique could improve prognosis by minimizing theneurological complications and the morbidity.30 Emmert et al.31 also reported that the aortic no-touch OPCAB provided superiorneurological outcomes than on-pump CABG and no-touch technique should be properlyapplied. Halbersma et al.32investigated the four-year clinical outcomes after OPCAB with no-touch technique andconcluded that it was a safe and efficient choice for patients with multivessel orleft main CAD. Compelling data have indicated that the combination of OPCAB andclampless strategies can reduce stroke risk. However, the major shortcoming ofno-touch OPCAB is its greater technical requirement so that it is not applicable forevery surgical team or every patient.33 Nevertheless, further investigations should be still carriedout to compare no-touch OPCAB and HCR.However, Song et al.27 Commonly, there are threestrategies for HCR: (1) performing LIMA-LAD grafting first and then followed by PCI,the interval varies from several hours to a few weeks; (2) vice versa; (3) combinedLIMA-LAD grafting and PCI at the same time in a hybrid operative unit. The optimalsequence of LIMA-LAD grafting and PCI has been debated but still remains unclear. Infact, most centers choose their own surgical procedures mainly based on preferencesof physicians, considerations of patients, economic issues and available resources.Although several studies have indicated that both simultaneous and staged HCRcontribute to excellent results, most centers prefer to adopt the latter one withLIMA-LAD grafting performed first.34 The CABG-first approach is recommended by the American Collegeof Cardiology Foundation/American Heart Association35 and it has some obvious advantages. It can reducethe overlapping from two different teams so that they can perform in their mostfamiliar way and avoid to interacting with each other in operation room. Thenantiplatelet and antithrombotic strategies can be well managed and adjustedaccording to physicians from different teams.36 However, the disadvantages include that patients have toundergo at least two surgeries and need more time to recover. Moreover, hemorrhagictendency and overload of kidneys also deserve significant attention. Currently, nostudy has compared the clinical outcomes of staged HCR and simultaneous HCRdirectly, so further research should be placed on it.In the current analysis, neither staged HCR nor simultaneous HCR makes a differenceto the short-term outcomes, which is consistent with former studies.37And retractor-stabilizer, such as robot, provides access that LIMA-LAD grafting canbe performed with accuracy and precision with minimally invasive thoracotomy orsternotomy.38 Practically,with the assistance of a surgical robot, it offers an excellent visual field andreduces operation time. However, some drawbacks of HCR also deserve our attention.Our study detects that the hybrid procedure required longer operation time andincurred much higher in-hospital costs than OPCAB. In Bachinsky`s study,23 despite lower postoperative costs,the HCR group still needs more overall hospital costs owning to its higherprocedural costs. Consequently, pros and cons of HCR should be weighed andconsidered carefully before operation.In the present analysis, we also confirm that HCR apparently decreases the ventilatortime, ICU stay, hospital stay and blood transfusion rate comparing to OPCAB.Although these items may not directly influence the main outcomes, they are alsoimportant criteria to judge a surgical procedure. Several reasons may account forthese advantages of HCR. With the development of surgical procedures, endoscopictechnique and mini incision are widely utilized in HCR to help patients easesuffering and recover sooner.Some limitations of the present analysis should be also emphasized. Firstly, allincluded studies belong to observational studies and no single RCT has beenconducted so far. Secondly, some included studies contain relatively small samples(fewer than 50 patients) and remain imbalance of patient number between groups sothat deviation of results may inevitably exist. Thirdly, long-term patency is moreconvincing than short-term and mid-term outcomes, but very limited references werepublished with long-term follow-up so far. Finally, some uncontrolled factors mayinterfere with the current analysis. Variables like gender ratio and LVEF atbaseline have not been adjusted. And diverse surgery procedures, stents (DES or barestent) as well as antiplatelet strategies may disturb the accuracy of resultstoo.HCR shows similar results with OPCAB in short-term clinical outcomes. HCR decreasesthe ventilator time, ICU stay, hospital stay, blood transfusion rate and increasesthe operation time and hospitalization costs. Although repeated vesselrevascularization is greater with HCR, it has a lower mid-term MACCE rate and couldprovide a safe and reproducible alternative for patients with multivessel CAD.


In their article, Kesternich et al.  address a higher self-reported risk aversion,a lower Abitur grade (German high school GPA),as well as the fact that at least one parent is a medical doctor2 or in that of a classification table is not provided. Thus, an evaluation of the presented results is difficult.are significantly and positively correlated with one or both intentions. Not significantly correlated are, amongst others, previous practical experiences in the health sector, the expected income, the First National Boards Examination grade (“Physikumsnote”), or the waiting period prior to the beginning of the studies. Unfortunately, the article does not include descriptive statistics for the subgroups, such as the number of students with waiting period who consider to become a country doctor . The quality of the model fit in the form of pseudo-RIn the discussion, the authors present a number of suggestions for future student selection procedures, aiming at an increase of GPs in rural areas. To achieve that, it is suggested to decrease the influence of the Abitur grade by including additional criteria to assess the motivation for medical studies:Voluntary social commitment or work experience in the health sector as stated in the curriculum vitae: In the multivariate model, previous practical experience in the health sector was not predictive of the intention to work as a GP or a country doctor, data concerning social commitment are not reported.Estimating the willingness to work as a GP in a rural area by means of multiple mini interviews (MMI): Even though MMIs are correlated with the evaluation of undergraduate practical medical work, we consider this suggestion – based on both international  and our Consideration of semesters not enrolled at university, e. g. by increasing the waiting period quota: In the study, waiting semesters are not significantly correlated with the intention to become a GP or a country doctor, respectively. The study does not mention that in many German Universities, about 40% of the students from the waiting period quota do not pass the First National Boards Examination (“Physikum”) . Thus, eWe are particularly critical of the following suggestion: “In particular, grade requirements for admission could be lowered for candidates who […] have a family background of rural medicine.”  (p. 7). Politics are confronted with the difficult problem of finding a remedy for the shortage of country doctors and GPs. From our point of view, the authors’ proposals are neither supported by their empirical findings, nor would they lead to the desired result. An expansion of the waiting period quota would result in a decrease of graduates, further exacerbating the shortage of country doctors. A Cochrane report  as well In our opinion, it is a sensible suggestion by Kesternich et al. to include “the specialization choice of students as a criterion when evaluating entry requirements.”  (p. 6). The authors declare that they have no competing interests.


Correction to:International Journal of Obesity (2017) 41, 1232–1236; doi:10.1038/ijo.2017.89Since publication the authors of this paper have requested that it be made open access under the CC BY licence.


International Journal of Qualitative Studies on Health and Well-being. Now, these articles are being republished in issue 12(S2). The articles that were republished in the issue 12(S2) are listed below:A number of articles were erroneously published in the issue 12(1) of Journal of Qualitative Studies on Health and Well-Being, 12 (S2), doi: 10.1080/17482631.2017.1358581Larsson, I. & Jormfeldt, H. (2017). Perspectives on power relations in human health and well-being. Håman L., Lindgren, E.-C & Prell, H. (2017). “If it’s not Iron it’s Iron f*cking biggest Ironman”: personal trainers’s views on health norms, orthorexia and deviant behaviours. Journal of Qualitative Studies on Health and Well-Being, 12 (S2), doi: 10.1080/17482631.2017.1364602Jonsson, L, Larsson, C., Christina, Berg, C., Korp, P., & Lindgren, E.C. (2017). What undermines healthy habits with regard to physical activity and food? Voices of adolescents in a disadvantaged community. Journal of Qualitative Studies on Health and Well-Being, 12 (S2), doi: 10.1080/17482631.2017.1333901Lindgren, E.C., Annerstedt, C., & Dohsten, J. (2017). “The individual at the centre” – a grounded theory explaining how sport clubs retain young adults. Journal of Qualitative Studies on Health and Well-Being, 12 (S2), doi: 10.1080/17482631.2017.1361782Lindgren, E.C., & Barker-Ruchti, N. (2017). Balancing performance-based expectations with a holistic perspective on coaching: a qualitative study of Swedish women’s national football teamJournal of Qualitative Studies on Health and Well-Being, 12 (S2), doi: 10.1080/17482631.2017.1358580coaches’ practice experiences. Taylor & Francis apologizes for these errors.


The crystalline phases were examined by X-ray diffraction (XRD). The crystallinity percentage decreased with increasing zirconia content for the as-synthesized samples. The existence of zirconia as secondary phase on the grain boundaries; as observed from scanning electron micrographs (FESEM); resulted in negative values of microstrain. The crystallite size was computed and the results showed that it increased with increasing annealing temperature. Thermo-gravimetric analysis (TGA) assured the thermal stability of the nano crystals over the temperature from room up to 1200 °C depending on the zirconia content. The corrosion rate was found to decrease around 25 times with increasing zirconia content from x = 0.0 to 1.0. Microhardness displayed both compositional and temperature dependence. For the sample (x = 0.6), annealed at 1200 °C, the former increased up to 1.2 times its original value (x = 0.0).Zirconia doped Hydroxyapatite (HAP) nanocrystals [Ca Bone is a biological composite of two components; collagen; the biological part, and hydroxyapatite (HAP) which is composed of rod like particles, similar to the mineral part embedded in the collagen fibrils1456Several researchers synthesized HAP; focusing on the development of powder processing methods, composition adjustment and preparation conditions, to find the most effective preparation technique which achieves high strength HAP without altering the biocompatibility nature2+ position. The (PO4)3− could also be substituted by (CO3)2− to produce B-type carbonated HAP. Other researchers mentioned that the later can be replaced by silicate4)4−.Ionic incorporations in HAP ceramics, such as silver (Ag), magnesium (Mg), iron (Fe), copper (Cu), strontium (Sr) and zinc (Zn), have gained more interest due to their role in the biological processes after implantationet al. fabricated ZrO2/HAP scaffolds and they get good mechanical properties with higher cell affinity with no detectable degradationet al. synthesized microporous zirconia/HAP composites. Due to the diffusion of Ca2+ from HAP to ZrO2, HAP transformed into a mixture of HAP, α and β-tri calcium phosphate (TCP) and calcium zirconate. In addition, Young’s modulus and hardness of the composite depended on the internal porosity levelet al.S. H. An 2+ and ZrO2+ between HAP and zirconiaet al.et al. They reported that the transformation of ZrO2 from monoclinic to tetragonal phase was responsible for the reinforcing mechanismet al.et al.et al.et al.Z. Evis studied the reactions in zirconia/HAP composites. He concluded that the HAP unit cell volume increased with increasing zirconia content due to the ionic exchange of Ca2) nano particles. This resulted in higher bonding strength, improved mechanical properties, biocompatibility and high corrosion resistanceet al. synthesized composite of partially stabilized zirconia/HAP. They discussed the hypothetical incorporation of Ca2+ by Zr4+ in the HAP structure. They supposed that the mechanism is that each 2 Ca2+ ions are replaced by one Zr4+ to keep the charge balance and symmetryet al. investigated the surface characteristics of the annealed HAP/zirconia composite. They concluded that the HAP/zirconia has a mechanical compatibility as well as a potential for good biocompatibility with bone tissueOne of the most common applications is the use of HAP as a coating layer on zirconia  ions, keeping (Ca + Zr)/P = 1.67. The authors reported that the phase transformations could be tailored by adjusting zirconium content28J. B. Miecznik 2+ by zirconia in HAP matrix with different concentrations. However, the influence of zirconia incorporation in HAP matrix on (PO4)3− crystallographic site have been scarcely reported. In this piece of work, we aimed to investigate the effect of zirconia doping content on HAP microstructure and explore the physical properties of the obtained nanocrystals.All reported literature was concerned with one of the following (i) coating zirconia surface by HAP nanoparticles, (ii) preparing (HAP + zirconia) as binary or ternary composite, (iii) substituting CaXRD patterns of the as-synthesized HAP dopant with zirconia (Zr-HAP) samples are presented in In case of the samples annealed at 1300 °C in 2) content. There is a large difference in crystallinity between the as-synthesized and annealed samples. For the annealed samples, it varies from 46.2 up to 95.1%, however, it doesn’t exceed 36.6% in case of the as-synthesized samples.The crystallinity was illustrated in The crystallite size was plotted versus x in The microstrain (ε) and crystal size contributions, that are independent factors, result in the total broadening of the diffraction peaksThe UDM crystal size behavior is found to be decreasing with small values in most cases, while for the as-synthesized samples, UDM was slightly decreased. As reported in ; the UDM−3. The strain for the annealed samples varied from −4.29 × 10−3 up to 2.8 × 10−3. Zirconia phase possesses minimum lattice strain as compared with that calculated for HAP which varied from 0.35 × 10−3 to −2.78 × 10−3.The lattice strain calculated from UDM, was plotted in The relation between stress and strain is expressed by Hook’s law, which is valid for significantly small strains. As illustrated in Hook’s law assumed the homogeneous isotropic nature of the crystal. However, in real samples, the assumption of perfect isotropy is not fulfilled. Moreover, all the proportionality constants associated with the stress/strain relation are no longer independent when the strain energy density u is considered.The uniform energy deformation mode (UEDM) crystal size varies in a decreasing manner for the annealed samples while for the as-synthesized samples, it decreases as shown in From the crystallographic data illustrated in The (c) constant of the HAP unit cell increased slightly as shown in 3 at x = 0.4 as illustrated in The HAP unit cell volume has the same trend of (a) constant, the largest unit cell volume is 536.739 Åx) was determined using the formulaThe theoretical density  asymmetric stretching vibrations and bending (ν2) modes of carbonate groups−1 are referred to ν2 (bending mode) of PO43− ions while those at 562.8 and 602.5 cm−1 are assigned to ν4 (bending mode) as well as 1030.3 cm−1 is attributed to ν3 (anti-symmetric stretch) of PO43− ions3940−1 is ascribed to the absorbed water molecule343542− appeared at 3434.8 cm−1 354344The bands appeared at 1453.7, 1421.8 and 874 cm−1 could be assigned to the zirconia; the bands at 427.5 cm−1 at x = 0.2 and 525.1 cm−1 at x = 1.0 could be attributed to Zr–O-Zr stretching mode28362 as observed from FTIR spectra. It is clear that the band splitting increased with increasing x due to the bands of zirconia that appears as matched with XRD data.The splitted weak bands 400–525 cmThermo-gravimetric analysis (TGA) was carried out for the samples of x = 0.0, 0.6 and 1.0 from room temperature (R. T.) up to 1200 °C as shown in In case of the samples annealed at 1200 °C; x = 0.0 looks like hexagonal crystals with attached boundaries, hard edges and inter-granular porosity. As seen in the micrograph; When comparing the sample with x = 0.4 at 1200 °C shown at 2 decorating the surface in a more regular pattern. There is a higher amount of porosity than that observed for x = 0.4. However; the pores of x = 0.6 are well distributed and smaller than those at x = 0.4. The pore size is about 0.7 μm. The spherical particles of zirconia tend to fill these open voids as illustrated in The predominant shape for x = 0.6 is a hexagonal one while small grains of ZrOThe last micrograph of x = 1.0 is represented in t) increased from 0.75 μm at x = 0.0 to become 0.83 μm at x = 1.0. The root mean square roughness (Rq) increased from 0.185 to 0.189 μm from x = 0.0 to 1.0.The micrographs of FESEM were processed by gwyddion 2.45 software to investigate the surface roughness of the samples, annealed at 1200 °C. The ratio between the negative values of lateral strain and longitudinal strain of a sample is known as Poisson’s ratio4646The calculated values of Poisson’s ratio for the annealed samples are reported in  where υ The microhardness is defined to be the resistance of materials to be indentedV) is estimated accordingHardness measurements correlated between the microstructure and mechanical characteristics of a material. The Vickers hardness number  is obtained at x = 0.6, 1200 °C.In a case of the theoretical microhardness; it is clear that there is a huge difference between theoretical and measured values which reached 20 times. The maximum value of HIt has been well-established that a decrease in grain size results in an increase in the hardness or the yield strength according to the Hall-Petch equation51o represents the hardness of a single crystal of the material under investigation, b is a constant and d is the grain size. The calculated values are illustrated in where H represents the hardness and HThe bulk modulus - or compressibility (k) - is defined as the hydrostatic pressure necessary to cause a unit relative change in volume of a substance, and it is always a positive value. It could be calculated for hexagonal systems theoretically fromFor all samples, it has nearly similar value of 84.6 GPa owing to the hexagonal symmetry.Corr) of the doped samples is shifted to positive direction with a significant decrease in the anodic current. (Corr) of the samples was significantly decreased with increasing x. The value of ICorr is for x = 1.0 is 12 times lower than that for the pure HAP sample (x = 0.0). Correspondingly, the corrosion rate decreased from 66.76 μm/year for x = 0.0 to 2.589 μm/year at x = 1.0. In addition, the polarization resistance (Rp) increases significantly with increasing x.The evaluation of the corrosion behavior for the investigated samples annealed at 1200 °C was carried out after immersion in (simulated body fluid) SBF solution at 37 ± 0.5 °C for 24 hrs. current.  denotes 1 + R2(W1 + C1)] which consists of Ohmic resistance (R1) in series with the other part of a circuit and represents the solution resistance, R2 in paralleled with the capacitor C1. There is a Warburg element (W1) in series with the capacitor at x = 0.0 however, it becomes in series with R2 at x = 0.4 and 1.0. The equivalent circuit parameters are reported in  measurements were carried out and illustrated in orted in .The dielectric constant (ε′) was determined from the measured capacitance of the samplesThe detailed phase evaluation using XRD analysis indicates the absence of diffraction peaks corresponding to zirconia phase in the as-synthesized samples. This suggests that zirconia particles were completely entrapped in the HAP lattice. The as-synthesized patterns also exhibit broad diffraction peaks, which is elucidated by poor crystallinity accompanied by small crystallite size.2/nmc).In the annealed samples; zirconia reveals clear peaks at x ≥ 0.4 (ICDD card no. 01-081-1544), which gives an idea about its solubility limit in HAP matrix. Zirconia secondary phase was crystallized in tetragonal crystal symmetry with space group . Herein, the peak intensities of α-TCP arise with increasing zirconia content. One could argue that the decomposition of HAP–ZrO2 started at annealing temperature >1200 °C.where HAP decomposes into α/β -TCP with the appearance of the second phase of CaZrO1.95 which points to the existence of oxygen vacancies in zirconia unit cell. The so-called polycrystalline tetragonal zirconia displays excellent mechanical properties with an enhanced ionic conductivity at low temperatures as compared to cubic zirconiaIt is noticed that the formed zirconia phase corresponds to ZrOThe broad lines of XRD patterns for the as-synthesized samples originated from two sources, namely the small crystal size and the lattice distortion that increased with the incorporation of zirconia into the HAP matrix56s is expected to decrease with increasing zirconia content. This was explained by supposing that zirconia particles acted as a separator between HAP grains owing to existence on the grain boundaries of the later as observed in FESEM. In addition, the difference in the thermal expansion coefficient between hexagonal HAP and tetragonal zirconia crystals could inhibit the lattice expansion and/or crystal growth of HAP grains. The improvement of crystal growth of zirconia on the expense of HAP ones is reported in  is relatively high due to the expected large surface/volume ratio values as a direct consequence of small crystallite size. For the annealed samples, the lattice strain values increased slightly with rising zirconia content. However, microstrains for the as-synthesized and 1000 °C annealed samples, possess high values amongst all since zirconia are incorporated in the HAP crystals inducing more internal strains in the lattice.The obtained negative values of the microstrains are expected due to the existence of zirconia as a secondary phase on the grain boundaries thereby exerting a pressure on the HAP hexagonal matrix. The external compression could induce the negative strain distortion. However, the positive strain could be attributed to the internal stress in the crystal itself due to the thermal expansion which accompanies the crystal growthIn performing both USDM and UEDM computations, the anisotropic nature of the elastic constants was taken into consideration whereas the deformation energy density (u) is supposed to have the same value in all crystallographic directions (isotropic nature)3/mPure hydroxyapatite unit cell is described in terms of a hexagonal structure with dimensions a = b = 9.432 Å, c = 6.881 Å, α = β = 90°, γ = 120° adopting the space group P62+ or phosphate ions have occupied some position in HAP unit cell and one assumed four probabilities: The 1st is that Zr4+ could replace Ca(I) ion positions, 2nd: Zr4+ replace P5+ positions, 3rd: ZrO1.95 substitute the phosphate group and the last one is that carbonate substitutes the phosphate position which is categorized as (B-type). The ionic radii of Zr4+ is larger than that of P5+, therefore, the 2nd probability is not preferredth) is evident from FTIR spectra. In addition, there is no significant A type. However, the decrease of (a) constant stopped at x = 0.4, then rise up to x = 1.0. This increase of (a) may due to an incorporation of ZrO2+ into Ca(I) position. ZrO2+ has a radius (2.1 Å) which is more than 2 times of that of Ca2+ radius (0.99 Å)252+ or ZrO1.95 in c- direction.In case of the as-synthesized samples, the decrease of (a) could be explained by supposing that ions with smaller size than Ca2+ among the available Ca2+ sites. Moreover, it was believed that in some cases, high temperature site preference plays a significant role in the appearance of tetragonal zirconia phase especially at large zirconia contents. Therefore, the lattice parameters in case of the annealed samples represent opposite trends where (a) constant has higher values at x = 0.4 than the other zirconia contents. This is directly related to its solubility limit in the HAP matrix. Above x = 0.4, zirconia could exist as a separate phase as matched from XRD results. The (c) constant keeps the same trend of the as-synthesized samples because it is related to the crystallographic direction of the substituting positions.For the annealed samples, one could expect the redistribution of ZrOThe (c/a) ratio is close to the trend of (a) more than (c) because the value of (a) is larger than (c). One demonstrated that (c/a) values decay with increasing the annealing temperature owing to the inhibition of crystal growth in (c) direction. This will induce the formation of more spherical shape . This behavior is reflected in the hardness values.Increasing zirconia content to x = 0.6, supports our hypotheses about surface pining diffusion, especially the pores are interconnected and they are open pores as illustrated in The spherical shape (at x = 1.0) represent zirconia particles with size 135 nm. In addition, there is a large amount of disconnected pores with size about 1.4 μm. The overall argument is that the existence of zirconia secondary phase in the HAP at this annealing temperature (1200 °C) enhanced the densification in a limited proportion while the porosity is less pronounced. This could be highly employed in biomedical implants where the surface roughness along with porous nature of the bioceramics is highly desirable. In addition, the grain size decreased from 1.4 μm at x = 0.0 to 1.06 μm at x = 1.0. This decrease is mainly attributed to the strain caused by zirconia phase on the grain boundaries of the hexagonal one.The biological HAP doesn’t possess a smooth surface because of a large number of structural substitutions66The computed Poisson’s ratio takes into consideration the anisotropic nature. All annealed samples could be considered as a partially auxetic materials. The later is a type of materials that exhibit a negative Poisson’s ratio where it expands under the applied stresshkl). (ii) The microcracks formed in the ceramic samples which are observed in FESEM micrographs. (iii) The existence of a secondary crystalline phase (ZrO1.95) which has different hardness values and affected strongly on the overall values. The increase in hardness with increasing zirconia content is mainly due to the decrease in grain size. For the samples annealed at temperatures higher than 1000 °C, the hardness increases up to x = 0.6 and then decreases, where the maximum hardness is achieved at x = 0.6. Hardness values are obviously rising with the annealing temperature due to enhanced densification and compactness. However, the hardness decreased at T > 1200 °C because of crumbled grains due to the significant ratio of zirconia on the grain boundaries, the phase transition of HAP to α-TCP is a factor working on reducing the hardness to 1.4 GPa. The measured values of the hardness are in good correlation with the appearance of zirconia phase. The porosity is lowered with zirconia content up to x = 0.4 and then increased. This finding is in line with the hardness as the later gives the opposite trend. The samples annealed at 1200 °C didn’t follow the same trend as the value of porosity is lower than that obtained for corresponding annealing temperatures. Minimum porosity at x = 0.6 at 1200 °C coincides with the maximum hardness. With decreasing the grain size, the relative volume of grain boundaries increases, leading to an increase in the resistance to indentation. Therefore, the presence of zirconia inhibited the grain growth of HAP particles. Thus, the annealed samples containing zirconia nano spheres can be produced by further consolidation, for its developed strengthThe hardness is governed by the grain size, porosity, densification and/or existence of a secondary phase. Moreover, it was found that the samples obeyed Hall–Petch relationship, where the hardness decreased with increasing grain size. This phenomenon is displayed from the dislocation movement or migration. The later could be inhibited by grain boundaries; therefore by decreasing the grain size, the dislocation free path will be consequently reducedet al. calculated the bulk modulus67The computed bulk modulus displays one value because it doesn’t depend on the lattice parameters. W.Y. Ching p) with increasing the zirconia content indicates an improvement in the corrosion resistanceThe increase of polarization resistance (R1.95) as identified from XRD results. Another possible reason is the appeared porosity  as in line with FESEM observations.The centers of Nyquist semicircles seem to be situated below the Z′ axis, meaning that the samples contain inhomogeneity. The later was formed during the annealing process at elevated temperatures and are evident from the oxygen deficient zirconia phase  and the 2The large capacitance values as obtained from the Nyquist plot fitting pointed to large relaxation times. This could be advantageous for several applications. However, in Bode plots, the pure HAP at x = 0.0 displays the highest total impedance. Therefore, the Ohmic resistance is the main contributor to resistance in this case and could be explained by supposing that zirconia particles improved the conductivity. Further studies are needed at high temperature to assure the evidence of ionic conductivity in the doped samples.The large values of (ε′) at lower frequencies are attributed to space charge polarization and the alignment of dipoles in the direction of the field. This enhances the obtained large relaxation time values for (Z′–Z″) plots as mentioned above. As the frequency increases the electron exchange cannot follow up the electric field variation and the polarization becomes frequency independent as shown in ac) was calculated and presented as a function of frequency in ac) of the doped samples is higher than that of the pure sample at the same frequency, due to the existence of holes owing to the oxygen vacancies in zirconia crystal (ZrO1.95). The development of the polarization in the samples could improve the bone growthThe similarity between the dielectric constant and dielectric loss behaviors; (except at x = 0.8); could be clarified by increasing the ratio of zirconia which is distinguished by oxygen vacancies. The later acts as a trapping center for the charge carriers which lead to greater loss values. The ac conductivity (σ10(PO4)6−x(ZrO2)x(OH)2]; (0 ≤ x ≤ 1) in step 0.2 was synthesized using Co-precipitation assisted microwave irradiation. The ratio of Ca/(Zr + P) was adjusted to be 1.67 for all concentrations as the equation:All raw materials used in the preparation were analytical grade reagents and used as received without any further purification. Hydroxyapatite doped with zirconia [Ca4)2HPO4] and zirconium oxychloride [ZrOCl2. 8H2O] were slowly dropped on CaCl2. 2H2O with continuous stirring. The pH of the solution was adjusted and kept at 11 ± 0.05 for all concentrations. The stirring was maintained at a constant speed for 6 hrs. The obtained suspensions were involved into the microwave in a water bath for 20 mins as follow: 5 mins ON, 4 mins OFF. The solutions were aged for 24 hrs to precipitate, then thoroughly washed with doubled distilled water and dried at 60 °C. The obtained powders were pressed into pellets with 4 mm radius, using a uniaxial press of 60 MPa for 10 sec. The pellets were annealed in Lenton furnace (UAF16/5) at different temperatures at; 1000, 1100, 1200 and 1300 °C for 1 h in air with a heating/cooling rate of 10 °C/min. The block diagram illustrating the synthesis procedure is shown in The aqueous solutions of [ to identify the formation of the samples in the desired phases. All the diffraction charts obtained were scanned in the range 4 ≤ 2θ ≤ 60° of angles with step size of 0.02 and a step time of 0.5 s. The corrected broadening βhkl equivalent to the diffraction peak of HAP was estimated using the equationX-ray diffraction analyses were carried out using  diffraction peak and V112/300 is the hollow intensity between (112) and (300) peaks of HAP, respectively.where Xs was computed from Scherrer’s equationThe crystallite size Ds is the Sherrer’s crystallite size (nm); k is the shape factor (k = 0.9), λ is the target wave length of the X-ray (λ = 0.154056 nm for CuKα radiation); θ is Bragg diffraction angle (°) and β is the corrected full width at half maximum (in radians).where DThe microstrain resulting in line broadening β is calculated from the relationBy considering that the present strain is uniform, which reflects the isotropic nature of the crystal, Williamson–Hall (W-H) equation is expressed asBy plotting (β cos θ) on the y-axis and (4 sin θ) on the x-axis, the crystallite size was obtained from the y-intercept and the lattice strain from the slope of the linear fitting.By supposing small strains to exist in the as-synthesized and annealed samples, the stress-strain behavior will obey Hook’s law ashkl) is the modulus of elasticity or Young’s modulus. As a result, where (Ehkl) is determined for hexagonal systems from the following relationThe uniform stress can be obtained from the slope of the straight line plotted between 11, S13, S33, and S44 are the elastic compliances and their values are 7.49 × 10−12, 4.0 × 10−12, 10.9 × 10−12 and 15.1 × 10−12 m2/N respectively58where SFor a tetragonal polycrystalline zirconia, Young’s modulus is calculated from11 = 3.46 × 10−12, S33 = 4.06 × 10−12, S12 = −0.96 × 10−12, S13 = −0.59 × 10−12, S44 = 17 × 10−12, S66 = 15.4 × 10−12 m2/Nwhere SThe energy density (U: energy per unit volume) could be substituted for hkl  cos θ on the y-axis and The plot of β−1. Thermo-gravimetric (TGA) analysis was carried out from room temperature up to 1200 °C in a DTG-60 SHIMADZU analyzer using an air flow rate of 100 ml/min and a heating rate of 10 °C/min. The surface morphology was examined using field emission scanning electron microscope (FESEM) model QUANTA-FEG250 (Netherland). Micrographs were recorded at an operating voltage of 10 kV on the powdered samples. Microhardness experiments were carried out using (TTS UNLIMITED INC. model: HWDM-7/Japan) with situ imaging mode. Corrosion behavior of the annealed samples was evaluated in SBF as previously reported by D. Qiu et al.2. The temperature of SBF solution was adjusted at 37 ± 0.5 °C. Open circuit potential was working for 1 h to achieve the steady state. For Electrochemical impedance spectroscopic analysis (EIS), a frequency range was applied from 0.01 Hz up to 60 kHz. The potential was applied from −0.5 to +0.5 V. EIS data were analyzed using Ivium software. Dielectric and ac conductivity measurements were carried out at room temperature on a disk shaped sample coated with silver paste using LCR meter model (HP 4192A).FT-IR spectrometer (Perkin-Elmer system 2000) was used for recording FTIR spectra in the range of 4000–400 cmHAP doped with zirconia nanoparticles were successfully synthesized using microwave assissted co-precipitation method. The annealing temperature was found to play a significant role in the phase formation as well as the crystallinity and the appearance of the secondary phases. The mechanical properties were highly accentuated up to x = 0.6 and then decayed. Additionally, the highest measured hardness value was obtained at x = 0.6 which was annealed at 1200 °C with value 2.85 GPa. The calculated Poisson’s ratio showed a partially auxetic behavior. The hardness was found to satisfy Hall-Petch relation. In addition, a nice correlation was established between measured, calculated physicomechanical properties and the observed morphology. The corrosion resistance increased 1.67 times by increasing zirconia content from x = 0.0 to x = 1.0 which means that zirconia was successful as a corrosion inhibitor. Owing to the superior mechanical properties of the samples annealed at 1200 °C, the discussed results may suggest a new methodology for fabricating biomimetic nano doped HAP. Other potential applications could be suggested upon future investigations.How to cite this article: Mansour, S. F. et al. Physico-mechanical and morphological features of zirconia substituted hydroxyapatite nano crystals. Sci. Rep.7, 43202; doi: 10.1038/srep43202 (2017).Publisher's note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.


Many advantages have been attributed to dental zirconia ceramics in terms of mechanical and physical properties; however, the bonding ability of this material to dental structure and/or veneering ceramics has always been a matter of concern. On the other hand, hydroxyapatite (HA) shows excellent biocompatibility and good bonding ability to tooth structure, with mechanically unstable and brittle characteristics, that make it clinically unacceptable for use in high stress bearing areas. The main purpose of this study was to introduce two simple yet practical methods to deposit the crystalline HA nanoparticles on zirconia ceramics.zirconia blocks were treated with HA via two different deposition methods namely thermal coating and air abrasion. Specimens were analyzed by scanning electron microscopy, energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD).In both groups, the deposition techniques used were successfully accomplished, while the substrate showed no structural change. However, thermal coating group showed a uniform deposition of crystalline HA but in air abrasion method, there were dispersed thin islands of HA.Thermal coating method has the potential to significantly alter the surface characteristics of zirconia. The simple yet practical nature of the proposed method may be able to shift the bonding paradigm of dental zirconia ceramics. This latter subject needs to be addressed in future investigations. The popularity of zirconia has increased in the past 10 years. It is suitable for use in many dental applications due to having unique mechanical properties, chemical stability and esthetic characteristics. Stabilized tetragonal zirconia polycrystalline ceramics with 3 mol% of yttria (3Y-TZP) have enhanced mechanical properties and are reliable for posterior multi-unit resin-bonded restorations, implant abutments and intracanal posts .Despite good mechanical properties, Y-TZP ceramics have poor bonding ability to tooth structure and veneering ceramics due to their inherent non-polar nature . Various10(PO4)6(OH)2” known as calcium hydroxide phosphate [Hydroxyapatite (HA) with the formula “Cahosphate  is the mhosphate ,10. Biolhosphate  which ishosphate . It is chosphate ,13 and ihosphate ,15 leadihosphate –20. Radihosphate , 19. In hosphate . HydroxyIn order to deposit HA on a surface, different techniques have been used. common methods are sol-gel , ion beam assisted deposition, vacuum deposition, ion-beam sputtering (depositing thin films by ion sputtering), electrophoretic deposition ,20, highIn this experimental in vitro study, HA was coated on the surface of Y-TZP ceramic by two sophisticated deposition methods namely air abrasion and thermal coating. The main objective was to find a simple/practical way to coat the Y-TZP ceramics with HA.In this short communication, two experimental coating methods were evaluated namely thermal coating process and air particle abrasion. The Y-TZP dental ceramic blocks  with dimensions of 4×4×4mm were ground finished by 600-grit silicon carbide abrasive papers , cleaned for 10 minutes in an ultrasonic bath  containing ethyl acetate and then air-dried for 30 seconds. For thermal coating method, a slurry of 10g nanoparticulate (less than 100nm) HA powder , 1g of poly vinyl alcohol  and 50cc of distilled water was prepared. The mixture was heated in a magnetic stirrer with hot plate at 100°C with 1000 rpm speed for 30 minutes to form a uniform suspension. The blocks were then soaked in this slurry for 5 seconds at 45° angle and a sintering procedure started according to the following protocol: Room temperature to 300°C (10 minutes), 300°C to 600°C (10 minutes), 600°C to 900°C (30 minutes), 900 to 1200°C (120 minutes) and cooling  accomplished in a furnace . In air abrasion method, the outer surface of zirconia blocks was blasted with HA nano particles at 4 bar pressure, from a distance of 10mm for 15 seconds using a commercial sandblasting machine  . Then, tImages were collected in the secondary electron imaging mode with 15kV working voltage and 10–12mm working distance. The composition analysis was performed with an energy dispersive spectroscopy  X-ray setup. The EDS provided qualitative data and assessed the presence of different elements in the surface of prepared samples.® diffractometer . The Cu K radiation was used at a wavelength of 1.5406À at a current of 0.8 mA and accelerating voltage of 45 kV. Data were collected by the step counting of 0.02, and dwell time of 15 s/step in the range of 10≤2Ø≤100.The prepared zirconia blocks were examined with X-ray diffraction (XRD) in order to find out the phase of the HA structure. The XRD spectra were collected using a multifunctional UnisantisPhase identification of zirconia blocks were performed with X’pert High Score 2.2 software  with reference to the database supplied by International Center for Diffraction Data (ICDD).Scanning electron microscopic analysis of the thermally coated block showed a uniform coating on the zirconia surface with various cracking features, which demonstrated a difference in thermal expansion coefficient of zirconia and HA nano powders. In EDS analysis, we saw different elements such as phosphorous and calcium, which demonstrated the presence of HA on the surface of thermally coated sample. The EDS results also showed zirconium and yttrium reflections of substrate. The XRD patterns recorded from thermally coated samples revealed that the crystalline HA formed on the surface of zirconia block. In XRD patterns, there was no reflections belonging to zirconia substrate due to well coating of HA on the surface of zirconia block . Also, iIn order to exploit the benefit of HA, different coating methods are presented but, there are still no standard guidelines on aspects of specific methods, coating thickness, surface considerations, effects of crystallinity or crystallite size on bond, texture, and porosity. The main purpose of these experimental deposition protocols is to produce HA coatings, which may positively improve the adhesive, compositional, and structural properties of coated substrates.The temperature used in coating process is very critical. The crystal structure of HA significantly changed at 600–800°C at which semi-crystalline transformation occurred. While in sintering process from 800°C to 1000°C, crystalline cells improved perfectly, from 1000–1200°C, a densification process occurred and the mechanical behavior of HA improved. It was also shown that raising the sintering temperature may increase the stability of HA .Surface area, crystallinity, composition and density of the coating are the factors that have significant influence on the dissolution rate of coating. The crystalline HA coats observed after a post deposition heat treatment of 600°C may significantly reduce the tensile bond strength of the coating . The sol−6/K and 10.8 ×10−6/K, respectively [3/M20. The main Bragg peaks in thermal coating group according to JCPDS file No.4-697 [2 [2 coexist in the XRD pattern at 30°, 35°, 51°, 59°, 60°, 73°, 75°, 82°, 84°, 74° and 75°. Shi et al. [In the same way, high temperature deposition processes may affect the substrate’s grain structure and adversely reduce its long-term performance. One of the features seen in the high temperature processes like atmospheric plasma spraying is cracking, which may be attributed to the rapid and uncontrolled cooling of the thick HA coatings . The craectively . HoweverNo.4-697  observed4-697 [2 ,34. In c4-697 [2  and cubi4-697 [2  ZrO2 coei et al.  confirmeIn the experimental model presented here, two practical methods were assessed namely thermal coating and air abrasion process. In both techniques, the yttria-zirconia substrate was stable. Thermal coating group showed a uniform deposition of crystalline HA but in air abrasion method, there were dispersed thin islands of HA. Thus, thermal coating method had the potential to significantly alter the surface characteristics of zirconia and may be able to shift the bonding paradigm of dental zirconia ceramics. This latter subject needs to be addressed in future investigations.