Qualitative SEM analysis of fracture surfaces for dental ceramics and polymers broken by flexural strength testing and crown compression.

PURPOSE: To perform qualitative analysis using scanning electron microscopy (SEM) of fracture surfaces for ceramic and polymeric dental materials broken via standardized flexural and crunch-the-crown (CTC) tests. MATERIALS AND METHODS: Zirconia, glass-ceramic, and polymeric (Trilor; TRI, Juvora; JUV, Pekkton; PEK) materials were loaded using crowns for CTC tests, discs (zirconia and glass-ceramics) for piston-on-3 ball tests, bars (polymer) for 3-point bend tests, and bars (zirconia, glass-ceramics) for 4-point bend tests. SEM was used to characterize the fracture surfaces and identify fracture surface features (e.g., origin, mist, hackle, and the direction of crack propagation [DCP]). Electron dispersive spectroscopy was used to identify the local chemistry. RESULTS: Fracture surface features were found to be less visually apparent for glass-ceramics than zirconia. For zirconia bars, fractures originated roughly midway between the corner and center for processing defects related to sintering. Fractures originated at the bottom corners of glass-ceramic bars (void or surface flaw) and PEK bars (surface flaw). TRI bar failures exposed glassy fibers. Fracture features were generally less discernable for discs compared to bars for zirconia and glass-ceramics. Ceramic crowns fractured into 2 to 3 pieces, with fractures originating at the occlusal surface and clear evidence for the DCP. Failures of TRI and JUV specimens (bars and crowns) were less catastrophic than for the ceramics, with exposed fibers (TRI) and surface cracks (JUV). PEK crown and bar fractures presented dimple (ductile) features formed due to microvoid coalescence followed by brittle crack propagation. CONCLUSIONS: The critical flaws responsible for failure initiation were a function of material composition and test configuration. Fractographic analysis can reveal problems associated with the manufacturing of materials, their handling, grinding and finishing/polishing procedures, the structural design and choice of material, and the quality of the final laboratory-delivered restoration.

A course in medical device design & commercialization for medical students pursuing surgical fields.

BACKGROUND: The modern surgeon faces an ever-changing landscape of procedural innovation. The demands of present-day healthcare highlight the importance of successfully developing new medical devices and technologies. This effort requires multidisciplinary collaborations of professionals ranging from manufacturers and engineers to researchers and healthcare providers. Surgeons regularly interact with complex equipment and user interfaces without substantial formal education on their design and development. The objective of this study was to ascertain the impact of a 10-week BME course into a medical school curriculum on surgery-bound students' knowledge of product design and gauge their ability to develop an actual product to meet a real need in a surgical field. METHODS: A Medical Device Design and Commercialization co-enrolled elective course was offered to medical students at a single institution. Five students with an expressed surgical and procedural interest were enrolled. At the beginning of the course, they were tasked with developing a product to meet a clinical need they observed. At the conclusion of the course, students filled out a questionnaire about their level of comfort and knowledge of the material using a 5-point Likert scale. This survey was administered to a control group of medical students who did not take the course. RESULTS: The BME student cohort was able to successfully identify a post-operative need, develop a prototype of a novel device, and present their product to attending surgeons. A total of 35 survey entries were received: five from the experimental group and 30 from the comparison group. The experimental group scored higher than the comparison group for all survey questions and reached the level of statistical significance in 13 of the 15 questions (p < 0.05). Survey respondents reported similar degrees of knowledge and comfort in recognizing unmet needs in a hospital setting and formulating a comprehensive statement describing them. CONCLUSION: The principles of biomedical engineering are integral to advancing the field of surgery. Presently, a small cohort of medical students/residents successfully acquired and applied basic BME concepts in a relatively short period of time relative to other training paradigms. Our findings also suggest medical students recognize unmet needs in the hospital setting, and those who completed a BME course felt more able to take steps to meet those needs. Early integration of biomedical engineering principles in medical training may help produce more innovative and well-rounded surgeons.

An experimental study of flexural strength and hardness of zirconia and their relation to crown failure loads.

STATEMENT OF PROBLEM: Dental zirconia is often marketed and selected for restorative use based upon the biaxial flexural strength of prefabricated specimens (disks) without considering other mechanical and physical properties. PURPOSE: The purpose of this in vitro study was to test whether 4-point flexural strength, biaxial flexural strength, and/or hardness may correlate with failure loads for crowns made of different zirconia materials. MATERIAL AND METHODS: Three brands of zirconia (BruxZir, Cercon, and Katana) were used to fabricate anatomically contoured crowns, rectangular bars, and circular disks. The sample size was n=15 specimens per zirconia brand and specimen shape. The bars were tested for 4-point flexural strength by using the 4-point bending (4PB) test and Vickers hardness (VH), while the disks were tested for biaxial flexural strength by using a piston-on-3 ball (POB) test. Crowns were attached to resin abutments and compressed with a steel spherical indenter through a polyethylene sheet to assess the failure loads by using the "crunch the crown" (CTC) test. One-way ANOVA (α=.05) was used to test for statistically significant differences between groups, and Weibull analysis was used to assess the variability of the measured flexural strengths, failure load, and hardness. RESULTS: Statistical differences (P<.001) were found in comparing Cercon, BruxZir, and Katana ([4260 N=4186 N]>3195 N, respectively) with the CTC test and (396 MPa>[281 MPa=275 MPa], respectively) the 4PB test. No statistical differences (P=.084) were found among the zirconia brands (Cercon [384 MPa]=Bruxzir [359 MPa]=Katana [416 MPa]) for the POB test. No significant correlations (P>.05) were found between the 4PB, POB, or VH tests and the corresponding CTC test. The Weibull modulus varied for the different specimen geometries. CONCLUSIONS: The piston-on-3 ball, 4-point bending, and Vickers hardness test results were not correlated with the corresponding crunch-the-crown test.

Fabrication and characterization of a thick, viable bi-layered stem cell-derived surrogate for future myocardial tissue regeneration.

Cardiac tissue surrogates show promise for restoring mechanical and electrical function in infarcted left ventricular (LV) myocardium. For these cardiac surrogates to be usefulin vivo, they are required to support synchronous and forceful contraction over the infarcted region. These design requirements necessitate a thickness sufficient to produce a useful contractile force, an area large enough to cover an infarcted region, and prevascularization to overcome diffusion limitations. Attempts to meet these requirements have been hampered by diffusion limits of oxygen and nutrients (100-200 µm) leading to necrotic regions. This study demonstrates a novel layer-by-layer (LbL) fabrication method used to produce tissue surrogates that meet these requirements and mimic normal myocardium in form and function. Thick (1.5-2 mm) LbL cardiac tissues created from human induced pluripotent stem cell-derived cardiomyocytes and endothelial cells were assessed,in vitro, over a 4-week period for viability (<5.6 ± 1.4% nectrotic cells), cell morphology, viscoelastic properties and functionality. Viscoelastic properties of the cardiac surrogates were determined via stress relaxation response modeling and compared to native murine LV tissue. Viscoelastic characterization showed that the generalized Maxwell model of order 4 described the samples well (0.7

3D printed mesh reinforcements enhance the mechanical properties of electrospun scaffolds.

BACKGROUND: There is substantial interest in electrospun scaffolds as substrates for tissue regeneration and repair due to their fibrous, extracellular matrix-like composition with interconnected porosity, cost-effective production, and scalability. However, a common limitation of these scaffolds is their inherently low mechanical strength and stiffness, restricting their use in some clinical applications. In this study we developed a novel technique for 3D printing a mesh reinforcement on electrospun scaffolds to improve their mechanical properties. METHODS: A poly (lactic acid) (PLA) mesh was 3D-printed directly onto electrospun scaffolds composed of a 40:60 ratio of poly(ε-caprolactone) (PCL) to gelatin, respectively. PLA grids were printed onto the electrospun scaffolds with either a 6 mm or 8 mm distance between the struts. Scanning electron microscopy was utilized to determine if the 3D printing process affected the archtitecture of the electrospun scaffold. Tensile testing was used to ascertain mechanical properties (strength, modulus, failure stress, ductility) of both unmodified and reinforced electrospun scaffolds. An in vivo bone graft model was used to assess biocompatibility. Specifically, reinforced scaffolds were used as a membrane cover for bone graft particles implanted into rat calvarial defects, and implant sites were examined histologically. RESULTS: We determined that the tensile strength and elastic modulus were markedly increased, and ductility reduced, by the addition of the PLA meshes to the electrospun scaffolds. Furthermore, the scaffolds maintained their matrix-like structure after being reinforced with the 3D printed PLA. There was no indication at the graft/tissue interface that the reinforced electrospun scaffolds elicited an immune or foreign body response upon implantation into rat cranial defects. CONCLUSION: 3D-printed mesh reinforcements offer a new tool for enhancing the mechanical strength of electrospun scaffolds while preserving the advantageous extracellular matrix-like architecture. The modification of electrospun scaffolds with 3D-printed reinforcements is expected to expand the range of clinical applications for which electrospun materials may be suitable.

A Project Course Sequence in Innovation and Commercialization of Medical Devices.

There exists a need for educational processes in which students gain experience with design and commercialization of medical devices. This manuscript describes the implementation of, and assessment results from, the first year offering of a project course sequence in Master of Engineering (MEng) in Design and Commercialization at our institution. The three-semester course sequence focused on developing and applying hands-on skills that contribute to product development to address medical device needs found within our university hospital and local community. The first semester integrated computer-aided drawing (CAD) as preparation for manufacturing of device-related components (hand machining, computer numeric control (CNC), three-dimensional (3D) printing, and plastics molding), followed by an introduction to microcontrollers (MCUs) and printed circuit boards (PCBs) for associated electronics and control systems. In the second semester, the students applied these skills on a unified project, working together to construct and test multiple weighing scales for wheelchair users. In the final semester, the students applied industrial design concepts to four distinct device designs, including user and context reassessment, human factors (functional and aesthetic) design refinement, and advanced visualization for commercialization. The assessment results are described, along with lessons learned and plans for enhancement of the course sequence.

Design and validation of a low cost, high-capacity weighing device for wheelchair users and bariatrics.

Accessible high-capacity weighing scales are scarce in healthcare facilities, in part due to high device cost and weight. This shortage impairs weight monitoring and health maintenance for people with disabilities and/or morbid obesity. We conducted this study to design and validate a lighter, lower cost, high-capacity accessible weighing device. A prototype featuring 360 kg (800 lbs) of weight capacity, a wheelchair-accessible ramp, and wireless data transmission was fabricated. Forty-five participants (20 standing, 20 manual wheelchair users, and five power wheelchair users) were weighed using the prototype and a calibrated scale. Participants were surveyed to assess perception of each weighing device and the weighing procedure. Weight measurements between devices demonstrated a strong linear correlation (R2 = 0.997) with absolute differences of 1.4 ± 2.0% (mean±SD). Participant preference ratings showed no difference between devices. The prototype weighed 11 kg (38%) less than the next lightest high-capacity commercial device found by author survey. The prototype's estimated commercial price range, $500-$600, is approximately half the price of the least expensive commercial device found by author survey. Such low cost weighing devices may improve access to weighing instrumentation, which may in turn help eliminate current health disparities. Future work is needed to determine the feasibility of market transition.

Increased trabecular bone and improved biomechanics in an osteocalcin-null rat model created by CRISPR/Cas9 technology.

Osteocalcin, also known as bone γ-carboxyglutamate protein (Bglap), is expressed by osteoblasts and is commonly used as a clinical marker of bone turnover. A mouse model of osteocalcin deficiency has implicated osteocalcin as a mediator of changes to the skeleton, endocrine system, reproductive organs and central nervous system. However, differences between mouse and human osteocalcin at both the genome and protein levels have challenged the validity of extrapolating findings from the osteocalcin-deficient mouse model to human disease. The rat osteocalcin (Bglap) gene locus shares greater synteny with that of humans. To further examine the role of osteocalcin in disease, we created a rat model with complete loss of osteocalcin using the CRISPR/Cas9 system. Rat osteocalcin was modified by injection of CRISPR/Cas9 mRNA into the pronuclei of fertilized single cell Sprague-Dawley embryos, and animals were bred to homozygosity and compound heterozygosity for the mutant alleles. Dual-energy X-ray absorptiometry (DXA), glucose tolerance testing (GTT), insulin tolerance testing (ITT), microcomputed tomography (µCT), and a three-point break biomechanical assay were performed on the excised femurs at 5 months of age. Complete loss of osteocalcin resulted in bones with significantly increased trabecular thickness, density and volume. Cortical bone volume and density were not increased in null animals. The bones had improved functional quality as evidenced by an increase in failure load during the biomechanical stress assay. Differences in glucose homeostasis were observed between groups, but there were no differences in body weight or composition. This rat model of complete loss of osteocalcin provides a platform for further understanding the role of osteocalcin in disease, and it is a novel model of increased bone formation with potential utility in osteoporosis and osteoarthritis research.

Navigation of a virtual exercise environment with Microsoft Kinect by people post-stroke or with cerebral palsy.

One approach to encourage and facilitate exercise is through interaction with virtual environments. The present study assessed the utility of Microsoft Kinect as an interface for choosing between multiple routes within a virtual environment through body gestures and voice commands. The approach was successfully tested on 12 individuals post-stroke and 15 individuals with cerebral palsy (CP). Participants rated their perception of difficulty in completing each gesture using a 5-point Likert scale questionnaire. The "most viable" gestures were defined as those with average success rates of 90% or higher and perception of difficulty ranging between easy and very easy. For those with CP, hand raises, hand extensions, and head nod gestures were found most viable. For those post-stroke, the most viable gestures were torso twists, head nods, as well as hand raises and hand extensions using the less impaired hand. Voice commands containing two syllables were viable (>85% successful) for those post-stroke; however, participants with CP were unable to complete any voice commands with a high success rate. This study demonstrated that Kinect may be useful for persons with mobility impairments to interface with virtual exercise environments, but the effectiveness of the various gestures depends upon the disability of the user.

Team-Based Development of Medical Devices: An Engineering-Business Collaborative.

There is a global shift in the teaching methodology of science and engineering toward multidisciplinary, team-based processes. To meet the demands of an evolving technical industry and lead the way in engineering education, innovative curricula are essential. This paper describes the development of multidisciplinary, team-based learning environments in undergraduate and graduate engineering curricula focused on medical device design. In these programs, students actively collaborate with clinicians, professional engineers, business professionals, and their peers to develop innovative solutions to real-world problems. In the undergraduate senior capstone courses, teams of biomedical engineering (BME) and business students have produced and delivered numerous functional prototypes to satisfied clients. Pursuit of commercialization of devices has led to intellectual property (IP) disclosures and patents. Assessments have indicated high levels of success in attainment of student learning outcomes and student satisfaction with their undergraduate design experience. To advance these projects toward commercialization and further promote innovative team-based learning, a Master of Engineering (MEng) in Design and Commercialization was recently launched. The MEng facilitates teams of graduate students in engineering, life sciences, and business who engage in innovation-commercialization (IC) projects and coursework that take innovative ideas through research and development (R&D) to create marketable devices. The activities are structured with students working together as a "virtual company," with targeted outcomes of commercialization (license agreements and new start-ups), competitive job placement, and/or career advancement.

Biomechanical Analysis of Screws Versus K-Wires for Lateral Humeral Condyle Fractures.

BACKGROUND: Good outcomes have been described for pediatric lateral condyle fractures treated by open reduction and fixation using either screws or Kirschner wires (K-wires). No studies have compared the biomechanical properties of the 2 fixation methods. We hypothesized that screw fixation would be more biomechanically stable than K-wire fixation. METHODS: Synthetic humerus models were used for biomechanical testing, following a previously published protocol. A miter saw was used to make an oblique cut to simulate a Milch type II fracture. Fractures were anatomically reduced and fixed with either 2 divergent 0.062-inch K-wires placed bicortically or a 4.0-mm lag screw placed obliquely (perpendicular to the fracture line). Specimens were then embedded in polymethyl methacrylate bone cement for testing. Mechanical testing using displacement control was performed applying compression or distraction from 0 to 1.5 mm at a rate of 0.5 mm/s for 10 cycles. The maximum force was calculated based on the maximum force averaged over the 10 cycles. Stiffness was calculated based on the slope of the force-displacement curve of the 10th cycle. A 2-sample t test was used to determine significant differences between the stiffness and maximum force comparing the K-wire and screw groups. A P-value of <0.05 was considered statistically significant. RESULTS: Stiffness and maximum force in tension testing were significantly greater with screw fixation compared with K-wire fixation. Testing in compression revealed statistically significant increased maximum force and a trend towards increased stiffness. CONCLUSION: Screw fixation in a synthetic bone model of pediatric lateral condyle fractures (Milch type II) provides increased biomechanical stability of the construct as compared with K-wires. CLINICAL RELEVANCE: If similar effects were seen in vivo, increased biomechanical stability with screw fixation could decrease the occurrence of complications such as loss of reduction and nonunion.

A new cortical thickness mapping method with application to an in vivo finite element model.

Finite element modelling of musculoskeletal systems, with geometrical structures constructed from computed tomography (CT) scans, is a useful and powerful tool for biomechanical studies. The use of CT scans from living human subjects, however, is still limited. Accurate reconstruction of thin cortical bone structures from CT scans of living human subjects is especially problematic, due to low CT resolution that results from mandatory low radiation doses and/or involuntary movements of the subject. In this study, a new method for mapping cortical thickness is described. Using the method, cortical thickness measurements of a coxal (pelvis) bone obtained from CT scans of a cadaver were mapped to the coxal geometry as obtained through CT scans of a live human subject, resulting in accurate cortical thickness while maintaining geometric fidelity of the live subject. The mapping procedure includes shape-preserving parameterisation, mesh movement and interpolation of thickness using a search algorithm. The methodology is applicable to modelling of other bones where accurate cortical thickness is needed and for which such data exist.

Diabetes-related impairment in bone strength is established early in the life course.

AIM: To evaluate properties of bone quantity/quality using young non-obese Type 1 (T1D)-diabetic (NOD) prone and syngenic non-diabetic (NOD.scid) mice. METHODS: Quantitative bone assessment of tibia was conducted using dual-energy X-ray absorptiometry (DXA) for the evaluation of body mass, bone mineral content, body fat mass and lean mass. Qualitative assessment was accomplished by three-point breakage for assessment of force to failure and micro-computed tomography for evaluation of trabecular and cortical properties of bone. In addition, fasting blood was evaluated prior to sacrifice at week eleven and fifteen to evaluate and compare glucose homeostasis between the strains of mice. RESULTS: Our findings support a perturbation in the relationship between bone quantity, quality, and subsequently, the association between structure and strength. There were no differences in DXA-assessed body composition (body fat, % fat mass and lean mass) and bone composition (bone mineral content and bone mineral density) between strains. However, relative to NOD.scid, NOD mice had lower trabecular bone volume, relative trabecular bone volume, trabecular number and trabecular total material density (P < 0.05). Conversely, NOD mice had greater cortical total mean volume (P < 0.05). General linear models analysis adjusted for body weight revealed a significant contribution of T1D to bone health as early as 5 wk. CONCLUSION: It is well-established that diabetes is a significant risk factor for increased fractures, although the underlying mechanisms are not fully understood. Investigation of bone parameters encompassing strength and structure early in the life course will facilitate the elucidation of the pathogenesis of impaired bone integrity.

The role of medial comminution and calcar restoration in varus collapse of proximal humeral fractures treated with locking plates.

BACKGROUND: Proximal humeral fractures that are treated with locked plate constructs remain susceptible to collapse into a varus position. The objectives of the present study were to examine how medial comminution affects fracture stability and to determine the effect of calcar fixation on osteosynthesis stability. METHODS: Eleven matched pairs of cadaveric humeri were osteotomized to create standard three-part fractures involving the surgical neck and the greater tuberosity. Five matched pairs were randomly assigned to have the medial calcar region remain intact. Six matched pairs had removal of a 10-mm medially based wedge of bone to simulate medial comminution. All fractures were stabilized in a uniform fashion with a proximal humeral locking plate. The constructs were secured, and the superior portion of the humeral head was subjected to compressive loading to induce varus collapse. Load-to-failure and energy-to-failure values along with stiffness and displacement at the time of failure were determined. RESULTS: Medial comminution decreased the mean load to failure by 48% (523 N) (p = 0.015) and the mean energy to failure by 44% (2009 Nmm) (p = 0.013). The use of calcar screw fixation increased the mean load to failure by 31% (219 N) (p = 0.002) and the mean energy to failure by 44% (1279 Nmm) (p = 0.006). CONCLUSIONS: Medial comminution significantly decreased the stability of proximal humeral fracture fixation constructs. Calcar restoration with screw fixation significantly improved the stability of repaired fractures in cadaveric specimens. CLINICAL RELEVANCE: The data suggest that medial comminution is a predictor of poor stability of proximal humeral fractures and that stability may be improved through calcar restoration.

A biomechanical analysis of controllable intraoperative variables affecting the strength of rotator cuff repairs at the suture-tendon interface.

BACKGROUND: The tissue-suture interface remains the weakest aspect of a rotator cuff repair, highlighting the importance of identifying techniques to improve stitch strength. Choice of suture-passing devices, size of the tissue bite, and stitch configuration are variables that may influence stitch strength and therefore repair stability. PURPOSE: To evaluate the effect that size of the tissue penetrator device and tissue bite size have upon the holding strength of commonly used stitches. STUDY DESIGN: Controlled laboratory study. METHODS: Three different-sized tissue-penetrating devices, small circular, midsized circular, and large rectangular, were used to place sutures in 192 infraspinatus tendon grafts of sheep. Tissue bite sizes of either 0.5 cm or 1.0 cm for 4 different stitches, a simple, mattress, modified Mason-Allen (MMA), and massive cuff (MAC) stitch, were tested. Grafts were cyclically loaded and then loaded to failure. Mixed multivariate regression analysis was used to test the effect of instrument, bite size, and stitch configuration on peak-to-peak displacement, cyclic elongation, and load to failure. RESULTS: The average ultimate load to failure with the smallest penetrating device was 112 N, significantly higher than with both the midsized (95 N) and large devices (91 N) (P < .001). The average load to failure was 31 N higher for a 1.0-cm bite size when compared with a 0.5-cm bite size (P < .001). The largest load-to-failure differences were found with the type of stitch placed: simple, 48 N; mattress, 69 N; MMA, 130 N; and MAC, 152 N (all P < .02). For simple and mattress stitches, each additional pass of the suture increased the load to failure by 21 N. In MMA and MAC stitches, an additional pass resulted in an increase in the load to failure by 50 N. Cyclic elongation did not differ by instrument type (all P > .5). The elongation of stitches with a 1.0-cm bite size was 0.14 mm higher than stitches with a 0.5-cm bite size (P < .001). No meaningful difference in peak-to-peak displacement was seen for bite size, instrument type, or stitch construct. CONCLUSION: The strength of rotator cuff stitches was significantly affected by the different-sized tissue-penetrating instruments and size of the bite. However, the greatest predictor of time-zero stitch strength is the type of stitch placed. CLINICAL RELEVANCE: This study highlights the importance of stitch configuration in the repair of rotator cuff tears.

The association between knee airbag deployment and knee-thigh-hip fracture injury risk in motor vehicle collisions: A matched cohort study.

INTRODUCTION: In the U.S. alone, an estimated 30,000 knee-thigh-hip (KTH) injuries occur annually in frontal motor vehicle collisions. These fractures typically occur through occupant contact with the vehicle's knee bolster. Research has suggested that knee airbags (KABs) can mitigate the forces sustained during this contact, resulting in decreased injury risk; however, previous research has been limited by small sample sizes or by occurring in a controlled setting. The objective of the current study is to determine the effectiveness of KABs on KTH fracture risk using nationally representative, real-world data. METHODS: Using combined data from the Crash Injury Research and Engineering Network and the National Automotive Sampling Survey, a matched cohort study was conducted among front-seat occupants of vehicles involved in a frontal collision occurring from 2000 to 2009. Occupants exposed to a KAB deployment were matched to occupants with no KAB deployment based on age ±5 years, sex, seatbelt use, vehicle seating position (i.e., driver or front passenger), car vehicle body type, collision impact, and sampling weight. A Cox proportional hazards model was used to calculate risk ratios (RRs) and associated 95% confidence intervals (95% CI) to estimate the association between KAB deployment and lower extremity fracture risk. RESULTS: There was no association between KAB deployment and risk of lower extremity fracture (RR 0.83, 95% CI 0.52-1.31). A notable pattern in fracture risk, though not statistically significant, was observed, with a decreased risk of hip (RR 0.72, 95% CI 0.26-1.97) and thigh fracture (RR 0.81, 95% CI 0.32-2.05), and an increased risk of tibia/fibula (RR 1.23, 95% CI 0.52-2.90) and foot fracture (RR 1.96, 95% CI 0.72-5.32). CONCLUSIONS: The results of the current study suggest that KABs are not associated with the risk of lower extremity fractures. However, given the small sample size of the current study, it is difficult to definitively say whether the observed injury pattern is representative of the true pattern.

A novel device to quantify the mechanical properties of electrospun nanofibers.

Mechanical deformation of cell-seeded electrospun matrices plays an important role in cell signaling. However, electrospun biomaterials have inherently complex geometries due to the random deposition of fibers during the electrospinning process. This confounds attempts at quantifying strains exerted on adherent cells during electrospun matrix deformation. We have developed a novel mechanical test platform that allows deposition and tensile testing of electrospun fibers in a highly parallel arrangement to simplify mechanical analysis of the fibers alone and with adherent cells. The device is capable of optically recording fiber strain in a cell culture environment. Here we report on the mechanical and viscoelastic properties of highly parallel electrospun poly(ε-caprolactone) fibers. Force-strain data derived from this device will drive the development of cellular mechanotransduction studies as well as the customization of electrospun matrices for specific engineered tissue applications.

Biomechanical evaluation of 3 arthroscopic self-cinching stitches for shoulder arthroscopy: the lasso-loop, lasso-mattress, and double-cinch stitches.

BACKGROUND: The tissue-suture interface remains the most common site of failure in rotator cuff repairs. Improving stitch strengths may lead to lower failure rates. PURPOSE: To compare biomechanical properties of 3 self-cinching stitches to the simple, mattress, modified Mason-Allen, and massive cuff stitches. STUDY DESIGN: Controlled laboratory study. METHODS: In sum, 336 sheep infraspinatus tendon grafts were randomized among 7 stitches. Each graft was cyclically loaded on a mechanical testing system from 5 to 30 N for 20 cycles and then loaded to failure. A mixed-effect multivariate regression model was used to test significance of suture type on cyclic elongation, peak-to-peak displacement, and ultimate load. Estimated means and standard deviations are reported from the regression model. RESULTS: Ultimate load for the simple stitch was significantly lower than for the other stitches. The lasso-loop and mattress stitch demonstrated similar ultimate loads. The double-cinch had a higher ultimate load than the lasso-loop or mattress stitch, although it was significantly weaker than the modified Mason-Allen, lasso-mattress, and massive cuff. The lasso-mattress had a superior ultimate load to the modified Mason-Allen and a similar ultimate load to the massive cuff stitch. One significant difference was found in cyclic elongation (1.42 mm for the simple to 1.80 mm for the double-cinch), and the cinching mechanism accounted for 0.2-mm higher elongation. CONCLUSION: Self-cinching stitches lead to superior tissue-holding strength at the tissue-suture interface when compared with equivalent non-self-cinching stitches. Self-cinching stitches have greater elongation values. How these differences in cyclic elongation clinically influence gap formation at the repair site is unknown. The greater displacement seen in the self-cinching stitches is a potential concern because minimal gap formation is desired for a strong repair. CLINICAL RELEVANCE: The lasso-loop stitch is a stronger alternative to a simple stitch, and the double-cinch and lasso-mattress stitches are stronger alternatives to a mattress stitch.

Micromechanics of postmortem-retrieved cement-bone interfaces.

The cement-bone interface plays an important role in load transfer between cemented implant systems and adjacent bone, but little is known about the micromechanical behavior of this interface following in vivo service. Small samples of postmortem-retrieved cement-bone specimens from cemented total hip replacements were prepared and mechanically loaded to determine the response to tensile and compressive loading. The morphology of the cement-bone interface was quantified using a CT-based stereology approach. Laboratory-prepared specimens were used to represent immediate postoperative conditions for comparison. The stiffness and strength of the cement-bone interface from postmortem retrievals was much lower than that measured from laboratory-prepared specimens. The cement-bone interfaces from postmortem retrievals were very compliant (under tension and compression) and had a very low tensile strength (0.21 +/- 0.32 MPa). A linear regression model, including interface contact fraction and intersection fraction between cement and bone, could explain 71% (p < 0.0001) of the variability in experimental response. Bony remodeling following an arthroplasty procedure may contribute to reduced contact between cement and bone, resulting in weaker, more compliant interfaces.