Virtual mechanical testing is a method for measuring bone healing using finite element models built from computed tomography (CT) scans. Previously, we validated a dual-zone material model for ovine fracture callus that differentiates between mineralized woven bone and soft tissue based on radiodensity. 1. The objective of this study was to translate the dual-zone material model from sheep to two important clinical scenarios: human tibial fractures in early-stage healing and late-stage nonunions. CT scans for N = 19 tibial shaft fractures were obtained prospectively at 12 weeks post-op. A second group of N = 33 tibial nonunions with CT scans were retrospectively identified. The modeling techniques were based on our published method. 2. The dual-zone material model was implemented for humans by performing a cutoff sweep for both the 12-week and nonunion groups. Virtual torsional rigidity (VTR) was calculated as VTR = ML/φ [N-m. 2. /°], where M is the moment reaction, L is the diaphyseal segment length, and φ is the angle of twist. As the soft tissue cutoff was increased, the rigidity of the clinical fractures decreased and soft tissue located within the fracture gaps produced higher strains that are not predicted without the dual zone approach. The structural integrity of the nonunions varied, ranging from very low rigidities in atrophic cases to very high rigidities in highly calcified hypertrophic cases, even with dual-zone material modeling. Human fracture calluses are heterogeneous, comprising of woven bone and interstitial soft tissue. Use of a dual-zone callus material model may be instrumental in identifying delayed unions during early healing when callus formation is minimal and/or predominantly fibrous with little mineralization. ACKNOWLEDGEMENTS:. This work was supported by the National Science Foundation (NSF) grant CMMI-1943287

Introduction. Patient-specific biomechanical modeling using Finite Element Analysis (FEA) is pivotal for understanding the structural health of bones, optimizing surgical procedures, assessing outcomes, and validating medical devices, aligning with guidance issued by standards and regulatory bodies. Accurate mapping of image-to-mesh-material is crucial given bone's heterogeneous composition. This study aims to rigorously assess mesh convergence and evaluate the sensitivity of material grouping strategies in quantifying bone strength. Method. Subject-specific geometry and nonlinear material properties were derived from computed tomography (CT) scan data of one cadaveric human vertebral body. Linear tetrahedral elements with varying edge lengths between 2mm and 0.9mm were then generated to study the mesh convergence. To compare the effectiveness of different grouping strategies, three approaches were used: Modulus Gaping (a user-defined absolute threshold of Young's modulus ranging from 500 MPa to 1 MPa), Percentual Thresholding (relative parameter thresholds ranging from 50% to 1%), and Adaptive clustering (unsupervised k-means-based clustering ranging from 10 to 200 clusters). Adaptive clustering enables a constant number of unique material properties in cross-specimen studies, improving the validity of results. Result. Mesh convergence was evaluated via fracture load and reached at a 1mm mesh size across grouping strategies. All strategies exhibit minimal deviation (within 5%) from individually assigned material parameters, except Modulus Gaping, with a 500 MPa threshold (32% difference). Computational efficiency, measured by runtime, significantly improved with grouping strategies, reducing computational cost by 82 to 94% and unique material count by up to 99%. Conclusion. Different grouping strategies offer comparable mesh convergence, highlighting their potential to reduce computational complexity while maintaining accuracy in the biomechanical modeling of bones and suggesting a more efficient approach than individual element materials. The higher efficiency of FEA may increase its applicability in clinical settings with limited computational resources. Further studies are needed to refine grouping parameters and assess their suitability across different subjects

Device-associated bacterial infections are a major and costly clinical challenge. This project aimed to develop a smart new biomaterial for implants that helps to protect against infection and inflammation, promote bone growth, and is biodegradable. Gallium (Ga) doped strontium-phosphate was coated on pure Magnesium (Mg) through a chemical conversion process. Mg was distributed in a graduated manner throughout the strontium-phosphate coating GaSrPO4, with a compact structure and a Ga-rich surface. We tested this sample for its biocompatibility, effects on bone remodeling and antibacterial activities including Staphylococcus aureus, S. epidermidis and E. coli - key strains causing infection and early failure of the surgical implantations in orthopaedics and trauma. Ga was distributed in a gradient way throughout the entire strontium-phosphate coating with a compact structure and a gallium-rich surface. The GaSrPO4 coating protected the underlying Mg from substantial degradation in minimal essential media at physiological conditions over 9 days. The liberated Ga ions from the coatings upon Mg specimens inhibited the growth of bacterial tested. The Ga dopants showed minimal interferences with the SrPO4 based coating, which boosted osteoblasts and undermined osteoclasts in in vitro co-cultures model. The results evidenced this new material may be further translated to preclinical trial in large animal model and towards clinical trial. Acknowledgements: Authors are grateful to the financial support from the Australian Research Council through the Linkage Scheme (ARC LP150100343). The authors acknowledge the facilities, and the scientific and technical assistance of the RMIT University and John Curtin School of Medical Research, Australian National University

To unravel the relation between mechanical loading and biological response, cell-seeded hydrogel constructs can be used in bioreactors under multi-axial loading conditions that combines compressive with torsional loading. Typically, considerable biological variation is observed. This study explores the potential confounding role of mechanical factors in multi-directional loading experiments. Indeed, depending on the material properties of the constructs and characteristics of the mechanical loading, the mechanical environment within the constructs may vary. Consequently, the local biological response may vary from chondrogenesis in some parts to proteoglycan loss in others. This study uses the finite element method to investigate the effects of material properties of cell-seeded constructs and multiaxial loading characteristics on local mechanical environment (stresses and strains) and relate these to chondrogenesis (based on maximum compressive principal strain (MCPS) - Zahedmanesh et al., 2014) and proteoglycan loss (based on fluid velocity (FV) - Orozco et al., 2018). The construct was modelled as a homogenized poro-hyperelastic (using a Neohookean model and Darcys law) cylinder of 8mm diameter and equal height using Abaqus. The bottom surface was fully constrained and dynamic unconfined compression and torsion loading were applied to the top surface. Free fluid flow was allowed through the lateral surface. We studied the sensitivity of the maximum values of the target parameters at 9 key locations to the material parameters and loading characteristics. Six input parameters were varied in preselected ranges: elastic modulus (E=[20,80]kPa), Poissons ratio (nu=[0.1,0.4]), permeability (k=[1,4]e-12m4/Ns), compressive strain (Comp=[5,20]%), rotation (Rot=[5,20]°) and loading frequency (Freq=[1,4]Hz). A full-factorial design of experiment method was used and a first-order polynomial surface including the interactions fitted the responses. MCPS varies between 7.34% and 33.52% and is independent of the material properties (E, nu and k) and Freq but has a high dependency on Comp and a limited dependency on Rot. The maximum value occurs centrally in the construct, except for high values of Rot and low Comp where it occurs at the edges. FV vary between 0.0013mm/sec and 0.1807mm/sec and dominantly depends on E, k and Comp, while its dependency on Rot and Freq is limited. The maximum value usually occurs at the edges, although at high Freq it may move towards the center of the superficial and deep zones. This study can be used as a guideline for the optimized selection of mechanical parameters of hydrogel for cell-seeded constructs and loading conditions in multi-axial bioreactor studies. In future work, we will study the effect in intact and injured cartilage explants

Summary Statement. Subject specific FE models of human Achilles tendon were developed and optimum material properties were found. Stress concentration occurred at the midsection but dependent on stiffening and thinning of tendon, indicating that they are two major factors for tendon rupture. Introduction. Achilles tendon injuries are common, occurring about 250,000 per year in the US alone, yet the mechanisms of tendinopathy and rupture remain unknown. Most Achilles tendon ruptures occur at 2 to 6 cm above the insertion to the calcaneus bone. Previous angiographic studies have suggested that there is an avascular area in this region. However, it is not understood why that region receives poor blood supply and prone to rupture. The aim of this study is to investigate influence of geometry and material properties on Achilles tendon rupture with mechanical experiment and corresponding subject-specific finite element (FE) analysis. Patients & Methods. Mechanical experiment was performed on 10 fresh human Achilles tendons. High frequency ultrasound images were used to measure cross sectional areas at the midsection of the tendon. Cyclic testing was performed to measure mechanical properties and failure loads. Subject-specific FE models of these tendons were generated with Free Form Deformation (FFD) technique. FE mechanical simulations that mimic the experimental cyclic loading were performed on these subject specific models. Tendon material properties were described as transversely isotropic hyperelastic and the optimum material parameters for the human Achilles tendon were obtained. Linear portion of the cyclic loading data was used as boundary conditions. Measured strains from the experiment were compared with predicted strains from the FE analysis. This process was repeated until optimum parameters were found. The influence of geometry and material properties on the Achilles tendon rupture was then investigated– first with subject-specific geometry with average material properties and then with subject-specific material properties with average geometry. Results. Our results indicate that a significant variation exist in the geometry and material properties in human Achilles tendons. Stress concentrations occurred at the midsection of the tendon, supporting previous studies that reported tendon rupture at the region. In particular the thinning of midsection in geometry is highly correlated with the collagen uncrimpping rate in material properties where thinner midsection leads to faster uncrimpping of collagen fibres. Variations in geometry led to shifts in the location of stress concentration within the midsection while variations in material property led the change in the magnitude of stress concentration. Discussion/Conclusion. Our results indicate that Achilles tendon rupture is highly dependent on subject-specific geometry and material properties. In particular the mid section is the location of stress concentration but depending on the geometrical shape, multiple stress concentrations occur, making the tendon more prone to rupture while the material properties influenced the magnitude of stress concentration. Our results indicate stiffening and thinning of tendon may lead to higher risk for tendon rupture

Introduction and Objective. Individuals with type 2 diabetes (T2D) have a 3-fold increased risk of bone fracture compared to non-diabetics, with the majority of fractures occurring in the hip, vertebrae and wrists. However, unlike osteoporosis, in T2D, increased bone fragility is generally not accompanied by a reduction in bone mineral density (BMD). This implies that T2D is explained by poorer bone quality, whereby the intrinsic properties of the bone tissue itself are impaired, rather than bone mass. Yet, the mechanics remain unclear. The objective of this study is to (1) assess the fracture mechanics of bone at the structural and tissue level; and (2) investigate for changes in the composition of bone tissue along with measuring total fluorescent advanced glycation end products (fAGEs) from the skin, as T2D progresses with age in Zucker diabetic fatty (ZDF (fa/fa)) and lean Zucker (ZL (fa/+)) rats. Materials and Methods. Right ulnae and skin sections were harvested from ZDF (fa/fa) (T2D) and ZL (fa/+) (Control) rats at 12 and 46 weeks (wks) of age (n = 8, per strain and age) and frozen. Right ulnae were thawed for 12 hrs before micro-CT (μCT) scanning to assess the microstructure and measure BMD. After scanning, ulnae were loaded until failure via three-point bending. Fourier transform-infrared microspectroscopy (FTIR) was used to measure various bone mineral- and collagen-related parameters such as, mineral-to-matrix ratio and nonenzymatic cross-link ratio. Finally, fAGEs were measured from skin sections using fluorescence spectrometry and an absorbance assay, reported in units of ng quinine/ mg collagen. Results. At 12 and 46 wks bone size was significantly smaller in length (p < 0.01), cortical area (p < 0.001) and cross-sectional moment of inertia (p < 0.001) in T2D rats compared to age-matched controls. A slight reduction in BMD was observed in T2D rats compared to controls at both ages, however, this was not significant. Structural properties of T2D bone were significantly altered at 12 and 46 wks, with bending rigidity increasing approximately 2.5-fold and 1.5-fold in control and T2D rats with age, respectively (p < 0.0001). Similarly, yield and ultimate moment significantly reduced in T2D rats with age in comparison to controls (p < 0.0001). Energy absorbed to failure was significantly reduced in T2D rats at 46 weeks of age compared to controls (p < 0.01). The amount of energy absorbed to failure increased approximately 1.4-fold from 12 to 46 wks in control rats, however, in T2D rats a reduction was seen with age, although not significant. At 12 wks, there was no significant deficits in tissue material properties, whereas, at 46 wks a significant reduction in yield stress, yield strain and ultimate stress was observed for T2D rats in comparison to controls (p < 0.05). Conclusions. These findings show that longitudinal growth is impaired as early as 12 wks of age and by 46 wks bone size is significantly reduced in T2D rats compared to controls. The reduction in T2D structural properties is likely attributed to the bone geometry deficits. At 12 wks of age, the tissue material properties are not altered in T2D bone versus controls. However, at 46 wks, bone strength is reduced in T2D, leading to the conclusion that tissue properties are altered as the disease progresses

Collagen materials are extensively used in regenerative medicine. However, they still present limitations such as a mono-domain composition and poor mechanical properties. On the other hand, tissue grafts overcome most of these limitations. In addition, the potential of tissue grafts in musculoskeletal tissue engineering has not been fully investigated. Herein, we ventured to assess the potential of a decellularised porcine peritoneum for musculoskeletal applications by comparing its characteristics with a commercial collagen scaffold employed in tendon. Results indicated that the porcine peritoneum had higher mechanical properties and a lower crosslinking ratio (p < 0.01). Furthermore, it presented a lower resistance to collagenase digestion, which suggests a faster remodelling in vivo of the tissue graft. Immunohistochemistry analysis showed a preserved and multicomponent structure in the porcine peritoneum contrary to the collagen matrix, confirming the multifunctional nature of the tissue graft. Regarding the cell-response assessment, tenocytes and ADSCs were able to grow on both materials, however, proliferation was enhanced by the porcine peritoneum (p<0.01). Immune response by THP-1 showed an acute inflammatory response by macrophages to the collagen matrix, contrary to that observed in the porcine peritoneum which triggered a mild reaction. The in-progress in vivo study in a rabbit tendon model will elucidate the potential of porcine peritoneum for tendon repair applications. The present study shows how the multifunctionality of the porcine peritoneum provides higher cytocompatibility than a mono-domain collagen matrix with human tenocytes and ADSC. Besides, its lower immune response in vitro suggests better remodelling after implantation

Crosslinking has been already used for about 80 years to enhance the longevity of polyethylene cables. The polymer alteration has been achieved with peroxide, silane or irradiation. The medical devices industry discovered the benefit of this technology for its tribological applications like hip or knee bearings in the 2000s as crosslinking improves considerably the abrasion resistance of the material. The more current methods used are Gamma and Beta irradiation. On the basis of economical (rising prices of Cobalt), environmental (the radioactive source can not be turned off), technological (low dose rate) drawbacks for Gamma respectively low penetration for Beta irradiation we decided to investigate an alternative technology: the X-Ray irradiation, which provides a homogeneous crosslinking in a relatively short time. We analyzed the wear, mechanical, thermal, oxidative and network properties of two vitamin E doped UHMWPE: first crosslinked with E-Beam, second with X-Ray. There wasn't any significant difference between the X-Ray and the E-Beam crosslinked material

Introduction

Experimental bone research often generates large amounts of histology and histomorphometry data, and the analysis of these data can be time-consuming and trivial. Machine learning offers a viable alternative to manual analysis for measuring e.g. bone volume versus total volume.

The objective was to develop a neural network for image segmentation, and to assess the accuracy of this network when applied to ectopic bone formation samples compared to a ground truth.

Background. Simply stated, carbon reinforced carbon (C/C) may be considered as fibre reinforced pyrocarbon. Pyrocarbon is used e.g. in finger joints and artificial heart valves. Aim of the present study was to evaluate if C/C could broaden the field of orthopaedic applications compared to pyrocarbon. Technically, C/C is used e.g. for brakes of F-1 race cars. Methods. The mechanical strength of the C/C material was characterised by a biaxial flexural bending test according ISO 6474-1. Three C/C shoulder heads articulating against vitamin E stabilised, highly cross-linked UHMWPE (E-XLPE) underwent a shoulder simulator study up to 106 cycles. The Coefficient of Friction (CoF) of C/C disks (Ra: 0.045 μm) against cartilage was analysed by a reciprocal cartilage wear tester. The test was conducted in cell culture medium for 4 h and 12 h using bovine cartilage. All test data is compared to the corresponding test results with Al2O3 ceramic. Conclusions. The strength of C/C is 30 % lower than that of Al2O3 ceramic. Its wear rate measured in the shoulder simulator against E-XLPE is in tendency higher than that of ceramic heads. The CoF against cartilage is double compared to the same test with Al2O3. - C/C seems to have limited a potential as material for orthopaedic application. However, more investigations and optimisation of the C/C type and quality are necessary. Level of evidence. Laboratory test on material samples. Study financed by Mathys Ltd Bettlach

Polyethylene wear of joint replacements can cause severe clinical complications, including; osteolysis, implant loosening, inflammation and pain. Wear simulator testing is often used to assess new designs, but it is expensive and time consuming. It is possible to predict the volume of polyethylene implant wear from finite element models using a modification of Archard's classic wear law [1–2]. Typically, linear elastic isotropic, or elasto-plastic material models are used to represent the polyethylene. The purpose of this study was to investigate whether use of a viscoelastic material model would significantly alter the predicted volumetric wear of a mobile-bearing unicompartmental knee replacement. Tensile creep-recovery experiments were performed to characterise the creep and relaxation behaviour of the polyethylene (moulded GUR 4150 samples machined to 180×20×1 mm). Samples were loaded to 3 MPa stress in 4 minutes, and then held for 6 hours, the tensile stress was removed and samples were left to relax for 6 hours. The mechanical test data was used fit to a validated three–dimensional fractional Maxwell viscoelastic constitutive material model [3]. An explicit finite element model of a mobile–bearing unicompartmental knee replacement was created, which has been described previously [4]. The medial knee replacement was loaded to 1200 N over a period of 0.2 s. The bearing was meshed using quadratic tetrahedral elements (1.5 mm seeding size based on results of a mesh convergence study), and the femoral component was represented as an analytical rigid body. Wear predictions were made from the contact stress and sliding distance using Archard's law, as has been described in the literature [1–2]. A wear factor of 5.24×10. −11. was used based upon the work by Netter et al. [2]. All models were created and solved using ABAQUS finite element software (version 6.14, Simulia, Dassault Systemes). The fractional viscoelastic material model predicted almost twice as much wear (0.119 mm. 3. /million cycles) compared to the elasto-plastic model (0.069 mm. 3. /million cycles). The higher wear prediction was due to both an increased sliding distance and higher contact pressures in the viscoelastic model. These preliminary findings indicate the simplified elasto-plastic polyethylene material representation can underestimate wear predictions from numerical simulations. Polyethylene is known to be a viscoelastic material which undergoes creep clinically, and it is not surprising that it is necessary to represent that viscoelastic behaviour to accurately predict implant wear. However, it does increase the complexity and run time of such computational studies, which may be prohibitive

Osteochondral (OC) grafting is one available method currently used to repair full thickness cartilage lesions with good results clinically when grafting occurs in patients with specific positive prognostic factors. However, there is poor understanding of the effect of individual patient and surgical factors. With limited tissue availability, development of Finite Element (FE) models taking into account these variations is essential. The aim of this study was to evaluate the effect of altering the material properties of OC grafts and their host environment through computer simulation. A generic FE model (ABAQUS CAE 2017) of a push-out test was developed as a press-fit bone cylinder (graft) sliding inside a bone ring (host tissue). Press-fit fixation was simulated using an interference fit. Overlap between host and graft (0.01mm–0.05mm) and coefficient of friction (0.3–0.7) were varied sequentially. Bone Young's moduli (YM) were varied individually between graft and host within the range of otherwise derived tissue moduli (46MPa, 82MPa, 123MPa). Increasing both overlap and frictional coefficient increased peak dislodging force independently (overlap: 490% & frictional coefficient: 176% across range tested). Increasing bone modulus also increased dislodging force, with host bone modulus (107%, 128%, and 140% increase across range, when Graft YM = 123MPa, 82 MPa, and 46MPa, respectively) having a greater influence than graft modulus (28%, 19% and 10% increase across range, when Host YM = 123 MPa, 82MPa and 46MPa, respectively). As anticipated increasing overlap and friction caused an increase in force necessary to dislodge the graft. Importantly, differentially changing the graft and host material properties changed the dislodging force indicating that difference between graft and host may be an important factor in the success or failure clinically of osteochondral grafting

Periprosthetic joint infections (PJI) are one of the most common reasons for orthopedic revision surgeries. In previous studies, it has been shown that silver modification of titanium (Ti-6Al-4V) surfaces by PMEDM (powder mixed electrical discharge machining) has an antibacterial effect on Staphylococcus aureus adhesion. Whether this method also influences the proliferation of bacteria has not been investigated so far. Furthermore, the effect is only limitedly investigated on the ossification processes. Therefore, the aim of this work is to investigate the antibacterial effect as well as the in vitro ossification process of PMEDM machined surfaces modified by integration of silver.

In this study, we analyzed adhesion and proliferation of S. aureus in comparison to of surface roughness, silver content and layer thickness of the silver-integrated-PMEDM surfaces (N = 5). To test the in vitro ossification, human osteoblasts (SaOs-2) and osteoclasts (differentiated from murine-bone-marrow-macrophages) were cultured on the silver surfaces (N = 3).

We showed that the attachment of S. aureus on the surfaces was significantly lower than on the comparative control surfaces of pure Ti-6Al-4V without incorporated silver, independently of the measured surface properties. Bacterial proliferation, however, was not affected by the silver content. No influence on the in vitro ossification was observed, whereas osteoclast formation was drastically reduced on the silver-modified surfaces.

We showed that 1 to 3% of silver in the surface layer significantly reduced the adhesion of S. aureus, but not the proliferation of already attached bacteria. At the same time, no influence on the in vitro ossification was observed, while no osteoclasts were formed on the surface. Therefore, we state that PMEDM with simultaneous silver modification of the machined surfaces represents a promising technology for endoprostheses manufacturing to reduce infections while at the same time optimizing bone ingrowth.

Background. Bone is a hierarchically structured hard tissue that consists of approximately 70 wt% low-crystallinity hydroxyapatite. Intricate tubular channels, such as Haversian canals, Volkman's canals, and canaliculi are a preserved feature of bone microstructure. These structures provide pathways for vasculature and facilitate cell-to-cell communication processes, together supporting viability of cellular components and aiding in remodeling processes. Unfortunately, many commercial bone augmentation materials consist of highly crystalline phases that are absent of the structuring present within the native tissue they are replacing. This work reports on a the development of a novel bone augmentation material that is able to generate biologically analogous tubular calcium phosphate mineral structures from hydrogel-based spheres that can be packed into defects similar to those encountered in vivo. Experimental. Calcium loaded spheres were made by adding 5 wt% agar powder to 1 M calcium nitrate solutions, before heating the mixture to 80–90 oC and feeding droplets of gel into a reservoir of liquid nitrogen. Deposition of tubular mineral was initiated by exposure to ammonium phosphate solutions at concentrations between 500 mM and 1 M, and was characterized by micro-XRF mapping, XRD and SEM techniques. For an ex vivo model, human bone tissue was collected from patients undergoing elective knee replacement surgery. The United Kingdom National Research Ethics Service (East of Scotland Research Ethics Service) provided ethical approval (11/ES/1044). The augmented defect of the model was characterised by micro-XRF mapping and micro-CT techniques. Results and Discussion. Immersion of calcium-loaded hydrogel spheres in physiological solutions rich in phosphate promotes the release of calcium rich streams from the sphere surface, resulting in the precipitation of tubule structures. Micro-XRF mapping, XRD and SEM, revealed tubules possessed hierarchically structuring and consisted of low-crystallinity hydroxyapatite, making them analogous in composition and structure to incritate features of bone microstructure. When brought into close proximity with one another, spheres become fused in a matter of minutes by the entanglement and subsequent interstitial mineralisation of the mineral tubules. Micro-XRF mapping and micro-CT analysis of an augmented ex vivo human tissue defect model demonstrated the extensive deposition of low-crystallinity tubular mineral throughout a tissue defect. Conclusions. This is possibly the first example of a bone augmentation material that is able to generate biologically analogous structures in situ, and therefore may serve as a better scaffold for bone formation over synthetic alternatives. Moreover, the formation of structured mineral aids in achieving rapid hardening of the augmenting calcium-loaded hydrogel shperes within the defect space

Summary Statement. Wear of total knee replacement (TKR) is a clinical concern. This study demonstrated low-conformity moderately cross-linked-polyethylene fixed bearing TKRs showed lower volumetric wear than conventional-polyethylene curved fixed bearing TKRs highlighting potential improvement in TKR performance through design and material selection. Introduction. Wear of total knee replacement (TKR) continues to be a significant factor in the clinical performance of the implants. Historically, failure due to delamination and fatigue directed implant design towards more conforming implants to reduce contact stress. However, the new generations of more oxidatively-stable polyethylene have improved the long-term mechanical properties of the material, and therefore allowed more flexibility in the bearing design. The purpose of this study was to investigate the effect of insert conformity and material on the wear performance of a fixed bearing total knee replacement through experimental simulation. Methods. The wear of TKR bearings were investigated using a physiological six station Prosim knee wear simulator (Simulator Solutions, UK). Six samples of each test configuration (Sigma CR fixed bearing knees (DePuy Synthes, UK) were studied, and compared with previously reported data, tested under identical conditions (1, 2). The central axis of the implant was offset from the aligned axes of applied load and tibial rotation to replicate a right knee. High kinematics, under anterior-posterior displacement control was used for this study (3). The lubricant was 25% (v/v) calf serum supplemented with 0.03% (v/v) sodium azide solution in deionised water, as an antibacterial agent, and was changed approximately every 0.33Mc. Wear was assessed gravimetrically and moisture uptake accounted for using unloaded soak controls. Results. The wear rates for the moderately cross-linked inserts (XLK) were significantly lower than the conventional polyethylene (GVF) for all geometries (ANOVA, p<0.05). There was a significant reduction in wear rate as the insert geometry became less conforming for both materials (ANOVA, p<0.05). The wear scars areas were comparable in size and shape between materials, within a geometry group. The size of the wear scar changed with conformity, with the curved inserts showing the largest scars in both anterior-posterior and medial-lateral dimensions, and the flat inserts showing the smallest wear scars. Discussion/Conclusion. The introduction of a moderately cross-linked polyethylene insert was shown to significantly reduce the wear of a fixed bearing total knee replacement compared with a conventional material. There was a trend for reducing wear rate with reducing conformity for both materials, suggesting that reduced conformity results in higher contact pressures and reduced contact area, leading to a reduced surface for wear to occur. Both material and conformity were shown to have a significant impact on the wear of a fixed bearing TKR, and therefore provide opportunity for enhancing wear performance through material and design selection

Using Python scripting it is possible to automate the pre-processing, solving and post-processing stages of finite element analysis using ABAQUS software. This is particularly useful when running multiple models parametrically. When the model involves a bony part, it is necessary to assign material properties based on the CT scan to represent bone heterogeneity, and unfortunately this cannot currently be done from within ABAQUS using software such as Bonemat [1]. To address this issue a Python package was written called ‘py_bonemat_abaqus’ to assign material properties from within ABAQUS. The purpose of this study was to compare the material assignments of py_bonemat_abaqus and Bonemat, to compare the processing speed, and to describe the workflow. The software packages were compared using a CT scan of a half pelvis downloaded from the VAKHUM database, and the associated hexahedral finite element mesh of the left half pelvis. To examine different element types, the hexahedral mesh was converted to linear and quadratic tetrahedral elements by dividing each hexahedron into 5 tetrahedral elements. The equations used to convert the Hounsfield Unit (HU) values to apparent density (papp), and to convert the apparent density to elastic modulus (E) are shown in Equations 1&2 [2]. Equation 1: papp = −0.021075 + 0.000786 HU. Equation 2 E = 2.0173 papp. 2.46. The time taken to analyse the models by each software was assessed using a Windows 7 PC with a 64-bit operating system, 4 CPUS, 8 GB of RAM and an Intel Core I5-3470 processor. The mean difference between the moduulus assignment made by py_bonemat_abaqus and Bonemat was −0.05 kPa (range −10.19 to 4.50 kPa, standard deviation 0.62 kPa). The Python package took a similar time to run for all element types; this was between 109 and 126 s. Bonemat software was significantly faster, and took between 5 and 20 s. Finally, the Python package was successfully used from within a Python script to perform material assignment from within ABAQUS software in a fully automated manner. Material assignments were almost equivalent between the two software packages, with any differences explainable by rounding effects. To put the differences into context, a difference of −0.05 kPa is 0.00000002% of the typical modulus of cortical bone (20.7 GPa), and 0.00000003% of the modulus of trabecular bone (14.8 GPa) [3]. The Python package was slower to process the models, but was successfully able to assign material properties from within ABAQUS software as part of an automated script

Prosthetic joint infection (PJI) is an important cause of arthroplasty failure. There is no method to disclose the presence or map the distribution of the in vivo biofilm on infected arthroplasty despite the recognition that such a tool would aid intraoperative decision making and improve novel implant design. The aim of this study was to test the efficacy of four dyes to disclose bacterial biofilm in an in vitro setting.

Four dyes with known affinity to bacterial biofilm were assessed to determine their efficacy to disclose biofilms in an in vitro model of PJI. Three dyes (Methylene Blue, Indocyanine Green and Rose Bengal) have established clinical utility and the other, Thioflavin T, is known to fluoresce in the presence of amyloid a known biofilm constituent. The efficacy of the dyes to discriminate between biofilms of different mass and vitality (high, low or the non-inoculated control) was determined after three minutes exposure of the biofilm to the dyes by calculating the amount of dye bound to the biofilm via sonication and spectrophotometry, quantification of the dye through standardised photographic imaging of the stained biofilm and the calculation of inter-observer agreement. Each experiment was performed in triplicate for each dye and repeated three times.

For each of the disclosure dyes assessed there was significant difference demonstrated between the amount of dye bound to the high and low mass biofilms (p<0.05) as well as in the amount of dye quantified in photographic and fluorescent image assessment between biofilms of differing mass (p<0.01). There was excellent agreement between three observers, for each disclosure dye, in determining the biofilm mass of each stained disc (Kappa>0.91).

This study demonstrates the efficacy of biofilm disclosure dyes in an in vitro PJI model which could one day be used to disclose and map the clinical biofilm in vivo.

In this study we explore the hypothesis that there is a correlation between the ratio of the intensities of specific peaks of the Raman spectrum of bone tissue and the material properties of that particular type of bone. Raman spectroscopy is a powerful analytical technique capable of providing rich chemical information on the composition of skeletal tissue matrices and it has been used extensively to interrogate bone in the past. Spectra are presented of a selection of animal bones, each having greatly differing material properties, the differences having been produced by evolution in response to their greatly differing functions. The main examples described are deer antler (a bone naturally selected for toughness), tympanic bulla from a fin whale (naturally selected for stiffness) and the intermediate ‘standard’ bone from adult mammalian limbs which must be both tough enough to resist fracture and stiff enough to resist deformation during physiological loading (from an ovine femur in our case). In order to illustrate the specific relationship between material properties and Raman spectra additional mineralized tissues also with differing functions and of known Young's moduli are also introduced. The results show that a strong correlation exists between the mineral to collagen ratio of these different bone tissues as measured with Raman spectroscopy and their (previously published) Young's moduli. Raman spectra have been retrieved through skin and tissue in other studies in the past, an amalgamation of refined versions of those in vivo techniques with the work introduced here paves the way for the emergence of novel systems for assessing the material properties of bone tissue at specific anatomical sites in vivo in the future

Material loss at the head-stem taper junction may contribute to the high early failure rates of stemmed large head metal-on-metal (LH-MOM) hip replacements. We sought to quantify both wear and corrosion and by doing so determine the main mechanism of material loss at the taper. This was a retrospective study of 78 patients having undergone revision of a LH-MOM hip replacement. All relevant clinical data was recorded. Corrosion was assessed using light microscopy and scanning electron microscopy, and graded according to a well-published classification system. We then measured the volumetric wear of the bearing and taper surfaces. Evidence of at least mild taper corrosion was seen in 90% cases, with 46% severely corroded. SEM confirmed the presence of corrosion debris, pits and fretting damage. However, volumetric wear of the taper surfaces was significantly lower than that of the bearing surfaces (p = 0.015). Our study supports corrosion as the predominant mechanism of material loss at the taper junction of LH-MOM hip replacements. Although the volume of material loss is low, the ionic products may be more biologically active compared to the particulate debris arising from the bearing surfaces

Summary. Micromotions between stem and neck adapter depend on prosthesis design and material coupling. Based on the results of this study, the amount of micromotion seems to reflect the risk of fretting-induced fatigue in vivo. Introduction. Bimodular hip prostheses were developed to allow surgeons an individual reconstruction of the hip joint by varying length, offset and anteversion in the operation theatre. Despite these advantages, the use of these systems led to a high rate of postoperative complications resulting in revision rates of up to 11% ten years after surgical intervention. During daily activities taper connections of modular hip implants are highly stressed regions and contain the potential of micromotions between adjacent components, fretting and corrosion. This might explain why an elevated number of fretting-induced neck fractures occurred in clinics. However, some bi-modular prostheses (e.g. Metha, Aesculap, Ti-Ti) are more often affected by those complications than others (e.g. H-Max M, Limacorporate, Ti-Ti or Metha, Ti-CoCr) implying that the design and the material coupling have an impact on this failure pattern. Therefore, the purpose of this study was to clarify whether clinical successful prostheses offer lower micromotions than those with an elevated number of in vivo fractures. Materials and Methods. Two different bimodular hip designs (Metha and H-Max M, n = 6 each) were tested in vitro. Embedded Ti6Al4V (Ti) stems were assembled with Ti or CoCr29Mo (CoCr) necks and sinusoidally loaded (f = 1 Hz, 10,000 cycles) ranging from 0.23 to 4.30 kN (peak to peak, represents going upstairs) using a servohydraulic testing machine (MiniBionix II, MTS). Based on the results of four eddy-current sensors, micromotions were assessed in the region of the crack origin of fractured prostheses (lateral radius). Due to the test set-up, the recorded displacement includes, beside the real micromotions, the elastic deformation between sensor holder and reflector. The amount of the elastic deformation was determined using the finite-element technique. For statistical analyses Twoway-ANOVAs were performed (α = 0.05). Results. The H-Max M prostheses exhibited significantly lower micromotions compared to Metha prostheses (1.8 ± 2.2 µm vs. 4.1 ± 3.2 µm, p = 0.03). For Ti-Ti couplings, Metha prostheses showed a trend towards higher micromotions compared to H-Max M (6.5 ± 1.6 µm vs. 3.6 ± 1.5 µm, p = 0.08). Independent of the design, prostheses with Ti neck adapters caused significantly higher micromotions than those with CoCr adapters (5.1 ± 2.1 µm vs. 0.8 ± 1.6 µm, p < 0.01). No differences between the clinically used Metha prostheses with CoCr neck adapters and H-Max M prostheses with Ti necks were found (2.6 ± 2.0 µm, p = 0.25). Discussion. Both, the material coupling and the design influence the interface micromotions. The magnitude of micromotions might explain why bimodular hip systems are susceptible to fretting-induced fractures; however, the threshold for critical micromotions is still not known. The results of this study indicate that the amount of micromotion at taper interfaces could be directly linked to the risk of clinical failure