- Dept of Mechanical and Materials Engineering
McLaughlin Hall, Stuart St
Kingston, ON
K7L 3N6
Canada - 613 548 3232 6356
- University of Wisconsin-Madison, Mechanical Engineering, Faculty Memberadd
- Bone Biomechanics, Orthopaedic Implants, Finite Element Analysis, Mechanobiology, Designedit
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of the translational and rotational stiffnesses of a L4-L5 functional spinal unit using a specimen-specific finite element model, Journal of the Mechanical Behavior of Biomedical Materials, http://dx.doi.org/10.1016/ j.jmbbm.2012.04.002... more
of the translational and rotational stiffnesses of a L4-L5 functional spinal unit using a specimen-specific finite element model, Journal of the Mechanical Behavior of Biomedical Materials, http://dx.doi.org/10.1016/ j.jmbbm.2012.04.002 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Thousands of children are born in the United States annually with limb deformities and leg length inequalities [1]. While many others suffer injuries or infections affecting future growth, leaving them with similar limb deformities [1].... more
Thousands of children are born in the United States annually with limb deformities and leg length inequalities [1]. While many others suffer injuries or infections affecting future growth, leaving them with similar limb deformities [1]. Current tools used to treat these deformities are limited and often require prolonged use of external fixation limb deformity correction devices (LDCDs) with transcutaneous pins that cause pain, unsightly scars, and infections. Implantable lengthening LDCDs exist, but can only acutely correct angular deformity and, in some instances, have limited use in children due to concerns of growth plate injury. This paper describes the design and evaluation of a prototype LDCD which addresses these concerns. An initial 5:4 scale prototype has been manufactured, for use in design evaluation. The proposed LDCD is capable of one linear distraction and two angular correction degrees of freedom and is designed for extramedullary implantation. Device distraction is achieved through the combined movement of three racks, arranged in a triangular pattern. To meet the restrictive physical envelope requirements while still providing sufficient load capacity, a novel pseudo-differential gearing system was designed and incorporated into the device. Device validation was achieved through a combination of analytical and experimental methods including kinematic and dynamic simulation, finite element strength analysis, and experimental evaluation of a device prototype.
Several surgical techniques and devices have been developed to help patients born with limb deformities, limb length inequalities, and extreme short stature. People with such ailments often experience pain, dysfunction, and joint... more
Several surgical techniques and devices have been developed to help patients born with limb deformities, limb length inequalities, and extreme short stature. People with such ailments often experience pain, dysfunction, and joint degeneration. The primary method of treating such deformities is an osteotomy followed by callus distraction [1]. Commonplace lengthening devices are external fixators and intramedullary devices, but each has its drawbacks. Traditional external fixators, such as the Ilizarov device and Taylor spatial frame, are cumbersome, painful, and produce large residual scars [2]. Due to pin tract infection rates of 10–20%, lengthening with these methods requires careful surveillance [3]. Intramedullary lengthening devices can cause severe complications such as intramedullary infection [4]. Surgeons have recently experienced success with a motorized, intramedullary nail (Fitbone), but pediatric use of this device can be limited due to interference with open growth plates [5]. The investigators have designed an extramedullary device that retains the attractive qualities of an intramedullary nail, without the risk of deep infection or damage to growth plates. Additionally, the device can be equipped with a six-axis force-torque sensor capable of measuring forces and moments in real time.
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This work outlines a process for finite element (FE) modeling implementations of temperaturecontrolled radiofrequency (RF) ablation (TCRFA) with an automated temperature controller to investigate effects of changes in control temperature... more
This work outlines a process for finite element (FE) modeling implementations of temperaturecontrolled radiofrequency (RF) ablation (TCRFA) with an automated temperature controller to investigate effects of changes in control temperature and contact ...
University of Wisconsin, Madison, WI, USA, http://www.engr.wisc.edu/groups/BM/ 2 Human Mobility Research Centre, Kingston General Hospital, Queen's University, Kingston, ON, Canada, http://me.queensu.ca/hmrc/ 3 School of... more
University of Wisconsin, Madison, WI, USA, http://www.engr.wisc.edu/groups/BM/ 2 Human Mobility Research Centre, Kingston General Hospital, Queen's University, Kingston, ON, Canada, http://me.queensu.ca/hmrc/ 3 School of Rehabilitation Science, McMaster University, ...
Although it is long accepted that aseptic loosening is the main reason for revision of total joint replacements, preclinical assessment methods of primary fixation are not well developed. Reasons for aseptic loosening are multifactorial... more
Although it is long accepted that aseptic loosening is the main reason for revision of total joint replacements, preclinical assessment methods of primary fixation are not well developed. Reasons for aseptic loosening are multifactorial including the patient, surgical approach, biological reactions, wear, micro-motion at the implant–bone interface, load transfer from the joint to the host bone, and bone adaptation. The objective of this study was to highlight a few preclinical methods to investigate orthopaedic implant primary fixation relative to the transfer of loads and displacements at the implant–bone interface. The last generation of metal-on-metal hip prostheses used a high-precision low clearance bearing to provide a low friction ball and socket joint. During implantation the acetabular component deforms under a press-fit; however, excessive deformation of the acetabular component can lead to premature failure of the joint replacement. It is therefore important to establish an accurate method of quantifying cup deformation and develop finite element models to better understand the effects of the press-fit. Methods to measure press-fit deformation of monoblock acetabular cups for metal-on-metal total hip arthroplasty and resurfacing were investigated. The purpose of the present study was to compare cup deformation with two experiments simulating press-fit of an acetabular cup into the pelvis. Rim deformation and cup strain were measured for two common tests: (1) a two-point pinching of the cup rim and (2) a press-fit implantation into a cavitated polyurethane foam block. In the pinch test, the rim displaced linearly and symmetrically with force. The press-fit test, ostensibly a closer representation of surgical procedure, produced more complex displacement and strain responses due to the foam block shape, and the cup surface-foam block interaction. The current study demonstrated two methods to measure real-time hip cup deformation and strain during press-fitting that may be used for preclinical assessment of primary fixation.
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Reverse shoulder arthroplasty (RSA) is commonly used to treat patients with rotator cuff tear arthropathy. Loosening of the glenoid component remains one of the principal modes of failure and represents a significant complication that... more
Reverse shoulder arthroplasty (RSA) is commonly used to treat patients with rotator cuff tear arthropathy. Loosening of the glenoid component remains one of the principal modes of failure and represents a significant complication that requires revision surgery. This study assessed the effects of various factors on glenoid baseplate micromotion for primary fixation of RSA. A half-fractional factorial design of experiment was used to assess four factors: central element type (central peg or screw), central cortical engagement according to length (13.5 or 23.5 mm), anterior-posterior (A-P) peripheral screw type (nonlocking or locking), and cancellous bone surrogate density (10 or 25 pounds per cubic foot [pcf]). Glenoid baseplates were implanted into high- or low-density Sawbones™ rigid polyurethane foam blocks and cyclically loaded at 60 degrees for 1000 cycles (500 N compressive force range) using a custom-designed loading apparatus. Micromotion at the four peripheral screw positions was recorded using linear variable displacement transducers (LVDTs). Central peg fixation generated 358% greater micromotion at all peripheral screw positions compared to central screw fixation (p < 0.001). Baseplates with short central elements that lacked cortical bone engagement generated 328% greater micromotion than those with long central elements (p = 0.001). No significant effects were observed when varying A-P peripheral screw type or bone surrogate density. There were significant interactions between central element type and length (p < 0.001). A central screw and a long central element that engaged cortical bone reduced RSA baseplate micromotion. These findings serve to inform surgical decision-making regarding baseplate fixation elements to minimize the risk of glenoid loosening and thus, the need for revision surgery.
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Maximum insertion torque (IT) for threaded dental implants is a primary clinical measurement to assess implant anchorage, and strongly influences the clinical outcome. Insertion torque is influenced by surgical technique, implant designs,... more
Maximum insertion torque (IT) for threaded dental implants is a primary clinical measurement to assess implant anchorage, and strongly influences the clinical outcome. Insertion torque is influenced by surgical technique, implant designs, and patient factors such as bone density and quality. In this study, an analytical model was proposed for IT to estimate contributions from the thread and taper separately. The purpose of this study was to test if the analytical model could 1. differentiate the parallel-walled and tapered implant; and, 2. represent four factors: bone surrogate density, drill protocol, implant surface finish and cutting flute. The IT was modeled as the sum of the torques from the thread's inclined plane and interface shear stress from the tapered body integrated over the surface area, respectively, with two main parameters: effective force, F', F' and effective pressure, p'. The effective force, relates to the clamping force from the thread, while the effective pressure, p', associates with the contact pressure at the bone-implant interface. The model performed well (R2 = 0.88-1.0) and differentiated between the parallel-walled (p'= 0) and tapered implants (p'= 0.12). The model's parameters could individually represent the effects of the four factors. High bone surrogate density, two-step drill protocol, and rough surface increased both F' and p'. The cutting flute had opposing effects on F' and p' (β4 = 0.35 and -0.24, respectively); and therefore, had the lowest net effect on IT. The proposed analytical model therefore improves the understanding of the principal contributors to dental implant IT by considering thread and taper mechanics independently.
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Serial Ponseti casting occasionally fails to completely correct idiopathic clubfoot deformities and recurrence of deformity occurs. As these bones are largely unossified, statistical shape modelling (SSM) from MRI considers the entire set... more
Serial Ponseti casting occasionally fails to completely correct idiopathic clubfoot deformities and recurrence of deformity occurs. As these bones are largely unossified, statistical shape modelling (SSM) from MRI considers the entire set of shape features simultaneously and may provide a more accurate assessment of differences in bone morphology between two groups. The purpose of this study was to compare the shape of the talus in normal and clubfeet using direct geometric measurements and SSM. Both methods found significant differences between the control and clubfoot groups.
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ABSTRACT In this review, the methods and outcomes of cadaveric experiments that have measured anterior-posterior translation, internal-external rotation, and varus-valgus rotation at discrete flexion angles are summarized. The... more
ABSTRACT In this review, the methods and outcomes of cadaveric experiments that have measured anterior-posterior translation, internal-external rotation, and varus-valgus rotation at discrete flexion angles are summarized. The contribution of the cruciate and collateral ligaments to joint stability was quantified by comparing changes in kinematics as a result of ligament resection. The prevailing trend in the literature indicates that ligaments are maximally engaged towards extension, and that passive joint motion increases through the flexion arc. When ligaments are compromised due to injury or pathology, an understanding of the passive path of motion is essential to effective treatment. We have highlighted the various studies that have combined experimental data with computational techniques to explore treatment alternatives and improve our understanding of joint stability in different populations. The use of computational methods will likely continue to become more important as in vivo methods are developed to evaluate joint motion, and provide an opportunity to improve the treatment of joint disease.
Research Interests: Philosophy and Humanities
In the United States, approximately eight million osseous fractures are reported annually, of which 5-10% fail to create a bony union. Osteoblast-specific deletion of the gene Pten in mice has been found to stimulate bone growth and... more
In the United States, approximately eight million osseous fractures are reported annually, of which 5-10% fail to create a bony union. Osteoblast-specific deletion of the gene Pten in mice has been found to stimulate bone growth and accelerate fracture healing. Healing rates at four weeks increased in femurs from Pten osteoblast conditional knock-out mice (Pten-CKO) compared to wild-type mice (WT) of the same genetic strain as measured by an increase in mechanical stiffness and failure load in four-point bending tests. Preceding mechanical testing, each femur was imaged using a Skyscan 1172 micro-computed tomography (μCT) scanner (Skyscan, Kontich, Belgium). The present study used µCT image-based analysis to test the hypothesis that the increased femoral fracture force and stiffness in Pten-CKO were due to greater section properties with the same effective material properties as that of the WT. The second moment of area and section modulus were computed in ImageJ 1.46 (National Inst...
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Crown therapy is commonly used in veterinary medicine to provide support to teeth which have previously fractured, received root canal therapy, have significant wear, or experienced other detrimental removal of tooth substance. As with... more
Crown therapy is commonly used in veterinary medicine to provide support to teeth which have previously fractured, received root canal therapy, have significant wear, or experienced other detrimental removal of tooth substance. As with several aspects of veterinary medicine, many of the recommendations or guidelines for crown therapy originate from human dentistry, which are then transferred to veterinary patients. Due to the significant difference in the anatomy of teeth and function of the oral cavity between humans and dogs, these guidelines need to be studied to determine the appropriateness of their use in veterinary patients. This article evaluates the relationship between surface area of the preparation and clinical outcome of full veneer crown therapy of the canine tooth in dogs. Although there appeared to be a positive relationship between preparations with greater surface area and successful clinical outcome, it was not found to be statistically significant.
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Most studies investigating human lumbar vertebral trabecular bone (HVTB) mechanical property-density relationships have presented results for the superior-inferior (SI), or "on-axis" direction. Equivalent, directly measured data... more
Most studies investigating human lumbar vertebral trabecular bone (HVTB) mechanical property-density relationships have presented results for the superior-inferior (SI), or "on-axis" direction. Equivalent, directly measured data from mechanical testing in the transverse (TR) direction are sparse and quantitative computed tomography (QCT) density-dependent variations in the anisotropy ratio of HVTB have not been adequately studied. The current study aimed to investigate the dependence of HVTB mechanical anisotropy ratio on QCT density by quantifying the empirical relationships between QCT-based apparent density of HVTB and its apparent compressive mechanical properties--elastic modulus (E(app)), yield strength (σ(y)), and yield strain (ε(y))--in the SI and TR directions for future clinical QCT-based continuum finite element modeling of HVTB. A total of 51 cylindrical cores (33 axial and 18 transverse) were extracted from four L1 human lumbar cadaveric vertebrae. Intact vert...
Research Interests: Mechanical Engineering, Biomechanical Engineering, Materials Science, Biomedical Engineering, Medicine, and 14 moreTomography, Anisotropy, Finite Element Analysis, Humans, Male, Bone Density, Middle Aged, Mechanical Stress, Elastic Modulus, Materials Testing, X ray Computed Tomography, Mechanical Processes, Biomechanical Phenomena, and lumbar vertebrae
Acrylic bone cement is widely used to anchor orthopedic implants to bone and mechanical failure of the cement mantle surrounding an implant can contribute to aseptic loosening. In an effort to enhance the mechanical properties of bone... more
Acrylic bone cement is widely used to anchor orthopedic implants to bone and mechanical failure of the cement mantle surrounding an implant can contribute to aseptic loosening. In an effort to enhance the mechanical properties of bone cement, a variety of nanoparticles and fibers can be incorporated into the cement matrix. Mesoporous silica nanoparticles (MSNs) are a class of particles that display high potential for use as reinforcement within bone cement. Therefore, the purpose of this study was to quantify the impact of modifying an acrylic cement with various low-loadings of mesoporous silica. Three types of MSNs (one plain variety and two modified with functional groups) at two loading ratios (0.1 and 0.2wt/wt) were incorporated into a commercially available bone cement. The mechanical properties were characterized using four-point bending, microindentation and nanoindentation (static, stress relaxation, and creep) while material properties were assessed through dynamic mechanical analysis, differential scanning calorimetry, thermogravimetric analysis, FTIR spectroscopy, and scanning electron microscopy. Four-point flexural testing and nanoindentation revealed minimal impact on the properties of the cements, except for several changes in the nano-level static mechanical properties. Conversely, microindentation testing demonstrated that the addition of MSNs significantly increased the microhardness. The stress relaxation and creep properties of the cements measured with nanoindentation displayed no effect resulting from the addition of MSNs. The measured material properties were consistent among all cements. Analysis of scanning electron micrographs images revealed that surface functionalization enhanced particle dispersion within the cement matrix and resulted in fewer particle agglomerates. These results suggest that the loading ratios of mesoporous silica used in this study were not an effective reinforcement material. Future work should be conducted to determine the impact of higher MSN loading ratios and alternative functional groups.
Research Interests: Materials Engineering, Mechanical Engineering, Materials Science, Biomedical Engineering, Nanoindentation, and 15 moreNanoparticles, Nanotechnology, Medicine, Mechanical properties, Porosity, Orthopedics, Bone Cement, Temperature, Microtechnology, Surface Properties, Materials Testing, Silicon Dioxide, Mechanical Processes, Biomedical Engineering and Bioengineering, and Reinforced Polymer
Soluble particulate fillers can be incorporated into antibiotic-loaded acrylic bone cement in an effort to enhance antibiotic elution. Xylitol is a material that shows potential for use as a filler due to its high solubility and potential... more
Soluble particulate fillers can be incorporated into antibiotic-loaded acrylic bone cement in an effort to enhance antibiotic elution. Xylitol is a material that shows potential for use as a filler due to its high solubility and potential to inhibit biofilm formation. The objective of this work, therefore, was to investigate the usage of low concentrations of xylitol in a gentamicin-loaded cement. Five different cements were prepared with various xylitol loadings (0, 1, 2.5, 5 or 10 g) per cement unit, and the resulting impact on the mechanical properties, cumulative antibiotic release, biofilm inhibition, and thermal characteristics were quantified. Xylitol significantly increased cement porosity and a sustained increase in gentamicin elution was observed in all samples containing xylitol with a maximum cumulative release of 41.3%. Xylitol had no significant inhibitory effect on biofilm formation. All measured mechanical properties tended to decrease with increasing xylitol concentration; however, these effects were not always significant. Polymerization characteristics were consistent among all groups with no significant differences found. The results from this study indicate that xylitol-modified bone cement may not be appropriate for implant fixation but could be used in instances where sustained, increased antibiotic elution is warranted, such as in cement spacers or beads.
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Bone surrogates are proposed alternatives to human cadaveric vertebrae for assessing interbody device subsidence. A synthetic vertebra with representations of cortices, endplates and cancellous bone was recently developed as an... more
Bone surrogates are proposed alternatives to human cadaveric vertebrae for assessing interbody device subsidence. A synthetic vertebra with representations of cortices, endplates and cancellous bone was recently developed as an alternative surrogate to polyurethane foam blocks. The ability of the two surrogates to replicate subsidence has not been fully assessed, and was evaluated by indenting them with ring-shaped indenters and comparing their performance with human cadaveric vertebrae using qualitative characteristics and indentation metrics. The sensitivity of each surrogate to a centrally or peripherally placed indenter was of particular interest. Many indentation characteristics of the foam blocks were similar to those of human cadaveric vertebrae, except their insensitivity to centrally and peripherally placed indenters, owing to their homogeneous mechanical properties. This is distinctly different from the cadaveric vertebrae, where a peripherally placed indenter indented significantly less than a centrally placed indenter, because of endplates. By contrast, the synthetic vertebra was sensitive to peripherally placed indenters owing to its bi-material composition, including a thickened peripheral endplate. However, an overly strong synthetic endplate resulted in unrepresentative indentation shape and depth. Both surrogates produced similar results to human cadaveric vertebrae in certain respects, but neither is accurate enough in terms of material property distribution to model subsidence completely in human cadaveric vertebrae.
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The purpose of this study was to compare computed tomography density (ρCT ) obtained using typical clinical computed tomography scan parameters to ash density (ρash ), for the prediction of densities of femoral head trabecular bone from... more
The purpose of this study was to compare computed tomography density (ρCT ) obtained using typical clinical computed tomography scan parameters to ash density (ρash ), for the prediction of densities of femoral head trabecular bone from hip fracture patients. An experimental study was conducted to investigate the relationships between ρash and ρCT and between each of these densities and ρbulk and ρdry . Seven human femoral heads from hip fracture patients were computed tomography-scanned ex vivo, and 76 cylindrical trabecular bone specimens were collected. Computed tomography density was computed from computed tomography images by using a calibration Hounsfield units-based equation, whereas ρbulk, ρdry and ρash were determined experimentally. A large variation was found in the mean Hounsfield units of the bone cores (HUcore) with a constant bias from ρCT to ρash of 42.5 mg/cm(3). Computed tomography and ash densities were linearly correlated (R (2) = 0.55, p < 0.001). It was demo...
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Prosthetic joint infection is one of the most serious complications that can lead to failure of a total joint replacement. Recently, the rise of multidrug resistant bacteria has substantially reduced the efficacy of antibiotics that are... more
Prosthetic joint infection is one of the most serious complications that can lead to failure of a total joint replacement. Recently, the rise of multidrug resistant bacteria has substantially reduced the efficacy of antibiotics that are typically incorporated into acrylic bone cement. Silver nanoparticles (AgNPs) are an attractive alternative to traditional antibiotics resulting from their broad-spectrum antimicrobial activity and low bacterial resistance. The purpose of this study, therefore, was to incorporate metallic silver nanoparticles into acrylic bone cement and quantify the effects on the cement's mechanical, material and antimicrobial properties. AgNPs at three loading ratios (0.25, 0.5, and 1.0% wt/wt) were incorporated into a commercial bone cement using a probe sonication technique. The resulting cements demonstrated mechanical and material properties that were not substantially different from the standard cement. Testing against Staphylococcus aureus and Staphyloco...
Research Interests: Materials Science, Biomedical Engineering, Biofilms, Medicine, Metal Nanoparticles, and 13 moreTransgenic Mice, Cell line, Silver, Animals, Staphylococcus aureus, Antimicrobial, Staphylococcus epidermidis, Fourier transform infrared spectroscopy, Bone Cements, Osteoblasts, Materials Testing, Polymethyl Methacrylate (PMMA), and Biomechanical Phenomena
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Research Interests: Biomedical Engineering, Finite Element, Finite Element Analysis, Humans, Compressive Strength, and 13 moreBone Density, Experimental Study, Mechanical Stress, Finite Element Model, Analysis of Variance, Elastic Modulus, Bone Substitutes, X ray Computed Tomography, Fused Deposition Modelling, Electrical And Electronic Engineering, Bone and Bones, Compression test, and Mechanical Property
The knowledge of spinal kinematics is of paramount importance for many aspects of clinical application (i.e. diagnosis, treatment and surgical intervention) and for the development of new spinal implants. The aim of this study was to... more
The knowledge of spinal kinematics is of paramount importance for many aspects of clinical application (i.e. diagnosis, treatment and surgical intervention) and for the development of new spinal implants. The aim of this study was to determine the translational and rotational stiffnesses of a functional spinal unit (FSU) L4-L5 using a specimen-specific finite element model. The results are needed as input data for three-dimensional (3D) multi-body musculoskeletal models in order to simulate vertebral motions and loading in the lumbar spine during daily activities. Within the modelling process, a technique to partition the constitutive members and to calibrate their mechanical properties for the complex model is presented. The material and geometrical non-linearities originating from the disc, the ligaments and the load transfer through the zygapophysial joints were considered. The FSU was subjected to pure moments and forces in the three anatomical planes. For each of the loading scenarios, with and without vertical and follower preload, the presented technique provides results in fair agreement with the literature. The novel representation of the nonlinear behaviour of the translational and rotational stiffness of the disc as a function of the displacement can be used directly as input data for multi-body models.
Research Interests: Engineering, Materials Engineering, Mechanical Engineering, Biomedical Engineering, Structural Engineering, and 14 moreSpine, Finite element method, Medicine, Finite Element Analysis, Humans, Kinematics, Female, Male, Stiffness, Nonlinear system, Rotation, Weight Bearing, Mechanical Processes, and Biomechanical Phenomena
Research Interests: Materials Engineering, Mechanical Engineering, Materials Science, Biomedical Engineering, Medicine, and 15 moreCeramics, Osteoporosis, Humans, Porosity, Compressive Strength, Calcium Phosphates, Temperature, Fracture Healing, Time Factors, Cost Benefit Analysis, Musculoskeletal system, Elastic Modulus, Statistical models, Bone Substitutes, and Fractures Bone
Research Interests: Materials Engineering, Mechanical Engineering, Materials Science, Biomedical Engineering, Water, and 12 moreNanoparticles, Medicine, Porosity, Cement, Physical processes, Absorption, Composite Material, Materials Testing, Structure activity Relationship, Silicon Dioxide, Mechanical Processes, and Orthopedic Procedures
It is known that conventional scaffold manufacturing techniques have low reproducibility and control of the micro-architecture features. Although there have been advances in bone tissue engineering fabrication, there is no consensus on... more
It is known that conventional scaffold manufacturing techniques have low reproducibility and control of the micro-architecture features. Although there have been advances in bone tissue engineering fabrication, there is no consensus on the optimized parameter designs or clear understanding of the microfluidic interactions required for tissue regeneration. In this work, we introduce a new inexpensive fabrication method of producing pore designs of 3D-elastomeric structures with high controlled geometry of orthogonal arrays. The present fabrication method utilizes a permanent and reusable micro-machined mould along with a micro-casted process to efficiently fabricate diverse 3D feature directly. This fabrication method, without multiple process steps, would be suitable to support experiments of controlled environment for flow effects in 3D bone scaffolds.
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The key to the development of a successful implant is an understanding of the effect of bone remodelling on its long-term fixation. In this study, clinically observed patterns of bone remodelling have been compared with computer-based... more
The key to the development of a successful implant is an understanding of the effect of bone remodelling on its long-term fixation. In this study, clinically observed patterns of bone remodelling have been compared with computer-based predictions for one particular design of prosthesis, the Thrust Plate Prosthesis (Centerpulse Orthopedics, Winterthur, Switzerland). Three-dimensional finite-element models were created using geometrical and bone density data obtained from CT scanning. Results from the bone remodelling simulation indicated that varying the relative rate of bone deposition/resorption and the interfacial conditions between the bone and the implant could produce the trend towards the two clinically observed patterns of remodelling.
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Methods used to evaluate bone mechanical properties vary widely depending on the motivation and environment of individual researchers, clinicians, and industries. Further, the innate complexity of bone makes validation of each method... more
Methods used to evaluate bone mechanical properties vary widely depending on the motivation and environment of individual researchers, clinicians, and industries. Further, the innate complexity of bone makes validation of each method difficult. Thus, the purpose of the present research was to quantify methodological error of the most common methods used to predict long-bone bending stiffness, more specifically, flexural rigidity (EI). Functional testing of a bi-material porcine bone surrogate, developed in a previous study, was conducted under four-point bending test conditions. The bone surrogate was imaged using computed tomography (CT) with an isotropic voxel resolution of 0.625 mm. Digital image correlation (DIC) of the bone surrogate was used to quantify the methodological error between experimental, analytical, and computational methods used to calculate EI. These methods include the application of Euler Bernoulli beam theory to mechanical testing and DIC data; the product of ...
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When accurate physical models are fabricated from patient specific computed tomography (CT) data, the physical models can be used as a source of preoperative planning, surgical template, or as replacement implants [1,2]. The creation of... more
When accurate physical models are fabricated from patient specific computed tomography (CT) data, the physical models can be used as a source of preoperative planning, surgical template, or as replacement implants [1,2]. The creation of the physical models generally follows a three step process: 1. CT imaging; 2. three-dimensional (3D) surface model generation; 3. physical model fabrication. Quantifying the errors within each step can help reduce the overall error of the physical model. Therefore, the objective of the current study was to determine the accuracy of surface models and physical models created from CT data. The errors within the process that were quantified include the CT slice thickness and spacing, the algorithms used to create the 3D surface models from the thresholded CT data, and the creation of initial graphics exchange specification (IGES) computer aided design (CAD) models from the stereolithographic (STL) surface models. In addition this study looks at the accu...
The high incidence of osteoporosis and related fractures demands for the use and development of methods capable of detecting changes in bone mechanical properties. The most common clinical and laboratory methods used to detect changes in... more
The high incidence of osteoporosis and related fractures demands for the use and development of methods capable of detecting changes in bone mechanical properties. The most common clinical and laboratory methods used to detect changes in bone mechanical properties, such as stiffness, strength, or flexural rigidity, include: mechanical testing, medical imaging, medical image-based analytical calculations, and medical image-based finite element analysis. However, the innate complexity of bone makes validation of the results from each method difficult. The current study presents the design, fabrication, and functional testing of a bi-material and computed tomography scan compatible bone-surrogate which provides consistent reproducible mechanical properties for methodological evaluation of experimental, analytical, and computational bone bending stiffness prediction methods.
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Research Interests: Medicine and Vancomycin
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During the last few years there has been renewed interest in hip resurfacing. The advantages of such prostheses include minimal bone resection and more physiological loading of the proximal femur. The purpose of this study was to... more
During the last few years there has been renewed interest in hip resurfacing. The advantages of such prostheses include minimal bone resection and more physiological loading of the proximal femur. The purpose of this study was to investigate the stress distribution to the upper femur following a metal-on-metal hip resurfacing and the influence of a short stem on femoral bone loading. An accurate and validated finite element (FE) model of the proximal femur was utilised. This was created from CT data of cadaveric femurs. The validation process included weighing, modal analysis, strain gauging and ultrasound material testing of the bone. The maximum elastic modulus in the principal direction was 22.9EGPa. The elastic moduli of the cement and implant were 1.8 and 200 GPa respectively. The joint force and 4 muscle loads were applied accordingly and adapted to the specific geometry of the bone. The load case represented the 45% position in the gait cycle, corresponding to toe-off. The hi...
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INTRODUCTION Computer models of bones are essential tools for research in orthopaedics, preclinical analysis of orthopaedic implant designs, and in computer-aided surgery. In these applications, solid models of bones are routinely created... more
INTRODUCTION Computer models of bones are essential tools for research in orthopaedics, preclinical analysis of orthopaedic implant designs, and in computer-aided surgery. In these applications, solid models of bones are routinely created from computed tomography (CT) scan data; however, there are few studies [1-3] that have quantified the effects of the process parameters, on the error of the resulting geometry. The purpose of this study was to determine the magnitude of the error in solid models generated from CT-scan data and to which factors the error was most sensitive.
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Aseptic loosening is the most common reason for the long-term revision of cemented arthroplasties with fracture of the cement being a postulated cause or contributing factor. In our previous studies we showed that adding an antibiotic to... more
Aseptic loosening is the most common reason for the long-term revision of cemented arthroplasties with fracture of the cement being a postulated cause or contributing factor. In our previous studies we showed that adding an antibiotic to a polymethylmethacrylate (PMMA) bone cement led to detrimental effects on various mechanical properties of the cement such as bending strength, compressive strength and fracture toughness (KIC). This finding implied that the mechanical failure of antibiotic-loaded PMMA bone cement was influenced by its pore volume fraction. Up to now this aspect has not been studied. Hence the purposes of this study were to determine (1) the influence of antibiotic (telavancin) loading on the KIC of a widely used PMMA bone cement brand (Palacos®R) and (2) the influence of pore size and pore distribution on the fracture behavior of the KIC specimens. For (2) both experimental and numerical methods (extended finite element method [XFEM]) were used allowing a compariso...