Browsing by Author "Peter L. Mente, Committee Member"

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Design and In Vitro Evaluation of Five Epiphyseal Plate Fracture Stabilization Methods in Canines
(2008-12-05) Lee, Erica Shengkai; Ola L.A. Harrysson, Committee Chair; Denis J. Marcellin-Little, Committee Co-Chair; Peter L. Mente, Committee Member
Epiphyseal growth plate fractures of the distal femur are commonly seen in young canines that have not completed full ossification of the growth plate. Current treatment techniques involve the use of crossed Kirschner wires and commercial stainless steel plates. This raises concerns of either providing not enough stability or providing too much to the point where stress shielding is observed in the surrounding tissues or the full growth potential of the bone cannot be realized. To prevent this, a second surgery must be performed to remove these stabilization implants after proper healing of the fracture. Currently, resorbable polymers have been used to treat fractures, primarily in the cranio-maxillofacial area. This study aimed to mechanically evaluate the effectiveness of custom designed polycaprolactone (PCL) resorbable bilateral bone plates and lateral titanium plates to the current epiphyseal plate fracture repair techniques of crossed Kirschner wires and lateral commercial stainless steel bone plates. Forty identical models of the distal femur with pre-designed epiphyseal plate fractures were produced for the fixation of these five repair methods. The model constructs underwent nondestructive cranio-caudal bending, medio-lateral bending and torsional loading tests as well as destructive cranio-caudal bending and torsional loading failure tests. The study showed no statistically significant differences among the constructs for the destructive tests, suggesting the models failed prior to reaching the yield and ultimate strengths and torques of the actual constructs. However, from nondestructive tests, the constructs repaired with custom designed titanium plates displayed comparable mechanical properties to the commercial stainless steel plates. Structural stiffnesses of the titanium plate repaired constructs were not statistically significant from the commercial plate repaired constructs for nondestructive cranio-caudal bending medio-lateral bending and torsional loading tests. The study also displayed excellent mechanical properties of the two thicknesses (4mm and 2mm) of custom designed resorbable PCL plates. Results showed both 4mm and 2mm resorbable plates were statistically more structurally stiff when responding to cranial forces compared to Kirschner wire repaired fractures. Both 4mm and 2mm resorbable plates were also more structurally stiff when responding to medial forces compared to Kirschner wire repaired fractures and due to their bilateral attachment, also provided a marginally greater stability than the laterally attached metal plates. The resorbable 4mm and 2mm plate constructs were also marginally better in structural stiffness in response to torsional loading than the Kirschner wire constructs. Additionally, results indicated that the 2mm resorbable plate was statistically comparable to the thicker 4mm plate, in cranial bending, medial bending, and torsional bending. Custom designed titanium plates could be an effective alternative to commercial stainless steel plates for fractures observed by more mature canines, and both resorbable 4mm and 2mm PCL plates could be a more effective alternative to Kirschner wire epiphysis plate fracture repair techniques in young canines.
Design And Study of Biodegradable Small Diameter Vascular Grafts
(2003-11-13) Agrawal, Pankaj; Peter L. Mente, Committee Member; Alan E. Tonelli, Committee Member; Bhupender S. Gupta, Committee Chair
In this research, the focus has been on designing and producing small diameter woven grafts having a biodegradable material. Woven tubes in diameters ranging from 3 to 6.5 mm are developed using a narrow width Muller loom. The material used is Polyglactin 910 biodegradable yarn of 56 denier and the structures developed are plain but with different degrees of tightness. The pick density is varied from 32 to 44 picks per inch and end density is varied by using different number of total ends. Accordingly, the experimental work in this thesis involved weaving of 5 different sets of tubular structures and examining their behaviors. Since the woven grafts needed to be heat set to develop a circular shape that was resilient, preliminary studies were conducted on the yarns to determine heat setting conditions that led to optimum set with minimum degradation in properties. Process parameters required to manufacture such structures are identified. The effects of degradation time and structural variables on the mechanical properties of the grafts are studied. The variables were the construction parameters and the days of degradation; and the properties examined were the change in mass and thickness of the graft, and the elastic recovery, compliance and porosity properties of the structures. Statistical analysis of variance is conducted to identify significant effects in several instances.
Effects of Mechanical Stimuli on Biological Interactions with Amino Acid-Derivatized Fullerenes at the Tissue and Cellular Levels
(2007-07-05) Rouse, Jillian Grace; Peter L. Mente, Committee Member; Elizabeth G. Loboa, Committee Co-Chair; Nancy A. Monteiro-Riviere, Committee Chair
Engineered nanomaterials have structural features with at least one dimension in the 1—100 nm range. Because of their small size, nanoparticles possess unique chemical, mechanical, electrical, optical, magnetic, and biological properties that make them ideal candidates for a variety of novel commercial and medical applications. Particularly, carbon-based nanomaterials such as fullerenes, nanotubes, and nanowires are considered key elements in the development of new nano-applications with the potential to be used in everything from biomedicine and drug delivery systems to nanoelectronics and energy conservation mechanisms. Relatively unknown, however, is how exposure to nanoscale particles effects normal biological functions and processes. A major focus of recent toxicological research has begun to investigate the interactions between the biological environment and engineered nanoparticles and to determine appropriate safety standards that should be considered when interacting with nanomaterials. The purpose of this research is to investigate how fullerene-based amino acids interact with the biological environment both at the tissue and cellular levels and to identify factors, such as mechanical stimulation, that increase these interactions.
Viscoelastic Responses of the Lumbar spine during Prolonged Stooping
(2005-08-15) Shin, Gwanseob; Elizabeth G. Loboa, Committee Co-Chair; Gary A. Mirka, Committee Co-Chair; David B. Kaber, Committee Member; Peter L. Mente, Committee Member
There is considerable evidence that awkward postures of the low back are related to the incidence of low back disorders (LBDs). Specifically, the stooped or fully flexed posture maintained over a prolonged period of time has been known to lead to LBDs in many industrials tasks but the specific biomechanics/physiology of this link is not fully developed. This study combined empirical work with finite element analyses to explore this relationship. The empirical work focused on quantifying the time-dependent responses of the lumbar spine during a prolonged stooped posture by assessing the changes in the sagittal plane range of lumbar flexion and the electromyographic activity of the back extensor musculature in the isokinetic lifts during and after prolonged stooping. Ten healthy participants performed a regimen of a 10-minute stooping period followed by a 10-minute upright standing recovery period, with an isokinetic lift every 2.5 minutes. Results showed significant creep effects of the flexion angle and the increased activity of extensor muscles during stooping to compensate for the reduced extensor moment producing capability of the passive tissues. The 10-minute upright standing did not produce a full recovery of the lumbar spine tissues but a 30-second rest break in the middle of the stooping period moderated these viscoelastic responses. A three-dimensional finite element (FE) model of the lumbar spine was developed to predict the responses of the passive and active tissues of the low back during the prolonged stooping and recovery period. This model employed a nonlinear stress-strain relationship describing the viscoelastic material properties of individual components of the lumbar spine. The trunk flexion tasks that were performed in the in vivo empirical work were simulated in the FE model and the predicted results (range of motion, muscle activation levels, etc.) were compared with experimental results to validate the model. The predicted results by the FE model showed high correlation (R>0.9) with the in vivo experimental results, confirming the capability of the FE model as a potential tool for risk assessment of the prolonged stooping tasks. Results of the in vivo experiment suggested the importance of proper duty cycles in reducing LBD risks due to repetitive prolonged stooping in work-related tasks. The FE model of this study showed potential to simulate various prolonged stooped postures in occupational tasks and predict time-dependent stress/strain of individual spinal tissues. The data from these simulations can be used to design better work postures and duty cycles that can reduce the risks for LBDs, without sacrificing work productivity.