No description available.

This thesis focuses on evaluating the osteogenic potential of two synthetic bone graft materials either in vitro and/or in established rodent bone defect models.

No description available.

The number of clinical procedures performed in the USA using bone graft substitutes was estimated at 1.1 million in 2010 and is projected to reach 1.3 million in 2015. This increasing demand for bone graft substitutes is a result of an ever-ageing population coupled with recent reports in the clinical literature of concerns regarding the safety of allograft and recombinant bone morphogenetic proteins such as rh- BMP-2 and the supply of autograft, which has led to an increased clinical interest in synthetic alternatives to allograft; autograft; and recombinant growth factors. One such synthetic material is silicate-substituted hydroxyapatite (SiCaP). Mechanical testing revealed SiCaP to have similar mechanical behaviour to morcellised cancellous bone. In computated spinal and hip models the simulated stresses in SiCaP were determined to be low when in situ, indicating a stressshielding effect from the implanted metalwork and surrounding bone. We also found an inverse relationship between porosity and Young's Modulus. Our results indicated that the strut-porosity of a material substrate should be increased to maximise the potential for formation of a precursor to bone-like apatite after implantation in osseous defects and further confirmed previous reports that betatricalcium phosphate is less bioactive than hydroxyapatite. We demonstrated a direct link between the amount of strut-porosity and the osteoinductivity of SiCaP. We learned that adding a resorbable carrier phase did not impair the osteoinductive potential of SiCaP, suggesting that osteoinductivity is not necessarily determined in the first 24-48 hours post implantation. Most notably from our studies we determined that the osteoinductivity of SiCaP correlated with its performance in orthotopic defects. Our research confirmed our hypothesis that modifying the micron-scale physical structure of a hierarchical porous SiCaP based biomaterial influences its functional performance in vitro and such modifications can be applied to improve its performance outcomes in ectopic and orthotopic treatment sites in vivo.

Failure of a primary hip arthroplasty is often caused by osteolysis which compromises the patient’s periprosthetic bone stock. Impaction allografting involves the use of morselized allograft bone and cement to stabilize the implant and restore this periprosthetic bone stock. Although clinical results of impaction allografting are favourable, regions of necrotic bone graft have been shown to exist for many years post-operatively and may ultimately lead to implant failure. Previous laboratory research has identified a correlation between mechanical stimuli and bone growth; therefore, the purpose of this study was to develop an in vivo device that would enable the investigation of the effect of mechanical load on bone graft incorporation in impacted allograft hip prostheses. An actuator was developed with a finite volume to enable its subcutaneous implantation along the tibia (20mm x 10mm x 10mm) and spine (35mm x 25mm x 15mm) in a rat bone chamber model. The actuator was designed to deliver a dynamic, (1Hz), compressive, (-6N), load that was controlled telemetrically throughout a 6-week long in vivo study. Independent validations of the mechanical actuator and the electrical control system were performed prior to an electromechanical validation of the integrated system. The responsiveness, quantity and magnitude of the load were investigated. The mechanical actuator was motor-driven and the electrical control system was based on radio frequency signal transmission. The electromechanical actuator conformed to the volumetric restrictions of the rat bone chamber model (tibia: 13mm x 17mm x 10mm; spine: 35mm x 30mm x 11mm). A wide range of operating frequencies (0.5 to 3.0 ± 0.05Hz) was achieved and a telemetrically controlled load was produced for 20 seconds per day throughout a simulated 6 week in vivo study. Due to inefficiencies of the mechanical actuator and voltage limitations of the control system, the magnitude of the compressive load produced by the actuator (-1.67 ± 0.10N) was less than specified by the design criteria. Future work to optimize the actuator design and fabrication is warranted in order to increase the maximum load magnitude; however, the current design provides a novel means to begin the investigation of the role of mechanical load on bone graft incorporation in impaction allografting.

Failure of a primary hip arthroplasty is often caused by osteolysis which compromises the patient’s periprosthetic bone stock. Impaction allografting involves the use of morselized allograft bone and cement to stabilize the implant and restore this periprosthetic bone stock. Although clinical results of impaction allografting are favourable, regions of necrotic bone graft have been shown to exist for many years post-operatively and may ultimately lead to implant failure. Previous laboratory research has identified a correlation between mechanical stimuli and bone growth; therefore, the purpose of this study was to develop an in vivo device that would enable the investigation of the effect of mechanical load on bone graft incorporation in impacted allograft hip prostheses. An actuator was developed with a finite volume to enable its subcutaneous implantation along the tibia (20mm x 10mm x 10mm) and spine (35mm x 25mm x 15mm) in a rat bone chamber model. The actuator was designed to deliver a dynamic, (1Hz), compressive, (-6N), load that was controlled telemetrically throughout a 6-week long in vivo study. Independent validations of the mechanical actuator and the electrical control system were performed prior to an electromechanical validation of the integrated system. The responsiveness, quantity and magnitude of the load were investigated. The mechanical actuator was motor-driven and the electrical control system was based on radio frequency signal transmission. The electromechanical actuator conformed to the volumetric restrictions of the rat bone chamber model (tibia: 13mm x 17mm x 10mm; spine: 35mm x 30mm x 11mm). A wide range of operating frequencies (0.5 to 3.0 ± 0.05Hz) was achieved and a telemetrically controlled load was produced for 20 seconds per day throughout a simulated 6 week in vivo study. Due to inefficiencies of the mechanical actuator and voltage limitations of the control system, the magnitude of the compressive load produced by the actuator (-1.67 ± 0.10N) was less than specified by the design criteria. Future work to optimize the actuator design and fabrication is warranted in order to increase the maximum load magnitude; however, the current design provides a novel means to begin the investigation of the role of mechanical load on bone graft incorporation in impaction allografting.

Failure of a primary hip arthroplasty is often caused by osteolysis which compromises the patient’s periprosthetic bone stock. Impaction allografting involves the use of morselized allograft bone and cement to stabilize the implant and restore this periprosthetic bone stock. Although clinical results of impaction allografting are favourable, regions of necrotic bone graft have been shown to exist for many years post-operatively and may ultimately lead to implant failure. Previous laboratory research has identified a correlation between mechanical stimuli and bone growth; therefore, the purpose of this study was to develop an in vivo device that would enable the investigation of the effect of mechanical load on bone graft incorporation in impacted allograft hip prostheses. An actuator was developed with a finite volume to enable its subcutaneous implantation along the tibia (20mm x 10mm x 10mm) and spine (35mm x 25mm x 15mm) in a rat bone chamber model. The actuator was designed to deliver a dynamic, (1Hz), compressive, (-6N), load that was controlled telemetrically throughout a 6-week long in vivo study. Independent validations of the mechanical actuator and the electrical control system were performed prior to an electromechanical validation of the integrated system. The responsiveness, quantity and magnitude of the load were investigated. The mechanical actuator was motor-driven and the electrical control system was based on radio frequency signal transmission. The electromechanical actuator conformed to the volumetric restrictions of the rat bone chamber model (tibia: 13mm x 17mm x 10mm; spine: 35mm x 30mm x 11mm). A wide range of operating frequencies (0.5 to 3.0 ± 0.05Hz) was achieved and a telemetrically controlled load was produced for 20 seconds per day throughout a simulated 6 week in vivo study. Due to inefficiencies of the mechanical actuator and voltage limitations of the control system, the magnitude of the compressive load produced by the actuator (-1.67 ± 0.10N) was less than specified by the design criteria. Future work to optimize the actuator design and fabrication is warranted in order to increase the maximum load magnitude; however, the current design provides a novel means to begin the investigation of the role of mechanical load on bone graft incorporation in impaction allografting. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

Hydroxyapatite (HA) bioceramics are commercially available as bone graft substitute materials. The aim of the current research was to characterise the electrical properties of hydroxyapatite-barium titanate (HABT) composites and to assess in vitro biological responses to the composites in order to investigate their potential use as bone graft substitutes. A range of HABT ceramics of different compositions was manufactured and their electrical properties were measured. The microstructure and piezoelectric properties of the ceramics were both dependent on the proportion of barium titanate (BT) present. Composites containing more than 70% BT displayed piezoelectric charge coefficients (d33) of up to 86.3±7.9pCN-1 (95% BT). The ferroelectric nature of the 90 and 95% BT materials was confirmed by assessment of their ferroelectric hysteresis loops. The highest piezoelectric voltage coefficient (g33) recorded was 14x10-3Vm-1Pa-1 (90% BT). Following the assessment of the electrical properties, the HABT ceramic containing 90% BT was selected for the assessment of biological responses to the composites. The proliferation, viability, activity and morphology of human osteoblast-like cells cultured on HABT were comparable to those cultured on hydroxyapatite (HA) up to 7 days after seeding. The remnant polarisation of poled HABT induced an increase in cell attachment. This influence was independent of the nature (positive or negative) of the polarisation. Poling was not found to influence cell morphology, activity or differentiation in the first 7 days of incubation. At 14 days after seeding, results were inconsistent, indicating some variations in cell population and differentiation depending on the composition and poling of the ceramics respectively. This study has substantially defined the electrical properties of a range of HABT ceramics. It indicates their in vitro biocompatibility and thus their potential for use as bone graft substitutes. These results provide a benchmark against which future work investigating the influence of mechanical loading and longer term studies may be measured.

No description available.

The aim of this study was to test the application of an in situ–formed synthetic polyethylene glycol (PEG) as a biodegradable membrane with a variety of graft materials and hyperbaric oxygen (HBO) for enhanced bone regeneration. Critical-sized rabbit calvarial defects were created in bilateral parietal bones. Group 1 served as a control with unfilled defects, Group 2 had defects filled with morcelized autogenous bone, and Group 3 had defects filled with biphasic calcium phosphate. One defect was protected PEG membrane and half the animals were subjected to HBOT treatment. The unsupported membrane didn’t produce the desired bone regeneration in the unfilled and bone grafted groups. HBO didn't ameliorate the bone grafted or ceramic filled defects over the 6-week time period. Caution is recommended with the membrane over unsupported defects. Future assessments with HBO should be completed at the 12-week time point.