| The first part of this study investigated the solidification mechanisms of chitosan-GP/blood implant in vitro with and without added clotting factors, and investigated different methods for adding the factors into the implants in an in vivo cartilage repair model. Using thromboelastography, in vitro studies found that chitosan-GP/blood implants solidify through coagulation mechanisms which lead to a dual fibrin-polysaccharide clot scaffold that resists enzymatic lysis and is physically more stable than normal blood clots. Clotting factors, especially thrombin and the combo rhFVIIa + TF, significantly reduced in vitro and in vivo clotting times of the implants, which demonstrated the potential of clotting factors for enhancing the practical clinical use, the implant residency, and the therapeutic activity of chitosan-GP/blood implants for repairing cartilage.;Finally, the long-term (6.5 months) cartilage and bone repair of microdrilled defects treated with chitosan-GP/blood implants with thrombin was investigated in bilateral, full-thickness, trochlear defects in skeletally mature rabbit knees. This study showed that thrombin-solidified implants enhanced cartilage repair tissue integration, promoted a higher structural integrity, elicited a more hyaline-like tissue and promoted a more complete bone repair of the drill holes, compared to defects treated by microdrilling and thrombin-alone. Microdrill hole diameter had no specific effect on cartilage repair. The subchondral bone plate was regenerated in all defects, but it was significantly more porous and incompletely mineralized compared to intact knees. All repaired defects showed subchondral bone plate thickening outside the defect area. Bone below control defect bone contained more residual drill holes and thicker trabeculae. Low osteoclast numbers suggested that bone was no longer remodeling at 6.5 months post-drilling. In summary, thrombin-solidified chitosan-GP/blood implants generated a more hyaline and structurally integrated osteochondral unit, features needed for long-term durability. Furthermore, we observed that debridement and drilling can also lead to long-term subchondral bone changes outside a cartilage defect.;The innovation of this research project lies in the original idea of adding blood clotting factors to the hybrid implant to accelerate its solidification and reduce surgical waiting time. The improved clinical ease-of-use through better control of the in situ solidification further supports the concept of a liquid implant for cartilage repair, as it can easily adapt itself to most osteochondral defect shapes, which is a considerable advantage with regards to other pre-formed implants. Furthermore, the initial liquid state of the implant allows it to be delivered by arthroscopy, a minimally invasive surgical procedure compared to an arthrotomy. The completion of this thesis project contributed not only to the technological development of a chitosan-GP/blood implant with clotting factors but in several other ways to the advancement of knowledge within the field of biomedical engineering. (Abstract shortened by UMI.);In the second part of this study, micro-computed tomography (micro-CT) was used to characterize the subchondral bone structure of intact trochlea and acute, microdrilled, trochlear defects. As current methods were lacking to analyze three-dimensional (3D) volumes of interest (VOI) in bone with curved articular bone surfaces, 2 novel VOI models with adapted surfaces were developed. These VOIs were shown to be better than previously used simple geometric VOI shapes for quantifying structural features of subchondral bone below a curved articular surface because simple geometric shapes failed to include 17% of subchondral bone structure. Depthdependent bone structural differences were best captured when using a smaller 250 mum deep "curved-rectangular adapted surface" (C-RAS) VOI model than a 1 mm deep "rectangular adapted surface" (RAS) VOI model. |
