Three-dimensional Stem Cell Aggregates for Cartilage Tissue Engineering

Abstract

Osteoarthritis is the degradation of the knee cartilage within the joints that is often painful and can be debilitating and affect movement, thus impacting the overall quality of life. Current approved treatment methods include microfracture, autologous chondrocyte implantation (ACI) and osteochondral autograft transfer system (OATS). Tissue engineering approaches that are still under clinical trials include naturally derived or synthetic biocompatible scaffolds that possess good mechanical properties, or minimally manipulated devices like decellularized juvenile cartilage that are yet to demonstrate long-term benefits. Using the therapeutic potential of undifferentiated stem cells not only provides a sustainable and long-term approach but also promotes natural healing of the damages cartilage through biochemical cues. The current thesis work describes the evaluation of 3D stem cell aggregates for the regeneration of the osteochondral interface to overcome some of the limitations posed by the above surgical techniques. In vitro and in vivo studies were completed to evaluate the performance of aggregates in both a hydrogel system and a rat in vivo system. Compared to conventional cell suspensions, aggregates had improved cellular response, biochemical content and higher chondroinductive gene expression. Furthermore, the chondrogenic nature of the aggregate was next investigated as a consequence of cellular media priming and substrate coating. Specifically, ‘raw materials’ such as chondroitin sulfate and aggrecan in the culture medium outperformed growth factors in chondroinductive gene expression and collagen production, thus producing chondromimetic cellular aggregates. In vivo studies demonstrated the feasibility and efficacy of cellular aggregate technology with two different cell densities and combining them with fibrin at the defect site. In the Sprague-Dawley rat knee, implants with higher cell density aggregates received higher morphology scores, better immunohistochemistry staining, and demonstrated the best defect filling compared to the fibrin-alone group. Moreover, this thesis has taken the cell-aggregate technology from an in vitro proof of concept study to a translational in vivo animal model, thus opening new avenues of investigation for further refinement of the technology. The important next steps will be to characterize the mechanical properties of the scaffolds in an in vivo model, and further explore the regenerative-potential of the stem cell aggregates in a large animal model.