Articular cartilage degeneration, due to injury and osteoarthritis, is an irreversible disease condition with existing treatment options. Damaged cartilage in the patellofemoral and temporomandibular joints are met with unsatisfactory treatment options that often fail to halt the disease progression. Tissue engineering aims to solve this unmet need by engineering a functional replacement tissue as well as by promoting a healthy regenerative environment within the damaged joint. A key component in engineering neocartilage with such properties is the cell source. Costal chondrocytes of the rib cage have recently been recognized for their ability to form robust cartilage implants. However, clinical translation of this cell source is still hindered because mechanical properties of the engineered implants need to be improved, and treatment with the engineered implant needs to be demonstrated in an appropriate preclinical model. Toward translating tissue engineering technologies to clinical applications, the global objectives of this research are:​ 1) to engineer biomimetic cartilage implants from costal chondrocytes, through the development of mechanical stimulation techniques, and 2) to evaluate the safety and efficacy of engineered cartilage implants orthotopically in a relevant large animal model.

To address these objectives, this research 1) confirmed costal chondrocytes, of non-articular cartilage origin, to be appropriate for use in articular joints, 2) designed and developed compressive stimulation regimens that improved the compressive properties of neocartilage, 3) designed and developed tensile stimulation regimens that enhanced the tensile properties and anisotropy of neocartilage, and 4) investigated the safety and efficacy of neocartilage in healing an orthotopic defect in a minipig model.

Costal chondrocytes were confirmed to be suitable for articular cartilage tissue engineering. Costal cartilage is densely populated with chondrocytes, rendering a good donor source of cells. Neocartilage derived from passaged costal chondrocytes, through the self-assembling process, were cohesive and robust. When compared to the native articular cartilage of the patellofemoral joint for their potential as a replacement tissue, the implants exhibited 45% of native cartilage salient properties. These results indicated that costal chondrocytes are suitable for articular cartilage tissue engineering, with the potential for further improvement with mechanical stimulation.

Neocartilage derived from costal chondrocytes was shown for the first time to respond to mechanical stimulation, in particular, the passive axial compressive stimulation. During the self-assembling process, neocartilage in the matrix synthesis phase and maturation phase are amenable to passive axial compression, providing flexibly in the timing of the stimulation. When compressive magnitude was examined, 3.3 kPa and 5 kPa were found efficacious in improving neocartilage compressive properties. Stimulation with a higher magnitude was found ineffective. Neocartilage tensile properties were improved through the application of a bioactive regimen (TGF-β1, chondroitinase ABC, and lysyl oxidase like 2). This work demonstrated that mechanical and bioactive stimuli are both critical in creating mechanically robust neocartilage from costal chondrocytes.

Further improvements in tensile properties were achieved with tensile stimulation. A beneficial tensile stimulation regimen has not been achieved in prior studies;​ this work showed for the first time that tensile stimulation, especially continuous tensile stimulation, was highly effective in creating neocartilage with native tissue-like tensile properties. Anisotropy was also achieved with this stimulation. Therefore, this research contributed significantly toward overcoming two of the major challenges posed by cartilage tissue engineering. The examination of this regimen in a human chondrocyte-derived neocartilage also showed that tensile stimulation was beneficial toward neocartilage development and mechanical robustness, demonstrating the translation potential of this stimulation regimen.

Finally, robust neocartilage implants, derived from costal chondrocytes and improved through mechanical and bioactive stimuli, showed safety and efficacy when examined orthotopically in a large animal model. A novel surgical technique, called the intra-laminar fenestrated technique, was successfully developed and implemented to model TMJ disc thinning in vivo. Neocartilage implants, of allogeneic origin, did not provoke any adverse immunological response from the host. They were effective in promoting repair tissue formation in the defect and integration between implant and native tissue, resulting in closing and healing of the defect.

Overall, this research made strides in bringing tissue engineered neocartilage implants from a clinically relevant cell source toward a translational pathway. The successful engineering of implants and demonstrated treatment of an orthotopic defect established the foundational work for future preclinical studies. With further research, scaffold-free tissue engineered implants could significantly widen clinical treatment options for patients suffering from patellofemoral and temporomandibular joint degeneration.