Arthritis is a degenerative pathology affecting one in five adults in the United States. In the temporomandibular joint (TMJ), displacement of the fibrocartilaginous TMJ disc is correlated with degeneration in the disc and surrounding joint components, and can progress to debilitating arthritis. While non-invasive strategies are first indicated, surgery may be necessary if function is lost and pain is not mitigated. In this case, the disc may be merely removed, due to lack of suitable disc replacements. Therefore, the global objectives of this work were 1) to elucidate mechanisms underlying TMJ disc displacement and degeneration, and 2) to employ a clinically relevant cell source to engineer biochemically and biomechanically robust neocartilage to address pathologies of the TMJ.

Toward addressing these objectives, this thesis 1) characterized native TMJ discal attachments and pathologic TMJ discs, 2) investigated alternative cell sources for engineering mechanically and biochemically robust neocartilage, 3) engineered a cartilage spectrum using clinically relevant costochondral cells, and 4) developed a neocartilage implantation method in a large animal model for TMJ disc degeneration.

The results of this work include proposed mechanisms regarding TMJ dysfunction, generation of functional costochondral cell neocartilage, and development of an in vitro and in vivo large animal model for disc degeneration. Regarding joint dysfunction, anterior disc displacement was suggested to be associated with weakening of both the posterior and lateral attachments, while partial lateral displacement was suggested to be associated with weakening of the lateral attachment. In a case study of Panthera tigris TMJs, it was demonstrated that in the presence of severe joint degeneration, structure-function relationships are compromised and the disc’s functional properties are reduced. Toward engineering cartilage for replacing pathologic disc tissue, three clinically relevant cell sources were investigated:​ marrow-derived stromal cells, expanded articular chondrocytes, and expanded costochondral cells. Inasmuch as costal chondrocytes represent a clinically relevant cell source that can potentially be employed in autologous treatments, these cells were carried forward to generate a cartilage spectrum. Appropriate biochemical and biophysical stimuli were then used to achieve neocartilage maturation, including a 300% increase in collagen content and a 320% increase in tensile strength over control. Ex vivo, in an intermediate zone defect model in the porcine TMJ disc, physical fixation via suture was used to enhance neocartilage stabilization, and, when combined with an enzymatic cross-linking regimen composed of lysyl oxidase, CuSO4, and hydroxylysine, led to a 4-fold increase in the interface shear modulus over control. In the culmination of this work, costochondral cell neocartilage achieved mechanical properties within range or exceeding those of the TMJ disc, specifically, a tensile modulus of 6 MPa and compressive instantaneous and relaxation moduli over 1200 kPa and 250 kPa, respectively. Finally, surgical feasibility in vivo was demonstrated, establishing the miniature swine as a suitable large animal model for TMJ disc degeneration. In this thesis, significant strides were taken toward elucidating mechanisms underlying TMJ disc displacement and degeneration, and toward generating functional cartilage to address disc degeneration.