The temporomandibular joint (TMJ), or jaw joint, is one of the least understood and underresearched joints of the body. Responsible for the hinging motion of the jaw, correct TMJ function is critical to both talking and chewing. Integral to proper TMJ function is the presence of a biconcave fibrocartilaginous disc situated between the articulating surfaces of the TMJ. This disc serves the role of enhancing load distribution and providing shock absorption, similar to the functions of the menisci of the knee joint and the intervertebral discs of the spine. Unfortunately, the TMJ disc, like all fibrocartilaginous tissues of the body, is unable to repair itself following disease- or injury-induced degradation associated with temporomandibular joint disorders (TMD). While current clinical options can address the painful symptoms associated with early TMD, they are unable to prevent further degradation of the joint. It is, therefore, critical that long-term clinical treatments be established to address the approximately 10 million individuals affected by severe TMD in the United States alone.

Tissue engineering approaches may offer new hope for those suffering from severe TMD. Motivated by the potential of tissue engineering, this thesis had two global objectives:​ 1) to develop and optimize a biomimetic TMJ disc neotissue to repair or replace discs damaged by early TMD, and 2) to identify a treatment modality that promotes neotissue maturation and fosters integration between self-assembled neofibrocartilage and native TMJ disc tissue. Toward the first goal, while compressive properties of neofibrocartilage constructs have previously been promoted to reach native tissue values, their tensile properties severely lag behind. Thus, this thesis sought to tailor the use of exogenous agents to promote TMJ disc-specific extracellular matrix organization in engineered fibrocartilage. To begin, a treatment regimen consisting of the biophysical agent chondroitinase-ABC (C-ABC) and the biochemical agent transforming growth factor-β1 (TGF-β1) was optimized to enhance the functional properties of self-assembled neofibrocartilage constructs. This optimized regimen of bioactive agents was then combined with biomechanical stimulation via passive axial compressive loading to drive the in vitro development of self-assembled, TMJ disc-shaped neotissues toward attaining the anisotropic functionality of the native disc. Finally, the passive axial compressive loading mechanism was further optimized to drive tissue-specific matrix organization and, thus, functional anisotropy in TMJ disc-shaped neotissues.

Toward the second goal of this thesis, achieving integration between native fibrocartilage and engineered repair tissues is a significant challenge, as the wound edges of fibrocartilaginous defects are metabolically inactive, greatly hindering integration. Integration, however, is critical to graft success, as it ensures that the implant remains stabilized and is, therefore, able to competently function in vivo. To address this challenge, the bioactive agent regimen previously developed was combined with exogenous application of the enzyme responsible for collagen crosslinking, lysyl oxidase (LOX), on neofibrocartilage constructs. The combination of LOX+CABC+TGF-β1 was found to synergistically enhance the tensile properties of engineered neofibrocartilage to values on par with native tissue. Further, translating this technology to both an in vitro and in vivo fibrocartilage defect model found this combination pre-treatment to prime the neofibrocartilage constructs for significantly enhanced integration potential with native TMJ disc neotissue. Specifically, the tensile properties of the integration interface achieved in vivo were on par with intact native fibrocartilage properties.

Overall, through 1) engineering a biomimetic, functionally anisotropic TMJ disc-shaped neotissue and 2) establishing novel methods to promote neofibrocartilage integration, this thesis provides a foundation toward achieving a clinically relevant repair tissue to help treat TMD before they compromise a patient’s entire joint. Further, methods developed in this study have the potential to be translated toward development of other clinically relevant tissues to aid patients suffering from any type of fibrocartilage pathology