Extracellular matrix characterization and tissue engineering of the temporomandibular joint disc
Almarza, Alejandro Jose
Athanasiou, Kyriacos A.
Doctor of Philosophy thesis
The temporomandibular joint (TMJ) disc is a specialized fibrocartilaginous tissue located between the mandibular condyle and the glenoid fossa-articular eminence of the temporal bone. It has been observed that up to 70% of patients with temporomandibular joint disorders (TMDs) suffer from displacement of the disc. When the displaced disc becomes an obstacle to movement and degeneration is severe, surgeons have no choice but to replace the disc with various allopastic or biological materials. Tissue engineering may provide a better alternative for discectomy patients. Toward this end, the work described in this thesis provides a systematic approach for tissue engineering the TMJ disc. Initial studies first characterized the biochemical composition of the porcine TMJ disc. It was determined that the majority of the porcine TMJ disc matrix is collagen, while glycosaminoglycans are present in small quantities. Once this biochemical standard was established, an appropriate scaffold composed of poly(glycolic) acid (PGA) non-woven meshes for TMJ disc tissue engineering was identified. Dynamic spinner flask seeding was determined to be the most effective method for seeding TMJ disc cells on PGA, based on an increased production of collagen. The addition of two growth factors, whether insulin-like growth factor-I (IGF-I), basic fibroblast growth factor (bFGF), or transforming growth factor-beta1 (TGF-beta1), at high concentrations of 100 ng/ml for IGF-I and bFGF and 30 ng/ml for TGF-beta1, improved the cellularity of constructs after six weeks in culture, but did not improve matrix production. Ascorbic acid concentration was found to be an important factor affecting attachment of passaged TMJ disc cells onto PGA. A concentration of 25 mug/ml of medium was observed to be more beneficial than no ascorbic acid and 50 mug/ml of medium. A high cell seeding density of 75 million cells per ml of construct produced twice more collagen than previous attempted seeding densities. In the last portion of this work, the effects of hydrostatic pressure were examined as part of an in vitro tissue engineering approach. A constant hydrostatic pressure regimen of 10 MPa for 4 hrs was shown to increase collagen expression in 2D and 3D, and increase collagen production. Surprisingly and perhaps counter-intuitively, an intermittent exposure of the hydrostatic pressure regimen at 1 Hz was observed to be detrimental to TMJ disc cells. The results of this work established general criteria, both in terms of biochemical and biomechanical factors, toward addressing the complex problem of regeneration of the TMJ disc.