Engineering stratified tissues for in situ cartilage regeneration.

다국어 초록 (Multilingual Abstract)

Patients suffering from cartilage damage due trauma or disease may benefit from biological replacements developed using tissue engineering techniques. Current tissue engineering strategies, however, often fail to restore the unique structural organization of the tissue leading to inferior function. Articular cartilage has a zonal architecture consisting of superficial, middle, and deep chondrocytes, followed by transition and integration into the underlying bone. The cell layers have different morphological, biochemical and mechanical properties, which are crucial to the physiological role of the tissue. Regeneration of the structural organization will be important to the success of cartilage tissue engineering.
The overall goals of this thesis were to engineer structurally organized cartilage and osteochondral tissues, study heterotypic cell interactions relevant to cartilage repair and homeostasis, and design a practical tissue engineering strategy that can be clinically applied. It was hypothesized that a scaffold that encourages the appropriate cell and matrix organization, and facilitates relevant cell-cell interactions, may improve the functional outcome of tissue engineered cartilage. Multi-layered hydrogels were developed using photopolymerization techniques to engineer cartilage with the zonal properties of the native tissue. Superficial, middle, and deep zone chondrocytes were isolated and encapsulated in respective layers of a tri-layered hydrogel. The polymerization conditions supported cell viability and matrix synthesis. Cell and matrix products were confined to their respective layers resulting in stratified, heterogeneous cartilage with similar zonal characteristics of the native tissue. Further coculture studies revealed that interactions between zone-specific cells affected the biological and mechanical properties of engineered cartilage. Specifically, superficial cells regulated deep cell proliferation and increased deep cell biosynthetic activity in a bi-layered hydrogel. The stratified cartilage constructs demonstrated greater mechanical strength compared to homogeonous cartilage constructs, implying potential benefits to isolating and organizing zonal chondrocytes for tissue engineering purposes.
A bi-layering technique was then applied to the engineering of osteochondral composite tissues. Chondrocytes were cocultured with bone-marrow derived mesenchymal stem cells (MSCs) or fully differentiated osteoblasts. In both cases, cartilage and bone like matrix were spatially maintained in the distinct layers. However, MSCs uniquely stimulated the chondrocytes in this coculture system, evidenced by increased production of proteoglycan and collagen type II. (Abstract shortened by UMI.).