Date of Award
Master of Science (MS)
The thesis constitutes the studies about the two aspects of tendon and ligament tissue engineering: regeneration and maturation. Injuries to tendon and ligament are among the most common injuries to the body, particularly in the young and physically active population. Associated with the problems of incomplete healing and recurrent injury, these injuries are not only responsible for large health care cost, but also result in lost work time and individual morbidity. Tissue engineering holds promise in treating these conditions by replacing the injured tissue with engineered tissue exhibited similar mechanical and functional characteristics. Collagen plays a central role in tendon and ligament regeneration, as collagen type I is responsible for more than 60% and 80% of the dry weigh of tendon and ligament structures, respectively. The hierarchical organization of collagen type I in bundles confers most of the mechanical properties of tendons and ligaments. Consequently, tendon or ligament tissue engineering studies are mainly focused on seeding cells into collagen gels. However, up to now, no cell-collagen constructs have been able to achieve sufficient mechanical properties and the complex architecture of the tendon and ligament is never fully reproduced. A major cause for low mechanical property of regenerating tendon or ligament is the slow maturation. The maturation of the engineered tissue is dominated by the maturation degree of extracellular matrix, such as collagen crosslink density. To overcome the slow growth and maturation of tissue engineering grafts, one goal of this project is to accelerate the tissue maturation using gene therapeutics approach. Therefore, in the first part of this thesis, two different genes, lysyl oxidase (LOX) and decorin, were transfected into fibroblasts by retrovirus infection. LOX initiates the covalent cross-linking of collagen and elastin in the extracellular space by oxidizing specific lysine residues in these proteins to peptidyl α-aminoadipic-δ-semialdehyde (AAS). These aldehyde residues can spontaneously condense with vicinal peptidyl aldehydes or with ε-amino groups of peptidyl lysine to generate the covalent crosslinkages, which stabilizes and insolubilizes polymeric collagen or elastin fibers in the extracellular matrix. Decorin is considered a key regulator of matrix assembly because it limits collagen fibril formation and thus directs tendon and ligament remodeling due to tensile forces. In this study, we found that the mechanical property of the tissue-engineered grafts was significantly increased by over-expressing LOX or decorin gene. And decorin over-expression uniformed the mean diameter of the collagen fibers. In the second part of this thesis, ECM-based hydrogel system was used to control the delivery of chemotaxic growth factors, such as hepatocyte growth factor (HGF), for recruiting endogenous stem cells. This approach was used to attract endogenous stem cells to the lesion site for tendon or ligament regeneration. In this study, we found that stem cells could be recruited effectively to the local site where HGF were released by chemically modified hyaluronic acid (HA) and gelatin (Gtn) based hydrogels both in vitro and in vivo.
Zhao, Jing, "Tendon and ligament repair: regeneration and maturation" (2008). All Theses. 335.