Development and characterization of peptide nanofibers for cartilage regeneration

Abstract

Articular cartilage is a tissue that is continuously exposed to cyclical compressive stresses, but exhibits no capacity for self-healing following trauma. Cartilage has a dense extracellular matrix that is sparsely populated with cells, and the whole tissue lacks blood and lymphatic vessels, which complicates the cell infiltration response that ordinarily occurs during inflammation. In addition, the only cell type capable of synthesizing new cartilage matrix lies deeper in the tissue, near the bone boundary, and due to the dense extracellular matrix, chondrocytes cannot migrate to the defect site following injury. Consequently, cartilage tissue cannot effectively respond to treatment options. Treatment options exist for the short-term reduction of pain in smaller defects, but larger injuries necessitate tissue donation, and there is a severe shortage of articular cartilage that can be donated for autografting. Microfracture and autologous chondrocyte implantation are the current treatment options that use cellular therapy for the repair of cartilage. However, the cartilage tissue that forms in the course of these treatments is not the functional hyaline cartilage, but rather fibrous cartilage, which is mechanically weaker and degenerates over time. Tissue engineering studies using biodegradable scaffolds and autologous cells are gaining importance as effective long-term treatment options for the postinjury production of hyaline cartilage. Such scaffold systems are designed to be biodegradable and bioactive, which allows them to induce new tissue formation in shorter periods of time. In this dissertation, peptide nanofibers mimicking glycosaminoglycan molecules, which are important constituents of cartilage extracellular matrix, are designed and the effectiveness of these materials in terms of chondrocyte differentation are tested under in vitro conditions. As a follow-up study to in vitro experiments, the capacity of bioactive peptide nanofibers to support cartilage regeneration is evaluated in the rabbit osteochondral defect model. Structural and mechanical properties of newly deposited cartilage are highly dependent on the quality and quantity of its extracellular matrix, which also has a major impact on the integration of replacement cartilage into the surrounding healthy tissue. Signals provided by bioactive peptide nanofibers to cells at the defect site can strongly alter the quality of the newly synthesized extracellular matrix. Consequently, we designed glycosaminoglycanmimetic peptide nanofibers that closely imitate the structure of the native cartilage extracellular matrix and demonstrated that these nanofiber networks are able to induce the synthesis of collagen II and aggrecan molecules, which are the main constituents of cartilage tissue, during chondrogenic differentiation.