Growth factors may enhance current cartilage repair techniques via multiple mechanisms including recruitment of chondrogenic cells (chemotaxis), stimulation of chondrogenic cell proliferation (mitogenesis) and enhancement of cartilage matrix synthesis. Two
growth factors that have been studied in cartilage repair are
insulin-like growth factor (IGF) and
platelet derived growth factor (PDGF). IGF plays a key role in cartilage homeostasis, balancing
proteoglycan synthesis and breakdown. Incorporating IGF into a
fibrin clot placed in an equine cartilage defect improved the quality and quantity of repair tissue and reduced synovial
inflammation. PDGF is a potent mitogenic and
chemotactic factor for all cells of mesenchymal origin, including chondrocytes and mesenchymal stem cells. Resting zone chondrocytes cultured with PDGF demonstrated increased cell proliferation and
proteoglycan production, while maturation of these cells along the endochondral pathway was inhibited. Pretreating chondrocytes with PDGF promotes heterotopic cartilage formation in the absence of any mechanical stimulus. PDGF has also been shown to be a potent stimulator of meniscal cell proliferation and migration. These studies and others suggest a potential role for these potent
biological regulators of chondrocytes in cartilage repair. More work needs to be performed to define their appropriate dosing and the optimum delivery method. Combining tissue
growth factors with a
biological matrix can provide a physical scaffold for cell adhesion and growth as well as a means to control the release of these potent molecules. This could result in
biological devices that enhance the predictability and quality of current cartilage repair techniques.