FT-IR imaging spectroscopy of genetically modified bovine chondrocytes

Repair of articular cartilage defects remains a challenging problem in orthopaedic surgery. Although novel tissue engineering technologies have facilitated the synthesis of cartilage-like tissue for implantation into defect sites, questions persist as to how to best evaluate the integration of these matrices into cartilage and to assess their capability for regeneration and repair of the tissue. In the current study, Fourier transform infrared imaging spectroscopy (FT-IRI) was utilized to study compositional changes in genetically modified bovine chondrocytes. With this technique, it was possible to evaluate the integration of the newly formed matrix into the articular cartilage substrate, and the content and distribution of the collagen and proteoglycan components in the repair tissue compared to native articular cartilage. Bovine chondrocytes were treated with an adenovirus (Ad) vector encoding bone morphogenetic protein-7 (AdBMP-7), transplanted onto bovine cartilage explants in vitro and the matrix evaluated by FT-IRI after 3 weeks of growth. Data were acquired from a 400×400-μm region of a histological specimen at 7-μm spatial resolution. FT-IR images were created based on collagen and proteoglycan content. It was apparent from these images that the AdBMP-7-treated chondrocyte matrix produced significantly more proteoglycan compared to both naı̈ve chondrocyte matrix, and to native bovine articular cartilage. However, the distribution of proteoglycan was very heterogeneous. In contrast, there was significantly less type II collagen in both AdBMP-7 and in naı̈ve chondrocyte matrix compared to the articular cartilage substrate. Overall, the new information obtained by FT-IR imaging spectroscopy will facilitate in design of new materials for cartilage regeneration and repair.