Tissue engineering hypertrophic cartilage for bone regeneration

• Main Author: Bardsley, Katie
• Other Authors: Crawford, Aileen ; Hatton, Paul ; Brook, Ian
• Published: University of Sheffield 2014
• Subjects: 617.6
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.617173

The repair of complex bone defects remains a surgical challenge and it is hoped that tissue-engineering may offer an unlimited source of bone tissue and circumvent many of the drawbacks associated with current clinical approaches. Currently, the majority of bone tissue-engineering research has been focused on the differentiation of mesenchymal stem cells (MSCs) into osteoblasts. Tissue-engineering via the endochondral ossification pathway to prepare a hypertrophic cartilage graft, however, may be a more advantageous approach. This tissue is able to survive the relatively low oxygen tensions found in defects and it may provide growth factors that promote angiogenesis and bone tissue regeneration. Surprisingly little research has been directed at hypertrophic cartilage engineering. The aim of this project was therefore to investigate the ability of nasal chondrocytes to form a hypertrophic cartilage graft capable of regenerating bone tissue in vivo. The methodology used in this study was based on the typical tissue-engineering approach and encompassed scaffold fabrication, tissue characterisation and in vivo studies. Rat nasal chondrocytes consistently differentiated to form hypertrophic cartilage grafts on both PGA and PLLA/calcium phosphate scaffold materials. These grafts expressed collagen type X and alkaline phosphatase, co-located with large chondrocytes, in a tissue that had morphological features in common with hypertrophic cartilage. Gene and protein expression studies demonstrated a decrease in hyaline cartilage markers and an increase in markers for hypertrophic chondrocytes as differentiation proceeded. Vital and decellularised grafts cultured on the PGA scaffold material significantly increased bone regeneration in vivo when compared to empty defects (4mm) in the rat cranium. Decellularised grafts that were reseeded with MSCs also promoted significant bone tissue regeneration after 12 weeks. This regeneration, however, occurred at a slower rate compared to the other grafts evaluated. Foetal calf serum (FCS) was shown to have a significant effect on the differentiation of the rat nasal chondrocytes. A defined, serum-free medium was therefore developed which was able to support the hypertrophic differentiation of the chondrocytes. Finally proof of concept studies demonstrated the ability of a Quasi-vivo® bioreactor to support hypertrophic differentiation of nasal chondrocytes under flow conditions. It was concluded that nasal chondrocytes could be seeded onto scaffold materials and cultured under defined conditions to prepare a hypertrophic cartilage graft capable of stimulating bone tissue regeneration in vivo. The use of a decellularised hypertrophic cartilage demonstrated substantial clinical potential for use as a new regenerative graft material.