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The proportion of people aged 65 and over will increase rapidly in the near future. Degeneration of load-bearing bones in the elderly, and traumas from sports injuries and other accidents, often require the inception of bone substitutes. In Australia, the incidence of knee and joint replacement surgery in 2002/2003 was 280 per 100,000 population, or a total of almost 56,000 procedures (Australian Orthopaedic Association National Joint Replacement Registry, 2004 Annual Report). This incidence is increasing (Figure 1). A significant proportion of these patients will require revision or replacement of their joint prostheses within 10 years because of loosening or failure of the prosthetic implant - 13.1% of hip replacements are revision procedures, while knee revision procedures account for 9.3% of all knee replacements.
Figure 1 - rate of joint replacement surgery in Australia, 1994/5 to 2002/3 (Source: Australian Orthopaedic Association National Joint Replacement Registry, 2004 Annual Report)
Joint replacement surgery cost the Australian health system almost $400 million in 2001/2, with over 60% of this cost being the cost of the prostheses themselves (Figure 2). These figures do not include the costs of allogeneic bone grafts, which are used to repair defects in revision operations at an average cost of around $1,500 per procedure.
Figure 2 - Annual cost of Joint Replacement Surgery in Australia (Source: Australian Orthopaedic Association National Joint Replacement Registry, 2004 Annual Report)
When placed in the international context, it is clear that joint replacement surgery and the development of joint prostheses are multi-billion dollar industries, and the development of improved prosthetics has enormous commercial as well as health value. In particular, a bone substitute that reduces the requirement for revision operations would have significant implications for health expenditure, and for the wellbeing of patients. In addition, bone and cartilage prostheses have many other applications in orthopaedic as well as plastic surgery practice.
Research in this area is receiving increasing attention globally. Various artificial bone substitutes, such as metals, polymeric materials and ceramics, are being explored to replace the diseased or damaged bones. However, the existing metallic bone substitutes are dense and suffer from the problems of adverse reaction, biomechanical mismatch and lack of appropriate space for the in-growth of new bone tissues and vascularization; shortening the lifetime of the bone substitutes. Also, polymeric scaffold materials are too weak to sustain the cyclic loading during the healing process. In both cases, though, the metals group at Deakin has developed improved approaches. When combined with the broader expertise at Deakin in surface modification and the new insights in cell engineering provided by the research team at Barwon Biomedical Research, there is a major opportunity to create new products with significant commercial potential. There are also other areas for collaborative development related to new stem cell lines and the development of cartilage.
Where the scaffold and tissue are not in a load-bearing situation, polymers and fibres are the appropriate substrates on which to engineer tissue. Nanofibres, with their large surface area, hold enormous promise in this regard. Deakin has established world-leading capability in the production of nanofibres by electrospinning, and will produce biocompatible, non-woven, textile substrates (incorporating microfibres as well as nanofibres) to develop products with Barwon Biomedical Research to replace soft tissue such as cartilage.
Scaffold functionality will be enhanced through, for example, surface treatments (including cold plasma treatment of fibres), changes in surface topography, enhancements of biocompatibility, and the incorporation of slow release drugs. The ultimate aim is to develop clinically useful bone and cartilage products or prostheses derived from a combination of novel materials science developments with a new approach to the in vitro growth of autologous bone and cartilage precursors. It is anticipated that seeding scaffolds with such cells will enhance integration of the product/prosthesis with existing bony structures, avoiding some of the medium and long term complications of existing technologies, such as loosening and avulsion of the prosthesis.