Micro- and nano-patterning of titanium surfaces for optimal osseointegration of orthopaedic implants

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Currently, orthopaedic surgeons are limited to the type of materials they can use in load bearing joint replacements (e.g. knee and hip) due to the need to support the weight and function of the body. Commonly used are titanium (Ti) and its alloys. Such procedures, however, have a limited lifespan due to a combination of lack of direct bone contact with the metal exacerbated by soft tissue formation; this allows micromotion and ultimately failure. Surgeons face a mounting pressure due to firstly an aging population (in the developed world in 1950, there were 9.3 people under 20 for every person over 65, by 2025 this ratio is forecast to be 0.59 people under 20 for every person older than 65) and associated problems of rheumatoid arthritis and secondly a more sports active younger populations and problems associated with osteoarthritis. Due to the present lifespan of these procedures (The 10 year failure rate for revision hip surgery was 26% in a Norwegian study of 4762 operations) patients will have to wait longer with pain before surgeons will consider operations. The metals are hard to work with due their material properties and so success to date with surface treatments to encourage direct bone growth and hence develop implants for life have been limited.We have recently demonstrated that specific nanoscale cues in the topography of a material surface can mean the difference between stem cell differentiation to bone and stem cell differentiation to fibrous tissue. Furthermore, we believe that this is merely an introduction to the range of effects obtainable through nanoscale design. That such small alterations in the material surface can have such large effects on stem cells makes it clear that nanoscale design could have significant impact in the rational design of orthopaedic biomaterials. Crucial issues for the development of 'intelligent' orthopaedic biomaterials such as bioactive load-bearing stems are: (1) ability to pattern into suitable materials (e.g. Ti) this has not previously been achieved other than using non-specific and random roughening, (2) achieving both mechanical interdigitation (microfeatures) and direct bone bonding (nanocues and microcues) and (3) generating prototype designs using this technology, which will permit the scale-up and development by industry thereby significantly impacting and benefiting patient health.