Nanostructured Apatites: The Next Generation of Bioactive Materials?

Serena Best
Department of Materials Science and Metallurgy, University of Cambridge,
Pembroke Street, Cambridge CB2 3QZ, UK
Email: smb51@cam.ac.uk

Bone is a composite on a number of different structural scales. At the macrostructural scale two morphologically distinct forms of the tissue may be identified in long bones; these are referred to as cortical and cancellous bone. On the microscopic level, a collagen-bone mineral composite is formed into densely packed concentric lamellar structures called osteons. At the ultrastructural level, bone contains both a nano-scale mineral component, apatite and an organic component, collagen. However, in spite of its elegant structure, bone suffers from a number of degenerative diseases and with an ageing population World-wide, there is an ever increasing need to find long term solutions for bone replacement.
Synthetic hydroxyapatite (Ca10(PO4)6(OH)2) has been of interest as an orthopaedic biomaterial for more than 30 years due to its chemical similarity to bone mineral. Bone will bond directly to the material in its pure, sintered form. One approach to bone repair has been to produce synthetic bone grafts with chemically substituted apatites to encourage more rapid bone attachment and, in particular, investigations in to effects on biological response of the incorporation of carbonate and silicate ions in the hydroxyapatite crystal lattice. This area of research has proved to be particularly successful with evidence of very rapid bone repair and the rapid formation of a synthetic-natural material composite.
We have continued to build on the ideas of biomimetic materials development and characterization and a number of projects are now on-going to produce bioactive and biodegradable composites. It has been found that the dimensions of the bioactive reinforcing phase can have a significant influence on the mechanical- and biological performance of the materials. There are a number of methods of applying bioactive coatings on metallic and polymeric biomaterials and the techniques that are available include vacuum plasma spraying, electrohydrodynamic atomization and RF magnetron sputtering to provide surfaces with a range of topographical and compositional characteristics.
This lecture will describe the ideas and research activities on-going in the area of substituted apatites and will explore the prospects for a new generation of orthopaedic biomaterials.