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A study to assess the biocompatibility and how well a new form of coated titanium implant can spur on bone growth has been carried out using a range of techniques including Raman spectroscopy, microcomputer tomography, scanning electron microscopy, atomic force microscopy, and energy dispersive X-ray analysis. Tissue engineering scaffolds that can stimulate bone cell growth (osteogenesis) are being investigated as one way to create implants that are more like living bone than conventional alloy implants. Such materials should be incorporated more naturally into the implant site and also have a much-reduced risk of being rejected by the body's immune system. Now, Marco Lopez-Heredia, Jerome Sohier, Sophie Quillard, and Pierre Layrolle of INSERM at the University of Nantes, Cedric Gaillard of the Centre for Technology Transfer in Le Mans, and Michel Dorget of INRA also in Nantes, France, have investigated the osteogenic properties of a new implant material. The material is porous titanium coated by electrodeposition with calcium phosphate and is produced in an appropriate shape and form using rapid prototyping. Titanium is commonly used in the manufacture of orthopaedic and dental devices used where load bearing is necessary. However, titanium is a heavy metal, whereas the bone it replaces is a highly porous living composite tissue. As such biomedical researchers are keen to find materials that behave more like real bone so that there is a reduced likelihood of stresses at the interface between bone and implant causing a break. Given titanium's long history in this area, the obvious next step would be to use a highly porous version of the metal that would retain some of the mechanical properties of the solid metal but behave more like porous bone in other respects. The French team turned to rapid prototyping, sometimes known as 3D printing, which can produce a designed object using computer aided design (CAD) software from a given material. The resulting titanium scaffolds had a porosity of around 50% and a pore size of almost 1000 micrometres, which are very close to the theoretical CAD design values. The researchers have also side-stepped conventional high-temperature deposition techniques to apply a calcium phosphate coating to their designer porous titanium by using an electrochemical method. The resulting coating consists in carbonated hydroxyapatite and bonds well to the surface of the porous titanium. The result, revealed by MicroRaman spectrometer at an excitation wavelength of 514 nanometres, is a much more even coating throughout the titanium's network of pores. By coupling this coated, porous titanium with mesenchymal stem cell technology for generating the necessary bone marrow cells the team was able to use the scaffold to generate a final product closely resembling living bone in many ways. The rat bone marrow cells (RBMC) seeded on the coated titanium scaffold proliferate rapidly and colonize the entire porous network. The team have now demonstrated how well their scaffold can act as a support for controlled production of rat bone marrow cells over a period of just three days. An Alamar Blue Assay revealed little difference between cell growth in the coated and uncoated control material. However, four weeks after actual implantation into dorsal subcutaneous pouches of syngenic, or genetically identical, rats, showed much greater osteogenic activity with the coated implant. "This study opens up the possibility of using high strength porous scaffolds with appropriate osteoconductive and osteogenic properties to reconstruct large skeletal parts in the maxillofacial and orthopaedic fields," the researchers say. Such a material will not only have applications in hip replacements and dental surgery, but could be used to reconstruct large bone defects caused by cancer radiotherapy, or the progression of osteoporosis. Related links:
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Layrolle, constructing bone-building scaffolds |
