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Realignment: ENHANCING IMPLANT PERFORMANCE THROUGH STRUCTURAL REARRANGEMENTS IN HYDROXYAPATITE

Final Report Summary - REALIGNMENT (Realignment: ENHANCING IMPLANT PERFORMANCE THROUGH STRUCTURAL REARRANGEMENTS IN HYDROXYAPATITE)

The project Realignment directed attention to improve the characterization and functionality of calcium phosphate implants for regenerative medicine. In the past, materials have been used as fillers to restore the load bearing ability of bone, with the latter trend to improve integration. The use of calcium phosphates has relied on the intrinsic biocompatibility of the mineral phase of bone, but did not address means of improving the functionality. This project has made a significant contribution to the field of calcium phosphates with a new characterization method, a new in-situ process for imparting a surface charge to implants and a new processing strategy for calcium phosphates.

For a century, reports in scientific publications have noted temperature-induced changes in hydroxyapatite, but the degree of change has remained unexplored. There is one ion in the structure of hydroxyapatite that is sensitive to heating and is the most difficult to detect. A new technique has been developed for quantifying the hydroxyl ion content – an indicator of the apatite composition and thermal processing history. A very small hydroxyapatite sample mixed with an active agent causes a discernable change on heating that is directly related to the hydroxyl content. Orthopaedic implant manufacturing companies have a new process that may be included in the quality control of hydroxyapatite implants.

Quality control testing of the OH content involves three stages and is easy. Firstly, the hydroxyapatite implant is crushed and then mixed with the active agent. Secondly, about 50mg of the powdered mixture is heated to 800 oC for a thermal reaction. Thirdly, the weight loss is measured and represents the hydroxyl content. Sample preparation requires about 20 minutes, testing takes 90 minutes and the interpretation needs 10 minutes; a total time of 2 hours. Such fast processing provides rapid feedback to the implant company to track the processing of implants. Furthermore, the hydroxyl ion content can also be measured in an amorphous phase, but this requires further work for technology transfer to industry.

Currently available orthopeadic prosthesis with hydroxyapatite coatings have not been optimized, and may include a new and simple strategy developed in the Realignment project. Research findings have shown the importance of topography and a charged surface for improved bone response. We have patterned the surface with topographical features and added an in-situ charging strategy for imparting a charge. The coating is produced with a crystal alignment that maximizes the charge from the hydroxyapatite. This charge is confined to the outer layer where interaction takes place with the biological environment. The process is new, simple and cheap. Repeated in-vitro testing is presently being conducted, with results that can further be investigated in in-vivo studies and the clinical setting.

The outcome of this work a) contributes to the design of calcium phosphates, b) provides a new quality control tool to orthopaedic companies and c) offers a new strategy to optimize the performance of implants. The findings will interest the materials science research community, implant manufacturers, and surgeons (in orthopaedics, maxillofacial surgery and dentistry).

Additional landmarks from this project are:
• The first production of oxyapatite with a direct evidence of the outcome. A new method allows oxyapatite to be prepared in a day compared to several days by the previous attempts of others that produced lower purity oxyapatite.
• A new strategy for making nanosized alpha tricalcium phosphate, tetracalcium phosphate and peroxy-apatite.
At the socio-economic level for Riga Technical University, this project has illustrated the use of simple strategies for solving complex problems without the need of access to expensive equipment. The outcome of this Reintegration project will provide employment to the Marie Curie Fellow until December 2015 for implementing a new teaching program on biotechnology.