This project explains a new approach towards processing Hydroxyapatite (HA) coating on polymeric substrates in general and PEEK (polyetheretherketone) in particular to improve tissue compatibility, enhance bone apposition and performance of the implant in the body. After many years of experience with coating various types of metallic substrates, we were asked by a well-known spine surgeon if we can deposit an HA coating on a polymeric substrates for application in spine implants. The question for us was how to coat a polymeric implant and heat treat the coating without damaging the substrate, considering the fact that the melting point of polymers is normally lower than the crystallization temperature of HA. We briefly explored methods to (a) deposit HA on PEEK with good bonding strength of the coating and (b) heat-treat it using different techniques without damaging the substrate. We have also explored the effect of an intermediate layer between the polymer and HA coating to further protect the substrate during the heat-treatment. We are pleased to report in this application that these efforts were successful in showing the feasibility of our approach. t is notable that we selected PEEK as our first candidate because it has a higher melting point compared to other polymers. Confirmation that we can successfully modify the surface properties of PEEK has given us confidence that we can adapt this approach to other polymers, including ultra-high molecular weight polyethylene. In this study we propose to produce the HA coating on polymeric implants using an Ion Beam Assisted Deposition (IBAD) at room temperature followed by a post deposition heat-treatment using microwave technique. The advantages of the proposed technology are: The coating is a thin and dense layer with high fracture resistance suitable for all sorts of biomedical devices and implants. The crystallinity of the coating can be controlled precisely through the novel heat treatment approach (proposed in this study). The microwave and laser techniques allow the heat to be focused in a small thickness of the film without any damage to the polymeric substrate. At the same time, depositing the coating at room temperature will eliminate any potential thermal degradation of the polymeric implant. The chemical composition of the coating can be precisely controlled. The presence of the thermal barrier coating layer between the HA and substrate will further protect the substrate from any excessive heat and thermal degradation. It will also help the nucleation of HA crystals during heat-treatment expediting the process. Both early and long-term bone responses will be assessed in a rabbit model. The proposed study investigates a new technique for coating polymeric devices that can have a great impact on the development of the next generation of polymeric implants and a significant innovation in biomedical coating technology. It has the potential to dramatically enhance the feasibility of using low-modulus polymers in applications that were previously considered impractical because of concerns over the poor tissue integration of uncoated materials.
Polymers offer significant advantages over metals and alloys for many biomedical applications. Although polymers are widely used for articulating surfaces, their use as fixation surfaces is complicated by the fact that they tend to incite fibrous rather than osseous ongrowth in vivo. The proposed study investigates a new technique for coating biomedical polymers with a hydroxyapatite coating to facilitate early bone ingrowth and accelerated implant fixation. The safety and efficacy of this new HA coating will be determined in vitro and in vivo using PEEK as the test substrate. From a clinical perspective, successful development of a bioactive and mechanically robust coating on biomedical polymers has the potential to dramatically enhance the use of these materials in orthopedics, spine surgery and dentistry.