Nano-Hydroxyapatite Coated Femoral Stem Implant by Electrophoretic Deposition
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0975-DD06-05
Nano-Hydroxyapatite Coated Femoral Stem Implant by Electrophoretic Deposition Heng Zhang, Jay Krajewski, Zongtao Zhang, Mark Masopust, and Danny T. Xiao Inframat Corporation, 74 Batterson Road, Farmington, CT, 06032-2597 ABSTRACT A nanostructural hydroxyapatite (HA) coating was deposited to a porous Ti6Al4V femoral stem implant using electrophoretic deposition (EPD) to improve the bond strength, healing speed, and durable service life. The nanostructure of HA and micro-pores created in the coating can enhance the bioactivity and increase the adhesion between the implant and hard tissue. In order to achieve homogenous HA coating on the stem implant with a porous surface profile, a compensation electrode was designed and prepared. Rotation of the implant was conducted during the coating process so that a uniform coating could be achieved. The EPD combined with a dip coating was used to compensate for the complex profile and led to a homogenous coating throughout both peak and valley areas. This developed coating process is able to deposit homogeneous HA coating on a complicated implant surface. Compared to the coating made by plasma thermal spray, the EPD HA coating can cover inner cores and exhibit a better adhesion and bioactivity. The EPD HA coating possesses significantly improved corrosion resistance compared to thermal spray HA coating. Most importantly, the biomechanical property was significantly promoted based on an in vivo animal test. INTRODUCTION Hydroxyapatite coating on the surface of orthopedic implants will increase the bioactivity, improve the blood coagulation, speed up the osteoblast growth and accelerate the patientís healing after implantation. However, a commercial plasma thermal sprayed HA coating experiences dissolution and cracking in body fluid due to forming amorphous phase during the rapid quenching, and the inability to coat the porous holes and inner surfaces of complicated geometry due to the inherent line-of-sight process of thermal spray. An electrophoretic deposition process, followed by a low temperature sintering, has been applied to deposit HA coatings on porous titanium alloy implants since 1990 [1]. The EPD possess is suitable for porous surfaces and complex shaped implants while maintaining a controllable grain size. However, sintering shrinkage cracking and Ti/HA interfacial reaction prohibited this process from further development and commercialization. HA coatings have been successfully deposited on porous Ti plates using this process. However, after a calcination (200-900 oC), it was found that severe cracking of the HA occurred because of thermal expansion mismatch [2-3]. A novel approach using a nanostructured HA (nano-HA) coating on titanium implants through the EPD process to improve the performance of the Ti alloy implants has been conducted [4-7]. A nano-HA coating with a grain size of ∼50 nm and micrometer sized porosities can provide higher surface bioactivity and osteoblast growth than conventional
micrometer sized HA coatings, leading to a significa
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