In-situ Control of the Nanostructure of Hydroxyapatite Coatings for Biomedical Implants

Faculty Mentor - Dr. Renato Camata
Fig. 2 - Atomic Force Microscopy image of the surface of a typical HA coating deposited on titanium alloy by pulsed laser deposition.

Calcium phosphate coatings consisting primarily of crystalline hydroxyapatite (HA) [Ca10(PO4)6(OH)2] are commonly deposited onto orthopedic and dental metallic implants to speed up formation of bone around the implant devices. Pulsed laser deposition (PLD) is one of the means of placing a thin HA coating on these implants as it allows control over chemistry and structure of the coating. However, the multiple excitation pathways resulting from the laser-target interaction during PLD lead to a complex initial state of interacting ions, clusters, nanoparticles and droplets. The relative importance of these various constituents has not been established for HA deposition. Atomic force microscopy (AFM) images of typical HA coatings deposited by PLD reveal a high density of nanoscale objects whose origin is not well understood (see Fig. 2). A significant fraction of these objects is likely to nucleate and grow in the ablation plume and subsequently become a determining factor of the nanoscale morphology and phase make-up of the final coating. This, in turn, is certain to affect the biocompatibility of the film. In this ten-week project, an undergraduate student will deposit HA coatings by PLD and perform in-situ size distribution measurements using a Low Pressure Differential Mobility Analyzer. Size distributions measured in-situ with the Differential Mobility Analyzer will be correlated with x-ray diffraction, AFM images (such as the one shown in Fig. 2), and transmission electron microscopy to establish the role of nanoparticles in PLD of HA and how they impact the nanostructure of the films. NSF has recently funded a Major Research Instrumentation Grant (DMR#0116098) for a PLD facility at UAB, which was commissioned in summer 2002. Two of the first users of this facility were undergraduate students in the summer 2002 REU program (Andreece Richardson, Jennifer Kirchhoff) who are currently preparing their results for presentation at the MRS and NCUR meeting in 2003 [7,8].