(505e) Solution Deposited Hydroxyapatite Coatings for Titanium Based Orthopedic Implants Conference: AIChE Annual MeetingYear: 2019Proceeding: 2019 AIChE Annual MeetingGroup: Materials Engineering and Sciences DivisionSession: Biomaterials in Industry and the Clinic Time: Wednesday, November 13, 2019 - 2:24pm-2:42pm Authors: Kasinath, R., DePuy Synthes Joint Reconstruction Vass, S., DePuy Synthes Joint Reconstruction Smith, B., DePuy Synthes Joint Reconstruction text-align:center;line-height:110%"> line-height:110%;font-family:" times new roman>Solution deposited hydroxyapatite coatings for titanium based orthopedic implants text-align:center;line-height:110%"> 110%;font-family:" times new roman>Rajendra Kasinath, Stephanie Vass, Bryan Smith text-align:center;line-height:110%"> 110%;font-family:" times new roman>DePuy Synthes Joint Reconstruction, Warsaw, IN 46581, USA 110%"> Introduction: Hydroxyapatite (HA) coated implants have been shown to promote biological fixation (bone in-growth and periprosthetic defect bridging) in numerous animal studies. [1-2] While plasma sprayed HA (PSHA) implants have gained widespread clinical acceptance for use on coated hip stems, acetabular cups and tibial and femoral knee components in cementless arthroplasty, they are not optimal for complete coverage on porous metal substrates given line-of-site limitations. To address this need, there have been attempts to solution deposit HA employing wet chemical techniques. However, solution deposition of HA is highly challenging considering its narrow thermodynamic window between heterogeneous and homogeneous nucleation and growth. "Biomimetic" processes have attempted to address other deficiencies in PSHA coatings (lack of phase purity, residual grit blast media), and while these processes are described to deposit "bone-mineral-like" HA films, they generally take days to complete and are too slow to be commercially viable. In this work, we report a solution deposited HA process that is tuned for preferential heterogeneous nucleation and growth on a substrate as opposed to homogeneously in solution. Methods: Prior to deposition, substrates were etched in a caustic solution to increase substrate surface area. Solution/ surface conditions (pH, temperature, ionic strength, surface roughness) and hydroxide etch were optimized and translated into design controls to enable full scale processing on porous metal implants. Coating morphology was characterized by scanning electron microscopy. X-ray diffraction and Rietveld analysis were employed to study composition and structure. As-coated porous cylindrical implants with 8 mm endcaps (6 mm x 6 mm diameter, 1 mm gap) were tested in a canine gap model, where HA-coated, porous-coated titanium specimens were compared to titanium porous-coated controls. Specimens (n= 6 per group) were implanted in the proximal humerus using a randomized design and histologically evaluated after 6 weeks. Results: A typical coating sequence was between 4-6 hours. Representative coatings were conformal, ~8 µm thick and consisted of highly oriented HA spherulites growing on the substrate surface (Figure 1a). X-ray diffraction indicated that the coating preferentially exhibited c-axis growth (Figure 1b). Coating composition was phase-pure crystalline HA but Rietveld analysis revealed amorphous content that was likely poorly diffracting grain boundaries. Solution deposited HA coated porous metal implants tested in a canine cancellous bone-plug model demonstrated improved bone in growth within the porous coating (Figure 2) versus bare titanium controls. 0in;margin-left:60.75pt;margin-bottom:.0001pt;text-indent:-.25in">(a) (b) Figure 1 (a) Micrographs showing conformal HA coatings on a porous substrate (inset shows spherulitic c-axis growth), and (b) shows a representative X-ray diffractogram of the coating; preferred c-axis orientation is evident given the observed 002 peak intensity compared to 211. Figure 2 (Right) Bone ingrowth for bare titanium versus solution deposited HA coated gap-fit implants, (left) cross-sectional histology slice with ROIs to measure % bone area fraction. Conclusions: Solution deposited HA coatings were successfully deposited on porous metal implants using a commercial-scale system. Morphology and structural characterization revealed coatings consisted of HA spherulites and did not contain other crystalline phases. Animal study results suggested that these coatings, using a gap-fit model, showed substantially more bone in-growth compared to bare metal implants. References: 1. Søballe K., Acta Orthop. Scand., 2003; 64:1-58. 2. Vasudev D.V., Ricci J.L., Sabatino C., Li, P., Parsons, J.R. J Biomed Matls. Res. Part A, 2004;69:629-636.