Laser processing of bioactive tricalcium phosphate coating on titanium for load-bearing implants

Laser-engineered net shaping (LENS(TM) a commercial rapid prototyping (RP) process, was used to coat titanium with tricalcium phosphate (TCP) ceramics to improve bone cell-materials interactions. During LENS(TM) coating process, the Nd:YAG laser melts the top surface of Ti substrate in which calcium phosphate powder is fed to create a TCP-Ti composite layer. It was found that an increase in laser power and/or powder feed rate increases the thickness of the coating. However, coating thickness decreased with increasing laser scan speed. TCP coating showed columnar titanium grains at the substrate side of the coating and transitioned to equiaxed titanium grains at the outside. When the scan speed was reduced from 15 to 10 mm s(-1) coating hardness increased from 882 +/- 67 to 1049 +/- 112 Hv due to an increase in the volume fraction of TCP in the coating. Coated surfaces showed uniformly distributed TCP particles and X-ray diffraction data confirmed the absence of any undesirable phases, while maintaining a high level of crystallinity. The effect of TCP coating on cell-material interaction was examined by culturing osteoprecursor cells (OPC1) on coated surfaces. The results indicated that TCP coating had good biocompatibility where OPC1 cells attached and proliferated on the coating surface. The coating also initiated cell differentiation, ECM formation and biomineralization. (C) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.