Laser Induced Hierarchical Coatings on Titanium Alloy

Biomaterials research is an exciting and challenging area. It is exciting because of its potential applications and need for improving the quality of life. It is challenging because of the complexity with which natural biomaterials function in their environments. The gap that exists in terms of maturity and sophistication of the currently used synthetic materials from natural biomaterials is huge. It is only in the last few decades with the evolution of advanced material analytical techniques that researchers are starting to understand the complexity of nature. One such particular feature that has attracted our interest is the hierarchical nature of the bioimplant surfaces.

The present work is one small step in that direction where we tried to engineer a surface that is multi-scale in nature and biocompatible at these length scales. During a discovery phase a multi-scale textured zirconia coating was done on titanium alloy using a pulsed laser. Following proof of concept a bioactive calcium phosphate based coating was deposited on titanium alloy surface using a continuous wave laser. Based on detailed morphological and chemical analysis it was evident that the multi-phase coating had a multi-scale arrangement. Owing to the complexity of the coating a fractal based approach was used to interpret the morphology of the coatings. It appeared that at higher laser processing speeds star shaped calcium titanate features exist inside calcium phosphate and titania ring like structures. By tailoring a thermal model with current material system temperature calculations were made for various laser processing speeds. Using temperature predictions and knowledge of the phase constituents the series of self assembling steps that led to the formation of star and ring shaped arrangement are discussed. The biocompatibility of the coatings was evaluated by immersing in simulated body fluids.

The morphological and chemical evolution of hydroxyapatite precipitation along the calcium phosphate rich ring like structures coupled with the porous structure supports the possibility of enhanced osteointegration. The presence of calcium titanate ensured an interaction between the substrate and the precursor coating material. Wear measurements indicated that the laser processed samples possessed better mechanical properties than unprocessed surfaces.