Characterization and In Vivo Studies of Nanothickness Ca- and P-Based Coatings

Abstract

Objective: This series of laboratorial and in-vivo studies describe the characterization, evolution, and in-vivo performance of various Ca- and P-based nanothicknesses and microstructures ion beam assisted depositions (IBAD) onto Ti-6Al-4V implants. Materials and Methods: Characterization- The 4 mm in diameter and 10 mm in length implant rods (Ti-6Al-4V) with IBAD I, IBAD II, and control (alumina-blasted/acid-etched, AB/AE) surfaces were provided by an implant manufacturer. The in-vitro characterization comprised the following techniques: (1) SEM/EDS, (2) XPS/Depth Profiling (3) Thin-film XRD (4) AFM + ToF-SIMS for coating thickness determination (5) AFM- Ra determination. In-vivo- Three animal experiments were carried out for evaluation of the nanothickness bioceramic coatings. All experiments comprised a proximal tibia model with 4-6 implants placed along the bones. Times in-vivo ranged from 2-5 weeks. Static (bioactivity, bone to implant contact) and dynamic (mineral apposition rates- MAR) histomorphometric measurements were recorded. Biomechanical testing was performed by pullout and torque to interfacial failure testing. Results: Combination of the characterization techniques showed that all bioceramic coatings were Ca- and P-based bioceramics of amorphous microstructure. AFM +ToF-SIMS showed that IBAD II coatings were thicker (300-500 nm) compared to IBAD I coatings (30-50 nm). Surface roughness did not change significantly for the IBAD implant groups compared to control. The in-vivo results showed higher degrees of osseoactivity, torque to failure, and MAR for the coated implants at different times in-vivo. IBAD II had higher biomechanical fixation at early implantation times compared to other groups. Conclusions: The results obtained in the in-vitro part this study support that both IBAD I and IBAD II coatings are Ca- and P- based amorphous bioceramics in the nanothickness range with theoretical high dissolution rates. The increased osseoactivity observed for IBAD coated and the high MAR values observed for IBAD coated compared to AB/AE implants support the effect of the bioceramic coating presence in the overall bone healing. A thickness effect was reveled through biomechanical testing where IBAD II (300-500nm thickness) presented higher performance.