Anodized titania: Processing and characterization to improve cell-materials interactions for load bearing implants.

摘要

The objective of this study is to investigate in vitro cell-materials interactions using human osteoblast cells on anodized titanium. Titanium is a bioinert material and, therefore, gets encapsulated after implantation into the living body by a fibrous tissue that isolates them from the surrounding tissues. In this work, bioactive nonporous and nanoporous TiO2 layers were grown on commercially pure titanium substrate by anodization process using different electrolyte solutions namely (1) H3PO 4, (2) HF and (3) H2SO4, (4) aqueous solution of citric acid, sodium fluoride and sulfuric acid. The first three electrolytes produced bioactive TiO2 films with a nonporous structure showing three distinctive surface morphologies. Nanoporous morphology was obtained on Ti-surfaces from the fourth electrolyte at 20V for 4h. Cross-sectional view of the nanoporous surface reveals titania nanotubes of length 600 nm. It was found that increasing anodization time initially increased the height of the nanotubes while maintaining the tubular array structure, but beyond 4h, growth of nanotubes decreased with a collapsed array structure. Human osteoblast (HOB) cell attachment and growth behavior were studied using an osteoprecursor cell line (OPC 1) for 3, 7 and 11 days. Colonization of the cells was noticed with distinctive cell-to-cell attachment on HF anodized surfaces. TiO2 layer grown in H2SO4 electrolyte did not show significant cell growth on the surface, and some cell death was also noticed. Good cellular adherence with extracellular matrix extensions in between the cells was noticed for samples anodized with H3PO 4 electrolyte and nanotube surface. Cell proliferation was excellent on anodized nanotube surfaces. An abundant amount of extracellular matrix (ECM) between the neighboring cells was also noticed on nanotube surfaces with filopodia extensions coming out from cells to grasp the nanoporous surface for anchorage. To better understand and compare cell-materials interactions, anodized nanoporous sample surfaces were etched with different patterns. Preferential cell attachment was noticed on nanotube surfaces compared to no cells on etched patterned surface. Cell adhesions and differentiation were more pronounced with vinculin protein and alkaline phosphatase, respectively, on anodized surfaces. MTT assays showed increase in living cell density and higher proliferation on H3PO4, HF and nanotube surfaces. When anodized surfaces were compared for cell materials interaction, it was noticed that each of the surfaces has different surface properties that led to variations in cell-materials interactions. It was clear that rough surface morphology, high surface energy, and low value of the contact angles were important factors for better cell materials interaction. Mineralization study was done in simulated body fluid (SBF) with ion concentration nearly equal to human blood plasma to further understand biomimetic apatite deposition behavior. Similar to cell-materials interaction, variation in mineral deposition behavior was also noticed for films grown with different electrolytes. These results clearly show that nonporous titania in H3PO4, HF electrolytes and nanotubes can significantly increase biocompatibility of Ti implants, which has the potential to reduce the healing time and increase in vivo lifetime for these implants.