In recent years, patterned ultra-hydrophilic thin films have received attention because of their potential as bio-compatible surfaces for implants. However, mechanical properties of the studied surfaces are not sufficiently robust for the majority of applications. Via an ion-beam assisted deposition process, we have fabricated nanostructurally stabilized, pure cubic zirconia thin films possessing properties of hardness (16 GPa) and wettability, which are expected to benefit tribology and wear reduction. These transparent, zirconia coatings are maximally wettable by water and bovine calf serum, which is explained by the Wenzel model based on the nanotextured surface and surface energy.

The effect of aging on hydrophilic properties of cubic zirconia was determined by water contact angle (CA) measurements on samples stored in a laboratory environment from February of 2005 until now. Measurements for samples without any cleaning showed CA of around 90°, indicating surface adsorption of moisture, organic contaminants, and/or gases over time. A cleaning procedure consisting of sonication in organic solvents followed by calcination at temperatures ranging from 300°C to 600°C was found to effectively burn off residual organic contaminants, yielding CA about 10° to 20°. X-ray diffractometry and atomic force microscopy analysis of these samples revealed that the cleaning procedure induced no apparent changes in the crystal structure and nanotextured surface.

We conclude that the observed loss of ultra-hydrophilic properties was due to organic contaminants. Our results reveal a cleaning method for the long-term maintenance of the wettability of zirconia, making it a viable material for applications involving hard, hydrophilic surfaces, such as biomedical implants.

The steric and electrostatic complementarity of natural proteins and other macromolecules are a result of evolutionary processes. The role of such complementarity is well established in protein-protein interactions, accounting for the known protein complexes. To our knowledge, non-biological systems have not been a part of such evolutionary processes. Therefore, it is desirable to design and develop nonbiological surfaces, such as implant devices (e.g. bone growth for non-cemented fixation), that exhibit such complementarity effects with the natural proteins.

Cell attachment and spreading in vitro is generally mediated by adhesive proteins such as fibronectin and vitronectin [1]. The primary interaction between cells and adhesive proteins occurs through integrin and an RGD amino acid sequence. The adsorption of adhesive proteins plays an important role in cell adhesion and bone formation to an implant surface [1]. The ability of the implant surface to adsorb these proteins determines its aptitude to support cell adhesion and spreading and its biocompatibility. For example, the enhancement of osteoblast precursor attachment on hydroxyapatite (HA) as compared to titanium and stainless steel was related to increased fibronectin and vitronectin absorption [2].

The role of surface characteristics, such as topography, has been studied in recent years without the emergence of a comprehensive and consistent model [1]. For example, while no statistically significant influence of surface roughness on osteoblast proliferation and cell viability was detected in the study of metallic titanium surfaces [3], the TiO2 film enhances osteoblast adhesion, proliferation and differentiation upon an increase in roughness [4].

We designed and produced ceramic [5] and metallic coatings via an ion beam assisted deposition process with spatial dispersion (roughness) comparable to the size of proteins (3–20nm). Our ceramic and cobaltchrome (CoCr) coatings exhibit high hardness and contact angles with serum of 0° and 40° to 50°, respectively. Furthermore, our theoretical calculations and quantum-mechanical modeling clearly indicate that the spatial electric potential variation across our designed ceramic surfaces is comparable to the electrostatic potential variation of proteins such as fibronectin, promoting increased absorption on these surfaces. Therefore, an increase in the concentration of adhesive proteins on the designed surfaces results in the enhancement of the focal adhesion of cells. Our experimental results of the adhesion and proliferation of osteoblast-like stromal cells from mouse bone marrow indicate that our nanostructured coatings are three to five times better than growing on HA and orthopaedic grades of titanium and CoCr. Our results are consistent with the steric and electrostatic complementarity of nanostructured surfaces and adhesive proteins. This paper presents the adhesion and proliferation of osteoblast-like cells on micro-and nanostructured surfaces and provides new models describing the mechanism responsible for the enhancement of cell adhesion on nanostructured ceramic and metallic surfaces compared with orthopaedic materials.