Abstract
Many biomaterials’ surfaces exhibit directional properties, i.e., possess spatial anisotropy on a range of spatial scales spanning from the domain of the naked eye to the sub-micrometer level. Spatial anisotropy of surface can influence the mechanical, physicochemical, and morphological characteristics of the biomaterial, thus affecting its functional behavior in relation, for example, to the host tissue response in regenerative processes, or to the efficacy of spatially organized surface patterns in avoiding bacterial attachment. Despite the importance of the availability of quantitative data, a comprehensive characterization of anisotropic topographies is generally a hard task due to the proliferation of parameters and inherent formal complications. This fact has led so far to excessive simplification that has often prevented researchers from having comparable results. In an attempt to overcome these issues, in this work a systematic and multiscale approach to spatial anisotropy is adopted, based on the determination of only two statistical parameters of surface, namely the texture aspect ratio Str and the roughness exponent H, extracted from atomic force microscopy images of the surface. The validity on this approach is tested on four commercially available implant materials, namely titanium alloy, polyethylene, polyetheretherketone and polyurethane, characterized by textured surfaces obtained after different machining. It is found that the “two parameters” approach is effective in describing the anisotropy changes on surfaces with complex morphology, providing a simple quantitative route for characterization and design of natural and artificial textured surfaces at spatial scales relevant to a wide range of bio-oriented applications.
Highlights
The surface of many implant materials is often marked with lays originating from various machining and finishing processes
In the light of the results obtained here, and within some limitations detailed in the following, we found that for surfaces possessing a single lay our approach accounts well for the micro topographies observed, and highlights that the anisotropy changes towards small scales are determined by the interplay between the inheritance of the machining/finishing processes and the spatial distribution of features specific to the sample
Our study, carried out on four implant materials with different surface textures, suggests that the strong anisotropic character of their topographies can be well described by a multiscale approach based on solely two parameters, accounting, respectively, for the spatial and vertical variations of the spatial lengths
Summary
The surface of many implant materials is often marked with lays originating from various machining and finishing processes Such lays can appear oriented along one preferential direction or exhibit patterns sometimes very difficult to describe visually. Anisotropic biomaterials’ surfaces may be preferred for developing tissue-engineering constructs as they present morphology and function more closely resembling the native tissue [5]. Their role has been highlighted in relation to architectural reconstruction and scaffold design of blood vessels [6] and skeletal muscle tissue [5,6,7]. Geometries of biomaterials for tissue anisotropy reconstruction can be formed as orientated fibers produced via electrospinning and flow shear, or micropatterning of substrates obtained through methods such as lithography, soft lithography, direct laser writing and abrasion wear [7]
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