Surface microtopography design and manufacturing through topography descriptors: an application to prosthetic implant surfaces

A surface microtopography design and manufacturing methodology is presented that handles the intrinsic geometrical complexity of a surface microtopography by introducing topography descriptors. The concept of topography descriptor is a generalization originating from known techniques of three-dimensional surface topography analysis. Topography descriptors may be seen as transfer functions that can be defined to map selected microtopographic properties of a surface to scalar values that can be used for quantitative evaluation and/or comparison purposes; they are intended to provide a compact representation of otherwise complex morphologic information by selecting only the information which is deemed relevant to a specific function, context, or application domain. When properly defined, topography descriptors can help in the assessment of the functional performance of different surface microtopographies; also, they can provide support to the development of virtual microtopography models specialized in the replication of specific aspects of a surface morphology, which may be useful, for example, to investigate the relationships between surface morphology and function, or between surface morphology and manufacturing process parameters for surface generation. In this work, the proposed methodology is applied to the design of the microtopography of the coated surface of a prosthetic implant. Topography descriptors are identified which are suitable to describe microtopographic properties related to a specific functional property: the bone-implant interfacial shear strength. Such topography descriptors are evaluated over real specimens, obtained by Vacuum Plasma Spray deposition of porous titanium or fluorinated hydroxyapatite over a titanium alloy substrate, in order to assess their relationship with functional performance. Then, a dedicated procedural model, embedding Vacuum Plasma Spray simulation algorithms, is developed to generate virtual microtopographies with the intent of understanding the relationships between topography descriptors and manufacturing process parameters, for process planning purposes. The developed models and obtained results are discussed and their suitability as tools for surface topography design and manufacturing is assessed.