Multiscale remodelling and topographical optimisation for porous implant surface morphology design

Abstract

Solid titanium and its alloys have been the most prevalent materials for dental and orthopaedic implants attributable to their advantageous mechanical and biocompatible properties. Nevertheless, there still is a range of biomechanics and biomaterials issues with titanium implants, such as delayed/insufficient osseointegration and limited shear-load bearing capacity in clinic. In order to tackle these problems, various physical and chemical treatment technologies have been developed to modify surface morphology of such implantable dental prostheses. Fully porous coating (FPC) is one of such techniques, where beads or particles are sintered to bond onto a solid core of implants under specific conditions. This process forms a layer of porous structure on the surface of the implant, whose morphology relies on the bead size, volume fraction and pattern of distribution. Given the critical roles that porous surface could play to enhance osseointegration, a major interest consists in how to optimise morphological parameters. This chapter aims to address this issue through a new multiscale modelling and design framework for optimising the surface morphology to enhance bone–implant interface stability and osseointegration in a biomechanics context. Four different measurements in the microscopic model are used as the design criteria to assess osseointegration outcomes: (1) peri-implant bone density, (2) uniformity of periimplant bone density, (3) bone–implant contact (BIC) ratio, and (4) Tresca stress (maximum shear). To achieve these osseointegrative criteria, multiobjective optimisation is formulated with respect to the design variables of particle size, volume fraction and gradient. The optimised surface morphology allows creating a better microenvironment for cell attachment, differentiation and proliferation. While cells are seeded in a passive way during implantation in vivo, the tailored surface topography enables to better engage cellular activities in both biomechanical and biochemical aspects, thereby generating better short- and long-term clinical outcomes.