Multiscale design of surface morphological gradient for osseointegration.

Rapid and stable osseointegration signifies a major concern in design of implantable prostheses, which stimulates continuous development of new implant materials and structures. This study aims to develop a graded configuration of a bead/particle coated porous surface for implants by exploring how its micromechanical features determine osseointegration through multiscale modeling and remodeling techniques. A typical dental implantation setting was exemplified for investigation by using the remodeling parameters determined from a systematic review of bone-implant-contact (BIC) ratio published in literature. The global responses of a macroscale model were obtained through 48 month remodeling simulation, which forms the basis for the 27 microscopic models created with different particle gradients ranging from 30 to 70μm. The osseointegration responses are evaluated in terms of the BIC ratio and the averaged 10% peak Tresca shear stress (PTS). Within the sampling designs considered, the configuration with 50-30-30μm particle sizes provides the best outcome, counting 20% more BIC ratio and 0.17MPa less PTS compared with the worst case scenario, also outperforming the best uniform morphology of 70μm particles. Furthermore, the response surface method (RSM) was utilized to formulate the bone remodeling responses in terms of gradient parameters across three layers. Gradient 30.0-30.0-32.1 is found an optimal gradient for BIC ratio, and 70-45.4-40.8 the best for the minimum PTS. The multiobjective optimization was finally performed to simultaneously maximize BIC ratio and minimize PTS for achieving the best possible overall outcome. Due to strong competition between these two design objectives, a Pareto front is generated. To make a proper trade-off, the minimum distance selection criterion is considered and the gradient of 37.1-70.0-67.7 appears an optimal solution. This study provides a novel surface configuration and design methodology for individual patient that allow optimizing topographical gradient for a desirable patient-specific biomechanical environment to promote osseointegration.