A New Approach for Designing Biodegradable Bone Tissue Augmentation Devices by Using Degradation Topology Optimization

The current study proposed a topology optimization method accounting for base material degradation and create a degradable device that retains sufficient stiffness through the degradation process to provide load bearings for tissue regeneration in orthopaedic applications. Degradable materials are less stiff than permanent materials and suffer further stiffness reduction through time when considering those as substitutes to replace permanent materials for many reconstruction applications. Merely replacing the permanent material with a degradable material in the same design may lead to early device failure. Since many degradable materials lose material through bulk erosion without shape change, the proposed optimization method creates a density distribution map for selected time points during degradation. These different density distributions are then linearly superposed using both time and degraded base stiffness weighting factors. In this paper, the method is applied to design a degradable spine interbody fusion cage device from poly(propylene fumarate)/beta-tricalcium phosphate (PPF/β-TCP). The weighted optimization study successfully produced designs that maintained device stiffness better than either non-weighted or conventional designs. Any bulk degrading material can be designed using this process for any skeletal reconstruction application.