Water as blowing agent in polyurethane resins creating porous cancellous bone surrogates for biomechanical osteosynthesis applications

This study examines the role of water as a blowing agent in generating porous polyurethane foams used as synthetic cancellous bone surrogates in biomechanical osteosynthesis testing. Polyurethane foams, typically used to replicate bone structures, often fail to fully mimic the intricate morphology and mechanical properties of natural bone, especially in open-cell, cancellous structures. By varying water content, with and without a cell-stabilizing agent, foams with distinct morphological and mechanical characteristics were produced. Morphometric analysis and mechanical compression testing were conducted on foams with water content ranging from 0.25 to 3 >wt.%. Results indicate that decreasing water content yields denser, mechanically stiffer foams, whereas the stabilizer consistently enhanced cellular stability and uniformity. Quantitative analysis, including bone volume to total volume ratio, trabecular thickness, and connectivity density, demonstrated that specific water-stabilizer combinations align more closely with human trabecular bone. These findings suggest that optimized water-based foaming in polyurethane can improve synthetic bone models' biomechanical fidelity, offering valuable implications for testing orthopedic implants.