The mechanical response of commercially available bone simulants for quasi-static and dynamic loading

Bone is a complex hierarchal structured material with varying porosity and mechanical properties. In particular, human cranial bone is essentially a natural composite consisting of low porosity outer and inner tables and a cancellous interior, or diploë. Experimental studies of biomechanically accurate cranial bone analogues are of high importance for biomechanical, forensics, and clinical researchers, which could improve the understanding and prevention of traumatic injury. Many reported studies use commercially available bone surrogates to draw biomechanical and forensics conclusions; however, their mechanical properties are not tabulated over a range of strain rates. This study elucidates the mechanical viability of three leading commercially available bone surrogates, i.e. Synbone, Sawbone, and Bonesim, over a large range of strain rates (10^-3 to 10³ s^-1). Quasi-static compression testing was conducted using a universal testing machine and a Split-Hopkinson Pressure bar system equipped with high-speed video was used to determine the dynamic mechanical behavior of these materials. Micro-computed X-ray tomography (XRT) were performed on each material to investigate their pore structures and distributions. All materials exhibited strain rate dependent strength behavior, particularly at high loading rates (≥10³ s^-1). The Young's modulus was found to increase with strain rate from 10^-3 to 10^-1 s^-1 for transversely and longitudinally loaded surrogate materials except for Synbone and the higher density Bonesim. The higher density Bonesim was determined to be the most suitable cranial bone simulant tested based on a combination of transverse Young's Modulus (1500 MPa), yield strength (19 MPa), ultimate strength (49 MPa), and ultimate strain (17%). These materials show limited promise for applications where the measured elastic properties and strengths are of interest.