Evaluating Differences in Elastic Modulus of Regenerated and Uninjured Mouse Digit Bone through microCT Density-Elasticity Calculation and Nanoindentation Testing

Bone is an essential, healing structure in vertebrates that ensures daily function. However, the regenerative capacity of bone declines with age, compromising quality of life in the elderly and increasing cost of care. Here, for the first time, the elasticity of regenerated bone in a mouse digit amputation model is evaluated in order to better investigate biomechanics of skeletal regeneration. Amputation of the distal one third of the digit (third phalangeal element - P3) results in de novo regeneration of the digit, where analyzing the structural quality of this regenerated bone is a challenging task due to its small scale and triangular shape. To date, the evaluation of structural quality of the P3 bone has primarily focused on mineral density and bone architecture. This work describes an image-processing based method for assessment of elasticity in the whole P3 bone by using microcomputed tomography-generated mineral density data to calculate spatially discrete elastic modulus values across the entire P3 bone volume. Further, we validate this method through comparison to nanoindentation-measured values for elastic modulus. Application to a set of regenerated and unamputated digits shows that regenerated bone has a lower elastic modulus compared to the uninjured digit, with a similar trend for experimental hardness values. This method will be impactful in predicting and evaluating the regenerative outcomes of potential treatments and heightens the utility of the P3 regenerative model.