Development and mechanical testing of synthetic 3D printed models of healthy and metastatic vertebrae

The spine is frequently affected by metastases, which can disrupt the normal distribution of bone tissues, reduce load-bearing capacity, and lead to spinal instability. However, the assessment of spinal instability remains unclear for most patients. A comprehensive understanding of metastatic vertebrae is crucial to identify and subsequently treat those at a high risk of fractures. The aim of the study is to evaluate the mechanical properties of synthetic 3D printed models of healthy and metastatic vertebrae to replicate the mechanical behavior of ex-vivo vertebrae. The goal was to explore the possibility of providing an alternative solution by producing a large number of repeatable samples with high accuracy. Using an innovative approach that incorporated Digital Anatomy Printing and Digital Materials, over a hundred models (both healthy and metastatic) were printed based on medical images and subjected to compression loading. Initially, the study focused on characterizing the properties of digital materials and then assessed the influence of morphology on the models. At the end the stress-strain analysis indicated a correspondence between the fracture mode of metastatic synthetic models and ex-vivo models. Once this method and the associated evidence are generalized on a larger sample, they could contribute to the development of new biomechanical-based criteria within current scoring systems. This would provide clearer guidelines for assessing spinal instability and open new avenues for research on fracture risk prediction.