From digital to physical model: the use of 3D-printed models in wound ballistic reconstruction.

Synthetic models (also called "surrogates") simulating human tissues are widely used in wound ballistics. Although there are a large number of commercial models showing interesting properties, these are limited to generic shapes. The result of the interaction between the projectile and the target varies based on several parameters; therefore, using a case-specific, custom-shaped synthetic model would enhance the accuracy of the findings. For this purpose, the authors created, based on Post-Mortem Computed Tomography (PMCT) measurements, case specific 3D-printed synthetic models. The first ballistic tests were performed on simple plates printed with different materials and compared against polyurethan Synbone® products in order to select the most suited materials for synthetic head models. Further tests were realised on head models printed with PLA (polylactic acid), PETG (polyethylene terephthalate glycol-modified) and TPU (thermoplastic polyurethane) polymers as well as on two head models composed of powder and resin. The bullet's behaviour, its deformation, the wound channel and other qualitative aspects were directly compared to the findings of the real case reported in Riva et al in Int J Legal Med 135:2567-2579, 2021, as well as to the "open shape" head model created by Riva et al in Forensic Sci Int 294:150-159, 2019. Finally, although the results of this study did not completely fulfil the requirements to simulate human bones, its concept in reproducing case specific head models with easily available 3D printing materials, is very promising.