From digital to physical model: testing of a workflow for case-specific 3D-printed bone simulants.

Bone simulants are used for a variety of purposes in wound ballistic experimentation. Synthetic simulants have several advantages over biological (either human or animal) material. Generic synthetic simulants are available, but the shapes and sizes of these materials cannot cover the full range observed in human individuals. This is a disadvantage, e.g., in forensic reconstructions where accurate and case-specific simulants are often desirable. One way to circumvent this problem is to print bone simulants, based on scanned victims' data. The current study is intended to explore the feasibility of this method, find suitable materials, and determine optimal printer settings. For this purpose, two porcine scapulas and two porcine femurs were scanned with a Computed Tomography (CT) scanner and replicated with a 3D printer based on the scan data. Polylactic acid (PLA), thermoplastic polyurethane (TPU), and nylon-carbon fibre (PA6-CF) were used as printing materials. Cancellous bone was replicated by printing a honeycomb pattern with a 60% infill. Cortical bone was replicated by printing a rectilinear pattern with a 100% infill. Both the biological originals and their printed replicas were embedded in gelatine and shot with 6,35 mm Browning and .22 Long Rifle bullets. Penetration capacity, projectile deformation and fracture characteristics were compared. The results were most promising with the TPU prototypes. For the PLA and PA6-CF, the fracture characteristics and projectile deformation differed from those observed with the biological originals. Also, the penetration depth into the gelatine behind the bone simulants was lower with these materials.