3D Printed lattice microstructures to mimic soft biological materials

Objective. Our group has developed a method for 3D printing mechanically-realistic soft tissue, as a building block towards developing anatomically realistic 3D-printed biomechanical testbed models. Methods. A Polyjet 3D printer was used to print lattice microstructures, which were tested in compression to evaluate the elastic profile. Lattice properties including element diameter, element spacing (ES), element cross-sectional geometry, element arrangement, and lattice rotation were varied to determine their effect on the stress-strain curve. As a case study, a single 3D printed sample was tuned such that its elastic profile matched plantar fat. Results. Element diameter and ES had the largest effect on the stress-strain profile, and rotating the lattice microstructure tends to linearize the curves. A simple cubic lattice microstructure of cylindrical elements, with 0.5 mm diameter columns and 1.2 mm spacing had a stress-strain curve the was closest to plantar fat. The elastic modulus at 10, 30, and 50% strain was 7.55, 9.50, and 252 kPa respectively. Physiologic plantar fat at the same strain values has moduli values of 1.08, 7.13, and 188 kPa. Significance. We demonstrated that lattice microstructures can decrease the young's modulus of soft 3D printed materials by three orders of magnitude. By creating a method for fine-tuning the elastic profile of 3D-printed materials to behave like human soft tissue, we provide an attractive alternative to more exotic and time-consuming techniques such as molding and casting.