Multi-axis 3D printing of gelatin methacryloyl hydrogels on a non-planar surface obtained from magnetic resonance imaging

Abstract

3D printing of hydrogels is currently limited to triaxial printers that have inherent disadvantages like being optimized for planar print substrates, limitations in surface quality, and the need for support structures when printing overhangs. Multi-axis 3D printing of hydrogels has the potential to overcome all these disadvantages, making especially non-planar print substrates available for 3D printing that were e.g., extracted by imaging techniques like magnetic resonance (MRI) of bones. Therefore, we aim to pave the way towards multi-axis 3D printing of hydrogels in this contribution. In a first step, MRI scan data of a tibia was processed to obtain a smoothed bone surface that was fed afterwards into a curved slicing and path planning algorithm, thus generating non-planar layers composed of curved printing paths. The printing paths were translated into a 3D printed hydrogel based on gelatin methacryloyl by a newly developed print head mounted to a seven-axis kinematic that also allows UV curing of the printed hydrogel inks to solid hydrogels after printing. The properties of the 3D printed hydrogels were compared to molded hydrogels, showing that the 3D printed hydrogels were less stiff and had a higher equilibrium degree of swelling in water than the molded hydrogels. Summarizing, the results demonstrate the advantages of multi-axis 3D printing for hydrogel processing, but also shed light into open research questions concerning cross-linking chemistry and formulation of hydrogel inks relevant both for triaxial and multi-axis 3D printing.