Modeling and analysis of post-processing conditions on 4D-bioprinting of deformable hydrogel-based biomaterial inks

Deformable structures have been actively developed for several biomedical applications including drug delivery and tissue engineering using 3D-bioprinting methods. However, structural shape-transformation usually consists of a series of bending behaviors in response to external stimuli, which require complex aggregation and multi-materials design. To overcome these complexities, this work explores an alternative approach using only a single hydrogel-based material to realize such bending mechanisms. Numerical simulations are first implemented to realize bending deformation by spatially assigning distinct material parameters to different sections of the structure. The bending phenomenon is also shown experimentally using hydrogel-based biomaterial inks. Specifically, a deformable structure is fabricated by finely controlling different post-processing conditions such as cooling time, crosslinking duration, and heating rate during swelling to mimic the effect of different material parameters. Moreover, the bending deformation can be further analyzed using computer vision methods to inversely determine the desired material coefficients in the simulation. Relationships among bending mechanisms, material parameters, and post-processing procedures are found and shown to affect the final bending orientation. These results yield insightful approaches to the inverse design of functional biomedical devices with desired deformation behavior.