(471b) Effects of Processing Conditions on the Macroscopic Properties of Cellulose Filled Hydrogel Scaffolds Using UV Rheology

Hydrogel scaffolds are useful tools in observing and studying a variety of cells in synthetic complex environments. The anisotropic nature of some extracellular matrices require fabrication methods that permit structural alignment within the hydrogel. Extrusion based 3D printing of hydrogel scaffolds promotes shear induced alignment of anisotropic nanofillers or fibers and allows fast manufacturing and control via in situ polymerization. In this manufacturing method, shear at the walls of the nozzle align rod-shaped particles in the direction of extrusion, while ultraviolet light can be used to induce local crosslinking of the polymer solution to form a hydrogel. However, modulation of the final hydrogel scaffold by using this extrusion-based printing requires knowledge of the viscoelastic and optical properties of the polymer solution during the printing process. Also, to encapsulate cells in a 3D printed hydrogel at a high viability via “ink” extrusion and fast photopolymerization, optimization of the photo initiator concentration and light irradiation time is vital. In this work, a rheometer with an ultraviolet-light lamp attached is used to characterize the effects of photo initiator amount, light irradiation time, and initial polymer modulus on the final modulus of a crosslinked biocompatible hydrogel. Using alginate, photocurable polyethylene diacrylate, and high-aspect-ratio cellulose nanocrystals we characterize the crosslinking of a hydrogel when it is exposed to ultraviolet light to form a scaffold that’s representative of the extracellular matrix. Due to the simultaneous crosslinking and light attenuation within the hydrogel, there exists an optimum photo initiator amount and irradiation time to control the final modulus. These settings are used to assess the final properties of a hydrogel formed immediately after experiencing the high concomitant shear forces of extrusion printing. It is found that the presence of long anisotropic fillers affects polymer solution transmittance and viscoelasticity upon shearing which leads to major changes in the final modulus of the scaffold.