Designing 3D Printable, Nanofibrous Bacterial Cellulose Granular Hydrogels

• Vishmi Rajapaksha, Chemical Engineering, University of Delaware

• Victoria Muir, Chemical and Biomolecular Engineering, University of Delaware

Bacterial Cellulose (BC) is a nanofibrous polysaccharide with high water retention whose fibrous architecture resembles key structural features of fibrous musculoskeletal tissue. BC naturally forms continuous nanofibrous pellicles at the top of liquid cultures, making it difficult to dictate the shape it forms in and challenging to print with. Herein, we form a printable granular hydrogel with BC fragments as microgels and an interstitial matrix of methacrylated hyaluronic acid (MeHA), which exhibits shear thinning and self healing properties. To fabricate this material, we use mechanical fragmentation via blending to break the BC pellicle into microgels of entangled nanofibers. The microgels are then packed together in 2 different densities through centrifugation before adding a MeHA interstitial matrix in varying rations of MeHA:BC. 

We used rheology to characterize our inks and found that increasing packing density results in increased yield stress and storage modulus, and decreased yield strain, but did not affect the self healing nature of our inks. This shows that packing density can be used to tune the rheological properties and printability of our inks. Additionally, we discovered that varying the interstitial content did not impact rheology (yield stress/strain, storage modulus, recovery). This suggests that the organization of the jammed BC largely governs the rheology of our gels, not the MeHA interstitial matrix. We then used extrusion printing to determine how the degree of jamming impacts the printability window and spreading nature of ink. Preliminary printing experiments suggest that higher jammed systems have improved printability but increased ink spreading. These findings show that creating BC microgels and controlling their organization converts a traditionally non-printable fibrous biomaterial into a tunable granular ink.