Correlating structural and rheological properties of bulk and granular chitosan-collagen I hydrogels

Granular hydrogels resulting from the dense packing of hydrogel microparticles have recently attracted a lot of attention, both from a fundamental perspective and for application as biomaterials. However, comparisons between the properties of bulk and granular hydrogels of similar compositions remain scarce. Here we have prepared chitosan-collagen I granular hydrogels via fragmentation of bulk hydrogels and centrifugation of the resulting microparticle suspension. Microparticles exhibited a fibrillated collagen I core embedded in a chitosan shell, suggesting that the fragmentation process is controlled by the protein microstructures dispersed in the polysaccharide matrix. Rheological studies indicated that the granular hydrogels were less elastic (lower storage modulus) but more ductile (higher critical shear strain) than the corresponding bulk hydrogels. Moreover, their rheological properties were more sensitive to collagen content and collagen fiber organization, which impacted both particle compressibility and inter-particle interactions. Extension of the herein-described approach should allow us to improve our understanding of existing correlations between the mechanical properties of bulk hydrogels, hydrogel microparticles and granular hydrogels.