A top-down approach to dense collagen I-chitosan microgels and granular hydrogels

Chitosan and collagen I are two of the most used biopolymers for the preparation of hydrogel microparticles or microgels. Still, the combination of chitosan and collagen within micron-sized particles was scarcely reported. Usual fabrication methods are based on water-in-oil emulsions but are limited to low polymer concentration (< 10 mg mL−1). Here, we report the preparation of concentrated chitosan-collagen I microgels by fragmentation of a dense chitosan-collagen hydrogel. Hydrogels were prepared by neutralisation of concentrated chitosan-collagen I solutions (> 25 mg.mL-1) using ammonia under liquid or gaseous form. Resulting particles all consisted of a fibrillated collagen I core embedded in a chitosan shell, replicating the initial microstructure of the hydrogel. Preparation process and collagen content impacted particle sizes and colloidal behaviour. Particles were further processed into granular hydrogels using a centrifugal force. Rheological properties of these hydrogels were dependent on collagen content and collagen fibers organisation. This work discloses a new route to obtain dense and tunable chitosan-collagen I hydrogel microparticles and could be extended to other binary biopolymer systems.