Fibrillar biocompatible colloidal gels based on cellulose nanocrystals and poly(N-isopropylacrylamide) for direct ink writing

Abstract

Hypothesis: Hydrogels based on cellulose nanocrystals (CNC) have attracted great interest because of their sustainability, biocompatibility, mechanical strength and fibrillar structure. Gelation of colloidal particles can be induced by the introduction of polymers. Existing examples include gels based on CNC and derivatives of cellulose or poly(vinyl alcohol), however, gel structure and their application for extrusion printing were not shown. Hence, we rationalize formation of colloidal gels based on mixture of poly(N-isopropylacrylamide) (PNIPAM) and CNC and control their structure and mechanical properties by variation of components ratio.

Experiments: State diagram for colloidal system based on mixture of PNIPAM and CNC were established at 25 and 37 °C. Biocompatibility, fiber diameter and rheological properties of the gels were studied for different PNIPAM/CNC ratio.

Findings: We show that depending on the ratio between PNIPAM and CNC, colloidal system could be in sol or gel state at 25 °C and at gel state or phase separated at 37 °C. Physically crosslinked hydrogels were thermosensitive and could reversibly change it transparency from translucent to opaque in biologically relevant temperature range. These colloidal hydrogels were biocompatible, had fibrillar structure and demonstrate shear-thinning behavior, which makes them a promising material for bioapplications related to extrusion printing.

Keywords: Cellulose nanocrystals; Colloidal gel; Direct ink writing; Fibrillar gel; Injectable hydrogel; Shear-thinning.