HYDROGELS AND AEROGELS BASED ON CHEMICALLY CROSS-LINKED CELLULOSE NANOCRYSTALS

Abstract

Cellulose nanocrystals (CNCs) make up a promising new class of renewable nanomaterials with unique properties including nano-dimensions, high strength, light weight, liquid crystalline behaviour, biodegradability and general biocompatibility. The objective of this work was to study the use of chemically cross-linkable cellulose nanocrystals in gels, specifically injectable hydrogels and aerogels.

First, aldehyde-functionalized CNCs (CHO–CNCs) were used to reinforce injectable hydrogels based on carboxymethyl cellulose and dextran. The mechanical properties, internal morphology, and swelling of injectable hydrogels with unmodified and modified CNCs at various loadings were examined. The maximum storage modulus was observed in hydrogels with 0.250 wt. % of unmodified CNCs and 0.375 wt. % of CHO–CNCs. CHO–CNCs acted as both a filler and a chemical cross-linker, making the CHO–CNC-reinforced hydrogels more elastic, more dimensionally stable, and capable of facilitating higher nanoparticle loadings, compared to hydrogels with unmodified CNCs. When immersed in purified water or 10 mM PBS buffer, all CNC-reinforced hydrogels maintained their original shape for more than 60 days. No significant cytotoxicity to NIH 3T3 fibroblast cells was observed for the hydrogels or their individual components. These properties make CNC-reinforced injectable hydrogels of potential interest for various biomedical applications such as drug delivery vehicles or tissue engineering matrices.

Next, chemically cross-linked “all-CNC” aerogels were prepared based on similar hydrazone cross-linking with hydrazide-functionalized CNCs (NHNH2-CNCs) and CHO-CNCs. These ultra lightweight (5.6 mg/cm3) and highly porous (99.6%) aerogels displayed bimodal pore distribution (mesopores <50 nm and macropores >1 µm). Chemically cross-linked CNC aerogels showed enhanced mechanical properties and shape recovery ability, particularly in water, compared to previous reports of physically cross-linked CNC aerogels. Specifically, the aerogel shape recovers at least 85% after 80% compressive strain, even after 20 compress and release cycles. These CNC aerogels can absorb significant amounts of both water (160 ± 10 g per g) and dodecane (72 ± 5 g per g) with cyclic absorption capacity. It is demonstrated that CNC aerogels may have application as superabsorbents and for oil/water separations.