Recently, flexible, injectable, and strain-sensitive hydrogels have attracted great research interest for application as electronic skin and wearable strain sensors. The synergistic integration of high flexibility, rapid self-healing, and antifreezing properties makes injectable, strain-sensitive, and self-healing guar gum hydrogels still a great challenge. Here, inspired by the strong hydrogen bonding of glycerol and water, the chelation cross-linking between glycerol and borax, we constructed a compact three-dimensional dynamic cross-linked net formed of glycerol–water–borax. Under stress, dynamic interactions of glycerol–water–borax net act as sacrificial bond energy for effective dissipation, which enables the hydrogel to achieve high flexibility, stretchability, and injectability. More importantly,because of the presence of glycerol, the antifreeze and moisturizing properties of the gel are improved. The hydrogel also exhibited an ultrafast self-healing ability of only 15 s. In addition, the results show that the hydrogel has self-adhesive properties and strain sensitivity. The hydrogels have the potential to be used to make flexible, wearable, and 3D-printable electronic skin and strain-sensitive sensors.

Tunicate is a kind of marine animal, and its outer sheath consists of almost pure Iβ crystalline cellulose. Due to its high aspect ratio, tunicate cellulose has excellent physical properties. It draws extensive attention in the construction of robust functional materials. However, there is little research on its biological activity. In this study, cellulose enzymatic hydrolysis was conducted on tunicate cellulose. During the hydrolysis, the crystalline behaviors, i.e., crystallinity index (CrI), crystalline size and degree of polymerization (DP), were analyzed on the tunicate cellulose. As comparisons, similar hydrolyses were performed on cellulose samples with relatively low CrI, namely α-cellulose and amorphous cellulose. The results showed that the CrI of tunicate cellulose and α-cellulose was 93.9% and 70.9%, respectively; and after 96 h of hydrolysis, the crystallinity, crystalline size and DP remained constant on the tunicate cellulose, and the cellulose conversion rate was below 7.8%. While the crystalline structure of α-cellulose was significantly damaged and the cellulose conversion rate exceeded 83.8% at the end of 72 h hydrolysis, the amorphous cellulose was completely converted to glucose after 7 h hydrolysis, and the DP decreased about 27.9%. In addition, tunicate cellulose has high anti-mold abilities, owing to its highly crystalized Iβ lattice. It can be concluded that tunicate cellulose has significant resistance to enzymatic hydrolysis and could be potentially applied as anti-biodegradation materials.

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In this work, the tunicate cellulose nanocrystal (tCNC) was extracted from tunicate by bleaching and acid hydrolysis. It was used as ller in the preparation of sodium alginate-based enteric capsule. The addition of tCNC with high aspect ratio (65) rendered the enteric capsule excellent physical properties. Compared with the control sample, when the addition of tCNC was 10% (wt), the water contact angle of the capsule was enhanced by 46.0%, the opacity was increased by 356.8%, the maximum tensile stress was increased by 142.6%, the modulus of elasticity was increased by 240.3%, and the elongation at break was increased by 133.8%. In the in vitro degradation experiments, the capsule hardly degraded in the gastric environment (pH 1.2), while in the intestinal environment (pH 6.8), the degradation became slower with the increase of tCNC content, which was consistent with the properties of enteric capsule. This research developed a new direction for the application of tCNC in the pharmaceutical material productions.

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