Herein, we report a method of fabricating strong and thermosensitive double network (T-DN) poly(N-isopropyl acrylamide) (PNIPAM)-based hydrogels, i.e. rigid and brittle poly(2-acrylamido-2-methylpropanesulfonic acid sodium salt) (PNaAMPS) as the first and soft and ductile poly(N-isopropyl acrylamide-co-acrylamide) (P(NIPAM-co-AAm)) as the second interpenetrating each other. In particular, NIPAM was deliberately integrated into the double network as an adjustor of elastic modulus and hydrophilicity, besides thermosensitivity. Such double network construction strategy resulted in PNaAMPS/P(NIPAM-co-AAm) T-DN hydrogels of excellent mechanical properties (0.83–1.37 MPa) and desirable temperature-dependent swellabilities. Besides, T-DN hydrogels with various NIPAM contents exhibited good biocompatibility with high cell survival rates around normal body temperatures. Furthermore, crystal violet (CV) could be readily loaded to impart antibacterial functionality to the T-DN hydrogels against E. coli. The double network construction strategy could be adapted to fabricating high-strength antibacterial hydrogels for a broad range of biomedical applications.

Photoinduced self-crosslinking technology is a great facilitator of 3D bioprinting of silk fibroin (SF) by allowing rapid solidification of a deliberately formulated SF-based photocrosslinkable bioink. An SF-based, photocrosslinked hydrogel was fabricated with tyramine-modified sodium carboxymethyl cellulose (CMC-Na) as a co-crosslinkable constituent and Ru(bpy)₃Cl₂ (Ru(II)) and potassium persulfate (KPS) as blue light photoinitiators. Photorheological studies demonstrated that the photocrosslinking and viscoelasticity of the composite could be tuned by varying the relative content of the two constituents. Xanthan gum (XG) was employed in formulating the SF-based photocrosslinkable bioink, and the improved rheological properties and printability were evidenced by the resulting tunable shear-thinning behavior and shear thixotropy. 3D SF-based hydrogel scaffolds with uniform pores with a size of approximately 550 μm × 1000 μm were constructed via extrusion-based printing and a simple 30 s post-photocrosslinking combined process. Furthermore, the CMC-Na incorporated 3D hydrogel scaffolds exhibited sufficient structural strength, adequate filament fineness, and tunable transparency, which shows a promising prospect in the application of tissue engineering and regenerative medicine.

The influence of ethylene glycol methacrylate (EGMA) to the hydration and transition behaviors of thermo-responsive interpenetrating polymeric network (IPN) hydrogels containing sodium alginate, N-isopropylacrylamide (NIPAAm), and EGMA were investigated. The molar ratios of NIPAAm and EGMA were varied from 20:0 to 19.5:0.5 and 18.5:1.5 in the thermo-responsive alginate-Ca²⁺/P(NIPAAm-co-EGMA) IPN hydrogels. Due to the more hydrophilicity and high flexibility of EGMA, the IPN hydrogels exhibited higher lower critical solution temperature (LCST) and lower glass transition temperature (T_g) when the ratio of EGMA increases. The swelling/deswelling kinetics of the IPN hydrogels could be controlled by adjusting the NIPAAm/EGMA molar ratio. A faster water uptake rate and a slower water loss rate could be realized by increase the amount of EGMA in the IPN hydrogel (the shrinking rate constant was decreased from 0.01207 to 0.01195 and 0.01055 with the changing of NIPAAm/EGMA ratio from 20:0, 19.5:0.5 to 18.5:1.5). By using 2-Isopropylthioxanthone (ITX) as a photo initiator, the obtained alginate-Ca²⁺/P(NIPAAm-co-EGMA₃₆₀) IPN hydrogels were successfully immobilized on cotton fabrics. The surface and cross section of the hydrogel were probed by scanning electron microscopy (SEM). They all exhibited a porous structure, and the pore size was increased with the amount of EGMA. Moreover, the LCST values of the fabric-grafted hydrogels were close to those of the pure IPN hydrogels. Their thermal sensitivity remained unchanged. The cotton fabrics grafted with hydrogel turned out to be much softer with the continuous increase of EGMA amount. Therefore, compared with alginate-Ca²⁺/PNIPAAm hydrogel, alginate-Ca²⁺/P(NIPAAm-co-EGMA₃₆₀) hydrogel is a more promising candidate for wound dressing in the field of biomedical textile.