Nanocellulose-Reinforced 4D Printed Hydrogels: Thermoresponsive Shape Morphing and Drug Release AITranslate

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DOI：https://doi.org/10.1021/acsapm.3c02420

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Four-dimensional (4D) printed polymer composite hydrogels with stimuli-responsive shape-morphing features are attractive to fabricate dynamic multifunctional structures for the upcoming next generation of biomedical applications. Poly(N-isopropylacrylamide) (PNIPAM) is an attractive polymer choice, as it undergoes a phase transition at a temperature similar to our body, but it suffers from poor printability and low mechanical properties. In the present work, we demonstrated a thermoresponsive hydrogel printing ink, PNIPAM/Alginate (Alg) reinforced with elastic biosourced nanocellulose fibers, to enable anisotropic shape morphing at and above 36 °C. During direct ink writing, a shear-induced alignment of cellulose fibrils within the ink followed by ionic and light-driven cross-linking of the gel led to an improved shape fidelity of the bilayer printed architectures. Printed TEMPO-oxidized CNF (TCNF)-reinforced hydrogels revealed appreciable overall and higher directional mechanical properties as compared to the CNF-reinforced construct. The TCNF-based sample showed tensile strength, Young’s modulus, and toughness values of 150 kPa, 6.77 MPa, and 83 kJ m–3 and 50 kPa, 7.3 MPa, and 16 kJ m–3 in the longitudinal and transverse directions, respectively. Furthermore, a higher value of controlled drug release from the TCNF-containing printed sample than that from the casted sample revealed promising benefits of the former for antimicrobial activity. The cross-linked temperature-dependent degree of swelling, on immersion in water, of the printed dynamic hydrogel with temperature-programmable control is showcased by the optimized ink formulation. Different mechanical and physical properties in different printing directions, due to intrinsic anisotropy and fiber direction alignment, provided a facile method for 4D printing of thermoresponsive shape-morphing functional architectures. The present strategy reveals potential for exploration of the devised sustainable ink formulation in a variety of biomedical applications such as tissue engineering and soft robotic devices.