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

Abstract

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(Nisopropylacrylamide) (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.

Flax fibre reinforced alginate poloxamer hydrogel: assessment of mechanical and 4D printing potential

“…For instance, Goyal et al produced an alginate-based hydrogel less stiff but more actuation-capable alginate based hydrogel. 83 For non-alginate-based hydrogel Zheng et al have described the possibility of using them as grip. 84 Hence, depending on the material to be lifted, the stiffness and actuation capability must be adapted, by changing the amount of reinforcement, the stacking sequence printed.…”

“…17 presents two examples of the 4D printing using room humidity actuation. Rosette structures (inspired like Goyal et al by flowers 83 ) were printed using alginate-poloxamer hydrogel reinforced with 1% flax fibre weight fraction. Upon drying the specimen went from flat to 8 mm high on its highest point.…”

Controllable Shape Morphing Nanocomposite Hydrogels for Robust Multi-Stimuli-Responsive Actuators

“…Designing and developing smart hydrogels for soft actuators with controllable stimuli-responsive shape deformations have aroused tremendous research interests in recent years. − Taking advantage of delicate design of internal structure and precise control of external stimuli, , smart hydrogels can easily and programmatically change the shapes through controllable uneven swelling/deswelling. Following this principle, smart hydrogels with complex deformations such as bending, − folding, − and bucking and twisting − have been successfully explored as soft actuators for a wide range of applications. − Particularly, magnetism or near-infrared light stimuli-response contributes to the rapid and noncontact control ,,,, and superior mechanical properties serve to build the reusability and durability, , which enable the shape-deformable hydrogels to play a more important role in serving as actuators for extended promising applications.…”