3D Printing of Dual-Physical Cross-linking Hydrogel with Ultrahigh Strength and Toughness

Abstract

3D printing of hydrogels with high intrinsic mechanical performance has significant applications in many fields yet has been proven to be a fundamental challenge. Here, 3D printing of ultrahigh strength hydrogels is achieved by constructing cross-linkingDPC networks based on poly­(vinyl alcohol) (PVA) and chitosan (CS). The hybrid ink with moderate rheology for direct ink writing is employed to manufacture complex hydrogel structures, first. Then, the cyclic freezing–thawing followed by sodium citrate solution soaking realize the first network of PVA crystallization and the second one of CS ionic interaction between amino and carboxyl groups. The optimized DPC hydrogel displays a tensile strength of 12.71 ± 1.32 MPa at a strain of 302.27 ± 15.70%, Young’s modulus of 14.01 ± 1.35 MPa, and work of extension at fracture W ext of 22.10 ± 2.36 MJ m–3 because of the dominant energy dissipation of the stiff CS ionic network. Moreover, the tearing test supports that this DPC hydrogel possesses a high toughness of 9.92 ± 1.05 kJ m–2. This protocol can readily realize not only the hydrogel lattice, honeycomb, and spring, but also secondary-shaping hydrogel objects including whale, octopus, and butterfly via a local DPC strategy. Integrating the advanced 3D-printing technique with high-performance hydrogels uncovers a feasible strategy to broad practical applications in engineering, intelligent machine, and soft robotics.

Poly(vinyl alcohol) Hydrogels: The Old and New Functional Materials

“…Physical crosslinking chitosan (CS)/PVA blend hydrogels with only PVA gelated networks have been widely used in many fields [40,41]. A 3D-printing hydrogel was developed by cooperating the physically gelated PVA as the stretchable polymer network together with alkaline polysaccharide CS, as shown in Figure 3(b), which improved the mechanical strength of such blend system [42]. Solvents including DMSO, ethylene glycol, and glycerol could serve as plasticizers that promote structural stability and help produce firmer PVA hydrogels due to the penetration of the PVA gel matrix [43][44][45].…”

“…Figure3: Modification of PVA by: (a) CBA-PVA (chemically)[38], (b) CS/PVA (physically)[42], (c) GO/PVA (filler)[57], and (d) CS/ PVA/CeO 2 (polymer and filler)[58].…”

Growing Hydrogel Organ Mannequins with Interconnected Cavity Structures

“…During the extruded process at the printing window, the ink exhibits the essential shear‐thinning behavior, resulting in a sharp decline in G ′. [ 22 ] The hydrogel filaments can remain the exact shape after being extruded from the nozzle and deposit on the platform owing to the rapidly viscoelastic recovery at room temperature.…”

PVA‐Based Hydrogels: Promising Candidates for Articular Cartilage Repair

“…Biopolymers added in PVA hydrogels are usually polysaccharides (cellulose, [ 27 ] chitosan, [ 60 ] soy fiber, [ 69 ] cotton fiber [ 70 ] ) or proteins such as normal collagen or human‐like collagen (HLC), [ 26,71 ] among which chitosan is reported to be successfully added by novel 3D printing technique. [ 72 ] In situ degradability requires attention when these biopolymers are applied. For example, bacterial cellulose (BC) that cannot be degraded by human enzymes is frequently used as strengthening cellulose.…”