Spin-coating-assisted fabrication of ultrathin physical hydrogel films with high toughness and fast response

Abstract

Hydrogel films have promising applications in medical dressings, flexible electronics, etc. However, it is challenging to fabricate ultrathin hydrogel films with high toughness and controllable thickness. Here, we report a facile approach to prepare tough physical hydrogel films by spin-coating of a poly(acrylic acid-co-acrylamide) (P(AAc-co-AAm)) solution and subsequent gelation in FeCl3 solution to form carboxyl-Fe3+ coordination complexes. The thickness of the obtained gel films, ranging from several to hundreds of micrometers, was easily tunable by adjusting the spin conditions and polymer concentration. The thus obtained hydrogel films showed excellent mechanical properties, with tensile breaking strengths of 0.6-14.5 MPa, breaking strains of 140-840%, Young's moduli of 0.1-61.7 MPa, and tearing fracture energies of 300-1300 J m-2. Based on this approach, responsive tough hydrogel films can also be prepared by spin-coating of a poly(acrylic acid-co-N-isopropylacrylamide) (P(AAc-co-NIPAm)) solution. The obtained gel films showed a fast response (<60 s) and a large output force (∼0.2 MPa) triggered by a concentrated saline solution, making them an ideal material in the design of chemomechanical devices. Furthermore, a bilayer hydrogel film was fabricated by two-step spin-coating of P(AAc-co-NIPAm) and P(AAc-co-AAm) solutions, which showed reversible bending deformation under external stimuli. This simple yet effective approach should be applicable to other systems to prepare versatile hydrogel films with tunable thickness and promising applications in diverse areas.

Engineering Tough Metallosupramolecular Hydrogel Films with Kirigami Structures for Compliant Soft Electronics

“…Our group also prepared tough supramolecular hydrogel films by spin-coating of a poly(acrylamide-coacrylic acid) solution followed by incubating the films in ferric ion solution to form robust carboxyl-Fe 3+ coordination complexes that physically crosslink the copolymer chains. [30] The resultant hydrogel films with thickness of 5-110 μm had σ b of 0.6-14.5 MPa, ε b of 140-840%, E of 0.1-61.7 MPa, and tearing fracture energy (G) of 300-1300 J m −2 . However, the directional diffusion of Fe 3+ ions from one side of the spin-coated solution film resulted in through-thickness gradient of the hydrogel film.…”

“…[10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] In recent years, there are several attempts to develop tough hydrogel films. [28][29][30][31][32][33] For example, Gong et al successfully developed tough hydrogel films by spincoating to form the first physical network and subsequent polymerization to form the second network. [28] The obtained gel films with thickness of 5-100 μm possessed excellent mechanical properties, with tensile breaking stress (σ b ) of 0.2-7 MPa, breaking strain (ε b ) of 200-1000%, and Young's modulus (E) of 0.1-100 MPa.…”

Multi-level encryption of information in morphing hydrogels with patterned fluorescence

“…The bilayer hydrogel deformed into a roll at room temperature and recovered to the flat shape at an elevated temperature. 49 Multiple conditions are required to decrypt the information concealed in the bilayer hydrogel: heating to flatten the bilayer gel and UV light irradiation from the right direction. This scenario is demonstrated in Fig.…”

Dual‐responsive shape memory hydrogels with self‐healing and dual‐responsive swelling behaviors

“…Smart hydrogels could vary in volume, structure and other properties when the hydrogels are subjected to an external stimulation, such as temperature, pH, solvent, ionic strength, etc.. [42][43][44][45][46][47] Notably, the ions carried on the polymer chain of the hydrogels will provide the hydrogels with both pH-responsive and saline-responsive swelling properties. 48 Considering the excessive consumption of nonrenewable resources and severe environmental pollution, the exploration of hydrogels from renewable resources has drawn significant attention.…”

“…Smart hydrogels could vary in volume, structure and other properties when the hydrogels are subjected to an external stimulation, such as temperature, pH, solvent, ionic strength, etc. 42–47 . Notably, the ions carried on the polymer chain of the hydrogels will provide the hydrogels with both pH‐responsive and saline‐responsive swelling properties 48 …”