Controlled Thermoreversible Formation of Supramolecular Hydrogels Based on Poly(vinyl alcohol) and Natural Phenolic Compounds

Abstract

Supramolecular materials based on noncovalent bonds have attracted considerable attention in several fields due to their special characteristics such as self-healing, shape memory, and stimuli-responsive properties among others. [1][2][3][4][5][6][7][8][9][10] Indeed, multiple hydrogen bonding are ideal reversible noncovalent interactions for preparing supramolecular networks combining high strength and excellent reversibility. [11][12][13][14][15][16][17][18][19][20][21] Supramolecular Thermoresponsive Hydrogels Supramolecular hydrogels have promising applications in a wide variety of fields including 3D bioprinting, sensors and actuators, biomedicine, and controlled drug delivery. This communication reports the facile reversible thermotriggered formation of novel pH-responsive supramolecular hydrogels based on poly(vinyl alcohol) (PVA) bonded via dynamic H-bridge with small phenolic biomolecules. PVA and phenolic compounds form a clear solution when they are physically mixed in water at high temperature, but a fast gelation is produced at room temperature through multiple strong H-bonding interactions. The structure and type of functional groups of different phenolic molecules allow preparing hydrogels with tailor-made viscoelastic properties, controlled low phase transition temperature, and pH-dependent swelling behavior. This combination makes these supramolecular networks very interesting candidates to be used in 3D bioprinting and topical drug delivery of thermolabile biomolecules.

Elastic and Thermoreversible Iongels by Supramolecular PVA/Phenol Interactions

“…As it can be seen in Figure 2 were not modified after the gel formation process (Figure 2). Contrary to what was reported regarding the formation of supramolecular PVA-GA hydrogels, [43] no significant shifts were observed in the C=O stretching band and phenyl C−OH stretching corresponding to GA for the iongels prepared in the present work. This is probably attributed to the high IL content in the iongel formulation, which can overlap the visualization of peaks shifting in the iongel formed through multiple hydrogenbonding interactions.…”

“…They are able to resist large deformations, recovering their initial shape after load remove with a non-linear evolution of compression stress versus strain ( Figure 6.A and video S3 and S4 of the SI). the PVA-GA hydrogel previously reported [43] are given in Figure 7 (C,D), respectively.…”

“…[48,49] Our recent results showed that phenolic compounds can induce the organization of PVA chains within hydrogels in semi-crystalline domains with a spatial arrangement completely different than that of the neat PVA. [43] For this reason, it was important to investigate the diffraction pattern of the prepared iongels in order to get insights regarding the IL effect on the PVA/phenol supramolecular assembly. From Figure S2, it can be observed that the supramolecular iongels showed a characteristic XRD spectrum of an amorphous material, suggesting that the ILs are playing an important role in the supramolecular interactions, preventing to some extent the organization of the typical PVA/phenol arrangement previously observed in hydrogels.…”

“…Two bands at 1426 and 1085 cm can be assigned to the in‐plane OH bending and COH stretching of PVA, respectively. [ 44 ] The C=O and COH stretching bands corresponding to GA can be seen at 1662 and 1309 cm, respectively. The stretching corresponding to CN of the IL dicyanimide anion [ 45 ] can also be observed at 2250 cm in the iongel spectrum.…”

High strength and bioactivity polyvinyl alcohol/collagen composite hydrogel with tannic acid as cross‐linker

“…With the increase of TA content, the protofilament fibers gradually disappeared and the fibers became thicker. [ 48 ] These results indicate that TA could promote the combination of original independent PVA and COL macromolecular chain rather than the separation of COL fibrous structure and PVA dense structure. TA played a role of a bridge between PVA and COL macromolecular chains and hydrogen bonds were formed between PVA (or COL) and TA.…”