Cross-linking induced thermo-responsive self-healing hydrogel with gel-sol–gel transition constructed on dynamic covalent bond

Injectable, self-healing and degradable dynamic hydrogels with tunable mechanical properties and stability by thermal-induced micellization

Dynamic hydrogels possessing injectable, degradable and self-healing abilities have attracted considerable attention in the biomedical field in recent years, but it is difficult to tune the mechanical properties and stability of conventional dynamic hydrogels. In this work, we synthesized ABA-triblock copolymers via RAFT polymerization, where the A block consisted of thermo-sensitive poly(N-isopropylacrylamide-co-diacetone acrylamide) and the B block was hydrophilic poly(acrylamide). Subsequently, dynamic hydrogels were obtained based on the acylhydrazone bonds between the triblock copolymers and adipic acid dihydrazide (ADH). The obtained hydrogels exhibited injectable and self-healable abilities. In response to the thermal-induced micellization of their temperature-responsive blocks, the mechanical strength of the hydrogels not only increased, but also they exhibited high stability even at pH 2.0. Moreover, the hydrogel in the stable state could be degraded by the fracture of its trithiocarbonate groups. In addition, the hydrogels exhibited good cytocompatibility and controlled release behavior for doxorubicin (DOX). Considering these attractive tunable properties, these dynamic hydrogels show various potential applications in the biomedical field, such as drug carriers and cell or tissue engineering scaffolds.

Elastic and Self-Healing Copolymer Coatings with Antimicrobial Function

The revolutionary self-healing function for long-term and safe service processes has inspired researchers to implement them in various fields, including in the application of antimicrobial protective coatings. Despite the great advances that have been made in the field of fabricating self-healing and antimicrobial polymers, their poor transparency and the trade-off between the mechanical and self-healing properties limit the utility of the materials as transparent antimicrobial protective coatings for wearable optical and display devices. Considering the compatibility in the blending process, our group proposed a self-healing, self-cross-linkable poly{(n-butyl acrylate)-co-[N-(hydroxymethyl)acrylamide]} copolymer (AP)-based protective coating combined with two types of commercial cationic antimicrobial agents (i.e., dimethyl octadecyl (3-trimethoxysilylpropyl) ammonium chloride (DTSACL) and chlorhexidine gluconate (CHG)), leading to the fabrication of a multifunctional modified compound film of (AP/b%CHG)-grafted-a%DTSACL. The first highlight of this research is that the reactivity of the hydroxyl group in the N-(hydroxymethyl)acrylamide of the copolymer side chains under thermal conditions facilitates the "grafting to" process with the trimethoxysilane groups of DTSACL to form AP-grafted-DTSACL, yielding favorable thermal stability, improvement in hydrophobicity, and enhancement of mechanical strength. Second, we highlight that the addition of CHG can generate covalent and noncovalent interactions in a complex manner between the two biguanide groups of CHG with the AP and DTSACL via a thermal-triggered cross-linking reaction. The noncovalent interactions synergistically serve as diverse dynamic hydrogen bonds, leading to complete healing upon scratches and even showing over 80% self-healing efficiency on full-cut, while covalent bonding can effectively improve elasticity and mechanical strength. The soft nature of CHG also takes part in improving the self-healing of the copolymer. Moreover, it was discovered that the addition of CHG can enhance antimicrobial effectiveness, as demonstrated by the long-term superior antibacterial activity (100%) against Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria and the antifouling function on a glass substrate and/or a silica wafer coated by the modified polymer.

Self- and Cross-Fusing of Furan-Based Polyurea Gels Dynamically Cross-Linked with Maleimides

Bio-based polyureas (PUs) with main-chain furan rings were synthesized by the polyaddition of 2,5-bis(aminomethyl)furan with various diisocyanates, such as methylene diphenyl diisocyanate. Several PU's were soluble in polar organic solvents, and were cast to form thermomechanically stable films with softening temperatures of over 100 °C. The furan rings of the PU main chains underwent a dynamic Diels-Alder (DA) reaction with bismaleimide (BMI) cross-linkers. While the mixed solution of PU and BMI did not show any apparent signs of reaction at room temperature, the DA reaction proceeded to form gels upon heating to 60 °C, which became a solution again by further heating to 80 °C (retro-DA reaction). The solution phase was maintained by rapid quenching from 80 °C to room temperature, while the gel was reformed upon slow cooling. The recovered gels exhibited self-healing properties. A scratch made by a hot knife at temperatures above 80 °C disappeared spontaneously. When two different gels were cut using a knife at room temperature, placed in contact with each other, and heated to 60 °C, they fused. The ability to control the DA/retro-DA reaction allowed gels of varying composition to heal.

Microstructure and Self-Healing Capability of Artificial Skin Composites Using Biomimetic Fibers Containing a Healing Agent

The aging and damage of artificial skin materials for artificial intelligence robots are technical problems that need to be solved urgently in their application. In this work, poly (vinylidene fluoride) (PVDF) fibers containing a liquid agent were fabricated directly as biomimetic microvasculars, which were mixed in a glycol-polyvinyl alcohol-gelatin network gel to form biomimetic self-healing artificial skin composites. The self-healing agent was a uniform-viscous buffer solution composed of phosphoric acid, acetic acid, and sodium carboxymethyl cellulose (CMC-Na), which was mixed under 40 °C. Microstructure analysis showed that the fiber surface was smooth and the diameter was uniform. SEM images of the fiber cross-sections showed that there were uniformly distributed voids. With the extension of time, there was no phenomenon of interface separation after the liquid agent diffused into the matrix through the fiber cavity. The entire process of self-healing was observed and determined including fiber breakage and the agent diffusion steps. XRD and FT-IR results indicated that the self-healing agent could enter the matrix material through fiber damage or release and it chemically reacted with the matrix material, thereby changing the chemical structure of the damaged matrix. Self-healing behavior analysis of the artificial skin indicated that its self-healing efficiency increased to an impressive 97.0% with the increase in temperature to 45 °C.