Self-healing gels based on constitutional dynamic chemistry and their potential applications

Abstract

As representative soft materials with widespread applications, gels with various functions have been developed. However, traditional gels are vulnerable to stress-induced formation of cracks. The propagation of these cracks may affect the integrity of network structures of gels, resulting in the loss of functionality and limiting the service life of the gels. To address this challenge, self-healing gels that can restore their functionalities and structures after damage have been developed as "smart" soft materials. In this paper, we present an overview of the current strategies for synthesizing self-healing gels based on the concept of constitutional dynamic chemistry, which involves molecular structures capable of establishing dynamic networks based upon physical interactions or chemical reactions. The characterization methods of self-healing gels and the key factors that affect self-healing properties are analyzed. We also illustrate the emerging applications of self-healing gels, with emphasis on their usage in industry (coatings, sealants) and biomedicine (tissue adhesives, agents for drug or cell delivery). We conclude with a perspective on challenges facing the field, along with prospects for future development.

Functional self-healing materials and their potential applications in biomedical engineering

“…For example, PEGchitosan and chitosan-based hydrogels possess high biocompatibility and were proposed for drug delivery as an injectable hydrogel [26,27,97]. A rapid self-healing hydrogel A6ACA was also proposed to be used as a new generation of tissue adhesive due to its excellent adhesion ability [37,52]. Furthermore, some unique properties of self-healing materials are quite intriguing to in vivo applications.…”

“…Thus, either a tensile test or a rheological measurement was widely accepted as the characterization method to quantify the healing extent in the literature reports. Healing efficiency relying on a tensile test can be defined as the ratio of the stress of the healed and original material [52,62]. This method is more suitable for self-healing materials which are able to stand the stress of clamps [7,63,64].…”

“…With the capability to respond to certain external stimuli, rationally designed smart materials with self-healing properties hold great potential for applications in the fields of which specific environmental conditions are inevitable. For example, low pH-stimulated self-repairing materials are desired for tissue adhesion in the stomach which contains corrosive acid solution for digestion [37,52]. In addition, stimulus-responsive properties bring other functionalities into the same system beyond self-healing function, broadening the scope of applications in which multiple functionalities are required simultaneously.…”

Mussel-mimetic self-healing polyaspartamide derivative gel via boron-catechol interactions

“…An inexpensive and biocompatible self-healing hydrogel for injectable cell therapy carrier was also investigated by Yang et al [14]. Recently, some significant work has focused on non-covalent hydrogels, which are cross-linked by reversible interactions based on metal-ligand coordination in the polymer chains; these can provide stimuli responsiveness, magnetic self-healing and good mechanical properties [8][9][10][15][16][17][18][19][20]. Because of the thermodynamics and kinetic properties of metal-ligand coordination bonds, metal-ligand interactions can provide stable, reversible crosslinking points between polymers [21].…”

“…Covalent bonding or non-covalent interactions (such as hydrogen bonding [5,6], !-! interactions [7], metal-ligand coordination bonding [8][9][10], or guest-host interactions [11] can form soft three-dimensional polymeric network hydrogels, which are defined as chemical gels or physical gels, respectively. In covalent hydrogels, it is difficult to induce a sol-gel transition in response to external stimuli or provide a selfhealing mechanism.…”