Autonomic Self‐Healing of Hydrogel Thin Films

Abstract

Soft yet strong: Colloidal hydrogel films, which are constructed using a layer‐by‐layer polyelectrolyte approach, are easily damaged by mechanical disruption, but can also autonomically heal (see picture). The healing event occurs within seconds once the film has been resolvated. The lability of the coulombic interactions between hydrogel particle and linear polymer plays a direct role in its ability to self‐heal.

Polyelectrolyte exchange and diffusion in microgel multilayer thin films

“…Microgels were synthesized using a previously described aqueous free-radical precipitation polymerization method [37,38]. Microgels composed of NIPAm (78 %), AAc (20 %), and BIS (2 %) were synthesized with a total monomer concentration of 120 mM.…”

“…To further investigate polyelectrolyte exchange (or lack thereof), we measured the degree of polyelectrolyte redistribution following mechanical film disruption. It has been shown previously that dry microgel films can be easily damaged upon stretching, poking, or scratching, and this damage can be healed upon immersion in water or even exposure to a humid environment [37,41]. By stretching and scratching the film and causing mechanical perturbation, the degree to which this perturbation influences PLL* redistribution can be determined.…”

“…Because microgels intrinsically hold properties that are both colloidal and polymeric, a variety of functionalities can be incorporated, such as environmental responsivity or tunability [34,35]. This has led to the utilization of microgels in a variety of applications, either as individual entities for applications such as drug delivery [36] or as building blocks in the construction of multi-layer films that exhibit characteristics such as self-healing behavior [37], resistance to cell adhesion [38], or drug delivery depots [1,2]. Multi-layer films composed using microgel building blocks have been of particular interest in more recent years because they alleviate the swelling constraints of hydrogel bulk materials [39] and additionally permit the incorporation of multiple responsivities in a controlled manner [40].…”

“…As noted above, studies of these multilayer films have revealed dynamic behavior of microgel multi-layer thin films. [37,38] However, an understanding of the interactions at play that allow for such behavior is under-developed and a deeper understanding of these materials is desired. More recent research on microgel-polyelectrolyte films has been devoted to obtaining a better understanding of the role of the microgel in dynamic film behavior [41], but as noted therein, additional studies are necessary to understand the fundamental parameters of these microgel film components.…”

Macromolecular self-assembly and nanotechnology in China

“…The LbL assembly is also promising in fabricating intrinsic self-healing films capable of repairing deep cuts or scratches on the films [54,55]. Taking advantage of exponential LbL assembly to rapidly fabricate thick polyelectrolyte multi-layer films and adjust polyelectrolyte inter-diffusion, intrinsic self-healing films composed of alternately deposited branched poly(ethylenimine) (bPEI) and PAA were fabricated.…”