Self‐Healing Zwitterionic Microgels as a Versatile Platform for Malleable Cell Constructs and Injectable Therapies

Injectable and malleable hydrogels that combine excellent biocompatibility, physiological stability, and ease of use are highly desirable for biomedical applications. Here, a simple and scalable strategy is reported to make injectable and malleable zwitterionic polycarboxybetaine hydrogels, which are superhydrophilic, nonimmunogenic, and completely devoid of nonspecific interactions. When zwitterionic microgels are reconstructed, the combination of covalent crosslinking inside each microgel and supramolecular interactions between them gives the resulting zwitterionic injectable pellet (ZIP) constructs supportive moduli and tunable viscoelasticity. ZIP constructs can be lyophilized to a sterile powder that fully recovers its strength and elasticity upon rehydration, simplifying storage and formulation. The lyophilized powder can be reconstituted with any aqueous suspension of cells or therapeutics, and rapidly and spontaneously self‐heals into a homogeneous composite construct. This versatile and highly biocompatible platform material shows great promise for many applications, including as an injectable cell culture scaffold that promotes multipotent stem cell expansion and provides oxidative stress protection.     

Self‐Healing Hydrogels

Over the past few years, there has been a great deal of interest in the development of hydrogel materials with tunable structural, mechanical, and rheological properties, which exhibit rapid and autonomous self‐healing and self‐recovery for utilization in a broad range of applications, from soft robotics to tissue engineering. However, self‐healing hydrogels generally either possess mechanically robust or rapid self‐healing properties but not both. Hence, the development of a mechanically robust hydrogel material with autonomous self‐healing on the time scale of seconds is yet to be fully realized. Here, the current advances in the development of autonomous self‐healing hydrogels are reviewed. Specifically, methods to test self‐healing efficiencies and recoveries, mechanisms of autonomous self‐healing, and mechanically robust hydrogels are presented. The trends indicate that hydrogels that self‐heal better also achieve self‐healing faster, as compared to gels that only partially self‐heal. Recommendations to guide future development of self‐healing hydrogels are offered and the potential relevance of self‐healing hydrogels to the exciting research areas of 3D/4D printing, soft robotics, and assisted health technologies is highlighted.     

Self‐Healing Materials

Self‐healing materials are able to partially or completely heal damage inflicted on them, e.g., crack formation; it is anticipated that the original functionality can be restored. This article covers the design and generic principles of self‐healing materials through a wide range of different material classes including metals, ceramics, concrete, and polymers. Recent key developments and future challenges in the field of self‐healing materials are summarised, and generic, fundamental material‐independent principles and mechanism are discussed and evaluated.     

Writing,Self‐Healing,and Self‐Erasing on Conductive Pressure‐Sensitive Adhesives

A simple strategy for enabling conductive pressure sensitive adhesives (PSAs) to work as light‐responsive materials is reported. Direct laser‐writing of PSA substrates was achieved by means of a continuous‐wave He‐Ne laser focused through the objectives of an optical microscope. This approach takes advantage of cooperative interplay between viscoelastic properties of PSAs and enhanced thermal conductivity provided by an extra overlayer of gold. In particular, the thickness of the gold layer is a crucial parameter for tuning the substrate responsiveness. Self‐healing and self‐degradation processes can be exploited for controlling the lifetime of the written information, whereas additional protective coatings can be introduced to achieve permanent storage.