Hydrogels, due to their excellent biochemical and mechnical property, have shown attractive advantages in the field of wound dressings. However, a comprehensive review of the functional hydrogel as a wound dressing is still lacking. This work first summarizes the skin wound healing process and relates evaluation parameters and then reviews the advanced functions of hydrogel dressings such as antimicrobial property, adhesion and hemostasis, anti-inflammatory and anti-oxidation, substance delivery, self-healing, stimulus response, conductivity, and the recently emerged wound monitoring feature, and the strategies adopted to achieve these functions are all classified and discussed. Furthermore, applications of hydrogel wound dressing for the treatment of different types of wounds such as incisional wound and the excisional wound are summarized. Chronic wounds are also mentioned, and the focus of attention on infected wounds, burn wounds, and diabetic wounds is discussed. Finally, the future directions of hydrogel wound dressings for wound healing are further proposed.

Functional Hydrogels as Wound Dressing to Enhance Wound Healing.

As a mussel-inspired material, polydopamine (PDA), possesses many properties, such as a simple preparation process, good biocompatibility, strong adhesive property, easy functionalization, outstanding photothermal conversion efficiency, and strong quenching effect. PDA has attracted increasingly considerable attention because it provides a simple and versatile approach to functionalize material surfaces for obtaining a variety of multifunctional nanomaterials. In this review, recent significant research developments of PDA including its synthesis and polymerization mechanism, physicochemical properties, different nano/microstructures, and diverse applications are summarized and discussed. For the sections of its applications in surface modification and biomedicine, we mainly highlight the achievements in the past few years (2016-2019). The remaining challenges and future perspectives of PDA-based nanoplatforms are discussed rationally at the end. This timely and overall review should be desirable for a wide range of scientists and facilitate further development of surface coating methods and the production of PDA-based materials.

Versatile Polydopamine Platforms: Synthesis and Promising Applications for Surface Modification and Advanced Nanomedicine

Diabetic wound healing and angiogenesis remain a worldwide challenge for both clinic and research. The use of adipose stromal cell derived exosomes delivered by bioactive dressing provides a potential strategy for repairing diabetic wounds with less scar formation and fast healing. In this study, we fabricated an injectable adhesive thermosensitive multifunctional polysaccharide-based dressing (FEP) with sustained pH-responsive exosome release for promoting angiogenesis and diabetic wound healing. The FEP dressing possessed multifunctional properties including efficient antibacterial activity/multidrug-resistant bacteria, fast hemostatic ability, self-healing behavior, and tissue-adhesive and good UV-shielding performance. FEP@exosomes (FEP@exo) can significantly enhance the proliferation, migration, and tube formation of endothelial cells in vitro. In vivo results from a diabetic full-thickness cutaneous wound model showed that FEP@exo dressing accelerated the wound healing by stimulating the angiogenesis process of the wound tissue. The enhanced cell proliferation, granulation tissue formation, collagen deposition, remodeling, and re-epithelialization probably lead to the fast healing with less scar tissue formation and skin appendage regeneration. This study showed that combining bioactive molecules into multifunctional dressing should have great potential in achieving satisfactory healing in diabetic and other vascular-impaired related wounds.

Efficient Angiogenesis-Based Diabetic Wound Healing/Skin Reconstruction through Bioactive Antibacterial Adhesive Ultraviolet Shielding Nanodressing with Exosome Release.

Mussel-inspired chemistry, owing to its unique and versatile functions to manipulate dynamic molecular-scale interactions, has emerged as a powerful tool for the rational design and synthesis of new hydrogels. In particular, possessing a myriad of unique advantages that are otherwise impossible by conventional counterparts, mussel-inspired hydrogels have been widely explored in numerous fields such as biomedical engineering, soft electronics and actuators, and wearable sensors. Despite great excitement and vigor, a comprehensive and timely review on this emerging topic is missing. In this review, we discuss (1) the fundamental interaction mechanisms underpinning the spectacular wet adhesion in natural mussels and mussel-inspired materials; (2) the key routes to engineering hydrogels by leveraging on the interactions of mussel-inspired building blocks; (3) the emerging applications of mussel-inspired hydrogels, especially in the areas of flexible electronics and biomedical engineering; (4) the future perspectives and unsolved challenges of this multidisciplinary field. We envision that this review will provide an insightful perspective to stimulate new thinking and innovation in the development of next-generation hydrogels and beyond.

Mussel-inspired hydrogels: from design principles to promising applications

Mussel‐Inspired Hydrogels for Self‐Adhesive Bioelectronics

Skin-Inspired Antibacterial Conductive Hydrogels for Epidermal Sensors and Diabetic Foot Wound Dressings

Tissue engineering is a promising and revolutionary strategy to treat patients who suffer the loss or failure of an organ or tissue, with the aim to restore the dysfunctional tissues and enhance life expectancy. Supramolecular adhesive hydrogels are emerging as appealing materials for tissue engineering applications owing to their favorable attributes such as tailorable structure, inherent flexibility, excellent biocompatibility, near-physiological environment, dynamic mechanical strength, and particularly attractive self-adhesiveness. In this review, the key design principles and various supramolecular strategies to construct adhesive hydrogels are comprehensively summarized. Thereafter, the recent research progress regarding their tissue engineering applications, including primarily dermal tissue repair, muscle tissue repair, bone tissue repair, neural tissue repair, vascular tissue repair, oral tissue repair, corneal tissue repair, cardiac tissue repair, fetal membrane repair, hepatic tissue repair, and gastric tissue repair, is systematically highlighted. Finally, the scientific challenges and the remaining opportunities are underlined to show a full picture of the supramolecular adhesive hydrogels. This review is expected to offer comparative views and critical insights to inspire more advanced studies on supramolecular adhesive hydrogels and pave the way for different fields even beyond tissue engineering applications.

Supramolecular Adhesive Hydrogels for Tissue Engineering Applications.

Biomimetic Composite Scaffolds to Manipulate Stem Cells for Aiding Rheumatoid Arthritis Management

A fast, sensitive, and convenient dual-emission water detector was robustly fabricated. This detector was prepared with blue fluorescent carbon dots (CDs) and red fluorescent Cu nanoclusters (NCs), and showed two well-resolved and intensity-comparable fluorescence peaks under a single excitation wavelength. Moreover, it showed strong red fluorescence in organic solvent due to the aggregation-induced emission enhancement (AIEE) properties of the Cu NCs, but the red fluorescence was gradually quenched with an increasing amount of water, whereas the blue fluorescence remained constant. The differences in response result in a continuous fluorescence color change from red to blue that can be clearly observed by the naked eye. Thus, as-prepared Cu NC-based dual-emission nanomaterials can be used for ratiometric fluorescence detection of trace amounts of water in organic solvents by taking advantage of the water sensitivity of their fluorescence intensity ratios (red/blue) and their low detect limits (<0.02% v/v). These studies demonstrate that a novel and sensitive dual-emission ratiometric water detector has been found, which shows promise for application in environmental monitoring, food inspection, and life science.

Ratiometric fluorescence detection of trace water in organic solvents based on aggregation-induced emission enhanced Cu nanoclusters.

A series of dual-emission fluorescent probes was prepared from copper nanoclusters (Cu NCs) and carbon dots (CDs). They show two emission peaks (blue at 469 nm and red at 622 nm) when photoexcited at 365 nm. Upon exposure to sulfide, the Cu NCs will be deteriorated because they react with sulfide to form CuS. This results in the quenching of the red fluorescence of the Cu NCs, while the blue fluorescence of the CDs remains constant. Thus, the color of the nanocomposite changes from red to blue. The ratio of the fluorescences at the two wavelengths decreases linearly in the 2–10 ppb (26–128 nM) sulfide concentration range, and the limit of detection is 0.33 ppb (4.3 nM). The nanocomposite also was placed in an agar gel and then incorporated into a paper strip for fluorometric monitoring of gaseous hydrogen sulfide.

Shanliang Song

Papers

Skin-Inspired Antibacterial Conductive Hydrogels for Epidermal Sensors and Diabetic Foot Wound Dressings

Supramolecular Adhesive Hydrogels for Tissue Engineering Applications.

Biomimetic Composite Scaffolds to Manipulate Stem Cells for Aiding Rheumatoid Arthritis Management

Ratiometric fluorescence detection of trace water in organic solvents based on aggregation-induced emission enhanced Cu nanoclusters.

A dual emission nanocomposite prepared from copper nanoclusters and carbon dots as a ratiometric fluorescent probe for sulfide and gaseous H2S.