On-Demand Dissolution of a Dendritic Hydrogel-based Dressing for Second-Degree Burn Wounds through Thiol-Thioester Exchange Reaction

Construction and Performance Study of a Dual-Network Hydrogel Dressing Mimicking Skin Pore Drainage for Photothermal Exudate Removal and On-Demand Dissolution

In recent years, negative pressure wound dressings have garnered widespread attentions. However, it is challenging to drain the accumulated fluid under negative pressures for hydrogel dressings. To address this issue, this study prepared a chemical/physical duel-network PEG-CMCS/AG/MXene hydrogel composed by chemical disulfide crosslinked network of four-arm polyethylene glycol/carboxymethyl chitosan (4-Arm-PEG-SH/CMCS), and the physical network of hydrogen bond of agar (AG). Under near-infrared light (NIR) irradiation, the PEG-CMCS/AG/MXene hydrogel undergoes photothermal heating due to integrate of MXene, which destructs the hydrogen bond network and allows the removal of exudate through a mechanism mimicking the sweat gland-like effect of skin pores. The photothermal heating effect also enables the antimicrobial activity to prevent wound infections. The excellent electrical conductivity of PEG-CMCS/AG/MXene can promote cell proliferation under the external electrical stimulation (ES) in vitro. The animal experiments of full-thickness skin defect model further demonstrate its ability to accelerate wound healing. The conversion between thioester and thiol achieved with L-cysteine methyl ester hydrochloride (L-CME) can provides the on-demand dissolution of the dressing in situ. This study holds promises to provide a novel solution to the issue of fluid accumulations under hydrogel dressings and offers new approaches to alleviating or avoiding the significant secondary injuries caused by frequent dressing changes.

In situ gelation strategy based on ferrocene-hyaluronic acid organic copolymer biomaterial for exudate management and multi-modal wound healing

Exudate management remains a major concern in slow or non-healing wound management. Therefore, there is a need to devise a massive exudate-absorbing, exudate-locking, and stable extracellular matrix structure-maintaining functional wound dressing. Inspired by metal-organic frameworks, we chemically introduced sandwich ferrocene (Fc) into hyaluronic acid (HA) to fabricate an innovative metal Fc-HA organic copolymer (FHoC) as the skeleton material for in situ gelation, which was then gently compressed into a pre-hydrogel patch (FHoCP). Fc promoted the rearrangement of polymer chains to form additional microcrystalline and hydrophobic regions, which improved hydrogel transition and the exudate-locking ability. Thus, the simple composition FHoCP(5) absorbed 150 times its weight of water and maintained a firm three-dimensional network, which contributed to reducing inflammation and acted as a physical barrier against hemostasis and anti-bacterial invasion. Meanwhile, multi-modal processes, including fibroblast migration, angiogenesis, and antibacterial effects, were integrated into the gelled FHoCP(5) guided by Fe to promote wound healing. This study suggested that FHoC biomaterial could accelerate the closure of chronic wounds. We believe that this unique FHoCP(5)-based in situ gelation strategy could provide a solid drug-loaded scaffold for cell or adjunctive drug therapies, which holds great potential for the development of multifunctional biomaterials. STATEMENT OF SIGNIFICANCE: Hydrogels that absorb excessive exudates while maintaining stable ECM-like network as well as exert multimodal wound healing activities are ideal dressings for accelerating chronic wound contraction. Herein, we reported an innovative metal ferrocene-hyaluronic acid organic copolymer patch (FHoCP) and FHoCP-mediated in situ gelation strategy. Ferrocene (Fc) induced in situ gelation by promoting polymer chain rearrangement, acting as a physical barrier for hemostasis and anti-bacterial invasion, and absorbing massive exudates, resulting in reducing delayed inflammation. As the structural core, rigid Fc enhanced the stability of the hydrogel backbone, and hydrophobic Fc improved fibroblast migration. In addition, Fe²⁺ chemically inhibited bacteria and increased angiogenesis. These results indicated the potential of FHoCP-based hydrogel for application in clinical skin reconstruction.

A sustained release of alendronate from an injectable tetra-PEG hydrogel for efficient bone repair

Significant efforts on construction of smart drug delivery for developing minimally invasive gelling system to prolong local delivery of bisphosphonates are considered as promising perspectives for the bone-related diseases, which provide the hydrogels with unique bioactivities for bone repair in clinic. Herein, we have constructed an alendronate (ALN)-conjoined injectable tetra-PEG hydrogel with excellent biocompatibility, uniform network, and favorable mechanical properties in one-pot strategy. In views of the quick ammonolysis reaction between N-hydroxysuccinimide (NHS)-ester of tetra-PEG-SG and amine groups of tetra-PEG-NH₂ polymer and ALN molecules, the uniform networks were formed within seconds along with the easy injection, favorable biocompatibility and mechanical properties for hydrogel scaffolds. On account of the simultaneous physical encapsulation and chemical linkage of the ALN within the hydrogels, the ALN-conjoined tetra-PEG hydrogel exhibited a sustained drug release delivery that could persistently and effectively facilitate viability, growth, proliferation, and osteogenesis differentiation of stem cells, thereby allowing the consequent adaptation of hydrogels into the bone defects with irregular shapes, which endowed the ALN-conjoined tetra-PEG hydrogel with depot formulation capacity for governing the on-demand release of ALN drugs. Consequently, the findings imply that these drug-based tetra-PEG hydrogels mediate optimal release of therapeutic cargoes and effective promotion of in situ bone regeneration, which will be broadly utilized as therapeutic scaffolds in tissue engineering and regenerative medicine.

Polythioesters Prepared by Ring-Opening Polymerization of Cyclic Thioesters and Related Monomers

Polyhydroxyalkanoates (PHAs) are biodegradable and biocompatible polyesters with a wide range of applications; in particular, they currently stand as promising alternatives to conventional polyolefin-based "plastics". The introduction of sulfur atoms within the PHAs backbone can endow the resulting polythioesters (PTEs) with differentiated, sometimes enhanced thermal, optical and mechanical properties, thereby widening their versatility and use. Hence, PTEs have been gaining increasing attention over the past half-decade. This review highlights recent advances towards the synthesis of well-defined PTEs by ring-opening polymerization (ROP) of cyclic thioesters - namely thiolactones - as well as of S-carboxyanhydrides and thionolactones; it also covers the ring-opening copolymerization (ROCOP) of cyclic thioanhydrides or thiolactones with epoxides or episulfides. Most of the ROP reactions described are of anionic type, mediated by inorganic, organic or organometallic initiators/catalysts, along with a few enzymatic reactions as well. Emphasis is placed on the reactivity of the thio monomers, in relation to their ring-size ranging from 4- to 5-, 6- and 7-membered cycles, the nature of the catalyst/initiating systems implemented and their efficiency in terms of activity and control over the PTE molar mass, dispersity, topology, and microstructure.

Evaluation of Bacterial Cellulose Dressing versus Vaseline Gauze in Partial Thickness Burn Wounds and Skin Graft Donor Sites: A Two-Center Randomized Controlled Clinical Study

Objective

Bacterial cellulose (BC) dressing, which can maintain a moist environment and prevent the invasion of pathogens, has become a competitive dressing material for burn wound treatment. This study was conducted to evaluate the treatment efficacy of a novel China-made BC dressing for the treatment of second-degree burn wounds and skin graft donor sites.

Methods

212 patients with second-degree burn wounds or skin graft donor sites were enrolled from two research centers. They were randomly assigned to the BC dressing group (study group) or the Vaseline gauze (VG) dressing group (control group). Wound conditions were assessed before and after treatment. Dressings were changed according to the condition of the wound bed. Healing rate and healing time were recorded as primary endpoints to evaluate the efficacy of BC dressing against VG dressing. Erythema, swelling, exudation, bleeding, subeschar purulence, and pain were assessed as secondary endpoints.

Results

207 participants completed the trial and their wounds all healed within 28 days. The average healing times for superficial and deep secondary burn wounds and skin graft donor sites in the BC group were 8.12, 15.77, and 10.55 days, respectively. In the VG group, the average healing times for superficial and deep secondary burn wounds and skin graft donor sites were 9.30, 15.27, and 11.19 days, respectively. The healing time of superficial burn wounds in the BC group was statistically shorter than that in the VG group. There was no difference in the frequency of dressing changing between two groups. The BC dressing showed equal efficacy with the VG dressing at all secondary endpoints.

Conclusion

The novel BC dressing could be used for the management of second-degree burn wounds and skin graft donor sites. With a shorter healing time in superficial secondary burn wound than that of the VG dressing, the BC dressing showed noninferiority in the treatment of superficial and deep secondary burn wounds and skin graft donor sites versus the VG dressing. This study is registered with the Chinese Clinical Trial Registry (registry number: ChiCTR1800014377 (http://www.chictr.org.cn)).

Tacticity Control of Cyclic Poly(3-Thiobutyrate) Prepared by Ring-Opening Polymerization of Racemic β-Thiobutyrolactone

We report here on the ring-opening polymerization (ROP) of racemic β-thiobutyrolactone (rac-TBL), as the first chemical synthesis of poly(3-thiobutyrolactone) (P3TB), the thioester analogue of the ubiquitous poly(3-hydroxybutyrate) (P3HB). The ROP reactions proceed very fast (TOF >12 000 h^-1 at r.t.) in the presence of various metal-based catalysts. Remarkably, catalyst systems based on non-chiral yttrium complexes stabilized by tetradentate amino alkoxy- or diamino-bis(phenolate) ligands {ONXO^R1,R2 }^2- (X=O, N) provide access to cyclic P3TB with either high isoselectivity (P_m up to 0.90) or high syndiotactic bias (P_r up to 0.70). The stereoselectivity can be controlled by manipulation of the substituents on the ligand platform and adequate choice of the reaction solvent and temperature as well. The cyclic polymer topology is evidenced by MALDI-ToF MS, NMR and TGA. Highly isotactic cyclic P3TB is a semi-crystalline material as revealed by DSC.

Hydrogels in Burn Wound Management-A Review

Inert hydrogels are of a great importance in burn first aid. Hydrogel dressings may be an alternative to cooling burn wounds with streaming water, especially in cases of mass casualty events, lack of clean water, hypothermia, or large extent of burns. Hydrogels that contain mostly water evacuate the heat cumulating in the skin by evaporation. They not only cool the burn wound, but also reduce pain and protect the wound area from contamination and further injuries. Hydrogels are ideally used during the first hours after injury, but as they do not have antimicrobial properties per se, they might not prevent wound infection. The hydrogel matrix enables incorporating active substances into the dressing. The active forms may contain ammonium salts, nanocrystal silver, zinc, growth factor, cytokines, or cells, as well as natural agents, such as honey or herbs. Active dressings may have antimicrobial activity or stimulate wound healing. Numerous experiments on animal models proved their safety and efficiency. Hydrogels are a new dressing type that are still in development.

S-Carboxyanhydrides: Ultrafast and Selective Ring-Opening Polymerizations Towards Well-defined Functionalized Polythioesters

Aliphatic polythioesters are popular polymers because of their appealing performance such as metal coordination ability, high refractive indices, and biodegradability. One of the most powerful approaches for generating these polymers is the ring-opening polymerization (ROP) of cyclic monomers. However, the synthesis of precisely controlled polythioesters via ROP of thiolactones still faces formidable challenges, including the minimal functional diversity of available thiolactone monomers, as well as inevitable transthioesterification side reactions. Here we introduce a hyperactive class of S-carboxyanhydride (SCA) monomers derived from amino acids that are significantly more reactive than thiolactones for ultrafast and selective ROP. Inclusion of the initiator PPNOBz ([PPN]=bis(triphenylphosphine)-iminium) with chain transfer agent benzoic acid, the polymerizations that can be operated in open vessels reach complete conversion within minutes (1-2 min) at room temperature, yielding polythioesters with predictable molecular weight, low dispersities, retained stereoregularity and chemical recyclability. Most fascinating are the functionalized SCAs that allow the incorporating of functional groups along the polythioester chain and thus finely tune their physicochemical performance. Computational studies were carried out to explore the origins of the distinctive rapidity and exquisite selectivity of the polymerizations, offering mechanistic insight and explaining why high polymerizability of SCA monomer is able to facilitate exquisitely selective ring-opening for enchainment over competing transthioesterification and backbiting reactions.

Dynamic Covalent Bonds in Polymeric Materials

Dynamic covalent bonds (DCBs) have received significant attention over the past decade. These are covalent bonds that are capable of exchanging or switching between several molecules. Particular focus has recently been on utilizing these DCBs in polymeric materials. Introduction of DCBs into a polymer material provides it with powerful properties including self-healing, shape-memory properties, increased toughness, and ability to relax stresses as well as to change from one macromolecular architecture to another. This Minireview summarizes commonly used powerful DCBs formed by simple, often "click" reactions, and highlights the powerful materials that can result. Challenges and potential future developments are also discussed.

Recent advances of on-demand dissolution of hydrogel dressings

Wound management is a major global challenge and a big financial burden to the healthcare system due to the rapid growth of chronic diseases including the diabetes, obesity, and aging population. Modern solutions to wound management include hydrogels that dissolve on demand, and the development of such hydrogels is of keen research interest. The formation and subsequent on-demand dissolution of hydrogels is of keen interest to scientists and clinicians. These hydrogels have excellent properties such as tissue adhesion, swelling, and water absorption. In addition, these hydrogels have a distinctive capacity to form in situ and dissolve on-demand via physical or chemical reactions. Some of these hydrogels have been successfully used as a dressing to reduce bleeding in hepatic and aortal models, and the hydrogels remove easily afterwards. However, there is an extremely wide array of different ways to synthesize these hydrogels. Therefore, we summarize here the recent advances of hydrogels that dissolve on demand, covering both chemical cross-linking cases and physical cross-linking cases. We believe that continuous exploration of dissolution strategies will uncover new mechanisms of dissolution and extend the range of applications for hydrogel dressings.