On Demand Dissoluble Supramolecular Hydrogels: Towards Pain Free Burn Dressings

Introduction: Despite decades of efforts, state-of-the-art synthetic burn dressings to treat partial-thickness burns are still far from ideal. Current dressings adhere to the wound and necessitate debridement. This work describes the first “supramolecular hybrid hydrogel (SHH)” burn dressing that is biocompatible, self-healable, and on-demand dissoluble for easy and trauma-free removal, prepared by a simple, fast, and scalable method. These SHHs leverage the interactions of a custom-designed cationic copolymer via host-guest chemistry with cucurbit[7]uril and electrostatic interactions with clay nanosheets coated with an anionic polymer to achieve enhanced mechanical properties and fast on-demand dissolution. The SHHs show high mechanical strength (>50 kPa), self-heal rapidly in ∼1 min, and dissolve quickly (4–6 min) using an amantadine hydrochloride (AH) solution that breaks the supramolecular interactions in the SHHs. Neither the SHHs nor the AH solution has any adverse effects on human dermal fibroblasts or epidermal keratinocytes in vitro. The SHHs also do not elicit any significant cytokine response in vitro. Furthermore, in vivo murine experiments show no immune or inflammatory cell infiltration in the subcutaneous tissue and no change in circulatory cytokines compared to sham controls. Thus, these SHHs present excellent burn dressing candidates to reduce the time of pain and time associated with dressing changes.

Materials and

Methods: We first designed and synthesized different SHH formulations to optimize the concentration of key components while targeting specific physical properties. SHHs were synthesized with four main components: 1) rationally designed a water-soluble cationic copolymer (CP) as the guest, 2) cucurbit[7]uril (CB[7]) molecules as the host, 3) exfoliated clay nanosheets (CNSs), and 4) sodium polyacrylate (SPA, anionic) as the inorganic fillers to improve mechanical properties. Custom-designed water-soluble acrylamide-random-[3-(methacryloylamino)propyl]trimethylammonium chloride (Am-r-MATMAC) copolymers (CPs) were initially synthesized, allowing the cationic CP guest to interact strongly with the electronegative portals of CB[7] host molecules. CB[7] and the CP were then combined with inorganic clay nanosheets (CNSs) stabilized with sodium polyacrylate (SPA) to enhance the mechanical properties of SHH. Following synthesis, the SHHs underwent physical characterization, including dissolution time, mechanical properties, self-healing ability, pH stability, and swelling behavior. Then, we tested the in vitro biocompatibility of SHHs and dissolution agent using human dermal and epidermal cells. Additionally, we evaluated the in vivo biocompatibility of SHHs using a mouse model via histology and immunohistochemistry.

Results, Conclusions, and Discussions: We created a simple, quick, and scalable method to synthesize a supramolecular hybrid hydrogel (SHH) via the supramolecular assembly of Am-r-MATMAC CP with CB[7] hosts and CNSs. Our SHH design and synthesis feature green chemistry – whereby we eliminated many toxic and reactive chemicals commonly used in traditional approaches – which also results in rapid hydrogel formation (∼15 s to gelation). As such, these SHHs are the first of their kind as burn dressings and drastically differ from the existing lengthy and potentially hazardous methods of hydrogel preparation. Furthermore, the host-guest exchange mechanism between the Am-r-MATMAC CP and CB[7] in the SHHs, enables rapid on-demand dissolution (4–6 min) of the hybrid hydrogels. This dissolution is facilitated by the introduction of a competitive guest, AH (20 & 40 mM), without any significant adverse effects on either dermal and or epidermal cells in vitro (cell viability >90%) and in vivo. Supramolecular crosslinks with CNSs provided distinctive functions of high mechanical strength (G' > 50 kPa; G' > G'') and fast self-healing capability (1 min) for SHH-4. In addition, SHH-4 showed high biocompatibility in vitro and in vivo. In vitro, immunogenicity assessment showed a lower immune response to SHHs compared to positive (LPS) controls. Moreover, after subcutaneous hydrogel implantation in mice, in vivo, histology, immunofluorescence, and systemic cytokine analyses indicated no immune and inflammatory responses beyond sham controls. As such, we posit that SHH is a promising alternative to commercial hydrogels currently used in clinical burn wound treatment. Due to the ease of their fabrication, which only involves two steps of mixing, we expect these novel SHHs will enable large-scale yet low-cost fabrication, addressing a critical bottleneck for translation to clinical applications. We expect SHH-based dressings to provide easy burn care, eliminate mechanical and surgical debridement, promote wound healing, and enhance the healing process to treat second-degree burns. As a result, SHHs will reduce 1) pain and psychological burden of patients, 2) use and side effects of heavily used analgesics and opioids, 3) hospital stay and costs, and 4) time demand on highly qualified hospital personnel by reducing the dressing change time significantly.

Acknowledgements (Optional): This research was supported partially by grants from the National Institutes of Health (NIH 5R21GM136002, NIH 1R21GM141683, and NIH 5R01HL145031), National Science Foundation (NSF Grant CHE-1904465 and EEC-1941543), a Massachusetts General Hospital (MGH) Executive Committee on Research (ECOR) Interim Support Fund, and a Shriners Hospital Research Grant (SHC 85125, and 85128). We also acknowledge the support and use of facilities at the Morphology and Imaging Shared Facility and Regenerative Medicine Shared Facility provided at the Shriners Hospital for Children – Boston. The authors thank Dr. Basak Uygun for fruitful discussions on this work, Dr. David Wilbur for assistance with NMR data collection and analysis, Dr. Nicole Brousaides for the preparation of histology samples, Dr. Leon G. Leanse for his help in animal procurement and initial training in the animal protocol.