11.2.4　Thermal stimulation wound dressings

As an ancient yet effective method，the application of local heat around the wound can increase blood flow，stimulate the proliferation of fibroblasts，and reduce inflammation.The local heating method can strengthen the metabolism around the wound and promote wound healing.In recent years，many scientific studies have confirmed that the use of photothermal therapy（PTT）can promote wound tissue regeneration，and this therapy has been widely used clinically as adjuvant therapy.Currently，PTT mostly uses lasers with a small area and high energy as the light source，showing excellent tissue penetration ability and minimal damage to surrounding tissues and has been successfully combined with nano-drugs for the treatment of tumor-related or bacterial wounds.

Combining photothermal materials into hydrogels or other scaffold materials is an important way to achieve thermal stimulation wound dressings.For example，Yang et al.developed a multifunctional scaffold containing nano-hydroxyapatite/graphene oxide（nHA/GO）composite particles.Under the NIR irradiation，the scaffold can effectively kill human osteosarcoma cells and also promote tissue regeneration，providing a promising clinical tool for treating osteosarcoma resection tissue damage.In addition，the use of photothermal antibacterial hydrogels are also an important strategy for the treatment of bacterial wound infections.As shown in Figure 11-6，Wang et al.constructed a composite hydrogel（CS/AM NSs hydrogel）with outstanding antibacterial ability by incorporating antimonene nanosheets（AM NSs）with extraordinary photothermal properties into the network structure of chitosan（CS）.When being cultured with bacteria，CS/AM NSs hydrogel could aggregate on the surface of the bacteria through the interaction of CS and bacterial cell membrane.Subsequently，the inherent bactericidal properties of CS would kill certain bacteria.Under the NIR，AM NSs could effectively convert light energy into heat energy to eliminate residual bacteria.Due to the synergy between the capture effect of CS and the photothermal effect of AM NSs，CS/AM NSs hydrogel showed good antibacterial properties against Escherichia coli（E.coli）and Staphylococcus aureus（S.aureus）.

With the abuse of antibiotics，rapid and effective sterilization of wounds infected by drug-resistant bacteria inevitably becomes a serious challenge in the field of wound healing.Chang et al.prepared a multifunctional composite（PDA/Cu-CS）hydrogel mainly composed of polydopamine（PDA）and copper-doped calcium silicate ceramic（Cu-CS）.The PDA/Cu complex in the composite hydrogel played a key role in enhancing photothermal performance and antibacterial activity.The unique“hot ions effect”produced by heating copper ions through the photothermal effect of the composite hydrogel showed high-efficiency，rapid，and long-term inhibition of methicillin-resistant S.aureus and E.coli.The composite hydrogel showed significant biological activity and could effectively remove existing infections in the wound area，and significantly promoted angiogenesis and collagen deposition during the healing process of infectious skin wounds.In addition，Guo et al.developed an injectable double network hydrogel adhesive with high self-healing efficiency and photothermal antibacterial activity to treat multidrug-resistant bacterial infections（MRSA）in the wound.The hydrogel exhibited good tissue adhesion，degradability，photothermal antibacterial activity.(https://www.daowen.com)

Usually，laser-based PTT still has limitations.Since the penetration depth of NIR is usually less than 1 cm，long-distance light irradiation cannot be achieved，which will hinder its practical application in wound healing.By using appropriate photothermal materials，solar energy can be effectively converted into heat energy.Therefore，it is expected to use sunlight to locally heat the wound to promote wound healing.Zhang et al.proposed a strategy of using self-adhesive photothermal hydrogel films to accelerate wound healing under sunlight（Figure 11-7）.The polyacrylamide hydrogel contains PDA and rGO，which can adhere to the wound and convert solar energy into heat energy，thereby locally heating the wound.The increase of local temperature reduces inflammation and enhances epithelial regeneration，angiogenesis，and collagen deposition.