Study on soluble microneedles loaded with aPexos and EGCG for healing of burn wounds in rats

[Objective] To use Chitosan Methacryloyl (CSMA) loaded with artificial platelet-derived exosomes (aPexos) as the needle body material, and gelatin and carboxymethyl chitosan (CMCS) loaded with Epigallocatechin gallate(EGCG) as the backing material to prepare microneedles, aims to investigate the therapeutic effect and mechanism of aPexos-EGCG microneedles in the treatment of burn wound healing. [Methods] First, aPexos were extracted using ultrasound and gradient ultracentrifugation. The concentration, morphology, and growth factor content (TGF-β1, PDGF-BB, VEGF) of the exosomes were assessed using NTA, transmission electron microscopy, and ELISA kits. The aPexos and EGCG were then dissolved in the needle body and backing materials, respectively. The aPexos and EGCG were loaded into the needle body and backing layer, respectively. The morphology, mechanical properties, and puncture performance of the microneedles were examined, and the preparation conditions for the microneedles loaded with aPexos-EGCG were optimized. Finally, animal experiments and tissue staining were conducted to assess the efficacy of the aPexos-EGCG microneedles in promoting burn wound healing in rats. [Results] The size distribution of aPexos was mainly in the range of 50-150 nm, with an average diameter of 132.7±3.8 nm and an average concentration of approximately 2.88×1013±3.62×1012 particles/mL. The concentrations of TGF-β1, PDGF-BB, and VEGF were approximately 1 363±135.9 ng/mL, 63.5±14.8 ng/mL, and 1 606.0±77.5 pg/mL, respectively. Mechanical property testing of the microneedles indicated that, compared with the blank microneedles, the drug-loaded microneedles had sufficient piercing ability to penetrate the stratum corneum of the skin. The results of the rat burn wound healing experiment showed that the wound healing rates of the d 3, d 7, aPexos-EGCG microneedle group compared to the control group showed significant differences, with respective values of (47.64±12.5)% vs (18.11±6.40)%, (87.45±5.57)% vs (79.85±5.03)%(P<0.05). Hematoxylin-eosin (HE) staining revealed more intact epidermal layers in the aPexos-EGCG microneedle group. Masson staining showed that the collagen deposition percentage in the aPexos-EGCG microneedle group was higher than in the control group. Immunofluorescence staining results indicated that the aPexos-EGCG microneedle group had a reduced content of M1-type macrophages and an increased content of M2-type macrophages. Additionally, the vascular markers CD31 and α-SMA showed elevated expression in this group, with significant differences compared to the other groups (P<0.05). [Conclusion] The aPexos-EGCG microneedle developed in this study exhibits good mechanical properties, capable of successfully penetrating the skin's stratum corneum and delivering aPexos and EGCG. aPexos promotes wound repair, while EGCG regulates the ratio of M1 and M2 macrophages at the wound site and suppresses the inflammatory response. This microneedle can effectively promote wound healing in rats with burn injuries, offering a novel approach for tissue repair.