| Chronic wounds have been a severe threat to patients and bring a heavy economic burden.Therefore,improving research level and speeding up the healing process are extremely important.The key reason for the poor healing outcomes of chronic wound is the imbalanced microenvironment,which leads to multiple pathological changes of the tissue and disturbs the normal repair process.Therefore,a promising strategy to treat chronic wounds is to improve the pathological microenvironment,activating cells to participate in the repair.A large number of studies have confirmed that the electrospun micro/nanofibrous scaffolds could promote cells adhesion and spreading.However,supporting cell growth alone cannot resolve the problem of chronic wounds.Mesenchymal stem cells（MSCs）derived exosomes could promote tissue repair because they contain most of the bioactive factors secreted by MSCs.Compared with MSCs,exosomes had many advantages such as low immunogenicity and high stability.Therefore,in this thesis,electrospun micro/nanofibers loaded with exosomes derived from adipose-derived mesenchymal stem cells were prepared,and their biological functions were evaluated at the molecular,cellular,and animal levels to investigate their regulation on the diabetic chronic wounds in rats.The main work and conclusions are as follows:（1）PLLA micro/nanofibrous scaffolds were prepared by electrospinning.The fibrous wound dressings were either further modified by a layer of polydopamine（PDA）or grafted with phospholipid molecules（DSPE-PEG-NH2）,respectively,to obtain Exos@PDA-PLLA and Exos@DSPE-PLLA.By comparing the effects of the two modification methods,it was found that both PDA-PLLA and DSPE-PLLA could effectively immobilize exosomes.（2）The effects of the exosomes-loaded electrospun micro/nanofibrous wound dresssing on key cells involved in wound repair,including fibroblasts,keratinocytes and macrophages were evaluated.The results showed that Exos@DSPE-PLLA could promote fibroblasts proliferation,migration and genes（Col I,Col III,VEGF,TGF-β1,α-SMA,HIF-1α）expression,It also promotes keratinocytes proliferation.Besides,Exos@DSPE-PLLA promoted the expression of macrophages anti-inflammatory genes（Arginase 1,CD 206,IL-10）and inhibited the expression of pro-inflammatory genes（IL-1β,TNF-α）,indicating that macrophages shifted to M2 type（Anti-inflammatory type）polarization.Similarly,Exos@PDA-PLLA could also promote the polarization to M2.However,it inhibited the proliferation of fibroblasts and keratinocytes.（3）Exos@DSPE-PLLA was used to treat a full-thickness skin defect wound in type I diabetic rats to evaluate its effects on wound repair in vivo.By comparing the healing rate and quality,it was found that Exos@DSPE-PLLA promoted the deposition of collagen and cell proliferation.It also alleviated the inflammatory response by promoting the phenotypic shift of macrophages from M1 type to M2 type.Furthermore,it could promote the formation of blood vessels. |
