Chitosan hydrogel encapsulated with LL-37 peptide promotes deep tissue injury healing in a mouse model

Background:LL-37 peptide is a member of the human cathelicidin family,and has been shown to promote the healing of pressure ulcers.However,the low stability of this peptide within the wound environment limits its clinical use.Chitosan(CS)hydrogel is commonly used as a base material for wound dressing material.Methods:CS hydrogel(2.5%w/v)was encapsulated with LL-37.Cytotoxicity of the product was examined in cultured NIH3 T3 fibroblasts.Effects on immune response was examined by measuring tumor necrosis factor-α(TNF-α)release from RAW 264.7 macrophages upon exposure to lipopolysaccharides.Antibacterial activity was assessed using Staphylococcus aureus.Potential effect on pressure ulcers was examined using a mouse model.Briefly,adult male C57 BL/6 mice were subjected to skin pressure using magnets under a 12/12 h schedule for 21 days.Mice were randomized to receive naked LL-37(20μg),chitosan gel containing 20μg LL-37(LL-37/CS hydrogel)or hydrogel alone under the ulcer bed(n=6).A group of mice receiving no intervention was also included as a control.Results:LL-37/CS hydrogel did not affect NIH3 T3 cell viability.At a concentration of 1–5μg/ml,LL-37/CS inhibited TNF-αrelease from macrophage.At 5μg/ml,LL-37/CS inhibited the growth of Staphylococcus aureus.The area of the pressure ulcers was significantly lower in mice receiving LL-37/CS hydrogel in comparison to all other 3 groups on days 11(84.24%±0.25%),13(56.22%±3.91%)and 15(48.12%±0.28%).Histological examination on days 15 and 21 showed increased epithelial thickness and density of newly-formed capillary with naked LL-37 and more so with LL-37/CS.The expression of key macromolecules in the process of angiogenesis(i.e.,hypoxia inducible factor-1α(HIF-1α)and vascular endothelial growth factor-A(VEGF-A))in wound tissue was increased at both the mRNA and protein levels.Conclusion:Chitosan hydrogel encapsulated with LL-37 is biocompatible and could promote the healing of pressure ulcers.

Early Detection Methods of Deep Tissue Pressure Injuries:A Systematic Review

Deep tissue pressure injuries(DTPIs)have witnessed a growing prevalence in hospitals and other health care units especially among individuals with pathological conditions that give rise to restricted mobility,impaired sensation,and reduced tissue tolerance.The etiology of DTPIs has been a subject of controversy,to which several explanatory models have been proposed,including direct mechanical insult,ischemia-reperfusion,lymphatic occlusion,and inflammatory cytokines.In line with these pathophysiological scenarios,ultrasound,subepidermal moisture detection,and biomarker technologies have been proposed as potential early detection methods of DTPIs.This paper provides a systematic review involving these three methods.The conclusion is that combining and implementing these methods at different time periods during DTPIs development and progression respectively is likely to be the most universal,effective and promising way for DTPIs diagnosis.

dECM restores macrophage immune homeostasis and alleviates iron overload to promote DTPI healing

Due to its highly insidious and rapid progression,deep tissue pressure injury(DTPI)is a clinical challenge.Our previous study found that DTPI may be a skeletal muscle injury dominated by macrophage immune dysfunction due to excessive iron accu-mulation.Decellularized extracellular matrix(dECM)hydrogel promotes skeletal muscle injury repair.However,its role in po-larizing macrophages and regulating iron metabolism in DTPI remains unclear.Here,porcine dECM hydrogel was prepared,and its therapeutic function and mechanism in repairing DTPI were investigated.The stimulus of dECM hydrogel toward RAW264.7 cells resulted in a significantly higher percentage of CD2o6+macrophages and notably decreased intracellular divalent iron levels.In mice DTPI model,dECM hydrogel treatment promoted M1 to M2 macrophage conversion,improved iron metabolism and reduced oxidative stress in the early stage of DTPI.In the remodeling phase,the dECM hydrogel remarkably enhanced revascularization and accelerated skeletal muscle repair.Furthermore,the immunomodulation of dEcM hydrogels in vivo was mainly involved in the P13k/Akt signaling pathway,as revealed by GO and KEGG pathway analysis,which may ameliorate the iron deposition and promote the healing of DTPI.Our findings indicate that dECM hydrogel is promising in skeletal muscle repair,inflammation resolution and tissue injury healing by effectively restoring macrophage immune homeostasis and normalizing iron metabolism.