RecruitingClinical trialPhase Ⅱ Clinical Study of Human Umbilical Cord Mesenchymal Stem Cells in the Treatment of Venous LegThis project adopts a prospective clinical trial study to compare and evaluate the efficacy of local transplantation of human umbilical cord mesenchymal stem cells combined with silver ion dressing and simple silver ion dressing in the treatment of venous lower extremity ulcer wounds. To improve the healing rate and quality of life of patients.