This 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.

Chronic wounds refer to the pathological changes such as cell senescence, imbalance of synthesis and degradation of extracellular matrix, and decreased activity of growth factors caused by different reasons when the wound is prolonged and does not heal after conventional treatment for more than 1 month without healing tendency. Chronic wound can be caused by a variety of diseases, including arterial disease, diabetes, vasculitis, venous disease and skin malignant tumor, chronic venous insufficiency (CVI) is a disease leading to chronic wound, Venous ulcer (VLU) of lower limbs is the advanced manifestation of CVI, and the incidence of this disease ranges from 0.4% to 1.3% in China. 60% of VLU patients' ulcer wounds heal in 3-6 months, 33% in 12 months, and 7% May be permanently unhealed. The probability of recurrence is as high as 70% in patients 3-5 months after wound healing, which not only seriously affects the health and quality of life of patients, but also causes a very heavy social medical burden. At present, the conventional treatment for VLU mainly includes drug therapy, stress therapy, wound treatment and surgical treatment, but the therapeutic effect is not ideal.

Inclusion Criteria:

1. Age from 18 to 70, no gender limitation;
2. It met the diagnostic criteria of venous ulcer of lower limbs in Clinical Vascular Surgery (5th edition), and the following conditions were met: the ulcer lasted for more than 1 month; The wound area was between 10cm2 and 40cm2. Wound depth: All wounds were deep tissue ulcers below the epidermis.
3. Participate in the clinical study voluntarily, observe the study procedure, and observe the curative effect cooperatively.

Exclusion Criteria:

1. Pregnant or lactation women; Women who have planned to have children recently (within 6 months);
2. Patients with peripheral artery disease with ankle-brachial index (ABI) < 0.8;
3. Patients with active clinical systemic infection;
4. Serious skin wound infection is not under control;
5. low immune function and systemic failure; Severe heart, liver, lung, kidney and other important organ lesions (ALT, AST, Cr & GT; Normal 1.5 times, congestive heart failure ejection fraction &lt; Normal 30%) and severely impaired hematopoietic function;
6. Abnormal coagulation function or current anticoagulant treatment;
7. Systemic autoimmune diseases in the active stage;
8. With systemic organ or hematological malignancy;
9. PERSONS infected with HIV or addicted to drugs, tobacco and alcohol;
10. Have a clear history of mental illness;
11. Participation in clinical studies of any drug within 1 month prior to treatment (or the 5 half-life of the investigational drug, whichever is longer).