A randomized, double-blind, single-center, placebo-controlled, parallel-controlled clinical trial for umbilical cord mesenchymal stem cell injection for the treatment of inhaled lung injury

INTERVENTION: High dose group:2×10^8 cells/10mL;Medium dose group:1×10^8 cells/10mL;Low dose group:0.5×10^8 cells/10mL ;Placebo group:0 cells/10mL; CONDITION: Inhalation lung injury PRIMARY OUTCOME: Simple score of lung contusion; INCLUSION CRITERIA: (1) Comply with the diagnostic criteria for inhaled lung injury, the severity of the disease is moderate and above; (2) Aged between 18 and 60 years old male and female; (3) burn area (TBSA) = 30%, and the depth of burn is deep second degree burn and below; (4) Patients who voluntarily participate in this clinical study and can cooperate with doctors to carry out research and sign informed consent.