Stratatech Corp., a Madison company that produces cell-based skin substitutes for medical research, said a clinical trial has shown that burn patients receiving grafts of its product approached full healing without further skin grafts.The company said all 10 patients in the trial received a single application of its StrataGraft human skin substitute for treatment of severe burns. None required a regrafting of the patient's own tissue over the site after 28 days. All seven patients who were assessed after three months achieved complete wound closure, Stratatech said.