For the purpose of easy operation and avoiding too many patients accumulated at the same time, recruitment will be done separately in 10 cycles. The first research nurse need to perform wound dressing in experimental group for 2 patients per hour, thus 12-13 patients a day. It will be stopped as soon as 26 patients are recruited in the first week of each cycle so as to facilitate spreading the attending time of patients in the coming 6-week wound cleansing visits, therefore they do not need to wait long. That means it takes 2 months to accomplish recruitment plus 6 weeks wound cleansing and data collection for 24-26 subjects, therefore 20 months is required for 244 subjects. It is envisaged that the study will take 24 months.