There is some controversy concerning the usefulness of animal models in testing chronic wound dressings for efficacy. The pathology of the chronic wound is even more complex than the healing wound, and difficult to mimic. One predictor for efficacy of a chronic wound dressing is testing the dressing in vitro with chronic wound fluid or proteins that mimic the environment and protein concentration as well as makeup of chronic wound exudate. During the course of developing a modified cotton product for commercialization, two models for studying the performance of the modified cotton fiber under conditions that mimic chronic wound fluid exudate were made. One model consisted of assaying the modified fiber in diluted chronic wound fluid containing high elastase activity similar to that of the chronic wound . More recently, we have developed a model utilizing albumin concentrations that mimic those levels of albumin found in the chronic wound in the presence of elastase. Another purpose in utilizing the albumin model is to better understand how albumin may compete for binding sites on different functional groups of modified cotton cellulose, and compare capacities for competitive protease binding. Using these types of models, we have begun to study and compare more closely the mechanisms for competitive binding through ion pairing between the enzyme and cotton as shown in Figure 2.5 with the "inhibitor-active site". Figure 2.8 shows the results of an experiment designed to evaluate the capacity of a type of charge sequestrant wound dressing currently in development that removes elastase from solution. The results of this 24-hour assay where the dressing is challenged with a constant concentration of elastase and evaluated for continued removal of the protease from solution suggest good capacity of the charge sequestrant wound-dressing motif.
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