Semi-interpenetrating Polyurethane Network Foams Containing Highly Branched Poly(N isopropyl acrylamide) with Vancomycin Functionality

Wound dressings have been used to clean, cover, and protect the wound from the external environment. A wound dressing must provide a moist environment, remove the excess of exudate, avoid maceration, protect the wound from infection and maintain an adequate exchange of gases. The growing problem of antibiotic resistance has necessitated the need for improved wound diagnosis, dressing and treatment. Currently the only way to check the progress of wounds is by removing bandage dressings, which is both painful and risky, giving pathogens the chance to attack. Smart wound dressing is feasible for treating chronic wounds because it provides information regarding the wound condition in real-time for appropriate medical action. Numerous foamed materials are available for wound dressing. Among them, hydrophilic polyurethane (PU) foam is widely used due to their remarkable properties, particularly lack of cytotoxicity and high fluid uptake, than its counterparts. This versatile class of polymers is synthesized by step-growth polymerization of polyfunctional alcohols and isocyanates. Moreover, the resulting PUs are modified to improve their functionality. Besides fillers and additives, addition of another polymer can optimize the polymer properties. A good example is the interpenetrating polymer networks (IPNs).

Highly branched poly(N-isopropylacrylamide) (HB-PNIPAM) can be tapped within a semi-IPN hydrogel to produce a functional cell-adhesive substrate. In addition, HB-PNIPAM with end groups capable of binding to fungi or bacteria exhibits desolvation transition. Previous findings revealed that when these polymers are attached to hydrogel membranes, they could reduce the bacterial burden in infected wounds. Consequently, addition of solvatochromic dye like Nile red increases the fluorescence intensity resulting in effective detection of the Gram-positive species. These findings have inspired the development of a new PU foam-based system containing functional polymers for accurate diagnosis of infected wounds.

Herein, a team of researchers from the University of Bradford: Dr. Thomas Swift, Dr. Richard Hoskins, Mr. Edward Dyson, Mr. Marc Daignault and Professor Stephen Rimmer together with Mr. John Hicks and Mrs. Dorothy Buckle from Smith and Nephew Wound Management and Professor Ian Douglas and Professor Sheila McNeil from the University of Sheffield investigated the feasibility of using semi-IPN foams containing HB-PNIPAM with vancomycin functionality for detecting the presence of Gram-positive species. The HB-PNIPAM was labelled with Nile red an changes in fluorescent light emitted by the dye can be used to indicate the presence of the bacteria. The authors used Staphylococcus aureus bacteria to illustrate the potential application of the foams as a clinically relevant exemplar. The research work is currently published in the journal, ACS Applied Bio Materials.

The research team showed that the thermal response of the material was largely influenced by its architecture and the observed color changes were dependent on the temperature. Unlike non-modified foams, the modified material foams exhibited a remarkable shrinkage decrease at temperatures below 20 °C. This was partly attributed to the influence of HB-PNIPAM and open-pore structures in the foams. In addition, the foams were highly selective in the adsorption of Gram-positive bacteria such as Staphylococcus aureus rather Gram-negative bacteria like Pseudomonas aeruginosa. The presence of Gram-positive bacteria was indicated by the increase in the fluorescence intensity from 590 – 800 nm. Furthermore, PU foams offer a range of advantages such as retention of extrudate, reduced need to change the dressing frequently and improved wound healing.

In summary, the authors demonstrated, for the first time, the immobilization of HB-PNIPAMs functionalized with vancomycin to form a stable S-IPN foam material for potential application as a clinical diagnostic tool. The foam materials exhibited improved selectively for effective detection of Gram-positive microorganisms that are indicated by the fluorescence intensity during the adsorption of the bacteria. Generally, the produced foams were tough, robust and easy-to-use. In a statement to Medicine Innovates, the authors explained their innovative foam would be a significant advance in wound care and a promising candidate for active wound dressing for improved bacteria detection and clinical therapy.