pH-Indicating Colorimetric Hydrogel for Wound Dressing and Medical Grade Silicone Adhesive for Skin Electronics: Towards Multifunctional Bionic Skin Patch (2016)

The physiological milieu of the normal skin is slightly acidic with a pH value ranged between 4 and 6; for chronic or infected wounds with a higher bacterial load, its pH value is above 7.3. Motivated by the fact that monitoring the pH value is an effective way to monitor the status of the wound, a novel smart hydrogel wound dressing incorporating modified pH indicator dyes was developed. Phenol red (PR) was used as the dye and successfully modified with methacrylate to allow a copolymerization with the alginate/Polyacrylamide (PAAm) hydrogel matrix. This covalent attachment prevented the dye from leaching out of the matrix. The prepared pH responsive hydrogel dressing exhibited a porous internal structure, excellent mechanical properties and high swelling ratio, as well as appropriate water vapor transmission rate. All these characteristics indicated the hydrogel’s suitability for wound dressing materials. The responses of the alginate/P(AAm-MAPR) hydrogel dressing with different calcium and water content were also characterized to consider the case of exudate accumulation into the hydrogel. It was observed that increased calcium content and reduced water content could significantly improve elongation at the break of the hydrogel. The leachability of the dye was evaluated by monitoring the absorbance at 568 nm on a UV-Vis spectrometer. From day 3 to day 7, no loss of the dye was detected, which demonstrated that the covalent attachment of the dye to hydrogel substrate can effectively eliminate the dye leaching problem. The color of the hydrogel dressing underwent a transition from yellow (pH 5, 6 and 7) to bisque (7.4 and 8) and finally to red (pH 9), as pH increased. This range of color change matches the clinically meaningful pH range of chronic or infected wounds. Therefore, the developed hydrogel could be used as a wound dressing to monitor the wound healing process by a simple colorimetric display. A second aspect of my research involved the exploration of medical grade adhesives, specifically in combination with surface electromyography (sEMG). Sensors to detect sEMG signals have been widely used by researchers and clinicians in order to capture electrical signals from muscles. While sEMG sensors require an adhesive layer to attach on human skin, the most commonly available ones use acrylic adhesives due to their strong tackiness and low cost. However, the acrylic adhesives are not reusable, difficult to remove and cause skin stripping in some individuals. In addition, they have a tendency to leave residues on skin. Therefore, the adhesion performances of several commercial medical grade silicones were evaluated to find non-irritative alternatives to acrylic adhesives. The silicone adhesives were tacky, non-toxic, non-irritative, and residue-free after removal. Moreover, they were easily washable and allowed multiple cycles of adhesion/debonding. These advantages render the material to be an ideal solution for prolonged use of the electronic patch. Quantitative analyses on the adhesive performances, including peel strength, reusability, and durability, were performed in this research.