A pH-Indicating Colorimetric Tough Hydrogel Patch towards Applications in a Substrate for Smart Wound Dressings.

Li Liu,Ravin Narain,Masanori Nagao,Xinda Li,Hyun-Joong Chung,Anastasia Elias

doi:10.3390/polym9110558

Abstract

The physiological milieu of healthy skin is slightly acidic, with a pH value between 4 and 6, whereas for skin with chronic or infected wounds, the pH value is above 7.3. As testing pH value is an effective way to monitor the status of wounds, a novel smart hydrogel wound patch incorporating modified pH indicator dyes was developed in this study. Phenol red (PR), the dye molecule, was successfully modified with methacrylate (MA) 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 patch exhibited a porous internal structure, excellent mechanical property, and high swelling ratio, as well as an appropriate water vapour transmission rate. Mechanical responses of alginate/P(AAm-MAPR) hydrogel patches under different calcium and water contents were also investigated to consider the case of exudate accumulation into hydrogels. Results showed that increased calcium amount and reduced water content significantly improved the Young’s modulus and elongation at break of the hydrogels. These characteristics indicated the suitability of hydrogels as wound dressing materials. When pH increased, the color of the hydrogel patches underwent a transition from yellow (pH 5, 6 and 7) to orange (7.4 and 8), and finally to red (pH 9). This range of color change matches the clinically-meaningful pH range of chronic or infected wounds. Therefore, our developed hydrogels could be applied as promising wound dressing materials to monitor the wound healing process by a simple colorimetric display, thus providing a desirable substrate for printed electronics for smart wound dressing.

Highlights

Wound healing is a complex regeneration process which requires collaborative efforts of many different tissues and cell lineages [1,2]
To prepare MA-Phenol red (PR) for the subsequent synthesis of hydrogel patch, THF was used as the solvent due to its low boiling point
A series of pH indicating colorimetric alginate/P(AAm-MAPR) hydrogels were synthesized for potential wound dressing application

Summary

Introduction

Wound healing is a complex regeneration process which requires collaborative efforts of many different tissues and cell lineages [1,2]. Under normal circumstances the skin surface is acidic [4,5] with varied pH from 4 to 6, which supports the skin’s natural barrier function and helps to counteract microbial colonisation [6,7]. This acidic milieu is affected by wounds that cause a fluidic mixing with body’s internal fluid, whose pH value is 7.4. Polymers 2017, 9, 558 exist in the range of 7.5–8.9, which is an alkaline environment [8,9] Within this alkaline condition, the healing progression is decreased when compared to the wounds with a pH close to neutral [10,11]

Methods

Results

Conclusion