Introduction

Patients with burn wounds or other poor-healing wounds, like diabetes wounds, often suffer from various complications such as infections. Until now the common medical bandages have to be removed to monitor the wound healing progress. To examine if there is an infection, which implies the presence of pathogenic bacteria, samples of the wound have to be taken and studied in a specialized laboratory. This is a long time and expensive process and we want to simplify and accelerate this procedure. The solution for the problem is a hydrogel, which is characterized by containing water, forming a solid three-dimensional network structures and being water insoluble. Most hydrogels could swell in aqueous solutions; for our purpose, as a wound bandage, it can be used to absorb some of the wound fluid. Furthermore it can be attached hermetically and the moisture provided by the hydrogel leads therefore to ideal wound healing conditions. An optimal polymer for such a hydrogel is chitosan (poly-1,4-β-D-glucopyranosamine). It has beneficial properties like biocompatibility, biodegradability, and film forming ability. Furthermore, chitosan has reactive amine side groups, which offer possibilities for modifications, like the linkage of a fluorophore to detect the pathogenic bacteria. [2]
The hemostatic chitosan is reported to have intrinsic antifungal, antibacterial, and antiviral properties. Furthermore it promotes scar free wound healing and has care effects, and is antiallergic [3]. In addition human epithelium could heal along the chitosan matrix, so no wound distance grid is necessary [1]. It is an ideal scaffold material to manufacture different types of hydrogels, salves, pastes or solid bandages. Besides its great described antimicrobial characteristics, it has a skin cooling effects. Most chitosan hydrogel topical wound dressings are formed using an expensive or toxic crosslinking agent, which we want to avoid.
Due to that we can deliver an optimal wound healing and monitoring bandage for these affected patients without the need to disrupt the healing process. The hydrogel should help preventing or treat wound infections of any degree of burns.

Production

To evaluate an ideal hydrogel, various compositions were tested, like pure chitosan or chitosan in combination with agarose, agar or alginate. During this work various promising hydrogels could be produced. The kind of hydrogels we want to create are due to their compounds not toxic, biodegradable, biocompatible, while at the same time having a low-cost and easy to manufacturing processes. They are easy to produce in different sizes and thicknesses. While being flexible they keep their stability, which makes it comfortable for patients to wear, and easy to manufacture, handle and apply on patients. The pH-level of some of our hydrogels are easy to regulate by rinsing it with the proper pH-level solution. We were focused to work with basic laboratory equipment. For the preparation of chitosan hydrogels, an acidic environment is usually required to dissolve chitosan. We manufactured our chitosan containing hydrogel in aqueous acetic acid.

Chitosan-Alginate

A long time continuous mechanical stirring (6 hours) is required to dissolve the chitosan in the acetic acid-deionized water solution. Under continuous pH measurement it was mechanically stirred for 12 hours. This solution needs to rest for at least 12 hours for further processing.

Chitosan Hydrogel solidified in Alginate-Quercetin solution

The alginate/quercetin solution was poured into a mold and then liquid-friezed. The 2% chitosan solution was then poured onto it and streaked out to the certain thickness, covered with the alginate/quercetin solution, placed into the 37° incubator for 24 hours.

After the solidification process the arosed solid hydrogel was rinsed with ultrapure water. Placed into an aqueous solution it will swell massively after time.
The swelling degree of the hydrogel was calculated by

$\mathrm{DS}\frac{\mathrm{Ww\; -\; Wd}}{\mathrm{Ww}}x100$

The bandages were saturated with the liquid in which it was immersed. Our manufactured hydrogel has a degree of swelling of almost 600 %.

Chitosan Hydrogel with high pH-level

Manufacturing process of our chitosan hydrogel with a high pH-level was performed by rinsing the 2% chitosan solution with a defined NaOH solution with the desired pH-level.