Supercritical solvent impregnation of natural bioactive compounds in N-carboxybutyl chitosan membranes for the development of topical wound healing applications

Abstract

Wound dressings are usually applied with the objective of accelerating wound healing by preventing bacterial infection and accelerating tissue regeneration. The main goals of wound care are prevention of infection and/or inflammation, maintenance of a moist environment, protection of the wound with minimum scar formation, stimulating healthy healing responses. According to modern insights, a wound dressing should present flexibility, controlled adherence to the surrounding tissue, gas permeability, durability, capacity to absorb fluids exuded from the wounded area and the ability to control water loss. Delivery of pharmacologically active compounds like antibiotics/analgesics across the skin is also an attractive alternative to oral dosing. This work addresses the use of natural-based polymers and of “greener” processes to develop biocompatible drug release systems for biomedical applications. Healing of dermal wounds with such natural polymers are attractive primarily because they are biocompatible and present non-irritant and non-toxic properties, being its application on dermis easy and safe. Moreover, they are inexpensive, readily available, capable of multitude of chemical modifications and potentially degradable. Film and foam-like structures of N-carboxybutyl chitosan (CBC) and agarose (AGA) were prepared and characterized in order to evaluate their possible application as wound dressing materials mainly in what concerns their fluid handling properties and sustained drug release capacity. Polymeric biomaterials were loaded with two natural bioactive compounds namely, quercetin (known to present an anti-inflammatory action) and thymol (known to present an anaesthetic action) and using a Supercritical Solvent Impregnation (SSI) technique, in order to develop topical membrane-type natural-based wound dressings. Impregnation experiments were carried out with supercritical carbon dioxide (scCO2) at 10.0 and 20.0 MPa, and at 303.0 and 323.0 K to study the influence of impregnation conditions on the loaded amounts of quercetin and thymol. For quercetin, ethanol was used as co-solvent in order to improve its solubility in the supercritical fluid phase. Drug release kinetics studies were also performed for all the impregnated systems using UV spectrophotometry. Similar release profiles were observed for the same bioactive compound but the total released amount (for each bioactive compound) is always higher when membranes were loaded at higher pressure/temperature conditions. Higher diffusion coefficients in water were obtained for thymol what may be justified by its smaller molecular volume and higher solubility in water, when compared to quercetin. A more sustained release was observed for quercetin which can be mainly due to its lower solubility in water, higher molar volume (which difficult the diffusion of the molecule through the polymeric network) and also due to the known specific favourable interactions between quercetin and CBC which were detected by Scanning Electron Microscopy (SEM) and FTIRATR analyses. These interactions can greatly enhance the sustained release of this natural drug from the polymeric matrix by slowing its release and making it dependent on the external induced degradation of the biopolymer. Obtained results demonstrate that, by the conjugation of different materials with a “tunable” impregnation process, it is possible to prepare different biomaterials, with a specific set of properties, which enable them to be used for wound healing purposes.