The supercritical solvent impregnation of textiles with therapeutic components

Abstract

Hospital-acquired infections have become common. One of the mechanisms by which they spread is through adherence to the textiles used as apparel or as bedding. One effective method to reduce the spread of this type of infection is by functionalising the material, i.e. adsorbing antimicrobial agents onto the textile fibre. Current industrial processes used to perform this process are by adsorption of the appropriate antimicrobial agents onto the fibre's surface. This method has several drawbacks – the use of water as a medium for absorption, which requires treatment for re-use. Synthetic compounds are used; these are harmful to aquatic life and accumulate in the food chain. Therefore, investigating an alternative method to functionalise textiles while avoiding these drawbacks is required. An alternative approach is to absorb the antimicrobial agent into the fibre matrix using a waterless mass-transfer medium such as supercritical carbon dioxide (scCO2). The absorbed antimicrobial agent diffuses to the fibre's surface over time during use. Besides being waterless, this approach could result in higher amounts of antimicrobial agent retention than the conventional methods since the whole fibre matrix, not just the surface, act as the agent's reservoir. scCO2 is particularly attractive in this respect due to its moderate critical parameters: its critical temperature and pressure are 31oC and 7.4 MPa, respectively. Thus, thermal degradation of temperature-sensitive therapeutic components and materials can be avoided—no aqueous waste results directly from this alternative process. Synthetic compounds generally have a lower lethal concentration value (LC50) than natural compounds (the amount required to be potent to a specific microbe). This means that more of the natural compound is required, by mass, to achieve the same effect as the synthetic. In addition, synthetic compounds also have a higher likelihood of being non-biodegradable. Since the alternative method could show higher retention of the agent inside the fibre matrix, it follows that this method could achieve the same effect as synthetic compounds applied at ambient conditions. Although some studies have shed light on the feasibility of the sorption of antimicrobial agents into polymeric material using scCO2 as the medium, no comprehensive study could be found that compared the performance of the different commonly used materials used in hospitals when loaded with natural antimicrobial compounds. This work compares the performance of fabric samples loaded with antimicrobial extracts of the plant, under supercritical and ambient conditions, against specific microbes. The fabric types are lycra, cotton, and polyester. The extracts are the essential oils and resin obtained from buchu (Agathosma crenulata), tea tree (Melaleuca alternifolia), and hops (Humulus lupulus). The results show that, indeed, all the textile fibres investigated retained a higher amount of the agent within them when the agent was infused under high pressure and subjected to a slow depressurisation. Further, antimicrobial tests showed that the potency was much more persistent than that of control samples. This investigation thus confirms the hypothesis that infusion of bioactive compounds under high pressure using scCO2 results in higher retention of the agents, which can be active over an extended period. In addition, the immersed cotton samples exhibit an activity greater than the polyester and lycra samples. This is despite cotton having the lowest solute retention. It further opens the path to using natural compounds to produce functional textiles.