Microcapsules for Functionalization of Fibrous Materials: From Formulation Development to Long-term Microbial Infection Control

Doctoral thesis, 2023

In response to growing concerns regarding the impact of antimicrobial agents on the environment and public health, a more sustainable approach to their use in products is needed. The problem originates from rapid and uncontrolled release, leading to difficulties in maintaining long-term efficacy. A common solution to prolong the lifetimes of materials is to increase the dose of active substances, however, this causes significant losses, pollution, and antimicrobial resistance development in microorganisms. A more sustainable solution would be materials that release these substances in a controlled manner, only slightly surpassing effective concentrations.

This thesis explores the utilization of microcapsule functionalization as a means of enabling a controlled release of active substances from fibrous materials. Successful control requires (i) a toolbox for tuning the release profiles from microcapsules and (ii) an effective functionalization strategy that retains the release rate-limiting properties of the microcapsules in the fibrous material. An improved theory for microcapsule morphology prediction following internal phase separation was first established, incorporating the importance of both thermodynamically controlled intermediate morphologies and the kinetics of formation. This allowed for improved morphology control during formulation, facilitating the development of microcapsule formulations capable of achieving both immediate release in response to pH changes and UV light exposure, as well as sustained long-term release over several weeks to months. A method for functionalizing wet-spun and solution-blown biobased polysaccharide fibers with these microcapsules was consequently developed and evaluated. The microcapsules were embedded within the fibers, retaining their rate-limiting properties and demonstrating the potential for creating a macroscopic controlled release material.

As a proof of concept, a prototype material was evaluated for long-term microbial infection control. In this material, microcapsules loaded with the antimicrobial agent octenidine dihydrochloride (OCT) were incorporated into a cellulose nonwoven textile. In vitro experiments confirmed that the sustained OCT release from the material prototype effectively provided long-term infection control against S. aureus for more than one week. In contrast, a control material loaded using conventional impregnation lost its antimicrobial efficacy after just 30 minutes. This highlights the possibilities associated with controlled release of actives, not only for infection control but also a wider range of applications.