Doctoral defence: Liis Preem “Design and characterization of antibacterial electrospun drug delivery systems for wound infections”

On 18 February at 14:00 Liis Preem will defend her doctoral thesis “Design and characterization of antibacterial electrospun drug delivery systems for wound infections“.

Supervisors:
Associate Professor Karin Kogermann, University of Tartu
Associate Professor Andres Meos, University of Tartu
Professor Tanel Tenson, University of Tartu

Opponent:
Professor Hanne Hjorth Tønnesen, University of Oslo (Norway)

Summary
Nonhealing wounds represent an escalating socioeconomic problem in modern society. Several factors contribute to the wound pathologies, but it is increasingly recognized that biofilm and microbial unbalance that overwhelms hosts’ immune responses play a major part in it. Advanced wound dressings that have the capability to deliver antimicrobial drugs to the site of action at controlled rate for extended period, establishing localized, clinically relevant drug concentrations, can potentially improve therapeutic outcomes. Electrospinning (ES) is a simple and flexible method to produce polymeric nano- and microfiber matrices, enabling to incorporate different drugs and control their release. In addition, fiber matrices have several structural properties that make them promising wound dressing materials. Still, much is unknown about different aspects of the design on the performance and quality of these matrices. In the present thesis, ES was used to produce different nano- and microfiber matrices, using different carrier polymers and antibacterial drugs. ES affected the solid-state form of the drug and polymer crystallinity, also induced interactions between different components of the matrix. Different matrices released the drug differently. One of the most important, although not universal, factors controlling drug release was the wetting and buffer penetration into the matrix. Novel hydrogel-based methods to study drug release and diffusion appeared to mimic the in vitro antibacterial activity testing conditions and probably wound environment better compared to the release into buffer solution. Traditional disc diffusion tests enabled to evaluate the efficacy of released drugs against different microorganisms, whereas novel methods helped to reveal differences in the antibacterial activity of differently designed electrospun fiber matrices. It was shown that prolonged release of the drug helped to prevent biofilm formation on the fiber matrix, whereas some carrier polymers could promote biofilm formation on matrices without the drug. Different sterilization methods can effectively sterilize fiber matrices, although this could change the matrix properties, depending on the process conditions and matrix materials.