PhD defence by Yuyan Liu

Principal supervisor

Professor Rafael Taboryski, DTU

Co-supervisor

Associate Professor Paul Kempen, DTU

Examiners

• Associate Professor Ada-Ioana Bunea, Chair. (DTU Nanolab)
• Professor Jasmina Casals-Terre (UPC Barcelona Tech)
• Senior R&D scientist Esben Kjær Unmack Larsen (Coloplast)

Chairperson at defence

Professor Stephan Sylvest Keller, DTU

Abstract

In the world of aquaculture, keeping fish healthy without overusing antibiotics is a growing challenge. One promising solution comes from nature itself: a group of marine bacteria called Phaeobacter that naturally produce an antibacterial compound. These bacteria can help inhibit harmful microbes, but to work effectively, they need to grow on surfaces and in stable communities called biofilms.

This PhD research explores how to design and fabricate special surfaces that support Phaeobacter to form biofilms. This study explored various plastics to understand how surface energy influences bacterial behavior. Interestingly, while some materials attracted more bacteria initially, long-term cultured bacteria offer similar antibacterial activity across all types of polymer materials. This suggests that practical factors like cost and scalability can guide material choice instead.

Using advanced cleanroom techniques, this study created tiny patterns like microscale pits and pillars on silicon molds, which were then used to replicate patterns onto plastic materials. To move closer to real-world applications, this study tested scalable fabrication methods like nanoimprint and injection molding, and fine-tuned the process to make sure the tiny patterns were copied accurately.

This study developed test platforms, including both static and dynamic systems, to support bacterial growth. This study also explored different ways to visualize the bacteria growing on these surfaces, helping us take a closer look at where they settle and how they behave.

Finally, this study created multi-scale structures combining nano-, micro-, and macro-features to better understand how different pattern scales affect bacterial performance.

This research opens the door to sustainable, bacteria-based solutions for fish farming and beyond, potentially supporting more sustainable food production.