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Title of the thesis: Exploring liquid-liquid phase separation of silk proteins as a tool for bio-inspired materials assembly

Thesis defender: Jennifer Tersteegen
Opponent: Prof. Ilja Voets, Eindhoven Technical University, Netherlands
Custos: Prof. Markus Linder, Aalto University School of Chemical Engineering

Harnessing silk protein droplets for bio-inspired material design

Nature provides us with a vast number of materials that possess exceptional properties. One such example is spider silk. It is at the same time very strong and highly elastic. Spider silk is made of proteins that are produced in the silk gland and form solid fibers during the spinning process. The precise mechanisms of this process are still not fully resolved. This, however, is a requirement to enable the large-scale, industrial use of spider silk.

This thesis studies the role of liquid-liquid phase separation in the assembly process of spider silk proteins. Liquid-liquid phase separation leads to the demixing of a solution into two or more distinct phases. In the case of spider silk, droplets are formed that show a very high silk concentration, while the silk concentration in the surrounding phase is low. These droplets are also called biomolecular condensates, and their formation is also hypothesized to occur within the silk gland of spiders.

Within this work, silk condensates are investigated from different perspectives. First, the effect of varying conditions during production on the properties of silk condensates is examined. This has implications, for example, for the design of the production process, especially considering its upscaling. Next, the non-equilibrium behavior of silk condensates is studied by applying an electric field. Silk condensates show highly diverse, voltage-dependent behaviors, which are linked to pH changes in the solution. Processes in nature take place under non-equilibrium conditions, thus, electric fields proved to be a very suitable method to study condensates under these conditions. Finally, the use of condensated silk protein in the production of novel composites was investigated. For this, the silk protein was combined with delignified wood, resulting in a strong adhesive system.

In summary, this work sheds light on the intricate mechanisms involved in the assembly of protein-based materials. It furthermore provides different approaches on how condensates can be manipulated to alter this assembly process.

Keywords: Liquid-liquid phase separation, biomolecular condensates, non-equilibrium, recombinant spider silk protein, bio-inspired materials

Thesis available for public display 7 days prior to the defence at .

Contact information: 
E-mail: jennifer.tersteegen@aalto.fi 
LinkedIn: https://www.linkedin.com/in/jennifer-tersteegen-84395a201/