Using the ciliate Coleps hirtus (Ciliophora, Prostomatea) to engineer bio-based strengtheners for preservation of carbonate stone

• Applicant: Dr. Matea Urbanek
• Subject Area: Biomaterials ; Construction Material Sciences, Chemistry, Building Physics
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 520612707

The most severe decay patterns occurring on sedimentary carbonate building stone are disintegration and scaling. Disintegration is understood as a loss of cohesion between single grains while scaling means a detachment of stone layers. In order to restore the lost cohesion, strengtheners capable to bridge different distances need to be employed. Applications of living organisms in the preservation of built heritage are currently limited to biomineralization through bacteria by precipitation of calcium carbonate. These treatments are capable to protect the surface and increase the resistance towards weathering, however, such a deposition of a carbonate layer is considered to be only a surface phenomenon not capable to bridge larger distances and gain a higher mechanical strength. The goal of this proposal is to apply solutions containing ciliates Coleps hirtus where they will be mineralized and the cohesion of the substrate will be increased. As C. hirtus employs protective structures composed of amorphous calcium carbonate (ACC) the project aims to design cementing solutions that control ACC mineralization during the lifespan of the organisms. To enhance the mechanical properties of biogenic ACC particles, dispersions of liquid calcium carbonate precursors or polymer-induced liquid precursors, will also be blended with C. hirtus to obtain a biomimetic crystallization reproducing the microstructure of stones. The engineered strengtheners will be designed to preserve evolutionarily optimized protective structures of the biogenic ACC structures, that is, to be armorlike, adaptable, non-brittle and tough protective structures. The methodological approach will be based on on-line humidity-induced crystallization experiments by addition of buffer components and additives to the aqueous solution to trigger (partial) crystallization. In order to study the corresponding kinetics and analyze the engineered products, a combination of ATR-FTIR, XRD and electron microscopy will be used. Furthermore, treatment performance of cured strengtheners blended with and applied on carbonate substrates will be also evaluated by means of mechanical tests on small-scale specimens. Temperature induced-crystallization and -transformation experiments will help to shed light on the mechanisms involved in the ACC biomineral stabilization and the mechanisms of mineralization control of biomineral-based precursors, processes never studied before on the species C. hirtus. The project will contribute to expand the application range of strengtheners made from living materials for the built heritage preservation. The results will provide a base to tackle genetic programming of these living organisms in order to provide strengtheners with predetermined functions, in future projects. In addition, the use of living organisms will have a positive impact on environment and energy consumption, as opposed to traditional treatments using lime- and cement-based materials.

• DFG Programme: Research Grants
• Co-Investigators: Professor Dr. Denis Gebauer; Dr. Marie-Louise Lemloh