Overview:
Our project is focused on the reduction of greenhouse emissions created by the building industry. New building construction is expected to increase significantly over the next few decades due to urbanization and economic development. Most of the currently available building materials are not sustainable, leading to further increases in CO2 emissions, as 11% of energy-related CO2 emissions worldwide originate from materials and construction, 8% of those emissions come from cement alone [1]. In a similar vein, we want to develop building materials that meet the demands of the contemporary world. Our goal is to produce building materials with qualities similar to cement and traditional building materials, but with a lower environmental impact.
How it all began:
In our first brain storming session we were thinking about the main global issues and the climate crisis was one of our first thoughts as it has flooded the media in the past years. We dove deeper into that topic and were thinking about the main contributors to carbon emissions. First things that came to our mind were traffic and electricity for households but we were all surprised when we learned that the building sector contributes to 39% of energy-related CO2 emissions [1]. We chose to explore the field of living building materials further after being inspired by the work of Heveran et al., whose research aims to manufacture bricks using a gelatin scaffold and calcium carbonate precipitation facilitated by cyanobacteria [2]. As one of our advisors, Ben Leyland, has experience with cyanobacteria and Dr. Christoph Schwarz was very kind in sharing detailed information on cultivation and transformation, we settled on using cyanobacteria for calcium precipitation and received our strains from Dr. Christoph Schwarz. As a host for producing polymers we decided pretty quick on Pichia pastoris as the Department of Biotechnology at the University of Natural Ressources and Life Sciences (BOKU) engineered a strain that is able to grow on CO2 [3] and we not only could use the strain but also receive valuable knowledge on yeast cultivation.
Our Microorganisms:
Cyanobacteria: The ability of cyanobacteria to sequester carbon dioxide from the environment and precipitate it as solid calcium carbonate was an especially promising idea for our project. This process would not only be less carbon intensive than conventional cement manufacture, it could potentially also be carbon-negative. As a strain we decided to use Synechocystis PCC 6803 as it is reported to have a especially high capability of calcium deposition [4,5]. If attached to suitable polymeric scaffolds the material can yield robust and tough composites.
Pichia pastoris: To form these polymeric scaffolds, we used Pichia pastoris - a model eukaryotic system to express a variety of polymers. Besides gelatin (collagen), we also wanted to produce two more polymers: spider silk and polyhydroxybutyrat (PHB). These polymers are used to create a hydrogel, which gives our bricks the desired shape and structure.
Our Biopolymers:
Gelatin:
As already mentioned, Heveran et al. used a gelatin scaffold as a polymer. We wanted to take our project further and produce gelatin in our yeast. This idea came up because we wanted to reduce the need of animal products as farming has a large impact on CO2 emissions.
Spider Silk:
Spider silk is a very promising fibrous biomaterial, consisting of different types of proteins. It is used as a novel material in many research fields due to its remarkable properties. The proteins contain highly repetitive sequences and also purification protocols are not standardized [9]. Hence, we wanted to challenge ourself and find out whether we can produce it in our Pichia pastoris.
PHB:
During our research regarding different polymers which are suitable for our project we also stumbled across polyhydroxybutyrate. It is naturally produced by different microorganisms and has a high potential of replacing petrochemical based polymers due to its properties [10]. As an additive it also stabilizes polymerization and was therefore chosen for our project.
Additives:
Heveran et al. used river sand to mix the gelatin and Cyanobacteria together [2]. We further wanted to try desert sand as there is currently no large-scale use in the building industry [6]. Additionally, we want to determine whether adding lignin, a typical waste product of the pulp and paper sector, will enhance the qualities of our living brick [7,8], contributing to our considerations of sustainable development goals. In the process of our human practices research, we also added construction rubble to our brick mixtures, as a possible recycling opportunity for an unused waste product.
References
- [1] IEA (2019), Global Status Report for Buildings and Construction 2019, IEA, Paris
- [2] Heveran, C., Williams, S. L., Qiu, J., et al. (2020). Biomineralization and Successive Regeneration of Engineered Living Building Materials. Matter. 2, 481-494.
- [3] Gassler, T., Sauer, M., Gasser, B., et al. (2020). The industrial yeast Pichia pastoris is converted from a heterotroph into an autotroph capable of growth on CO2. Nat Biotechnol. 38, 210–216.
- [4] Yan, H., Han, Z., Zhao, H., et al. Characterization of calcium deposition induced by Synechocystis sp. PCC6803 in BG11 culture medium. (2013). Chinese Journal of Oceanology and Limnology. 32, 503-510.
- [5] Han, Z., Yan, H., Zhou, S., et al. Precipitation of calcite induced by Synechocystis sp. PCC6803 l. (2013). World J Microbiol Biotechnol. 29, 1801-1811.
- [6] Zhiming, Z. Green manufacturing of silicate materials using desert sand as a raw-material resource. (2022). Construction and building materials. 338, 0950-0618.
- [7] Wang, D., Jang, J., Kim, K. et al. Biomacromolecules “Tree to Bone”: Lignin/Polycaprolactone Nanofibers for Hydroxyapatite Biomineralization. (2019). Biomacromolecules. 20, 2684−2693.
- [8] Klapiszewski, Ł., Klapiszewska, I., Slosarczyk, A. Lignin-Based Hybrid Admixtures and their Role inCement Composite Fabrication. (2019). Molecules. 24, 3544.
- [9] Jung, D., Yang, Y. and Cha, H. Novel In Silico Analyses of Repetitive Spider Silk Sequences to Understand the Evolution and Mechanical Properties of Fibrous Protein Materials. (2019). Biotechnology Journal. 14, 1900139.
- [10] McAdam, B., Fournet, M., McDonald, P. et al. Production of Polyhydroxybutyrate (PHB) and Factors Impacting Its Chemical and Mechanical Characteristics. (2020). Polymers. 12, 2908.