Conditions for CaCO3 Biomineralization by Trichoderma Reesei with the Perspective of Developing Fungi-Mediated Self-Healing Concrete

Concrete, a widely used building material, often suffers from cracks that lead to corrosion and degradation. A promising solution to enhance its durability is the use of fungi as self-healing agents, specifically by harnessing their ability to promote calcium carbonate (CaCO3) precipitation on their cell walls. However, the ideal conditions for CaCO3 precipitation by the filamentous fungal species Trichoderma reesei are still unclear. In this study, the biomineralization properties of T. reesei in liquid media are investigated. Two different calcium sources, calcium chloride (CaCl2) and calcium lactate are tested, at varying concentrations and in the presence of different nutritional sources that support growth of T. reesei. This study also explores the effects on fungal growth upon adding cement to the medium. Calcium lactate promotes greater fungal biomass production, although less crystals are formed as compared to samples with CaCl2. An increasing calcium concentration positively influences fungal growth and precipitation, but this effect is hindered upon the addition of cement. The highest amounts of biomass and calcium carbonate precipitation are achieved with potato dextrose broth as a nutritional source. By identifying the optimal conditions for CaCO3 precipitation by T. reesei, this study highlights its potential as a self-healing agent in concrete.

Screening fungal strains isolated from a limestone cave on their ability to grow and precipitate CaCO 3 in an environment relevant to concrete

Fungi-mediated self-healing concrete is a novel approach that promotes the precipitation of calcium carbonate (CaCO ₃ ) on fungal hyphae to heal the cracks in concrete. In this study, we set out to explore the potential of fungal species isolated from a limestone cave by investigating their ability to precipitate CaCO ₃ and to survive and grow in conditions relevant to concrete. Isolated strains belonging to the genera Botryotrichum sp. , Trichoderma sp. and Mortierella sp. proved to be promising candidates for fungi-mediated self-healing concrete attributed to their growth properties and CaCO ₃ precipitation capabilities in the presence of cement.

Current state and future prospects of pure mycelium materials

In the context of the ongoing transition from a linear to a circular economy, ecologically friendly renewable solutions are put in place. Filamentous fungi can be grown on various organic feedstocks and functionalized into a range of diverse material types which are biobased and thus more sustainable in terms of their production, use and recycling. Pure mycelium materials, consisting only of mycelial biomass, can adopt versatile properties and appear promising as a substitute for current petrochemically produced polymeric materials or, in the case of myco-leather, as a substitute for animal-based leather. In recent years, a handful of private companies have been innovating to bring products based on pure mycelium materials to the market while scientific interest in these promising biomaterials is now starting to gain momentum. In this primer, we introduce pure mycelium materials, frame different production methods, review existing and potential future applications, thereby offering a vision on future advances for this emerging fungi-based technology.

Mechanical characteristics of bacterial cellulose-reinforced mycelium composite materials

BACKGROUND

While mycelium is considered a promising alternative for fossil-based resins in lignocellulosic materials, the mechanical properties of mycelium composite materials remain suboptimal, among other reasons due to the weak internal bonds between the hyphae and the natural fibres. A solution could be provided by the hybridisation of mycelium materials with organic additives. More specifically, bacterial cellulose seems to be a promising additive that could result in reinforcing mycelium composites; however, this strategy is underreported in scientific literature.

RESULTS

In this study, we set out to investigate the mechanical properties of mycelium composites, produced with the white-rot fungus Trametes versicolor, and supplemented with bacterial cellulose as an organic additive. A methodological framework is developed for the facile production of bacterial cellulose and subsequent fabrication of mycelium composite particle boards based on a hybrid substrate consisting of bacterial cellulose and hemp in combination with a heat-pressing approach. We found that, upon adding bacterial cellulose, the internal bond of the composite particle boards significantly improved.

CONCLUSIONS

The addition of bacterial cellulose to mycelium composite materials not only results in a strengthening of internal bonding of mycelium material, but also renders tuneable mechanical properties to the material. As such, this study contributes to the ongoing development of fully biological hybrid materials with performant mechanical characteristics.

A review on the potential of filamentous fungi for microbial self-healing of concrete

Concrete is the most used construction material worldwide due to its abundant availability and inherent ease of manufacturing and application. However, the material bears several drawbacks such as the high susceptibility for crack formation, leading to reinforcement corrosion and structural degradation. Extensive research has therefore been performed on the use of microorganisms for biologically mediated self-healing of concrete by means of CaCO₃ precipitation. Recently, filamentous fungi have been recognized as high-potential microorganisms for this application as their hyphae grow in an interwoven three-dimensional network which serves as nucleation site for CaCO₃ precipitation to heal the crack. This potential is corroborated by the current state of the art on fungi-mediated self-healing concrete, which is not yet extensive but valuable to direct further research. In this review, we aim to broaden the perspectives on the use of fungi for concrete self-healing applications by first summarizing the major progress made in the field of microbial self-healing of concrete and then discussing pioneering work that has been done with fungi. Starting from insights and hypotheses on the types and principles of biomineralization that occur during microbial self-healing, novel potentially promising candidate species are proposed based on their abilities to promote CaCO₃ formation or to survive in extreme conditions that are relevant for concrete. Additionally, an overview will be provided on the challenges, knowledge gaps and future perspectives in the field of fungi-mediated self-healing concrete.

A comprehensive framework for the production of mycelium-based lignocellulosic composites

Environmental pollution and scarcity of natural resources lead to an increased interest in developing more sustainable materials. For example, the traditional construction industry, which is largely based on the extraction of fossil fuels and raw materials, is called into question. A solution can be found in biologically augmented materials that are made by growing mycelium-forming fungal microorganisms on natural fibres rich in cellulose, hemicellulose and lignin. In this way, organic waste streams, such as agricultural waste, are valorised while creating a material that is biodegradable at the end of its life cycle - a process that fits in the spirit of circular economy. Mycelium-based materials have properties that are promising for a wide range of applications, including the use as construction materials. Despite this promise, the applicability and the practicality of these materials are largely unexplored and moreover, individual studies use a wide range of different experimental approaches and non-standardized procedures. In this review, we critically evaluate existing data on the composition of mycelium-based materials and process variables with the aim of providing a comprehensive framework of the production process. The framework illustrates the many input factors during the production that have an impact on the final characteristics of the material, and the unique potential to deploy more tuneable levels in the fabrications process that can serve to prototype a diversity of new unprecedented applications. Furthermore, we determine the applicability of existing data and identify knowledge gaps. This framework is valuable in identifying standardized approaches for future studies and in informing the design and process of new applications of mycelium-based materials.

Mechanical, physical and chemical characterisation of mycelium-based composites with different types of lignocellulosic substrates

The current physical goods economy produces materials by extracting finite valuable resources without taking their end of the life and environmental impact into account. Mycelium-based materials offer an alternative fabrication paradigm, based on the growth of materials rather than on extraction. Agricultural residue fibres are inoculated with fungal mycelium, which form an interwoven three-dimensional filamentous network binding the feedstock into a lightweight material. The mycelium-based material is heat-killed after the growing process. In this paper, we investigate the production process, the mechanical, physical and chemical properties of mycelium-based composites made with different types of lignocellulosic reinforcement fibres combined with a white rot fungus, Trametes versicolor. This is the first study reporting the dry density, the Young’s modulus, the compressive stiffness, the stress-strain curves, the thermal conductivity, the water absorption rate and a FTIR analyse of mycelium-based composites by making use of a fully disclosed protocol with T. versicolor and five different type of fibres (hemp, flax, flax waste, softwood, straw) and fibre processings (loose, chopped, dust, pre-compressed and tow). The thermal conductivity and water absorption coefficient of the mycelium composites with flax, hemp, and straw have an overall good insulation behaviour in all the aspects compared to conventional materials such as rock wool, glass wool and extruded polystyrene. The conducted tests reveal that the mechanical performance of the mycelium-based composites depends more on the fibre processing (loose, chopped, pre-compressed, and tow), and size than on the chemical composition of the fibres. These experimental results show that mycelium-composites can fulfil the requirements of thermal insulation and have the potential to replace fosile-based composites. The methology used to evaluate the suitability and selection of organic waste-streams proved to be effective for the mycelium-material manufacturing applications.