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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - BioMIC-FUEL (Bio-inspired photonics for enhanced microalgal photosynthesis in biofuels)

Teaser

Summary

Microscopic photosynthesising algae are a very attractive source of biomass energy and much effort has been made to optimise biofuel production. The key challenge for making microalgal production commercially feasible is to improve the spatial efficiency at which algae can grow, because high cell densities lead to low photosynthetic efficiency as a result of self-shading. The development of photobioreactors that provide algae with artificial irradiation and regulate the flux of gases is a key approach to maximise algal photosynthesis. However, these systems are expensive and thus limit the scaling-up of bioenergy generation.

Nature has found simple ways to grow microalgae with high photosynthetic efficiency at high densities. On tropical coral reefs, microalgae are harboured within the animal tissue of corals as part of a natural symbiosis. The current design of the coral-algal symbiosis represents the result of an optimisation process that has taken place over millions of years in response to environmental drivers such as the competition f or space and light. Corals are highly optimised photosynthesising systems that despite the high densities of algae have remarkable photosynthetic efficiency on a tissue systems level. This is largely because of the evolution of simple light scattering mechanisms within the coral tissue and skeleton and niche adaptation of the microalgae to different cell layers in order to best suit the local physico-chemical microenvironment.

Project aims and approach: We apply a multidisciplinary framework that integrates concepts of aquatic microbial ecology and optics into the design of biologically inspired bioenergy generation. Specifically, we learn from corals how to grow microalgae for improved biofuel production. The specific objectives are to 1) explore the in vivo light field, optical properties and photosynthetic efficiency of a range of coral species from different light regimes, 2) understand the nanophotonic and structural properties of corals underlying the optimised light modulation and 3) apply the biophotonic insight to design novel photonic materials for the improved growth of microalgae. A coral-inspired design is developed in a CAD environment and optimised via optical optical modeling approaches and microecological theory. Microalgae are 3D bioprinted in hydrogels that serve as algal microhabitats with defined optical and chemical response. The energy budget of the artificial microalgal system is evaluted through direct measurement of photosynthetic efficiency (via microsensors and chlorophyll a fluorimetry). In contrast to other bionics approaches, this project additionally integrates concepts of micoroenvironmental ecology through investingating how the local physico-chemical environment shapes the life of the 3D bioprinted microalgal community. These research objectives have important societal impacts, especially within Europe where the development of a resource-efficient, low-carbon economy through biofuels is a key research agenda.

Work performed

During the outgoing phase all three work packages have been studied. As part of WP1 (exploring coral optical properties) the following studies were carried out.
1) Characterisation of the light modulation properties of green fluorescent pigments in corals.
The spectral tuning properties of a range of corals have been studied and the role of red and green fluorescent proteins as well as photoconvertible proteins has been studied on light absorption and propagation in coral tissues. The results suggest an important role of green fluorescent proteins in spectral tuning of coral photosynthesis, especially for thick tissued corals.
2) The Development of a 3D Monte Carlo model of light absorption in corals.
A 3D tetrahedral mesh-based Monte Carlo Model has been developed for simulating realistic light propagation in corals. The input architecture was generated based on optical coherence tomography scans of various coral surfaces. The model was developed as a rapid tool to characterise light propagation for different coral micro-geometries.
3) Characterisation of optical properties with diffuse reflectance spectroscopy
A theoretical model has been developed to extract the optical properties of corals non-invasively with two optical fibers. The model used data previously generated by the fellow. The model showed that in most shallow water corals the skeleton homogenizes incident irradiation.
4) Optical properties of corals characterised with visible light Optical Coherence Tomography.
In collaboration with researchers from Northwestern University, the fellow aided in developing and applying a new method to characterise the optical properties of corals in vivo using visible light optical coherence tomography. These results aid in providing an overview of the light harvesting strategies of various corals.

As part of WP2 (understanding the nanophotonic properties of corals):
1) Characterisation of the nanophotonic properties of Green fluorescent pigment granules.
The nanophotonic properties of green fluorescent pigment granules have been investigated. Specifically, the ultrastructure of the granules was assessed using scanning electron microscopy, transmission electron microscopy and super resolution microscopy. The photonic properties have been studied with a high resolution spectral imaging system.

As part of WP3 (developing novel photonic materials for enhanced algal growth):
1) Development of novel 3D bioprinted hydrogel for ultra-high density microalgal growth.
A bio-inspired microalgal culturing platform with optimized light delivery has been developed. A 3D bioprinted hydrogel system has been fabricated using the coral architecture and coral optical properties as templates. Extensive studies on the performance of this photobioreactor system have been carried out and showed that productivity was strongly enhanced compared to several conventional culturing techniques.

Final results

\"The novel microalgal culturing platform is currently evaluated for performance and scalability. It is expected that this culturing system provides the basis for scalable and commercially viable systems. Thus, the research resulting from biomicfuel is expected to have important socio-economic impacts on the growing microalgae biofuel and bioproduct economy. Biomicfuel has also provided the ground foundation for various future research initiatives, including ongoing grant applications within the Horizon 2020 framework (incl. ITN: \"\"BEEP\"\", Bio-inspired and bionic materials for enhanced photosynthesis).
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