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 for 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.
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 key aspects involve 1) the study of the physico-chemical properties, in particular optics, of the coral tissue, 2) the engineering of a 3D artificial microenvironment, mimicking environmental characteristics of the coral tissue, 3) the manipulation of the artificial microenvironment to optimise dense microalgal production. Microenvironmental sensing tools (electrochemical and fiber-optic microsensos) and biomedical optics approaches are used to define tissue optical properties (e.g. through optical coherence tomography and diffuse light spectroscopy). A coral-inspired design is then 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) for different optical and chemical microhabitats. In contrast to other bionics approaches, this project additionally integrates concepts of micoroenvironmental ecology through investigating how the local physico-chemical environment shapes the life of the 3D bioprinted microalgal community.
The project develops a completely new approach to studying the microenvironmental ecology of corals while at the same time creating light-scattering media for the improved production of biofuels. A living architecture that can grow biofuels, harness sun light and at the same time provide structural functions has been a vision for the conceptual development of bio cities. The optimised light management of corals will inspire new integrated solutions to produce sustainable, clean energy with minimal use of space. Nature has optimised the use of energy on many different spatial scales in response to a complex suite of environmental factors. The result is an effective recycling of energy that supports the beauty and diversity of life on earth. The successful integration of ecological concepts into the design of bio-inspired photonics will be key to revolutionising the alternative energy sector.
The highly optimised architectural complexity of corals is used as a template for designing efficient photobioreactors.