Employing photocurable biopolymers to engineer photosynthetic 3D-printed living materials for production of chemicals

Abstract

Photosynthetic microorganisms, such as cyanobacteria and microalgae, have great potential as living cell factories for chemical and fuel production. Immobilisation of cells is an effective technique for enhancing productivity and longevity of the production system, as well as aiding in the separation of cells from the medium. Alginate crosslinked with divalent ions is commonly used for immobilisation, however its ionic crosslinking is reversible in high ionic strength or in the presence of chelating agents leading to matrix degradation. To address these challenges, photocurable materials present a potential solution, especially when coupled with 3D-printing technologies to create complex, tunable 3D architectures for various applications. In this context, we propose a bioink composed of alginate, photocurable galactoglucomannan-methacrylate and photosynthetic cells for 3D-printing green biocatalysts for solar-chemical production. We demonstrate the applicability of this photocurable bioink for the immobilisation of photosynthetic microbes either capable of producing ethylene (specifically-engineered Synechocystis cell factories) or transforming cyclohexanone to ε-caprolactone (specifically-engineered Chlamydomonas cell factories), both of which are industrially relevant chemicals. Films produced from photocurable bioinks demonstrate high mechanical stress tolerance compared to films prepared via conventional ionic crosslinking, showing resistance to high ionic strength in the medium. Furthermore, both Synechocystis and Chlamydomonas cells entrapped within 200 μm-thick hydrogel layers, 3D-printed on glass support surfaces, demonstrated notably high (ethylene) or similar (biotransformation of cyclohexanone to ε-caprolactone) production titres and space–time yields compared to the conventional biocatalysts. These engineered living materials, being biocompatible and biobased, particularly when used in conjunction with 3D-printing, provide convenient scalability and potential to enhance sustainability in the chemical industry.