Abstract
The immobilization of enzymes in biocatalytic flow reactors is a common strategy to increase enzyme reusability and improve biocatalytic performance. Extrusion-based 3D bioprinting has recently emerged as a versatile tool for the fabrication of perfusable hydrogel grids containing entrapped enzymes for the use in such reactors. This study demonstrates the suitability of water-in-oil high internal phase emulsions (HIPEs) as 3D-printable bioinks for the fabrication of composite materials with a porous polymeric scaffold (polyHIPE) filled with enzyme-laden hydrogel. The prepared HIPEs exhibited excellent printability and are shown to be suitable for the printing of complex three-dimensional structures without the need for sacrificial support material. An automated activity assay method for the systematic screening of different material compositions in small-scale batch experiments is presented. The monomer mass fraction in the aqueous phase and the thickness of printed objects were found to be the most important parameters determining the apparent activity of the immobilized enzyme. Mass transfer limitations and enzyme inactivation were identified as probable factors reducing the apparent activity. The presented HIPE-based bioinks enable the fabrication of flow-optimized and more efficient biocatalytic reactors while the automated activity assay method allows the rapid screening of materials to optimize the biocatalytic efficiency further without time-consuming flow-through experiments involving whole printed reactors.
Highlights
Biocatalysis is the key to a variety of biotechnological applications, ranging from large-scale industrial processes like the production of high fructose corn syrup (Kirk et al, 2002) to more sophisticated analytical methods like biosensors (Hasan et al, 2014; Rocchitta et al, 2016)
This study aims at formulating aqueous solutions of acrylic acid (AA) and PEG-DA 700 as the internal phase of high internal phase emulsions (HIPEs) in order to enhance printability and allow the 3D printing of composite materials consisting of porous polymeric scaffolds filled with enzyme-laden hydrogels
This study demonstrates the applicability of HIPEs as enzymecontaining bioinks for the extrusion-based 3D printing of enzymatically active composite materials to be employed in biocatalytic reactors
Summary
Biocatalysis is the key to a variety of biotechnological applications, ranging from large-scale industrial processes like the production of high fructose corn syrup (Kirk et al, 2002) to more sophisticated analytical methods like biosensors (Hasan et al, 2014; Rocchitta et al, 2016). Enzymes act as catalysts even at mild reaction conditions Due to their high chemo- and regioselectivity, they are suitable for the production of high-value products like enantiomerically pure chiral compounds (Nestl et al, 2014). The immobilization of enzymes offers a way to realize processes combining different spatially separated reactions. These compartmentalized enzymatic cascades may prevent undesirable effects like product inhibition or crossreactivities (Rabe et al, 2017). This limitation can be counteracted by increasing the surface-area-to-volume ratio of the hydrogel structures (Schmieg et al, 2018)
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