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.
Nowadays, the performance of experiments in automated microliter scale format is common practice in the biopharmaceutical process development. The increased number of experiments, reduced sample volumes, and usage of robotic platforms require the adjustment of photometric measurements to determine the protein concentration. This work presents the qualification and usage of a disposable measurement device that can be used with conventional microplate photometers. The application of the microfluidic device (μF‐device) allows absorption measurements of protein concentrations from around 0.1 to 100 mg/mL with an accuracy of 99.2% dependent on given protein extinction coefficients. The integrated four measurement chambers of increasing height (100–1500 μm) allow the direct calculation of calibration curves and the determination of protein concentrations independent of used optical path lengths with a sample volume of 36 μL. This study contains the validation of the analytical μF‐device according to ICH Guidelines as well as a representative case study. A salt gradient screening with chromatography columns in microliter scale performed on a liquid handling station presents the usability of the μF‐device. It is shown that an improvement of the repeatability and accuracy of the chromatograms could be achieved by μF‐device implementation in comparison to photometric measurements performed in microtiter plates.
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