Resonant Mixing in Glass Bowl Microbioreactor Investigated by Microparticle Image Velocimetry

Abstract

Microbioreactors are gaining increased interest in biopharmaceutical research. Due to their decreasing size, the parallelization of multiple reactors allows for simultaneous experiments. This enables the generation of high amounts of valuable data with minimal consumption of precious pharmaceutical substances. However, in bioreactors of all scales, fast mixing represents a crucial condition. Efficient transportation of nutrients to the cells ensures good growing conditions, homogeneous environmental conditions for all cultivated cells, and therefore reproducible and valid data. For these reasons, a new type of batch microbioreactor was developed in which any moving mixer component is rendered obsolete through the utilization of capillary surface waves for homogenization. The bioreactor was fabricated in photosensitive glass and its fluid volume of up to 8 µL was provided within a bowl-shaped volume. External mechanical actuators excited capillary surface waves and stereo microparticle image velocimetry (µPIV) was used to analyze resulting convection at different excitation conditions in varied reactor geometries. Typical vortex patterns were observed at certain resonance frequencies where best mixing conditions occurred. Based on the results, a simplified 1D model which predicts resonance frequencies was evaluated. Cultivation of Escherichia coli BL21 under various mixing conditions showed that mixing in resonance increased the biomass growth rate, led to high biomass concentrations, and provided favorable growth conditions. Since glass slides containing multiple bowl reactors can be excited as a whole, massive parallelization is foreseen.

Enhanced inertial focusing of microparticles and cells by integrating trapezoidal microchambers in spiral microfluidic channels

“…50 This technique has recently been used to investigate vortex formation in glass micro bioreactors under the inuence of capillary waves. 51 This technique shall be utilized to analyse and observe ow velocity proles inside the Dean ow inducing microchambers to gain a better perspective on the local ow conditions that shall lead to focusing enhancement as long as the tracer particles (smaller than the particles that experience fractionation) are following the ow and are unaffected by inertia. The soware calculates a cross-correlation of intensities within an interrogation window, a sequence of usable images needs a high seeding density.…”

Microsensor in Microbioreactors: Full Bioprocess Characterization in a Novel Capillary-Wave Microbioreactor

“…The cwMBR was fabricated as previously described by Meinen et al [ 21 ] by femtosecond laser direct writing in photosensitive Foturan ® glass (Schott, Mainz, Germany), forming a round cavity with an upper diameter of 4 mm and a depth of 1 mm. The optical transparent glass design enables the read-out of optical sensor spots from outside the cwMBR.…”

“…The cultivation medium is mixed by capillary waves induced by the vertical oscillation of the cwMBR, as described by Frey et al [ 20 , 44 ] and Meinen et al [ 21 ]. Therefore, the cwMBR mounting was placed on a quadratic polyvinyl chloride platform with an electromagnetic exciter (Ex 45 S, Visaton, Haan, Germany) under each corner.…”

“…This makes them less suitable for high parallelization and automatization and increases media and test substance consumption. Therefore, a 7 µL MBR was developed, which was previously presented by Frey et al [ 20 ] and Meinen et al [ 21 ] and is further optimized in this paper. This MBR is a promising tool combining minimal cultivation volume with integrated optical sensors for process characterization.…”

“…The MBR consists of a photosensitive Foturan ® glass chip with an internal cavity holding a sessile droplet. The glass chip is fabricated by femtosecond laser direct writing, which is an ablation process forming a frustum-shaped cavity, as described by Meinen et al [ 21 ]. By placing the MBR chip in a 3D-printed mounting, optical fibers for the sensor read-out can be guided to the specific position.…”