2.1 Microplate Bioreactor Design
Microscale mixing is achieved by integrating Redbud Lab’s MXR, a novel microfluidic mixing technology consisting of 1 x 105Redbud Posts per cm2, as surface attached impellers in each well (Figure 1A). Redbud posts are approximately 50 µm tall and 4 µm in diameter and are made using a flexible polymer doped with magnetic material. When a magnetic field is applied, the posts experience a torque that works to align their dominant axis with the magnetic field, effectively creating an array of micro-stir bars with one end attached to the surface. The magnetic fields used to drive Redbud Posts are generated by a Redbud Stage (Redbud Labs, RBS-CUST-MWP) modified to accept a multiwell plate (Figure 1B.). The stage provides control over the actuation rate of the posts and has been modified further for compatibility with an incubator for environmental controls (temperature, humidity, %CO2, etc.).
Multi-well chips (Redbud Labs, MXR-CUST-MWP(-96)) designed to evaluate planar mixing were prepared using RBL-posts affixed to an acrylic substrate (RBL proprietary method). Biocompatible adhesive spacers were cut with CO2 laser to model standard 96-well XY dimensions. An acrylic lid with fluid delivery ports was affixed atop the spacer to seal the wells resulting in 4 identical chambers with 16 µL volumes (6.73 mm well diameter, and 0.4 mm spacer height