On chip porous polymer membranes for integration of gastrointestinal tract epithelium with microfluidic 'body-on-a-chip' devices.

We describe a novel fabrication method that creates microporous, polymeric membranes that are either flat or contain controllable 3-dimensional shapes that, when populated with Caco-2 cells, mimic key aspects of the intestinal epithelium such as intestinal villi and tight junctions. The developed membranes can be integrated with microfluidic, multi-organ cell culture systems, providing access to both sides, apical and basolateral, of the 3D epithelial cell culture. Partial exposure of photoresist (SU-8) spun on silicon substrates creates flat membranes with micrometer-sized pores (0.5-4.0 µm) that--supported by posts--span across 50 µm deep microfluidic chambers that are 8 mm wide and 10 long. To create three-dimensional shapes the membranes were air dried over silicon pillars with aspect ratios of up to 4:1. Space that provides access to the underside of the shaped membranes can be created by isotropically etching the sacrificial silicon pillars with xenon difluoride. Depending on the size of the supporting posts and the pore sizes the overall porosity of the membranes ranged from 4.4 % to 25.3 %. The microfabricated membranes can be used for integrating barrier tissues such as the gastrointestinal tract epithelium, the lung epithelium, or other barrier tissues with multi-organ "body-on-a-chip" devices.

Investigation of portable in situ fluorescence optical detection for microfluidic 3D cell culture assays.

A portable fluorescence optical detection system was developed to demonstrate real-time in situ analysis of cells that are three-dimensionally cultured in an extracellular matrix under microfluidic environment. The system was designed to provide a large field of view in the lateral plane to average out cellular processes in an axial layer and simultaneously diffraction-limited axial resolution. In this proof-of-concept study, the detection system was applied to quantitative analyses of short-term measurements of cell staining and cell cytotoxicity and long-term monitoring of a cell-invasion assay. For assays, colon cancer cells were cultured in a Matrigel or alginate matrix. The measured data were largely consistent with predicted results and revealed quantitatively cell dynamics specific to 3D cell cultures. The detection system has a potential as a single package to investigate 3D cultures in a microfluidic system.

An actively mixed mini-bioreactor for protein production from suspended animal cells.

Biopharmaceutical production would benefit from rapid methods to optimize production of therapeutic proteins by screening host cell line/vector combination, culture media, and operational parameters such as timing of induction. Miniaturized bioreactors are an emerging research area aiming at improving the development speed. In this work, a 3 mm thick mini-bioreactor including two 12 mm wide culture chambers connected by a 5 mm wide channel is described. Active mixing is achieved by pressure shuttling between the two chambers. Gas-liquid phase exchange for oxygen and carbon dioxide is realized by molecular diffusion through 50 microm thick polymethylpentene membranes. With this unique design, a velocity difference between the middle area and the side areas at the interfaces of the culture chambers and the connecting channel is created, which enhances the mixing efficiency. The observed mixing time is on the order of 100 s. The combination of high permeability toward oxygen of polymethylpentene membranes and fluid movement during active pressure shuttling enables higher volumetric oxygen transfer coefficients, 5.7 +/- 0.4-14.8 +/- 0.6 h(-1), to be obtained in the mini-bioreactors than the values found in traditional 50 mL spinner flasks, 2.0-2.5 h(-1). Meanwhile, the calculated volume averaged shear stress, in the range of 10(-2)-10(-1) N/m(2), is within the typical tolerable range of animal cells. To demonstrate the applicability of this mini-bioreactor to culture suspended animal cells, the insect cell, Spodoptera frugiperda, is cultured in mini-bioreactors operated under a K(L)a value of 14.8 +/- 0.6 h(-1) and compared to the same cells cultured in 50 mL spinner flasks operated under a K(L)a value of 2.2 h(-1). Sf-21 cells cultured in the mini-bioreactors present comparable length of lag phases and growth rates to their counterparts cultured in 50 mL spinner flasks, but achieve a higher maximum cell density of 5.3 +/- 0.9 x 10(6) cell/mL than the value of 3.4 +/- 0.4 x 10(6) cell/mL obtained by cells cultured in 50 mL spinner flasks. Sf-21 cells infected with SEAP-baculovirus produce a maximum SEAP concentration of 11.3 +/- 0.7 U/mL when cultured in the mini-bioreactor. In contrast, infected Sf-21 cells cultured in 50 mL spinner flasks produce a maximum SEAP concentration of 7.4 +/- 0.9 U/mL and onset of production is delayed from 18 h in minibioreactor to 40 h in spinner flasks.