Simple bioreactor with the square, 5-slit pnc-Si chip

Hi all!

Above is an image of the bioreactor made from the square, 5-slit pnc-Si chip and a PDMS structure.  Fused-silica capillary tubings were inserted into the bioreactor to form the inlet and the outlet for the transfer of the cells into the lower compartment, which is made entirely out of PDMS.  Note that the well side is facing up and the membrane side is directly in contact with the PDMS structure.

Currently this bioreactor is designed to host non-adherent cell lines or for the collection of precious proteins secreted from cells (i.e. insulin from hybridoma).  The height of the lower compartment is only ~20 μm, so cells are placed close to  the membrane in the lower compartment even if they cannot adhere to the membrane (the average diameter of some cells are only ~10 μm).  Cells from the well side can be placed directly on top of the membrane simply from their own settlement due to gravity.  Below is an image of the inside of the bioreactor viewed under the 4X objective (400X magnification):

As can be seen, between each slit there is a rectangular PDMS pillar. There are 4 pillars total and they serve two purposes:

1) To prevent the PDMS structure from collapsing onto the pnc-Si membrane.  The length and width of the membrane slit is ~3000 μm and ~100 μm, respectively; and the spacing between each slit is ~450 μm.  Since the height of the chamber is only ~20 μm, the aspect ratio of our system would be about 20 μm/3000 μm = ~0.006.  For such a low aspect ratio the PDMS will collapse simply due to its flexibility and electrostatic attraction with the pnc-Si substrate.

2) To take away space where the cells are least exposed to the membrane.  Since we are working with precious proteins the concentration matters.  By taking away some space we concentrate the precious proteins to the membrane region to more directly stimulate the cells.  Likewise, precious proteins secreted by the cell can be collected in a more concentrate fashion.

This basic 5-slit bioreactor is expected to have useful applications in the study of cell-cell interaction of non-adherent cell lines (the collaboration with Deborah Fowell) and the collection of precious proteins produced by cells (Karl’s Project at Drexel).

PS: Eventually i will include better images (less junk in the 4X image) and also implement a nice method for introducing cells into the system without membrane rupturing (i am getting there).

Henry