PDMS-chip

A microfluidic device suitable for organ-on-a-chip, made out of PDMS

To get more experience with cell culturing in a microfluidic device and to get a better comparison between microfluidic devices and static cultures, we have decided to use an extra chip made out of PDMS.

What is PDMS?

Polydimethylsiloxane (PDMS) is a mineral-organic polymer, which can be used for the fabrication of microfluidic devices. The PDMS is mixed with a cross-linking agent and heated to obtain cross-linked elastomeric PDMS. PDMS is hydrophobic, so water can flow through a channel in the PDMS, without adsorption. The PDMS together with glass is oxidised using a plasma to obtain silanol (Si) terminations on the surface. When the PDMS and the glass are connected, it creates Si-O-Si bonds, so a closed system is created.

Advantages

PDMS microfluidic devices for cell-culturing have some advantages. The most important one is that PDMS is gas permeable, so there is a balance in the atmospheric pressure. The chip is transparent from 240 nM till 1100 nM frequencies and also has a low auto fluorescence to get a good visual through a microscope. The cost of the production is also low compared to other microfluidic devices.

Issues

There are also some issues with the usage of microfluidic PDMS system. The integration of electrodes is very limited with PDMS. The PDMS bonds good to glass with plasma treatment, but does not bond good with metal. This can be a problem using electrodes to measure the impedance of the beating heart cells. PDMS is hydrophobic so hydrophobic molecules, like proteins or hydrophobic drugs can be absorbed into the PDMS. This can interfere with cell signalling and the determination of drug response in cells. If drug response test is carried out, this information must be taken into account. 

Setup

Cells are seeded in the PDMS chip by a syringe close to the PDMS (E). After the cells are seeded medium is pumped through the system by filling a big syringe (A) with medium and placing it into a pump (B). The pump regulates the fluidic flow, so the desired shear stress is created in the chip. The medium goes from the syringe through the tubing © into the inlet in the chip, then it flows along the cells creating the shear stress, it leaves the chip trough the outlet and is being led away by the tubing (G). The assays which are carried out with the cells are added to the chip by the small syringe (E). With the connector (D) the fluids which reaches the chip can be regulated, so the assays can be added.

Down below, a close-up can be seen of the PDMS-chip. The channel were the cells are cultured in is located between the inlet and the outlet..