Filters

Polycarbonate track-etch (PCTE) membranes are the primary type of filters used in our chambers and instrument systems. This is a very thin membrane ranging between 6-10µm in nominal thickness. This membrane type offers excellent uniformity in pore size and density, as well as other benefits such as low extractables, low protein binding, and negligible absorption. These characteristics make it ideally suited for use in chemotaxis assays as well as other high purity screening assays.

PVP Treatment –PCTE membranes are available pre-treated with the wetting agent polyvinylpyrrolidone (PVP) which makes the surface hydrophilic. PVP-treated membranes are used when the media solutions cannot wet out the membrane by themselves. This occurs primarily when working with very small pore sizes or high viscosity media solutions. Certain cell types such as neutrophils do not adhere well to PVP treated membranes and tend to drop off after migrating. While this is problematic when quantifying filters on the membrane, some researchers using the ChemoTx® sytem or the MB-series 96-well chambers and quantifying in the plate find this to be an advantage. Extra-cellular matrix proteins do not adhere well to PVP treated membranes either. If your assay requires such coating, we recommend using PVP-free membranes.

Polycarbonate membranes are available in the following pore sizes and corresponding pore densities:

Pore size (+0/-20%) 2µm 3µm 5µm 8µm 10µm 12µm 14µm
Density (pores/mm2)
(tolerance +/- 15%)
2 x 104 2 x 104 4 x 103 1 x 103 1 x 103 1 x 103 5 x 102

 

Many factors other than cell type enter into the pore size selection process. Please see our page on Experiment Design. Please see the charts below for pore size availability for specific products.

The ChemoTx® disposable system and the reusable 96-well chambers use relatively large pieces of PCTE membrane that are difficult to handle by themselves. For convenient handling, these instruments use filters bonded to anodized aluminum frames, referred to as “framed filters.” Framed filters with adhesive (Stock# ending in “/A”) are available for use in the MB series chambers only. The adhesive makes it possible to remove the microplate from the chamber with the filter still attached for spinning in a centrifuge.