Stainless Steel Membrane Filter Tweezers
Stainless Steel Membrane Filter Tweezers

Stainless Steel Membrane Filter Tweezers

Rounded "pads" with electropolished finish won't damage delicate membrane filters: plus, they allow the grasping of the very edge of a filter so as not to disturb the active sample area.

SKU Product Name Price
Stainless Steel Membrane Filter Tweezers (Pad) Miracle Tip Ends SSTWE Stainless Steel Membrane Filter Tweezers (Pad) Miracle Tip Ends
Length | 120 mm

Q. What is a Polycarbonate or Polyester Track Etch filter membrane?

A. These types of filter membranes are precise, two-dimensional micro porous screens with straight through, cylindrical pores.

As in the case of other screen-type filters, particle capture takes place only on the surface, therefore there is more accurate separation cut-off. The precision cylindrical pores of Track Etch membranes have the most accurate size cut-off of any membrane. In depth filters, particles get caught throughout the torturous paths within the matrix as well as on the surface of the membrane.

Track Etch filters are also very thin (between 6 - 15 microns thick) but very durable (can withstand over 3,000 psi when properly supported).   They range in color from opaque to almost transparent and black.

Q. What are the benefits of using Sterlitech Polycarbonate or Polyester filter membranes?

A. Sterlitech Polycarbonate Track Etch (PCTE) and Polyester Track Etch (PETE) filters offer the lowest, non-specific binding of any filter membrane. The capture of samples occurs on a flat, glass-like smooth surface with an even distribution of particles captured on a single plane, simplifying microscopic and SEM examination of samples captured on the surface of the membrane.

  • Sterlitech Track Etch filter membranes are manufactured and produced under class 100 condition during critical manufacturing steps. Therefore, the membrane is free of contaminants and pyrogens.
  • Sterlitech PCTE and PETE membranes offer very low extractables. Both PCTE and PETE membranes are integral, plastic films, therefore, there is no sloughing or particle shedding.
  • Sterlitech PCTE and PETE membranes are biologically inert. 
  • They offer superior strength, with pressure tolerances in excess of 3,000 psi (when placed in an appropriate filter holder).
  • Both filter membranes offer excellent chemical resistance and thermal stability, with PETE offering a higher chemical resistance.

Q. Will Sterlitech Track Etch filter membranes keep liquid behind the filter and let gases pass through?

A. The need for a gas vapor barrier requires the use of a hydrophobic filter with a water contact angle greater than 120°. If the contact angle is less than 120°, the filter will "bleed" through. The best filter material to use for a vapor barrier is made of PTFE (Teflon™). Most hydrophilic membranes generally have a contact angle that is less than 50°, and an hydrophobic membrane generally has a water contact angle greater than 120°. Raw polycarbonate film has a contact angle of approximately 70°, which is neither hydrophilic nor hydrophobic. It is for this reason that on most Sterlitech PCTE filter membranes, we apply the wetting agent PVP. As a result they are considerably more hydrophilic than standard membranes. They also have a typical water contact angles that range from 70° to 90°.

Sterlitech PETE filter membranes are naturally hydrophilic with a contact angle of approximately 40°, therefore, no wetting agent is added in the manufacturing process.

Q. Do Sterlitech Track Etch filter membranes have any type of wetting agent on them?

A. Sterlitech Polycarbonate Track Etch filter membranes use a very mild wetting agent; PVP (Polyvinylpyrrolidone) to make them more hydrophilic and more easily wettable. PVP is a very useful and safe chemical, originally used as a blood plasma extender in surgeries. PVP does have some effects in chemotaxis where the cells seem to migrate faster with PVP on the membrane that, in certain chemotaxis experiments, is not desirable. However, in most cases, PVP is negligible and does not affect any analysis beign performed with the Sterlitech Track Etch membrane.

Sterlitech Polcarbonate Track Etch filter membrane is available with or without PVP. Sterlitech Polyester Track Etch membrane is natrually hydrophilic, therefore, it is made without PVP.

Q. What materials can I use to dissolve Polycarbonate or Polyester membranes?


Polycabonate membranes can be dissolved with:

  • N-mehyl-2pyrrolidone
  • Methylene chloride
  • Chloroform

Polyester membranes can be dissolved with:

  • m-Cresol
  • o-Chlorophenol
  • Hexafluoroisopropanol

Q. Can Polycarbonate membrane be bonded with adhesives?

A. Polycarbonate membranes can be adhesive bonded to each other or to other plastics, metals, glass or wood using commercially available one component, two component and pressure adhesives.

Q. How clear are the PCTE membrane filters? I am interested in looking at them under an optical microscope.

A. As a rule, PCTE and PETE filters range from opaque in the lower pore density ranges and translucent in the higher pore density ranges. Because most depth filters are fairly thick, they are usually opaque and cannot be made transparent.

When using with a microscope, note that the polycarbonate and polyester have two (2) refractive indices (Birefringent at 1.584 and 1.625). Under the microscope, the pores display outlines (shadows). The 2 indicates polarize transmitted light into two sets of rays at right angles to one another. Using a mounting medium of 1.584 in a combination with polarized light (matching one refractive index) and focusing in polarized light makes the pore outline invisible.

One can also use the Cyto-Clear Slides, which virtually eliminate distracting pore outlines in polycarbonate filters, the shadows from the pores, and ensures clear observation of the specimen. There is no need to dissolve the filter with chloroform, to use pore-clearing solutions, nor to transfer the cells to a slide. All the valuable benefits of the polycarbonate filter are preserved.

The procedure is simpler and requires less time than present protocols. There are only three steps: filtering the specimen, fixing and staining the cells, and mounting the membrane and sample between glass for examination and preservation.

Q. Do cells adhere to the surface of the Sterlitech track etch membranes?

A. Depending on the cell line, most exfoliated human cells adhere with some tenacity. Most epithelial cells will adhere if the membrane has a negative charge applied by gas plasma or has a suitable attractant applied to the surface of the membrane. Endothelial cells will generally not attach to the surface of Track Etch membranes.

Q. Should I use the shiny or dull side of the membrane?

A. The shiny side and dull side only appear on polycarbonate (PCTE) membranes, because polyester (PETE) membranes are shiny on both sides. With PCTE membranes, most users opt for the shiny side up, because it is the smoother surface.

This is particularly important in microscopy for optimum sample observation and for avoiding the necessity of continuously refocusing the microscope. However, in applications where you are trying to attach or adhere cells, it is better to use the dull or matte side.

It is fairly easy to determine the shiny side by simply holding the membrane up to the light and observing which side is more reflective. All filters disks are packaged with the same orientation—shiny side up. A blue paper is used to separate the membranes.

Q. I am looking for a black polycarbonate membrane pore size that is not listed. Can I dye the standard polycarbonate membrane? How do I do this?

A. Yes, but we usually recommend the PVP-free polycarbonate membranes. Note that black polycarbonate membranes are used for counting particulates and performing fluorescent microscopy.

If you need to create a black membrane that is not listed on this site, the standard method for rendering polycarbonate membranes black in a lab follows:

Dissolve 2 gm of Irgalan black (Chemical Index, acid black 107) in 1 liter of 2% acetic acid.
Soak membranes in Irgalan black solution for 24 hours.
Rinse with water, air dry.
To obtain a darker black, dry at 180ºF (82ºC) for 15 minutes.

**Note: There have been instances of Irgalan Black "bleeding" off of the membrane.   This is not common, but has occurred.

Q. Do you have a method for coating the PVP-Free Polycarbonate membranes for Chemotaxis?

A. General Chemotaxis Notes:

Membranes are used in the study of white blood cell reactions to toxins (chemotaxis), to determine the natural immunity in whole blood. Since immunity is transferable, this could lead to the development of vaccines for treatment of cancer and other diseases.

Membranes may be polycarbonate, with or without polyvinylpyrrolidone (PVP). It depends on the type of cells used. Apparently, Neutrophils have a tendency to round up and fall off the membrane when around PVP - not so with some of the other types of cells. Refer to each procedure.

Characteristics of PCTE Membrane and Advantages in Chemotaxis Studies

Uniform Properties yield reliable, consistent, and reproducible results. Less cell distortion for improved morphology.
Zero leaching of offensive surfactants yields reliable, consistent, and reproducible results.
Smooth, flat surface contributes to high cell visibility on proximal and distal surfaces. Improved morphologic resolution. Easy removal of excess cells from proximal surface.
Thinness of the membrane allows shorter incubation time. More assays made faster and simpler. Chamber sterilization not needed for most studies. Facilitates study of slower moving cells (e.g., monocytes and macrophages).
Low adsorption and absorption of cells causes higher yields. Enhanced radiometric analysis.
Non-staining results in improved contrast. Simplifies optical microscopic analysis routine.
Transparency simplifies optical microscopic analysis routine.
Heat sealable characteristics aids in experimenting with disposable chambers.
Strength of membrane means that less critical handling techniques needed.
Coating Membranes with Gelatin

Wash membrane with 0.5% Acetic Acid.
Make a stock gelatin solution with 50mg/10mL water.
Working solution is 1-mL stock to 1-liter water for a light coating.
Then the membranes are placed in a rolling boil of this solution in a beaker for 1 hour.
The membranes are individually pulled out and placed on filter paper to air dry. If an oven is used, use very low temperature for 20 minutes. Air-drying is best in a covered dish left over night. Keep clean.
When the membranes are dry, place them back in their original box.
NOTE: For Chemotaxis, the most important issue is to keep everything at 37 degrees C., the water bath, buffers, glassware, etc. for 1 hour.

Studies in cold produce cells that "round up", curl up and fall off.

Q. Why offer both polyester and polycarbonate track-etch filter membranes?

A. The greatest advantage of using polyester is that it has better solvent resistance and it is prone to fewer wrinkles in the manufacturing process. One of the main reasons polycarbonate was originally used and continues to be used by most people is that for over 30 years the end-users have known mainly polycarbonate.

Polycarbonate works better with live or fixed cells than does polyester. However, both polycarbonate  and polyester offer very high quality end product that is suitable for a large variety of applications.

Q. I am having a problem when I force liquids under pressure through a membrane with a very small pore size. Little or no liquid is seen to pass through the membrane, what could be the problem?

A. There could be a number of things going on to restrict the flow through the membrane.

First you want to take the original flow rate into consideration, for example a 25mm polycarbonate membrane with a 0.05 micron pore size and a flow rate of 0.4ml/min/cm2 is only going to get about 1.2 mil of liquid through a minute. This amount decreases with smaller pore sizes.

Another thing to consider is if the liquid is being properly prefiltered. With such small pore sizes, 0.05-0.01micron, you need to filter in a step down manner so as not to plug the pores. Step down means a series of filters with decreasing pore size.

This should eliminate most problems with flow through the membrane; other issues need to be evaluated on an individual basis.

Q. I just received a box of Sterlitech Track-Etch filter membranes and I am trying to use them, but there is no liquid passing through. What is wrong?

A. Believe it or not, in most cases end-users tend to use the blue separator paper instead of the membrane because the separator paper has the physical qualities that make it look more like a typical depth filter than the Track-Etch filter membrane.

Always remember that the filter membrane is usually opaque or translucent and is generally white or white with a yellow or green tint to it. The separator paper is usually blue or imprinted and should not be used for filtration.

Another reason for lack of filtration is due to particle loading on the membrane that would cause the filter to plug. Because Sterlitech Track-Etch filter membranes are made of plastic with cylindrical pores, they capture 100% of all particles larger than the pore size. Therefore, they have a higher incidence of plugging due to their high level of capturability. It is highly recommended that unless the end-user is capturing particles on the surface for analysis that a glass fiber prefilter is used on top of the track-etch membrane. The glass fiber prefilter will capture most of the larger particulate, thereby keeping it from loading up on the surface of the membrane and plugging it.

The use of a mesh spacer (drain disks) is also helpful for maximizing flow. A mesh spacer is set under the membrane and on top of the filter holder. The mesh spacer lifts the membrane off the mostly solid filter holder surface, allowing increased filtration by allowing tangential flow to occur. This is particularly applicable with stainless steel supports.

Q. We would like a higher density Polycarbonate membrane (PCTE). Is it available?

A. Yes, custom density PCTE is available.   Please contact our sales team for a quote (

Q. Are the polycarbonate and polyester track-etch membranes biocompatible?

A. Yes. Polycarbonate and polyester membranes are neither cytotoxic nor bactericidal. Both cells and bacteria will grow on the membranes when proper nutrients are supplied.

Q. What membrane works best for cell studies?

A. Sterlitech Polycarbonate (PCTE) and Polyester (PETE) membranes are ideal for cell studies. They are neither cytotoxic nor bactericidal. Cells will grow on the membranes if provided with a nutrient.

The membranes can be repeatedly autoclaved at 121°C (250°F), and no damage has been observed in membranes with a sustained exposure to temperatures of 140°C (284°F) in air or steam.

PCTE membranes are neutral biologically, being neither cytotoxic nor bactericidal. Cells and bacteria will grow on PCTE membranes when proper nutrients are supplied. PCTE membranes pass all USP Class VI tests for bio-compatibility and are completely safe to use in implant studies.

Randomly selected samples of polycarbonate and polyester track-etched membranes were tested by an independent laboratory with MEM Extract/L929 Mouse Fibroblast Cells. No evidence of cytotoxic response was noted during a seventy-two (72) hour exposure period, and the materials were judged to be negatively cytotoxic.

Q. Is there any way I can get rid of the pores on Sterlitech's Track-Etch filter membranes?

A. If you want to completely get rid of the pores, the easiest way to do so is to dissolve the filter away using chloroform or touch prep.

Q. How do I remove the PVP hydrophilic coating from the surfaces of a polycarbonate membrane filter?

A.  Sterlitech’s polycarbonate membranes are naturally hydrophobic but are coated with PVP to produce a hydrophilic version. While the full range of pores sizes (0.01um-30.0um) are available as hydrophilic filters, we are only able to offer a limited number of pore sizes (0.1um-10.0um) as hydrophobic (PVP-Free).

Fortunately, the PVP can be removed without much hassle.  Boil the membrane(s) for at least 1 hour in deionized ultra-pure water, remove, then air dry the membrane(s).  Once the membrane dries it will be hydrophobic and PVP-Free.

Q. Why are black polycarbonate membranes better than other membranes for counting bacteria?

A. Black polycarbonate membranes are better than cellulose membranes for the direct counting of bacteria, because they have a uniform pore size and a flat surface that retains all of the bacteria on top of the filter. Although cellulose filters also retain all of the bacteria, many become trapped inside the filter where they cannot be counted.