Polycarbonate Track-Etch (PCTE) FAQ

Polycarbonate (PC) and Polyester (PET) track-etch membrane filters are precision, two-dimensional microporous “screen” membranes with straight-through, cylindrical pores created by the track-etching process. Because the pore structure is uniform and non-tortuous, particles are captured primarily on the membrane surface, providing a highly accurate and reproducible separation cut-off compared to depth filter media. Track-etch membranes are known for having some of the most precise pore size distributions of any membrane filter, making them ideal for applications that require exact particle sizing and surface capture, such as microscopy, particle analysis, microbial enumeration, and sample preparation. These membranes are also very thin (typically ~6–15 µm) yet surprisingly durable, and can withstand high differential pressures (over 3,000 psi when properly supported). They are available in a range of appearances, from opaque to nearly transparent, including black options for enhanced contrast in imaging and microscopy.

Sterlitech Polycarbonate (PCTE) and Polyester (PETE) track-etched filter membranes offer ultra-low non-specific binding and a smooth, flat surface that captures particles on a single plane—ideal for microscopy, SEM, and particle analysis. Manufactured under Class 100 cleanroom conditions, they are contaminant- and pyrogen-free, with very low extractables and no fiber shedding. Both membranes are biologically inert, provide precise, uniform pore sizes, and deliver excellent chemical and thermal stability, with PETE offering higher solvent resistance.

No. Track-etched polycarbonate membranes are not recommended for vent filter applications. Although they are PVP-free and have a water contact angle of approximately 90°, they can wet out under low differential pressure, allowing liquid to pass through. For gas venting while blocking liquids, Sterlitech recommends hydrophobic PTFE membranes, hydrophobic polyethylene membranes, or oleophobic polyester membranes, which provide higher water entry pressure and allow gases and water vapor to pass while preventing liquid breakthrough.

Polycarbonate track-etch (PCTE) membranes are inherently hydrophobic. The hydrophobic PCTE membrane filters shown at https://www.sterlitech.com/hydrophobic-polycarbonate-membrane-filters.html do not have any wetting agents. Before use in water or aqueous solutions, these filters are usually pre-wet with a compatible low surface tension, water miscible fluid such as a low molecular weight alcohol.

The hydrophilic PCTE membrane filters shown at https://www.sterlitech.com/hydrophilic-polycarbonate-membrane-filters.html are treated with a wetting agent to render the membrane hydrophilic. The wetting agent consists of a few molecular thicknesses of polyvinylpyrrolidone (PVP) deposited on the membrane surfaces. The hydrophilic PCTE membrane filters can be used in water or aqueous solutions without pre-wetting.

Yes. Polycarbonate membranes can be bonded to themselves or to materials such as plastics, metals, glass, and wood using commercially available one-component, two-component, or pressure-sensitive adhesives. The best adhesive for polycarbonate membrane bonding depends on the substrate, environmental conditions, and performance requirements of the application.

Cell adhesion to Polycarbonate Track-Etched (PCTE) membranes depends on the cell type and surface treatment. Many exfoliated human cells adhere naturally, while most epithelial cells attach more readily to plasma-treated or coated membranes. Endothelial cells generally do not adhere well to standard track-etched membrane filters without additional surface modification. For optimal results in cell culture and cell migration studies, membrane selection and surface treatment should be matched to the specific cell line.

Some Polycarbonate Track-Etched (PCTE) membrane filters have a shiny side and a dull (matte) side due to the manufacturing process of the polycarbonate film. The shiny side is smoother, while the dull side has a slight surface texture. This difference is purely physical—both sides are chemically identical, and filter orientation does not affect filtration performance or particle retention. For microscopy and particle analysis, many users prefer to position the smooth, shiny side upstream to improve the visualization of captured particles or microorganisms.

Yes. Standard polycarbonate track-etched (PCTE) membranes can be dyed black, although PVP-free polycarbonate membranes are generally recommended for this process. Black polycarbonate membrane filters are commonly used for particle counting, fluorescence microscopy, and epifluorescence imaging because they provide excellent contrast. A commonly used laboratory method is to soak the membrane in a solution of Irgalan Black (Acid Black 107) dissolved in 2% acetic acid for 24 hours, followed by rinsing and air drying. Additional heating can be used to achieve a darker black appearance. Please note that while uncommon, there have been occasional reports of dye bleeding from the membrane.

Both polyester and polycarbonate track-etched membrane filters provide precise pore structures and excellent filtration performance, but each offers distinct advantages. Polyester track-etched membranes provide superior solvent resistance and are less prone to wrinkling during manufacturing. Polycarbonate track-etched (PCTE) membranes are widely used and have long been the industry standard, particularly for cell culture, microscopy, and cell-based assays, where they generally perform better with live or fixed cells. Both membrane types deliver high-quality, reproducible results and are suitable for a wide range of filtration, analytical, and life science applications.

Low or no flow through a small pore size membrane filter is usually caused by the membrane’s naturally low flow rate or by pore blockage. For example, a 25 mm polycarbonate track-etched membrane with a 0.05 µm pore size and a flow rate of 0.4 mL/min/cm² will only pass about 1.2 mL/min, and flow decreases further with smaller pore sizes. For 0.05–0.01 µm membrane filters, liquids should be properly prefiltered using a step-down filtration process, where a series of filters with gradually decreasing pore sizes is used before the final membrane. This helps prevent particles from plugging the pores and improves flow through the membrane. Other causes may need to be evaluated based on the liquid, pressure, membrane type, and application.

The most common cause is accidentally installing the blue separator paper instead of the Track-Etched (PCTE) membrane filter. The separator paper is blue or printed and is for packaging only—it is not intended for filtration. The actual polycarbonate track-etched membrane is thin, translucent or opaque, and typically white with a slight yellow or green tint. If the correct membrane is installed, low or no flow is often caused by membrane clogging. Because track-etched membrane filters have precise cylindrical pores, they retain nearly all particles larger than the pore size, making them more susceptible to plugging. For samples with high particulate loads, use a glass fiber prefilter to capture larger particles before they reach the membrane. To further improve flow, especially in stainless steel filter holders, use a mesh spacer (drain disk) beneath the membrane. This promotes tangential flow, increases the effective filtration area, and helps maximize flow rates.

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

Yes. Sterlitech polycarbonate track-etched (PCTE) and polyester track-etched membrane filters offer excellent biocompatibility and meet USP Class VI testing requirements. They are non-cytotoxic and non-bactericidal, making them suitable for cell culture, microbiology, tissue engineering, and other life science applications. When provided with the appropriate nutrients and culture conditions, cells and bacteria can grow normally on the membrane surface.

Sterlitech Polycarbonate Track-Etched (PCTE) and Polyester Track-Etched (PETE) membrane filters are excellent choices for cell culture, cell migration, and other cell-based studies. Both membrane types are non-cytotoxic, non-bactericidal, and support cell growth when used with appropriate nutrients and culture conditions. PCTE membranes meet USP Class VI biocompatibility requirements, making them suitable for demanding life science and implant research applications. Both PCTE and PETE membranes can be repeatedly autoclaved at 121°C (250°F) and have demonstrated stability during prolonged exposure to temperatures up to 140°C (284°F) in air or steam. Independent testing using MEM Extract/L929 Mouse Fibroblast Cells found no evidence of cytotoxicity after 72 hours, confirming that both membrane materials are well suited for cell culture and biological research applications.

If you need to completely remove the appearance of the pores on a Track-Etched (PCTE) membrane filter, the simplest method is to dissolve the membrane after filtration using a suitable solvent such as chloroform or Touch Prep®. This leaves the captured particles or cells behind for subsequent microscopic analysis without interference from the membrane pores.

Sterlitech polycarbonate track-etched (PCTE) membrane filters are naturally hydrophobic and are coated with polyvinylpyrrolidone (PVP) to create a hydrophilic surface. While hydrophilic PCTE membranes are available in pore sizes from 0.01–30.0 µm, PVP-free (hydrophobic) membranes are offered only in select pore sizes from 0.1–10.0 µm. If you need a PVP-free polycarbonate membrane, you can remove the PVP coating by boiling the membrane in ultrapure deionized water for at least 1 hour, then allowing it to air dry completely. Once dry, the membrane will return to its natural hydrophobic, PVP-free state.

Black polycarbonate track-etched (PCTE) membrane filters are ideal for bacterial counting because their uniform pore size and smooth, flat surface retain bacteria on the membrane surface, making them easier to detect and count by microscopy. In contrast, cellulose membrane filters can trap bacteria within the filter matrix, reducing visibility and counting accuracy. The black background also provides excellent contrast for fluorescence microscopy and epifluorescence-based microbial analysis, improving the detection of bacteria and other microorganisms.

Yes. Sterlitech can provide custom Polycarbonate Track-Etched (PCTE) and Polyester Track-Etched (PETE) membrane filters with non-standard specifications, subject to manufacturing capabilities. Customization options may include pore size, pore density, membrane thickness, and surface treatments to meet specific application requirements. To discuss your application or inquire about the availability of custom track-etched membrane filters, please contact Sterlitech at [email protected].

Yes. When stored under the recommended conditions of 5–35°C (41–95°F) and 20–80% relative humidity, track-etched membranes maintain their pore size, pore density, bubble point, and thickness for up to 8 years. For best performance, store membranes in their original packaging away from direct sunlight, excessive heat, and moisture until use.

Polycarbonate Track-Etched (PCTE) and Polyester Track-Etched (PETE) membrane filters are extremely thin and can easily accumulate static electricity, making them difficult to handle, position, or separate from packaging. Using a static eliminator helps reduce static cling and electrostatic repulsion, improving membrane handling and minimizing the risk of damage or contamination during installation.

Black dyed Polycarbonate Track-Etched (PCTE) membrane filters have very low autofluorescence, providing excellent contrast between fluorescently stained microorganisms and the dark membrane surface. This improves visibility and detection in epifluorescence microscopy and makes black PCTE membrane filters ideal for laser scanning cytometry and other fluorescence-based microbial analysis applications.

Polycarbonate Track-Etched (PCTE) membrane filters are manufactured from polycarbonate, which is produced using Bisphenol A (BPA). While significant residual BPA is not expected, Sterlitech does not test each lot for BPA, so the filters cannot be certified as BPA-free. Under harsh conditions, such as high temperatures or exposure to incompatible chemicals, trace amounts of BPA may be released. For BPA-sensitive applications, Polyester Track-Etched (PETE) membrane filters are recommended.

Polycarbonate Track-Etched (PCTE) membrane filters are thin, smooth, and naturally translucent. Depending on the pore size and pore density, they may appear transparent or opaque. For applications requiring greater optical clarity, custom low pore density PCTE membrane filters with the same pore size rating may be available and can provide improved transparency. Compared to conventional microporous membrane filters, PCTE membranes are significantly thinner and offer superior optical clarity, making them well suited for microscopy, particle analysis, and cell imaging applications. When performing microscopic studies of particles or cells on the membrane surface, the visibility of pore edges may sometimes interfere with imaging. This effect can be reduced using several techniques. One approach is to dissolve the membrane after filtration using suitable solvents, leaving the particles or cells behind for observation. Another method is refractive index matching combined with polarized light. Because PCTE membranes are birefringent and have two refractive indices—1.584 and 1.625—the pores can be made virtually invisible by wetting the membrane with a fluid that has a refractive index of 1.584 and illuminating it with properly oriented polarized light. This technique can significantly improve image quality and contrast for microscopy applications.

The polycarbonate track-etch (PCTE) membrane filters can be dissolved with dipolar aprotic solvents such as dimethylformamide (DMF), dimethyl sulfoxide (DMSO) and n-methyl-2-pyrrolidone (NMP). The PCTE membrane filters can also be dissolved with the organic chlorinated solvents dichloromethane (DCM or methylene chloride) and trichloromethane (TCM or chloroform). PCTE membrane filters can also be dissolved with toluene and potentially with other similar aromatic hydrocarbon solvents. The polyester track-etch (PETE) membrane filters can be dissolved with m-Cresol, o-Chlorophenol, hexafluoroisopropanol, and trifluoroacetic acid (TFA).

Both types of track-etch membranes can be dissolved with elevated temperature sodium hydroxide solutions.

Yes. PVP-free Polycarbonate Track-Etched (PCTE) membrane filters can be gelatin-coated for chemotaxis assays, including studies with white blood cells, neutrophils, monocytes, and macrophages. PVP-free membranes are often preferred for certain cell types because some cells, such as neutrophils, may round up or detach in the presence of PVP. For a light gelatin coating, wash the PCTE membrane with 0.5% acetic acid, then prepare a stock gelatin solution of 50 mg gelatin in 10 mL water. Dilute 1 mL of stock solution into 1 L of water, place the membranes in the solution at a rolling boil for 1 hour, then remove them individually and air dry on filter paper. Air drying overnight in a covered dish is preferred; if using an oven, use a very low temperature for about 20 minutes. Once dry, return the membranes to their original box and keep them clean. For best results in chemotaxis membrane studies, maintain all materials—including the water bath, buffers, and glassware—at 37°C for 1 hour. Cold conditions may cause cells to round up, curl, or detach from the membrane.

Polycarbonate Track-Etched (PCTE) membrane filters can be heat sealed to polycarbonate substrates for microfluidic devices using a heated die and compressive force. For the best seal quality and reproducibility, follow these general guidelines: Use a substrate with a melting temperature similar to or lower than the PCTE membrane. For optimal bonding, the substrate should ideally be polycarbonate.

Apply a heated, polished sealing die with a high-temperature nonstick coating to minimize plastic buildup and membrane adhesion.

Design a simple membrane geometry (such as a circular membrane) to improve sealing consistency. Use a minimum seal width of 2 mm whenever possible. Narrower seals may be feasible but require more process optimization.

A clear, transparent seal generally indicates a successful bond. For critical microfluidic applications, validate seal integrity using appropriate leak or pressure testing. The optimal combination of sealing temperature, contact pressure, and dwell time depends on your materials and device design and should be established experimentally.

Standard gold-coated Track-Etched membrane filters are coated as follows: Gold-coated Polycarbonate Track-Etched (PCTE) membranes: 40 nm gold coating on the front side and 20 nm on the back side.

Gold-coated Polyester Track-Etched (PETE) membranes: 100 nm gold coating on the front side. For specialized applications, custom gold coatings on both sides are available. Gold coating thicknesses of up to 100 nm or greater can be provided, subject to the membrane's adhesion characteristics. Additional plasma surface treatment or adhesion layers may be used to improve coating adhesion for specific membrane materials. Please contact [email protected] to discuss your application and custom coating requirements.