Frequently Asked Questions

<p><strong>Q: Do polycarbonate track-etch (PCTE) membrane filters contain Bisphenol-A (BPA)?</strong></p> <p>A: <span>Bisphenol-A (BPA) is the monomer used to manufacture polycarbonate. It is not expected that the polycarbonate track-etch (PCTE) membrane filters would contain significant residual amounts of BPA. However, the filters are not analyzed on a lot basis for residual BPA so they cannot be described as BPA free. The user is advised that extreme application conditions, including exposure to high temperatures and/or exposure to incompatible fluids, may attack the molecular structure of the polycarbonate and release trace amounts of BPA. For applications where trace amounts of BPA may cause concern, polyester track-etch (PETE) membrane filters may be considered.</span></p>

<p><span data-sheets-value="{&quot;1&quot;:2,&quot;2&quot;:&quot;The polyester track-etch (PETE) membrane filters and polycarbonate track-etch (PCTE) membrane filters are among the thinnest membrane filters that we offer.\u00a0 They are more susceptible to accumulating electrostatic charges which can make them difficult to manipulate and position.\u00a0 The static eliminators offered at https://www.sterlitech.com/static-eliminator.html can be used to mitigate handling problems associated with electrostatic repulsion and static cling.&quot;}" data-sheets-userformat="{&quot;2&quot;:9089,&quot;3&quot;:{&quot;1&quot;:0},&quot;10&quot;:0,&quot;11&quot;:4,&quot;12&quot;:0,&quot;16&quot;:8}">The polyester track-etch (PETE) membrane filters and polycarbonate track-etch (PCTE) membrane filters are among the thinnest membrane filters that we offer.  They are more susceptible to accumulating electrostatic charges which can make them difficult to manipulate and position.  The static eliminators offered at https://www.sterlitech.com/static-eliminator.html can be used to mitigate handling problems associated with electrostatic repulsion and static cling.</span></p>

<p><span data-sheets-value="{&quot;1&quot;:2,&quot;2&quot;:&quot;Polycarbonate track-etch (PCTE) membranes are inherently\nhydrophobic.\u00a0 The hydrophobic PCTE\nmembrane filters shown at https://www.sterlitech.com/hydrophobic-polycarbonate-membrane-filters.html do not have any wetting agents.\u00a0 Before use in water or aqueous solutions, these\u00a0filters are usually pre-wet with a compatible low surface tension, water miscible fluid such as a low molecular weight alcohol.\u00a0 \n\nThe 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.\u00a0 The wetting agent consists of a few molecular\nthicknesses of polyvinylpyrrolidone (PVP) deposited on the membrane\nsurfaces.\u00a0 The hydrophilic PCTE membrane filters can be used in water or aqueous solutions without pre-wetting.\n\n&quot;}" data-sheets-userformat="{&quot;2&quot;:9089,&quot;3&quot;:{&quot;1&quot;:0},&quot;10&quot;:0,&quot;11&quot;:4,&quot;12&quot;:0,&quot;16&quot;:8}">Polycarbonate track-etch (PCTE) membranes are inherently<br />hydrophobic.&nbsp; The hydrophobic PCTE<br />membrane filters shown at <a href="https://www.sterlitech.com/hydrophobic-polycarbonate-membrane-filters.html" target="_blank">https://www.sterlitech.com/hydrophobic-polycarbonate-membrane-filters.html</a> do not have any wetting agents.&nbsp; Before use in water or aqueous solutions, these&nbsp;filters are usually pre-wet with a compatible low surface tension, water miscible fluid such as a low molecular weight alcohol.&nbsp; <br /><br />The hydrophilic PCTE membrane filters shown at <a href="https://www.sterlitech.com/hydrophilic-polycarbonate-membrane-filters.html" target="_blank">https://www.sterlitech.com/hydrophilic-polycarbonate-membrane-filters.html</a> are treated with a wetting agent to render the membrane hydrophilic.&nbsp; The wetting agent consists of a few molecular<br />thicknesses of polyvinylpyrrolidone (PVP) deposited on the membrane<br />surfaces.&nbsp; The hydrophilic PCTE membrane filters can be used in water or aqueous solutions without pre-wetting.<br /><br /></span></p>

<p>Thickness, Bubble Point, Pore Size, and Pore Density remain unchanged when stored at a temperature from +5 to 35&deg;C and a humidity of 20 to 80 % for up to 8 years</p>

<p><span data-sheets-value="{&quot;1&quot;:2,&quot;2&quot;:&quot;Yes, in some cases within manufacturing capabilities, Sterlitech can provide track-etch membrane filters with non-standard custom specifications for pore diameter, pore density, membrane thickness, and surface treatments.\u00a0 Please contact us at [email protected] to discuss your application and to inquire about availability.&quot;}" data-sheets-userformat="{&quot;2&quot;:9089,&quot;3&quot;:{&quot;1&quot;:0},&quot;10&quot;:0,&quot;11&quot;:4,&quot;12&quot;:0,&quot;16&quot;:8}">Yes, in some cases within manufacturing capabilities, Sterlitech can provide track-etch membrane filters with non-standard custom specifications for pore diameter, pore density, membrane thickness, and surface treatments.&nbsp; Please contact us at [email protected] to discuss your application and to inquire about availability.</span></p>

<p><strong>Q. We would like a higher density Polycarbonate membrane (PCTE). Is it available?</strong></p> <p>A. Yes, custom density PCTE is available. &nbsp; Please contact our sales team for a quote ([email protected])</p>

<p><span data-sheets-value="{&quot;1&quot;:2,&quot;2&quot;:&quot;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).\u00a0 The PCTE membrane filters can also be dissolved with the organic chlorinated solvents dichloromethane (DCM or methylene chloride) and trichloromethane (TCM or chloroform).\u00a0 PCTE membrane filters can also be dissolved with toluene and potentially with other similar aromatic hydrocarbon solvents.\n\nThe polyester track-etch (PETE) membrane filters can be dissolved with m-Cresol, o-Chlorophenol, hexafluoroisopropanol, and trifluoroacetic acid (TFA).\n\nBoth types of track-etch membranes can be dissolved with elevated temperature sodium hydroxide solutions.\n&quot;}" data-sheets-userformat="{&quot;2&quot;:9089,&quot;3&quot;:{&quot;1&quot;:0},&quot;10&quot;:0,&quot;11&quot;:4,&quot;12&quot;:0,&quot;16&quot;:8}">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).&nbsp; The PCTE membrane filters can also be dissolved with the organic chlorinated solvents dichloromethane (DCM or methylene chloride) and trichloromethane (TCM or chloroform).&nbsp; PCTE membrane filters can also be dissolved with toluene and potentially with other similar aromatic hydrocarbon solvents.<br /><br />The polyester track-etch (PETE) membrane filters can be dissolved with m-Cresol, o-Chlorophenol, hexafluoroisopropanol, and trifluoroacetic acid (TFA).<br /><br />Both types of track-etch membranes can be dissolved with elevated temperature sodium hydroxide solutions.<br /></span></p>

<p><strong>Q. How do I remove the PVP hydrophilic coating from the surfaces of a polycarbonate membrane filter?</strong></p> <p>A.&nbsp; Sterlitech&rsquo;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).</p> <p>Fortunately, the PVP can be removed without much hassle.&nbsp; Boil the membrane(s) for at least 1 hour in deionized ultra-pure water, remove, then air dry the membrane(s).&nbsp; Once the membrane dries it will be hydrophobic and PVP-Free.</p>

<p><span data-sheets-value="{&quot;1&quot;:2,&quot;2&quot;:&quot;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. \nZero leaching of offensive surfactants yields reliable, consistent, and reproducible results. \nSmooth, flat surface contributes to high cell visibility on proximal and distal surfaces. Improved morphologic resolution. Easy removal of excess cells from proximal surface. \nThinness 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). \nLow adsorption and absorption of cells causes higher yields. Enhanced radiometric analysis. \nNon-staining results in improved contrast. Simplifies optical microscopic analysis routine. \nTransparency simplifies optical microscopic analysis routine. \nHeat sealable characteristics aids in experimenting with disposable chambers. \nStrength of membrane means that less critical handling techniques needed. \nCoating Membranes with Gelatin Wash membrane with 0.5% Acetic Acid. \nMake a stock gelatin solution with 50mg/10mL water. \nWorking solution is 1-mL stock to 1-liter water for a light coating. \nThen the membranes are placed in a rolling boil of this solution in a beaker for 1 hour. \nThe 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. \nWhen the membranes are dry, place them back in their original box. \nNOTE: 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 \&quot;round up\&quot;, curl up and fall off. \n&quot;}" data-sheets-userformat="{&quot;2&quot;:9089,&quot;3&quot;:{&quot;1&quot;:0},&quot;10&quot;:0,&quot;11&quot;:4,&quot;12&quot;:0,&quot;16&quot;:8}">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. <br />Zero leaching of offensive surfactants yields reliable, consistent, and reproducible results. <br />Smooth, flat surface contributes to high cell visibility on proximal and distal surfaces. Improved morphologic resolution. Easy removal of excess cells from proximal surface. <br />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). <br />Low adsorption and absorption of cells causes higher yields. Enhanced radiometric analysis. <br />Non-staining results in improved contrast. Simplifies optical microscopic analysis routine. <br />Transparency simplifies optical microscopic analysis routine. <br />Heat sealable characteristics aids in experimenting with disposable chambers. <br />Strength of membrane means that less critical handling techniques needed. <br />Coating Membranes with Gelatin Wash membrane with 0.5% Acetic Acid. <br />Make a stock gelatin solution with 50mg/10mL water. <br />Working solution is 1-mL stock to 1-liter water for a light coating. <br />Then the membranes are placed in a rolling boil of this solution in a beaker for 1 hour. <br />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. <br />When the membranes are dry, place them back in their original box. <br />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.&nbsp;<br /></span></p>

<p><strong>Q. Why are black polycarbonate membranes better than other membranes for counting bacteria?</strong></p> <p>A. Black <a href="/polycarbonate-membranes.html">polycarbonate</a> 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.</p>

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

<p><strong>Q. What membrane works best for cell studies?</strong></p> <p>A. Sterlitech <a href="/polycarbonate-membranes.html">Polycarbonate </a>(PCTE) and <a href="/polyester-pete-membranes.html">Polyester</a> (PETE) membranes are ideal for cell studies. They are neither cytotoxic nor bactericidal. Cells will grow on the membranes if provided with a nutrient. <br /><br />The membranes can be repeatedly autoclaved at 121&deg;C (250&deg;F), and no damage has been observed in membranes with a sustained exposure to temperatures of 140&deg;C (284&deg;F) in air or steam. <br /><br />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. <br /><br />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.</p>

<p><strong>Q. What are the advantatges of Sterlitech polycarbonate and polyester membrane filters?</strong></p> <!--p>A. Yes. <a href="/polycarbonate-membranes.html">Polycarbonate</a> and <a href="/polyester-pete-membranes.html">polyester</a> membranes are neither cytotoxic nor bactericidal. Both cells and bacteria will grow on the membranes when proper nutrients are supplied.</p--> <p>A. Yes, the polycarbonate track-etch (PCTE) membrane filters have good biocompatibility and pass USP Class VI testing. The PCTE membrane filters are neither cytotoxic nor bactericidal. Cells and bacteria will grow on the filters when proper nutrients are supplied and proper conditions are maintained.</p>

<p><strong>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?</strong></p> <p>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. <br /><br />Always remember that the filter membrane is usually&nbsp;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. <br /><br />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. <br /><br />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.</p>

<p><strong>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?</strong></p> <p>A. There could be a number of things going on to restrict the flow through the membrane. <br /><br />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.</p> <p>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.</p> <p>This should eliminate most problems with flow through the membrane; other issues need to be evaluated on an individual basis.</p>

<p><strong>Q. Why offer both polyester and polycarbonate track-etch filter membranes?</strong></p> <p>A. The greatest advantage of using <a href="/polyester-pete-membranes.html">polyester</a> is that it has better solvent resistance and it is prone to fewer wrinkles in the manufacturing process. One of the main reasons <a href="/hydrophobic-polycarbonate-membrane-filters.html">polycarbonate</a> was originally used and continues to be used by most people is that for over 30 years the end-users have known mainly <a href="/hydrophobic-polycarbonate-membrane-filters.html">polycarbonate</a>. <br /><br /><a href="/hydrophobic-polycarbonate-membrane-filters.html">Polycarbonate</a> works better with live or fixed cells than does <a href="/polyester-pete-membranes.html">polyester</a>. However, both <a href="/hydrophobic-polycarbonate-membrane-filters.html">polycarbonate</a>&nbsp; and <a href="/polyester-pete-membranes.html">polyester</a> offer very high quality end product that is suitable for a large variety of applications.</p>

<p><strong>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?</strong></p> <p>A. Yes, but we usually recommend the <a href="/hydrophobic-polycarbonate-membrane-filters.html">PVP-free polycarbonate</a> membranes. Note that black polycarbonate membranes are used for counting particulates and performing fluorescent microscopy. <br /><br />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: <br /><br />Dissolve 2 gm of Irgalan black (Chemical Index, acid black 107) in 1 liter of 2% acetic acid. <br />Soak membranes in Irgalan black solution for 24 hours. <br />Rinse with water, air dry. <br />To obtain a darker black, dry at 180&ordm;F (82&ordm;C) for 15 minutes. <br /><br />**Note: There have been instances of Irgalan Black "bleeding" off of the membrane.&nbsp;&nbsp; This is not common, but has occurred.</p>

<p><span data-sheets-value="{&quot;1&quot;:2,&quot;2&quot;:&quot;There is a visually apparent difference between the sides of some of the PCTE membrane filters.\u00a0 This is a result of the process used to manufacture the polycarbonate base film.\u00a0 One side of the film has a very smooth surface resulting in a shiny appearance.\u00a0 The other side has an inherent surface texture resulting in a dull or matte appearance.\u00a0 The difference is purely physical; both sides are chemically the same.\u00a0 Filter orientation does not affect particle retention.\u00a0 For applications involving\u00a0microscopic analyses of captured particles or microbes, most users prefer to orient the disk filter so that the smooth shiny side is facing upstream.&quot;}" data-sheets-userformat="{&quot;2&quot;:9089,&quot;3&quot;:{&quot;1&quot;:0},&quot;10&quot;:0,&quot;11&quot;:4,&quot;12&quot;:0,&quot;16&quot;:8}">There is a visually apparent difference between the sides of some of the PCTE membrane filters.&nbsp; This is a result of the process used to manufacture the polycarbonate base film.&nbsp; One side of the film has a very smooth surface resulting in a shiny appearance.&nbsp; The other side has an inherent surface texture resulting in a dull or matte appearance.&nbsp; The difference is purely physical; both sides are chemically the same.&nbsp; Filter orientation does not affect particle retention.&nbsp; For applications involving&nbsp;microscopic analyses of captured particles or microbes, most users prefer to orient the disk filter so that the smooth shiny side is facing upstream.</span></p>

<p>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.</p>

<p><span>The polycarbonate track-etch (PCTE) membrane filters are quite thin and translucent.&nbsp; Depending on pore size rating and pore density, the filters may appear transparent or may appear opaque.&nbsp; Please review https://www.sterlitech.com/blog/post/clarifying-the-matter-of-polycarbonates-membrane-clarity.&nbsp; In some instances, when PCTE membrane filters with standard specifications appear opaque, Sterlitech can provide custom low pore density filters with the same pore size rating that are transparent.&nbsp; For comparison, most conventional microporous membrane filters are considerably thicker and cannot be made transparent.&nbsp; Please contact us at [email protected] to discuss your application and to inquire about the availability custom PCTE membrane filters.</span><br /><span> </span><br /><span>When performing microscopic studies of particles or cells resting on the surface of PCTE membrane filters, some users may find the appearance of the pore edges to be a hindrance.&nbsp; There are some strategies that can be employed to reduce the appearance of the pore edges.&nbsp; One of the simplest strategies is to dissolve the membrane, with chloroform or toluene for examples, leaving behind the particles.&nbsp; Additionally, using a combination of wetting the membrane with a liquid that has the correct refractive index and illuminating the membrane with polarized light, it is possible to make the pores invisible.&nbsp; The PCTE membrane is birefringent and has two refractive indices, 1.584 and 1.625.&nbsp; To make the pores invisible, the membrane is wetted with a fluid that has a refractive index of 1.584 and is illuminated with properly oriented polarized light. </span></p>

<p><strong>Q. Can Polycarbonate membrane be bonded with adhesives?</strong></p> <p>A. <a href="/polycarbonate-membranes.html">Polycarbonate</a> 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.</p>