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Membrane materials commonly used in sterile filtration membranes and key points that need attention

Issuing time:2023-08-17 10:48

Medical sterile filtration is usually performed using filter membranes made of polyethersulfone (PES), polyvinylidene fluoride (PVDF) or nylon. A prominent factor in the selection of these membrane materials is their low protein binding Characteristics and wide chemical compatibility are the preferred selection conditions, such as sterile filtration of biological products (such as vaccines, monoclonal antibodies, blood products, recombinant proteins, etc.), buffer solutions, sterile filtration of culture solutions, filtration of lyophilized preparations, Sterilization filtration of antibiotic solutions, liquid medicine eye drops, sterilization filtration of large infusion solution (LVP), small injection (SVP),

sterilization filtration of normal saline and other solvents, etc.

PVDF membrane pore size distribution.jpg

Sterile filtration is mainly to remove microorganisms and particles in liquid or gas flow to obtain sterile or particle-free products, to ensure the safety and integrity of the final product by preventing contamination, using liquid or gas to pass through a filter membrane with a defined pore size , with the filter membrane acting as a physical barrier, allowing the desired material to pass through while retaining particles and microorganisms above a certain size, one thing we must know, sterile filtration will not sterilize the filtered liquid or gas, because it is Two concepts, the commonly used sterile filter membrane has a pore size of 0.2 µm or 0.22 µm, which is sufficient to remove bacteria and other microorganisms, because the diameter of general bacteria is about 0.5 µm, and the length is about 0.5-5 µm.

PES membrane biocompatibility.jpg

However, even if a filter membrane that meets the specifications is used, it is not absolutely possible to achieve 100% interception of bacteria, because in the process of filter membrane interception of bacteria, there are some Brevundimonas that belong to the bacterial genus of Caulobacteriaceae. It is a Gram-negative bacterium, usually with a rod-shaped or spherical shape, and its diameter is usually 0.3 to 0.5 microns. We can see that it is very close to the pore size of the filter membrane. In modern medicine, a certain species of Brevundimonas These species have been identified as opportunistic pathogens, which means they can cause infections in humans, especially in individuals with compromised immune systems. Rare, that is, this type of brevundimonas is very rare, so when the standards for filter membranes are specified, when attacked by test bacteria such as brevundimonas, the filter membrane should show a bacterial retention efficiency of 99.9999%.

Other specifications for the membrane, including the compatibility of the filter membrane with the solution to be filtered, the integrity test of the membrane, etc., are also important factors that we need to consider when selecting a sterile filtration membrane.

PVDF ultrafiltration membranes.jpg

What key points should we pay attention to when using sterile filtration membranes?

1. For pre-wetting before use, low surface tension liquids such as alcohol should be used to pre-wet the hydrophobic membrane (such as PVDF) to facilitate the passage of water-based solutions.

2. Flow rate control during the filtration process, avoid applying too high flow rate, otherwise it will cause the filter membrane to be clogged or even ruptured.

3. Temperature control, make sure to use the filter membrane within the recommended temperature range, because high temperature will weaken the filter membrane and affect its performance.

4. Sterilization before use, if the filter installed with the filter membrane is to be reused, it must be sterilized between uses. This is usually done using steam, but other methods such as autoclaving, gamma irradiation, or chemical sterilants can also be used, the caveat here is to always check the manufacturer's recommendations for the sterilization method, membranes and filters are know.

5. Endotoxin level. Endotoxin is a toxin produced by certain bacteria (mainly Gram-negative bacteria) and released when bacterial cells rupture or lyse. Endotoxin is composed of lipopolysaccharide (LPS), which can induce human And the inflammatory response of animals, so the filter you choose must ensure that the filter will not release endotoxins that may contaminate the product. Because not all filters are effective at removing endotoxins, they must be specifically designed to do so, primarily because such filters are often made of materials that have a high affinity for endotoxins, such as certain polymers or Modified surface, which is more conducive to enhanced endotoxin removal.

6. Integrity test. After using membrane filtration, an integrity test must be carried out to ensure that the filter membrane is not damaged. Bubble point test, diffusion flow test and pressure maintenance test are common methods for integrity testing. Here we are before The scheme has been described in detail, and will not be repeated here.

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