Filtration Training Course

REM would like to share some basic concepts about filtration with our valued team members.  The following clarifies some key aspects of filtration technology applied to the specific applications.  The following properties should be considered at the time of selecting the proper filter media for your customers.

Basics of filtration

SCREEN OR MESH FILTRATION


 

SCREEN OR MESH FILTRATION

Filtration through a mesh means that the screen will stop particles larger than the mesh size rating. Medical meshes adopted by GVS are medical grade and comply with the very strict international requirements for cleanliness. The screens are composed of monofilaments. Standard material is polyamide (PA6.6) or polyester (PE). Filtration through a mesh is mechanical filtration. Mesh does not have the ability to stop air, except in special situations. Mesh is specified by its mesh size, which is just one of the several key characteristics.

According to ISO1135, blood transfusion filters should have a mesh size of 200 micron and efficiency higher than 80%. Specific markets are using 170 micron mesh for this application. According to ISO8536, the IV drip chamber disc filters should have mesh size of 15 micron, and efficiency higher than 80%.

Note: Some of our filters are manufactured with different media instead of mesh. We use many hydrophobic and hydrophilic membranes, which are normally dedicated to very special applications.

 

 

ao = Open Area
d = Thread Diameter
w = Mesh Opening

 

 

 

 

Mesh characteristics

The mesh used by GVS for our medical filter products is manufactured with uniform weave and accurate open-mesh structure which guarantees the lowest possible flow restriction. The “windows” of the mesh normally have a square shape.

Raw materials used for the monofilament are polyamide (PA 6.6) or polyester (PE). Other raw materials are available but not very popular.

  • Mesh opening (micron): this is the size of any window or opening.  The openings are tested by electronic analysis image systems during production.
  • Open area: this is a percentage (%) of the total mesh area which is "open" to let the flow go through.  It's important to have high open area percentage to reduce flow restriction.  This is also tested by electronic analysis image systems during production.
  • Mesh count: this is the quantity of threads per cm or per inch (n/cm) or (n/in).
  • Thread diameter (micron): this is the diameter of the filament.  It is also tested by electronic analysis image systems during production.
  • Weight of the mesh (g / m2) or (oz /yd2): important to qualify the quality of the mesh.
  • Thickness of the mesh.  Thickness is expressed in microns (μm) and its stability is very important to achieve the proper handling of the mesh during production.
  • Mesh used by GVS have efficiency which is always higher than that of international standards.

 

Sterilization Stability

This characteristic allows proper performance at elevated temperatures. The mesh used in GVS filters is usually compatible with any of the current sterilization methods: EtO, Gamma or e-beam radiation, or steam sterilization with no adverse affects.

 

Biosafety

These tests are conducted in compliance with ISO-10993 and USP Class VI.

Tests conducted are:
Cytotoxicity, Sensitization, Irritation or Intracutanous Reactivity, Systemic Toxicity (Acute), Hemocompatibility (Hemolysis)

 

Pyrogenicity

Pyrogens are chemical or biological agents that can be present on the filters mesh or other components, if they're introduced into the human body, they mainly cause the rise in temperature. Pyrogens may also be related to disintegration or death of bacteria. Filters that are pyrogenic can make solutions pyrogenic. They cannot be removed by sterilization, so it is very important that non-pyrogenic filter media and components are used in the production of medical filter devices. The test to determine the pyrogenicity is the LAL test (Limulus Amebocyte Lysate test).

 

Extractables

Extractables are contaminants (typically chemicals) that elute from filters which might affect quality of the effluent. Wetting agents (surfactants) or manufacturing or sterilization residuals are the main cause of undesired extractables. Typical problems caused by extractables are found in the following applications:

  • HPLC analysis (strange result)
  • Cell culture (cytotoxicity)
  • Microbiological analysis (affects the microorganism)
  • Environmental analysis (contaminants)

Flushing of the line prior to use can reduce Extractables and their adverse effects.
The amount of extractables allowed for mesh filters are described in following regulations:

  • 21CFR177.1500 (PA)
  • 21CFR177.1630 (PE)

 

Filter Efficiency (FE)

This is the quantity of particulate retained compared to the total quantity of particulate to which the filter is challenged. It is expressed in % and refers to a specific size of particles.

 

Effective Filtration Area (EFA)

This is the actual filtration area in a device that is subject to filtration. For instance, in a tubular filter, the frame (socket, two ribs and top cover) made by plastics should be eliminated from the calculations of the device EFA. In mesh filters you should only eliminate the seal area.

MEMBRANE FILTRATION

SCREEN OR MESH FILTRATION

Filtration through a membrane means that the filter material will stop particles larger than the pore size rating. This enables an absolute pore size rating for the membranes for which they are clearly classified. Bacterial retention claims can be made based on the pore size of the membrane.

Hydrophilic – Hydrophobic Membranes

  • Hydrophilic membranes have permeability of aqueous solutions and once wetted, they stop gasses. This means that aqueous solutions pass through hydrophilic membranes but gas is stopped when the membrane is wet until the applied pressure exceeds the “bubble point”, at which time the air will evacuate the pore, the liquid is expelled,and the gas will go through. Dry hydrophilic membrane allows gas to pass through. Our HI-FLO PES membranes are hydrophilic membranes.
  • Hydrophobic membranes have permeability to the gas,but they stop aqueous solutions. In other words, they do the opposite job when compared to hydrophilic membranes.This means that gas will pass through these membranes,but aqueous solutions will be stopped. If air or gas can reach the hydrophobic membrane, it will go through, but if the contact with the hydrophobic membrane is not possible,then the gas will not pass through. The pressure at which aqueous solutions will pass through a hydrophobic membrane is called the water breakthrough (WBT) or water intrusion pressure (WIP).

PTFE membranes are hydrophobic membranes. PES membranes are hydrophilic membranes.

Pore size

Pore size is determined by the size of the particle that is expected to be retained with a defined with a high degree of efficiency. Pore size is typically stated in micrometers or microns (μm), and should clearly be designated as either nominal or absolute. Nominal pore size is the ability to retain a majority (60% –98%) of particles having a specific dimension. Retention efficiency is also depending on such process conditions as concentration, operating pressure etc. Rating parameters can vary among manufacturers. When the pore size, or retention, is “nominal”, it should be stated at a particle size and a percent, i.e., 99.97% retention of 0.3μm particles. Absolute pore size is the ability to retain the 100% of particles of a specific dimension under defined test conditions(particle size, challenge pressure, concentration, detection method).

Pore size and challenge organism

Pore size                    Challenge Organism

0.1 micron                Acholeplasma laidlawii

0.2 micron                Brevundimonas diminuta

0.45 micron              Serratia marcescens

0.8 micron                Lactobacillus species

1.2 micron                Candida albicans  

The above table shows proper pore size of hydrophilic membranes to be used to retain the corresponding bacteria. Hydrophobic membranes are about ten times more efficient in retaining bacteria in air than they are in liquids using the same pore size.

Chemical compatibility

This is the ability of the membrane to resist to chemicals without mechanical or chemical damage from chemical exposure. Information about the liquid used with a specific filter material should be outlined before application to determine compatibility, GVS can assist customers in choosing the proper filter (and housing) materials.

Extractables

Extractables are contaminants (typically chemicals) that elute from the filter which might affect quality of the effluent.Wetting agents (surfactants), manufacturing or sterilization residuals are the main cause of undesired extractables.Typical problems caused by extractables are found in the following applications:-

  • HPLC analysis (strange result)
  • Cell culture (cytotoxicity)
  • Microbiological analysis (affects the microorganism)
  • Environmental analysis (contaminants)

Flushing of the line prior to use can reduce Extractables and their adverse effects.

Binding

This is the property of substances to be filtered having affinity with membranes.This could be a positive effect in some circumstances, but most of the time it can create adverse effects. Particularly it could lead to loss of active components of the liquid to be filtered reducing its beneficial effect. Our PES HI-FLO membrane is low protein binding.

Thermal Stability

This characteristic allows unchanged performance at elevated temperatures. Some membranes can only be sterilized by EtO. Others can be gamma, beta or e-beam sterilized, as well as EtO. Others

MEMBRANE FILTRATION (continued)

can be also steam sterilized with no adverse affects. Membrane performance is sometimes reduced at temperature higher than 25°C, and high temperatures can also reduce chemical stability. PTFE membrane is widely stable(any type of sterilization) if the product is designed properly. PES membrane is suggested for EtO and irradiation(no steam sterilization).

Biosafety

These tests are conducted in compliance with ISO-10993 and USP class VI, see specifications Tests that are conducted are: – Cytotoxicity – Sensitization – Irritation intracutaneous reactivity – Systemic toxicity (acute) – Hemo- compatibility(Hemolysis)

Pyrogenicity

Pyrogens are chemicals on the filter media and other components that are caused by the waste of dead bacteria. When introduced to a patient, they can elevate the patient's temperature, and can cause complications –even death. Filters that are pyrogenic can make solutions pyrogenic. They cannot be removed by sterilization, so it is very important that non-pyrogenic filter media and components are used in the production of medical filter devices.The test to determine the pyrogenicity is the LAL test (Limulus Amebocyte Lysate test).

Bubble Point (BP)

Typically this test is performed on hydrophilic membranes and its aim is to verify the membrane filter integrity. This test is typically performed with water; however, it can be conducted on hydrophilic membranes using liquids other than water that will wet the membrane. The BP is an indication of the membrane pore size, as related to actual bacterial retention. This test can also be performed on hydrophobic membranes if the correct solvent (instead of aqueous solution) is used, and is compatible with the entire

product.

Water Breakthrough (WBT)

This is the test performed on hydrophobic membranes, and it is also related to the pore size of the membrane. The WBT pressure (sometimes referred to as water intrusion pressure)is the pressure it takes to force an aqueous solution through a hydrophobic membrane.

Water Flow Rate (WFR)

Typically this test is performed on hydrophilic membranes.The WFR has the aim to measure the flow of a liquid through a wetted hydrophilic membrane, at a fixed test pressure and time. This test is typically performed with water; however, it can be performed with other solutions, as long as the filter media is compatible with the liquid.

Air Flow (AF)

This is a flow rate typically related to hydrophobic membranes.It is the amount of air that passes through a fixed surface of membrane with a specific applied pressure.

Filter Efficiency (FE)

Quantity of particulate or bacteria retained compared to the total quantity of particulate or bacteria to which the filter is challenged. It is expressed in % and referred to a specific size of particles.

Effective Filtration Area (EFA)

This is the actual filtration area in a device that is subject to filtration. For instance, whereas a 25 mm device may start out with a disc of filter media that is cut to 25 mm, the sealing surfaces should be eliminated from the calculations of the device EFA.

POLYMERS FOR INJECTION

POLYMERS FOR INJECTION

Thermoplastics and thermosets are the two basic groups of plastic materials. Thermoplastic resins can be repeatedly melted and solidified by heating and cooling so that any scrap generated in processing can be theoretically reused. No chemical change generally takes place during forming. Usually, thermoplastic polymers are supplied in the form of pellets,which often contain additives to enhance processing or to provide necessary characteristics in the finished product (e.g., color, conductivity,etc.). The temperature service range of thermoplastics is limited by their loss of physical strength and eventual melting at elevated temperatures.

Main Thermoplastic resin used in Medical Applications

Thermoplastic Elastomers (TPE)

TPEs are a family of polymers that can be repeatedly stretched without permanently deforming the shape of the part. Unlike rubber-like elastomers,they do not require curing or vulcanization, as they are true thermoplastics.Thermoplastic elastomers (TPEs) may be processed by conventional thermoplastic techniques such as injection molding, extrusion and blow molding. Thermoplastic elastomers have replaced rubber in many applications. There are six main thermoplastic elastomer groups found commercially; styrenic block copolymers, polyolefin blends (TPOs), elastomeric alloys, thermoplastic polyurethanes (TPUs),thermoplastic copolyesters and thermoplastic polyamides.

TYPICAL PROPERTIES OF TPE ARE:

  • Low coefficient of friction
  • Improved physical properties
  • Non-sticking, even at 40 shore A
  • Excellent resiliency for product requiring peristaltic motion

Acrylonitrile Butadiene Styrene (ABS)

ABS is an impact-modified acrylic-based multi-polymer for molding and extrusion of medical applications, used for injection molding and extrusion of medical devices, medical packaging, as well as food packaging, toys and appliance parts.ABS has perhaps the best balance of properties when cost is a factor.It has good chemical and stress-resistance as well as a combination of toughness with rigidity and creep resistance. It is chemically resistant to water, aqueous salt solutions, dilute acids and alkalis, saturated hydrocarbons and a wide variety of vegetable and animal fats and oils.

TYPICAL PROPERTIES OF ABS ARE:

  • Improved chemical resistance
  • High impact strength
  • Good mechanical strength and stiffness
  • Good environmental stress cracking resistance (ESCR)
  • Outstanding surface quality, excellent feel and appearance
  • Good processability
  • High scratch resistance

Methacrylate acrylonitrile butadiene styrene polymer (MABS)

Is a transparent, amorphous thermoplastic based on an MABS polymer (also called “transparent ABS”). Grades are designed primarily for injection moulding, but can also be extruded. MABS gains its impact strength from a rubber phase made from polybutadiene, embedded submicroscopically into the matrix of styrene, acrylonitrile and methyl methacrylate. These basic building blocks are precisely balanced so that, despite its high impact strength and good rigidity, MABS has excellent transparency, setting it apart from most impact-modified thermoplastics. MABS offers an ideal combination of properties typical of ABS, such as a balanced stiffness/toughness ratio and the high transparency well known in PMMA moulding compositions. This special combination of properties makes MABS unique among transparent thermoplastics.

TYPICAL PROPERTIES OF MABS ARE:

  • Excellent transparency – even after sterilization
  • Good tensile strength and stiffness
  • High impact strength (better than PMMA)
  • Good resistance to chemicals and environmental stress cracking (superior to polycarbonate)
  • Outstanding surface quality, excellent feel and appearance
  • Easy processing (like ABS and much better than polycarbonate)

Polymethyl-methacrylate (PMMA)

PMMA (polymethyl-methacrylate) is an amorphous thermoplastic material with very good optical properties. PMMA ishard, stiff and medium strong, easy to scratch, notch sensitive,but easy to polish. Exceptional outdoor performance,such as weather and sunlight resistance, without reduction of optical or mechanical properties.

TYPICAL PROPERTIES OF PMMA ARE:

  • Tough
  • Transparent
  • Bondable
  • Gamma, e-beam and EtO sterilizable
  • Easy to process
  • Chemically resistant
  • Alcohols and lipid resistant
  • Resistant to plasticizers found in flexible PVC tubing

POLYMERS FOR INJECTION (continued)

  • Free of Bis-Phenol A (BPA) Nonyl Phenols


Polyvinyl Chloride (PVC)

It is similar in structure to polyethylene but each unit contains a chlorine atom. The chlorine atom renders it vulnerable to some solvents, but also makes it more resistant in many applications (PVC has extremely good resistance to oils and very low permeability to most gases). Polyvinyl chloride is transparent and has a slight bluish cast. When blended with phthalate esters plasticizers, PVC becomes soft and pliable, providing tubing of any dimension.PVC is the most widely used member of the vinyl family. Common applications include chemical processing tanks, valves, fittings & piping systems.PVC Sheets, Rods & Tubes offer excellent corrosion and weather resistance.It has a high strength-to-weight ratio and is a good electrical and thermal insulator. PVC is also self-extinguishing per UL flammability tests. PVC maybe used to temperatures of 140°F (60°C).

TYPICAL PROPERTIES OF PVC ARE:

  • Good Flexibility
  • Good Thermal Stability
  • Good Processability
  • Acceptable Food Contact
  • High Impact Resistance


Polypropylene (PP)

It is similar to polyethylene, but each unit of the chain has a methyl group attached. It is translucent, autocavable, and has no known solvent at room temperature. It is slightly more susceptible to strong oxidizing agents than conventional polyethylene because of its many branches (methyl groups, in this case). Polypropylene is noted for its excellent chemical resistance in corrosive environments. This polymer is easily welded and machined. Homo-polymerand copolymer grades, as well as a popular heat-stabilized formulation, are used in various applications throughout the chemical and semiconductor industries.

TYPICAL PROPERTIES OF PP ARE:

  • Clean/High Purity
  • Good Dimensional Stability
  • Good Organoleptic Properties
  • High Clarity
  • High Flow
  • High Stiffness
  • Homopolymer
  • Low Warpage
  • Narrow Molecular Weight Distribution
  • Nucleated


Nylon (PA6)

This is a group of linear polymers with repeated amide linkages along the backbone. These are produced by an amidation of diamines with dibasic acids, or polymerisation of amino acids. Nylon is strong and tough. It resists abrasion, fatigue and impact. Nylon offers excellent chemical resistance with negligible permeation rates when used with organic solvents. However, it has

poor resistance to strong mineral acids, oxidizing agents and certain salts.

TYPICAL PROPERTIES OF PA 6 ARE:

  • Good Chemical Resistance
  • Good Colorability
  • Good Corrosion Resistance
  • Good Processability
  • Good Toughness
  • Good Wear Resistance
  • High Rigidity
  • High Strength
  • Low Friction


Polycarbonates (PC)

This is a special type of polyester, in which dihydric phenols are joined through carbonate linkages (O-CO-O). These linkages are subject to chemical reaction with bases, concentrated acids, etc. and make PC soluble in various organic solvents. PC is window-clear, amazingly strong, and rigid. It is autoclavable, non-toxic and the toughest of all thermoplastics. PC maintains its resistance to impact in a wide range of temperatures and even under very severe environmental conditions.It withstands both low and high temperature from -50°C up to +130°C and has extremely good optical properties together with a high resistance to sunlight exposure (UV radiation).

TYPICAL PROPERTIES OF PC COPOLYMER ARE:

  • Good Dimensional Stability
  • Good Thermal Stability
  • High Clarity
  • High Heat Resistance
  • High Impact Resistance


Polyoxymethylene (POM)

It is produced by polymerization of formaldehyde. Acetal retains its dimensions and other properties at elevated temperatures. It offers excellent resistance to strong acids and bases. Naturally opaque, Acetal(POM) copolymer provides high strength and stiffness coupled with enhanced dimensional stability and ease of machining. As a semi-crystalline material, acetal is also characterized by a low coefficient of friction and good wear properties especially in wet environments.Because of its high strength, modulus, and resistance to impact and fatigue, Acetal is used as a weight-saving metal replacement.

TYPICAL PROPERTIES OF POM COPOLYMER ARE:

  • High crystallinity
  • Ideal combination of strength, stiffness and toughness
  • Outstanding tribological properties, i.e. low friction and wear
  • Low fatigue under mechanical stress
  • Excellent chemical and hydrolysis resistance
  • Withstands sterilization with hot steam, plasma and ethylene oxide
  • High dimensional stability
  • Good processability

Mark the following statements as True or False

  • Filtration through a mesh means that the screen will stop particles larger than the mesh size rating
  • Medical meshes adopted by GVS are medical grade and comply with the very strict international requirements for cleanliness
  • Mesh does not have the ability to stop air, except in special situations
  • Mesh is specified by its mesh size, which is just one of the several key characteristics

What are Pyrogens?

  • Aliens from the planet Pyro
  • Chemical or biological agents that can be present on the filters mesh or other components
  • Gluten free treats
  • New car from China

If introduced into the human body, Pyrogens can cause

  • Rise in body temperature
  • Sneezing fit
  • In an attachment.

Mark the following statements as true or false

  • Pyrogens can be removed by sterilization
  • Filters that are pyrogenic can make solutions pyrogenic
  • The test to determine the Pyrogenicity is the LAL test (Limulus Amebocyte Lysate test)

What are Extractables?

  • Super heroes
  • Contaminants that elute from filters which might affect quality of the effluent
  • 60's rock band

Filter Efficiency (FE)

This is the quantity of particulate retained compared to the total quantity of particulate to which the filter is challenged. It is expressed in  and refers to a specific size of particles.

Wrap-Up

Understanding filtration will help REM sales staff tailor products to our customers specific applications. 

This course has been produced so that REM Sales staff are aware of the different types of filtration.