Originally Published MPMN April 2004

PRODUCT UPDATE

Clearing the Air

Filters find many uses in medical device manufacturing

Susan Wallace

From clearing smoke from operating rooms to protecting sensitive electronics, filters are essential parts of medical devices. They are also used in manufacturing processes to help ensure sterility. What follows is a roundup of some advances in filtration technology. 

Polyester Filters Are Washable and Reusable

Dust cartridges from Airguard (Louisville, KY) are made with 100% spunbonded polyester media. They are used in pulse-jet dust collectors. Applications for such systems include situations in which there is residue from metalworking or chemical or plastics manufacturing. 

The spunbonded media have high initial efficiency, high filtration efficiencies on fine particulate, and good dust-cake release characteristics. The media are long wearing and highly resistant to abrasion. Cartridges are washable and can be used repeatedly. They resist most chemicals, including many acids, alkalis, oxidizing agents, and solvents. 

Specialized media, such as aluminized, are also offered by the company. Aluminized media are suitable for static dissipation, which is desirable for safety and facilitates material handling. They are also well suited for cartridges used in powder-coating operations.

The company provides PTFE laminated media as well. PTFE cartridges are engineered specifically for dusts with high moisture content. 

So Smoke Doesn't Get in Your Eyes

Procedures such as electrosurgery or laser surgery release a certain amount of smoke into the air. These operations require a high-performance vent with filtration capabilities. Specialized media reduce the chance of contaminated smoke leaving a collection canister. 
Gore Medical Membrane Technologies (Elkton, MD) supplies a membrane for surgical-smoke filtration as an all-in-one, multifunctional laminate. The product combines a microfiberglass prefilter with a hydrophobic PTFE membrane and is offered in many forms. It combines high smoke-holding capacity and long life with a robust barrier to fluid penetration. 

Additionally, the high smoke-particle retention of Gore-Tex media may offer extended suction system life. And, according to the company, hydrophobic Gore-Tex ePTFE membranes have significantly higher resistance to leakage than other microporous membranes.

Diagnostic Wicks Have Highly Uniform Liquid-Flow Properties

Transorb wicks from Filtrona Richmond Inc. (Colonial Heights, VA) are used as wicking components in lateral-flow diagnostic devices such as midstream pregnancy and ovulation tests. They can also be used in other applications that require collection and transfer of sample liquids or reagents.

The company offers Transpad wicks as well. They are used for sample collection and transfer media in lateral-flow test strip formats. The low protein binding and highly uniform liquid-flow characteristics of this media make it suitable for this application. 

The products are custom designed to control the rate of flow and amount of liquid delivered to the test site. The wicks are constructed using continuous fibers to optimize uniformity of liquid transfer characteristics.

Synthetics--The Fabrics of Lifesaving Applications

Precision-woven synthetic fabrics are suited for medical and diagnostic applications. The SaatiCare fabrics from Saatitech (Somers, NY) are used for blood filtration in arterial, cardiotomy, and transfusion filters. They are also used for drug-infusion systems, flow control devices, moisture barriers, biopsy bags, and EMI and RFI shielding. 

SaatiCare fabrics have a narrow aperture-size distribution, ensuring accurate and predictable filtration. A proprietary finishing system ensures that the fabric will meet specified pyrogen levels and be in compliance with USP Class VI requirements. 

Diagnostic test strips use the company's screen membranes to ensure rapid and uniform spreading and precise prefiltration. 

The fabrics are available custom fabricated into slit rolls, stamped parts, tubes, pleated elements, bags, and various other forms. Ultrasonic cutting and welding, pleating, and laser and cold cutting are all performed in a Class 10,000 cleanroom under ISO 9001 guidelines. A variety of pore sizes, thicknesses, and flow rates, as well as special hydrophilic and hydrophobic finishes, are available. 

Filters Ensure a Tight Fit

MagnaFlex air filters, made by Universal Air Filter Co. (Sauget, IL), feature bend-to-fit flexibility. They have a magnetic installation method and sealing strip that ensures a tight fit for medical electronics enclosures.

The units are designed for medical enclosures that cannot accept a rigid air filter frame because of obstructions. The magnetic sealing strip eliminates mounting hardware and simultaneously locks the flexible filters in place. The resulting tight seal prevents unfiltered airflow from bypassing the air filter. 

Each filter is supplied in a flame-retardant, polypropylene frame. This makes it possible for the filter to follow a contour and bend around obstructions. Frames come in thicknesses ranging from 0.03 to 0.12 in. A solvent-resistant, two-part epoxy bonding material is used to securely unite frame and air-filter media.

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