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Medical Plastics: Getting heavy with super-bugs

By Lou Reade
Posted 29 January 2013

The rise in hospital-acquired infections – including super bugs – has prompted materials developers to step up developments in anti-microbial technologies, which can help to kill germs on contact.

Microban International has carried out in-vitro testing to simulate planktonic and biofilm growth on high consistency rubber (HCR) silicone, which is often used to make urinary catheters. Urinary infections are an expensive source of hospital-acquired infections: existing technologies have had limited success in reducing infection rates.

But Microban’s silver antimicrobial technology, developed for HCR silicone, is engineered to meet stricter FDA guidelines that encourage manufacturers to adopt tougher measures in order to reduce patient infection.

Initial results with the antimicrobial technology exceed FDA guidelines, says the company, showing greater than 5 log reductions in Proteus vulgaris, Pseudomonas aeruginosa, Staphylococcus aureus and Escherichia coli versus unprotected HCR silicone. It was also effective on biofilm formation.

“The ability of antimicrobial technologies to reduce biofilm formation is critical to reducing infection rates,” said Gina Sloan, director of microbiology at Microban.

Biofilms are communities of bacteria that can resist antibiotic treatment and are more likely to cause recurrent infections. The study shows that the technology prevents the formation of biofilm on HCR silicone.

Advanced additives have also been used to improve catheter design. One Chinese catheter manufacturer chose Mevopur masterbatches and compounds from Clariant in the development of catheter tubing that is exported to Europe and the US. Catheters are a USP Class VI regulated item, with potential for material migration.

Overcoming challenges

Mevopur materials are available as single multiple additives in polymer-specific carriers, in a range of medically approved plastics including TPU, PEBA, and nylon 12. This overcomes the challenge of using different polymers to achieve a balance of softness and flexibility in one place and rigidity elsewhere in multi-layer thin-wall extrusions.

Clariant’s functional innovations and visualisation aids are designed to help manufacturers minimise the potential for extractables and leachables from catheter tubing.

These include: colour to identify the catheter, available as a pre-colour compound or masterbatch in the polymer required for the application; laser marking additives to eliminate inks and potential solvent residues when adding depth gradations, logos and identifications to catheters; MedX anti-microbial agents from Sanitized, which can be incorporated to support the development of catheters with surfaces that are active against bacteria; and surface lubrication, using non-fluorine based additives.

“Our strength lies in helping catheter tubing manufacturers to achieve their design and functionality desires using pre-evaluated materials,” said Steve Duckworth, head of the medical and pharmaceutical segment at Clariant.

Sanitised manufactures the active MedX anti-microbial ingredient – silver, on a glass carrier – according to strict quality control and impurity check requirements stipulated by Clariant. Clariant then carries out biological evaluation based on the ISO10993 test protocols developed for medical raw materials.

The active ingredients are then incorporated into a masterbatch, using a range of polymers for medical applications.

Because the anti-microbial agent is integrated into the polymer, it removes the need for device manufacturers to undertake a secondary antimicrobial coating operation on their medical device, with the associated cost and validation processes that are required.

Latest additions

And German plastics giant BASF showcased the latest additions to its antimicrobial HyGentic product portfolio at the Compamed trade show in Düsseldorf last November.

HyGentic SBC is a transparent, injection-mouldable styrene butadiene block co-polymer granulate material that contains antimicrobial silver ions. The granulate is used to make devices such as inhalers and ventilation filters.

HyGentic PA is an antimicrobial glass-fibre-reinforced, injection-mouldable polyamide granulate that is suited to the production of operating elements for medical devices.

“These materials are effective against a range of fungi and bacteria,” explained Edgar Eichholz, business development manager for medical device materials. “Medical devices produced with HyGentic can be disinfected by conventional procedures.”

In addition to its HyGentic materials, BASF is working on other materials that prevent microbial build-up on medical device and equipment surfaces.

Its medical devices team at its R&D centre in Tarrytown, New York in the US produces customised formulations and tests them for antimicrobial effectiveness against microorganisms – including ‘super bugs’ like MRSA – then incorporates them into a variety of materials.

“The selective combination of organic and inorganic antimicrobial ingredients produces synergy effects and boosts the efficiency of the individual components,” said Eichholz.

The company is also researching new generations of materials with novel surface effects that are of interest for medical devices and equipment.

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