Material gains

According to Solvay Speciality Polymers, designing with plastics isn’t harder, just different.  As part of its drive to push the use of high performance polymers for metal replacement, the company is offering its expertise as well as going one step further to create a real life case study of its own to highlight the advantages of polymers in medical device design

Over recent years, the trend for replacing metal parts with high performance polymers has increased, not least in the medical device sector. Advantages such as lighter weight, resistance to higher temperatures and degradation plus displaying high strength and toughness, have made these materials cost-effective alternatives to traditional materials like metal. As medical device manufacturers face increased price pressures, new ways of looking at product development processes are increasingly important.

Solvay Speciality Polymers, a global supplier of medical grade thermoplastics, is at the forefront of the drive to replace metal with high performance polymers in the medical sector.

Dane Waund, global market manager for healthcare at the company explains: “We think of ourselves as more than a plastics company. Solvay is part of the healthcare sector and supply chain. As such, we feel the need to educate and pass on best practices where we can be of benefit.”

Confidential agreements

Active in the metal replacement market for over 20 years, Solvay has developed considerable expertise. Bound by confidentiality agreements, however, with its OEM partners, the company has been unable to publicise much of its work highlighting the extreme suitability of polymers as a replacement for metal in the medical sector.

“We recognise that specifying plastics for medical devices can be daunting for those who have been used to working with and designing with metals. So, we offer our expertise and help provide a step-by-step process and practical advice to make the change,” says Waund. 

Visitors to the American Academy of Orthopaedic Surgeons (AAOS) in New Orleans, will have witnessed Solvay’s expertise first hand as the company hosted an educational summit at the conference. The first of several to be held this year at a range of global locations, the event is designed to enable the company to move closer to the customer, offering insight and information on critical topics at various levels in the healthcare field.

Presenting a paper on “Coming to Grips with Specifying High Performance Plastics: a Surgical Retractor Metal Replacement Case Study”, Waund revealed Solvay’s recent project on metal-to-plastic conversion engineered via a seven step procedure that analysed end-use performance , biological safety and economics. It also offered techniques to demystify the challenge of metal replacement.

Next step innovation

“We decided to take our innovation to another level,” reveals Waund, “Because we can’t openly discuss the work we were doing with our customers, we made the decision to develop our own case studies highlighting the benefits of using polymers in medical applications.

As a result, Solvay developed designs for both single and repeat use medical applications, replacing traditional metal instruments with alternatives using medical grade plastics.

“We selected a Hohmann retractor for this replacement project,” says Waund. “As a popular part and one that is commonly used in surgery, the device offered plenty of challenges, such as the mechanical load the instrument has to bear, for us to be able show that high performance polymers can be used as a replacement material.

“Polymers offer several advantages for the medical device sector. One of the main drivers is cost. This makes their application for single-use devices feasible. There has also been considerable interest in product appearance and ergonomic designs that are comfortable  and offer a range of grip options. Basically, the polymers we are working with here enable the design of instruments which offer comparable performance to stainless steel but with added advantages,” he says.

Solvay selected two of its high performance plastics for the metal replacement study. Exhibiting prototypes utilising the products at the AAOS gave Waund a feel for how they would be received.

Positive reaction

“The response was extremely positive,” he says. “The fact that we can colour code them to avoid confusion was popular as was their durable feel. Someone commented, ‘when you think of plastic, you don’t think of this,’ which was encouraging to hear.”

For single-use medical devices, the company worked with Ixef polyarylamide (PARA) due to its strength, excellent surface finish and compatibility with gamma radiation sterilisation.

“This polymer is ideal for single-use applications,” says Waund.  “It may prove particularly relevant in preventing the re-use of single-use devices, as the material visually impairs when autoclaved.”

For  repeat-use devices, Solvay used  AvaSpire polyaryletherketone resin (PAEK), which is tailored to provide unique  combinations of performance and value.

Ideally suited

“PAEK provides a range of features making it well-suited for repeat-use medical devices,” says Waund. “This includes a high stiffness to weight ratio, hydrolytic stability at elevated temperatures, improved ductility and toughness, excellent chemical resistance as well as fantastic aesthetics and colourability.”

Stiffness is a critical requirement for retractors, making PAEK  ideal for these applications. It is also easy to process, allowing device designs to incorporate long, thin geometries to be produced either via extrusion and machining or injection moulding.

“The combination of hydrolytic stability  and chemical resistance make high performance polymers ideal for the manufacture of repeat-use devices. This is especially crucial throughout the cleaning and sanitation process, which involves aggressive chemical cleansing  and steam sterilisation. This can be a tough challenge for many plastics to face, but PAEK copes well,” says Waund.

Solvay is keen to recognise the companies it has worked with in the process to hone this high performance polymer expertise.

“Between us and the customer is a raft of additional expertise such as injection moulding, rapid prototyping, stock shape suppliers, and machine houses,” says Waund. “For this study we particularly benefited from collaborations with Paragon Medical, Mack Medical and Total Plastics, who provided their expertise and cost analysis.”

The project has clearly paid dividends for the company, which is making definite in-roads into highlighting the benefits of high performance polymers in the medical device sector. As Waund points out: “There is a lot of metal to replace,” making this area of medical device technology potentially very profitable for those involved.