Why material innovation is crucial for device development

^{Lorna O’Gara, Ultrapolymers looks at polymer innovation in healthcare through inter-material replacement.}

Medical device manufacturers continuously strive to develop innovative products that are compliant with regulatory bodies and competitive.

Next-generation product development based on raw material innovation is one way OEMs can achieve this target.

Polymers offer properties such as durability, lightweight, chemical resistance, transparency and their ability to be easily shaped.

They can be combined with various additives to customise colour, modify impact strength or provide resistance to sterilisation methods. Reinforcement with glass fibre additives, surface modification or antimicrobial additivation are attributes available when working with polymers in demanding applications.

When advising on material selection, it is key to look at the main performance characteristics required of the device, taking into account any influencing factors, such as environment. Evaluating how the device will be processed, including which secondary operations will be required such as surface coatings, laser marking, bonding methods, printing etc. can also not be overlooked.

Getting input from all stakeholders at the earliest possible stage of the design process is important to ensure that the material most suited to the application is selected.

Engineering materials alternatives

Designers have to evaluate the advantages and disadvantages associated with each resin type. In some cases, resins selected for historical reasons can exceed the design requirements and be over engineered for the specific end use. An example is where materials such as Polycarbonate (PC) and Polyethylene Terephthalate (PET) are commonly used because they fulfil particular needs such as transparency, physical and chemical properties. By exploring options such as INEOS Styrolution’s Zylar grades, clear and tough methylmethacrylate butadiene styrene (MBS) grades made by modifying a styrene acrylic copolymer (SMMA) with an impact modifier, significant advantages can be gained. Zylar is a transparent and easily colourable material, it has a 14- 30% density advantage over some other clear engineering materials and it provides processing advantages that can lead to reduced cycle times, improved production efficiency and reduced electricity consumption. Zylar is inherently hydrophobic therefore does not require pre-drying and is a non-corrosive material resulting in less wear on the processing moulds.

Looking at the trends in drug delivery, an opportunity arises for generic drug manufacturers when US patents expire. Treatments can be made available to patients in developing countries, where limited access to medical facilities will drive an increase in self-administration. Manufacturers will be urged to develop lower cost devices to deliver their drugs.

For replacement of over specified materials such as PC/ABS (blends of Polycarbonate and Acrylonitrile-Butadiene-Styrene) or ABS in drug delivery device components, polyolefins can provide an excellent combination of stiffness and toughness.

PVC alternatives

Where medical devices require flexibility, such as medical tubing or film, it is worth looking at why Polyvinyl Chloride (PVC) has been so successful.  PVC was originally developed to replace rubber and glass to make flexible tubing and containers and began to dominate this market when the need for single use pre-sterilised medical components increased.

PVC is the dominant material used for the storage of IV fluids, dialysis solutions, as well as blood and blood-derived products. It can be sterilised with steam, EtO (Ethylene Oxide) and via Gamma or E-Beam irradiation. PVC can be solvent bonded or joined together through high radio-frequency (RF) welding. The use of PVC in medical devices has however created discussion with many patients and hospitals demanding a safer, more environmentally-friendly option. PVC is a chlorinated plastic that forms dioxin when burned, which when released has been found to have toxic and carcinogenic effects.

Also concerning is that phthalates are used as plasticizers for flexible PVC, including for blood bags, IV bags, catheters, tubing. The plasticizer may migrate from the device to the patient through contact with the skin or mucous membranes. Studies on certain animals have shown reproductive and endocrine disrupting effects.

Manufacturers of medical devices are faced with a need to replace incumbent phthalate- and plasticizer-based materials. With regulatory changes coming, manufacturers have two choices; opt to switch to a different type of PVC, softened with a phthalate-free plasticizer, or choose to evaluate alternative polymer solutions.

For tubing and other flexible products, the main alternatives are usually silicone, ethylene vinyl acetate (EVA), polyesters, various polyolefins, elastomers and certain polyurethanes.

High density polyethylene (HDPE) is commonly used for IV solution containers. It is cost-effective, has a low sealing temperature and is recyclable. Because of its polarity however, it cannot be sealed by RF welding.

EVA can be used for kink-resistant medical tubing, as well as for pharmaceutical bag applications where they are filled ascetically; as EVA can’t withstand steam sterilisation by autoclave. For infusion therapy, thermoplastic elastomers (TPEs) have been developed.

Ultrapolymers supplies the Marfran.Med range of medical TPE and TPO compounds. These materials feature excellent transparency, are suitable for sterilisation using steam, Gamma and EtO and can be tailor-made to fit customers’ specific requirements.

Another material option worth considering would be INEOS Styrolution’s Styroflex, a styrene thermoplastic elastomer (S-TPE). This is suitable for film and tubing applications as well as for injection moulding and combines transparency with toughness, tear resistance, excellent bondability to other materials, good barrier properties and is sterilisable.

Finally, thermoplastic polyurethane (TPU) combines excellent toughness with strength and barrier properties. TPU provides sealing through RF welding as well, however it is a more expensive choice.

Ultrapolymers has been working closely with LyondellBasell on development projects using Purell KTMR07, Lyondellbasell’s innovative, complete polyolefinic solution for use in flexible medical applications. Purell KTMR07, a Polybutene-1 (PB-1) material, is suggested to be used in a blend with Purell polypropylene (PP) to achieve the required property balance.

When blending PB-1 with PP, a homogenous single-phase polymer structure is achieved thanks to the very high compatibility between the two materials.

PB-1 can be used as an impact modifier, to achieve a reduction in glass transition temperature and to improve the optical properties of the PP-based solution.

This new solution is phthalate and plasticizer free and allows device manufacturers to offer product differentiation based on material innovation in next generation development programmes.

This Purell polyolefin blend is recyclable and does not require complicated separation, which could help hospitals in their efforts to reduce (PVC) waste.

Key application areas include intravenous and transfusion tubing, catheters, nasogastric and dialysis tubing, respiratory tubing and tubing for parenteral feed pumps. Also IV bags, dialysis bags and blood bags are amongst the key focus areas.

Various blend ratios have been proposed and successfully tested to produce medical tubing in a range of shore hardnesses. In parallel, a further evaluation of processing parameters required when working with a dry blend or compound of Purell KTMR07 and Purell PP has been performed (data is available on request).