Polyolefins for use in medical devices

These advances have resulted in quicker diagnoses, improved medical treatments, increased product shelf life and improved home health care.

Implementing a new medical device or packaging application in the medical market often takes several years from design to market release. Therefore, the device needs to offer a good return on investment and be of interest to the market for a reasonable length of time. It needs to be unique and innovative, not only satisfying functional needs but also providing a long life cycle for the product. It must address environmental and disposal issues, satisfy regulatory requirements and provide a competitive advantage.

Many different materials offer advantages and disadvantages for a given application, so careful selection is important. Material selection occurs fairly early in the development cycle, as tool design cannot be completed until the material is defined. It is therefore important to select the right material supplier that understands these requirements and offers long term availability for high quality products, with regulatory support. A supplier who will respond swiftly and efficiently to any requests and give support in material selection and application development in order to reduce the risk of a material change being necessary at a late stage in the development of a new product line.

Polyolefins in medical packaging and devices

Polymerisation technologists have developed over the last 50 years a wide variety of polyolefin materials that can now be produced with properties ranging from tough and rigid to soft and flexible. These developments have enabled polyolefins to replace other polymers and other materials such as glass, metal, paper and board, making polyolefins the world's fastest growing polymer family.

Approximately a quarter of disposable and a third of non-disposable medical devices are produced using polypropylene. Polyethylene accounts for approximately one tenth of disposable devices and a slightly higher usage in non-disposable articles. Polyethylene is widely used in blow moulded bottles and in tubes.

Polyolefins offer benefits versus other plastic materials, including productivity, aesthetics, low odour and taste, and functionality.

Productivity:
Polyolefins offer faster, improved processing; the possibility to produce thinner walled, lightweight articles with complex designs. Polyolefins have a wider operating window than many other plastics and can used with a wide range of mould and machine combinations and process techniques, including extrusion (film and fibre), blow moulding and injection moulding.

Aesthetics:
Polyolefins offer good transparency with a wide range of stiffness/softness and impact levels. They offer good stress whitening properties, low distortion and good contact clarity.

Low odour and taste:
Polyolefins can offer low smell and taste transfer properties, and shelf life barrier extension due to the high barrier of diffusion properties.

Functionality:
Polyolefins have good chemical inertia, and they can be used in many applications such as syringes, bottles, closures and containers. Polyolefins have good top load/stacking performance. They can be used in applications were heat stability is required, including for some grades for hot fill. Polyolefins have good hinge integrity, often used in applications with a living hinge that can be moulded as a single part. Grades are available that are suitable for freezer storage, with very low ductile-brittle transition temperatures. Polyolefins can be sterilised using steam (autoclave at 121°C) ETO and specialist grades are available for gamma and e-beam sterilisation.

Regulatory:
Polyolefins can be used in medical applications, with compliance certification possible (depending on grade) for MDD 93/42/EC, European and United States Pharmacopoeia and DMF listing.

Types of polypropylene and typical customer applications

There are three basic types of polypropylene - Homopolymers, Random Copolymers and Heterophasic Copolymers. In general terms, each type exhibits its own characteristic physical properties. Typically, homopolymers have the best rigidity, random copolymers have the best transparency, while heterophasic copolymers have the best impact resistance. However, within each group it is possible to exert an additional degree of change through the manipulation of selected determinants. Consequently their moulding performances and their physical properties can be modified by changing their molecular weights (melt flow rates) and their molecular weight distributions, by altering the concentrations of the co-monomer, and by the presence or absence of selected additives. It is particularly noteworthy that variants with high melt flow rates (from all three types) are exceptionally responsive to pressure and shear during processing, with flow increasing markedly as the shear is increased. It is this phenomenon, known as thixotropy or psuedoplasticity, which makes them suited to the production of components with thin walls.

Basell offers a range of polypropylene and polyethylene resins typically used by customers in medical and pharmaceutical applications, marketed under the trade name Purell. Basell can offer customers a higher degree of supply security, a long period of no change in additive formulation and dedicated pharmaceutical certification.

Polypropylene Homopolymers

Typically the higher stiffness properties of polypropylene homopolymer resins make them ideal candidates for caps and closures, containers, various parts in syringe applications and needle safety devices, cosmetic packaging, inhaler systems, clamps, connectors, holders and in diagnostic equipment such as pipette tips and vials. In addition, certain attributes can be manipulated to give added benefits and properties for more specific application requirements.

Basell offers the following Purell polypropylene resins typically used by customers in medical applications:

Purell Specialty Homopolymers

Purell HP371P

• Specially modified for gamma sterilisation
• Good flow, good transparency, good impact and stiffness

Purell HM671T

• Specially modified for gamma sterilisation
• Good flow, good transparency, good impact and stiffness Purell HP570U

Purell HP570U

• High flow, high stiffness, no antistatic agent

Customers have used these materials for applications such as 3-part syringes, medical and non-medical devices requiring gamma sterilization, filters and strainers and spouts for pouches. High flow, low warpage materials offer benefits for diagnostic devices and lab ware such as microtitre plates.

Heterophasic Copolymers

The key benefit of heterophasic polypropylene is a good balance of stiffness and low temperature toughness. The material is used by customers in applications were impact properties are required, including parts for inhaler systems, connectors and caps.

Random Copolymers

Random copolymers are often selected for trials due to their transparency. Customers report that Basell’s Purell random copolymers have good flow properties that provide some processing advantages. Examples of typical applications are containers and parts for inhaler systems. Diagnostic equipment such as multiple well test trays, pipette tips, vials and reaction vessels are also reported to be manufactured using random copolymers.

Basell produces Purell RP373R random copolymer with a slip additive and nucleant which can be used in customers’ 2-part syringe applications.

Polyethylene resins and their applications

The main types of polyethylene are low density Polyethylene, high density polyethylene and linear low density polyethylene. Customers use Basell’s Purell low density and high density polyethylene resins in medical and pharmaceutical applications.

As with polypropylene, each type offers different benefits and functionality for a medical device. High density polyethylene provides stiffness, chemical resistance and barrier properties, while low density polyethylene offers resistance to stress cracking (ESCR) and excellent impact properties, and due to the nature of this product some grades contain no additives, making them suitable for applications where interactions with medication or test reagent are key. Polyethylene is reported to be widely used in medical and pharmaceutical packaging. The resins are available with different flow characteristics and specialty products are available

Speciality HDPE grades:-
Purell ACP 6541A

• good flowability versus similar MFR materials,
• good ESCR
• good Organoleptics

Specialty LDPE grades
Purell 2007H

• antiblock additive, suitable for film applications

Purell 33AC

• good Organoleptics and ESCR performance used in collapsible tubes

Purell 2410T

• High flow grade

Environmental Considerations

Thermoplastic materials used in medical devices and pharmaceutical packaging should not impose an unacceptable burden on the environment. This is an important requirement, and should pertain to the production of the raw material, its subsequent conversion into the medical component and its eventual disposal.

Polyolefin materials exhibit a number of life-cycle benefits, including:

• Relatively low energy consumption during polymerisation and conversion.
• High yields during polymerisation.
• Minimal environmental impact during polymerisation and conversion, for instance, through emissions to the air, discharges to water and solid waste generation.
• Inherently low density and therefore low component weight.