A multilayered approach

Coextrusion’s role in medical engineering

The use of multicomponent technology under clean room conditions provides an excellent foundation for the development of new medical and pharmaceutical products. The objective is, alongside improved cost aspects, to achieve improved functionality in new tubing products with the help of coextrusion technology.

In many cases, coextrusion of multiple polymer layers in the production of micro-dimensional tubing for medical engineering is still uncharted territory.

Microextruders allow for the production of multilayer tubing from up to four different polymer materials. The smallest achievable inner tubing diameter is about 100 µm, with a minimal wall thickness of approximately 50 µm. Microextruders can work at minimal material throughput rates, with an output of less than 30 grams per hour.

The advantages are obvious

Application-specific distribution of layer thicknesses 

• Embedding of several color stripes and x-ray contrast stripes 
• Integration of functional layers, e.g. for light protection properties or gas barrier
• Use of bonding agents for incompatible polymers against delamination

Which materials can be used?

In theory, any polymer can be used in coextrusion. In practice, however, those thermoplastics are used that have already proven their worth in other processing techniques in medical engineering and pharmaceuticals: polyurethanes, polyamides, polyolefins, thermoplastic elastomers, and to some extent soft PVC as well.

Our multilayer tubing innovations for medical applications

To protect light-sensitive solutions and ensure loss-free dosage of sensitive drugs, RAUMEDIC has developed the products RAUSORB, RAUINERT and RAUSONERT. These three application examples from medical engineering reflect the growing importance of multilayer extrusion.

Protecting light-sensitive pharmaceuticals is increasingly important

Pharmaceuticals that are activated by exposure to light, or that break down in a photochemical reaction are increasingly used for special therapies. Substances like vitamin A and sodium nitroprusside take their activation energy from visible and invisible light in different ranges of wavelengths.

To provide the required protection for these substances, the development of black tubing seemed to solve the problem. This, however, makes it impossible to monitor the infusion solution. As a result, any gas bubbles, impurities or other problems cannot be detected when they occur.

Other solutions available on the market involve transparently colored tubing, or windowed tubing made of a clear material including semi-circular segments of light-proof coextrusion materials embedded in the tubing wall. But these solutions are merely a compromise at best, since they do not comply with the applicable pharmacopoeias and relevant standards.

Drug-compatible infusion tubing for highly sensitive drugs

For decades, soft PVC has proven its worth as an efficient and easy-to-process material for flexible infusion lines. Even today, well over 90% of all infusion tubing is still made from soft PVC. With advances in the development of highly effective new drugs, however, and especially in the oncology domain, an increasing number of problems have begun to arise involving drug compatibility with the PVC tubing material. Many highly-sensitive drugs are adsorbed on the tubing’s surface, with the result that only a fraction of the intended dose actually reaches the patient.

Conversely, “undesirable side effects” may occur, if plasticizers and other additives are released from the PVC material by the infusion solution. This happens most often when the infusion solution contains fatty substances or lipid-like solubilizers.

Filling tubing for PVC-free infusion bags

As in the realm of food packaging technology, a trend towards the use of lightweight, flexible and unbreakable polymeric materials is developing in containers for infusion solutions, too.

For infusion bags, the first step was the use of PVC films, tubing and connectors containing plasticizers. Since the early 1990s, there has been an intensive search for alternative materials free of plasticizers and chlorine. For films, the industry quickly achieved adequate levels of quality that had already proven their value in the food industry. The films in question were multilayer films made from polypropylene or polyethylene/bonding agent/polyester that comply with the requirements for transparency and sterilizability with water vapor at 250 °F (121 °C).

These PVC-free film bags require special filling tubing. Whereas the outer layer should be weldable to all common films, the inner layer should provide excellent bonding to all common connector materials, such as polycarbonate, polypropylene or hard PVC, during the steam sterilization process. Naturally, this combination of properties cannot be achieved in a single polymer formulation. By means of coextrusion technology, RAUMEDIC develops medical filling tubes for infusion bags.