Thermoplastic elastomers: How to find the perfect fit for injection moulding and extrusion plants

Actega explains why its ProvaMed thermoplastic elastomers (TPE) are ideal for all conventional injection moulding and extrusion plants.

Thousands of tracheotomies and laryngectomies are carried out every year. These procedures lead to function loss of the upper airways, which could be anything from filtering, warming and moistening breathing air through to voice loss.

Tracheostomy tubes and speaking aids are essential and the industry offers an extensive range of ultra-modern tubes and aids which are optimally tailored to the demands and requirements of each individual patient.

Although metal tubes are offered, these have thin walls and are rigid, with a larger inner volume than silicone and plastic tubes which feature thicker walls, minimally limit inner volume and are distinguished by a high degree of wearing comfort, and a comparatively lighter weight.

Most tube wearers could benefit from tracheal tubes made from lightweight, soft plastic material as these lead to less irritation of the sensitive tracheal mucus membranes and less mechanical irritation of the tracheostoma. Additionally, plastic is advantageous compared to metal tubes, as metal cannot be inserted during radiotherapy due to reflections on the tracheostomy tubes possibly preventing the calculated radiation dose from being applied or causing uncontrolled radiation exposure.

As in many areas of medical technology, most plastic-based tracheostomy tubes are manufactured from polyvinyl chloride (PVC). However, an increasing number of customers are requesting solutions from the manufacturers of medical technology which are free of PVC and plasticisers.

All tubes in technical medical applications are obliged to comply with a wide variety of requirements as they are used in highly-sensitive areas where it is often a matter of life and death. The material compound used must also be developed with care and display maximum quality, as the wrong material mix could result in fatal consequences.

The material group, TPE possess good processability which makes them ideal for all conventional injection moulding and extrusion plants. TPE also have very low emissions, good reusability and are cost effective. Additionally, they can be sterilised, conform with the Food and Drug Administration, International Standards Organisation and United States Pharmacopeia classes, whilst displaying very good sealing and adhesion properties. Actega’s ProvaMed TPE are an example.

These tracheostomy tubes are typically manufactured in extrusion or injection moulding processes, and their material properties need to be adapted accordingly. Extrusion requires exact setting of the material flow properties to the processing method while injection moulding offers the possibility of manufacturing the tracheostomy tubes and neck flange in a single step. Multi-component injection moulding enables economic manufacturing of multiple components such as a connector made from a thermoplastic and the soft components made using TPE. This is particularly applicable when the material’s adhesion properties need to comply with the connector material, therefore requiring optimisation. ProvaMed TPE display perfect adhesion to polystyrene and acrylonitrile butadiene styrene (ABS). The more diverse the types of tubes, the more extensive the areas of application and the more detailed the requirements.

Another area of focus is represented by solvent bondability. Micro-tubes are often inserted through the neck flange in the case of transporting air to the cuff or for optional secretion removal, where the micro-tubes need to be bonded to the outer tubes. The ProvaMed portfolio provides some suitable solutions for this.

Manufacture and printing are followed by sterilisation. TPE can display their particular advantages as only minimal changes in terms of mechanics and optics can be ascertained after sterilisation.

The terms single-lumen tubes and mono-layer need some explanation. After all, lumen comes from the Latin and literally means light. Mono-layer, however, is actually a biological term and refers to a culture of single-layer cell layers based on individual cells. Nevertheless, the use of these terms within the context of medical tubes makes sense as lumen describes the cavity of an organ or vessel and, within the context of single-lumen tubes, represents the cavity in a tube. Mono-layer describes an individual layer in the corresponding tube. Single-lumen tubes and mono-layers are suitable for a range of applications. For transporting liquids and medication, they are used for infusions, enteral and parenteral feeding, and in urology and endoscopy. Their classic tube geometry can also be fitted with additional features.

Multi-lumen or multi-chamber tubes represent key solutions for special areas of application in which air, material or liquids are transported and several functions can be carried out simultaneously in the same space such as suction and rinsing. They are used in acute dialysis, as central-venous catheters in urology, and as liquor drainage in the case of hydrocephaly.

Multi-layer tubes make it possible to realise the most complex characteristics profiles. The advantages of a wide variety of materials can be combined with this manufacturing process. The areas of application here include infusion lines and filling tubes for bag systems, pressure lines for angiography, administration of medication in oncology and highly-flexible working channels with low sliding friction coefficients in endoscopy.

Thread-reinforcement involves reinforcing using wound or braided metal or polyamide (PA) threads in order to guarantee resistance to tube bending, bursting or vacuum. One example for medical technology is represented by respiration tubes.

The range of materials available for manufacturing medical tubes is enormous, but not every material is suitable for all areas of application and not every material combination makes sense for the respective characteristics profile required. It always depends on the characteristics that are required for the application.

Interactions between tube material and pharmaceutical substances or those produced naturally by the body which could impair the human organism must be prevented at all costs. There must be no interaction with the plastic, medication absorption must be avoided, the material must be entirely resistant to media and should also in certain cases be ultraviolet-stable in order to avoid embrittlement, deformation and opacity. Accordingly, liquid content remains visible enabling visual flow control. Tube systems in clinical applications should also display radiopaque strips in the tube wall to enable the position of the tube to be tracked in the body and the localisation of implanted drainage or surgical components using x-rays. Bacterial resistance should be increased in the form of antimicrobial coating. Buckling resistance is necessary to guarantee the free flow of substances through tubes.

In the form of ProvaMed, Actega offers a TPE portfolio which is free of latex, silicone and phthalates displaying the requisite material qualifications in terms of normative, toxicological, biological and customised requirements. Materials can be adapted to a wide variety of requirement profiles outlined above and can also offer particularly good adhesive properties when bonded with thermoplastics such as polyethylene, polypropylene, polystyrene, ABS, polycarbonate and PA, which are also maintained even in the case of continuous media contact and increased temperatures.