Medical Catheters and Plastics – Part I

Looking at the application of plastics and polymers in medical devices, I will be focusing on the definition, manufacture, and use of medical catheters, for these series of blogs.

Catheters are thin tubes inserted into the body serving a broad range of functions. The word ‘catheter’ is derived from the Greek verb ‘kathiemai’ meaning ‘let down’ as the catheter is let down into the body. Depending on the material used to make the catheter, its manufacture and design, the catheter can be tailored for use in cardiovascular, neurological, gastrointestinal, urologic or ophthalmic applications. In the cardiovascular area, to cite an example, there are many kinds of cardiovascular catheters including electrophysiology catheters, PTCA (percutaneous transluminal coronary angioplasty) balloon catheters, intravascular ultrasound (IVUS) catheters, percutaneous transluminal peripheral angioplasty catheters, guiding catheters, angiography catheters and pulmonary artery catheters.

Cardiac catheters can be used for diagnostic evaluation of a patient or for interventional purposes. Diagnostic catheters are used to determine and evaluate the state of the patient with regards to certain cardiovascular diseases. Interventional catheters, on the other hand, are used for therapeutic purposes, i.e. for the treatment of an identified disease. Catheters are used in various applications within the cardiovascular sector. These range from the simple intravenous drug delivery to procedures such as ablation and angioplasty. Catheters are also used as delivery systems for the placement and delivery of permanent implants such as pacemakers and defibrillators.

Catheters need to be designed for the specific function that they are intended to perform. Catheters are designed with the following features in mind:

- Mechanical properties: The strength of the material of construction and the mechanical design of the catheter are important characteristics in determining the overall mechanical properties of the catheter. The material of construction decides the catheter’s resistance to bursting, its flexibility and the ability to steer the catheter through the vasculature. The mechanical design in combination with the material properties significantly impacts the performance of the catheter; the mechanical design includes the basic dimensions of inner and outer diameter and the size of the lumens.

- Radio opacity: The ability of x-rays to locate the catheter through the vascular system is an important property of the catheter. The radio opacity allows accurate placement of the catheter inside the body. Radio opacity can be obtained by compounding the catheter material with radio opaque agents or by the placement of radio opaque strips at different points in the catheter length.

- Surface and Friction: The ease of passage of the catheter over the metallic guidewire and the surface of the blood vessels without any undue damage is an important aspect of the catheter. The frictional properties of the catheter are an important measurement for this determination. The behavior of the surface of the catheter is an important consideration in their response to the bodily fluids.

- Atraumatic tip: It is important that the process of catheter insertion and its progress through the vasculature does not cause any damage to the surrounding tissues. This damage is minimized by the careful design of the catheter tip.

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Author
Ajay D Padsalgikar (Ph.D. - California, USA)
Trainer, Polymerupdate Academy