Catheters and their Making

Catheters are thin, hollow, flexible tubes that can be inserted into the body to collect urine from the urinary bladder or to allow insertion of a medical device to instill fluids, deliver medications or gases to patients. The most common use of a catheter is emptying urine out of the bladder and usually into an attached drainage bag following a surgery, due to incontinence or because of an incapacitating injury or illness.

Catheters may be soft or hard – that is thin, flexible tubes or a thicker, less flexible version.

Catheter history

History of urinary catheters shows that catheters have been in use since ancient times. The early catheters were made of reeds and the ancient Syrians were the ones who first used them. Hollow reeds and pipes were used as early as 400 BC to study the form and function of cardiac valves in dead bodies. Reeds were replaced by hollow metal tubes which were used as urinary catheters by ancient Greeks.

For many years, plain tubes made of available industrial compounds were used as epidermal catheters. In the 1950s and early 1960s, industrial polyvinyl chloride (PVC) or nylon tubing was cut to a suitable length, sterilized and then used as a catheter.

What are catheters made of

Modern-day catheters are made of a range of polymers like soft plastic, silicone rubber and latex. Other than this, the materials also used are nitinol, nylon, polyurethane, thermoplastic elastomers and polyethylene terephthalate. Foley catheter material is either silicone rubber or latex, depending on what it is used for.

Silicone catheters

The most commonly used catheter material is silicone. This is a favorite material and preferred over latex because of its inert quality and resistance to reaction with body fluids. Hence, there are no fears of complications from the silicone reacting with medical or body fluids when it comes into contact with them. Silicone is also more biocompatible, causes less cell death, is less likely to become coated with deposits, more resistant to bacterial colonization and therefore with less chances of infection.

However, one disadvantage of a silicone catheter is its mechanical weakness. Since it is a weak polymer it is prone to breakages causing it to fracture. This carries the risk of a fracture tip being left behind in the bladder. There have been some cases like this and which have necessitated a surgery to remove it.

Catheter material for advanced catheters

The most advanced catheters have a thin hydrophilic surface coating. Before insertion, the catheter is immersed in water which causes the coating to swell to a smooth, greasy film. This makes the catheter insertion an easier and less distressing process.

Catheter material for short-term use

Catheter materials for short-term use are usually plastic, latex rubber or polytetrafluoroethylene or PTFE-based Teflon coated latex. These can be used for up to 28 days. Latex rubber catheters without a coating are not used much. This is because without a coating they are likely to become encrusted with mineral deposits more rapidly and thickly than when coated. There is the possibility of discomfort due to high surface friction and also the risk of latex allergy.

Catheter material for long-term use

Catheter materials for long-term use, which is for more than 28 days, are silicone, silicone-elastomer-coated latex and hydrophilic- polymer-coated latex. These materials are believed to be safer for a long-term use because they cause least friction and tissue reaction. They are also less exposed to fast colonization by bacteria and encrusting by mineral deposits.

A newer catheter material in the market today is an alloy of silver which is designed to prevent or reduce catheter-associated urinary tract infections. Long-term catheter users are at a higher risk of UTI and this cannot be ruled out in any catheter material, however much expertise is put into its making. The silver alloy-coated catheter is antimicrobial and antibiotic or antiseptic impregnated one. Although its safety tests have been carried out but not much is known about the risks this catheter material carries or its long-term performance since it is fairly new to the market.