Lombard Medical Technologies plc, Polymer Coating Division, Sheffield, UK
Problems with current technology
Urinary incontinence is a major problem that affects the social lives of many people. There is, therefore, a need to develop products that will help the quality of life for those affected. Urinary catheterisation is performed to release urine from the bladder when the urethra is blocked or when users are unable to control the flow of urine themselves. The main types of urinary catheterisation are as follows.
- Indwelling catheterisation in which the catheter is inserted into the bladder via the urethra and left in continuously; this method is normally used for people suffering from spinal injuries or who have been hospitalised.
- Suprapubic catheterisation is another form of an indwelling catheter in which the catheter is inserted into the bladder via an incision in the abdominal wall.
- Intermittent catheterisation, which involves the temporary insertion of a catheter to remove urine from the body; this method may be necessary for people suffering from neurological disorders or who have undergone certain surgeries.
The most common types of risk that occur during or after catheterisation include:
- injury to the urethra caused by rough insertion of the catheter
- adherence to the urethral mucosa (sticky catheters)
- bladder stones, normally seen only after years of catheterisation
- infections as a result of the formation of a biofilm, which in turn can lead to encrustation and blockage of catheters.
Figure 1: Comparison of the coefficient of friction (COF) of two market leading catheters and a catheter coated with the novel technology.
(click image to enlarge)
Adherence to the urethral mucosa1,2 occurs as the catheter is inserted into the urethra; because of the difference in solute concentration, water is drawn from the catheter into the surroundings. Extensive work has been conducted to resolve the ongoing osmolality problem and there are products on the market that provide a partial solution. Although the osmolality problem may have been resolved to some degree, the overall performance of the catheter is compromised, for example, the adhesion of the top layer is affected and the coating is not as smooth.
Encrustation is another major problem affecting catheter users. This causes the catheters to be blocked, which leads to infections. Encrustation is the build up of crystals on the surface of the catheter. This crystal formation occurs as a result the formation of a bacteria biofilm: the bacteria Proteus mirabilis adheres to catheter surface and forms a biofilm. Urease enzymes present in the Proteus mirabilis bacteria generate ammonia from urea and increase the pH of the urine to alkaline; under these conditions, calcium and magnesium phosphates crystallise and became trapped on the surface of the catheter. These crystals block the urinary catheter and subsequent obstruction of urine flow, which can induce urine infections.
Catheters coated with antimicrobial agents such as nitrofurazone, silver oxide and silver alloy are available on the market, but none of them are fully resistant to biofilm formation.3 Therefore, work is required to resolve the growing problems related to catheters and catheter-associated urinary tract infections (CAUTIs).
Advantages of a new technology
Figure 2: The difference between new and current coating technologies in relation to the retention of water within the coating.
(click image to enlarge)
With this objective in mind, a novel urinary catheter coating has been developed, which is highly lubricious, durable and biocompatible. These properties have been demonstrated by having the coating tested for cytotoxicity, sensitisation and intracutaneous irritation; in all cases the results showed that the coating was biocompatible. The coating is applied to a polyvinyl chloride substrate by a dipping process and it is also possible to add antimicrobial agents to it to help fight CAUTIs.
Figure 3: Catheters stained with a dye to show degree of hydrophilicity. Uncoated catheter stained with Gentian violet (left). Catheter coated with novel technology and stained with Gentian violet (right).
Catheters from the market leading companies demonstrate excellent lubricity: coefficient of friction (COF) of 0.02–0.03. For marketing purposes improving this value would be advantageous; there would be no apparent benefit to the patient because patients cannot differentiate values of less than 0.05. Inhouse studies using a FTS 5000 friction test system (Harland Medical Systems LLC, Eden Prairie, Minnesota, USA) have shown that comparative COF values are achieved employing the novel coating (Figure 1).
In terms of “dry out,” the elimination of the problem relating to the “stickiness” of the catheter would represent a significant benefit to the patient. The coatings of the market leading catheters have non-adherent top coats whose function is to retard drying. The insertion of the catheter results in a “thick paste like” material being removed, which at the same time prevents the function of the active coating because it has also been removed. With the new technology, the coating remains lubricious for up to 10 minutes under ambient conditions and yet the coating still adheres to the substrate of the catheter. This delay in dry-out of the catheter is possible by incorporating an additive into the coating solution; in this way adhesion is not affected and the catheter is kept wetter for a longer period of time. The benefit of the delay in dry out with the new hydrophilic polymer coated catheters is shown in Figure 2.
The hydrophilicity of catheters coated with this technology has been demonstrated using a quality control technique whereby the catheters are stained with Gentian violent (Figure 3); the intensity of the purple colour is an indication of the degree of hydrophilicity.
Future use of the technology
The novel proprietary hydrophilic coating is an integrated, durable and lubricious coating, which has superior dry out characteristics and the capacity to incorporate antimicrobial additives. It employs a simple dipping production method using low cost biocompatible materials. The coating has the potential to overcome many problems associated with catheterisation, hence it is expected to be used for the catheters of the future. The coating also has the potential to be applied to other medical devices, including gastrointestinal instruments such as endoscopes and colonoscopes.
1. M. Fader et al., “Coated Catheters For Intermittent Catheterisation: Smooth or Sticky,” BJU International, 88, 373–377 (2001).
2. L. Waller, M. Telander, L. Sullivan, “The Importance of Osmolality in Hydrophilic Urethral Catheters: A Crossover Study,” Spinal Cord, 35, 229–233 (1997).
3. K. Getliffe, “Managing Problems With Urinary Catheters,” European Genitourinary Disease, 90–92 (2007).
Dr Kadem Al-Lamee is Managing Director and Dr Naveed Ahmed is Research Scientist at Lombard Medical Technologies plc, Polymer Coating Division, Sheffield Technology Park, 60 Shirland Lane, Sheffield S9 3SP, UK, tel. +44 1142 491 322, e-mail: email@example.com, www.lombard-medical.com.