Importance of high quality manufactured catheters
A particular cause for concern is the texture and shape of the apertures that are formed within the catheter wall. These apertures are required to allow drainage of urinary fluids and therefore they must be perfectly smooth and free from burrs. Most apertures are created by mechanical cutting or piercing/puncturing of the catheter body. These methods have limitations in that they cannot always reliably produce smooth apertures or guarantee the removal of any debris from the punctured or perforated catheter body (9).
Studies by the School of Biosciences at Cardiff University (10) using their artificial bladder model found that the process of encrustation is started by initial cell adhesion of Proteus Mirabilis to irregular surfaces surrounding the catheter eye or drainage holes. Micro-colonies form in the depressions of the cut surfaces allowing the formation of the biofilm from which the urease enzymes are released causing the precipitation of the struvite material. Although different polymeric materials have lower affinities for cell adhesions i.e. silicone material has a lower susceptibility to encrustation compared to latex catheters.The major initiation factor was deemed to be the quality of the of the aperture edge and surfaces. These workers (10) found using scanning electron microsopy that engineering techniques used in catheter manufacturing processes produce particularly rough irregular surfaces on the rims (edges) of the drainage holes (eyes), quoting:
‘Catheters available today with their rough, engineered, irregular surfaces around the eye holes and narrow central channels are readily colonized and blocked by crystalline bacterial biofilm. The development of cathters with larger internal diameters and smoother surfaces especially around the eye holes would substantially reduce the problems with current devices’.
An ultrasonic processing solution
Using ultrasonic processing technology, specialised tooling has been developed that can be used to cut and form an aperture through a catheter body, which has advanced the production of smooth apertures.
The tooling or sonotrodes are constructed from solid titanium are connected to thruster-booster coupling which is designed to vibrate the tip longitudinally from 15,000 to 40,000 Hz (11).
The high vibrational forces which are developed allow the titanium sonotrodes to precisely and efficiently cut through polymeric surfaces. This cutting action combined with an unique profile design allows the creation of aperture with smoother edges and surfaces.
In addition, this technology has solved another problem inherent in the general manufacturing process, that is, the removal of the chad or debris that is generated when the aperture is cut .
In conventional manufacturing processes the chad can be left partially attached to the edge if the cut is not made cleanly or it can be pressed through into the hole and lost within the catheter bore. In both scenarios, unless the error is detected immediately, currently by visual inspection, the chad can still be in situ when the catheter is inserted into the patient’s urinary tract, which would cause trauma to the surrounding tissues and/or dislodge to cause blockages or other serious complications.
The ultrasonic technique combines a vacuum drawing system within the ultrasonic cutting tool so that when an aperture is cut, the vacuum simultaneously removes the chad and conveys it to an electronic counter. If a chad is not counted for each aperture that is cut, then the manufacturing process is automatically stopped and can only be restarted when the faulty catheter is physically removed and disposed off, which ensures 100% elimination of a problem with missing chads.
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