Date of Completion


Embargo Period



Joerg Graf, Yu Lei

Field of Study

Biomedical Engineering


Master of Engineering

Open Access

Open Access


Indwelling urethral catheters are both important and convenient biomedical devices for many people. They provide incontinent and/or paraplegic patients an involuntary method of emptying their bladder. The catheters are inserted through the patient’s urethra to the posterior portion of the bladder. A balloon is inflated with water to keep it secure and in place. The tip of the catheter has an eye hole exposing the lumen of the catheter. The urine in the bladder drains through the lumen and out of the body into a collection bag. Catheters can potentially have 2 problems. First, they are prone to calcium/magnesium phosphate buildup on the surface and lumen of the catheter. This could obstruct the flow of urine making emptying the bladder difficult or impossible. Buildup on the surface of the catheter could also make removal of the catheter painful or even impossible without surgery. Secondly, catheters provide bacteria a route to travel to the kidneys to cause urinary tract infections. This could lead to long term problems such as chronic kidney disease.

The primary culprit for these infections is the bacterium Proteus mirabilis. This bacteria has the ability to swarm on the catheter surface and travel to the bladder. It then secretes an enzyme called urease. This enzyme catalyzes a hydrolysis reaction converting urea into ammonia which eventually leads to nucleation of calcium and magnesium phosphate which can adhere to the catheter. The bacteria then differentiates into a swarmer bacteria and travels along the catheter surface to the kidneys where it causes urinary tract infections. The bacteria can easily adhere to hydrophilic surfaces and express factors to adhere to hydrophobic surfaces.

This research will aim to prevent these problems through the use of antibacterial coatings on the surface and lumen of the catheters. Different techniques were tested such as disrupting the bacterial membrane as well as inhibiting bacterial attachment altogether. These coatings should extend the indwelling time of catheters significantly. By inhibiting the bacteria, urinary tract infections and catheter encrustation will be significantly reduced compared to the current catheter designs. Surface characterization techniques and antibacterial assays were run to test the efficacy of the coatings.

Of six coatings that were tested, two were able to inhibit biofilm formation significantly better than the current commercially used method of silicone according to a crystal violet assay. One of the coatings, 11-mercapto-trimethylamine (11-MTA) was able to permeabalize very well killing over 90% of all bacteria on the surface. These results showed that amphiphillic cationic molecules are lethal to the membranes of gram-negative bacteria. During this research, a long term, and effective method was developed for preventing urinary tract infections and catheters encrustations for patients who use long term urethral catheters.

Major Advisor

Mei Wei