PEG Hydrogel Coating of Medical Devices Ben Roedl – Team Leader Patrick Schenk – Communicator Darshin Patel – BWIG Brett Mulawka – BSAC Advisor: William Murphy, Professor of Biomedical Engineering, University of Wisconsin – Madison Client: Arthur J. Coury Ph.D., Vice President of Biomaterials Research, Genzyme Corp. December 3, 20062Abstract It has been proposed to examine and optimize a procedure for applying hydrogels to material surfaces. The ultimate goal for this project is to be able to coat a urinary catheter with a hydrogel in order to limit the infections that often result from long term catheter use. Polyethylene glycol (PEG) based hydrogels were used to do this and the characteristics of adhesion and thickness were mainly focused on. The PEG hydrogel was tested on multiple materials with unique surface chemistries in order to learn about the interactions between the reaction’s photoinitiator, actual hydrogel, and substrates. Experimental results reveal that the hydrogels formed were of non-uniform thicknesses ranging from zero to sixty microns. Also, the adherence of the hydrogels to the substrates was very poor. We hope some future changes in the hydrogel formation procedure will resolve the problems of non-uniform thickness and lack of adhesion. Before applying the hydrogel to a urinary catheter, the non-fouling properties of the hydrogel will also be tested.3Problem Statement Our objective is to form a Polyethylene glycol based hydrogel microlayer on material surfaces in order to examine and improve upon their characteristics and biocompatibility. When referring to biocompatibility, we are mainly focusing on the hydrogel’s non-fouling capabilities; meaning that no unwanted protein adhesion or interactions form when the hydrogel is placed in a physiological environment (1). The characteristics of greatest importance to the client, Arthur J. Coury, Vice President of Biomaterials Research at Genzyme Corp., are adhesion strength, biocompatibility, and a useable thickness. Adjustments to the existing Genzyme application process will be made in order to optimize these characteristics. Motivation The ultimate goal for this project is to coat a urinary catheter with a microlayer of PEG hydrogel that is approximately fifty microns thick, has very strong adherence, and is biologically inert with surface resistance to protein adhesion. We chose to coat this medical product because of the materials it is made out of, the current problems associated with its use, and the possible benefits of a PEG coating that are possible for a catheter. Urinary catheters are tube systems that are used to drain and collect urine from the bladder. They are often used when people have difficulty urinating on their own, have urinary incontinence, or urinary retention problems. There are several problems associated with long term catheter use. Urinary tract infection, kidney infection, blood infections, urethra damage, and blood in the urine are complications that can result from4continuous catheter use (2). These problems often happen because proteins adsorb on to the catheter surface and the Vroman effect ensues. This effect describes sequential sorption of proteins from a mixture, one on top of another over time. Protein desorption is unlikely, being thermodynamically and energetically unfavorable (3). These proteins build up and crystallize around the catheter, causing obstruction, blockage, backflow, and bacteria buildup (4). Since PEG is biologically inert, it should not interact with proteins of the body. By coating a catheter with this hydrogel we hope to eliminate the problems associated with protein crystallization and the subsequent infections that follow. Catheters are commonly made out of latex, silicon, polyvinyl chloride, and Teflon (2). Figure 1 shows pictures of multiple catheters including a straight catheter and a foley balloon catheter. Figure 1: Left, a straight catheter, right, a Foley balloon catheter (12,13) These materials work out well because latex and PVC are easily accessible resources that we can use for testing. PVC was obtained from blood bags donated by the American Red Cross. Latex will be obtained from non-powdered latex gloves. A common problem with catheters is that patients have an allergic reaction to latex catheters, which will hopefully be eliminated with a PEG coating. Catheters are currently coated with silver nitrates, antibiotics, and other materials in an effort to prevent infections and increase the catheter’s operational time in vivo. A study done on a variety5of silver alloys and oxides showed that the antimicrobial property of silver reduced the number of infections, but only from 14% (uncoated treatment), to 12% (silver coated treatment) (5). Also, the study mentioned that silver coated catheters are seven dollars more expensive than the uncoated version. The current coatings seem to limit infections, but we have not discovered any PEG coated catheters and hope to find that this hydrogel greatly improves infection resistance without greatly increasing cost. Client Requirements Dr. Coury would mainly like us to deliver a detailed procedure for applying a hydrogel to a material with the desired thickness and adherence. The client would like a uniform microlayer between 25 and 100 microns. The adhesion strength should be as high as possible, meaning strong force can be applied with a metal spatula and most of the hydrogel will remain adhered to the material. An illustrative example of this would be trying to remove the sticky label off a plastic soda bottle and not being able to get it all off. The client would also eventually like us to expose the hydrogels to physiologically imitated environments. In an effort to do this, we created all solutions at a pH of 7.35, which is the pH of the human body. We plan to expose the hydrogels to bovine albumin, which would show the interaction between the hydrogels and the most abundant protein in blood, accounting for roughly 60% of the plasma proteins (6). Hydrogels A Hydrogel is formed by networking polymer chains, commonly through crosslinking. The chains are water-soluble, and have remarkable absorption properties. In6some gels, over 99% of the weight is composed of water. Because of this water content, hydrogels maintain a great deal of flexibility, which mimics natural tissue. Common uses for hydrogels include contact lenses, disposable
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