Thesis - Master's of Science in Bioenginering
Clemson University, May 2018 - August 2019
My master's thesis investigated the elution of vancomycin from an infection-resistant orthopedic implant coating. The coating was created with ENBIO Ltd. (Dublin, Ireland) as part of Dr. Sarah Helms' Ph.D. project. I worked on an animal study, in vitro antibacterial testing, and materials characterization testing to analyze the coating and its release of antibiotics. A paper on this work is currently being revised for publication.
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My advisor for this project was Dr. John DesJardins, Professor of Bioengineering at Clemson University. My committee consisted of Dr. Jeffery Anker, Associate Professor of Analytical Chemistry at Clemson, and Dr. Jeremy Mercuri, Associate Professor of Bioengineering at Clemson. I also worked with Emily Shook (undergraduate bioengineering student at Clemson), Gretchen Schober (graduate chemistry student at Clemson), Liam O'Neill (ENBIO Ltd., Dublin, Ireland) and the team at Godley-Snell Research Center.
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Project Abstract
Implant infections are a critical concern in the biomedical field. The modification of implant surfaces to impart an infection-resistant layer has been done previously, most often through the addition of an antibiotic to the surface. The release of the antibiotic is critical to the coating’s success, as the antibiotic concentration in the body must maintain at or above the drug’s minimum inhibitory concentration long enough to prevent the bacteria in the wound from adhering to the implant and to allow the adhesion of host cells. This study investigated the release of vancomycin from a novel 3H-vancomycin and chitosan antibiotic coating to determine the coating’s elution rate and its antimicrobial effectiveness.
A novel 3H-vancomycin and chitosan coating was created and deposited on the surface of 10 mm diameter titanium coupons and 33 mm long titanium limited-contact dynamic compression plates via the BioDep™ plasma deposition process (ENBIO, Dublin, Ireland). Surface and antibacterial characteristics of the coating containing 3H-vancomycin were analyzed and compared to those of a coating without the tritium tracer. Surface properties including vancomycin quantity, surface roughness, and surface morphology were studied. Implants which received a coating that included 3H-vancomycin had a higher amount of vancomycin on the surface, were rougher, and had a different surface morphology than did uncoated implants or those coated with only regular vancomycin. Kirby-Bauer testing revealed that the implants with the radiolabeled coating had a higher degree of antibacterial efficacy, due to the higher amount of antibiotic on the surface.
An animal model was created using seven female New Zealand white rabbits. Bone and soft tissue histology revealed no negative effects of the coating on tissue morphology. Blood smears stained with a Brown-Brenn stain showed a reduction in bacterial presence between 12 and 48 hours post-implantation. IHC staining of soft tissues showed a small amount of vancomycin in the tissues of two of the rabbits, but due to the staining pattern, this result was considered to be a potential false positive. Low levels of radioactivity in the blood and tissue samples prevented the confirmation of vancomycin presence and elution by liquid scintillation analysis.
This study was able to successfully create a 3H-vancomycin and chitosan antibacterial coating, apply it to implants, and measure surface and in vitro antibacterial characteristics. Antibiotic elution was confirmed by the presence of vancomycin in the tissues. However, low radioactivity measurements in blood and tissue samples prevented this vancomycin elution from being quantified by liquid scintillation analysis. Future studies should test samples that have a standardized amount of vancomycin present on the surface, use a liquid scintillation counter with a lower limit of detection, and analyze more tissues to gain a proper understanding of vancomycin elution from the coating into the body.