Date of Award

12-2011

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Bioengineering

Advisor

Vertegel, Alexey

Committee Member

Chumanov , George

Committee Member

Webb , Ken

Abstract

Postoperative wound site infections remain a major source of illness with approximately 500,000 infections per year, among an estimated 27 million surgical procedures. Such infections account for approximately one quarter of the estimated 2 million nosocomial infections in the United States which causes about 90,000 deaths each year. More than 70% of the bacteria that causes such infections are resistant to at least one of the antibiotics and result in longer hospitalization; besides requiring second option treatments that may be less effective, more toxic and expensive. Hence, there is a frenetic search for alternatives and in this regard, antimicrobial peptides and metallic nanoparticle like silver and copper, which possess broad spectrum antimicrobial activity and evince low rates of resistance, are touted to play major roles. This study looks to achieve two major objectives-1) to tackle surgical site infections specifically due to hernia meshes, using a novel antimicrobial peptide as a coating and 2) to explore the possibility of using copper nanoparticles as a viable alternative to nanocrystalline silver in topical wound dressings, wherein it performs the dual role of preventing infections and promoting wound healing.
With regards to the first objective, the study demonstrated that both synthetic and biological meshes coated with the enzyme were active against S.aureus, the pathogenic species of interest. The bactericidal effect could largely be attributed to leached enzyme in the case of synthetics but to a lesser extent in the case of biologics. The long term viability of this coating was proven by performing accelerated one year equivalent shelf life studies; with no apparent loss in enzyme activity. Also, the protective effects of the biologic mesh against denaturation of the enzyme during sterilization and lyophilization were noted. All these results indicate that such a peptide based coating could act as a viable alternative to currently available antibiotic therapy in treating mesh related infections.
The progress made on the second objective is basically restricted to analyzing the infection control aspect and host cell cytotoxicity of these copper nanoparticles. 2 nm copper nanoparticles stabilized with polyacrylic acid were synthesized and antibody attachment was carried out by physical adsorption. An optimum antibody: nanoparticle ratio of 1:1 showed a six times and ten times lower minimum inhibitory concentration (MIC) than the bare nanoparticles, for two different strains of P.aeruginosa. However, this effect was not significant for gram positive S.aureus and varying the antibody ratio did not affect the MIC's. The antibody effect was only seen at a low nanoparticle concentration and this could be a possible reason why its effect was relatively less pronounced in S.aureus, as its possesses a significantly higher MIC than P.aeruginosa; proving that its less susceptible to these copper nanoparticles. Also, the mechanism of antibody related targeting needs to be investigated as non-specific antibody produced the same effect as that of the specific antibody. This is probably due to the fact that the antibodies, which can theoretically bind a few nanoparticles per molecule, lead to a local increase in nanoparticle concentration when they encounter bacteria and this effect is prominent only at low nanoparticle concentrations. The host cytotoxicity issues associated with the usage of such metallic nanoparticles was studied using MTT assay and it showed that the nanoparticles were more toxic towards the fibroblasts than bacteria even at sub MIC concentrations thereby practically ruling out its applicability as a topical wound healing agent. Hence, work needs to be done to possibly encapsulate these particles into a biocompatible matrix thereby preventing host cytotoxicity while selectively attracting bacteria into it by providing directional cues.
The approaches developed here are universal and can potentially be used for treatment of other surgical device-associated infections.

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