Tea tree oil derived plasma polymer films: biocompatibility, antibiofilm effects and fundamental properties

Igras, Emma Toni (2012) Tea tree oil derived plasma polymer films: biocompatibility, antibiofilm effects and fundamental properties. Masters (Research) thesis, James Cook University.

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Novel plasma polymer thin films derived from tea tree oil have the potential to act as biocompatible, infection resistant surface coatings for medical implants. In order to prove or disprove this hypothesis, variant thin films were manufactured then characterized by determining a set of fundamental properties. Polymers were tested for biocompatibility by murine implantation and semi-quantitative histological analysis of the implant site. Finally polymer infection resistance was assessed by enumeration of bacterial biofilm growth onto polymer housed within a biofilm culture circuit.

Background: Implanted medical devices (IMDs) are ensconced in all areas of modern healthcare and their role is expanding. IMDs encompass a broad spectrum of temporary and permanent devices including catheters, sutures, joint replacements, intraocular lenses and cardiac valves to name a few. Demand for medical implants is fuelled by an aging Western population where devices replace damaged, worn and diseased tissues, aid in administration of supportive therapies or act as diagnostic equipment. Development of increasingly sophisticated implanted medical devices is greatly facilitated by advancing analytic, production, materials and information technologies. In combination, demand for medical implants and the ability to produce them support a large scale, multi-billion dollar medical implant industry. The two main causes of IMD failure are lack of biocompatibility and biofilm related implant infection. A biocompatible surface treatment that kills biofilm therefore has potential to reduce the massive morbidity and financial burdens associated with failed medical implants. Since the advent of modern implant medicine, a select group of 20 or so synthetic, biocompatible polymers including poly(ethylene), poly(urethane) and poly(vinyl chloride) have dominated implant production. Although touting excellent biocompatibility profiles, none of these well used biopolymers demonstrate active antibiofilm activity. Attempts to confer infection resistance to medical implants based on traditional polymers have proven expensive, contributed to bacterial resistance and have shown little efficacy. The major obstacle to reducing IMD infection is pathological biofilm. Biofilm is a tenacious form of resistant bacteria sequestered in a protective matrix irreversibly attached to an implant surface. The medical device industry’s quest for a biocompatible surface polymer with durable antibiofilm effects is ongoing. Tea tree oil (TTO) is an essential oil harvested from an Australian plant and it kills bacterial biofilm. TTO vapor can be used to create novel surface coatings through plasma polymerization. Plasma polymers are a new and unique class of biocompatible thin films that adhere to almost any surface. Under controlled production parameters, plasma polymers inherit desirable functional groups from parent monomer. Plasma polymer films built from TTO may therefore exhibit the class property of biocompatibility and preserve antibiofilm functions of essential oil precursors. If so, TTO plasma polymer thin films have potential as a new breed of biocompatible, anti-infective medical implant coatings.

Methods: TTO derived plasma polymer thin films were generated in the laboratory under three different power parameters (25, 50 and 75 W). Biocompatibility of novel polymer thin films was determined by implanting polymer coated discs into BALB/c mice. Explanted specimens were scrutinized histo-pathologically and compared to biocompatible controls using a semi-quantitative descriptor. Antibiofilm effect was gauged by quantifying biofilm growth on polymer films placed into a biofilm culture circuit. Clinically relevant Staphylococcal bacterial isolates were sourced to populate the biofilm generating circuit. The new materials underwent limited and relevant fundamental properties testing as a characterization tool. Properties assessed included film thickness as a function of deposition time, surface topography, hardness, degradation on exposure to ethanol and water, refractive index and dielectric constant.

Results: Results of biocompatibility testing showed little significant difference between TTO derived plasma polymers and control. Skin-implant interactions culminating in sinus formation were the main complication. Microscopically, tissue capsules around TTO polymer implants matured more quickly than control capsules but by 28 days groups were equal in capsular maturity. Small numbers made for weak statistical conclusions. Novel TTO derived plasma polymer thin films were not born out as antibiofilm coatings. PTFE control surfaces placed within the biofilm culture circuit produced fewer colony forming units than any TTO polymer film (p<0.01). All TTO polymer variants behaved similarly. S.epidermidis made less biofilm than S.aureus. Production times for plasma polymer thin films were short with films in the micron range deposited in less than an hour. A quadratic relationship between film thickness and deposition time was noted. As a group, the films were extremely smooth and pinhole free with hardness (0.5 to 0.8 GPa) and dielectric constant (2.46 to 2.63) comparable to conventional medical grade polymer coatings. Refractive index of 1.5 was consistent with film transparency similar to standard glass. Films degraded more rapidly in alcohol than in water.

Conclusions and Implications: TTO derived plasma polymer thin films are a new class of biocompatible surface treatments with potential to act as coatings for IMDs. Fundamental property analysis shows polymers can be produced in a time efficient manner and share similar physical properties with traditionally employed medical polymers. The films were not deemed to have antibiofilm effects. Several avenues of investigation are suggested in order to define the potentials and limitations of TTO plasma polymer thin films as medical coatings. Isolation of the functional antimicrobial moieties from the blend of monomers within TTO would lead to more tailored substrate selection. Expansion and control of polymer fabrication parameters would support discovery of the spectrum of product that can be manufactured and any adjustable polymer properties. Detailed chemical, molecular and structural analysis of films would help better characterize the surfaces. Interaction of films with biofilm and host could then be better understood and optimized leading to improved biocompatibility and antibiofilm performance.

Item ID: 29140
Item Type: Thesis (Masters (Research))
Keywords: biocompatible; biofilm; implanted medical device (IMD); plasma polymer; tea tree oil; thin film; surface coating material; polymer infection resistance
Date Deposited: 05 Sep 2013 22:30
FoR Codes: 09 ENGINEERING > 0903 Biomedical Engineering > 090399 Biomedical Engineering not elsewhere classified @ 50%
10 TECHNOLOGY > 1004 Medical Biotechnology > 100499 Medical Biotechnology not elsewhere classified @ 50%
SEO Codes: 92 HEALTH > 9202 Health and Support Services > 920299 Health and Support Services not elsewhere classified @ 25%
92 HEALTH > 9201 Clinical Health (Organs, Diseases and Abnormal Conditions) > 920199 Clinical Health (Organs, Diseases and Abnormal Conditions) not elsewhere classified @ 25%
97 EXPANDING KNOWLEDGE > 970111 Expanding Knowledge in the Medical and Health Sciences @ 50%
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