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In vitro antibacterial properties and UV induced response from Staphylococcus epidermidis on Ag/Ti oxide thin films
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. (Material i medicin)
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. (Material i Medicin)
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. (Material i medicin)
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Nanotechnology and Functional Materials.
2016 (English)In: Journal of materials science. Materials in medicine, ISSN 0957-4530, E-ISSN 1573-4838, Vol. 27, no 3, 49Article in journal (Refereed) Published
Abstract [en]

Implanted materials are susceptible to bacterial colonization and biofilm formation, which can result in severe infection and lost implant function. UV induced photocatalytic disinfection on TiO2 and release of Ag+ ions are two promising strategies to combat such events, and can be combined for improved efficiency. In the current study, a combinatorial physical vapor deposition technique was utilized to construct a gradient coating between Ag and Ti oxide, and the coating was evaluated for antibacterial properties in darkness and under UV light against Staphylococcus epidermidis. The findings revealed a potent antibacterial effect in darkness due to Ag+ release, with near full elimination (97%) of viable bacteria and visible cell lysis on Ag dominated surfaces. The photocatalytic activity, however, was demonstrated poor due to low TiO2 crystallinity, and UV light irradiation of the coating did not contribute to the antibacterial effect. On the contrary, bacterial viability was in several instances higher after UV illumination, proposing a UV induced SOS response from the bacteria that limited the reduction rate during Ag+ exposure. Such secondary effects should thus be considered in the development of multifunctional coatings that rely on UV activation. 

Place, publisher, year, edition, pages
2016. Vol. 27, no 3, 49
Keyword [en]
Silver; Titanium; UV; Antibacterial; SOS response; S. epidermidis
National Category
Medical Materials Materials Engineering Nano Technology
Research subject
Engineering Science with specialization in Materials Science
Identifiers
URN: urn:nbn:se:uu:diva-249179DOI: 10.1007/s10856-015-5662-5ISI: 000368728100007PubMedID: 26758896OAI: oai:DiVA.org:uu-249179DiVA: diva2:802245
Projects
ProViking EBM
Funder
Swedish Foundation for Strategic Research
Available from: 2015-04-12 Created: 2015-04-12 Last updated: 2017-12-04Bibliographically approved
In thesis
1. Antibacterial Strategies for Titanium Biomaterials
Open this publication in new window or tab >>Antibacterial Strategies for Titanium Biomaterials
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Titanium and titanium based alloys are widely used in dentistry and orthopedics to replace hard tissue and to mend broken bones. It has become a material of choice due to its low density, high strength, good biocompatibility and its capacity to integrate closely with the bone. Today, modern materials and surgical techniques can enable patients to live longer, and aid in maintaining or regaining mobility for a more fulfilling life. There are, however, instances where implants fail, and one of the primary causes for implant failure is infection.

This thesis deals with two possible ways of reducing or eliminating implant associated infections; TiO2 photocatalysis, where a surface can become antibacterial upon irradiation with UV light; and incorporation of silver, where a subsequent release of silver metal ions result in an antibacterial effect.

For the TiO2 photocatalysis strategy, a simple and cost effective chemical oxidation technique, using hydrogen peroxide (H2O2) and water, was used to create an active TiO2 surface on titanium substrates. This surface was shown to effectively degrade an organic model substance (rhodamine B) by generating reactive oxygen species (ROS) under UV illumination. However, it was shown that Ti-peroxy radical species remaining in the surface after the H2O2-oxidation process, rather than generation of ROS from a heterogeneous photocatalytic process, was responsible for the effect. This discovery was further exploited in a TiO2/H2O2/UV system, which demonstrated synergy effects in both rhodamine B degradation tests and in antibacterial assays.

For the silver ion release strategy, a combinatorial materials science approach was employed. Binary Ag-Ti oxide gradients were co-deposited in a reactive (O2) environment using a custom built physical vapor deposition system, and evaluated for antibacterial properties. The approach enabled synthesis and composition-structure-property evaluation unlikely to have been achieved by traditional means, and the gradient coatings demonstrated antibacterial properties against both S. aureus and S. epidermidis according to silver ion release. The release was shown to depend more on structural features, such as surface area, crystallinity and oxidation state, than on composition.

Ag-Ti oxide gradients were also evaluated under UV illumination, as Ag deposits on crystalline TiO2 can enhance photocatalytic properties. In this work, however, the TiO2 was amorphous and UV illumination caused a slight reduction in the antibacterial effect of silver ions. This was attributed to a UV-induced SOS response in the S. epidermidis bacteria.

The results of this thesis demonstrate that both TiO2 photocatalysis, or UV induced activation of Ti-peroxy radical species, as well as incorporation of silver are viable antibacterial strategies for titanium biomaterials. However, their clinical applications are still pending risk-benefit analyses of potential adverse host tissue responses. 

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. 72 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1250
Keyword
Titanium, silver, biomaterial, antibacterial, photocatalysis, hydrogen peroxide, reactive oxygen species, combinatorial materials science
National Category
Materials Engineering Medical Materials
Research subject
Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-249181 (URN)978-91-554-9241-0 (ISBN)
Public defence
2015-06-05, Siegbahn Hall, The Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Funder
Swedish Foundation for Strategic Research
Available from: 2015-05-12 Created: 2015-04-12 Last updated: 2015-07-07

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Unosson, ErikEngqvist, HåkanWelch, Ken

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