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Antibacterial Strategies for Titanium Biomaterials
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. (Material i medicin)
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 [en]
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: urn:nbn:se:uu:diva-249181ISBN: 978-91-554-9241-0 (print)OAI: oai:DiVA.org:uu-249181DiVA: diva2:802929
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
List of papers
1. Photocatalytic activity of low temperature oxidized Ti-6Al-4V
Open this publication in new window or tab >>Photocatalytic activity of low temperature oxidized Ti-6Al-4V
2012 (English)In: Journal of materials science. Materials in medicine, ISSN 0957-4530, E-ISSN 1573-4838, Vol. 23, no 5, 1173-1180 p.Article in journal (Refereed) Published
Abstract [en]

Numerous advanced surface modification techniques exist to improve bone integration and antibacterial properties of titanium based implants and prostheses. A simple and straightforward method of obtaining uniform and controlled TiO2 coatings of devices with complex shapes is H2O2-oxidation and hot water aging. Based on the photoactivated bactericidal properties of TiO2, this study was aimed at optimizing the treatment to achieve high photocatalytic activity. Ti-6Al-4V samples were H2O2-oxidized and hot water aged for up to 24 and 72 h, respectively. Degradation measurements of rhodamine B during UV-A illumination of samples showed a near linear relationship between photocatalytic activity and total treatment time, and a nanoporous coating was observed by scanning electron microscopy. Grazing incidence X-ray diffraction showed a gradual decrease in crystallinity of the surface layer, suggesting that the increase in surface area rather than anatase formation was responsible for the increase in photocatalytic activity.

National Category
Engineering and Technology Nano Technology
Research subject
Engineering Science with specialization in Nanotechnology and Functional Materials; Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-174919 (URN)10.1007/s10856-012-4602-x (DOI)000303357600005 ()
Available from: 2012-05-30 Created: 2012-05-30 Last updated: 2017-12-07Bibliographically approved
2. Stability and prospect of UV/H2O2 activated titania films for biomedical use
Open this publication in new window or tab >>Stability and prospect of UV/H2O2 activated titania films for biomedical use
2013 (English)In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 285, no Part B, 317-323 p.Article in journal (Refereed) Published
Abstract [en]

Biomedical implants and devices that penetrate soft tissue are highly susceptible to infection, but also accessible for UV induced decontamination through photocatalysis if coated with suitable surfaces. As an on-demand antibacterial strategy, photocatalytic surfaces should be able to maintain their antibacterial properties over repeated activation. This study evaluates the surface properties and photocatalytic performance of titania films obtained by H2O2-oxidation and heat treatment of Ti and Ti-6Al-4V substrates, as well as the prospect of assisting photocatalytic reactions with H2O2 for improved efficiency. H2O2-oxidation generated a nanoporous coating, and subsequent heat treatment above 500 °C resulted in anatase formation. Tests using photo-assisted degradation of rhodamine B showed that prior to heat treatment, an initially high photocatalytic activity (PCA) of H2O2-oxidized substrates decayed significantly with repeated testing. Heat treating the samples at 600 °C resulted in stable yet lower PCA. Addition of 3% H2O2 during the photo-assisted reaction led to a substantial increase in PCA due to synergetic effects at the surface and H2O2 photolysis, the effect being most notable for non-heat treated samples. Both heat treated and non-heat treated samples showed stable PCA through repeated tests with H2O2-assisted photocatalysis, indicating that the combination of H2O2-oxidized titania films, UV light and added H2O2 can improve efficiency of these photocatalytic surfaces.

Keyword
TiO2, Heat treatment, Photocatalysis, Hydrogen peroxide photolysis, Synergy
National Category
Biomaterials Science Engineering and Technology
Research subject
Engineering Science with specialization in Materials Science; Engineering Science with specialization in Nanotechnology and Functional Materials
Identifiers
urn:nbn:se:uu:diva-211548 (URN)10.1016/j.apsusc.2013.08.057 (DOI)000326579400032 ()
Funder
Swedish Foundation for Strategic Research
Available from: 2013-11-26 Created: 2013-11-26 Last updated: 2017-12-06Bibliographically approved
3. Synergetic inactivation of Staphylococcus epidermidis and Streptococcus mutans in a TiO2/H 2O2/UV system
Open this publication in new window or tab >>Synergetic inactivation of Staphylococcus epidermidis and Streptococcus mutans in a TiO2/H 2O2/UV system
2013 (English)In: Biomatter, ISSN 2159-2535, Vol. 3, no 4, e26727- p.Article in journal (Refereed) Published
Abstract [en]

TiO 2 photocatalysis can be used to kill surface adherent bacteria on biomaterials, and is particularly interesting for use with percutaneous implants and devices. Its efficiency and safety, however, depend on the activation energy required. This in vitro study investigates synergetic effects against the clinically relevant strains S. epidermidis and S. mutans when combining photocatalytic surfaces with H 2O 2. After 20 min exposure to 0.1 wt% H 2O 2 and UV light on TiO 2 surfaces, viabilities of S. epidermidis and S. mutans were reduced by 99.7% and 98.9%, respectively. Without H 2O 2 the corresponding viability reduction was 86% for S. epidermidis and 65% for S. mutans. This study indicates that low concentrations of H 2O 2 can enhance the efficiency of photocatalytic TiO 2 surfaces, which could potentially improve current techniques used for decontamination and debridement of TiO 2 coated biomedical implants and devices.

Keyword
antibacterial, photocatalysis, photolysis, synergy, titanium dioxide, hydrogen peroxide, UV light
National Category
Biomaterials Science Engineering and Technology
Research subject
Engineering Science with specialization in Nanotechnology and Functional Materials; Engineering Science with specialization in Materials Science
Identifiers
urn:nbn:se:uu:diva-211547 (URN)10.4161/biom.26727 (DOI)24135830 (PubMedID)
Funder
Swedish Foundation for Strategic Research
Available from: 2013-11-26 Created: 2013-11-26 Last updated: 2015-05-12Bibliographically approved
4. Reactive combinatorial synthesis and characterization of a gradient Ag–Ti oxide thin film with antibacterial properties
Open this publication in new window or tab >>Reactive combinatorial synthesis and characterization of a gradient Ag–Ti oxide thin film with antibacterial properties
2015 (English)In: Acta Biomaterialia, ISSN 1742-7061, E-ISSN 1878-7568, Vol. 11, 503-510 p.Article in journal (Refereed) Published
Abstract [en]

The growing demand for orthopedic and dental implants has spurred researchers to develop multifunc- tional coatings, combining tissue integration with antibacterial features. A possible strategy to endow titanium (Ti) with antibacterial properties is by incorporating silver (Ag), but designing a structure with adequate Ag+ release while maintaining biocompatibility has been shown difficult. To further explore the composition–structure–property relationships between Ag and Ti, and its effects against bacteria, this study utilized a combinatorial approach to manufacture and test a single sample containing a binary Ag–Ti oxide gradient. The sample, sputter-deposited in a reactive (O2) environment using a custom-built combinatorial physical vapor deposition system, was shown to be effective against Staphylococcus aureus with viability reductions ranging from 17 to above 99%, depending on the amount of Ag+ released from its different parts. The Ag content along the gradient ranged from 35 to 62 wt.%, but it was found that structural properties such as varied porosity and degree of crystallinity, rather than the amount of incor- porated Ag, governed the Ag+ release and resulting antibacterial activity. The coating also demonstrated in vitro apatite-forming abilities, where structural variety along the sample was shown to alter the hydrophilic behavior, with the degree of hydroxyapatite deposition varying accordingly. By means of combinatorial synthesis, a single gradient sample was able to display intricate compositional and structural features affecting its biological response, which would otherwise require a series of coatings. The current findings suggest that future implant coatings incorporating Ag as an antibacterial agent could be structurally enhanced to better suit clinical requirements. 

Keyword
Combinatorial materials science, Physical vapor deposition, Antibacterial, Silver, Titanium
National Category
Materials Engineering
Research subject
Engineering Science with specialization in Materials Science; Engineering Science with specialization in Nanotechnology and Functional Materials
Identifiers
urn:nbn:se:uu:diva-236382 (URN)10.1016/j.actbio.2014.09.048 (DOI)000347747900048 ()25281786 (PubMedID)
Projects
ProViking
Funder
Swedish Foundation for Strategic Research
Note

Epub 2014 Oct 02

Available from: 2014-11-19 Created: 2014-11-19 Last updated: 2017-12-05Bibliographically approved
5. In vitro antibacterial properties and UV induced response from Staphylococcus epidermidis on Ag/Ti oxide thin films
Open this publication in new window or tab >>In vitro antibacterial properties and UV induced response from Staphylococcus epidermidis on Ag/Ti oxide thin films
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. 

Keyword
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:nbn:se:uu:diva-249179 (URN)10.1007/s10856-015-5662-5 (DOI)000368728100007 ()26758896 (PubMedID)
Projects
ProViking EBM
Funder
Swedish Foundation for Strategic Research
Available from: 2015-04-12 Created: 2015-04-12 Last updated: 2017-12-04Bibliographically approved

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