Antibacterial Strategies for Titanium Biomaterials

74 Pages·2015·2.61 MB·English

Digital Comprehensive Summaries of Uppsala Dissertations
from the Faculty of Science and Technology 1250
Antibacterial Strategies for
Titanium Biomaterials
ERIK UNOSSON
ACTA
UNIVERSITATIS
ISSN 1651-6214
UPSALIENSIS
ISBN 978-91-554-9241-0
UPPSALA
urn:nbn:se:uu:diva-249181
2015
Dissertation presented at Uppsala University to be publicly examined in Siegbahn Hall,
The Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, Friday, 5 June 2015 at 09:15 for
the degree of Doctor of Philosophy. The examination will be conducted in English. Faculty
examiner: Professor Timo Närhi (University of Turku, Finland).
Abstract
Unosson, E. 2015. Antibacterial Strategies for Titanium Biomaterials. Digital Comprehensive
Summaries of Uppsala Dissertations from the Faculty of Science and Technology 1250. 72 pp.
Uppsala: Acta Universitatis Upsaliensis. ISBN 978-91-554-9241-0.
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; TiO photocatalysis, where a surface can become antibacterial upon irradiation with
2
UV light; and incorporation of silver, where a subsequent release of silver metal ions result in
an antibacterial effect.
For the TiO photocatalysis strategy, a simple and cost effective chemical oxidation technique,
2
using hydrogen peroxide (HO) and water, was used to create an active TiO surface on
2 2 2
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 HO-oxidation
2 2
process, rather than generation of ROS from a heterogeneous photocatalytic process, was
responsible for the effect. This discovery was further exploited in a TiO/HO/UV system, which
2 2 2
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 (O) environment using a custom
2
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 TiO can enhance photocatalytic properties. In this work, however, the TiO was
2 2
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 TiO photocatalysis, or UV induced activation
2
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.
Keywords: Titanium, silver, biomaterial, antibacterial, photocatalysis, hydrogen peroxide,
reactive oxygen species, combinatorial materials science
Erik Unosson, Department of Engineering Sciences, Applied Materials Sciences, Box 534,
Uppsala University, SE-75121 Uppsala, Sweden.
© Erik Unosson 2015
ISSN 1651-6214
ISBN 978-91-554-9241-0
urn:nbn:se:uu:diva-249181 (http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-249181)
“Truth is stranger than fiction”
Probably Lord Byron
To friends and family

List of Papers
This thesis is based on the following papers, which are referred to in the text
by their Roman numerals.
I Unosson, E., Persson, C., Welch, K., Engqvist, H. (2012) Photocata-
lytic activity of low temperature oxidized Ti-6Al-4V. Journal of
Materials Science: Materials in Medicine, 23(5):1173–1180.
II Unosson, E., Welch, K., Persson, C., Engqvist, H. (2013) Stability
and prospect of UV/H O activated titania films for biomedical use.
2 2
Applied Surface Science. 285:317–323.
III Unosson, E., Tsekoura, E.K., Engqvist, H., Welch, K. (2013) Syn-
ergetic inactivation of Staphylococcus epidermidis and Streptococ-
cus mutans in a TiO /H O /UV system. Biomatter, 3(4):1-6
2 2 2
IV Unosson, E., Rodriguez, D., Welch, K., Engqvist, H. (2015) Reac-
tive combinatorial synthesis and characterization of a gradient Ag-Ti
oxide thin film with antibacterial properties, Acta Biomaterialia.
11:503–510
V Unosson, E., Morgenstern, M., Engqvist, H., Welch, K. In vitro an-
tibacterial properties and UV induced SOS response from Staphylo-
coccus epidermidis on Ag/Ti oxide thin films. Submitted
Reprints were made with permission from the respective publishers.
Author’s Contributions
Paper I Major part of planning and evaluation. All experimental
work and major part of writing.
Paper II Major part of planning and evaluation. All experimental
work and major part of writing.
Paper III Part of planning and experimental work. Major part of eval-
uation and writing.
Paper IV Major part of planning, evaluation, experimental work and
writing.
Paper V Major part of planning and evaluation. Part of experimental
work and major part of writing.
Also published
López, A., Unosson, E., Engqvist, H., Persson, C. (2011) Direct and in-
teractive effects of three variables on properties of PMMA bone cement
for vertebral body augmentation, Journal of Materials Science: Materials
in Medicine. 22(6):1599–1606.
Engstrand, J., Unosson, E., Engqvist, H. (2012) Hydroxyapatite For-
mation on a Novel Dental Cement in Human Saliva, ISRN Dentistry.
2012, Article ID: 624056, 7 pages.
Persson, C., Unosson, E., Ajaxon, I., Engstrand, J., Engqvist, H., Xia, W.
(2012) Nano grain sized zirconia–silica glass ceramics for dental applica-
tions. Journal of the European Ceramic Society, 32(16):4105–4110.
Unosson, E., Cai, Y., Jiang, X., Lööf, J., Welch, K., Engqvist, H. (2012)
Antibacterial properties of dental luting agents: potential to hinder the
development of secondary caries. International Journal of Dentistry,
2012, Article ID: 529495, 7 pages.

Contents
Introduction .................................................................................................. 13

Aims and objectives ..................................................................................... 15

Titanium as a biomaterial ............................................................................. 16

Bacterial colonization and infection ............................................................. 19

Photocatalysis on TiO ................................................................................. 22

2
Chemical oxidation with H O ..................................................................... 24

2 2
Photocatalytic activity ............................................................................. 25

Surface characteristics ............................................................................. 27

Synergies in the TiO /H O /UV system ....................................................... 28

2 2 2
Added benefits with added H O ............................................................. 29

2 2
Stability of the system ............................................................................. 32

Effects against bacteria ............................................................................ 33

Silver as an antibacterial agent ..................................................................... 36

Mechanism of action ............................................................................... 36

Combinatorial materials science .................................................................. 38

Physical vapor deposition ........................................................................ 40

Composition-structure-property relationships .............................................. 41

Gradient thin film characteristics ............................................................ 41

Resulting properties ................................................................................. 44

UV-induced SOS response ........................................................................... 48

Photocatalysis on Ag-doped TiO ........................................................... 48

2
New gradient characteristics .................................................................... 49

Secondary effects of UV illumination ..................................................... 50

Concluding remarks ..................................................................................... 54

Future challenges .......................................................................................... 55

Analytical techniques ................................................................................... 56

Rhodamine B degradation ....................................................................... 56
Scanning electron microscopy (SEM) ..................................................... 57

Energy dispersive X-ray spectroscopy (EDS) ......................................... 57

Focused ion beam (FIB) .......................................................................... 58

Grazing incidence X-ray diffraction (GI-XRD) ...................................... 58

Surface roughness (R , R ) ...................................................................... 59

a q
Contact angle (CA) measurements .......................................................... 59

Bacterial viability assays ......................................................................... 59

Inductively coupled plasma–atomic emission spectroscopy (ICP-AES) 61

Svensk sammanfattning ................................................................................ 62

Acknowledgements ...................................................................................... 64

References .................................................................................................... 66