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Development of titanium-copper alloys for dental applications
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. (Materials in Medicine)
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Description
Abstract [en]

Titanium alloys find wide application in the medical implants industry, which includes areas of orthopaedic and dental implants. The reason for the popularity of the material is high mechanical strength, low density, and reported growth of bone onto the material, as well as corrosion resistance. Despite the general success of titanium materials, a drawback is that it is vulnerable to bacterial colonization, which can cause implant failure through inflammatory diseases. Peri-implantitis is one such disease, which can lead to irreversible bone loss and subsequently implant instability.

This thesis focuses on the use of copper (Cu) as an antibacterial element in titanium alloys, where the purpose is designing inherently antibacterial materials.

With an understanding that copper can reduce bacterial populations by ion release of Cu into solutions, as well as by direct contact of bacteria with Cu surfaces: studies on the effect of Cu ions on bacteria and cells were conducted, in addition to studies on Ti-Cux alloys.

Varying Cu concentrations in solution were introduced to bacteria (Staphylococcus epidermidis) and cells (MC3T3 murine calvarial osteoblasts), and it was found that the lethal dosage for Cu ions was in the range from 9x10-5 to 9x10-6 g/ml, for bacteria and cells. The Cu ions were also found to cause a stress response for this bacteria at concentrations between 9x10-6 to 9x10-7 g/ml, and recommended to be avoided for implant materials.

For Ti-Cux binary alloys, studies established that a 10wt%Cu alloy, which released 9x10-8 g/ml, reduced the bacterial population by 27 % in 6 hours in a direct contact test. This alloy was found to be composed of intermetallic (Ti2Cu) and hexagonal closed packed titanium (HCP-Ti) crystals. A separate study on aged heat treated Ti-Cux alloys, showed that an additional phase of Ti3Cu was present in lower volume fraction. The aged alloys of Ti-Cux showed higher volume fraction of Ti2Cu but only a slightly higher antibacterial ability, compared to those without ageing. The hardness of the Ti-Cux alloys was however detrimentally affected by ageing, especially for the 10wt%Cu alloy.

Investigations on the alloying of Cu with an existing implant alloy, Ti-10wt%Ta-1.6wt%Nb-1.7wt%Zr (TNTZ), was also performed and at higher wt%Cu alloys with three-phased microstructures were present. Alloying of Cu in the TNTZ material increased hardness and with further development of this novel alloy, a potential biomaterial for clinical applications could be designed.

In conclusion, the results of this thesis demonstrate that the use of Cu in proximity to cells and bacteria requires dose dependent consideration for material design, so that antibacterial materials can be developed that do not harm tissue. The appropriate design of alloys can also be performed so as to allow antibacterial ability to be achieved, along with ensuring appropriate mechanical and corrosion properties. Furthermore, Cu as an antibacterial element can be alloyed into various titanium alloy systems and with further development in this area; antibacterial alloys could benefit the implant industry and patients alike.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2019. , p. 65
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1868
Keywords [en]
Titanium, copper, antibacterial, Ti2Cu, biomaterials, Staphylococcus epidermidis, MC3T3 cells
National Category
Medical Materials
Identifiers
URN: urn:nbn:se:uu:diva-395303ISBN: 978-91-513-0782-4 (print)OAI: oai:DiVA.org:uu-395303DiVA, id: diva2:1361806
Public defence
2019-12-13, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2019-11-18 Created: 2019-10-17 Last updated: 2019-11-18
List of papers
1. Effect of copper ion concentration on bacteria and cells
Open this publication in new window or tab >>Effect of copper ion concentration on bacteria and cells
2019 (English)In: MDPI Materials Biomaterial, ISSN 1996-1944Article in journal (Refereed) Submitted
Abstract [en]

In the oral cavity dental implants - most often made of commercially pure titanium - come in contact with bacteria, and antibacterial management has been researched extensively to improve patient care. Antibiotic resistance becoming increasingly prevalent, have resulted in copper being investigated as an antibacterial element in alloys. In this study the objective was to investigate the copper ion concentrations at which cyto-toxicity is avoided while bacterial inhibition is ensured, by comparing Cu ion effects on selected eukaryotes and prokaryotes. To determine relevant copper ion concentrations, ion release rates from copper and a 10wt%Cu Ti-alloy were investigated. Survival studies were performed on MC3T3 cells and Staphylococcus epidermidis bacteria, after exposure to Cu ions concentrations ranging from 9x10-3 to 9x10-12 g/ml. Cell survival increased from <10% to >90% after 24 hours of exposure, by reducing Cu concentrations from 9x10-5 to 9x10-6 g/ml. Survival of bacteria also increased in the same range of Cu concentrations. The maximum bacteria growth was found at 9x10-7 g/ml, probably due to stress response. In conclusion, the minimum inhibitory concentrations of Cu ions for these prokaryotes and eukaryotes were found in the range from 9x10-5 to 9x10-6 g/ml. Interestingly the Cu ion concentration correlating to the release rate of the 10wt%Cu alloy (9x10-8 g/ml) did not kill the bacteria, although this alloy has previously been found to be antibacterial. Further studies should investigate in-depth the bacteria killing mechanism of copper.

Keywords
Copper ion, Ion release, Antibacterial, S. Epidermidis, MC3T3
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:uu:diva-395279 (URN)
Available from: 2019-10-16 Created: 2019-10-16 Last updated: 2019-10-17
2. Antibacterial investigation of titanium-copper alloys using luminescent Staphylococcus epidermidis in a direct contact test
Open this publication in new window or tab >>Antibacterial investigation of titanium-copper alloys using luminescent Staphylococcus epidermidis in a direct contact test
Show others...
2019 (English)In: Materials science & engineering. C, biomimetic materials, sensors and systems, ISSN 0928-4931, E-ISSN 1873-0191, Vol. 97, p. 707-714Article in journal (Refereed) Published
Abstract [en]

Commercially pure titanium (CP-Ti), used as oral implants, is often populated by various bacterial colonies in the oral cavity. These bacteria can cause Peri-implantitis, leading to loss of bone tissue and failure of implants. With the increased awareness of antibiotic resistance, research has been directed towards alternative solutions and recent findings have indicated titanium-copper (Ti-Cu) alloys as a promising antibacterial material. The aim of this study was to produce homogeneous Ti-Cu alloys, with various concentrations of copper, and to characterise their antibacterial properties through direct contact tests, using luminescent bacteria, in addition to traditional materials characterisation techniques. Samples of CP-Ti and four different Ti-Cu alloys (1, 2.5, 3 and 10 wt%Cu) were produced in an arc-furnace, heated treated and rapidly quenched. X-ray diffraction revealed that Ti2Cu, was present only in the 10 wt%Cu alloy, however, scanning electron microscopy (SEM) indicated precipitates at the grain boundaries of the 3 wt%Cu alloy, which were confirmed to be of a copper rich phase by energy dispersive x-ray spectroscopy (EDS) analysis. EDS line scans confirmed that the alloys were homogenous. After 6 h, a trend between copper content and antibacterial rate could be observed, with the 10 wt%Cu alloy having the highest rate. SEM confirmed fewer bacteria on the 3 wt%Cu and especially the 10 wt%Cu samples. Although the 10 wt%Cu alloy gave the best antibacterial results, it is desired that the Cu concentration is below similar to 3 wt%Cu to maintain similar mechanical and corrosive performance as CP-Ti. Therefore, it is proposed that future work focuses on the 3 wt%Cu alloy.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE BV, 2019
Keywords
Copper, Titanium, Antibacterial, S. epidermidis, Ti2Cu
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:uu:diva-378615 (URN)10.1016/j.msec.2018.12.050 (DOI)000457952800069 ()30678959 (PubMedID)
Available from: 2019-03-11 Created: 2019-03-11 Last updated: 2019-10-17Bibliographically approved
3. Development of antibacterial Ti-Cux alloys for dental applications: effects of ageing for alloys with up to 10wt%Cu
Open this publication in new window or tab >>Development of antibacterial Ti-Cux alloys for dental applications: effects of ageing for alloys with up to 10wt%Cu
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Peri-implantitis is a disease caused by bacteria, affecting dental implants in patients, who later require antibiotic treatments to avoid implant failure. This treatment has become more complicated recently due to growing antibiotic resistance. Titanium-copper alloys are a class of materials proposed to be appropriate as antibacterial biomaterials and have the potential to be a remedy against peri-implantitis and antibiotic resistance.

 

The aim of this study was to investigate materials in the Ti-Cux class, exploring how Cu content (up to 10%) and ageing affect the material and antibacterial properties. The use of electron microscopy, X-ray diffraction, hardness testing, bacteriological culture and electrochemical testing were employed to characterize the materials.

It was found that the alloys had two phases with Cu additions above 3 wt% and ageing increased the volume fraction of the Ti2Cu intermetallic compound. The hardness gradually increased with increased Cu additions, while ageing only affected the alloy with 10 wt%Cu dramatically (due to changes in microstructure). Ageing significantly decreased the corrosion rates of the Ti-Cux alloys. The aged 10wt%Cu alloy was the only alloy with an antibacterial effect after two hours, while after six hours bacteria killing occurred in all alloys with Cu additions above 5wt%.

 

In conclusion, it was possible to tune the material and antibacterial properties of Ti-Cux alloys by %Cu addition and ageing steps, which makes further optimisation towards an antibacterial material promising.

 

Keywords
titanium alloys, copper, Ti2Cu, biomaterial, antibacterial
National Category
Medical Materials
Identifiers
urn:nbn:se:uu:diva-395300 (URN)
Available from: 2019-10-16 Created: 2019-10-16 Last updated: 2019-10-17
4. Investigation of copper alloying in a TNTZ-Cux alloy
Open this publication in new window or tab >>Investigation of copper alloying in a TNTZ-Cux alloy
2019 (English)In: MDPI Materials Biomaterials, ISSN 1996-1944Article in journal (Refereed) Submitted
Abstract [en]

Alloying titanium with copper has recently been investigated with the aim to develop an antibacterial alloy. However, due to the low strength of pure titanium, alloys such as Ti-Nb-Ta-Zr have been developed. In the present study, an existing Ti-1.6wt.%Nb-10wt.%Ta-1.7wt.%Zr (TNTZ) material – that was initially designed to have higher strength than grade 4 titanium and closer to that of Ti-6Al-4V - was alloyed with copper to investigate its effect on the microstructure, as a first step towards the development of a novel antibacterial material. 

The initial design and modelling of the alloy system was performed using CALPHAD methods, to predict the phase transformations in the alloy. Following predictions, the alloys were produced using arc melting with appropriate heat treatments. The alloys were characterized using energy dispersive X-ray spectroscopy in scanning transmission electron microscopy (STEM-EDS) with transmission Kikuchi diffraction (TKD).

The manufactured alloys had a three-phased crystal structure that was found in the alloys with 3wt.%Cu and higher, in line with the modelled alloy predictions. The phases included the α-Ti (HCP-Ti) with some Ta present in the crystal, Ti2Cu, and a bright phase with Ti, Cu and Ta in the crystal. The Ti2Cu crystals tended to precipitate in the grain boundaries of the α-Ti phase and bright phase. The hardness of the alloys increased with increased Cu addition, as did the presence of the Ti2Cu phase. Further studies to optimize the alloy could result in a suitable material for dental implants.

Keywords
Titanium alloy; microstructures; biomaterial, TNTZ
National Category
Medical Materials
Identifiers
urn:nbn:se:uu:diva-395278 (URN)
Funder
The Swedish Foundation for International Cooperation in Research and Higher Education (STINT), GA SA2017-7127
Available from: 2019-10-16 Created: 2019-10-16 Last updated: 2019-10-17

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