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Investigation of copper alloying in a TNTZ-Cux alloy
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. (Materials in Medicine)ORCID iD: 0000-0001-6057-7571
Centre for High Resolution Transmission Electron Microscopy, Department of Physics, Nelson Mandela University, 6031 Port Elizabeth, South Africa.
Centre for High Resolution Transmission Electron Microscopy, Department of Physics, Nelson Mandela University, 6031 Port Elizabeth, South Africa.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. (Materials in Medicine)ORCID iD: 0000-0001-9529-650X
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2019 (English)In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 12, no 22, article id 3691Article in journal (Refereed) Published
Abstract [en]

Alloying copper into pure titanium has recently allowed the development of antibacterial alloys. The alloying of biocompatible elements (Nb, Ta and Zr) into pure titanium has also achieved higher strengths for a new alloy of Ti-1.6 wt.% Nb-10 wt.% Ta-1.7 wt.% Zr (TNTZ), where strength was closer to Ti-6Al-4V and higher than grade 4 titanium. In the present study, as a first step towards development of a novel antibacterial material with higher strength, the existing TNTZ was alloyed with copper to investigate the resultant microstructural changes and properties. The initial design and modelling of the alloy system was performed using the calculation of phase diagrams (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 3 wt.% 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.

Place, publisher, year, edition, pages
Switzerland: MDPI, 2019. Vol. 12, no 22, article id 3691
Keywords [en]
Titanium alloy; microstructures; biomaterial, TNTZ
National Category
Medical Materials
Identifiers
URN: urn:nbn:se:uu:diva-395278DOI: 10.3390/ma12223691ISI: 000502284400048PubMedID: 31717395OAI: oai:DiVA.org:uu-395278DiVA, id: diva2:1361660
Funder
The Swedish Foundation for International Cooperation in Research and Higher Education (STINT), GA SA2017-7127Available from: 2019-10-16 Created: 2019-10-16 Last updated: 2020-01-14Bibliographically approved
In thesis
1. Development of titanium-copper alloys for dental applications
Open this publication in new window or tab >>Development of titanium-copper alloys for dental applications
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
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
Titanium, copper, antibacterial, Ti2Cu, biomaterials, Staphylococcus epidermidis, MC3T3 cells
National Category
Medical Materials
Identifiers
urn:nbn:se:uu:diva-395303 (URN)978-91-513-0782-4 (ISBN)
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

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