2015 Fiscal Year Annual Research Report
抗菌性と骨適合性の両方に優れる溶解性制御型Ａｇ添加リン酸カルシウム膜の作製
| Project/Area Number |
15J00660
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| Research Institution | Tohoku University |
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Principal Investigator |
GOKCEKAYA OZKAN 東北大学, 工学研究科, 特別研究員(PD)
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| Project Period (FY) |
2015-04-24 – 2017-03-31
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| Keywords | silver / incorporation / antibacterial / calcium phosphate / hydroxyapatite / tricalcium phosphate / cytotoxiciy / HRTEM |
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| Outline of Annual Research Achievements |
The effectiveness of Ag containing calcium phosphates was tested toward Gram-negative bacteria (E. coli). The antibacterial activity performance of Ag-incorporated β-tricalcium phosphate and metallic Ag coexisted hydroxyapatite were conducted with various exposure time and initial bacteria concentration. The results have shown that Ag-incorporated β-tricalcium phosphate was effective as an antibacterial material toward E. coli for even high initial bacteria concentration compared to metallic Ag coexisted hydroxyapatite without any toxicity. The mechanism of excellent antibacterial activity is based on Ag release through the continuous dissolution of Ag-incorporated β-tricalcium phosphate. The study of Ag-containing calcium phosphates has been focusing on hydroxyapatite for decades. However, we pointed out the effectiveness of Ag-incorporated β-tricalcium phosphate compared to metallic Ag coexisted hydroxyapatite. To our best knowledge, no reports have discussed the bioresorbability of Ag-incorporated β-TCP with respect to the incorporation amount of Ag and the β-tricalcium phosphate phase fraction. To clarify the atomic position of Ag in β-tricalcium phosphate and hydroxyapatite, I joined to Prof. Chen’s Laboratory in WPI-AIMR, Tohoku University for training for transmission electron microscopy (TEM) observations. The Ag atoms were detected in β-tricalcium phosphate by high angle annular dark field scanning transmission electron microscopy (HAADF-STEM). Ca(4) sites in β-TCP structure are occupied by Ag atoms.
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| Current Status of Research Progress |
Current Status of Research Progress
1: Research has progressed more than it was originally planned.
Reason
The study of Ag-containing calcium phosphates has been focusing on hydroxyapatite for decades. However, this research showed the effectiveness of Ag-incorporated β-tricalcium phosphate for antibacterial applications. Furthermore, the study of atomic position of Ag atom in β-tricalcium phosphate structure is new information in this field, which gives an idea for the incorporation limit of the structure. The incorporation of Ag in β-tricalcium phosphate was occurred as an exchange of Ca(4) sites with Ag atoms. To clarify the position of Ag atoms in β-tricalcium phosphate structure, high angle annular dark field high resolution transmission electron microscopy (HAADF-STEM) is important technique due to the z contrast difference between Ca and Ag atoms. The atomic structure observations are ongoing. The skills for operating TEM machine are much improved by staying in Prof. Chen’s Laboratory for 6 months. Novel information on β-tricalcium phosphate structure is obtained as showing the incorporation of Ag into Ca(4) site for the first time by using a microscopic technique. In order to confirm the position of Ag atoms in β-tricalcium phosphate, STEM simulation study using software is going to be carried out. For detail explanation of Ag incorporation, HAADF-STEM observations are planned to conduct systematically with respect to the STEM simulations. The information of change in structural parameters and the limit of incorporation into calcium phosphates are valuable to understand the performance of bio-ceramics.
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| Strategy for Future Research Activity |
The research is going to focus on coating techniques of Ag-containing calcium phosphate. The facilities we had in Prof. Narushima’s Laboratory allow us to fabricate coating by RF (radiofrequency) magnetron sputtering. I am going to focus on fabrication of Ag and other additional elements containing amorphous calcium phosphate coatings by RF magnetron sputtering. Additionally, the in vitro evaluations of these coatings are going to be conducted. Co-doping of Ag+other elements (Nb, Ta, etc.) to amorphous calcium phosphate coatings is considered to control bioresorbability and to enhance cell-compatibility. The effectiveness of Ag-incorporated amorphous calcium phosphate coatings is going to be tested toward Gram-negative (E. coli) and Gram-positive (S. aureus) bacteria. We evaluated antibacterial activity of Ag-incorporated β-tricalcium phosphate and metallic Ag coexisted hydroxyapatite with various exposure time and initial bacterial concentration. The results have shown that Ag-incorporated β-TCP was effective as an antibacterial material toward E. coli for even high initial bacteria concentration with a controlled and sustained release of Ag ions, superior comparing to metallic Ag coexisted hydroxyapatite. For amorphous calcium phosphate coatings, the research focus is on controlling the dissolution of amorphous calcium phosphate and sustained release of incorporated ions to obtain long-lasting antibacterial activity and biocompatibility. The coatings are going to be observed with HRTEM.
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[Presentation] In vitro evaluation of Ag-containing calcium phosphates2015
Author(s)
O. Gokcekaya, K. Ueda, T. Narushima, K. Ogasawara
Organizer
Twenty-Fourth International Symposium on Processing and Fabrication of Advanced Materials
Place of Presentation
Centenary Memorial Hall, Senriyama Campus, Kansai University, Osaka, Japan
Year and Date
2015-12-18 – 2015-12-20
Int'l Joint Research / Invited
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