Summary of the Metarial sciensce theis: Study on preparation of biocompatibale hydroxyapatite coatings on titanium substrate by sol-gel method

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The thesis was designed to find appropriate technological conditions such as pH of solution, calcination temperature, firing time, measures of titanium metal surface treatment to fabricate hydroxyapatite coatings. (HA and FHA) on titanium substrate by solgel method capable of applying biomedical.

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Nội dung Text: Summary of the Metarial sciensce theis: Study on preparation of biocompatibale hydroxyapatite coatings on titanium substrate by sol-gel method

MINISTRY OF VIETNAM ACADEMY OF EDUCATION SCIENCE AND TECHNOLOGY AND TRAINING GRADUATE UNIVERSITY OF SCIENCE AND TECHNOLOGY ----------------------------------- NGO THI ANH TUYET STUDY ON PREPARATION OF BIOCOMPATIBALE HYDROXYAPATITE COATINGS ON TITANIUM SUBSTRATE BY SOL-GEL METHOD. Scientific Field: Metal Classification Code: 9.44.01.29 SUMMARY OF THE METARIAL SCIENSCE THEIS Hà Nội – 2019
The thesis was completed at: Graduate University of science and technology- Vietnam Academy of Science Scientific Supervisors: 1.Dr. Nguyen Ngoc Phong 2.Dr. Pham Thi San 1st Reviewer 2nd Reviewer: 3rd Reviewer: The thesis will be defended at Graduate University of Science And Technology, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Cau Giay District, Hanoi City. At… hour… date… month… 2019 The Thesis can be found in National Library of Vietnam and library of Graduate University of Science And Technology, Vietnam Academy of Science and Technology 1
INTRODUCTION In recently, biocompatible metal materials used in orthopedic surgery has been widely studied in the world. Due to the aging of the population in developed countries and the desire for patients to maintain a high quality life, and advances in the synthesis of materials and surgical procedures that allow implants materials are applied in many different ways. Therefore, the demand for high- performance implants to apply for cardiovascular, traumatic, orthopedic, spinal and dental problems has increased significantly. In 2012, worldwide, the market for bio-implant materials reached about 94.1 billion USD and by 2010 it was about 134.3 billion USD. Therefore, scientists are focusing on investigating to create new biomedical materials with good features. Implants used in orthopedic techniques are often made of metal materials due to their higher hardness and mechanical strength compared to organic materials or composite materials. Among biological implant materials, titanium and titanium alloys are considerably used in orthopedic implants due to its excellent properties such as low density, high perfomance, low electrical conductivity, high corrosion resistance. However, titanium and its alloy are impossible to bond biochemically with bone. In order to improve the properties and over-come the disadvantages of titanium and its alloy in biomedical applications, scientists have studied the compatibility layers coated on titanium and its alloys. Hydroxyapatite (HA) coatings on titanium and its alloys substrate was synthesised to provide the necessary conditions for bonding with tissues and prevent the release of metal ions from substrates when using in dental and orthopedic implant. Hydroxyapatite [HA, Ca10(PO4)6(OH)2] or fluor- hydroxyapatite [FHA Ca10(PO4)6(OH)2-xFx] wherein 0≤ x ≤ 2 with 2
HA by replacing F- for OH- which is attracted considerable attention due to its excellent bioactivity. HA has similar chemical composition with the mineral component of natutal bone tissue with ratio Ca / P = 1.67. In-vivo studies of HA coating showed that HA can improve bone growth amount of cells and tissues of the bone in the orthopedic and dental implants. There are some methods to prepare HA coating on titanium such as plasma spraying, ion pumps, sputtering, sol-gel method, the cathode deposition method, the anodized method, plasma electron oxidation (PEO)… In Viet Nam, the HA coatings for biomedical purposes have widely studied. However, the results shown that, most of studies do not demand the practical application. Therefore, we propose the thesis with entitle: “STUDY ON PREPARATION OF BIOCOMPATIBALE HYDROXYAPATITE COATINGS ON TITANIUM SUBSTRATE BY SOL-GEL METHOD”. The main contents and objectives of the thesis We focus on the sol-gel method to fabricate biocompatible coatings based on titanium substrate with high compatible property. The thesis was designed to find appropriate technological conditions such as pH of solution, calcination temperature, firing time, measures of titanium metal surface treatment to fabricate hydroxyapatite coatings. (HA and FHA) on titanium substrate by sol- gel method capable of applying biomedical. Influence of the parameters such as pH, temperature, concentration of electrolyte solution, viscosity ...on the coating formation will be studied. Characterizations of the coating will be studied by TEM, SEM, EDS, and X-ray, Adhesion strength…Electrochemical properties of the coating will be analyzed 3
by anodic polarization measurements, electrochemical impedance spectroscopy. Study to improve the adhesion strength of HA coating by the modification of suface of Ti substarte or using titanium porous substrate, or replace OH- group with F- to create FHA layer. Biocompatibility of coating layer will be investigated in- vitro in SBF. While, in vivo investigates were performed in Rabits. The new contributions of the thesis: -The relationship of the technological parameters and features of the material has been carefully studied, thereby clarifying the research results and making the process of manufacturing HA and FHA with basic parameters. - Improved quality of coating has been studied by manufacturing intermediate TiO2, Ti porous and FHA layers. - In-vivo and in-vitro tests with good results are a good first step for the study of practical application in the future. • In terms of application: A technological process has been developed for HA and FHA coatings by sol-gel method on titanium substrate with a good biocompatibility characterization was investigated by in-vitro and in-vivo tests. CONTENT OF THE THESIS CHAPTER I. OVERVIEW The thesis has summarized literature over the world about metal implant materials, some titanium surface treatment methods applied to biomedical, biocompatible calcium 4
phosphate (Ca-P) coatings, HA coatings CHAPTER II. EXPERIMENTAL 2.3. Fabrication of HA coating by sol-gel method 2.3.1. Prepare titanium substrate Commercial pure titanium sheet material (Commercially Pure Grade 2) is cut with a diameter of 25.4 mm (to study adhesion strength according to ASTM F1044-99 [91]) and ɸ 15 mm for other investigation. 2.3.2. Preparation process of sol HA and sol FHA 2.3.2.1. Preparation process of sol HA -Dissolve 0.2 mol H3PO4 in 100 mL C2H5OH solution, stired with a magnetic stirrer for 3 hours at room temperature (solution 1). - Dissolve 0.333 mol Ca (NO3)2.4H2O in 100 mL C2H5OH solution with magnetic stirrer for 3 hours (solution 2). - Mix together solution 1 and solution 2 and mix continuously this solution for 24 hours at room temperature. -Add slowly the 1M NH4OH solution into this mixture and stir for 3 hours. - Aging time for this mixture was in an oven at 40 0C for 72 hours in oder to formed sol HA. 2.3.2.2. Preparation process of sol FHA 5
-Dissolve 0.2 mol H3PO4 in 100 mL C2H5OH solution, stired with a magnetic stirrer and add slowly the NH4F solution with corresponding to molar ratio of P/F is 12; 6; 4; 3 respectively formula Ca10(PO4)6(F0.5OH1.5),Ca10(PO4)6(FOH),Ca10(PO4)6(F1.5OH0.5 ), Ca10(PO4)6(F2) and stirred with a magnetic stirrer for 3 hours at room temperature (solution 1). - Dissolve 0.333 mol Ca(NO3)2.4H2O in the 100 mL solution C2H5OH with magnetic stirrer for 3 hours (solution 2). - Mix together solution 1 and solution 2 and mixed continuously this solution for 24 hours at room temperature. -Add slowly the 1M NH4OH solution into this mixture and stir for 3 hours. - Aging time for this mixture is in an oven at 40 0C for 72 hours in oder to form sol FHA. 2.3.3. Preparation process of HA and FHA coating on Ti substate After preparating sol HA and sol FHA, fabrication of HA coating on titanium material follows the steps: - The HA coating on titanium substrate was preparared by sweep method. - The samlpe surface was plattened by spinning with speed 200 rpm, and dried at 80 0C for 1 hour. Then, the sample was cooled at room temperature for 1 hour and repeated 5 times. - At the end of the process, the samples were sintered at high temperature of range of 500 – 1000 0C. 6
After sintering, titanium samples coated with HA and FHA were characterized. 2.2. Characterization 2.2.1. Method of investigation of physical and mechanical properties Microstructure and composition of the HA coatings formed on the Ti were characterized using X-ray diffraction and SEM mothed.The adhesion strength of the HAcoatings was examined by pull-off method. 2.2.2. Electrochemical method 2.2.2.1. Nyquist impedance spectrum Nyquist impedance spectrum in SBF solution and scanned with frequency from 10 kHz to 10 mHz, 10mV of the voltage amplitude to investigated corrosion resistance of HA and FHA coatings on Ti substate. 2.2.2.2. Potentiodynamic polarization curves The corrosion resistance of materials with and without HA coating were characterized by potentiodynamic polarization curves in the voltage range from -250 mV to to 1600 mV, with a scanning speed of 1 mV/s in the Ringer solution with composition: NaCl 8.6 g/L; CaCl2.2H2O; 0.33 g/L; 0.3 g/L KCl. 2.2.3. Biocompatibility of HA coating 2.2.3.1. in-vitro Biocompatibility of titanium coated HA and FHA samples were assessed by in-vitro in SBF solution in a temperature of 37 0C ± 1 0C 7
and pH = 7.2-7.3. the coated HA, FHA on titanium substrate samples with dimension of ϕ15 mm x 2 mm in size that were soaked in 200 mL of SBF solution. 2.2.3.2. In- vivo In vivo tests were performed into 6 healthy rabbits with the titanium screws with and without HA coating at the femur of rabbits. After 3 months planted, indicators were evaluated such as: - Evaluation at the surgical site - Hematological indicators - The bone and implant materials images Chương 3. Results and discussion 3.1. Study on HA coating by sol-gel method 3.1.1. Characterization of sol HA 3.1.1.1. Study on the effect of pH values on phase formation Fig. 3.1. X-ray diffraction with change pH values of sol. 8
The X-ray diffraction (Figure 3.1) shown that at pH = 3, appearence of peaks of HA at the 2θ angle around of 270, 310, 320, 340. However, beside the peaks of HA, there are also peaks of α-TCP (Ca3 (PO4)2). As the pH value increases, the intensity of the peaks of the HA increases while the intensity of the α-TCP peaks decreases. At pH values of 7 and pH = 9 of sol, the intensity of HA peaks of the samples is quite high and approximate eachother. 3.1.1.2. Study on the effect of pH on the viscosity of sol The viscosity of sol HA at pH values of 3, 5, 7 and 9 was studied through relative viscosity parameters. The viscosity value of sol solutions is measured by the method of measuring the flow time of liquid through Ostwald viscometer capillary tube. Table 3.1. The viscosity of sol solution with change pH values N0 pH values of Sol Relative viscosity η 1 PH= 3 3,18 2 PH= 5 4,17 3 PH=7 5,13 4 PH= 9 6,49 From Table 3.1, the relative viscosity of sol HA solution increased with the pH value of the solution. The presence of NH4OH improved the performance of polymerization reactions, increases the chain of bonding [-Ca-O-P], and led to increasing concentration, so the viscosity of sol solution increased. Furthermore, the molecular mass of the colloidal particle increased led to the increasesing viscosity. However, with pH = 9, Sol solution has high viscosity affected to prepare HA coating on Ti substrate. At pH = 7, the viscosity of sol solution is 5.13 that can be 9
carried out easily. 3.1.1.3. Study on the effect of pH on the surface structure of the coating. In the initial studies of HA coating on Ti substrate, sol HA with pH values from 3-9 was coated on titanium metal and sintered at 800 0 C for 1 hour. Surface morphology of samples were investigated by SEM images (Figure 3.3). Fig. 3.3. The surface morphology of the HA coatings with change pH values of sol. With pH = 3 and pH = 5, the surface structure of the coating is inhomogeneous, there are many white porous aggregates. At pH = 7, the sample surface is a homogeneous structure. However, pH increased to 9, on the surface of the sample appeared many micro- cracks. In generally, with pH = 7, properties of sol HA have been 10
improved, easy to performed the HA coating samples with high uniformity. Therefore, the pH= 7 was chosen for subsequent studies. 3.1.1.4. Effect of sintering temperature on the characterization of sol HA. Fig.3.4. DTA and TGA diagram of sol HA At a temperature of 536,36 0C, a weak peak appeared because of phase transition of HA compounds. In the temperature range of 536,36 0C up to 1000 0C, the mass of sample was a little change. The results shown that the formation process of HA has completely finished. From the DTA and TGA diagram, we can conclude that the sintering temperature of the HA coating process by Sol - Gel method is higher than 500 0C. 11
3.1.2. Study on the effect of technological parameters on the characterization of HA coating on titanium substrate. 3.1.2.1. Calculatation of the thickness of the HA coating Titanium samples were covered with 5 to 7 sol layers. After each coating time, the surface of the sample was leveled by centrifugation for 1 minute at a speed of 200 rpm. Finally the sample was dried and sintered at a temperature of 800 0C for 1 hour. The weight difference of the sample before coating and after coating was used to calculate the average thickness of the sample. The thickness of the HA coatings measured directly on cross-section of the samples by SEM and compared with the calculated thickness as shown in Table 3.2. The results shown that the difference thicness between the two measurement methods was insignificant. Table 3.2. The average thickness of the HA coating with sol layers The average thickness (µm) Sol layers Calculated Actual thickness thickness 5 layers 15 14,6 6 layers 18 19,4 7 layers 21 21,0 12
In subsequent studies, to improve coating technology, we choose a fixed thickness of about 14-15 µm, the characterizations of the coating will be compared at the same thickness. a. The effect of sintering condition on the structure of the coating HA coated samples were sintered in air at temperature values from 500 0C to 1000 0C for 4 hours. However, at 1000 0C, the sloughing and separating occured on HA coating samples. Therefore, in Figure 3.6, there are not presence of SEM picture of the sample that was sintered at 1000 0C. Fig. 3.6. Surface morphology of the coating HA on Ti with sintering temperature In the temperature range from 500 0C to 700 0C, on the surface of the HA coating still existed spherical particles, they aggregated into clusters and porous surfaces. 13
The cohesion of HA particles increased with sintering temperature. When the sintering temperature continued increasing upto 900 0C, HA particles crystallized with a completely different morphology on surface of the sample compared with other samples. Figure 3.10, we can observe a 2-layers structure formed on Ti substrate includes: inner TiO2 layer and outer HA layer of the sample and is proved by EDS analysis results as shown in Table 3.3. Fig.3.10. SEM image on the cross- section of the sample. Table 3.3. Chemical composition of the coating % atom Point C O Ca P Ti ¤1 12,13 43,3 25,53 15,91 3,13 ¤2 6,86 34,69 0,18 0,01 58,26 The surface morphology of the HA coatings at 900 0C with the sintering time changed from 1 hour to 8 h hours was investigated. As the sintering time increased, the melting and cohesion of HA particles increased. There are no amorphous particles on surface of 14
the sample. However, at Figure 3.12 SEM images with lower magnification, cracks were was observed on the surface. The heated 6 hours and 8 hours samples appeared micro-cracks on the surface of the samples. Fig.3.12. Micro cracked image on the surface of HA coatings by sintering time b. The effect of the sintering condition on phase composition of coating. At a temperature of 900 0C, the intensity of the HA peaks changed insignificantly with sintering time. However, the intensity of the peaks of TiO2 increased significantly. The intensity of the TiO2 peaks increased due to the oxidation of titanium substrates increased. Thus, sintering temperature greatly affected to the formation of HA 15
phase and oxidation of Ti substrate. At 900 0C, the intensity of HA peaks are the highest. While, sintering time affected to the intensity of TiO2 peaks. Fig. 3.13. X-ray diffractions of HA samples with sintering temperature c. The effect of sintering condition on the adhesion strength of the coatings. The adhesion strength of the coatings were measured by pull- out method according to ASTM F1044-99, the results shown on Figure 3.15. The adhesion force of the coating increased markedly with the sintering temperature caused by the increased cohesion between the HA particles, and the thin TiO2 layer was formed during sintering process make the chemical bond between the layers 16
increased. Therefore the adhesion force of the sample increased. At 900 0C, the adhesion force of the sample was highest with a value of up to 8.6 MPa. The effect of sintering time in the range of 1 hour to 8 hours on the adhesion strength of the HA coating at 900 0C was also investigated. Fig 3.15. Adhesion strength of HA Fig. 3.16. Adhesion strength of coatings with the change of HA coatings with the change of sintering temperature. sintering time. In summary, at a sintering temperature of 900 0C for 4 hours, the adhesion strength of HA coatings was highest. d. The effect of sintering condition on corrosion resistance of the coatings. The effect of sintering condition on corrosion resistance of the coatings was measured by potentiodynamic curves (Figure 3.17 and 3.18). The electrochemical parameters were shown in tables 3.4 and 3.5. 17
Fig. 3.18. Potentiodynamic Fig.3.17. Potentiodynamic curves curves of HA / Ti in Ringer's of HA / Ti in Ringer's solution solution with the change of with the change of sintering sintering time. temperature. Table 3.4. Electrochemical parameters of samples with the change of sintering temperature Samples icorr(µA/cm2) Ecorr(mV) Ti pure 9,84 319 Ti-HA 5000C 3,93 304 Ti-HA 6000C 3,09 288 0 Ti-HA 700 C 2,39 382 Ti-HA 8000C 2,25 402 Ti-HA 9000C 1,09 445 Table 3.5. Electrochemical parameters of samples with the change of sintering time. Samples icorr(µA/cm2) Ecorr(mV)/ SHE 18
HA 1h 3,93 390 HA 2h 2,27 405 HA 4h 1,09 445 HA 6h 5,35 407 HA 8h 6,02 365 The corrosion resistance of HA/Ti materials achieved the highest level at 900 0C for 4 hours. 3.1.3. Improving the adhesion strength of HA coating 3.1.3.1. Improving the adhesion strength of HA coating by intermediate TiO2 layers. Fig. 3.26. Adhesion strength of HA Fig.3.34. Adhesion strength coatings on Ti substrate after of FHA coatings anodic oxidation At anodic voltage of 40 V, the adhesion strength of the HA coating achived the highest value of 17.84 MPa. These value was 2 times higher compered with the initial Ti sample. 19

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