05 марта 2016г.
One of the methods to improve the osseointegration properties of implants is applying to the surface bioactive hydroxyapatite (HA) Ca10(PO4)6(OH)2 coatings. For several reasons, the statistical frequency of dental implants rejections with hydroxyapatite coating applied by means of plasma spray technology constitute 4-6% [1]. To reduce rejection of implants in the postoperative period it is proposed to impregnate the porous coating of implants with liquid pharmaceutical substances [2, 3].
The authors have developed a technology for bioactive porous plasma spray coating on the implant surface. This technology provides the porous coatings with predicted distribution of macropores, micropores and nanochannels.
The aim of research is to analyse the structure and microhardness of the coating produced by the developed technology and use the coating as a container for storage of pharmaceutical substances.
The studies were conducted on the samples representing 10´10´2 mm plate of titanium alloy VT1-0 coated by plasma spraying of titanium powders with the grain size at 100μm, and chemically synthesized hydroxyapatite with the grain size at 40-90μm. The surface of the samples before the plasma sprayed coatings was abrasive blasting. The device "Chaika-20" is used after which the surface is cleaned in the ultrasonic bath PSB-GALS. Plasma spraying was carried out on the automated device UPN-28 ("REMPLAZMA", Moscow).
The formed porous coating is impregnated with the 3% Poviargol (silver nanoclusters stabilized hemodez) solution. The sample was treated in the ultrasonic bath PSB-GALS (frequency 18 kHz) for 10 min.
Homogeneity of the coatings was analysed using the MIM7 optical microscope. The distribution of open porosity was studied using the AGPM-6M image analyzer microstructures. The microhardness of the coating was measured by the HVS1000B hardness tester with the SP5 video measuring system.
The plasma was sprayed to form a multilayer coating consisting of titanium powder sublayer and three alternating layers of powder HA (bottom layer HA powder dispersion (D) 90 μm, the middle layer of powder HA D = 40 μm, the top layer of the HA D = 90 μm). Experiments were used to carry out a mode for plasma spraying based on the uniformity of the coating and the required physical, mechanical and morphological characteristics. The data obtained on the basis of experimental analysis of plasma spraying are shown in Table 1.
Table 1
Modes for plasma spraying of the multilayer composite coating
|
Dispersity of sprayed powder, μm
|
Arc current, A
|
Consumption conveying / plasma gas, l / min
|
Spraying distance, μm
|
Spraying time (coating thickness 50 μm), sec.
|
Spraying time (coating thickness
100 μm), sec.
|
|
Titanium powder D
more 90 μm
|
400
|
1/17
|
150
|
4-5
|
4-5
|
|
HA powder
D less 40 μm
|
300
|
1/17
|
50
|
5-6
|
8-10
|
|
HA powder
D less 90 μm
|
400
|
1/17
|
100
|
5-6
|
8-10
|
Optical microscopy showed that the surface coating formed by plasma spraying by the proposed technology has developed morphology and formed fused particles HA which advantageously represented the agglomerate particle diameter of 40-100 μm. Analysis of the samples AGPM-6M showed that the sprayed coating has the open porosity at 40% with the maximum pore diameter of about 90-100 μm. This is consistent with the necessary parameters of the porous ceramic (not less than 100 μm) for germination of bone tissue through the pore channels [3].
The microhardness measurements of the surface with the plasma sprayed coating layered before and after its impregnation by the liquid substance relative to the uncoated samples are shown in Table 2.
Table 2
Microhardness of the coating
|
Sample material
|
Type of coating
|
Load on indenter, N
|
Average micro hardness, HV
|
|
VT1-0
|
-
|
2,94
|
407.7 ± 100
|
|
HA coating (D=90 μm)
|
2,94
|
800 ± 100
|
|
multilayer composite coating
|
2,94
|
940± 100
|
|
multilayer composite coating impregnated Poviargol
|
2,94
|
950± 100
|
|
Bone tissue
|
-
|
2,94
|
400 ± 100
|
According to the research, the microhardness of plasma sprayed multilayer coating increases on average by 15% compared to the samples with the plasma sprayed HA D = 90 μm. This may be due to the compaction of the coating structure, as is present in the coating layer HA D = 40 μm. Microhardness of the multilayer coating is significantly higher than the microhardness of the bone tissue. Consequently, the coating formed by the proposed technology, and the surface of the implant when it is installed in the patient's body will not collapse and can serve as a container for storage of pharmaceutical
substances.
The reported study was partially supported by the grant of the President MD-462.2014.8. and MK-457.2014.8, RFBR grant of a research project № 15-03-02767 a, a part of the project of the state tasks in scientific activity № 11.1240.2014 / K (17.07.2014).
List of references
1. Fomin I.V., Lyasnikov V.N., Volozhin A.I., Doctorov A.A., Lepilin A.V. Improving osseointegration properties of titanium implants with plasma sprayed hydroxyapatite coating: Modern problems of implantology: theses 4th Intern. scientific-tehn. conf. Saratov, SSTU, 1998. №16. – P.62-67.
2. Lyasnikova A.V., Taran V.M., Markelova O.A., Dudareva O.A., Grishina I.P. 2013. Mathematical Modeling of Stress in Plasma Coatings Used in Medicine: Biomedical Engineering, Vol.47, No.3, P.142-145.
3. Lyasnikova A.V., Grishina I.P., Dudareva O.A., Markelova O.A. Investigation of the influence of characteristics of the starting powders and plasma spray condition on the properties of metal-ceramic coatings of implants: Design of composite materials, №1. – 2013. P.31-36.
