| ObjectiveThe synthesized nano silver/graphene oxide compounds was added to the polymethyl methacrylate base materials according to different mass fractions to modify it.At the same time,the mechanical and physical properties,antibacterial properties and biological safety of the composite materials were investigated,which provides scientific basis for further research of antibacterial base materials.Materials and MethodsNano silver/graphene oxide compounds were prepared according to different mass ratio of graphene oxide to silver were 1:1 and 1:2 by chemical reduction method.Scanning electron microscopy,energy spectrometer and transmission electron microscopy were used to analyze the morphology and elemental characterization of compounds,and the appropriate concentration of compounds was selected.Nano silver/graphene oxide/polymethyl methacrylate composite materials were prepared by ball mill blending method.The silicone rubber negative molds were made from standard specimens to make the specimens.The specimen size used for the cell proliferation experiment was 10 × 10 × 2mm3,20 pieces in each group(n1=20),the specimen size used for cell adhesion experiment was 10 × 10 × 2mm3,5 pieces in each group(n2=5),the specimen size used for the film adhesion test was 50×50×2mm3,5 pieces in each group(n3=5),the specimen size used for the bacterial adhesion experiment was 10 × 10 × 2mm3,5 pieces in each group(n4=5),the specimen size used for mechanical and physical performance testing was 50 × 20 × 4mm3,15 pieces in each group(n5=15).The experiment was divided into three parts:Part 1:Cytotoxicity experiment:first,the mass fraction of nano silver/graphene oxide compounds were set as 0%,0.1%,0.2%.0.25%,0.3%,0.5%.and 1%.respectively numbered as control group A.experimental groups B,C,D.E.and F.The cell counting kit-8 method was used to detect the proliferation activity of human gingival mesenchymal stem cells on the surface of test pieces on days 1,3,5,and 7 and the cell proliferation curve was recorded.The adhesion and morphology of human gingival mesenchymal stem cells cultured on the surface of specimens with mass fractions of 0%,0.1%,0.2%and 0.3%for 48 hours were observed in combination with scanning electron microscope to evaluate the cytotoxicity of composite materials.Part 2:Antibacterial experiment:According to the cytotoxicity experiment,the mass fraction of nano silver/graphene oxide compounds were set as 0%.0.1%,0.2%,and 0.3%,which numbered as control group A.and experimental group B,C,and D.The anti streptococcus mutans experiment was carried out by thin-film adhesion method.number of colonies were counted,and antibacterial rate of the composite materials were calculated.In combination with the scanning electron microscope,the adhesion and morphology of streptococcus mutans cultured on the surface of specimens for 48 hours were observed to evaluate the antibacterial effect of composites.Part 3:Mechanical and physical performance test:the mass fraction of nano silver/graphene oxide compounds were set as 0%.0.1%.0.2%and 0.3%according to the cytotoxicity experiment,respectively numbered as control group A.experimental groups B,C and D.1)The test pieces have been placed on the load bearing platform of electronic universal material testing machine with a span of 20 mm.a loading speed of 2.0 mm/min,a loading frequency of 1 Hz,until the test pieces fracture the bending load at break was recorded,the bending strength of test pieces was recorded.2)Friction test has been performed in the form of ball surface contact and reciprocating sliding friction,test pieces have been fixed on the base of friction and wear test machine.Under the condition of artificial saliva,the same smooth surface of each test piece has been selected and the loading force was set as 20N,the time was 20min,the frequency was 2Hz,the speed was 10mm/s,the scratch length was 5mm,and a steel ball with a diameter of 9.525mm was used.The friction coefficient changes and average friction coefficients of test pieces were recorded.3)The static drop method was used to measure the contact angle of each test piece,test pieces were fixed on the sample table of contact angle measuring instrument,three points on the same smooth surface for each test piece have been selected,and artificial saliva have been dropped on the test pieces surface,after the image was clear and stable,a photo was took.Statistical analysis was performed by IBM SPSS statistical software(Version R25.0.0.2).Results1.The results of scanning electron microscopy and transmission electron microscopy showed that when the mass ratio of graphene oxide to silver was 1:1,graphene oxide was a typical two-dimensional transparent sheet-like structure with smooth surface and partially wavy folds.Nano silver particles were well-dispersed,particle size was uniform,which ranges from 30 to 50 nm,particle shape was regular spherical,and there was no obvious agglomeration,which met the requirements of next experiments.The energy disperse spectroscopy results showed that the main constituent elements of the compounds were silver and carbon,of which the mass fraction of silver was about 71%.2.The results of cell proliferation experiments showed that the proliferation curve of human gingival mesenchymal stem cells on the surface of experimental groups with a mass fraction of 0%,0.1%,0.2%,and 0.3%on the 1,3,5,and 7 days showed an upward trend.The experimental groups with a mass fraction of 0.5%,1%showed a downward trend.Scanning electron microscopy showed that cells on the surface of experimental groups with a mass fraction of 0%,0.1%,0.2%,and 0.3%had good cell growth,regular morphology,and complete cell membranes.3.The antibacterial experiment results showed that the number of colonies of groups were(1540±2.4),(1250±1.5),(20±0.7),(2±0.1).The results of statistical analysis showed that the difference in the number of colonies was statistically significant(P<0.001),and fthe results of multiple comparisons showed that differences between the groups were statistically significant.The antibacterial rates of experimental groups were 20%,98.6%,and 99.9%.Scanning electron microscopy showed that the number of bacteria on the surface of control group was large and the morphology was regular,the morphology of bacteria of experimental groups changed,and the integrity of cell membrane was destroyed.4.1)The bending test results showed that the bending strength of experimentalgroups with a mass fraction of 0%,0.1%,0.2%,and 0.3%were(102.5 ± 1.58),(111.4 ± 0.20),(115.7±0.48)and(88.69±1.14)MPa,the statistical analysis results showed that the difference in average bending strength was statistically significant(P<0.001),and the results of multiple comparisons showed that differences between groups were statistically significant.2)The friction test results showed that the friction coefficients of materials showed a downward trend with time.The average friction coefficients of specimens in each groups were(0.094 ± 0.003),(0.086±0.003),(0.074±0.002),(0.071±0.002).The statistical analysis results showed that the difference of average friction coefficient was statistically significant(P<0.001),and the results of multiple comparisons showed that differences between groups except group C and group D were statistically significant.3)The contact angle results showed that the contact angles of the four groups of test pieces were(71.1±1.24),(67.3±0.86),(66.1±0.35)and(58.1±0.61)°.The statistical analysis results showed that the difference was statistically significant(P<0.001).The results of multiple comparisons showed that differences between groups were significant.Conclusions1.When the mass ratio of graphene oxide to silver was 1:1,the nano silver/graphene oxide compounds can be prepared by chemical reduction method,which showed uniform particle size and good dispersion and no obvious agglomeration.2.Nano silver/graphene oxide/polymethyl methacrylate composite materials with mass fraction less than 0.3%have no obvious cytotoxicity to gingival mesenchymal stem cells.3.Nano silver/graphene oxide/polymethyl methacrylate composite materials with mass fraction more than 0.2%have antibacterial effect to Streptococcus mutans.4.The mechanical and physical properties of composite materials with mass fraction of 0.2%can be appropriate. |
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