Effect Of Boron Nitride Based-nanocomposites On The Performance Of Glass Ionomer Cement

Glass ionomer cement（GIC）is a commonly used filling material in oral cavity,but its poor mechanical properties and antibacterial effect cannot fully meet the clinical requirements.Boron nitride-based nanocomposites have a wide range of potential applications in the biomedical field due to their excellent mechanical properties,biocompatibility and other characteristics.In this experiment,they were composited with GIC,and the effects of composites on the mechanical properties,dissolution rate,ion release ability,antibacterial properties and biocompatibility of glass ionomer cement were studied.The specific work content is as follows:1.Preparation and characterization of hexagonal boron nitride nanosheets-titanium dioxide nanoparticles/glass ionomer cement（h-BN-TiO₂/GIC）Molecular dynamics behavior,Energy stable state structure and design principle of hexagonal boron nitride（h-BN）and titanium dioxide（Ti O₂）to form hexagonal boron nitride-titanium dioxide（h-BN-TiO₂）was simulated and analyzed by the Forcite+module in molecular dynamics software（material studio,MS）.Firstly,h-BN-TiO₂nanocomposites were prepared by ball milling and thermal hydrolysis of titanium oxysulfate（Ti OSO₄）,the particle size,morphology and structure were characterized by TEM,AFM,Raman and XRD;Secondly,h-BN-TiO₂ nanocomposite with different mass fractions（0,0.3,0.7,1.1 and 1.5 wt.%）were added to GIC by in situ freeze-drying to prepare h-BN-TiO₂/GIC composites,and tested the mechanical properties,solubility,cross-section SEM observation and biological properties.The stable state adsorption energy of h-BN-TiO₂ composite was calculated by MS software to be-235 kcal/mol,which indicated that h-BN and Ti O₂ could be effectively combined in the form of electrostatic force.TEM revealed that Ti O₂ nanoparticles with diameters ranging from 2 nm to 20 nm were grown in situ on h-BNNs with lateral sizes ranging from 200 nm to 1μm.AFM shows that the h-BN-TiO₂ nanocomposite structure is a rivet-like two-dimensional-zero-dimensional nanocomposite system.Raman spectroscopy and XRD confirmed the existence of h-BN-TiO₂ nanocomposite.When the content of h-BN-TiO₂ nanocomposites was 1.1 wt.%,the microhardness and compressive strength were increased by 149.6%and 80.2%,respectively.As the content of h-BN-TiO₂ nanocomposites increased,the friction coefficient and solubility of GIC composites decreased,but the antibacterial properties increased.After 24 h,the cell survival rate in each group was greater than 75%,and the difference was not statistically significant（P>0.05）.2.Preparation and characterization of hexagonal boron nitride nanosheets-fluorinated graphene/glass ionomer cement（h-BN-FG/GIC）The Forcite+module in MS software was used to simulate and analyze the molecular dynamics behavior,energy stable state structure and energy stability of the hexagonal boron nitride-fluorinated graphene（h-BN-FG）formed by h-BN and fluorinated graphene（FG）.Firstly,h-BN-FG nanocomposites were prepared by ball milling and ultrasonic dispersion methods,and were characterized by TEM and XRD;Secondly,h-BN-FG nanocomposite with different mass fractions（0,0.5,1.0,1.5 and2.0 wt.%）were added to GIC by in situ freeze-drying to prepare h-BN-FG/GIC composites,and test the mechanical properties,dissolution rate,ion release ability,cross-section SEM observation and biological properties.The adsorption energy of the h-BN-FG composite material was calculated by MS software to be-3.42 kcal/mol,indicating that there are still electrostatic and van der Waals interactions between the h-BN-FG layers.The entire adsorption process is exothermic and has a stable structure.TEM revealed that h-BNNs exhibited thin and transparent two-dimensional nanostructures with lateral dimensions ranging from 500nm to 1μm.FT-IR and XRD confirmed the existence of h-BN-FG nanocomposites.When the content of h-BN-FG nanocomposites was 1.5 wt.%,the compressive strength and microhardness were increased by 146%and 108%,respectively.As the content of h-BN-FG nanocomposite increased,the friction coefficient and solubility of GIC composites decreased,the cumulative ion release decreased,but the antibacterial properties increased.The survival rate of cells in each group was greater than 75%,and the difference was not statistically significant（P>0.05）.In conclusion,the successfully prepared h-BN-TiO₂ and h-BN-FG nanocomposite were uniformly dispersed in the GIC matrix and formed h-BN-TiO₂/GIC and h-BN-FG/GIC composites,respectively.With the addition of nanocomposites,the mechanical properties of GIC composites were enhanced,and the friction coefficient and dissolution rate were significantly reduced.At the same time,GIC added with nanocomposites have excellent antibacterial properties and biocompatibility,which provides a new strategy for the multifunctional application of GIC in the oral field.