Low shrinkage light curable dental nanocomposites using SiO2 microspheres as fillers

Commercial resin matrixes of dental composites generally utilize diluents such as triethylene glycol dimethacrylate (TEGDMA) to reduce viscosity. However, the diluents exhibited adverse effects such as higher volume shrinkage and diminished mechanical properties of the dental composites. To overcome these adverse effects, developing of both inorganic fillers and resin monomers is necessary to improve the properties of dental composite. In this work, monodispersed silica microspheres with a diameter of 400 nm were synthesized via the Stöber process. The as-prepared particles were silanized with 3-methacryloxypropyltrimethoxysilane (γ-MPS) and used as fillers. Additionally, ethoxylated bisphenol A dimethacrylate (EBPADMA) with lower viscosity and higher molecular mass was introduced as a base resin monomer, which could be used as resin matrixes with a low amount of diluent. Various resin mixtures of EBPADMA, bisphenol A diglycidyl dimethacrylate (Bis-GMA) and TEGDMA were prepared, which had a similar filler content (71 wt.%), and their mechanical properties, volume shrinkage, depth of cure and light transmission were examined. Among them, the resin mixture containing 70% EBPADMA and 30% TEGDMA exhibited the best compression strength (238.1 ± 5.4 MPa), depth of cure (4.02 ± 0.04 mm) and the lowest volume shrinkage (2.27%).     

Shrinkage properties of a modified dental resin composites containing a novel spiro-orthocarbonate expanding monomer

ObjectivesThis study investigated the photopolymerization-induced shrinkage properties of conventional methacrylate-based composites modified by a novel spiro-orthocarbonate (SOC) expanding monomer.MethodsThe epoxy monomer and SOC expanding monomer were added to a methacrylate-based resin matrix at five different ratios ranging from 20 wt.% (SOC + Epoxy) (group 1) to 60 wt.% (SOC + Epoxy) (group 5). Volumetric shrinkage and contraction stress developing after polymerization were measured using X-ray micro-computed tomography and a universal testing machine, respectively.ResultsThe volumetric shrinkage of the resin composite samples ranged from 0.92% (group 5) to 3.85% (control group) 30 min after light curing. Group 5 had the lowest volumetric shrinkage (p < 0.05), followed by groups 4, 3, 2 and 1. The contraction stress of the materials ranged from 1.86 MPa (group 5) to 3.56 MPa (control group). The lowest contraction stress was also observed in group 5, 30 min after curing (p < 0.05).ConclusionIncluding SOC expanding monomer reduced volumetric shrinkage and contraction stress of composites in comparison with conventional methacrylate-based composites.     

Fluoridated hydroxyapatite nanorods as novel fillers for improving mechanical properties of dental composite: Synthesis and application

Fluoridated hydroxyapatite (FHA) in nanorod morphology and hexagonal cross section were synthesised via hydrothermal process using Apricot Tree Gum (ATG) as a surfactant. The synthesised FHA nanorods were then used as reinforcement in bisphenol A-glycol dimethacrylate (Bis-GMA) as base monomer of composite matrix. The FHA nanorods with different ratios were incorporated in the matrix to examine fluoride ion release and pH changes in the Simulated Body Fluid (SBF) and their mechanical properties. The resin without FHA reinforcement was used as the control sample. The Diametral Tensile Strength (DTS), Flexural Strength (FS), and Flexural Modulus (FM) of the reinforced composite were found to be higher compared to the control sample; the values increased from 34.8 to 45.4 MPa, 76.5 to 99.4 MPa, and 1.7 to 2.5 GPa, respectively. Moreover, findings revealed that the pH is reduced by releasing the fluoride ions into the SBF which can be effective for preventing secondary caries. The most optimum mechanical properties were achieved with 0.2 wt% of FHA reinforcement. The FHA nanocomposite meets the minimum standard requirements for dental applications and compared to other dental composites has advantage of preventing formation of secondary caries due to release of fluoride.     

Poly(vinyl alcohol)–hydroxyapatite biomimetic scaffold for tissue regeneration

Hydroxyapatite–poly(vinyl alcohol) composite blocks were produced by freeze–thawing in situ synthesized hybrid suspension. Matrix mediated precipitation of hydroxyapatite particles in the polymer, controlled the particle size in nanometer range (< 100 nm) and hydrogelation induced an ordered three-dimensional assembly of the particles. Morphological and crystallographic characterization revealed the formation of a macro-porous hydroxyapatite–poly(vinyl alcohol) nanocomposite block. Initial results indicate compositional dependence of modulus of elasticity of the composite.     

Synthesis of calcium carbonate vaterite crystals and their effect on stabilization of suspension polymerization of MMA

Spherical calcium carbonate vaterite crystals were synthesized and the effect of them on stabilization of suspension polymerization of methyl methacrylate was investigated. Suspension polymerization of methyl methacrylate could be stabilized with calcium carbonate vaterite crystals and sodium dodecylbenzene sulfonate of the concentrations from 25 to 100 ppm. Poly(methyl methacrylate) beads coated with spherical calcium carbonate vaterite crystals were prepared. With an increase in the concentration of sodium dodecylbenzene sulfonate from 25 to 100 ppm, the amount of calcium carbonate vaterite crystals adhered on the surface of poly methyl methacrylate bead increased and the mean diameters of the polymer beads decreased.     

UV resistibility of a nano-ZnO/glass fibre reinforced epoxy composite

The harmfulness of ultraviolet (UV) radiation (UVR) to human health and polymer degradation has been the focus recently in all engineering industries. A polymer-based composite filled with nano-ZnO particles can enhance its UV resistibility. It has been found that the use of appropriate amount of nano-ZnO/Isopropyl alcohol solvent to prepare a UV resistant nano-ZnO/glass fibre reinforced epoxy (ZGFRE) composite can effectively block the UV transmission with negligible influence on the crystal structure of its resin system. This paper aims at investigating the interfacial bonding behaviour and UV resistibility of a ZGFRE composite. The solvent effect in relation to the dispersion properties of ZnO in the composite is also discussed. XRD results indicated that 20 wt% Isopropyl alcohol was an effective solvent for filling nano-ZnO particles into an epoxy. SEM examination also showed that the bonding behaviour between glass fibre and matrix was enhanced after filling 20 wt% nano-ZnO particles with 20 wt% Isopropyl alcohol into the composite. Samples filled with 20 wt% nano-ZnO/Isopropyl alcohol and 40 wt% nano-ZnO/Isopropyl alcohol has full absorption of UVA (315–400 nm), UVB (280–315 nm) and a part of UVC (190–280 nm).     

Wear behavior of light-cured resin composites with bimodal silica nanostructures as fillers

To enhance wear behavior of resin composites, bimodal silica nanostructures including silica nanoparticles and silica nanoclusters were prepared and proposed as fillers. The silica nanoclusters, a combination of individually dispersed silica nanoparticles and their agglomerations, with size distribution of 0.07–2.70 μm, were fabricated by the coupling reaction between amino and epoxy functionalized silica nanoparticles, which were obtained by the surface modification of silica nanoparticles (~ 70 nm) using 3-aminopropyl triethoxysilane (APTES) and 3-glycidoxypropyl trimethoxysilane (GPS) as coupling agents, respectively. Silica nanoparticles and nanoclusters were then silanized with 3-methacryloxypropyl trimethoxysilane (γ-MPS) to prepare composites by mixing with bisphenol A glycerolate dimethacrylate (Bis-GMA) and tri (ethylene glycol) dimethacrylate (TEGDMA). Experimental composites with various filler compositions were prepared and their wear behaviors were assessed in this work. The results suggested that composites with increasing addition of silica nanoparticles in co-fillers possessed lower wear volume and smoother worn surface. Particularly, the composite 53:17 with the optimum weight ratio of silica nanoparticles and silica nanoclusters presented the excellent wear behavior with respect to that of the commercial Esthet-X, although the smallest wear volume was achieved by Z350 XT. The introduction of bimodal silica nanostructures as fillers might provide a new sight for the design of resin composites with significantly improved wear resistance.     

The conductive polyaniline/poly(ethylene terephthalate) composite fabrics

Conductive composite fabrics were prepared by chemical polymerization of aniline on poly(ethylene terephthalate) (PET) fabrics in the aqueous hydrochloride acid solutions using potassium dichromate as the oxidant. The effect of the polymerization conditions such as temperature, oxidant, aniline and hydrochloride acid concentrations was investigated on the electrical surface resistance and polyaniline (PAn) content of PAn/PET composite fabrics. The maximum PAn content and the lower electrical resistance of composite fabrics were observed at the HCl concentrations of 0.25 M and 1.5 M, respectively. The electrical surface resistance of the PAn/PET composite fabrics was decreased under vacuum five-fold more than the ones kept under in air. The properties of PAn/PET composite fabrics such as density, diameter and moisture regain were also investigated in comparison with the those of pure PET. The conductive composite fabrics were characterized by surface resistance, FTIR and TGA techniques.     

Synthesis of aligned porous poly(ε-caprolactone) (PCL)/hydroxyapatite (HA) composite microspheres

We synthesized poly(ε-caprolactone) (PCL)/hydroxyapatite (HA) composite microspheres with an aligned porous structure and evaluated their potential applications in bone tissue engineering. A range of HA particles (0, 5, 10 and 20 wt.% in relation to the PCL polymer) were added to a PCL solution in order to improve the biocompatibility of the porous PCL/HA composite microspheres. All the synthesized microspheres showed that the HA particles were distributed well in the PCL matrix, while preserving their aligned porous structure. The average size of the PCL/HA composite microspheres increased from 62 ± 7 to 179 ± 95 μm with increasing HA content from 0 to 20 wt.%. The incorporation of the HA particles to the PCL polymer led to a considerable improvement in in vitro bioactivity, which was assessed by immersing the PCL/HA composite microspheres in simulated body fluid (SBF). A number of apatite crystals could be precipitated on the surface of the aligned porous PCL/HA composite microspheres after soaking in the SBF for 7 days.     

Release of interfacial thermal stress and accompanying improvement of interfacial adhesion in carbon fiber reinforced epoxy resin composites: Induced by diblock copolymers

In this work, diblock copolymer Hydroxyl-Terminated poly (n-butylacrylate)-b-poly (glycidyl methacrylate) (OH-PnBA-b-PGMA) was synthesized by atom transfer radical polymerization (ATRP) and was then introduced into the interface between carbon fiber and epoxy resin. Micro-Raman spectroscopy and microbond test were employed to study the influence of grafted polymers on the interfacial properties. From the Micro-Raman spectroscopy results, the interfacial thermal stress in carbon fiber/epoxy resin micro-composite decreases from 546.9 MPa to 451.9 MPa due to the grafting of OH-PnBA₁₈₀-b-PGMA₇₀ on the carbon fiber. Meanwhile, the interfacial shear strength (IFSS) value increases rapidly from 29.8 MPa to 52.3 MPa, measured by microbond test. Therefore, it can be concluded that such a diblock copolymer can effectively both release the thermal stress and improve the interfacial adhesion. Moreover, it proves that the length of PnBA block has great influence on the interfacial properties of carbon fiber/epoxy composite.     

Preparation and properties of biomimetic porous nanofibrous poly(l-lactide) scaffold with chitosan nanofiber network by a dual thermally induced phase separation technique

A biomimetic nanofibrous poly(l-lactide) scaffold decorated by chitosan nanofiber network inside the macropores was fabricated using a dual thermally induced phase separation technique. The first phase separation was used to build a nanofibrous poly(l-lactide) scaffold with interconnected macropores, where chitosan nanofibers about 500 nm in diameter were incorporated via the second phase separation. The content of nanofibrous chitosan was determined to be 5.76 in weight percentage by elemental analysis. The composite scaffold showed the highest protein adsorption of 7225 ± 116 μg/cm³ and the most hydroxyapatite crystal deposition in the mineralization. Compared with non-nanofibrous poly(l-lactide) scaffold, nanofibrous poly(l-lactide) scaffold exhibited a much faster degradation, but it could be restrained by the introduced chitosan nanofibers. The bone mesenchymal stem cell culture results indicated that the cells would rather attach and stretch along the chitosan nanofibers in the composite scaffold that showed the highest viability and the best cytocompatibility may be attributed to the biomimetic nanofibrous network and good cell affinity of chitosan nanofibers.     

Calcium silicate ceramic scaffolds toughened with hydroxyapatite whiskers for bone tissue engineering

Calcium silicate possessed excellent biocompatibility, bioactivity and degradability, while the high brittleness limited its application in load-bearing sites. Hydroxyapatite whiskers ranging from 0 to 30 wt.% were incorporated into the calcium silicate matrix to improve the strength and fracture resistance. Porous scaffolds were fabricated by selective laser sintering. The effects of hydroxyapatite whiskers on the mechanical properties and toughening mechanisms were investigated. The results showed that the scaffolds had a uniform and continuous inner network with the pore size ranging between 0.5 mm and 0.8 mm. The mechanical properties were enhanced with increasing hydroxyapatite whiskers, reached a maximum at 20 wt.% (compressive strength: 27.28 MPa, compressive Young's modulus: 156.2 MPa, flexural strength: 15.64 MPa and fracture toughness: 1.43 MPa·m^1/2) and then decreased by addition of more hydroxyapatite whiskers. The improvement of mechanical properties was due to whisker pull-out, crack deflection and crack bridging. Moreover, the degradation rate decreased with the increase of hydroxyapatite whisker content. A layer of bone-like apatite was formed on the scaffold surfaces after being soaked in simulated body fluid. Human osteoblast-like MG-63 cells spread well on the scaffolds and proliferated with increasing culture time. These findings suggested that the calcium silicate scaffolds reinforced with hydroxyapatite whiskers showed great potential for bone regeneration and tissue engineering applications.     

Preparation of organic and carbon xerogels using high-temperature–pressure sol–gel polymerization

To prepare organic gels at temperatures higher than normal boiling point of solvent, a method was developed using sol–gel polymerization in atmosphere saturated by vapor of solvent. To illustrate the advantages of proposed method, two series of gels were prepared using the conventional (T_curing = 70 °C) and the high temperature (T_curing = 140–170 °C) sol–gel polymerization. While no drying shrinkage was observed in our proposed method, 5–18% linear shrinkage occurred in conventional method depending on resin concentration in sol. Moreover, rising of curing temperature reduced the required time for preparation of organic gels from 5 days to lower than 5 h. The effects of processing parameters were investigated on physical and mechanical properties of organic xerogels. The results revealed that resin concentration significantly affects both density and compressive strength of final xerogels. While the curing temperature had no obvious effect on density, the raising of curing temperature significantly enhance the strength of organic xerogels. Carbon xerogels prepared by pyrolysis of novolac aerogels in inert atmosphere. The textures of the carbon xerogels were denser than corresponding organic xerogels, as evidenced by scanning electron microscopy (SEM) images. N₂ adsorption tests indicated that carbon aerogels were mainly meso or macroporous depending on resin concentration in initial sol.     

Synthesis of a novel tertiary amine containing urethane dimethacrylate monomer (UDMTA) and its application in dental resin

A novel tertiary amine containing urethane dimethacrylate monomer UDMTA was synthesized with the aim of replacing Bis-GMA as one component of dental restorative materials. The structure of UDMTA was confirmed by FT-IR and ¹H-NMR spectra. UDMTA was incorporated into Bis-GMA/TEGDMA (50 wt%/50 wt%) resin system to replace Bis-GMA partly and totally. Double bond conversion, polymerization volumetric shrinkage, water sorption and solubility, flexural strength and modulus of UDMTA containing resin formulations were studied with neat Bis-GMA/TEGDMA resin formulation as a reference. Results showed that UDMTA could be used as a coinitiator in photocurable dental resin, UDMTA containing resin had higher double bond conversion and lower polymerization shrinkage than that of Bis-GMA/TEGDMA resin, and the UDMTA containing copolymer had higher flexural strength and flexural modulus than Bis-GMA/TEGDMA copolymer. When UDMTA was used to replace more than 25 wt% of Bis-GMA, the obtained copolymer had higher water sorption and solubility. The optimized resin composition is by replacing 25 wt% of Bis-GMA in Bis-GMA/TEGDMA (50/50 by wt%), for the prepared resin had the best comprehensive properties.     

Enhancement of dielectric and electrical properties in BT/SiC/PVDF three-phase composite through microstructure tailoring

A polymer composite with high dielectric permittivity was prepared by embedding silicon carbide (SiC) whisker with an average diameter of 500 nm–1 μm in poly(vinylidene fluoride) (PVDF). However, the high dielectric loss and electrical conductivity of the two-phase composite prohibits its potential applications. Barium titanate (BT) particles with average diameter of 100 nm and 1 μm were incorporated as a third phase to fabricate a three-phase composite. The morphology structure, dielectric and electrical properties before and after the addition of BT particles were investigated. The three-phase composite exhibits largely suppressed dielectric loss and electrical conductivity without sacrificing the high dielectric permittivity, which was extremely hard to be realized for two-phase composite. It is also found that the nano-size BT is more favorable in achieving high dielectric permittivity than the micro-size BT, where their dielectric loss and electrical conductivity are similar. Furthermore, electric modulus analysis confirms the largely suppressed electron conduction process which results in the enhanced dielectric and electrical properties in three-phase composite.     

Functional shape memory composite nanofibers with graphene oxide filler

In the present study, we prepared a series of graphene oxide (GO) filled shape memory polyurethane (SMPU) nanofibers and systematically investigated the morphological, thermal and mechanical properties, surface wettability, and the shape memory effect (SME) followed by the proposed programming model. The results show that GO can be well dispersed within the SMPU matrix, and the introduction of GO significantly improves the mechanical strength, surface wettability, and thermal stability of the SMPU. Compared with pristine SMPU nanofibrous mats, the prepared SMPU/GO nanofibrous mats have better SME and lower thermal shrinkage. When the loading amount of GO increased to 4.0 wt%, the thermal shrinkage ratio (R_ts) of composite nanofibrous mats could be as low as 4.7 ± 0.3%, while the average fixation ratio (R_f) and recovery ratio (R_r) could be as high as 92.1% and 96.5%, respectively. The study indicates that GO is a desirable reinforcing filler for preparing shape memory nanofibers with improved properties.     

Silk fibroin immobilization on poly(ethylene terephthalate) films: Comparison of two surface modification methods and their effect on mesenchymal stem cells culture

Silk fibroin (SF) has played a curial role for the surface modification of conventional materials to improve the biocompatibility, and SF modified poly(ethylene terephthalate) (PET) materials have potential applications on tissue engineering such as artificial ligament, artificial vessel, artificial heart valve sewing cuffs dacron and surgical mesh engineering. In this work, SF was immobilized onto PET film via two different methods: 1) plasma pretreatment followed by SF dip coating (PET-SF) and 2) plasma-induce acrylic acid graft polymerization and subsequent covalent immobilization of SF on PET film (PET-PAA-SF). It could be found that plasma treatment provided higher surface roughness which was suitable for further SF dip coating, while grafted poly(acrylic acid) (PAA) promised the covalent bonding between SF and PAA. ATR-FTIR adsorption band at 3284 cm^? 1, 1623 cm^? 1 and 1520 cm^? 1 suggested the successful introduction of SF onto PET surface, while the amount of immobilized SF of PET-SF was higher than PET-PAA-SF according to XPS investigation (0.29 vs 0.23 for N/C ratio). Surface modified PET film was used as substrate for mesenchymal stem cells (MSCs) culture, the cells on PET-SF surface exhibited optimum density compared to PET-PAA-SF according to CCK-8 assays, which indicated that plasma pretreatment followed by SF dip coating was a simple and effective way to prepare biocompatible PET surface.     

Size-scale effects of silica on bis-GMA/TEGDMA based nanohybrid dental restorative composites

The present study focuses on the effect of size-scale combination of silica on the mechanical and dynamic mechanical properties of acrylate based (50% Bis-GMA and 50% TEGDMA by weight) composites with an aim to overcome the conventional problem of high-volume fraction filling of acrylate based composites, typically used in restorative dentistry. Two classes of light-cured composites based on the size-scale combination of silica (7 nm + 2 μm; 14 nm + 2 μm) as the filler were prepared. FTIR spectroscopy revealed functionality and interactions whereas morphological investigations concerning the state of distribution and dispersion of nano- and micro-silica has been carried out by SEM–EDX Si-dot mapping. The dynamic mechanical properties, compressive, flexural and diametral tensile strengths were characterized. Micromechanical analysis of viscoelastic storage moduli following Kerner composite model has revealed an enhancement in the reinforcement efficiency of the nanohybrid composites based on the filler size-scale combination of 14 nm + 2 μm with 10 wt.% nanofiller loading. The compressive strength of the micro-filled composite (with 2 μm silica only) was found to remain comparable to that of the nanohybrid with 5 wt.% of 7 nm silica and 10 wt.% of 14 nm silica filled composites. Diametral tensile strength has been observed to be influenced by the size-scale combination and extent of nanofiller loading. The effective volume fractions in the composites validating the experimentally determined DTS were calculated following Nicolais–Narkis model. Our study demonstrates the conceptual feasibility of exploring the optimization of size-scale combinations of filler for enhancement in reinforcement efficiency by manipulating the volume fraction of filler induced immobilized polymer chains by resorting to the principle of micromechanics.     

Structure,morphology and cell affinity of poly(l-lactide) films surface-functionalized with chitosan nanofibers via a solid–liquid phase separation technique

Poly(l-lactide) films with a nano-structured surface by immobilizing chitosan nanofibers (CSNFs) for improving the cell affinity were fabricated via a solid-liquid phase separation technique. The successful grafting of CSNFs on the surface of poly(l-lactide) films was confirmed by the binding energy of N1s at 398.0 eV in the X-ray photoelectron spectroscopy and the amide I and II bands of chitosan at 1650 and 1568 cm^? 1 in the Fourier transform infrared spectroscopy. Compared with the poly(l-lactide) film, the hydrophilicity was improved with a lower water contact angle of 83.3 ± 1.9° and 75.3 ± 2.5° for the CSNFs-grafted and CSNFs-grafted/anchored poly(l-lactide) films respectively. The scanning electron microscopy and atomic force microscopy analyses showed that the grafted CSNFs with 50–500 nm in diameter were randomly arranged on the film surface and entangled with the anchored CSNFs on the outermost layer. The 3T3 fibroblasts culture indicated cells tended to attach and stretch along the CSNFs on the film surface. The cell viability measurement revealed that among all the samples, the film with both grafted and anchored CSNFs exhibited the highest cell proliferation rate that was twice as much of the poly(l-lactide) film at 7 d. Herein, engineering a nano-structured surface by solid–liquid phase separation will be a promising tool for surface modification of biomaterials.     

Tribological behavior of poly (phenyl p-hydroxybenzoate)/polytetrafluoroethylene composites filled with hexagonal boron nitride under dry sliding condition

The sliding friction and wear behavior of polytetrafluoroethylene (PTFE) composites filled with poly (phenyl p-hydroxybenzoate) (PHBA) and hexagonal boron nitride (h-BN) was investigated with a pin-on-disc tester. The tensile properties, ball indentation hardness, impact strength and thermal diffusivity were measured. The test results in this paper indicate that the tensile strength, elongation at break, and impact strength decreased, however, the ball indentation hardness and thermal diffusivity were increased when the content of h-BN was increased. PTFE composites filled with 20 wt% PHBA and 20 wt% h-BN exhibited a comparative friction coefficient to pure PTFE. Meantime, the wear rate of the composite decreased about 15 times compared to pure PTFE. The synergistic effect of h-BN with low friction and PHBA with high bearing ability promoted the low friction coefficient and wear rate of h-BN/PHBA/PTFE composites.