Hydroxyapatite Whiskers Research Articles

Strong and bioactive dental resin composite containing poly(Bis-GMA) grafted hydroxyapatite whiskers and silica nanoparticles

Abstract Novel light-curable bioactive dental resin composite with enhanced physical and mechanical properties was prepared by combining poly(Bis-GMA)-grafted silanized hydroxyapatite whisker (PGSHW) with silanized silica (s-SiO 2 ) nanoparticles in a bisphenol A glycidyl methacrylate (Bis-GMA)/triethylene glycol dimethacrylate (TEGDMA) based dental resin matrix. The effect of PGSHW/s-SiO 2 mass ratios on properties of the resin composites was investigated. The grafted poly(Bis-GMA) on silanized hydroxyapatite whisker (HW) optimized the PGSHW–matrix interfacial properties and improved the reinforcing efficiency of PGSHW in the composites. The addition of s-SiO 2 effectively increased the degree of conversion and filler packing density of the resin composites. Mechanical test showed that PGSHW/s-SiO 2 (mass ratio 2:4) hybrid fillers significantly improved flexural strength, flexural modulus, compressive strength and work of fracture of the resin composite, which were 39.1%, 61.1%, 50.1%, and 85.9% higher than those of the resin composite with single PGSHW filler, respectively. Besides, in vitro bioactivity test indicated that resin composites containing PGSHW had superior apatite forming ability. In conclusion, PGSHW/s-SiO 2 (2:4) filled resin composite was developed with significantly improved mechanical properties and desirable bioactivity, a combination not available in current HA filled dental resin composite, which may be a promising material to reduce the occurrence of both restoration fracture and secondary caries.

Novel bionic dental resin composite reinforced by hydroxyapatite whisker

Hydroxyapatite whisker (HW) was synthesised and used as a bioactive filler to reinforce dental resin composite. The effect of HW mass fraction on physical and mechanical properties of the composite was investigated by universal testing machine, microhardness tester and field emission scanning electron microscope (FE-SEM). HW had a superior reinforcing efficacy. Flexural modulus and Vickers microhardness of the resin composite were continuously improved with the increase of whisker fraction. Impregnation of 20 wt-% silanised HW into the resin dramatically improved flexural strength and compressive strength by 33·4 and 11·3% respectively. However, higher whisker fraction would not further enhance the strength of the composite, which might result from poor whisker dispersion. At higher filler loading, whisker tended to form agglomerations which were similar to the microstructure of enamel. It was revealed that HW could be a promising filler to fabricate bionic dental restoration with reliability.

Hydrothermal preparation and characterization of ultralong strontium-substituted hydroxyapatite whiskers using acetamide as homogeneous precipitation reagent.

The ultralong strontium- (Sr-) substituted hydroxyapatite (SrHAp) whiskers were successfully prepared using acetamide as homogeneous precipitation reagent. The effect of the Sr substitution amount on the lattice constants and proliferation of human osteoblast cells (MG-63) was further investigated. The results showed that the SrHAp whiskers with diameter of 0.2–12 μm and ultralong length up to 200 μm were obtained and the Sr substitution level could be facilely tailored by regulating the initial molar ratio of Sr/(Sr + Ca) in raw materials. The Sr2+ replaced part of Ca2+ and the lattice constants increased apparently with the increase of the Sr substitution amount. Compared with the pure HAp whiskers, the Sr substitution apparently stimulated the proliferation of MG-63 at certain extracted concentrations. Our study suggested that the obtained SrHAp whiskers might be used as bioactive and mechanical reinforcement materials for hard tissue regeneration applications.

Prepartion and Properties of Zinc-Doped Hydroxyapatite Whisker

Hydroxyapatite is well used as bone repair materials. Degradation property and biological activity can be further improved by addition Zn into the HAP crystals. Zinc-doped hydroxyapatite whiskers with different content of Zn were prepared with calcium nitrate, Zinc nitrate and diammonium phosphate at the degree of 95°C. Zinc-doped hydroxyapatite whiskers were characterized by XRD, FT-IR, SEM and EDS. It was indicated that zinc can be doped in hydroxyapatite with proper process and zinc-doped hydroxyapatite whiskers were produced successfully.

Polymer grafted hydroxyapatite whisker as a filler for dental composite resin with enhanced physical and mechanical properties

The objective of this study was to investigate the effect of surface graft polymerization of hydroxyapatite whisker (HW) on physical and mechanical properties of dental composite resin. Poly bisphenol A glycidyl methacrylate (Poly(Bis-GMA)) was grafted onto silanized hydroxyapatite whisker (SHW) via solution polymerization and the amount of the Poly(Bis-GMA) on the surface was effectively controlled by polymerization time. The obtained poly(Bis-GMA) grafted hydroxyapatite whisker (PGHW) with different polymer contents was filled into a resin matrix respectively, meanwhile the composites with HW and with SHW served as controls. Monomer conversion was characterized by Fourier transform infrared spectroscopy (FTIR) and volume shrinkage of the composite resin was measured with a density tester. Mechanical properties were tested with a universal testing machine. The results indicated that the composite filled with PGHW-1h (graft ratio of poly(Bis-GMA): 8.5wt.%) showed lower shrinkage and better mechanical properties, improving flexural strength by 6.5% and 11.9% compared with SHW filled composite and HW filled composite, respectively. However, PGHW with higher graft ratios aggregated seriously and formed defects in the composite, leading to deterioration of mechanical properties. It was revealed that the poly(Bis-GMA) on the surface of PGHW acted as a functional transition layer and enhanced interfacial compatibility and interaction between whisker and resin matrix, which facilitated the dispersion of PGHW in the composite and decreased the composite shrinkage. Thus, the graft polymerization of Bis-GMA on the surface of filler might be a promising modification method for the fabrication of dental materials.

Preparation and Characterization of Hydroxyapatite Whiskers

Hydroxyapatite whiskers were prepared with diammonium hydrogen phosphate, calcium nitrate, nitric acid, sorbitol, HAP seed and carbamide by hydrothermal homogeneous precipitation. The HAP seeds served as whiskers nuclei and sorbitol served as template. The prepared hydroxyapatite whiskers were characterized by XRD,SEM and FTIR. It was indicated that hydroxyapatite whiskers with high crystallinity grew alone Z axis with carbonated trend, and the appearance of HAP was smooth, less magazine and no reunion, the length-diameter ratio of the whiskers was in range of 125-8 with the average is 32.78.

Study on the Preparation of Strontium-Doped Hydroxyapatite Whisker

Hydroxyapatite is well used as bone repair materials, due to its properties that can be combined with strontium to improve mechanical property and degradation property. In this article, hydroxyapatite whiskers with different amount of doped strontium were prepared with diammonium phosphate, calcium nitrate and strontium nitrate at 94 °C. Fourier transform infrared spectroscopy (FTIR) was used to identify the functional groups. X-ray diffraction (XRD) analysis was carried out to study the phase composition and crystallinity of the whisker. The morphology of the whiskers was characterized by scanning electron microscope (SEM). It was indicated that strontium can be doped in hydroxyapatite with proper process and then the strontium-doped hydroxyapatite whiskers were produced successfully.

The Effect of Modification of Hydroxyapatite Whisker with Zinc Acetate via Sol-Gel Technology

Antibacterial activity of zinc oxide (ZnO) or strengthening of hydroxylapatite whisker (HAPw) had been studied and applied widely. However, antibacterial property of ZnO-HAPw was scarcely researched nowadays. The aim of this study was to further investigate several kinds of morphologies of ZnO-HAPw prepared by sol-gel technology at different pondus hydrogenii (pH) value and temperature. Four kinds of morphologies of ZnO-HAPw were granule, triangle, short rod and gongs nail at 70°C and pH=6.4, 37°C and pH=6.6, 70°C and pH=6.6, 70°C and pH=6.6. The SEM images of HAPw and ZnO-HAPw samples showed that the HAPw surface was smooth and no difference after annealing treatment. In addition, different shapes of nanoZnO fused uniformly on the HAPw surface. The EDS indicates nanoZnO fuses on HAPw surface.

In-situ grown hydroxyapatite whiskers reinforced porous HA bioceramic

To improve the mechanical properties of a porous bioceramic without reducing its porosity, a new kind of porous hydroxyapatite (HA) bioceramic with in-situ grown HA whiskers was fabricated using a simple sintering method. CaSO42H2O was used as a pore-forming medium and also as a catalyst for the growth of in-situ HA whiskers. The bioceramic was analyzed by XRD, SEM and mechanical tests. In-situ grown HA whiskers were stratified on the cliffs of pores in the bioceramic. The compressive strength is as high as 21.7 MPa with the porosity of about 26%. The results show that porous HA bioceramic can be improved in both compressive strength and porosity by the addition of CaSO42H2O. This novel HA bioceramic has a higher compressive strength without reducing its porosity in a certain weight ratio of CaSO42H2O, which depends on its two-step fracture pattern. This novel structure provides a new and promising reinforced pattern for porous materials. & 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Preparation and Characterization of Hydroxyapatite Whiskers

The HAP whiskers were prepared by hydrothermal homogeneous precipitation method at the constant temperature. Diammonium hydrogen phosphate, calcium nitrate tetrahydrate, urea and nitric acid were used as the main raw materials. Sorbitol was selected as the template agent and the hydroxyapatite whiskers seeds were served as the inducers. SEM, TEM, XRD and EDS were applied in characterization. The results show that the reaction products are the HAP whiskers with high crystallinity, smooth appearance and no agglomeration; the obtained HAP whiskers are monocrystal and the length-diameter ratio distribution of the HAP whiskers is concentrated at about 30.

Hydrothermal synthesis of calcium-deficient hydroxyapatite whiskers and their thermal transformation to polycrystalline β-tricalcium phosphate short fibers

Resorbable calcium phosphate fibers are of particular interest to reinforce biodegradable bone substitutes for load-bearing applications. The aim of the present study was to prepare calcium-deficient hydroxyapatite (dHAp) whiskers with a molar Ca/P ratio of 1·5 by a hydrothermal synthesis and to transform them to β-tricalcium phosphate (β-TCP) by a subsequent thermal treatment. For the hydrothermal synthesis, calcium tripolyphosphate was used and different amounts of 2-propanol were added to adjust the pH. Average whisker lengths of 160 µm were obtained at a 2-propanol content of 27 volume-percent. However, 33% dicalcium phosphate anhydrate (DCPA) were present as a secondary phase. The amount of DCPA could be reduced by increasing the amount of 2-propanol. Whisker samples consisting of 88% dHAp and 12% DCPA were selected to investigate microstructural changes and phase transformations during thermal treatment. Polycrystalline single phase -TCP short fibers were obtained after a thermal treatment at 1125°C.

Effects of the mold temperature on the mechanical properties and crystallinity of hydroxyapatite whisker‐reinforced polyetheretherketone scaffolds

Porous and bioactive polyetheretherketone (PEEK) scaffolds have potential to replace metallic scaffolds for biologic fixation of permanent implants adjacent to trabecular bone, such as interbody spinal fusion devices. The objective of this study was to investigate the effects of the mold temperature and PEEK powder on the mechanical properties and crystallinity of hydroxyapatite (HA) whisker-reinforced PEEK scaffolds prepared using compression molding and porogen leaching. Scaffolds were prepared at mold temperatures ranging 340-390°C with a 50 or 10 μm PEEK powder, 75 vol% porosity, and 20 vol% HA whiskers. Scaffold mechanical properties were evaluated in unconfined, uniaxial compression and the PEEK matrix crystallinity was measured using specular reflectance Fourier transform infrared spectroscopy. Increased mold temperature resulted in increased compressive modulus, yield strength, and yield strain, reaching a plateau at ~370°C. HA reinforcements were observed to be segregated between PEEK particles, which inhibited PEEK particle coalescence during compression molding at temperatures less than 365°C but also ensured that bioactive HA reinforcements were exposed on scaffold strut surfaces. Increased mold temperature also resulted in decreased PEEK crystallinity, particularly for scaffolds molded at greater than 375°C. The PEEK powder size exhibited relatively minor effects on the scaffold mechanical properties and PEEK crystallinity. Therefore, the results of this study suggested that HA-reinforced PEEK scaffolds should be compression molded at 370-375°C. The apparent compressive modulus, yield strength, and yield strain for scaffolds molded at 370-375°C was 75-92 MPa, 2.0-2.2 MPa, and 2.5-3.6%, respectively, which was within the range exhibited by human vertebral trabecular bone.

Electric poling of cement composites of hydroxyapatite whiskers with chitosan and their chemical properties in simulated body fluid

Electric poling of cement composites of hydroxyapatite whiskers with chitosan and their chemical properties in simulated body fluid

Synthesis of hydroxyapatite whiskers

The synthetic method of nanosized hydroxyapatite Ca5(PO4)3OH (∼80–100 nm) is optimized. The functional structure is analyzed in a wide temperature range using the combination of the high-temperature X-ray diffraction method, differential thermal analysis, and infrared spectroscopy. A novel method of obtaining hydroxyapatite whiskers without using hydrothermal conditions is developed.

Modified poly(vinylidene fluoride) hollow fiber composite membranes reinforced by hydroxyapatite nanocrystal whiskers

AbstractThe modified poly(vinylidene fluoride) (PVDF) hollow fiber composite membranes reinforced by hydroxyapatite (HAP) nanocrystal whiskers were fabricated with wet‐spinning method. The PVDF/HAP/N‐methyl‐2‐pyrrolidone dope solutions experienced delayed demixing mechanism, and the precipitation rate slightly increased as the HAP whisker content increased. The cross sections of PVDF‐HAP and neat PVDF hollow fiber composite membranes were composed of five distinct layers: two skin layers, two finger‐like sublayers, and a sponge‐like layer. The Young's modulus of and tensile strength of the PVDF‐HAP hollow fiber membranes gradually increased with the addition of nano‐HAP whiskers. The elongation ratio was also improved, which was different from the polymeric membranes modified by other inorganic nanofillers. The permeation flux of the PVDF‐HAP hollow fiber membranes slightly increased with the increase of HAP content in the composite membranes as its hydrophilicity was improved. The crystallization behaviors of PVDF in the composite membranes were also investigated. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Hydroxyapatite Whisker Effect on Strength of Calcium Phosphate Bone Cement

Hydroxyapatite whisker was the reinforcement phase to prepare whisker/calcium phosphate cement composites, which was obtained by homogeneous precipitation method, with 2.5~15 microns in length, 2~30 length/diameter ratio. Mechanical properties and microstructure of composites were tested. With the increase of hydroxyapatite whisker addition, composites strength reduces after the first rise. When hydroxyapatite whisker is added to 4%(wt), the composite achieves the maximum strength. SEM method was used to observe fracture microstructures of composite materials. As a result, dispersion degree of the HA whisker affects the strength of the material. Too much whiskers can form agglomerates, which weaken composite strength.

Mechanical properties of hydroxyapatite whisker-reinforced bis-GMA-based resin composites

ObjectiveTo evaluate the reinforcement efficacy of hydroxyapatite (HA) whiskers in bis-GMA-based dental restorative composites and determine the effect of volume fraction on the mechanical properties. MethodsSilanized HA whiskers and nano-scale powder were mixed in various proportions with bis-phenol A-glycidyl methacrylate (bis-GMA)-based polymer pastes. Equal parts of initiator and accelerator pastes were then mixed by hand. After curing at 25±2°C and storage in distilled water at 37°C for 24h, elastic modulus, fracture strength and work-to-failure in three-point bending, fracture toughness using a notchless triangular prism fracture method, and Vickers hardness were determined. Data were examined by means of one-way analysis of variance and linear regression. ResultsReinforcing efficacy was significantly dependent on filler morphology. Whiskers had good dispersibility and wettability with bis-GMA-based polymer, conferring good reinforcement and toughening, significantly better than did the HA nano-scale powder. SignificanceHA whiskers provided better mechanical properties in bis-GMA-based composites compared with the nano-scale powder. Such whisker-reinforced materials may be beneficial compared with currently used dental restorative materials.

Comparative evaluation of fluoride release from hydroxyapatite incorporated and conventional glass ionomer cement: An in vitro study

Glass ionomers are most commonly used esthetic restorative material, but has inferior mechanical properties. The search to improve its mechanical properties led to the use of hydroxyapatite (HA) whiskers as strengthening material for glass ionomer cement but its effect on fluoride release is still not clear. To evaluate and compare the fluoride release from HA incorporated glass ionomer and conventional glass ionomer cement (CGIC). This in vitro study comprised of total forty sample. Twenty Specimens of each HA incorporated glass ionomer and conventional glass ionomer were fabricated. Specimens were suspended individually in 25 mL of distilled water in a 50 mL plastic container and stored at 37°C. Distilled water was renewed every 24 h for 21 days. Fluoride release of sample was measured every 24 h for 7 days and weekly from 7 th day to 21 st day using Sension4 pH/ion selective electrode/mV meter. Descriptive statistics, Repeated Measure analysis of variance, Paired Sample t-test, Independent Sample t-test, scheffe post hoc test. There was a significant decrease in the mean fluoride release from day 1 to day 21 for both the groups hydroxyapatite glass ionomer cement and conventional glass ionomer cement ([HA-GIC] and CGIC). Though, the mean values of HA-GIC were slightly lower than C GIC, there was no statistically significant difference in the mean fluoride release between HA-GIC and CGIC throughout the experimental period. Within the limitations of this experimental design, definitive conclusions cannot be drawn and further investigations at a molecular level are needed to evaluate the trend of fluoride release from this material.

Micromechanical Model for the Orthotropic Elastic Constants of Polyetheretherketone Composites Considering the Orientation Distribution of the Hydroxyapatite Whisker Reinforcements

Hydroxyapatite (HA) whisker reinforced polyetheretherketone (PEEK) composites have been investigated as bioactive materials for load-bearing orthopedic implants with tailored mechanical properties governed by the volume fraction, morphology, and preferred orientation of the HA whisker reinforcements. Therefore, the objective of this study was to establish key structure-property relationships and predictive capabilities for the design of HA whisker reinforced PEEK composites and, more generally, discontinuous short fiber-reinforced composite materials. HA whisker reinforced PEEK composites exhibited anisotropic elastic constants due to a preferred orientation of the HA whiskers induced during compression molding. Experimental measurements for both the preferred orientation of HA whiskers and composite elastic constants were greatest in the flow direction during molding (3-axis, C33), followed by the transverse (2-axis, C22) and pressing (1-axis, C11) directions. Moreover, experimental measurements for the elastic anisotropy and degree of preferred orientation in the same specimen plane were correlated. A micromechanical model accounted for the preferred orientation of HA whiskers using two-dimensional implementations of the measured orientation distribution function (ODF) and was able to more accurately predict the orthotropic elastic constants compared to common, idealized assumptions of randomly oriented or perfectly aligned reinforcements. Model predictions using the 3-2 plane ODF, and the average of the 3-1 and 3-2 plane ODFs, were in close agreement with the corresponding measured elastic constants, exhibiting less than 5% average absolute error. Model predictions for C11 using the 3-1 plane ODF were less accurate, with greater than 10% error. This study demonstrated the ability to accurately predict differences in orthotropic elastic constants due to changes in the reinforcement orientation distribution, which will aid in the design of HA whisker reinforced PEEK composites and, more generally, discontinuous short fiber-reinforced composites.

Synthesis of strontium substituted hydroxyapatite whiskers used as bioactive and mechanical reinforcement material

The strontium substituted hydroxyapatite (SrHA) whiskers with 6.6mol% of Ca replaced by Sr were successfully synthesized via homogeneous precipitation method. The product had a width of 0.2–8μm and length up to 155μm. The human osteoblast-like cell (MG-63) culture showed that Sr substitution could stimulate the proliferation of MG-63 at certain extracted concentrations. Furthermore, the addition of SrHA whiskers could significantly improve the mechanical properties of calcium phosphate cement (CPC). The 5wt.% SrHA whisker reinforced CPC revealed the highest compressive strength of 2.92MPa, which was almost 2-times higher than that of the pure CPC. Our study indicated that SrHA whisker might be a potential candidate as a new bioactive and mechanical reinforcement material for hard tissue regeneration applications.