Manufacture of macroporous calcium hydroxyapatite bioceramics

Trabecular bones of almost all vertebrate organisms basically consist of macroporous (55–70% interconnected porosity) bone mineral, i.e. calcium hydroxyapatite (HA: Ca₁₀(PO₄)₆(OH)₂). The macroporosity observed in the trabecular bones then allows the ingrowth of the soft tissues and organic cells into the bone matrix. Sub-micron, chemically uniform, and high phase-purity HA powders produced in our laboratory were mixed, under vigorous ultrasonification, with methyl cellulose of appropriate amounts in the form of an aqueous slurry of proper viscosity and thickness. The ceramic cakes produced in this way were then slowly dried in an oven in the temperature range of 50–90 °C. Dried cakes of porous HA were physically cut into various prismatic shapes. These parts were then slowly heated in an air atmosphere to the optimum sintering temperature of 1250 °C. The HA bioceramic parts obtained by this novel ‘foaming technique’ were found to have tractable and controllable interconnected porosity in the range of 60–90%, with typical pore sizes ranging from 100–250 microns. Sample characterization was mainly achieved by scanning electron microscopy (SEM) studies and three-point bending tests.     

Fabrication and characterization of bioactive glass (45S5)/titania biocomposites

Bioactive glass (BG) (45S5) has been used successfully as bone-filling material in orthopedic and dental surgery but its lean mechanical strength limits its applications in load-bearing positions. Approaches to strengthen these materials decreased their bioactivity. In order to realize the optimal matching between mechanical and bioactivity properties, bioactive glass (45S5) was reinforced by introducing titania (TiO₂) in anatase form and treated at 1000 °C to form new bioactive glass/titania biocomposites. The prepared biocomposites were assessed by XRD, FT-IR, mechanical properties and SEM. The results verified that the increase of titania percentage to BG powder enhanced gradually the mechanical data of the prepared biocomposites. SEM and FT-IRRS confirmed the presence of a rich bone-like apatite layer post-immersion on the composite surface. It has been found that the new BG/titania biocomposite materials especially those containing high content of titania have high bioactivity properties and compressive strength values comparable to cortical bone. Therefore, these biocomposite materials are promising for medical applications such as bone substitutes especially in load-bearing sites.     

Fabrication and characterization of bioactive calcium silicate microspheres for drug delivery

The calcium silicate (CaSiO₃, CS) microspheres with diameter of 75–100 μm were fabricated by a spray-drying method. A new bone-like apatite layer fully covered the surface of the fabricated CS microspheres after soaking in simulated body fluid (SBF), suggesting the excellent activity of the material in inducing apatite deposition. The ionic extracts of CS microspheres promoted the proliferation of human osteoblast-like cells (MC3T3-E1). In addition, the porous structures of the CS microspheres resulted in favorable drug loading and sustained release property. Our study indicates that the fabricated multifunctional CS microspheres are a promising drug delivery system as an injectable bioactive filling material for bone-regeneration.     

Modelling the mechanical properties of microporous and macroporous biphasic calcium phosphate bioceramics

Macroporous biphasic calcium phosphate bioceramics, for use as bone substitutes, have been fabricated by cold isostatic pressing and conventional sintering, using naphtalen particles as a porogen to produce macropores. The resulting ceramics, composite materials made of hydroxyapatite and β-tricalcium phosphate (TCP) containing 45% macropores and with various microporosities, have been submitted to compression and three-point bending tests, toughness tests by single-edge-notched-bending (SENB), and spherical indentation tests. By combining two approaches at two different scales, one for closed porosity and one for open porosity, a model is established to describe mechanical properties as a function of the amount and morphology of porosity. The model assumes a quasi-continuous matrix containing macropores, the matrix being itself microporous, and considers that fracture always initiates on a macropore. The preliminary mechanical tests performed on the sintered ceramics tend to validate the modelling approach.     

Effect of feldspar addition into bioglass 45S5 composition: Crystallization kinetics and thermal transformation

Thermal transformations of glasses with formulations derived from Bioglass 45S5 with Al₂O₃ (≤2.5 wt %) and K₂O additions through K-feldspar were studied. Crystallization kinetics and transformations were followed-up by X-ray diffraction and differential thermal analysis. The activation energy of crystallization of Na₂CaSi₂O₆ was found to be lower than that of Bioglass 45S5 for the prepared samples. This behavior was attributed to an increase in phase separation in glasses. Nevertheless, transformations shifted towards higher temperatures with addition of feldspar, due to a decrease in pre-exponential factor. Cell parameters evolved progressively with increasing temperature without any abrupt changes. Al₂O₃ and K₂O remained as a part of a residual glassy phase.     

Evaluation of colloidal and polymeric routes in sol-gel synthesis of a bioactive glass-ceramic derived from 45S5 bioglass

This work studied the influence of two sol-gel synthesis routes in obtaining a bioactive glass-ceramic derived from the 45S5 composition: a polymeric and a colloidal route. The main difference between the routes is in the silica precursor employed. The tetraethyl orthosilicate metal alkoxide (Si(OC₂H₅)₄ - TEOS) is used in polymeric route and the silicic acid (H₄SiO₄) was used in the colloidal route. The synthesized xerogels were calcined at different temperatures to eliminate undesirable compounds and to verify the crystallization behavior. Afterwards, the calcined xerogels were submitted to in vitro bioactivity assay. The samples were also characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and laser diffraction. After calcination, the glass-ceramics obtained by the colloidal route showed greater number of bioactive phases and, consequently, of NBO bonds. The larger amount of NBO bonds resulted in a higher bioactivity of the materials synthesized by the colloidal route. In addition, the long hydrolysis step of the metal alkoxides was eliminated with colloidal synthesis. This allowed a significant reduction in the total synthesis time from 13 days to 24 h. To the best of our knowledge, this seems to be the first time this colloidal route has been employed in the synthesis of bioglass 45S5.     

A comprehensive study on compositional and structural changes in 45S5 bioglass products exposed to simulated body fluid

The interaction of fully dense 45S5‐bioglass derived samples produced by Spark Plasma Sintering (SPS) with simulated body fluid (SBF) solution was investigated in detail taking advantage of the Rietveld refinement method to quantitatively evidence the corresponding microstructural and compositional changes. It is observed that, when the original amorphous nature is mostly (75 wt%) preserved in the material during sintering (550°C, 2 minutes), the resulting specimens dissolve faster and determine relatively higher pH increase and ions release in the SBF solution. Correspondingly, a relatively lower amount of hydroxycarbonate apatite (HCA) is formed on their surface. In contrast, a more extensive apatite layer with trabecular structure is generated within 3 days storage on the surface of fully crystallized samples obtained at 600°C by SPS, which only consists of Na–Ca silicate grains (20 nm). Moreover, as the sintering temperature and dwell time were increased to 700°C and 20 minutes, respectively, a rhenanite‐like phase was also formed (about 15 wt%), other than crystallites growth to 90 nm. Interestingly, the presence of rhenanite provides a beneficial contribution for the production of the HCA layer, which was found the largest for this system when considering storage periods of 7 and 14 days, respectively.     

Fabrication and characterization of novel macroporous cellulose–alginate hydrogels

Novel macroporous hydrogels were prepared by blending of cellulose and sodium alginate (SA) solution, and then cross-linking with epichlorohydrin. The resulting cellulose/SA hydrogels were characterized by solid-state ¹³C NMR, wide-angle X-ray diffraction (WXRD), thermo-gravimetric analysis (TGA), scanning electron microscopy (SEM), rheological measurement, dynamic mechanical analysis (DMA) and swelling test to evaluate their structure, interior morphology, gelation time, compressive modulus, and equilibrium swelling ratio. Our findings revealed that the cellulose acted as backbone in the hydrogels, whereas SA contributed to the higher equilibrium swelling ratio. The combination of cellulose having semi-stiff chains and SA containing –COOH groups in the cross-linking hydrogel created the macroporous structure. This work provided a new pathway for preparation of hydrogel with large porous structure through incorporation of stiff polymer as support of pore wall and acidic polysaccharide as expander of pore size because of high water-absorbency.     

表面改性超细硅酸钙的制备及其性能表征

采用沉淀法,以硝酸钙[Ca(NO3)2·4H2O]和硅酸钠(Na2SiO3·9H2O)为原料,在合成超细硅酸钙的同时对其进行表面改性.比较了聚乙二醇、硬脂酸钠、十二烷基苯磺酸钠等不同分散剂对硅酸钙粒径的影响,并分析讨论了其分散作用机理.采用激光粒度仪对产物进行粒径分析,并用X射线衍射仪(XRD)、红外光谱仪(FT-IR)以及扫描电子显微镜(SEM)对产物的物相、微观形貌等进行了表征.实验结果表明,选择合适的分散剂并控制工艺条件,可制得团聚度小的硅酸钙超细粉体.当在反应中添加占硝酸钙质量1%的聚乙二醇时,所制得的硅酸钙粉体的平均粒径为0.12 μm,且晶粒尺寸均匀,结晶良好.     

Shear viscosity of nylon 6 melts reinforced with microfibrous calcium silicate hydrate

Steady shear viscosity of nylon 6 melts reinforced with xonotlite, microfibrous calcium silicate hydrate (6CaO · 6SiO₂ · H₂O), is investigated. The highly filled nylon 6 melt tends to exhibit a yield value, resulting in remarkable viscosity increase particularly at low shear rates. Addition of the xonotlite significantly increases activation energy of viscous flow of the nylon 6 melt, leading the viscosity to be strongly temperature dependent. Comparisons with the melts filled with glass fibers and wollastonite are made. Flow-induced orientation becomes more important at low volume fractions. Shortening of the xonotlite during shear flow measurement can also be observed.     

Effects of GPTMS concentration and powder to liquid ratio on the flowability and biodegradation behaviors of 45S5 bioglass/tragacanth bioactive composite pastes

Injectable composite pastes were prepared using melt-derived 45S5 bioactive glass and tragacanth crosslinked by (3-glycidyloxypropyl)trimethoxysilane (GPTMS). The effect of powder to liquid ratio (P:L = 1.0:2.0–1.0:2.5) and GPTMS/tragacanth ratio (0.0–1.5) on the injectability, swelling behavior, rheology, bioactivity, and cellular behavior of the pastes was investigated. Based on the results, the apparent stability and consistency of the pastes increased upon crosslinking by GPTMS. Due to the increased interactions between tragacanth and glass, a hysteresis loop with larger area was formed in the presence of GPTMS. With increase of GPTMS:tragacanth ratio from 0 to 1.5, the swelling percent dropped from 24.65 to 16.25% after 24 h and the degradation percent also went down from 27.89 to 9.11% after 21 days in the simulated body fluid. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay showed a drop in the optical density of MG63 osteoblasts up to 30.07% after exposure to the GPTMS-crosslinked composite pastes for 3 days. However, the number of viable cells gradually increased in the presence of the pastes and the cell morphology remained unchanged over time. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47604.     

Preparation of novel porous calcium silicate scaffold loaded by celecoxib drug using freeze drying technique: Fabrication,characterization and simulation

In the current investigation, the microarchitecture of bio-nanocomposite scaffold, which is fabricated by natural synthetic diopside and composed of magnetite nanoparticles (MNPs), is considered. The MNPs are tested with various weight fractions (0, 5, 10, and 15 wt%) and are manufactured by the freeze-drying technique using sodium alginate as base matrix for the first time. Due to the limitation of the mechanical properties of calcium phosphates (CaPs) and bioactive glasses (BG), clinical usage of calcium silicate ceramics (CSC) are greatly affected. Therefore, CSCs are produced with the incorporation of metal oxides into the base binary xCaO-ySiO₂, as well as the substitution of calcium ions. Furthermore, mechanical and biological properties of CSCs are enhanced, which are a result of the ability to give out bioactive ions and their distinct compositions. After that, the porous bio-nanocomposite scaffolds are investigated for biological and mechanical properties corresponding to hardness versus elastic modulus, apatite formation versus biodegradation rate, wetting properties versus roughness and electrical conductivity of the sample. Then, the composition, microstructure, and physical characteristics are also examined using different techniques such as X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) which is equipped with energy-dispersive X-ray spectroscopy (EDX). The obtained outcomes show that addition of diopside bioceramic enhances the mechanical and physical properties of the samples. It is shown that the prepared porous bio-nanocomposite scaffolds, containing 10 wt% MNPs, represents a better agreement in serving as a bone graft for the cancer disease treatment and hyperthermia term. The results indicate that the specimen with 10 wt% MNPs in the bio-nanocomposite release the celecoxib drug easier, however, its has better porosity and mechanical behavior that make it suitable candidate for bone implantations.     

Fabrication and characterization of SiC whisker reinforced reaction bonded SiC composite

SiC whisker reinforced reaction bonded SiC composites have been developed for fabricating large scale, complex shaped structural components. Here the composites were prepared with the method of slip casting and liquid silicon infiltration at 1650 °C. The distribution, morphology and reinforcing behaviors of the SiC whisker in the composite were investigated. It is revealed that the introduction of SiC whisker increases the porosity of the green body, and accordingly the bulk density of the composite. Whisker pullout can be clearly observed on the fracture surface, implying a moderate bonding strength between the whisker and matrix. After liquid silicon infiltration, the SiC whisker keeps its initial diameter and morphology in the case of 15 wt% whisker. The fracture toughness is enhanced by SiC whisker, reaching the peak value of 4.2 MPa m^1/2 at the whisker fraction of 20 wt%. Whisker pullout, whisker bridging and crack deflection are considered as the main toughening mechanisms.     

Fabrication and characterization of biodegradable poly(lactic acid)/layered silicate nanocomposites

In this study biocompatible/biodegradable poly(lactic acid) (PLA)/layered silicate nanocomposites (PLSNs) were successfully prepared by the intercalation of PLA polymer into organically modified layered silicate through the solution mixing process. Both X‐ray diffraction data and transmission electron microscopy images of PLSNs indicate most of the swellable silicate layers were disorderedly intercalated into the PLA matrix. Mechanical properties of the 0.1 wt% silicate‐containing fabricated nanocomposites performed by dynamic mechanical analysis have significant improvements in the storage modulus when compared to that of neat PLA matrix. Adding more layered silicates into PLA matrix induced a decrease in the mechanical properties of PLSNs, probably due to the presence of a large dimension of porosity in the fabricated nanocomposites. POLYM. ENG. SCI., 45:1615–1621, 2005. © 2005 Society of Plastics Engineers     

Synthesis and characterization of calcium silicate insulating material using avian eggshell waste

This work focuses on the synthesis of calcium silicate insulating material via solid state reaction using avian eggshell waste as alternative calcium source. The calcium silicate formulations were mixed in a molar ratio SiO₂:CaO (1:1) and fired at 1100 °C for 24 h. The calcium silicate formulations were characterized by XRD, TG-DTA, dilatometry, SEM/EDS, and thermophysical properties (thermal diffusivity, heat capacity per unit volume, and thermal conductivity). The synthesized calcium silicate materials are composed mainly of wollastonite with minor amounts of larnite and rankinite. It was found that a processing of the avian eggshell waste (raw eggshell waste and calcined eggshell waste) had an influence on the thermophysical properties. Calcium silicate pieces were prepared by uniaxial pressing at 82 MPa, curing, and then testing to determine their use as thermal insulating material. The microstructure was evaluated by SEM. The results showed that both raw and calcined avian eggshell wastes could be used as an alternative calcium source in the calcium silicate formulation. It was found that the calcium silicate pieces reached low thermal conductivity values (0.252–0.293 W/mK). Thus, the developed calcium silicate materials using avian eggshell waste act as a good thermal insulation ceramic material.     

Fabrication and properties of 3D printed zirconia scaffold coated with calcium silicate/hydroxyapatite

The scaffold of bone repair needs a variety of material combinations to meet its intended performance; a typical single material such as zirconia has excellent mechanical properties, while hydroxyapatite and calcium silicate are bioactive materials with different degradation rates. In this paper, porous zirconia scaffolds were fabricated using 3D printing technology. The surface of the scaffold was coated by dipping with different contents of calcium silicate and hydroxyapatite to improve the biological activity and mechanical properties. Mechanical tests show that the coating material can effectively fill the pores of the porous scaffold, increasing its compressive strength by an average of 55%. The simulated body fluid (SBF) test showed that the higher calcium silicate in the coating increased the degradation rate. Cell experiments showed that the coated scaffolds exhibited good cytocompatibility and were beneficial to the proliferation and differentiation of cells. In conclusion, coated scaffolds have potential applications in the field of bone repair.     

Fabrication and characterization of a mullite-foamed ceramic reinforced by in-situ SiC whiskers

In this study, a new mullite-foamed ceramic, reinforced with in-situ SiC whiskers (MCS) and applied as the insulating lining of thermal equipment used in cement production, was investigated. Compared with a conventional mullite-foamed ceramic (MC), the MCS phase composition, microstructure, compressive strength, thermal conductivity and alkali corrosion resistance were investigated by using X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and Factsage® software. The results showed that after being fired in granular coke, the SiC whiskers formed into MCS struts and were distributed in the pores between the interconnected needle-like mullite. Although the formation of SiC with higher conduction slightly increased MCS thermal conductivity, it significantly enhanced the compressive strength and alkali corrosion resistance of the foamed ceramic. Compared with the MC, although the MCS had higher bulk density (3.9%), and higher thermal conductivity (9.5% at 800 °C), it was more important that greatly improved compressive strength (by 60%) and better alkali corrosion resistance was achieved.     

Fabrication and characterization of hollow nanofibrous PA6 yarn reinforced with CNTs

Core-sheath nanofibrous yarns were obtained through electrospinning of polyamide 6 (PA6) solution containing different concentrations of multi-wall carbon nanotubes (MWNTs) as sheath and PVA multifilament as the yarn core. By dissolving PVA, for obtaining conductive hollow nanofibrous PA6/MWNTs yarn, two types of porosity could be obtained including hollow central tube due to the structure of hollow yarn and nano-porous areas embedded in electrospun nanofibers. SEM results showed that the diameters of nanofibers were varying in the range of 103–145 nm obeying MWNTs concentrations and TEM results revealed that the MWNTs were embedded in nanofiber matrix as straight and aligned form. DSC analysis showed that electrospinning process caused the formation of less-ordered γ phase in nanofibers. The electrical conductivity of yarns increased from 10^?13 S m^?1 to 2.4?×?10^?6 S m^?1 with increasing the concentration of nanotubes from 0 wt.% to 7 wt.%.     

Fabrication of a zirconia/calcium silicate composite scaffold based on digital light processing

Zirconia (ZrO₂) and calcium silicate (CS) are widely used in bone repair. Zirconia has excellent mechanical properties, while calcium silicate has exceptional biological activity. A porous ZrO₂/CS composite ceramic scaffold was formed by digital light processing (DLP) technology in this study. The microstructure analysis demonstrated that CS was embedded between ZrO₂ particles. Mechanical tests showed that interconnected CS particles could improve mechanical properties, while discrete CS particles led to a decrease in that. Cell experiments showed that adding CS to ZrO₂ had a positive effect on cell proliferation and differentiation. In vitro degradation test showed that the weight loss of scaffolds in four weeks increased form ?0.63%–1.42% with the increase of CS content. Moreover, the degradation of scaffold promoted the deposition of apatite, which was beneficial to the integration of the scaffold with living bone. In conclusion, the ZrO₂/CS composite scaffold had better biocompatibility compared with the ZrO₂ scaffold, which showed a potential solution for 3D printing bone repair scaffolds.     

Fabrication & characterization of macroporous CdSe nanostructure via colloidal crystal templating with electrodeposition method

Large area ordered arrays of macroporous Cadmium Selenide (CdSe) nanostructure, which possesses high refractive index and negligible absorption in the visible spectrum critical for the realization of photonic band gaps, was prepared via colloidal templating by galvanostatic electrodeposition. This work investigates the effect of electrodeposition parameters on the macroporous CdSe nanostructure. Field Emission Scanning Electron Microscope (FESEM) images showed two and three dimensional porous structures, consisting of interconnected close-packed arrays of pores. For CdSe thin film of thickness less than 1/3 of the diameter of a polystyrene sphere, it showed a monolayer of circular pores. As for film thickness close to the diameter of the sphere, the pores adopted irregular rounded triangular shapes. When the film thickness was more than one layer of the colloidal polystyrene template, the pores were spherical and had the same diameter as the polystyrene spheres. X-ray Diffraction (XRD) showed that the CdSe films prepared had a cubic structure with nanometer grain size, which was smaller than the diameter of the template spheres as well as the diameter of the interconnected channels. A range of 45–70 nm thick CdSe films with > 90% optical transmittance showed that there was negligible absorption at wavelength of 750 nm. In addition, the CdSe thin film exhibited a band gap energy of 2.07 eV, blue-shifted from the characteristic 1.7 eV of CdSe. This blue-shift characteristic of the deposited CdSe film further indicated that it was nanocrystalline which is potentially useful in photonic applications.