In vitro studies of novel CaO–SiO2–MgO system composite bioceramics

In this study, a series of CaO–SiO₂–MgO composites with different β-CaSiO₃ (CS)/Mg₂SiO₄ (M₂S) composite ratios were prepared to produce new bioactive and biodegradable biomaterials for potential bone repair. The mechanical properties of CS–M₂S composites increased steadily with the increase of M₂S ratios in composites. Dissolution tests in Tris–HCl buffer solution showed obvious differences with different CS initial composite ratio in composites. The dissolution rate increased with the increase of CS composite ratio, which suggested that the solubility of composites could be tailored by adjusting the initial CS/M₂S composite ratio. Formation of bone-like apatite on a range of CS–M₂S composites with CS weight percentage ranging from 0 to 100 has been investigated in simulated body fluid (SBF). The presence of bone-like apatite layer on the composite surface after soaking in SBF was demonstrated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM). The results showed that the apatite formation ability of the CS–M₂S composite with 70% CS was detected after 10 days immersion. In vitro cell experiments showed that the 50 and 70% CS composites supported greater osteoblast-like cell proliferation as compared with pure M₂S (p < 0.05). The results of this study suggested that the CS–M₂S composites with 50 and 70% initial CS composite amount might be more suitable for preparation of bone repair materials.     

Feasibility, tailoring and properties of polyurethane/bioactive glass composite scaffolds for tissue engineering

This research work aims to propose highly porous polymer/bioactive glass composites as potential scaffolds for hard-tissue and soft-tissue engineering. The scaffolds were prepared by impregnating an open-cells polyurethane sponge with melt-derived particles of a bioactive glass belonging to the SiO₂–P₂O₅–CaO–MgO–Na₂O–K₂O system (CEL2). Both the starting materials and the composite scaffolds were investigated from a morphological and structural viewpoint by X-ray diffraction analysis and scanning electron microscopy. Tensile mechanical tests, carried out according to international ISO and ASTM standards, were performed by using properly tailored specimens. In vitro tests by soaking the scaffolds in simulated body fluid (SBF) were also carried out to assess the bioactivity of the porous composites. It was found that the composite scaffolds were highly bioactive as after 7 days of soaking in SBF a HA layer grew on their surface. The obtained polyurethane/CEL2 composite scaffolds are promising candidates for tissue engineering applications.     

Micro-structural and tensile strength analyses on the magnesium matrix composites reinforced with coated carbon fiber

Magnesium matrix composites reinforced with SiO₂ coated carbon fibers have been investigated, with an emphasis given on the relation between the material strength and interfacial microstructure. The composites were studied as a function of aluminium (Al) content that is varied between 0 and 9 wt%. The obtained results indicate that the reactivity at the C/Mg–Al interface of the composite can be controlled by varying the Al content. The low Al content in C/Mg–1Al has been completely dissolved in the matrix with no segregation even after solidification, leading to the best mechanical performance. If the Al content is increased to ≥3 wt% (composites such as C/AZ31 and C/AZ91), the SiO₂ coatings are fully depleted due to an extensive formation of carbides at the interface. The precipitates are further identified as Al₂MgC₂ phase that is similar to binary carbide Al₄C₃. SiO₂ coating on the fiber layer prior to fabrication of composite is found to be a promising way to suppress the carbide formation and enable the use of Mg–Al matrix with appropriate Al content.     

Biomimetic coating of an apatite layer on poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactic acid); improvement of adhesive strength of the coating

A biodegradable polymer coated with a bonelike apatite layer on its surface would be useful as a scaffold for bone tissue regeneration. In this study, poly(l-lactic acid) (PLLA) was treated with oxygen plasma to produce oxygen-containing functional groups on its surface. The plasma-treated specimen was then alternately dipped in aqueous CaCl₂ and K₂HPO₄·3H₂O solutions three times, to deposit apatite precursors onto the surface. The surface-modified specimen then successfully formed a dense and uniform bonelike surface apatite layer after immersion for 24 h in a simulated body fluid with ion concentrations approximately equal to those of human blood plasma. The adhesive strength between the apatite layer and the specimen surface increased as the power density of the oxygen plasma used increased. The maximum adhesive strength of the apatite layer to the specimen was significantly higher than that to the commercially available artificial bone, HAPEX^TM. The resultant bonelike apatite–PLLA composite would be useful as a scaffold for bone tissue regeneration.     

Biofunctionalization of porous titanium coatings through sol–gel impregnation with a bioactive glass–ceramic

In implant technology, open porous Ti coatings are applied as functional surface layers on prosthetic devices to improve osseointegration. Since a successful clinical performance strongly depends on the (initial) quality of bone ingrowth in the porous structure, surface functionalization of the porous Ti to incorporate an additional osteoconductive capacity is recommended. In this paper, a bioactive glass–ceramic coating is applied into the open porous network of Ti coatings with a pore throat size of 1–20 μm through a sol–gel process. Using an all-alkoxide precursor route, homogeneous amorphous powders of three- (SiO₂–CaO–P₂O₅) and four-component (SiO₂–CaO–Na₂O–P₂O₅) bioactive glass compositions are prepared. By sol impregnation followed by a heat treatment, it is possible to deposit a micrometer thin bioactive glass–ceramic layer on the walls of the internal pore surface, while the original porosity and the open pore structure of the Ti coatings are maintained. The tensile adhesion strength of the Ti/bioactive glass–ceramic composite coatings is 22 to 29 MPa, suggesting a good mechanical adhesion.     

Proton-conducting membrane preparation based on SiO2-riveted phosphotungstic acid and poly (2,5-benzimidazole) via direct casting method and its durability

SiO₂-riveted phosphotungstic acid (T–PWA–SiO₂) was synthesized using the sol–gel method and thermally treated in a microwave synthesizer. The dissolving-detaching experiment shows that PWA in T–PWA–SiO₂ exhibits better fastness than in the sample without thermal treatment (PWA–SiO₂). The T–PWA–SiO₂ samples were then combined with poly(2,5-benzimidazole) (ABPBI) to prepare ABPBI/(T–PWA–SiO₂) composite membranes using the polyphosphoric acid direct-casting method. These composite membranes were characterized through X-ray diffraction and infrared spectroscopy. Then, the T–PWA–SiO₂ particles were combined with ABPBI through hydrogen bonding between PWA and C=N in ABPBI. Membrane morphologies were investigated using scanning electron microscopy. Results of the thermogravimetric analysis indicate thermal stability of the composite membranes below 200 °C. The proton conductivity and durability between ABPBI/(T–PWA–SiO₂) and ABPBI/(PWA–SiO₂) composite membranes were also compared. The conductivity and life of the composite membranes were enhanced using T–PWA–SiO₂. The conductivity of the ABPBI/(T–PWA–SiO₂) (46 wt%) composite membrane was approximately 0.055 S/cm at 180 °C under 100% relative humidity.     

Bioactive ceramic composites sintered from hydroxyapatite and silica at 1200∘C: preparation, microstructures and in vitro bone-like layer growth

Bioceramic composites were synthesized by sintering the powders of hydroxyapatite (HAp) mixed directly with additive of 0.5, 1.0, 2.0, 5.0 and 10 wt.%SiO₂, respectively, at 1200^∘C. X-ray diffraction (XRD) analysis indicated that the phase transformation from HAp to tricalcium phosphate (TCP) comprising α-TCP and Si-TCP occurred and became more prominent with the addition of SiO₂ and the increase in SiO₂ content. The observations of their surface microstructures showed that the addition of SiO₂ suppressed the grain growth and promoted the formation of crystalline-glassy composites denoted HAp + TCP/Bioglass. As the SiO₂ content is as high as 5 wt.%, the composite made a feature of crystalline clusters with different sizes consisting of HAp and TCP grains surrounded by the matrix of glassy phase. Furthermore, the dependence of in vitro bioactivity of these composites on the SiO₂ content was biomimetically assessed by determining the changes in surface morphology, i.e., bone-like apatite layer growth, after soaking in an acellular stimulated body fluid (SBF) for 3 days at 36.5^∘C. It was found that the HAp-SiO₂ composites showed a much faster bone-like layer growth than pure HAp, and the propensity of composites to exhibit a better bioactivity was getting more notable with increasing SiO₂ content, except for the case of the highest content of 10 wt.%. It was believed that the formation of the bone-like layer on the surfaces of these bio-composites is closely related to the increasingly provided silanol groups and transformed TCP phase in materials associated with the content of SiO₂ added.     

Design of bioactive bone substitutes based on biomineralization process

A material able to form bone-like apatite on its surface in the living body bonds to living bone through the apatite layer. Functional groups such as Si-OH, Ti-OH, Zr-OH, Nb-OH and Ta-OH induce apatite formation in the living body. On the basis of these findings, various kinds of bioactive materials with different mechanical properties can be designed. For example, bioactive titanium metal, its alloys and tantalum metal can be obtained by forming a thin sodium titanate or tantalate layer on their surfaces by NaOH solution and heat treatments.Bioactive organic polymers can be obtained by forming a thin CaO–SiO₂ or TiO₂ layer on their surfaces by a sol–gel method. These bioactive materials are believed to be useful as unique bone substitutes.     

In vitro apatite formation on organic–inorganic hybrids in the CaO–SiO<Subscript>2</Subscript>–PO<Subscript>5/2</Subscript>–poly(tetramethylene oxide) system

The osteoconduction potential of artificial materials is usually evaluated in vitro by apatite formation in a simulated body fluid (SBF) proposed by Kokubo and his colleagues. This paper reports the compositional dependence of apatite formation on organic–inorganic hybrids in the CaO–SiO₂–PO_5/2–poly(tetramethylene oxide) system, initiated from tetraethoxysilane (TEOS), triethyl phosphate (OP(OEt)₃), calcium chloride (CaCl₂) and poly(tetramethylene oxide)(PTMO) modified with alkoxysilane. Formation of an apatite layer was observed on the surface of the organic–inorganic hybrids with molar ratios of TEOS/OP(OEt)₃ ranging from 100/0 to 20/80. The rate of apatite formation remarkably decreased when the hybrids were synthesized with TEOS/OP(OEt)₃ ratios of 40/60 or less. Hybrids without TEOS showed no apatite formation in SBF for up to 14 days. Addition of small amounts of OP(OEt)₃ to TEOS in the hybrids led to the high dissolution of calcium and silicate, while addition of large amounts of OP(OEt)₃ decreased the dissolution of calcium and silicate ions and resulted in reduced apatite formation regardless of the dissolution of phosphate ions from the hybrids.     

Synthesis and electrorheological properties of polyaniline/silicon dioxide composites

This study was to synthesize the inherently conductive polymer polyaniline using an optimized process to prepare polyaniline/silicon dioxide (PANI/SiO₂) composites by in situ polymerization and ex situ solution mixing. PANI and PANI/SiO₂ composite films were prepared by drop-by-drop and spin-coating methods. The morphology of particles and films were examined by a scanning electron microscope (SEM). SEM measurements indicated that the SiO₂ were well-dispersed and isolated in composite films. The electrorheological (ER), characteristics of the PANI/SiO₂ composites were investigated. A volume fraction series (φ = 5–25 %) of the PANI/SiO₂/silicone oil dispersions were prepared and sedimentation stabilities were determined. An ER activity was observed from the samples, when subjected to external electric field strength thus, they were classified as smart materials. Some parameters affecting the ER properties of the dispersions such as volume fraction, shear rate, electric field strength, frequency, and temperature were investigated.     

OTS-modified HA and its toughening effect on PLLA/HA porous composite

In this paper, hydroxyapatite (HA) particles was modified with long-chain organic silane-Octadecyltrichlorosilane (OTS), and the modified particles were further used for preparing Poly(l-lactic acid) PLLA/HA porous composite. The modified particles were characterized by means of XRD, FTIR, and XPS techniques. Both XPS and FTIR results showed that OTS had been combined with HA, and the formation of P–O–Si bond, a covalent bond, on the HA particle surface was confirmed by XPS. OTS-modified HA particles were used to prepare porous composites by thermally induced phase separation method. The results showed that the composite had an interconnected pore structure with 100–300 μm macropores. With OTS dosage increasing during modification, the mechanical properties of PLLA/OTS-modified HA porous composites increased obviously. These results showed that OTS modification can effectively improve the interface compatibility between HA surface and PLLA.     

Bone-like apatite coating on Mg-PSZ/Al2O3 composites using bioactive systems

A biomimetic method was used to promote bioactivity on zirconia/alumina composites. The composites were composed of 80 vol% Mg-PSZ and 20 vol% Al₂O₃. Samples of these bioinert materials were immersed in simulated body fluid (SBF) for 7 days on either a bed of wollastonite ceramics or bioactive glass. After those 7 days, the samples were immersed in a more concentrated solution (1.4 SBF) for 14 days. Experiments were also performed without using a bioactive system during the first stage of immersion. A bone-like apatite layer was formed on the surface of all the materials tested, using wollastonite the bioactive layer was thicker and its morphology was close to that observed on the existing bioactive systems. A thinner apatite layer consisting of small agglomerates was obtained using bioactive glass. The thickness of the ceramic layers was within the range of 15 to 30 μm.     

The effect of residual glassy phase in a bioactive glass-ceramic on the formation of its surface apatite layerin vitro

A bioactive glass containing (in wt%) SiO₂ 48, P₂O₅ 9.5, Na₂O 20 and CaO 22.5 was transformed into a glass-ceramic through a heat treatment. The apatite formation on the surface of this glass-ceramic was examined in a simulated physiological solution. The data from X-ray diffraction, infrared reflection spectroscopy, scanning electron microscopy together with energy-dispersive X-ray analysis and composition imaging of backscattered electrons showed that the formation of the surface apatite layer depends on the relative amount of residual glassy phase in the glass-ceramic. The apatite layer was found to formin vitro on its surface if the glass-ceramic contained a residual glassy phase in a relative proportion more than a limiting volume. It lay on a layer rich in silica. However, only, a silica-rich layer was developed within the surface region of the glass-ceramic during the interaction with solution if the glass was almost completely crystallized. It is proposed that the apatite formation on the surface of the glass-ceramic is mainly caused by its residual glass. The residual glass facilitating apatite formation is considered to provide a negatively charged surface developed during its corrosion in the surrounding solution. The negatively charged surface attracts calcium ions and creates a solution within the glass — solution interface that is highly supersaturated with respect to hydroxyapatite. This leads to the formation of apatite on the surface of the glass-ceramic.     

An emulsification–solvent evaporation route to mesoporous bioactive glass microspheres for bisphosphonate drug delivery

Regular spherical mesoporous bioactive glass microspheres (MBG-MSs) with tunable SiO₂–CaO–P₂O₅ composition and adjustable mesoporous structure have been synthesized by a new approach of emulsification and solvent evaporation-induced self-assembly. Less ordered mesostructure and enhanced bioactivity resulting from the addition of CaO are investigated through scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction characterizations. The MBG-MSs have high storage capacities and sustained release patterns of anti-osteoporosis (alendronate sodium, NaAL) drugs which are hardly absorbed via oral administration. Furthermore, to some extent the dosage and release rate could also be controlled by CaO content. Cell viability and proliferation assay with rabbit bone marrow stromal cells indicates a positive effect of the CaO/P₂O₅ components on improving the cell growth cumulatively in about 2 weeks.     

Electrical and thermal conductivities of porous SiC/SiO2/C composites with different morphology from carbonized wood

Porous SiC/SiO₂/C composites exhibiting a wide range of high thermal and electrical conductivities were developed from carbonized wood infiltrated with SiO₂. As a pre-treatment, the samples were either heated at 100 °C or kept at room temperature followed by sintering in the temperature range 1200–1800 °C. The microstructure, the morphology, and the electrical and thermal conductivities of the composites were investigated. Pre-treatment at room temperature followed by sintering up to 1800 °C produced composites exhibiting a greater size of carbon crystallites, a higher ordering of the microstructure of carbon and β-SiC and a smaller amount of SiO₂, resulting in electrical and thermal conductivities of 1.17 × 10⁴ Ω⁻¹ m⁻¹ and 25 W/mK, respectively. The thermal conductivity could be further improved to 101 W/mK by increasing the density of the composite to 1.82 g/cm³. In contrast, the pre-treatment at 100 °C produced composites possessing a lower thermal conductivity of 2 W/mK.     

Evaluation of the flexural properties and bioactivity of bioresorbable PLLA/PBSL/CNT and PLLA/PBSL/TiO2 nanocomposites

Bioresorbable nanocomposites made from PLLA/PBSL blended with varying contents of carbon nanotubes (CNTs) and titanium dioxide (TiO₂) nanotubes were prepared through melt compounding followed by compression molding. The resulting flexural properties were investigated by flexural test and the bioactive behavior was assessed by FESEM and EDX. A higher flexural modulus value was obtained with the addition of nanofillers. The formation of a bone-like apatite layer was observed on the surface of the nanocomposite containing TiO₂ nanotubes after soaking in simulated body fluid (SBF) for 7 days. An increase in the water uptake of the PLLA/PBSL/TiO₂ nanocomposite occurred with increased filler loading. The nanocomposite containing CNT exhibited an increasing trend of water absorption similar to the PLLA/PBSL blend. With prolonged immersion in SBF, the pH value of the SBF reduced slightly and weight loss of the samples increased.     

Effect of silica coating thickness on the thermal conductivity of polyurethane/SiO2 coated multiwalled carbon nanotube composites

Silica coated multiwalled carbon nanotubes (SiO₂@MWCNTs) with different coating thicknesses of ∼4 nm, 30–50 nm, and 70–90 nm were synthesized by a sol–gel method and compounded with polyurethane (PU). The effects of SiO₂@MWCNTs on the electrical properties and thermal conductivity of the resulting PU/SiO₂@MWCNT composites were investigated. The SiO₂ coating maintained the high electrical resistivity of pure PU. Meanwhile, incorporating 0.5, 0.75 and 1.0 wt% SiO₂@MWCNT (70–90 nm) into PU, produced thermal conductivity values of 0.287, 0.289 and 0.310 W/mK, respectively, representing increases of 62.1%, 63.3% and 75.1%. The thermal conductivity of PU/SiO₂@MWCNT composites was also increased by increasing the thickness of the SiO₂ coating.     

Dispersions of carbon nanotubes/polyhedral oligomeric silsesquioxanes hybrids in polymer: the mechanical,electrical and EMI shielding properties

A hybrid was synthesized by grafting polyhedral oligomeric silsesquioxane (POSS) to multiwalled carbon nanotubes (MWCNTs). The MWCNT/polymer composites produced using silsesquioxane grafted MWCNTs as a filler had a high electromagnetic interference shielding effectiveness. Homogeneous dispersion of silsesquioxane grafted MWCNTs occurred throughout the polymer without any aggregation, while a pristine MWCNT aggregate that integrated several nanotube domains existed in the polymer matrix. A comparative study of the optical transmittance, electrical, and electromagnetic interference shielding properties of poly(l-lactide) (PLLA)/MWCNT composites based on pristine MWCNTs and silsesquioxane grafted MWCNTs was carried out. A high electromagnetic interference shielding effectiveness (15–16 dB) was obtained in the 36–50 GHz range at a relatively low filler loading (4 wt%) in the PLLA/silsesquioxane grafted MWCNT composite.     

Tunable BT@SiO2 core@shell filler reinforced polymer composite with high breakdown strength and release energy density

Barium titanate@silicon dioxide (BT@SiO₂) core@shell fillers with an average diameter of 100 nm were prepared by a facile sol–gel synthesis. The thickness of SiO₂ shell can be easily tuned by varying different mass ratio of BT to tetraethyl orthosilicate (TEOS). Polyvinylidene fluoride (PVDF) based composite films reinforced by BT and BT@SiO₂ were fabricated via a solution casting method. The effects of SiO₂ shell on morphology structure, wettability, interfacial adhesion, dielectric, electrical and energy performances of composites were investigated. Compared with BT/PVDF, BT@SiO₂/PVDF composites show significantly increased breakdown strength due to enhanced interfacial adhesion and suppressed charge carrier conduction. Benefiting from enhanced breakdown strength and reduced remnant polarization induced by SiO₂ shell, BT@SiO₂/PVDF shows increased release energy density (energy density which can be fully discharged and applicable). Especially, BT@SiO₂/PVDF with SiO₂ thickness of 4 nm exhibits the highest release energy density of 1.08 J/cm³ under applied electric field of 145 kV/mm.     

Electrophoretic deposition of porous CaO–MgO–SiO<Subscript>2</Subscript> glass–ceramic coatings with B<Subscript>2</Subscript>O<Subscript>3</Subscript> as additive on Ti–6Al–4V alloy

The sub-micron glass–ceramic powders in CaO–MgO–SiO₂ system with 10 wt% B₂O₃ additive were synthesized by sol–gel process. Then bioactive porous CaO–MgO–SiO₂ glass–ceramic coatings on Ti–6Al–4V alloy substrates were fabricated using electrophoretic deposition (EPD) technique. After being calcined at 850°C, the above coatings with thickness of 10–150 μm were uniform and crack-free, possessing porous structure with sub-micron and micron size connected pores. Ethanol was employed as the most suitable solvent to prepare the suspension for EPD. The coating porous appearance and porosity distribution could be controlled by adjusting the suspension concentration, applied voltage and deposition time. The heat-treated coatings possessed high crystalline and was mainly composed of diopside, akermanite, merwinite, calcium silicate and calcium borate silicate. Bonelike apatite was formed on the coatings after 7 days of soaking in simulated body fluid (SBF). The bonding strength of the coatings was needed to be further improved.