Wollastonite Particles Research Articles

Enhancing low cost stainless steel implants: bioactive silica-based sol-gel coatings with wollastonite particles

A hybrid organic-inorganic sol-gel coating with the addition of wollastonite particles is used as a potential solution to improve performance of low cost AISI 316L stainless steel. This work is focused on characterising the coatings by studying their synthesis and deposition, electrochemical, and in vitro and in vivo response. The coated implants presented in vitro Ca/P-rich apatitic precursors phases on their surface and acceptable electrochemical behaviour. The in vivo response regarding bone formation seems to be excellent either with the implant in contact with bone marrow, in contact with the endostium or in contact with the trabecular bone. The bioactive and regenerative responses of bone tissue to the TEOS-MTES-wollastonite system over-compensate the coating deterioration reaction, making these coatings as a good way to improve osseo-integration of stainless steel for long term use implants.

Feasibility of ceramic-polymer composite cryogels as scaffolds for bone tissue engineering

The purpose of the current study was to investigate whether the cryopolymerization technique is capable of producing suitable scaffolds for bone tissue engineering. Cryopolymers made of 2-hydroxyethyl methacrylate and acrylic acid with (W1 and W20) and without (W0) wollastonite particles were prepared. The elastic modulus of the specimens rose one order of magnitude from W1 to W20. Total porosity reached 56% for W0, 72% for W1 and 36% for W20, with pore sizes of up to 2 mm, large interconnection sizes of up to 1 mm and small interconnection sizes of 50-80 µm on dry specimens. Cryogels swell up to 224 ± 17% for W0, 315 ± 18% for W1 and 231 ± 27% for W20 specimens, while maintaining the integrity of the bodies. Pore sizes > 5 mm can be observed for swollen specimens. The biocompatibility of the samples was tested using human mesenchymal stem cells isolated from bone marrow and adipose tissues. Both types of cells attached and grew on the three tested substrates, colonized their inner regions and organized an extracellular cell matrix. Fibronectin and osteopontin levels decreased in the media from cells cultured on W20 samples, likely due to increased binding on the ECM deposited by cells. The osteoprotegerin-to-receptor activator of nuclear factor-κB ligand secretion ratios increased with increasing wollastonite content. Altogether, these results indicate that an appropriate balance of surface properties and structure that favours stromal cell colonization in the porous cryogels can be achieved by modulating the amount of wollastonite.

Preparation and properties of poly(ether ether ketone) composites reinforced by modified wollastonite grafting with silaneterminated poly(ether ether ketone) oligomers

Silane-terminated poly(ether ether ketone) oligomers were synthesized and grafted onto wollastonite (W) particles. The prepared grafted-wollastonite particles (g-W) were then incorporated into PEEK matrix via melt processing. Properties of the PEEK composites were investigated using differential scanning calorimetry (DSC), universal tester and rheometer. The researchers found the mechanical properties of the PEEK/g-W composites were markedly enhanced, complex viscosity of the PEEK/g-W composites increased, and both the peak crystallization temperature (Tc) and crystalline fraction (χc) of the PEEK composites with g-W were significant higher compared with those of the PEEK composites with W. It is our belief that these results are due to the strong interaction between the grafted-wollastonite particles and the PEEK matrix.

Influence of the Filler Particle Shape on the Nature of Failure of Polypropylene-Based Composites

An investigation was made of the influence of the filler particle shape on the nature of failure of PP-based composites. It was established that the filler particle shape affects the types of defect formed and the nature of failure of PP-based composites. The introduction of talc or wollastonite particles into PP leads to brittle failure of the composite up to its upper yield point. When spherical particles are used, the material retains plastic properties, and rupture occurs on neck propagation.

Analysis of the isothermal crystallization of CaSiO 3 in a CaO–Al 2O 3–SiO 2 melt through in situ observations

Abstract Crystal growth of Wollastonite (CaO·SiO 2) in a 42CaO–10Al 2O 3–48SiO 2 melt is observed in situ at 1320 ° C and 1370 ° C using a high-temperature confocal scanning laser microscope (CSLM). The crystallization is initiated by seeding the melt with Wollastonite particles, which is the primary phase at these temperatures and composition. At 1370 °C, a faceted growth form is observed, while at 1320 °C, dendritic, non-faceted growth occurs. The dendrite tip velocity is measured and compared with Ivantsov’s theory. The presented experimental technique proofs to be successful for characterizing isothermal crystallization of minerals in silicate melts.

Preparation and properties of poly(ether ether ketone) composites reinforced by modified wollastonite grafting with different oligomers

Different structure silane-terminated polymer oligomers were synthesized and grafted onto the surface of wollastonite particles. The prepared grafted-wollastonite particles (g-W) were then incorporated into poly (ether ether ketone) (PEEK) matrix via melting blend. The properties of the PEEK composites were investigated using differential scanning calorimetry, universal tester and rheometer. The results showed that the mechanical properties of the PEEK/g-W composites were markedly enhanced, the complex viscosity of PEEK/g-W composites was increased, and both the peak crystallization temperature ( Tc) and crystalline fraction ( χc) of the g-W-reinforced PEEK composites were significantly higher in comparison with those of non-treated wollastonite-reinforced PEEK composites. It is concluded that these results were due to the strong interaction between the grafted-wollastonite particles and the PEEK matrix, and the properties of the PEEK/g-W composites were slightly different because of the different structure of the polymer oligomers.

Surface modification of wollastonite by the mechano-activated method and its properties

Surface modification of wollastonite particles using titanate as a modification agent incorporated by simultaneous wet ultra-fine grinding in a laboratory stirred mill was investigated. The physical, physic-chemical and application properties of the modified wollastonite were measured and evaluated. The results showed that grinding intensity markedly influences the modification effect because of the mechano chemical effect. The hydrophilic surface of wollastonite was turned into a hydrophobic one after modification. The interaction between titanate and wollastonite under wet grinding circumstances was studied. It was suggested that physical adsorption and chemical adsorption of titanate coexisted on the wollastonite surface. The mechanical properties of polyethylene (PE) filled with the modified wollastonite powder were markedly improved.

Morphologic and nanomechanical characterization of bone tissue growth around bioactive sol–gel coatings containing wollastonite particles applied on stainless steel implants

Metals are the most widely used materials in orthopaedic and dental implants due to their excellent mechanical properties. However, they do not bond naturally with mineralized bone. Further, they can release metallic particles that may finally result in the removal of the implant. There are two strategies to avoid these drawbacks: one is to protect the metallic implant with a biocompatible coating and the other is to add bioactive particles to enhance implant fixation to the existing bone. In this work, surgical grade stainless steel implants coated with tetraethoxysilane (TEOS)–methyltriethoxysilane (MTES) and 10wt.% of commercial wollastonite particles were implanted in the Hokkaido femur rats. Transversal sections of the tibia samples were examined with SEM, AFM, histological analysis and nanoindentation experiments in air and under physiological conditions to characterize the hydroxyapatite deposits and the composition of the newly formed tissue around the implant. The results showed no presence of harmful ions or metallic particles in the surrounding tissues and that the coating promoted formation and growth of new bone in the periphery of the implant, both in contact with the old bone (remodellation zone) and the marrow (new bone). The relative mechanical behavior of old, remodeled and new bone tissues obtained in air cannot be directly extrapolated to live or in vivo-physiological response. This may be caused by the different degree of hydration and SBF/structure interaction among the three types of bones but these values are near the normal hydrated bone response.

Dissolving behavior and calcium release from fibrous wollastonite in acetic acid solution

The degradability of fibrous wollastonite (CaSiO 3) in an aqueous solution of acetic acid and leaching of Ca 2+ ions were investigated in the temperature range from 22 to 50 °C. The Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-OES) was used for the assessment of calcium and other selected cations in the leaching medium. The amount of calcium in the solvent can be significantly enhanced through leaching at higher temperature. Fibrous silica particles are the main by-product of the leaching process. The properties of by-product were examined by thermal analysis (simultaneous TG–DTA–EGA), infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The formation of silica layer on the surface of fibrous wollastonite particles is an important factor in the leaching process. Particles were covered by the silica layer and wollastonite core size was continually decreasing during leaching. The shape of resulting silica particles shows no significant changes during this process. Specific surface of the formed fibrous silica particles strongly depends on the leaching temperature.

Investigations on Pastes and Mortars of Ordinary Portland Cement Admixed with Wollastonite and Microsilica

Wollastonite is abundantly available in Rajasthan, Tamil Nadu, Uttarakhand, and Andhra Pradesh states of the Indian Union as a low-cost material. In this study, investigations were made on pastes and mortars to evaluate its potential as a new material for admixing with ordinary portland cement with or without microsilica. Its physical and chemical properties were analyzed. Wollastonite consists of 45.6% of CaO and 48% of SiO2 , mostly in amorphous form. It has an average specific surface area of 842.7 m2 /kg and retention on 45-micron sieve of 3.20%. When ground to fine powder, it attains an average particle size of 4 microns which is about 4.5 times finer than ordinary portland cement. Scanning electron microscope images show that wollastonite particles were solid, acicular in shape, and have rough surfaces. Several cementitious mix proportions of ordinary portland cement, wollastonite, and microsilica were investigated for normal consistency, initial and final setting time of paste, and compressive str...

Polymer nanocomposites for bone tissue substitutes

Following the quest for new composite biomaterials for bone tissue engineering, this work presents the processing of new nanocomposite made of polycaprolactone matrix and wollastonite particles. Wollastonite nanopowder was obtained by thermal treatment of polymethyloxosilane resin mixed with silica and calcium hydroxide. Bioactive character of the ceramic nanopowder was verified in simulated body fluid (SBF). The apatite formation on wollastonite grain surface after immersion in SBF was observed. Basic mechanical properties of the samples containing various amount of ceramic nanoparticles have been examined. It was shown that the presence of small amount of wollastonite nanoparticles (0.5–1.0 wt%) improves significantly the Young's modulus, tensile strength, and work-of-fracture of polymer matrix composite. Increased content of ceramic nanoadditive (>2%) in nanocomposites resulted in degradation of their mechanical characteristics.

Morphology, mechanical and thermal properties of composites of polypropylene and nanostructured wollastonite filler

Nanostructured wollastonite was synthesized by a sol–gel method and then used as a filler for polypropylene (PP). The obtained wollastonite particles were investigated using XRD, TEM and FTIR techniques. Non-isothermal crystallization measurements revealed that the wollastonite filler reduced the crystallization temperature of the matrix. TGA analyses showed improved thermal stability of the nanocomposite with respect to that of the pure polypropylene. From the DMA tan δ curves, it was concluded that the introduction of the filler into the PP matrix induced a slight shift of the β-transition (glass transition) towards higher temperature. The measurements of storage moduli showed that the nanocomposites have higher stiffness than the pure PP over the whole range of test temperature. An increase in stiffness was also confirmed by tensile measurements.

Development of novel bioactive composites by electrophoretic deposition

Electrophoretic deposition (EPD), which is normally available on electric conductive materials, was applied to insulating materials. Wollastonite particles were deposited into the pores of porous alumina and porous ultrahigh molecular weight polyethylene (UHMWPE) substrates by EPD to yield alumina-wollastonite and UHMWPE-wollastonite composites, respectively. These composites were soaked in simulated body fluid (SBF) to evaluate their apatite-forming ability. Apatite was induced from the wollastonite particles, which grew on the surfaces and covered the entire composite surfaces. The bonding strength of the apatite layer to the substrates was as high as 8.9 MPa for alumina and 5.2 MPa for UHMWPE due to an interlocking effect. Thus, the formed alumina-wollastonite and UHMWPE-wollastonite composites should be useful as bone substitutes.

Wollastonite‐reinforced polypropylene composites modified with novel metallocene EPR copolymers. I. Phase structure and morphology

AbstractSupermolecular structure of isotactic polypropylene/wollastonite/metallocene propylene–ethylene copolymers (iPP/W/EPR) composites was studied as a function of elastomer content (from 0 to 20 vol%) by optical, scanning, and transmission electron microscopy, wide‐angle X‐ray diffraction, and differential scanning calorimetry. Both, wollastonite and dispersed EPR particles, homogeneously incorporated into the iPP matrix, and affected the final phase structure and morphology of the iPP/wollastonite/EPR composites. Wollastonite particles were orientated plane‐parallel to the sample surface and hindered spherulite growth of the iPP matrix. EPRs enhanced plane‐parallel orientation of wollastonite and simultaneously enhanced the spherulite and crystallite growth in the iPP matrix during the solidification of polymer melt. Ternary iPP/wollastonite/EPR composites exhibited significant prevalence of separated microphase morphology (over core‐shell morphology) because of constitution similarity of P‐E and iPP chains. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers.

Preparation and characterization of composites of polyethylene with polypyrrole‐coated wollastonite

AbstractComposite sheets of polyethylene and polypyrrole‐coated wollastonite were prepared by extrusion and compression molding. Four compatibilizers were also evaluated, poly(ethylene‐co‐methyl acrylate) (EMA), maleated polyethylene (MAPE), poly(ethylene‐co‐vinyl alcohol) (EVOH), and poly(vinyl alcohol) (PVOH). The composite materials were characterized using X‐ray diffraction, thermogravimetric analysis, scanning electron microscopy (SEM), Raman spectroscopy, and mechanical properties determined by tensile tests. SEM micrographs showed that significantly improved interactions occurred between the PE matrix and polypyrrole‐coated wollastonite particles in the presence of EMA, MAPE, and EVOH. Raman spectroscopy confirmed that the polypyrrole coating on the wollastonite particles was not thermally degraded during melt processing. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Improvement of the bioactivity of organic–inorganic hybrid aerogels/wollastonite composites with TiO2

Organic–inorganic hybrid aerogels containing P and Ti have been synthesized by supercritical drying of alkogels prepared by hydrolysis and poly-condensation of metalo-organic precursors under high-power ultrasound. These materials become bioactive when doped with Ca. Wollastonite particles (CaSiO3) were added as an active phase, instead of incorporating Ca into the aerogel atomic network. These particles had previously been precipitated and were then added to the sol. The aerogels were studied by Fourier transform infrared analysis, scanning electron microscopy coupled with energy dispersive spectroscopy and X-ray diffraction and N2 adsorption. The stress–strain behaviours were evaluated under compression to obtain the Young’s modulus. It was found that the incorporation of TiO2 into wollastonite-P2O5 hybrid aerogels increased their capacity to form apatite and, consequently, improving their bioactive response.

Phase structure and morphology of wollastonite‐reinforced polypropylene composites modified with SEBS and SEBS‐g‐MA elastomers

AbstractSupermolecular structure of isotactic polypropylene/wollastonite/styrenic rubber block copolymers composites were studied as a function of elastomeric poly‐ (styrene‐b‐ethylene‐co‐butylene‐b‐styrene) triblock copolymer (SEBS) and the SEBS grafted with maleic anhydride (SEBS‐g‐MA) content (from 0 to 20 vol%) by optical, scanning, and transmission electron microscopy, wide‐angle X‐ray diffraction and differential scanning calorimetry. Wollastonite particles disturbed the spherulitization of polypropylene matrix. Both elastomers affected the crystallization of polypropylene matrix mainly by solidification effect. Although SEBS‐g‐MA encapsulated wollastonite particles more expressive than SEBS forming thus core‐shell morphology in higher extent, scanning electron micrographs indicated more constrained wollastonite particles in fractured surfaces of composites with SEBS elastomer. Moreover, SEBS‐g‐MA disorientated wollastonite particles and affected reorientation of the polypropylene crystallites stronger than SEBS elastomer. POLYM. ENG. SCI., 47:2145–2154, 2007. © 2007 Society of Plastics Engineers

Generation of hydroxyapatite patterns by electrophoretic deposition

Hydroxyapatite (HAp) patterns with distinct boundaries were generated by electrophoretic deposition (EPD) utilizing an insulating mask that partially blocks the electric field. For the EPD process, we selected two types of mask: a polytetrafluoroethylene (PTFE) board with holes and a resist pattern. A porous PTFE film, which differed from the mask PTFE, was employed as a substrate and attached to the mask. EPD was performed with a suspension of wollastonite particles in acetone, which were deposited on the substrate in the form of the patterned mask. The deposited wollastonite particles induced HAp patterns during a soak in simulated body fluid (SBF). As a result, minute HAp patterns, such as dots, lines, and corners were fabricated on the porous PTFE substrate with a minimum line width of about 100 microm.

Mechanical properties of wollastonite‐reinforced polypropylene composites modified with SEBS and SEBS‐g‐MA elastomers

AbstractMechanical properties of isotactic polypropylene/wollastonite/styrene rubber block copolymers (iPP/wollastonite/SRBC) composites were studied as a function of elastomeric poly(styrene‐b‐ethylene‐co‐butylene‐b‐styrene) triblock copolymer (SEBS) and SEBS grafted with maleic anhydride (SEBS‐g‐MA) content from 0 to 20 vol%. Microphase morphology was stronger influenced by SRBC elastomers than by different wollastonite types. Higher encapsulation ability of SEBS‐g‐MA than SEBS caused more expressive core‐shell morphology and consequently higher notched impact strength as well as yield parameters, but lower Young's modulus. Higher ductility of the composites with SEBS than with SEBS‐g‐MA has been primarily caused by better miscibility of the polypropylene chains with SEBS molecules. Surface properties of components and adhesion parameters also indicated that adhesion at SEBS‐g‐MA/wollastonite interface, which was stronger than the one at the SEBS/wollastonite interface, influenced higher encapsulation of wollastonite particles by SEBS‐g‐MA. POLYM. ENG. SCI., 47:1873–1880, 2007. © 2007 Society of Plastics Engineers

Fabrication of Poly-(DL-Lactic Acid)—Wollastonite Composite Films with Surface Modified β-CaSiO3 Particles

Bioactive poly-(DL-lactic acid) (PDLLA)-wollastonite composite films are successfully fabricated using surface modified wollastonite (m beta-CaSiO 3) particles through solvent casting-evaporation method. The surface modification of beta-CaSiO3 particles are conducted by reaction of the ceramic particles with dodecyl alcohol. Surface morphology, tensile strength, and bioactivity of the composite films are investigated. The results show that the particle distribution and tensile strength of the composite films with modified beta-CaSiO3 particles are significantly improved while the bioactivity is retained. As a result, the maximum tensile strength is enhanced 52.2% when compared with the PDLLA-beta-CaSiO3 composite films prepared using unmodified beta-CaSiO3 particles when the inorganic filler content is 15 wt%. Scanning electron microscopy (SEM) observation suggests that the modified m beta-CaSiO3 particles are homogeneously dispersed in the PDLLA matrix. The bioactivity of the composite films is evaluated by soaking in a simulated body fluid (SBF) and the result suggests that the modified composite film is still bioactive and can induce the formation of HAp on its surface after the immersion in SBF, despite the bonded dodecyl alkyl on the surface of the inorganic particles. All these results imply that the surface modification of beta-CaSiO3 with dodecyl alcohol is an effective approach to prepare PDLLA-beta-CaSiO3 composite with improved properties.