Effect of Mg content on the bioactivity and biocompatibility of Mg-substituted fluorapatite nanopowders fabricated via mechanical activation.

The aim of this work was preparation, characterization, bioactivity and biocompatibility evaluation of Mg-substituted fluorapatite (Mg-FA) nanopowders. Mg-FA nanopowders with a chemical composition of Ca10-xMgx(PO4)6F2, with x=0, 0.5, 1, and 2 were prepared by mechanically activated method. The in vitro bioactivity was investigated by soaking the powders in simulated body fluid (SBF) for various time periods to analyze the nucleation and growth of bone-like apatite on the surface of the samples. Cell viability and cell attachment were studied by MTT assay. Results indicated that the bioactivity of all of samples with different Mg content was improved compared with the pure FA. However, the mechanism of bioactivity is different and depends on the amount of Mg substitution. Finally, cell culture suggested that the addition of Mg(2+) has no adverse effect and Mg-FA samples have good biocompatibility. The Mg-FA material shows potential in satisfying the requirements of biomedical applications.

The effect of nanobioceramic reinforcement on mechanical and biological properties of Co-base alloy/hydroxyapatite nanocomposite.

The goal of the present research was to fabricate, characterize, and evaluate mechanical and biological properties of Co-base alloy composites with different amounts of hydroxyapatite (HA) nanopowder reinforcement. The powder of Co-Cr-Mo alloy was mixed with different amounts of HA by ball milling and it was then cold pressed and sintered. X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques were used. Microhardness measurement and compressive tests were also carried out. Bioactivity behavior was evaluated in simulated body fluid (SBF). A significant decrease in modulus elasticity and an increase in microhardness of the sintered composites were observed. Apatite formation on the surface of the composites showed that it could successfully convert bioinert Co-Cr-Mo alloy to bioactive type by adding 10, 15, and 20wt.% HA which have lower modulus elasticity and higher microhardness.

Effect of alumina contents on phase stability and mechanical properties of magnesium fluorapatite/alumina composites.

The aim of the present work was twofold: to prepare biphasic magnesium fluorapatite (MFA) composites with different amounts of alumina using a two-step sintering process, and to evaluate the effects of various amounts of alumina on the mechanical properties, phase stability, and densification of the composite samples. Initially, MFA powders were prepared with different amounts of alumina by mechanical activation and the MFA composite samples were subsequently prepared using the two-step sintering (TSS) method. In order to determine the appropriate temperature of the first step sintering, conventional sintering of MFA/50% alumina was carried out at temperatures in the range of 1000-1300°C. X-ray diffraction and scanning electron microscopy (SEM) techniques were used to characterize the prepared MFA/alumina composites. The results showed fracture toughness and hardness in the MFA/50% alumina composite samples to increase as a result of alumina addition to their maximum values of 5.82±1.05MPam(1/2) and 22.09±3.5GPa, respectively.

Effects of surface modification on the mechanical and structural properties of nanofibrous poly(ε-caprolactone)/forsterite scaffold for tissue engineering applications.

Composite scaffolds consisting of polymers reinforced with ceramic nanoparticles are widely applied for hard tissue engineering. However, due to the incompatible polarity of ceramic nanoparticles with polymers, they tend to agglomerate in the polymer matrix which results in undesirable effects on the integral properties of composites. In this research, forsterite (Mg2SiO4) nanoparticles was surface esterified by dodecyl alcohol and nanofibrous poly(ε-caprolactone)(PCL)/modified forsterite scaffolds were developed through electrospinning technique. The aim of this research was to investigate the properties of surface modified forsterite nanopowder and PCL/modified forsterite scaffolds, before and after hydrolytic treatment, as well as the cellular attachment and proliferation. Results demonstrated that surface modification of nanoparticles significantly enhanced the tensile strength and toughness of scaffolds upon 1.5- and 4-folds compared to unmodified samples, respectively, due to improved compatibility between matrix and filler. Hydrolytic treatment of scaffolds also modified the bioactivity and cellular attachment and proliferation due to greatly enhanced hydrophilicity of the forsterite nanoparticles after this process compared to surface modified samples. Results suggested that surface modification of forsterite nanopowder and hydrolytic treatment of the developed scaffolds were effective approaches to address the issues in the formation of composite fibers and resulted in development of bioactive composite scaffolds with ideal mechanical and structural properties for bone tissue engineering applications.

Development of novel aligned nanofibrous composite membranes for guided bone regeneration.

The ability to mimic the structure of the natural extracellular matrix is a successful key for guided bone regeneration (GBR). For the regeneration of highly organized structures such as heart and bone, aligned fibrous membranes could provide anisotropic mechanical and biological properties which are adequate topographic guidance to cells. Here, novel nanofibrous membranes were developed through electrospinning of PCL-forsterite nanopowder. The membranes were characterized with regard to structural and mechanical properties, degradation, bioactivity and cellular interactive responses. Results showed that optimized nanofibrous composite membrane with significantly improved tensile strength and elastic modules was achieved through addition of 10 wt% forsterite nanopowder into PCL membrane. Addition of forsterite nanopowder decreased the average fiber diameters from 872±361 nm (pure PCL membrane) to 258±159 nm (PCL-10 wt% forsterite membrane). At higher forsterite contents (>10 wt%), the agglomeration of nanoparticles was observed which resulted in reduced mechanical properties. Aligned fibrous membranes revealed smaller fiber sizes and significantly enhanced and anisotropic mechanical properties compared to random ones suggesting that fiber alignment has a profound effect on the structural properties of membranes. Forsterite nanopowder increased the degradation rate showing enhanced hydrophilicity and induced apatite formation in simulated body fluid. Furthermore, composite nanofibrous membranes possessed significantly improved cellular responses in terms of attachment, proliferation and mineralization of pre-osteoblasts compared to PCL membrane. Thus, the currently developed nanofibrous composite membranes embedded in forsterite nanopowder expected to be attractive in GBR membrane applications.

Comparative evaluation of biocompatibility of dense nanostructured and microstructured Hydroxyapatite/Titania composites.

This work deals with the biocompatibility of dense nano- and micro-structured Hydroxyapatite/Titania composites prepared by two step and conventional sintering, respectively. By application of two step sintering, it was shown that the final grain size of HA-15 wt.% TiO2 is maintained lower than 100 nm while by the application of conventional sintering it reaches higher than 100 nm. Biocompatibility of the dense bulks was evaluated by cell attachment and proliferation experiments. Cell morphology, and viability on each nano- and micro-structured Hydroxyapatite/Titania composites were examined at different time points. The nanostructured HA/Titania dense bulk exhibited higher cell viability than a microstructured one. In addition, the effects of ionic products from nano- and micro-structured bulk dissolution on osteoblasts were studied. The MTT test confirmed that the products from nanostructured HA/Titania dense bulk significantly promoted osteoblast proliferation within a certain concentration range.

Novel nanocomposite coating for dental implant applications in vitro and in vivo evaluation.

This study aimed at preparation and in vitro and in vivo evaluation of novel bioactive, biodegradable, and antibacterial nanocomposite coating for the improvement of stem cells attachment and antibacterial activity as a candidate for dental implant applications. Poly (lactide-co-glycolide)/bioactive glass/hydroxyapatite (PBGHA) nanocomposite coating was prepared via solvent casting process. The nanoparticle amounts of 10, 15, and 20 weight percent (wt%) were chosen in order to determine the optimum amount of nanoparticles suitable for preparing an uniform coating. Bioactivity and degradation of the coating with an optimum amount of nanoparticles were evaluated by immersing the prepared samples in simulated body fluid and phosphate buffer saline (PBS), respectively. The effect of nanocomposite coating on the attachment and viability of human adipose-derived stem cells (hASCs) was investigated. Kirschner wires (K-wires) of stainless steel were coated with the PBGHA nanocomposite coating, and mechanical stability of the coating was studied during intramedullary implantation into rabbit tibiae. The results showed that using 10 wt% nanoparticles (5 wt% HA and 5 wt% BG) in the nanocomposite could provide the desired uniform coating. The study of in vitro bioactivity showed rapid formation of bone-like apatite on the PBGHA coating. It was degraded considerably after about 60 days of immersion in PBS. The hASCs showed excellent attachment and viability on the coating. PBGHA coating remained stable on the K-wires with a minimum of 96% of the original coating mass. It was concluded that PBGHA nanocomposite coating provides an ideal surface for the stem cells attachment and viability. In addition, it could induce antibacterial activity, simultaneously.

Poly(ε-caprolactone)/nano fluoridated hydroxyapatite scaffolds for bone tissue engineering: in vitro degradation and biocompatibility study.

In this study, biodegradation and biocompatibility of novel poly(ε-caparolactone)/nano fluoridated hydroxyapatite (PCL-FHA) scaffolds were investigated. The FHA nanopowders were prepared via mechanical alloying method and had a chemical composition of Ca(10)(PO(4))(6)OH(2-x )F(x) (where x values were selected equal to 0.5 and 2.0). In order to fabricate PCL-FHA scaffolds, 10, 20, 30 and 40 wt% of the FHA were added to the PCL. The PCL-FHA scaffolds were produced by the solvent casting/particulate leaching using sodium chloride particles (with diameters of 300-500 µm) as the porogen. The phase structure, microstructure and morphology of the scaffolds were evaluated using X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy techniques. Porosity of the scaffolds was measured using the Archimedes' Principle. In vitro degradation of PCL-FHA scaffolds was studied by incubating the samples in phosphate buffered saline at 37°C and pH 7.4 for 30 days. Moreover, biocompatibility was evaluated by MTT assay after seeding and culture of osteoblast-like cells on the scaffolds. Results showed that the osteoblast-like cells attached to and proliferated on PCL-FHA and increasing the porosity of the scaffolds increased the cell viability. Also, degradation rate of scaffolds were increased with increasing the fluorine content in scaffolds composition.

Biphasic calcium phosphate coating on cobalt-base surgical alloy during investment casting.

The biphasic calcium phosphate (BCP) yields higher bioactivity and efficiency than the Hydroxyapatite (HA) alone. The HA/ß-TCP ratio significantly affects BCP bioactivity as well as the extent of BCP resorption. In this study, the BCP coating on ASTM F-75 cobalt base alloy during the investment casting process was investigated. For this purpose, molten metal was poured at 1,470°C into previously coated investment molds preheated to 750, 850, 950, 1,050°C in order to investigate the effect of mold preheating temperatures on coating phase transformations. For in vitro evaluation, samples were immersed in the simulated body fluid (SBF) at 37°C for 4 weeks and characterized by XRD, SEM, EDS, and optical microscopy. The weight percentages of HA and ß-TCP of the specimens were calculated to find that the HA/ß-TCP ratio significantly depended on the mold preheating temperature as it caused changes in the dissolution behavior of BCP coating and the bone-like apatite precipitation on coating during in vitro evaluation.

Novel magnesium-nanofluorapatite metal matrix nanocomposite with improved biodegradation behavior.

Designing and preparation of magnesium alloys with adjustable biocorrosion rates in the human body and precipitation ability of bone-like apatite layer have been of interest recently. Application of metal matrix composites (MMC) based on magnesium alloys might be an approach to this challenge. The aim of this work was fabrication and evaluation of biocorrosion and bioactivity of a novel MMC made of magnesium alloy AZ91 as matrix and fluorapatite (FA) nano particles as reinforcement. Biodegradable Magnesium-nano fluorapatite metal matrix nanocomposite (AZ91-20FA) was made via a blending-pressing-sintering method. In vitro corrosion tests were performed for evaluation of biocorrosion behavior of produced AZ91-20FA nanocomposite. The results showed that the addition of FA nano particles to magnesium alloy can reduce not only the corrosion rate in a simulated body environment but also accelerate the formation of an apatite layer.

Subcutaneous connective tissue reactions to three types of bioactive glass nanopowders.

Silica-based bioactive glasses are considered promising bone substitutes and tissue regeneration matrices, because of their bioactivity, biocompatibility, osteoconductivity, and possibly even osteoinductivity. The aim of this work was to evaluate the subcutaneous connective tissue reactions to 58S, 63S, and 72S bioactive glass nanopowders. Our previous study showed the antibacterial activities of 58S and 63S bioactive glass nanopowders on aerobic bacteria, while 72S showed no antibacterial effects at all. Bioactive glass nanopowders were prepared via the sol-gel technique. Characterization techniques such as X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), and X-ray fluorescent (XRF) were utilized to carry out the phase analysis, study of the structure, particle size and the composition of the synthesized bioactive glasses. To evaluate the subcutaneous connective tissue reactions, the specimens were placed in polyethylene tubes and implanted into the dorsal connective tissue of rats. Empty polyethylene tubes were used as the control and bioactive glass micropowders (NovaBone) was used as a FDA approved bone graft. The evaluation of inflammatory reactions was performed 3, 7, 15, and 28 days after implantation. Results showed a particle size of below 100 nm for samples with amorphous structure. The samples were well tolerated by the tissues over a 28-day evaluation period. The extra tissue reactions of the 72S specimen in comparison with 58S and 63S specimens could be attributed to its higher silica content. It may be concluded that biocompatible 58S and 63S bioactive glass nanopowders with antibacterial activities can be synthesized for the treatment of osseous defects.

Direct cytotoxicity evaluation of 63S bioactive glass and bone-derived hydroxyapatite particles using yeast model and human chondrocyte cells by microcalorimetry.

In this study, the cytotoxicity evaluation of prepared 63S bioactive glass and bone-derived hydroxyapatite particles with yeast and human chondrocyte cells was carried out using isothermal micro-nano calorimetry (IMNC), which is a new method for studying cell/biomaterial interactions. Bioactive glass particles were made via sol-gel method and hydroxyapatite was obtained from bovine bone. Elemental analysis was carried out by XRF and EDXRF. Amorphous structure of the glass and completely crystalline structure of HA were detected by XRD analysis. Finally, the cytotoxicity of bioactive glass and bone-derived HA particles with yeast and cultured human chondrocyte cells was evaluated using IMNC. The results confirmed the viability, growth and proliferation of human chondrocyte cells in contact with 63S bioactive glass, and bone-derived HA particles. Also the results indicated that yeast model which is much easier to handle, can be considered as a good proxy and can provide a rapid primary estimate of the ranges to be used in assays involving human cells. All of these results confirmed that IMNC is a convenient method which caters to measuring the cell-biomaterial interactions alongside the current methods.

Improvement of mechanical properties and biocompatibility of forsterite bioceramic addressed to bone tissue engineering materials.

This work deals with the fabrication and characterization of nanostructured forsterite bulk. This material may have better biocompatibility and mechanical properties than coarse grain forsterite for the development of bone tissue engineering materials. Nanostructured forsterite bulks were prepared by two step sintering of sol-gel derived forsterite nanopowder. Their sinterability and mechanical properties were then studied. Biocompatibility of the nanostructured forsterite bulk was also evaluated by cell attachment and proliferation experiments. In addition, the effects of ionic products from forsterite nanopowder dissolution on osteoblasts were studied. Results show that dense nanostructured forsterite bulk was prepared with hardness and fracture toughness of about 1102 Hv and 4.3 MPa m(1/2), respectively. Nanostructured forsterite was biocompatible and the MTT test confirmed that the products from forsterite nanopowder dissolution significantly promoted osteoblast proliferation within a certain concentration range. In addition, cells attached to and spread on the surface of nanostructured forsterite bulks. Mechanical properties of the nanostructured forsterite were much higher than that of hydroxyapatite. It was concluded that nanostructured forsterite is a bioactive ceramic with good biocompatibility that can be used as a bone tissue engineering material.

Effect of strontium ions substitution on gene delivery related properties of calcium phosphate nanoparticles.

Gene therapy has been considered a strategy for delivery of therapeutic nucleic acids to a specific site. Calcium phosphates are one gene delivery vector group of interest. However, low transfection efficiency has limited the use of calcium phosphate in gene delivery applications. Present work aims at studying the fabrication of strontium substituted calcium phosphate nanoparticles with improved gene delivery related properties. Strontium substituted calcium phosphate was prepared using a simple sol gel method. X-ray diffraction analysis, Fourier transform infrared spectroscopy, transmission electron microscopy, specific surface area analysis, zeta potential measurement and ion release evaluation were used to characterize the samples. This characterization showed strontium and carbonate co-substituted calcium phosphate which resulted in nano size particles with low crystallinity, high specific surface area, positive surface charge, and a high dissolution rate. These improved properties could increase the DNA concentration on the vector as well as the endosomal escape of the complex that leads to higher transfection efficiency of this novel gene delivery vector.

Mg2+ substituted calcium phosphate nano particles synthesis for non viral gene delivery application.

Gene therapy provides a unique approach to medicine as it can be adapted towards the treatment of both inherited and acquired diseases. Recently, calcium phosphate vectors as a new generation of the non viral gene delivery nano carriers have been studied because of their biocompatibility and DNA condensation and gene transfer ability. Substituting cations, like magnesium, affects physical and chemical properties of calcium phosphate nano particles. In this study, Mg(2+) substituted calcium phosphate nano particles have been prepared using the simple sol gel method. X-ray diffraction analysis, Fourier transform infra red spectroscopy, transmission electron microscopy, specific surface area analysis, zeta potential measurement and ion release evaluation were used for characterization of the samples. It was concluded that presence of Mg ions decrease particle size and crystallinity of the samples and increase positive surface charge as well as beta tricalcium phosphate fraction in chemical composition of calcium phosphate. These properties result in increasing the DNA condensation ability, specific surface area and dissolution rate of the samples which make them suitable particles for gene delivery application.

Antibacterial effects of sol-gel-derived bioactive glass nanoparticle on aerobic bacteria.

The aim of this work was to evaluate the antibacterial effect of bioactive glass nanopowders. The 58S, 63S, and 72S compositions were prepared via the sol-gel technique. Characterization techniques such as X-ray diffraction, transmission electron microscopy (TEM), Zetasizer, and X-ray fluorescent were used. The antibacterial activity was studied using Escherichia coli, Pseudomonas aeruginosa, Salmonella typhi, and Staphylococcus aureus. Cytotoxicity of the samples was evaluated using mouse fibroblast L929 cell line. The chemical compositions of the prepared samples were as predicted, and the particle size of the samples with an amorphous structure mainly ranged over 20-90 nm. At broth concentrations below 50 mg/mL, they showed no antibacterial activity. The 58S showed the highest antibacterial activity with the minimum bactericidal concentrations of 50 and 100 mg/mL for E. coli plus S. aureus and for P. aeruginosa, respectively. The 63S exhibited bactericidal and bacteriostatic effects on E. coli and S. aureus at concentrations of 100 and 50 mg/mL, respectively, at an minimum bactericidal concentrations of 100 mg/mL. However, 72S bioactive glass nanopowder showed no antibacterial effect. They showed no cytotoxicity. It was concluded that bioactive glass nanopowders could be considered as good candidates for the treatment of oral bone defects and root canal disinfection. (c) 2010 Wiley Periodicals, Inc. J Biomed Mater Res, 2010.

In vitro corrosion behavior of bioceramic, metallic, and bioceramic-metallic coated stainless steel dental implants.

OBJECTIVES: The most common metals and alloys used in dentistry may be exposed to a process of corrosion in vivo that make them cytotoxic. The biocompatibility of dental alloys is primarily related to their corrosion behavior. The aim of this work was to evaluate the corrosion behavior and thus the biocompatibility of the uncoated and coated stainless steels and compare the effect of type of coatings on corrosion behavior. METHODS: Three types of coatings, hydroxyapatite (HA), titanium (Ti), and a double-layer HA/Ti on AISI 316L stainless steel were made. HA coating was produced using plasma-spraying technique and Ti coating was made using physical vapor deposition process. In order to perform a novel double-layer composite coating, a top layer of HA was plasma-sprayed over a physical vapor deposited Ti layer on AISI 316L stainless steel. Structural characterization techniques including XRD, SEM and EDX were used to investigate the microstructure, morphology and crystallinity of the coatings. Electrochemical potentiodynamic tests were performed in physiological solutions in order to determine and compare the corrosion behavior of the coated and uncoated specimens as an indication of biocompatibility. RESULTS: Double-layer HA/Ti coating on AISI 316L SS had a positive effect on improvement of corrosion behavior. The decrease in corrosion current densities was significant for these coated specimens and was much lower than the values obtained for uncoated and single HA coated specimens. Ti coating on AISI 316L SS also has a beneficial effect on corrosion behavior. The results were compared with the results of corrosion behavior of HA coated commercially pure titanium (cpTi) and uncoated cpTi. SIGNIFICANCE: These results demonstrated that the double-layer HA/Ti coated 316L SS can be used as an endodontic implant and two goals including improvement of corrosion resistance and bone osteointegration can be obtained simultaneously.