Bioactive Particles Research Articles

A simple synthesis of amine-derivatised superparamagnetic iron oxide nanoparticles for bioapplications

Adsorption of 3-aminopropyltriethoxysilane (APTS) on magnetite nanoparticles during its formation has been investigated to optimise the preparation of stable aqueous dispersion of amine derivatised magnetite nanoparticles. APTS adsorbs chemically on the surface of magnetite particle modifying its surface which is evident from thermal and C, H, N analysis. The variation of particle size has been observed with change of APTS concentration. X-ray diffractogram shows the formation of pure inverse spinel phase magnetite with average crystallite size 7 nm when equimolar (Fe3O4: APTS = 1:1) quantity of APTS was used during its synthesis. The presence of free surface –NH2 groups and Fe–O–Si bonds was observed by FTIR. Raman spectrum further confirms the presence of surface –NH2 groups. Transmission electron microscopy shows formation of particles of average size between 7 nm and 12 nm. The effective hydrodynamic diameter of the APTS coated particle agglomerates is 45.8 nm in stable aqueous colloidal dispersion, which is evident from photon correlation spectroscopy. VSM measurements at room temperature of both silanised and unsilanised magnetite shows their superparamagnetic nature with saturation magnetisation 41 e.m.u/g and 56 e.m.u/g, respectively. Avidin has been immobilised on the surface through glutaraldehyde, which demonstrates the possibility of the synthesised material to be used in protein immobilisation to form bioactive magnetic particles.

Bacteriostatic textile-polymeric coat materials modified with nanoparticles

The aim of the present study was to develop a process for the preparation of nanoparticles with antybacterial/bacteriostatic properties including the conditions of using these particles in textile-polymeric coating materials with stable bacteriostatic properties. The developed functional particles consist of submicro-spheres (mainly of SiO2 -Fig. 1) made by the "sol-gel" technique. On their developed surface, "nanoislets" of an antibacterial agent such as metallic silver (Ag) were durably deposited (Figs 2 and 3). Such bioactive particles were then incorporated into either hydrophobic (with micro-porous structure) or hydrophilic (with compact structure) polyurethane coats during their production, obtaining the required uniform dispersion of single functional nanoparticles in the polymeric matrix (Fig. 4). To assess the performance stability of the bacteriostatic coating materials they were subjected to 10 standard laundering tests and no deterioration was found in their bacteriostatic properties, as well as in their structure and characteristics such as barrier and hygienic properties (watertightness, water vapor permeability or resistance of water vapor flow) as compared to those of corresponding unmodified materials (Figs 5,6, 7, Tables 1 and 2).

Investigation on the Porous Biomaterial for Bone Reconstruction with Addition of Bio-Mimetic Nano-Sized Inorganic Particles

The spherical nano-sized bioactive particles in the system of CaO-P2O5-SiO2 were bio-mimetically synthesized using micro-emulsion method. The microstructures and properties of the bio- mimetic nano-materials were characterized using XRD, FTIR, SEM/EDAX and TEM techniques. It was indicated that the nano-particles possessed glassy structural characteristics. The porous composite for bone tissue reconstruction was prepared by compounding poly (hydroxybutyrate-2-co-2-hydroxyvalerate) (PHBV) and the nano-particles of bio-mimetic bioactive glasses (BMBG). Bone-like hydroxyl- carbonate-apatite (HCA) could formed on the surface of porous composite by immersing the composite in simulated body fluid (SBF) at 37°C for 8 hours. With increase of immersion time, the morphology of HCA changed from spherical into flake-like crystals. The study on cells attachment of the porous PHBV/BMBG composite proved that the material possessed satisfactory bioactivity, bio-mineralization function and cells biocompatibility.

Protective hybrid sol–gel coatings containing bioactive particles on surgical grade stainless steel: Surface characterization

Metallic materials are the most used materials as orthopaedic or dental implants for their excellent mechanical properties. However, they are not able to create a natural bonding with the mineralized bone and they could release metallic particles that could finally end in the removal of the implant. One way to avoid these effects is to protect the metallic implant with a biocompatible coating. In this work there are analyzed two kinds of protective organic–inorganic sol–gel made coatings with the adding of glass-ceramic particles with the aim of generating bioactivity. The samples are surface characterized by SEM, XRD and XPS. Amorphous hydroxyapatite (aHAp) deposited on the samples after 30 days of immersion in simulated body fluid (SBF) is detected on the samples and its presence is considered as a first signal of bioactivity.

Effects of Polyethylene Glycol on Morphology of Bioactive CaO-SiO<sub>2</sub> Gel

CaO-SiO2 gels for bioactive organic-inorganic composites were prepared from tetraethoxysilane (TEOS) and calcium nitrate tetrahydrate (Ca(NO3)2⋅4H2O) by a sol-gel method with the addition of the various amount of polyethylene glycol (PEG). The effects of PEG on morphology and bioactivity of the gel were investigated. The samples with the starting compositions of Ca(NO3)2 : TEOS = 30 : 70 in molar ratiowere prepared with or without coexistence of PEG. All the examined gels were obtained as a crack-free bulk bodies after gelation and aging. FT-IR spectra of the prepared gels showed that the gels have similar contents of silanol groups regardless of the amount of PEG. SEM observation showed that the gel consists of aggregates of 2-3 μm spherical particles with a diameter of 2-3 μm when it was prepared with the addition of PEG at a molar ratio of PEG : TEOS = 0.002 : 1, while it consists of aggregates of spherical particles with a diameter of 50 nm at a molar ratio of PEG : TEOS = 0.004 or 0.007 : 1. The size of the CaO-SiO2 powder can be decreased with increasing the amount of the added PEG. All the samples, regardless of the amount of the added PEG, formed apatite on their surfaces in a simulated body fluid (SBF) within 1 d. These results suggest that bioactive fine spherical particles with various size can be obtained through sol-gel processing under co-existence of appropriate amounts of PEG.

Effects of bio-active ceramic resources in cutaneous wound healing and the role of TGF-β signaling

The wound healing process is a highly orchestrated process, which includes inflammation, re-epithelialization, granulation tissue formation, matrix formation and re-modeling. In this paper, we attempt to determine if bio-active ceramic resource powder particles had an effect on cutaneous wound healing. Furthermore, we investigated its related mechanism and the expression of Smads of cutaneous wound healing, which can be accelerated by bio-active ceramic ointment. Topically applied lesions of 5%, 10% and 15% bio-active ceramic ointment (AO) showed accelerated wound closure, re-epithelialization, and the related immediate down stream of TGF-beta (p-Smad2/3 and Smad3) was suppressed. In particular, 10% and 15% AO lesions became closed faster at Days 3 and 4 of post-wound and p-Smad2/3 was also suppressed. All AO lesions showed accelerated mild wound closure at Day 6, but there were no significant difference. Several papers reported that Smad3 may mediate the signaling pathways that is inhibitory to wound healing, as the deletion of Smad3 leads to enhanced re-epithelialization and contraction of the wound area. This study showed that topical, bio-active ceramic ointment applications accelerated wound closure, re-epithelialization and the suppression of Smad proteins (p-Smad2/3, Smad3). The data revealed that the suppression of Smad3, which was induced by bio-active ceramic resources powder particles affected re-epithelialization and cutaneous wound closure. At the end of this paper, we concluded that bio-active ceramic resources affect cutaneous wound healing by accelerating the re-epithelialization of keratinocytes and that is mediated by the suppression of related protein, Smad3.

Properties and morphology of bioceramics/poly(D,L-lactide) composites modified byin situ compatibilizing extrusion

Composites of poly(D,L-lactide) (PDLLA) with hydroxylapatite (HA) and PDLLA with tertiary calcium phosphate (TCP) were prepared by in situ modification with methylenediphenyl diisocyanate (MDI) and molded by piston extrusion at temperature between Tg and Tm of PDLLA. Mechanical properties of the composites increased obviously when compared with the unmodified bioactive ceramic particles/PDLLA composites. The effect of MDI contents on mechanical properties of the composites was studied. At the optimum conditions of 1.0/1.0molar ratios of NCO groups in MDI to OH groups in PDLLA, bending strength 68.4 MPa and bending modulus 2281.5 MPa, were achieved in composite HA/PDLLA/MDI with 15 wt % HA. Both increased by nearly 30% when compared with that of solution cast HA/PDLLA composites. Interfacial adhesion and compatibility between PDLLA and bioactive ceramic particles (HA and TCP) were investigated. Scanning electron microscopy (SEM) indicated that the interface between HA particles and PDLLA was blurred and HA particles were closely surrounded by PDLLA matrix in HA/PDLLA/MDI composites. Oriented fibrils along with longitudinal direction of extrusion die were also observed on the surfaces of HA/PDLLA/MDI composite. It is confirmed that MDI has improved interfacial adhesion and compatibility between HA particles and PDLLA phase. Fibril structures formed in the extrusion, and it contributed a great deal in enhancing the mechanical properties. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4085–4091, 2006

Nucleation and Growth of Bone-Like Apatite on Surfaces of Metals, Ceramics and Polymers in Simulated Body Fluids

The biomimetic approach of mineralization in vitro is adopted to investigate systematically the nucleation and growth of bone-like apatite on the surface of biomaterials such as bioceramics, metals and polymers, and those chemically surface-treated. The simulated environment is kept isothermic at the human body temperature of 36.5C with three kinds of simulated physiological fluids. The experimental results show that (1) inherent properties of biomaterials determine their bioactivity and the different crystalline structure of same materials results in the difference in bioactivity; (2) the bioactivity can effectively be improved by the surface treatment of biomaterials via chemical methods and by the addition of bioactive particles in a polymer matrix; (3) the bone-like apatite, nucleated and grown in the simulated body fluid with the same ion concentrations to that of the human plasma, possesses the same composition, structure and morphology despite of matrixes; (4) the difference in bioactivity with biomaterials is indicated by the different time for bone-like apatite to nucleate and to grow on their surfaces.

Stability of Suspensions of Bioactive Particles Using Hybrid Organic–Inorganic Solutions as Dispersing Media

Functional coatings incorporating different types of particles developed by the sol–gel method have been proposed in the last few years for diverse applications. This work focuses on the preparation of homogeneous coatings prepared from stable suspensions with 10 wt% of glass and glass ceramic particles in a hybrid organic–inorganic solution as dispersing media. For this purpose, the pH was shifted up to 6–7 by adding tetrapropylammonium hydroxide (TPAH) which behaves as a cationic surfactant being probably adsorbed on the particles surface, while the sol maintains stable. Rheological measurements were performed to study the stability of the suspensions prepared at different conditions such as the kind and concentration of dispersant and the pH conditions. After sintering at 450∘C/30 min, coatings around 2 μ m in thickness were obtained.

Soluble starch and composite starch Bioactive Glass 45S5 particles: Synthesis, bioactivity, and interaction with rat bone marrow cells

For many biomedical applications, biodegradable and simultaneously bioactive materials are desired. These materials should at the same time be able to support cell function and co-exist with the organism without triggering a relevant immune response. In this work, the synthesis as well as the bioactivity evaluation of newly developed polymer soluble potato starch and composite (with Bioactive Glass 45S5) micron-size particles are reported. An extremely interesting result is that although with different properties, both polymer and composite particles were able to form a calcium phosphate layer at their surface, which is a clear indication of their bioactivity. The cytotoxicity and the ability to support cell attachment and growth of the developed materials were also studied, and both polymer and composite materials were shown to be non-cytotoxic. Preliminary results show that both types of materials were found to allow rat bone marrow cells to attach and to proliferate on their surface and to express osteogenic markers, such as alkaline phosphatase and osteopontin. The obtained results indicate that the developed carriers might be used as substrates for cell culture in vitro, in order to form constructs that might be used as a part of a tissue engineering strategy.

A novel purification strategy for retrovirus gene therapy vectors using heparin affinity chromatography

Membrane separation and chromatographic technologies are regarded as an attractive alternative to conventional academic small-scale ultracentrifugation procedures used for retrovirus purification. However, despite the increasing demands for purified retroviral vector preparations, new chromatography adsorbents with high specificity for the virus have not been reported. Heparin affinity chromatography is presented here as a novel convenient tool for retrovirus purification. The ability of bioactive retroviral particles to specifically bind to heparin ligands immobilized on a chromatographic gel is shown. A purification factor of 63 with a recovery of 61% of functional retroparticles was achieved using this single step. Tentacle heparin affinity supports captured retroviral particles more efficiently than conventional heparin affinity chromatography supports with which a lower recovery was obtained (18%). Intact, infective retroviral particles were recovered by elution with low salt concentrations (350 mM NaCl). Mild conditions for retrovirus elution from chromatographic columns are required to preserve virus infectivity. VSV-G pseudotyped retroviruses have shown to be very sensitive to high ionic strength, losing 50% of their activity and showing membrane damage after a short exposure to 1M NaCl. We also report a complete scaleable downstream processing scheme for the purification of MoMLV-derived vectors that involves sequential microfiltration and ultra/diafiltration steps for virus clarification and concentration respectively, followed by fractionation by heparin affinity chromatography and final polishing by size-exclusion chromatography. Overall, by using this strategy, a 38% yield of infective particles can be achieved with a final purification factor of 2,000.

Characterization of Intra‐Cellular Ionic Concentrations of Monocytes in Contact with Bioactive Glasses and Hydroxyapatite Particles. A TEM Cryo‐X‐ray Analysis of Diffusible Ions

A cells viability can be altered by the presence of bioactive materials particles and their features. This paper compares the influence of hydroxyapatite particles and bioactive glass particles on intracellular ionic concentrations of the monocytes exposed to them. However, microanalysis of intracellular ions like sodium, potassium, and chlorine is a major problem. In order to limit diffusion phenomenon and to preserve the chemical identity of specimens, we used cryomethods (cryo‐preparation, and cryo‐x‐ray microanalysis) to study cells in contact with bioactive materials particles. We measured intracellular ionic concentrations by scanning transmission electron microscopy (STEM) associated with energy dispersive x‐ray spectroscopy (EDXS). Monocytes were exposed to bioactive glass particles and to hydroxyapatite particles during 2 days. The K/Na ratio was used as a sensitive criteria of viability of cells. Bioactive glass particles and, in a less manner, hydroxyapatite particles have an effect on intracellular ionic concentrations. These two types of bioactive particles alter cells. However, bioactive glass particles appear to alter cells more than hydroxyapatite particles.

STEM and EDXS Characterization of Physico‐chemical Reactions at the Periphery of Bioactive Glass Particles in Contact with Biological Fluids

Knowledge of the local concentration and species of ions released at the bioactive glass particles/biological fluids interface is essential to the understanding of the complex interfacial reactions and physico‐chemical properties of bioactive glasses. This work characterises the interface that bioactive glass particles develop after immersion into biological fluids for different delays (1, 2, 4, 28 days). The distribution of silicon, phosphorus, calcium, and aluminum varied across bioactive particles periphery. After 1 day of immersion into biological fluids, a Si–Al rich layer appeared at the bioactive glass surface. After 2 days, significantly higher concentrations of Ca and P are observed on top of this newly formed Si–Al layer, compared to the center of the glass particles. Then, an apatite (Ca–P) layer starts to build up and grows with time after immersion into biological fluids. The Ca/P atomic ratio increases with time from 1 to 1.6. A thick Ca–P rich layer was formed after 28 days. The Ca–P layer appeared to be generated by calcium and phosphate ions diffusing through the Si–Al layer, which contain at least traces of these ions.

Effect of the crystallization of bioactive glass reinforcing agents on the mechanical properties of polymer composites

Polymer composites based on the introduction of bioactive materials into polymer matrices can combine mechanical with bioactive properties suitable for many potential biomedical applications. In this work, glass-ceramics derived from the crystallization of bioactive glasses were tested as reinforcing agents in polymer composites. The kinetics of crystallization of soda-lime silica glasses containing phosphorous was studied to define conditions for obtaining glass-ceramics having different microstructures. This type of glass can be used in biomedical applications due to its ability to bind to bone (bioactive behavior). Evaluation of the mechanical properties of glass-ceramic bodies derived from bioactive glasses has allowed us to determine the relationship between microstructure and properties. A particular microstructure capable of leading to fine grained glass-ceramics with enhanced properties was then reproduced in bioactive glass particles. Thus, bioactive glass particles were crystallized to different levels and used as reinforcing agents in polymer (polysulfone) composites. Mechanical properties of composites were evaluated using a four-point bending test. Glass-ceramic reinforced composites showed higher elastic modulus than glass reinforced composites. Therefore, crystallization of silicate glasses used as reinforcing agents in polymer matrices is a possible way to enhance the mechanical properties of composites. Polymer composites having bioactive glass-ceramic particles display some mechanical properties comparable to human cortical bone.

A COMPARISON OF ASBESTOS AND URBAN PARTICULATE MATTER IN THE IN VITRO MODIFICATION OF HUMAN ALVEOLAR MACROPHAGE ANTIGEN-PRESENTING CELL FUNCTION

The mechanism for how inhaled particles cause or exacerbate human diseases is not known. It is clear, however, that some particles are more bioactive than others. One possible mechanism may involve a modification of antigen-presenting cell function. In this study, 2 forms of asbestos (crocidolite and Libby amphibole) and PM2.5 (an urban particle) were cultured with human alveolar macrophages (HAMs) to determine whether antigen-presenting cell (APC) function was altered. HAMs were exposed to the bioactive particles, asbestos and PM2.5, for 24 hours, then isolated free of extracellular particulates and nonviable cells. Isolated HAMs were then cultured with autologous lymphocytes in an 11-day APC assay using tetanous toxoid as the antigen and the resulting culture supernatants were assayed for lymphocyte-derived cytokines. Asbestos exposure, regardless of type, up-regulated a TH1 lymphocyte–derived cytokine, interferon gamma (IFNγ), and the TH2 lymphocyte–derived cytokines interleukin-4 (IL-4) and interleukin-13 (IL-13). PM2.5 exposure up-regulated all 3 cytokines also. Although cytokine production levels were significantly higher for the treatment compared to control cultures as a group, there was extreme variability in the responses between subjects. In addition, there was no correlation between an individual's cells’ response to asbestos verses PM, suggesting that more than one possible mechanism exists for a particle-induced APC effect and individual differential sensitivities to inhaled bioactive particles. This work supports the hypothesis that some inhaled particles can modify immune function by directly affecting APCs thus up-regulating the normal lymphocyte response to antigens in the lung.

Bioactive glass as a drug delivery system of tetracycline and tetracycline associated with β-cyclodextrin

The aim of this study was to evaluate the physical–chemical properties, in vivo biocompatibility and antimicrobial activity of bioactive glasses (BG) used as a controlled release device for tetracycline hydrochloride and an inclusion complex formed by tetracycline and β-cyclodextrin at 1:1 molar ratio. The BG as well as their compounds loaded with tetracycline (BT) and tetracycline: β-cyclodextrin (BTC) were characterized by FTIR spectroscopy, X-ray powder diffraction, differential scanning calorimetry and by scanning electron microscopy and energy dispersive spectroscopy. The in vivo test was carried out with female mice split into three groups treated with bioactive glass either without drugs, or associated with tetracycline, or with tetracycline: β-cyclodextrin by subcutaneous implantation. The histological examination of tissue at the site of implantation showed moderate inflammatory reactions in all groups after 72 h. The bacterial effect was tested on A. actinomycetemcomitans suspended in BHI broth, with or without bioactive particles. A considerable bacteriostatic activity was found with BT and BTC glasses, as compared to plain glass. The presence of cyclodextrin was important to slow down the release of tetracycline for a long period of time and it was verified that the presence of tetracycline or its inclusion complex, tetracycline: β-cyclodextrin, did not affect the bioactivity of the glass.

Preparation and biocompatibility of poly (methyl methacrylate) reinforced with bioactive particles

Calcium phosphates and bioactive glasses have been used in many biomedical applications for more than 30 years due basically to their bioactive behavior. However, ceramics are too brittle for applications that require high levels of toughness and easy processability. In this work, a biphasic calcium phosphate (BCP) and a bioactive glass composition (BG) were combined with polymers to produce composites with tailorable properties and processability. The BCP particles were synthesized by a precipitation technique. The BG particles were produced by sol-gel processing. The BCP particles were treated with a silane agent to improve the compatibility between particles and the polymer matrix. Dense samples were produced by hot pressing (200 °C) a mixture of 30 wt.% of particles in poly (methyl methacrylate). The samples produced were characterized by X-ray diffraction, infrared spectroscopy and scanning electron microscopy. Mechanical properties were evaluated by a three point bending test. Samples were also submitted to in vitro bioactivity test and in vivo toxicity test. Results showed that the production of the composites was successfully achieved, yielding materials with particles well dispersed within the matrices. Evaluation of the in vivo inflammatory response showed low activity levels for all composites although composites with silane treated BCP particles led to milder inflammatory responses than composites with non-treated particles.

Effects of bioactive glass particles and their ionic products on intracellular concentrations.

Numerous studies have described the bioactive properties of glass particles in the SiO(2)-CaO-Na(2)O-P(2)O(5) system. This kind of material is capable of developing a direct contact with bone through dissolution and physicochemical reactions. We have investigated the influence of bioactive particles, and ionic products from the same particles, on the intracellular concentrations in monocyte cells, which are among the first cells to colonize implantation sites. The only way to access these concentrations and particularly diffusible ionic concentrations (potassium, sodium, and chlorine) is to use cryomethods coupled to electron probe microanalysis. We have paid particular attention to the potassium:sodium ratio, the most sensitive criterion of viability. We have cultured cells with bioactive glass particles and in a conditioned medium obtained from the dissolution of the glass particles in the standard medium. Our study demonstrates that cells cultured in a conditioned medium are more active than cells cultured in a standard medium, or cells exposed to bioactive particles, and particles are more toxic for cells than are ionic products.

Bioactive glass ceramic particles as an alternative for mastoid obliteration: results in an animal model.

This study was conducted to evaluate the use of the bioactive glass ceramic particulate NovaBone Bioglass as a graft material for mastoid cavity obliteration in an animal model. Canal wall down procedures in otologic surgery may result in a problematic mastoid cavity. Mastoid cavity obliteration can potentially prevent or correct this problem. Many techniques and implant materials have been used for mastoid obliteration, but no single graft material has proved to be ideal. Mongolian gerbils received tympanic bulla obliteration using the NovaBone Bioglass particulate. Nine weeks after implantation, the animals were killed, and histologic sections were prepared. Histologic evaluation was performed to evaluate new bone formation within the implant. Wound healing occurred without complication. Mature trabecular bone was observed throughout the entire thickness of the implant material. Extensive neovascularity was observed within the graft material. There was no histologic evidence of inflammatory reaction or short-term resorption. The extensive new bone formation obtained with bioactive glass ceramic particles in this study makes this material a potential alternative resource as a graft material for mastoid obliteration.

Electrochemical evaluation of resistance to localised corrosion of vitreous coatings containing particles applied on metallic substrates for biomedical applications

CrCoMo alloys are generally known to be highly resistant to corrosion-induced failures and to spontaneously form passive oxide films when immersed in physiological environments. The stresses resulting from the use of the prosthesis can cause fracture and abrasion of the oxide film that covers the surface. This can result in crevice corrosion, with the corresponding decrease in pH leading to severe attack. Protective coatings deposited onto the metals would minimise the release of metallic ions from the substrate and the incorporation of bioactive particles would enable the adhesion to the bone tissue. This work describes the electrochemical behavior of CrCoMo alloys (F75) as cast, covered by a hybrid silica coating obtained by sol–gel. The silica sol–gel coating contains bioactive glass ceramic and vitreous particles of the system CaO–SiO 2–P 2O 5 previously obtained by fusion, crystallization and milling. The performance of the alloy with and without coating is evaluated in simulated body fluid (SBF) pH 7.31 at 37 °C. As cobalt base alloys are susceptible to crevice attack, coated pieces are also tested in SBF acid solution (pH 0.7) in order to simulate the acidic media and the high chloride concentrations that develop when a crevice is formed. The electrochemical behavior has been evaluated by potenciodynamic polarization and electrochemical impedance spectroscopy. It was found that for both pH conditions the samples coated with double layer of glass ceramic particles showed lower passive current densities than those with monolayers. The coating improves the protection potential of the base material in the neutral solution. Besides, in the acidic solution, all the samples remain passive but the protection potential shifts to potentials more active than those measured in the neutral SBF.