The in vitro bioactive of sol–gel bioactive glass powders with three-dimensional lamellar structure

In this study, three-dimensional lamellar structured bioactive glass powders were prepared using nonionic block copolymer surfactants as structure-directing agents through a sol–gel method. The characterization methods such as X-ray diffraction (XRD), Fourier transform infrared spectrograph (FTIR), transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM) were used for determination of the particles structure before and after immersion in simulated body fluid (SBF) for various numbers of days. The results show that the biomineralized products on the surfaces of the bioactive glass powders were apatite microcrystals with a low crystallinity, the composition and morphologies of the apatite microcrystals changed with the immersion time increased. The presence of the apatite layer indicates biomineralization.     

Characterisation of the bioactive behaviour of sol–gel hydroxyapatite–CaO and hydroxyapatite–CaO–bioactive glass composites

The fabrication and characterization of sol–gel derived hydroxyapatite–calcium oxide (HAp–CaO) material is investigated focusing on the effect of the addition of a bioactive glass on the material bioactive behaviour through the fabrication of a novel HAp–CaO (70 wt.%)–bioactive glass (30 wt.%) composite material. The bioactive behaviour of the materials was assessed by immersion studies in Simulated Body Fluid (SBF) and the alterations of the materials surfaces after soaking periods in SBF were characterized by Scanning Electron Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR). A brittle and weakly crystalline carbonate hydroxyapatite (HCAp) layer was found to develop on the surface of all samples, few hours after immersion in SBF, confirming the high bioactivity of the material. Alterations of the morphology of the developed HCAp layer, which led to a more compact structure, were observed on the surface of composite samples after 7 days of immersion in SBF. The presence of the CaO phase seems to accelerate the formation of HCAp, while the bioactive glass affects both the morphology and cohesion of the developed layer.     

Rheological evaluations and in vitro studies of injectable bioactive glass–polycaprolactone–sodium alginate composites

Composite pastes composed of various amounts of melt-derived bioactive glass 52S4 (MG5) and polycaprolactone (PCL) microspheres in sodium alginate solution were prepared. Rheological properties in both rotatory and oscillatory modes were evaluated. Injectability was measured as injection force versus piston displacement. In vitro calcium phosphate precipitation was also studied in simulated body fluid (SBF) and tracked using scanning electron microscopy, X-ray diffraction and FTIR analyses. All composite pastes were thixotropic in nature and exhibited shear thinning behavior. The magnitude of thixotropy decreased by adding 10–30 wt% PCL, while further amounts of PCL increased it again. Moreover, the composites were viscoelastic materials in which the elastic modulus was higher than viscous term. The pastes which were just made of MG5 or PCL had poor injectability, whereas the composites containing both of these constituents exhibited reasonable injectability. All pastes revealed adequate structural stability in contact with SBF solution. In vitro calcium phosphate precipitation was well observed on the paste made of MG5 and somewhat on the pastes with 10–40 wt% PCL, however the precipitated layer was amorphous in nature. Overall, the produced composites may be appropriate as injectable biomaterials for non-invasive surgeries but more biological evaluations are essential.     

Bioactive borosilicate glass scaffolds: in vitro degradation and bioactivity behaviors

Bioactive borosilicate glass scaffolds with the pores of several hundred micrometers and a competent compressive strength were prepared through replication method. The in vitro degradation and bioactivity behaviors of the scaffolds have been investigated by immersing the scaffolds statically in diluted phosphate solution at 37°C, up to 360 h. To monitor the degradation progress of the scaffolds, the amount of leaching elements from the scaffolds were determined by ICP-AES. The XRD and SEM results reveal that, during the degradation of scaffolds, the borosilicate scaffolds converted to hydroxyapatite. The compressive strength of the scaffolds decreased during degradation, in the way that can be well predicted by the degradation products, or the leachates, from the scaffolds. MTT assay results demonstrate that the degradation products have little, if any, inhibition effect on the cell proliferation, when diluted to a certain concentration ([B] <2.690 and pH value at neutral level). The study shows that borosilicate glass scaffold could be a promising candidate for bone tissue engineering material.     

Development of injectable biocomposites from hyaluronic acid and bioactive glass nano-particles obtained from different sol–gel routes

Bioactive glass nano-powders with the same chemical composition and different particle characteristics were synthesized by acid-catalyzed (the glass is called BG1) and acid–base catalyzed (BG2) sol–gel processes. Morphological characteristics of powders were determined by TEM and BET methods. The powders were separately mixed with 3% hyaluronic acid solution to form a paste. In vitro reactivity of pastes was determined by soaking them in simulated body fluid. Rheological behaviors of paste in both rotation and oscillation modes were also measured. The results showed that BG1 particles was microporous with mean pore diameter of 1.6 nm and particle size of ~ 300 nm while BG2 was mesoporous with average pore diameter of 8 and 17 nm and particle size of 20–30 nm. The paste made of BG2 revealed better washout resistance and in vitro apatite formation ability than BG1. According to the rheological evaluations, both pastes exhibited shear thinning but non-thixotropic behavior, meanwhile paste of BG2 had higher viscosity than BG1. The oscillatory tests revealed that the pastes were viscoelastic materials with more viscous nature. Both pastes could be completely injected through standard syringe using low compressive load of 5–50 N. Overall, The biocomposites can potentially be used as bioactive paste for the treatment of hard and even soft tissues.     

Modifying a dental ceramic by bioactive glass via the sol–gel route: Characterization and bioactivity investigation

The modification of a widely used dental ceramic by a bioactive glass via sol–gel method resulted in the fabrication of novel dental ceramic composites with bioactive behavior. The presence of leucite (Lt), apatite (Ap), various calcium silicate phases (CS) and a glassy aluminosilicate matrix were detected, while after sintering the predominance of wollastonite (W) among the other calcium silicate phases was observed, along with further crystallization of apatite. Concerning the bioactivity, the onset of the apatite formation was directly dependent on the bioactive glass amount, while a delay of the sintered specimens compared to the raw powders was also observed.     

Gold nanoparticles developed in sol–gel derived apatite—bioactive glass composites

The study is focussed on synthesis and characterisation of a new sol–gel derived composite system consisting of nanocrystalline apatite, bioactive glass and gold nanoparticles, which are of interest both for regenerative medicine and for specific medical applications of the releasable gold nanoparticles. Samples dried at 110°C and then heat treated for 30 min at 300 and 500°C were investigated by thermal analysis (DTA/TG), X-ray diffraction (XRD), UV–VIS–NIR, Fourier Transform Infrared (FTIR) spectroscopy, X-ray Photoelectron(XPS) spectroscopy, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). Gold nanoparticles and nanocrystalline apatite are developed already after heat treatment at 300°C. XPS analysis clearly revealed the presence of both metallic and ionic gold species. The development of gold nanoparticles was evidenced by UV–VIS–NIR and TEM analysis, and their size increased from few nanometers to 25 nm by increasing the treatment temperature from 300 to 500°C. The bioactivity of the samples immersed in simulated body fluid was demonstrated by XRD and SEM results.     

In vitro study of hydroxyapatite/polycaprolactone (HA/PCL) nanocomposite synthesized by an in situ sol–gel process

Hydroxyapatite (HA) is the most substantial mineral constituent of a bone which has been extensively used in medicine as implantable materials, owing to its good biocompatibility, bioactivity high osteoconductive, and/or osteoinductive properties. Nevertheless, its mechanical property is not utmost appropriate for a bone substitution. Therefore, a composite consist of HA and a biodegradable polymer is usually prepared to generate an apt bone scaffold. In the present work polycaprolactone (PCL), a newly remarkable biocompatible and biodegradable polymer, was employed as a matrix and hydroxyapatite nanoparticles were used as a reinforcement element of the composite. HA/PCL nanocomposites were synthesized by a new in situ sol–gel process using calcium hydroxide and phosphoric acid precursors in the presence of Tetrahydrofuran (THF) as a solvent. Chemical and physical characteristics of the nanocomposite were studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and Fourier transform infrared (FTIR) analyses. The results indicated that pure HA nanoparticles were well-incorporated and homogenously dispersed in the PCL matrix. It was found that the mechanical property of PCL was improved by addition of 20 wt.% HA nanoparticles. Furthermore, the biological property of nanocomposites was investigated under in vitro condition. For this purpose, HA/PCL scaffolds were prepared through a salt leaching process and immersed in a saturated simulated body fluid (SBF) after 3 and 7 days. It was found that a uniform layer of biomimetic HA could be deposited on the surface of HA/PCL scaffolds. Therefore, the prepared HA/PCL scaffolds showed good potential for bone tissue engineering and could be used for many clinical applications in orthopedic and maxillofacial surgery.     

Fabrication and characterization of bioactive composite coatings on Mg–Zn–Ca alloy by MAO/sol–gel

High corrosion rate and accumulation of hydrogen gas upon degradation impede magnesium alloys’ clinical application as implants. In this work, micro-arc oxidation (MAO) was used to fabricate a porous coating on magnesium alloys as an intermediate layer to enhance the bonding strength of propolis layer. Then the composite coatings were fabricated using sol–gel method by dipping sample into the solution containing propolis and polylactic acid at 40°C. The corrosion resistance of the samples was determined based on potentiodynamic polarization experiments and immersion tests. Biocompatibility was designed by observing the attachment and growth of wharton’s jelly-derived mesenchymal stem cells (WJCs) on substrates with MAO coating and substrates with composite coatings. The results showed that, compared with that of Mg–Zn–Ca alloy, the corrosion current density of the samples with composite coatings decreased from 5.37 × 10⁻⁵ to 1.10 × 10⁻⁶ A/cm² and the corrosion potential increased by 240 mV. Composite coatings exhibit homogeneous corrosion behavior and can promote WJCs cell adhesion and proliferation. In the meantime, pH value was relatively stable during the immersion tests, which may be significant for cellular survival. In conclusion, our results indicate that composite coatings on Mg–Zn–Ca alloy fabricated by MAO/sol–gel method provide a new type bioactive material.     

Effect of glass–ceramic microstructure on its in vitro bioactivity

Two routes were used to obtain a glass–ceramic composed of 43.5 wt % SiO₂ – 43.5 wt % CaO – 13 wt % ZrO₂. Heat treatment of a glass monolith produced a glass–ceramic (WZ1) containing wollastonite-2M and tetragonal zirconia as crystalline phases. The WZ1 did not display bioactivity in vitro. Ceramizing the glass via powder technology routes formed a bioactive glass–ceramic (WZ2). The two glass–ceramics, WZ1 and WZ2, were composed of the same crystalline phases, but differed in microstructure. The in vitro studies carried out on WZ2 showed the formation of an apatite-like layer on its surface during exposure to a simulated body fluid. This paper examined the influence of both chemical and morphological factors on the in vitro bioactivitity. The interfacial reaction product was examined by scanning and transmission electron microscopy. Both instruments were fitted with energy-dispersive X-ray analyzers. Measurements of the pH made directly at the interface of the two glass–ceramics were important in understanding their different behavior during exposure to the same physiological environment.     

Synthesis and characterization of smoke-like porous sol–gel indium tin oxide coatings on glass

A precursor for porous indium tin oxide (ITO) coatings with smoke-like surface feature was prepared from the hydrated metal [In(III)/Sn(IV)] salts and polyvinyl alcohol (PVA) solvated in a mixed aqueous-organic medium. Films were prepared by dip coating and cured at four temperatures (60 °C, 150 °C, 250 °C and 400 °C) where different surface features and morphological properties were obtained. The thickness of the films ranged from 0.5 to 1.2 μm. After the 60 °C cure, the surface showed a unique “smoke-like” feature of combustion products of PVA-ITO precursor. Increasing the cure temperature to 150 °C led to the development of In(III) and Sn(IV) moieties incorporated in crystalline PVA having the shape close to the hexagonal. Study of thermogravimetric analysis and differential thermal analysis of the material suggests that the gel to oxide transformation occurs by the removal of physisorbed water, PVA and nitrate ion followed by the condensation of hydroxide groups. Electrical parameters such as resistivity, conductivity, sheet resistance were evaluated by two- and four-point probe methods. Field emission scanning electron microscopy and transmission electron microscopy studies of the sample cured at 400 °C showed that the films were a porous network containing 5–40 nm clusters of ITO.     

In vitro and in vivo degradation of poly(l-lactide-co-glycolide) films and scaffolds

Poly(l-lactide-co-glycolide) (PLGA) was synthesized using a biocompatible initiator, zirconium acetylacetonate. In vitro and in vivo degradation properties of PLGA films (produced by solvent casting, 180 μm thick) and PLGA scaffolds (produced by an innovated solvent casting and particulate leaching, 3 mm thick) were evaluated. The samples were either submitted for degradation in phosphate buffered saline (PBS) at 37 °C for 30 weeks, or implanted into rat skeletal muscles for 1, 4, 12, 22 and 30 weeks. The degradation was monitored by scanning electron microscopy, atomic force microscopy, weight loss, and molecular weight changes (in vitro), and by microscopic observations of the materials’ morphology after histological staining with May-Grunwald-Giemsa (in vivo). The results show that the films in both conditions degraded much faster than the scaffolds. The scaffolds were dimensionally stable for 23 weeks, while the films lost their integrity after 7 weeks in vitro. The films’ degradation was heterogenous—degradation in their central parts was faster than in the surface and subsurface regions due to the increased concentration of the acidic degradation products inside. In the scaffolds, having much thinner pore walls, heterogenous degradation due to the autocatalytic effect was not observed.     

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.     

Preparation and complex characterization of silica holmium sol–gel monoliths

Amorphous, sol–gel derived SiO₂ are known to biocompatible and bioresorbable materials. Biodegradable and inert materials containing radioactive isotopes have potential application as delivery vehicles of the beta radiation to the cancer tumors inside the body. Incorporation of holmium in the sol–gel derived SiO₂ could lead to the formation of a biodegradable material which could be used as carrier biomaterial for the radiation of radioactive holmium to the various cancer sites. The homogeneity of the prepared sol–gel silica holmium monoliths was investigated by Back Scattered Electron Imaging of Scanning Electron Microscope equipped with Energy Dispersive X-ray Analysis, X-ray Induced Photoelectron Spectroscopy and Nuclear Magnetic Resonance Spectroscopy. The biodegradation of the monoliths was investigated in Simulated Body Fluid and TRIS (Trizma pre-set Crystals) solution. The results show that by suitable tailoring of the sol–gel processing parameters holmium can be homogeneously incorporated in the silica matrix with a controlled biodegradation rate.     

Synthesis and characterization of NiO nanoparticles by sol–gel method

Nickel oxide nanoparticles have been synthesized in the presence of agarose polysaccharide by sol–gel method. The structure, morphology, optical and magnetic properties of the product was examined by X-ray diffraction, transmission electron microscopy, UV–visible spectrophotometer and superconducting quantum interference device magnetometer. The result of thermogravimetric analysis of the precursor product showed that the proper calcination temperature was 400 °C. X-ray diffraction result revealed that the obtained product was nickel oxide with face-centered cubic structure. TEM image demonstrated that the nickel oxide nanoparticles have spherical shape with size around 3 nm. Analysis of FTIR spectra confirmed the composition of product. The optical absorption band gap of the NiO nanoparticles was estimated to be 3.51 eV. Magnetic measurement showed that the nickel oxide nanoparticles exhibit superparamagnetic behavior at 300 K. Moreover, the nanoparticles show ferromagnetic interactions at 4.2 K owing to the existence of uncompensated moments on the surface of the nanoparticles.     

Stiff macro-porous bioactive glass–ceramic scaffold: Fabrication by rapid prototyping template,characterization and in vitro bioactivity

Bioactive glass–ceramic scaffolds with interconnected pore networks suitable for bone regeneration were produced through rapid prototyping techniques by a photosensitive resin mold. The 45S5 Bioglass^® was used in this study with a composition (wt%): 45% SiO₂, 24.5% CaO, 24.5% Na₂O and 6% P₂O₅. All variables in the process were investigated systematically to devise an optimal process. Characterization methods such as XRD, FTIR and FESEM were used for determination of the in vitro bioactivity of the scaffolds after immersion in SBF. The results show that hydroxycarbonate apatite crystals formed and to be a layer in 14 days. The compressive strength of the scaffolds was approximately 12.37 ± 1.25 MPa for the well-defined interconnected pores with a mean diameter of 900 μm, which is thought to be a suitable porous network for vascularized bone regeneration. This scaffold has the potential to bond to bone for application in bone repair and regeneration.     

Porous and strong bioactive glass (13–93) scaffolds fabricated by freeze extrusion technique

Scaffolds fabricated by current methods often lack the combination of high strength and high porosity for skeletal substitution of load-bearing bones. In this work, freeze extrusion fabrication (FEF), a solid freeform fabrication technique, was investigated for the creation of porous and strong bioactive glass (13–93) scaffolds for potential applications in the repair of loaded bone. The process parameters for forming three-dimensional (3D) scaffolds with a pre-designed, grid-like microstructure by FEF were determined. Following thermal treatment of the as-formed constructs at temperatures up to 700 °C, scaffolds consisting of dense glass struts and interconnecting pores (porosity ≈ 50%; pore width ≈ 300 μm) were obtained. These scaffolds showed an elastic mechanical response in compression, with a compressive strength of 140 ± 70 MPa and an elastic modulus of 5.5 ± 0.5 GPa, comparable to the values for human cortical bone. The scaffolds supported the proliferation of osteogenic cells in vitro, showing their biocompatibility. These results indicate that 13–93 bioactive glass scaffolds created by the FEF method could have potential application in the repair and regeneration of load-bearing bones.     

Properties and in vitro characterization of polyhydroxybutyrate–chitosan scaffolds prepared by modified precipitation method

Porous polyhydroxybutyrate (PHB)–chitosan biopolymer scaffolds were prepared by co-precipitation from biopolymer solutions with propylene carbonate and acetic acid as solvents. A change of the fibrous character of chitosan precipitates to globular shaped forms with a polyhydroxybutyrate addition was found in suspensions. Scaffolds differ by porosity and morphology of polymers in microstructures, while chitosan represented more compact plate-like fibers and PHB characterized mainly fine fibrous globular agglomerates. Two structurally dissimilar phase regions were verified in blended scaffolds. A rise in the number of smaller pores, and fine structured polymer forms with PHB content were observed in the scaffolds. A significant reduction in the average molecular weight of biopolymers was found in pure chitosan scaffold, this after precipitation of the chitosan in the presence of propylene carbonate and in blends after mutual biopolymer mixing. Interactions between shortened chitosan chains, PHB and chitosan biopolymers in the blends were observed. An excellent fibroblast proliferation was found in scaffolds prepared from biopolymer blends.     

Synthesis,characterization and evaluation of bioactivity and antibacterial activity of quinary glass system (SiO2–CaO–P2O5–MgO–ZnO): In vitro study

Bioactive glasses in the systems SiO₂–CaO–P₂O₅–MgO (BGZn0) and SiO₂–CaO–P₂O₅–MgO–ZnO (BGZn5), were prepared by sol–gel method and then characterized. Surface reactivity was studied in simulated body fluid (SBF) to determine the effect of zinc (Zn) addition as a trace element. The effect of Zn addition to the glass matrix on the formation of apatite layer on the glass surface was investigated through X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT–IR) and scanning electron microscopy (SEM). Also, inductively coupled plasma–optical emission spectroscopy (ICP–sOES) was used to determine the concentrations of released ions in SBF solution after different time intervals in SBF solution. The antibacterial activity of Zn containing glass against Pseudomonas aeruginosa was measured by the halo zone test. The presence of Zn in glass composition improved chemical durability, slowed down the formation rate of Ca–P layer and decreased the size of crystalline apatite particles. Zn containing glass exhibited an excellent antibacterial activity against P. aeruginosa which could demonstrate its ability to treat bone infection.