Synthesis and characterisation of gelatin–nano hydroxyapatite composite scaffolds for bone tissue engineering

Abstract

Gelatin–hydroxyapatite (HAp) nanocomposites have been prepared by particulate leaching technique using glutaraldehyde (GTA) as cross-linking agent for polymer. The porosity in the scaffolds was controlled using sodium chloride as porogen agent. Microstructural investigation by scanning electron microscopy (SEM), revealed the formation of a well interconnected porous scaffold with pore size in the range of 100–200 μm. X-ray diffraction and Fourier transform infrared spectroscopy were used to confirm the formation of crystalline HAp as well the presence of both constituents in the composite samples. The bioactivity of the samples was evaluated by conducting MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assay and cell adhesion tests. The results suggest that the use of GTA in excess of 0˙25% can be detrimental to cell survival. Cell attachment on the nanocomposite scaffold was verified by microscopic analysis.     

Novel 3D scaffolds of chitosan–PLLA blends for tissue engineering applications: Preparation and characterization

This work addresses the preparation of 3D porous scaffolds of blends of chitosan and poly(l-lactic acid), CHT and PLLA, using supercritical fluid technology. Supercritical assisted phase-inversion was used to prepare scaffolds for tissue engineering purposes. The physicochemical and biological properties of chitosan make it an excellent material for the preparation of drug delivery systems and for the development of new biomedical applications in many fields from skin to bone or cartilage regeneration. On the other hand, PLLA is a synthetic biodegradable polymer widely used for biomedical applications. Supercritical assisted phase-inversion experiments were carried out in samples with different polymer ratios and different polymer solution concentrations. The effect of CHT:PLLA ratio and polymer concentration and on the morphology and topography of the scaffolds was assessed by SEM and Micro-CT. Infra-red spectroscopic imaging analysis of the scaffolds allowed a better understanding on the distribution of the two polymers within the matrix. This work demonstrates that supercritical fluid technology constitutes a new processing technology, clean and environmentally friendly for the preparation of scaffolds for tissue engineering using these materials.     

Bacterial cellulose–assisted synthesis of glass-ceramic scaffolds with TiO2 crystalline domains

Glass-ceramic 3D porous structures were obtained by from a polymeric template, which was successively loaded with calcium phosphates, by chemical reaction and a dried gel based on barium and titanium by physical attachment. The resulting composite was subjected to a freeze-drying procedure in order to maintain the spongy morphology. Under the effect of the subsequent thermal treatment at temperatures above 1000°C, the biocellulose membrane was completely removed, the mineral phases combined with each other through intense diffusion processes, and the mineral scaffolds acquired enough mechanical strength to become self-sustained. The as-prepared and thermally treated samples were characterized from physicochemical and biological point of view. The only crystalline phase emerged in the final masses was TiO₂, while the microstructure was individualized as peculiar 3D architectures with porous and branched appearance. All prepared materials were proven to be biocompatible with the mesenchymal stem cells, showing no cytotoxic effect and suitability for the field of tissue engineering.     

Rapid prototyping assisted fabrication of patient specific β-tricalciumphosphate scaffolds for bone tissue regeneration

Beta Tri calcium phosphate scaffolds were produced by inverse casting methodology using rapid prototyping technology. Β-TCP scaffold sintered at different temperatures were analyzed by using Scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, uniaxial compression test and cytotoxicity test. Results incorporate scaffold pore size, bonding, phase chance, porosity, mechanical strength, and cytotoxic profile with an increase in the sintering temperatures. Together, these properties are required for scaffold fabrication in the field of bone tissue regeneration.     

Electrospinning of polyvinylalcohol–polycaprolactone composite scaffolds for tissue engineering applications

Random nanofibrous composite scaffolds of PVA/PCL bilayer were fabricated by electrospinning method. The bilayer nanofibrous scaffolds were subjected to detailed structural, morphological, chemical, and thermal analysis using XRD, SEM, FTIR, and DSC. Morphological investigations revealed that the prepared nanofibers have uniform morphology and the average fiber diameters for bilayer samples A, B, and C are 203, 252, and 244 nm, respectively. The obtained scaffolds have a porous structure with porosity of 77, 89.2, and 78.3 % for bilayer samples A, B, and C, respectively. FTIR analysis ensured complete evaporation of solvent and formation of non-interactive bilayers. Biocompatibility of the membranes was investigated by studying the adhesion of mouse NIH 3T3 fibroblasts for 72 h, and its enhanced adhesion and proliferation proved its mettle as a potential scaffold for tissue engineering applications.     

Development of dual-responsive chitosan–collagen scaffolds for pulsatile release of bioactive molecules

Advancement in polymer science and engineering has led to the development of new polymeric systems for well-controlled delivery of therapeutic agents. In this work, thermo and pH responsive chitosan–collagen (CHT–CLG) scaffolds were prepared using a non-residue strategy. CHT–CLG scaffolds (pH sensitive) were produced by freeze drying method, cross-linked with glutaraldehyde, and coated with poly(N,N′-diethylacrylamide) (PDEAAm) in supercritical media to confer the thermoresponsive behavior. This green and integrated process generated a wide range of porous structures with different mechanical properties, reversible swelling ability and controlled biodegradability, depending on the scaffold composition and cross-linking degree. Microarchitectural analysis by scanning electron microscopy and mercury intrusion porosimetry demonstrated that the coating of the pores inner surface was efficiently achieved without compromising the porosity. The ability of these dual sensitive structures to control the release of a low molecular weight drug (ibuprofen, Ibu) and a model protein (BSA) was investigated. Additionally, a mathematical model was adjusted to the experimental release profiles in order to quantitatively describe the drug release and elucidate the underlying drug release mechanisms. The tunable morphological and mechanical properties together with the well-controlled pulsatile release of bioactive molecules make these structures attractive ON–OFF systems in biomedical and pharmaceutical fields.     

Effect of hollow silica support on the reduction performance of harmful gases of 3Pt–2MgO–3ZrO2–2CeO2 for DOC

The aim of the present study is to investigate the reduction of harmful gases using the diesel oxidation catalyst on hollow silica support with a large surface area. One side of the hollow polymer support was open and the other side was closed, so exhaust gas molecules can collide and stay on the back-side of the polymer membrane to prolong the reaction time. In the case of fresh 3Pt–2MgO–3ZrO₂–2MgO/hollow silica, the LOT 50 value of CO was about 175 °C, while that of fresh catalyst supported by Al₂O₃ support was 150 °C. The hollow silica-based diesel oxidation catalyst (DOC) showed inferior catalyst performance compared to that of the γ-Al₂O₃ support-based DOC. There was a reduction in the number of active sites because of the weak structure of hollow silica. In addition, the agglomeration of Pt particles by repeated calcinations and hydrothermal aging further reduced the catalyst performance. The catalyst performance can be improved by increasing the frequency of gas molecule collisions using the shape characteristics of hollow silica supports with a lager specific surface area.     

Emulsion–ion extraction technique for synthesis of hollow bicomponent oxide microspheres

Abstract

H ollow ox ide microspheres in the bicomponent systems Al₂O₃-28 wt-%SiO₂ (AS) ( mullite) , Al₂O₃- 13 wt-%T iO₂ (AT) , and Z rO₂-10 wt-%Y₂O₃ ( Z Y) were prepared by the emulsion-ion extraction technique. Monodisperse microsphere formation was found to depend on the experimental parameters adopted during ion ex traction and the surfactant concentration present in the emulsion system. Powder characteristics were investigated using X-ray diffraction, optical and scanning electron microscopy, and particle size analysis. The gel microspheres in the AS, AT , and ZY systems started crystallising at about 900, 800, and 400 °C respectively. The oxide microspheres were mostly spherical in morphology and the sphericity was retained even after calcination at 1300 °C for 1 h. Formation of hollow microspheres with a single spherical cavity was identified by SEM . All oxide microspheres calcined at 1300 °C for 1 h ex hibited a particle size distribution within the range 5-60 μm, the average size ( d₅₀) varying from 19 to 22 μm. BCT / 537     

Modelling of 3–3 piezocomposites for hydrophones

Abstract

Three-dimensional modelling of a 3-3 piezoelectric structure was carried out using finite element modelling software. Hydrostatic figures of merit were calculated for structures with increasing amounts of interconnecting porosity. In addition to using air as the second phase, polymer fillers were added to the three-dimensional model in order to observe the effect of polymer Young's modulus on the piezoelectric properties of the bulk material. Results show that increasing the porosity has the effect of improving the hydrostatic piezoelectric properties for applications such as low frequency hydrophones.     

Fluorescence method for monitoring isothermal curing and shelf life of an epoxy–anhydride system

A fluorescence technique with seven fluorescent probes was applied to monitor the curing and shelf life of an epoxy resin. As isothermal curing proceeded, the fluorescence emission bands of the probes exhibited blue shifts because of microviscosity and micropolarity changes. An intensity ratio method was applied in which ratios of the lowest and highest intensity changes in the emission bands were used to determine the degree of isothermal curing. A smooth and, in some cases, a linear correlation was found between the fluorescence intensity ratio and the degree of cure. This method enables the degree of cure to be monitored and allows comparable results from different types of probes to be monitored during the same curing process. The fluorescence technique and the ratio method offer the possibility of monitoring the precuring and the shelf life of the epoxy polymer. The method can be used to compare the kinetics of various monomers and resin formulations under constant curing conditions. Thus, the method would be useful for developing new resin formulations and technologies and could be applied to a variety of commercial and industrial uses of epoxy resins. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2607–2615, 2001     

Modelling of the strength–porosity relationship in glass-ceramic foam scaffolds for bone repair

Foam-like glass-ceramic scaffolds based on three different glass compositions (45S5 Bioglass and two other experimental formulations, CEL2 and SCNA) were produced by sponge replication and characterized from morphological, architectural and mechanical viewpoints. The relationships between porosity and compressive or tensile strength were systematically investigated and modelled, respectively, by using the theory of cellular solids mechanics or quantized fracture mechanics. Models results are in good agreement with experimental findings, which highlights the satisfactory predictive capabilities of the presented approach. The developed models could contribute to improve the rational design of porous bioceramics with custom-made properties. Knowing the scaffold recommended strength for a specific surgical need, the application of the models allows to predict the corresponding porosity, which can be tailored by varying the fabrication parameters in a controlled way so that the device fulfils the desired mechanical requirements.     

Preparation and characterisation of bioactive hydroxyapatite–silica composite nanopowders via sol–gel method for medical applications

Abstract

Abstract

This study focuses on preparation and characterisation of hydroxyapatite–silica composite nanopowders with different contents of silica. Hydroxyapatite–silica composite nanopowders with 10, 20, 30 and 40?wt‐% silica were prepared using a sol–gel method at 600°C with phosphoric pentoxide and calcium nitrate tetrahydrate as the source of hydroxyapatite, also tetraethylorthosilicate and methyltriethoxisilane as the source of silica. XRD, FTIR, SEM, EDAX and TEM techniques were used for characterisation and evaluation of the phase composition, crystallinity, crystallite size, functional groups, morphology and composition of the products. Dissolution behaviour of the products was evaluated at predetermined time periods by an atomic absorption spectrometer and a pH meter. Results indicated the presence of nanocrystalline hydroxyapatite phase and amorphous silica nanoparticles in composite nanopowders. Also, by increasing the content of silica in composite nanopowders, the crystallite size and crystallinity of hydroxyapatite phase decreased and the Ca ion release rate changed.     

Facile synthesis of multi-shelled MnO2–Co3O4 hollow spheres with superior catalytic activity for CO oxidation

Nano-oxide hollow structures have a wide range of applications in catalysis, but the preparation of multi-shelled composite oxide hollow structures still presents a major challenge. Herein, well-dispersed multi-shelled MnO₂–Co₃O₄ hollow spheres have been successfully prepared via a facile “Kirkendall effect” method employing carbon spheres as sacrifice templates. The shell of the hollow spheres was constructed by interconnected Co₃O₄ nanosheets and catkin-like MnO₂ nanorods. The interdiffusion of Carbon chain and MnO₄^? during synthesis could be the possible formation mechanism for the special morphology. Benefiting from the hierarchical porous structure, high surface area and strong synergistic effect between Co₃O₄ and MnO₂ was obtained, the as-prepared Co–Mn composite hollow spheres showed reliably high activity and recycle stability for CO oxidation, achieving the complete CO conversion at 137 °C without significant decrease in activity after five cycles and 10h constant-temperature reaction. We believe that this work will provide a new method for the preparation of multi-shell composite hollow spheres.     

Effect of different MgFe2O4 contents on 3D gel-printed porous TCP–MgFe2O4 composite scaffolds

Magnetic materials have shown significant influence in the process of bone regeneration. In order to combine the bone repairing capability of tricalcium phosphate (TCP) ceramic with magnetic material, porous TCP–MgFe₂O₄ composite scaffolds were successfully prepared by three-dimensional (3D) gel-printing technology, and the effect of different MgFe₂O₄ contents on TCP–MgFe₂O₄ composite scaffolds was studied. The viscosity of printing slurry prepared with polyvinyl alcohol as binder decreased with the increase of shear rate, showing shear thinning. Results show that following with MgFe₂O₄ content increasing from 30 to 70 wt%, the compressive strength of the composite scaffolds increased from 8.45 to 10.58 MPa, the saturation magnetization increased from 3.07 to 7.20 emu/g, and the weight loss rate of degradation in vitro increased from 1.83% to 2.1% after 4 weeks, respectively. Live and dead staining shows that MC3T3-E1 cells had better proliferation on TCP–MgFe₂O₄ composite scaffolds than TCP scaffolds. Compared with pure TCP scaffolds, the addition of MgFe₂O₄ improves the comprehensive performance of scaffolds and meets the application requirements of bone repairing.     

Preparation and characterization of PVDF-montmorillonite mixed matrix hollow fiber membrane for gas–liquid contacting process

Porous PVDF-hydrophobic montmorillonite (MMT) mixed matrix membranes (MMMs) were fabricated via wet spinning method and used in membrane gas absorption process. The effects of hydrophobic MMT nano-clay loadings (1, 3 and 5 wt% of polymer) on the structure and performance were investigated. The fabricated membranes showed both finger-like and sponge-like structure with an increase in the length of finger-like pores in their cross-section, which resulted in higher permeability and lower mass transfer resistance compared to plain PVDF membrane. Also, significant improvements for surface hydrophobicity, critical entry pressure of water and porosity with the addition of filler were observed. The CO₂ absorption test was conducted through the gas–liquid membrane contactor and demonstrated a significant improvement in the CO₂ flux with MMT loading and the membrane with 5 wt% MMT presented highest performance. For example, at the liquid water velocity of 0.5 m s⁻¹, CO₂ flux of the MMM with 5 wt% MMT of 9.73 × 10⁻⁴ mol m⁻² s⁻¹ was approximately 56% higher than the PVDF membrane without nano-filler. In conclusion, MMMs with improved absorption properties can be a promising candidate for CO₂ absorption and separation processes through membrane contactors.     

Solvothermal synthesis and characterization of Pd–Rh alloy hollow nanosphere catalysts for formic acid oxidation

Pd–Rh alloy hollow nanospheres deposited on multiwalled carbon nanotubes (MWCNTs) were synthesized in our study. Initially, Cu nanoparticles were attached onto the MWCNT surface through solvothermal reaction, and then Pd-based alloy hollow nanospheres were formed using Cu nanoparticles as sacrificial template. Electrochemical activity and stability for the oxidation of formic acid were studied by cyclic voltammetry and chronoamperometry. The results reveal that the alloy hollow nanostructures have high electrochemical activity and good stability for the oxidation of formic acid, which might make them good candidates for direct formic acid fuel cells.     

Hierarchical materials constructed by 1D hollow nickel–cobalt sulfide nanotubes supported on 2D ultrathin MXenes nanosheets for high-performance supercapacitor

To design and prepare novel composites with strong electrode structure and superior electrochemical performances via a facile and convenient synthesis method is a significant challenge to develop the high-performance materials for energy storage and conversion devices. Herein, we fabricated a novel hybridization of two dimensional (2D) Ti₃C₂-MXenes nanosheets and one dimensional (1D) nickel-cobalt sulfide (NiCo₂S₄) hollow nanotubes though the favorable electrostatic interaction between the negatively charged Ti₃C₂ and positively charged NiCo₂S₄ nanotubes. The electrode combined the good metallic conductivity of Ti₃C₂-MXenes and high pseudo-capacitance of NiCo₂S₄ demonstrated the outstanding electrochemical performance for supercapacitors. Herein, 2D Ti₃C₂-MXenes/1D NiCo₂S₄ hybrid electrode achieved an excellent specific capacitance of 1927 F g^-1 at 2 mV s^-1, long cycling stability for 4000 cycles and charming rate performances, which is mainly ascribed to the synergistic effect and interfacial interaction between two components. Particularly, the novel hybrid material with 1D and 2D hierarchical structures can provide additional electrochemical reaction sites, supply shorter paths for ions diffusion and electron transport, and effectively raise the charge transfer kinetics during the electrochemical process, which explores a new strategy aimed to develop 2D Ti₃C₂-MXenes energy storage devices with high electrochemical performance, and is possible potential for expansion into other application fields.     

In-vitro corrosion inhibition mechanism of fluorine-doped hydroxyapatite and brushite coated Mg–Ca alloys for biomedical applications

Magnesium alloys have received great attention as a new kind of biodegradable metallic biomaterials. However, they suffer from poor corrosion resistance. In this study, Mg–Ca alloy was coated with nano-fluorine-doped hydroxyapatite (FHA), and brushite (DCPD); via electrochemical deposition (ED). Coatings were characterized by X-ray diffraction (XRD), Fourier-transformed infrared spectroscopy (FTIR), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The results revealed that nano-fluorine-doped hydroxyapatite coating produced more dense and uniform coating layer, compared to the brushite coating. The compression tests of the ED-coated Mg alloy samples immersed in simulated body fluid for different time periods showed higher yield strength (YS) and ultimate tensile strength (UTS), compared to those of the uncoated samples. The degradation behavior and corrosion properties of the ED-coated Mg alloy samples were examined via electrochemical measurements and immersion tests. The results showed that FHA coating could effectively induce the precipitation of more Ca²⁺ and PO₄³⁻ ions than DCPD coating, because the nanophase can provide higher specific surface area. It was also found that FHA and DCPD coatings can significantly decline the initial degradation rate of the alloy. A corrosion mechanism of the ED-coated alloy is proposed and discussed in this paper.