Characterization of poly(3-hydroxybutyrate)/nano-hydroxyapatite composite scaffolds fabricated without the use of organic solvents for bone tissue engineering applications

Poly(3-hydroxybutyrate)/nano-hydroxyapatite (PHB/nHA) composite scaffolds were fabricated without the use of organic solvents at different mass fractions of HA nanoparticles. HA nanoparticles were homogeneously dispersed as primary particles in the polymer matrix of the scaffolds at 10 and 15 wt.% nHA content. Agglomeration of HA nanoparticles occurred when the nHA content of the scaffolds reached 20 wt.%. All the scaffolds had high porosities with interconnected porous structure and optimized pore size ranges. Mechanical properties of all the scaffolds were in the range of mechanical properties of cancellous bone. Scaffolds were biocompatible to MG-63 cells in the indirect method of cytotoxicity evaluation. Also, the morphology of the attached MG-63 cells in direct contact with the scaffolds indicated the appropriate cell-scaffold interaction. Thus, the PHB/nHA composite scaffolds investigated in this study tend to be favorable for bone tissue engineering applications.     

Crack resistance curves of GLARE laminates by elastic compliance

The objective of this work was to study the applicability of the elastic compliance technique for crack resistance curves evaluation of commercial GLARE laminates using small SE(B) and C(T) specimens. The experimental evaluation of R-curves of 25.0 mm wide SE(B) specimens of unidirectional GLARE 1 3/2 0.3 and 50.0 mm wide C(T) specimens of bidirectional GLARE 3 5/4 0.3 was performed. Fracture toughness was measured through a recently proposed experimental methodology based on standardized specimens and elastic-plastic methodologies (J-integral and CTOD δ₅), whereas crack growth was measured optically and estimated by elastic compliance. According to the results the elastic compliance technique seemed to be applicable to GLARE laminates, accurately predicting stable crack growth during the tests.     

Novel 3D porous multi-phase composite scaffolds based on PCL,thermoplastic zein and ha prepared via supercritical CO2 foaming for bone regeneration

The aim of this study was the design of novel biodegradable porous scaffolds for bone tissue engineering (bTE) via supercritical CO₂ (scCO₂) foaming process. The porous scaffolds were prepared from a poly(ε-caprolactone)-thermoplastic zein multi-phase blend w/o interdispersed hydroxyapatite particles (HA) and the porous structure achieved via the scCO₂ foaming technology. The control of scaffolds porosity was obtained by modulating materials formulation and foaming temperature (T_F). The scaffolds were subjected to morphological, micro-structural and biodegradation analyses, as well as in vitro biocompatibility tests. Results demonstrated that both HA concentration and T_F significantly affected the micro-structural features of the scaffolds. In particular, scaffolds with porosity and pore size distribution, mechanical properties and biodegradability adequate for bTE were designed and produced by selecting a T_F equal to 100 °C for all the compositions used. The biocompatibility of these scaffolds was assessed in vitro by using osteoblast-like MG63 and human mesenchymal stem cells (hMSCs).     

Chitosan-based polyelectrolyte complex scaffolds with antibacterial properties for treating dental bone defects

The aim of this study was to develop an antibacterial polyelectrolyte complex (PEC) scaffold for treating dental bone defects. The PEC scaffold was composed of chitosan (CS), γ-polyglutamic acid (γ-PGA), and carboxy-methyl-cellulose (CMC). The resulted network structures formed via electrostatic crosslinking were characterized by using FTIR, gel content, equilibrium swelling ratio, volume change, and SEM test. The antibacterial property, cell cytotoxicity, and in vivo biocompatibility tests were conducted according to an agar diffusion method, ISO10993-5, and ISO 10993-6, respectively. The resulted specimens showed an interconnected pore structure with pore sizes ranging 100-500 μm. The equilibrium swelling ratio, volume change, and antibacterial property were inversely proportional to the gel content. The PEC-2 scaffold composed of 8 wt.% CS, and 2 wt.% γ-PGA + 2 wt.% CMC had more-suitable gel properties (gel content of 55.3 ± 1.1 wt.% and volume change of 97.7 ± 1.4 v/v%) with inhibition zones of 14.4 ± 0.3 mm for Escherichia coli and 13.0 ± 0.7 mm for Staphylococcus aureus. The cytotoxicity and cell attachment tests of the PEC scaffolds showed satisfactory cell compatibility. Moreover, the in vivo biocompatibility test of the PEC scaffolds revealed little foreign body reaction. For this reason, the newly developed antibacterial PEC scaffold may be a good alternative for dental applications.     

Electrical properties of lead-free thick film NTC thermistors based on perovskite-type BaCoxCo2xBi1 − 3xO3

Lead-free thick film negative temperature coefficient (NTC) thermistors based on perovskite-type BaCo^II_xCo^III_2xBi_1 − 3xO₃ (x ≤ 0.1) were prepared by mature screen-printing technology. The microstructures of the thick films sintered at 720 °C were examined by X-ray diffraction and scanning electron microscopy. The electrical properties were analyzed by measuring the resistance-temperature characteristics. For the BaBiO₃ thick films, the room-temperature resistivity is 0.22 MΩ cm, while the room-temperature resistivity is sharply decreased to about 3 Ω cm by replacing of Bi with a small amount of Co. For compositions 0.02 ≤ x ≤ 0.1, the values of room-temperature resistivity (ρ₂₃), thermistor constant (B_25/85) and activation energy are in the range of 1.995-2.975 Ω cm, 1140-1234 K and 0.102-0.111 eV, respectively.     

Fabrication and characterization of novel hydroxyapatite/porous carbon composite scaffolds

Novel hydroxyapatite (HA)/porous carbon composite scaffolds were prepared by applying sonoelectrodeposition and a subsequent hydrothermal treatment to previous carbonized phenolic resin coated polyurethane sponges. The interconnected pore network and morphology of HA/porous carbon composite scaffolds were determined by scanning electron microscope (SEM), and the whole surface of porous carbons were evenly coated with the deposited HA layer which was confirmed by EDS and XRD. The porosity (83.5 ± 0.3%) and the bulk density (0.297 ± 0.009 g·cm⁻³) of HA/porous carbon scaffolds were detected by the Archimedes method. The compressive and flexural strength of the scaffolds is 1.187 ± 0.064 MPa and 0.607 ± 0.268 MPa, respectively. Compared with the polymeric surface of 24-well cell culture plates, these novel scaffolds significantly promote the proliferation of human osteoblast-like MG-63 cells, indicating that this novel HA/porous carbon composite scaffold could be used for in vitro 3D culture of osteoblasts.     

Poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid) based tissue engineering matrices

In this study, the aim was to produce tissue-engineered bone using osteoblasts and a novel matrix material, poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid) (PHBV). In order to prepare a porous PHBV matrix with uniform pore size, sucrose crystals were loaded in the foam and then leached leaving pores behind. The surface of the PHBV matrix was treated with rf-oxygen plasma to increase the surface hydrophilicity. SEM examination of the PHBV matrices was carried out. Stability of PHBV foams in aqueous media was studied. The pH decrease is an indication of the degradation extent. The weight and density were unchanged for a period of 120 days but then a significant decrease was observed for the rest of the study. Osteoblast cells were then isolated from rat bone marrow and seeded onto PHBV matrices. The metabolization and proliferation on the foams was determined with MTS assay which showed that osteoblasts proliferated on PHBV. It was also found that cells proliferated better on large pore size foams (300–500 m) than on the small pore size foams (75–300 m). Production of ALP was measured spectrophotometrically. The present study demonstrated that PHBV matrices are suitable substrates for osteoblast proliferation and differentiation.     

Structure and negative thermal expansion of Pb1 −xBixTiO3

Pb_1-xBi_xTiO₃ (x = 0.0-0.1) compounds were prepared to study the unique dopant effect of bismuth in PbTiO₃. Their thermal expansions and structures were investigated by high-temperature X-ray diffraction and X-ray Rietveld method. The results indicated that Bismuth substitution evidently weakened the tetragonality of PbTiO₃ solid solution, but increased the spontaneous polarization. Both the enhanced spontaneous polarization and the decreased tetragonality led to small volume shrinkage with temperature rising, where the average volumetric thermal expansion coefficient changed from − 1.99 × 10^− 5/°C for pure PbTiO₃ to − 0.56 × 10^− 5/°C for Pb_0.90Bi_0.10TiO₃. The Curie point of Pb_1 − xBi_xTiO₃ was slightly raised compared to PbTiO₃ and permitted one to use it in a wide temperature range.     

A new nanofiber fabrication technique based on coaxial electrospinning

In tissue engineering, nanofibrous scaffolds can achieve better biological responses than microfibrous scaffolds and electrospinning is a common method for producing fibrous scaffolds. However, not all biopolymers can be made into nanofibers through conventional electrospinning. The current investigation developed an innovative nanofiber fabrication technique based on coaxial electrospinning and used poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) as an example for achieving nanofibers. For obtaining PHBV nanofibers, core-shell structured fibers were fabricated first via coaxial electrospinning, with PHBV being the core and chitosan being the shell. The chitosan shell was then removed by washing electrospun scaffolds with water, leading to the formation of nanofibrous PHBV scaffolds. The PHBV nanofiber diameter was affected by the inner polymer (i.e., PHBV) solution concentration during coaxial electrospinning, which can be explained in terms of the coaxial electrospinning process and polymer solution viscosity. Compared to the approach of using a conductivity-enhancing salt in polymer solution to produce polymer nanofibers, the new technique not only eliminates the biocompatibility concerns but also provides a more effective way of reducing fiber diameters to the nano-size range.     

3D-macroporous hybrid scaffolds for tissue engineering: Network design and mathematical modeling of the degradation kinetics

In the present study it is reported the synthesis, characterization and subsequent degradation performance of organic-inorganic hybrid systems chemically modified by bi-functional crosslinker (glutaraldehyde, GA). The hybrids were prepared by combining 70% poly (vinyl alcohol) and 30% bioactive glass (58SiO₂-33CaO-9P₂O₅, BaG) via sol-gel route using foaming-casting method producing different macroporous tri-dimensional scaffolds depending on the degree of network crosslinking. The in vitro degradation kinetics was evaluated by measuring the mass loss upon soaking into de-ionized water at 37 °C for up to 21 days and different mathematical models were tested. The PVA/BaG hybrids scaffolds properties “as-synthesized” and after the degradation process were extensively characterized by Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), mechanical compressing tests and X-ray Micro-computed Tomography analysis (μCT). The results have clearly shown the effectiveness of tailoring the PVA/BaG hybrids properties and degradation kinetics mechanisms by chemically engineering the structure at nano-order level using different concentrations of the crosslinker. Moreover, these hybrid crosslinked nanostructures have shown 3D hierarchical pore size with interconnected architecture within the range of 10-450 μm for potential use in the field of bone regenerative medicine.     

Biodegradable and bioactive properties of a novel bone scaffold coated with nanocrystalline bioactive glass for bone tissue engineering

The development of the new technologies of bone tissue engineering requires the production of bioactive and biodegradable macroporous scaffolds. Hydroxyapatite (HA) ceramics are useful bone substitutes, but they degrade minimally. Tricalcium phosphates also show poor ability of Ca-P formation both in-vitro and in-vivo, although they are degradable. The present study introduces a biodegradable, bioactive, and macroporous scaffold with suitable mechanical properties. The prepared hydroxyapatite scaffold was coated with a nanocrystalline bioactive glass layer to be subsequently sintered at different temperatures. The bioactivity and degradability of the coated scaffolds were investigated by standard procedures. The ability to induce Ca-P formation in SBF (simulated body fluid) was also investigated semi-quantitatively. BS1 scaffolds (scaffolds sintered at 800 °C with a holding time of 2 h) showed remarkable bioactivity and degradability simultaneously. Formation of a nanocrystalline phase (Si₂PO₇) during the sintering considerably decreased the capability of BS1 scaffolds for Ca-P formation and the rate of degradation but enhanced their mechanical properties. The BS1 scaffolds showed not only significant bioactivity but also good degradability and suitable mechanical property.     

Processing, physico-chemical characterisation and in vitro evaluation of silicon containing β-tricalcium phosphate ceramics

For bone grafting applications, the elaboration of silicon containing beta-tricalcium phosphate (β-TCP) was studied. The synthesis was performed using a wet precipitation method according to the hypothetical theoretical formula Ca_3 − x(PO₄)_2 − 2x(SiO₄)_x. Two silicon loaded materials (0.46 wt.% and 0.95 wt.%) were investigated and compared to a pure β-TCP. The maturation time of the synthesis required in order to obtain β-TCP decreased with the amount of silicon. Only restrictive synthesis conditions allow preparing silicon containing β-TCP with controlled composition. To obtain dense ceramics, the sintering behaviour of the powders was evaluated. The addition of silicon slowed the densification process and decreased the grain size of the dense ceramics. Rietveld refinement may indicate a partial incorporation of silicon in the β-TCP lattice. X-ray photoelectron spectroscopy and transmission electron microscopy analyses revealed that the remaining silicon formed amorphous clusters of silicon rich phase. The in vitro biological behaviour was investigated with MC3T3-E1 osteoblast-like cells. After the addition of silicon, the ceramics remained cytocompatible, highlighting the high potential of silicon containing β-TCP as optimised bone graft material.     

Crystal growth and structure refinement of monoclinic Li2TiO3

Colorless platelet crystals of monoclinic Li₂TiO₃ with a maximum size of 5.0 mm × 5.0 mm × 0.5 mm were successfully grown by a flux method at 1373 K using a LiBO₂-Li₂O system flux. The stoichiometric chemical composition of Li₂TiO₃ was determined by the SEM-EDX, ICP-AES and density measurement using the single crystal samples. The thermal conductivity of the Li₂TiO₃ single crystals was evaluated using hot-disk method. A single-crystal X-ray diffraction study confirmed the monoclinic Li₂SnO₃-type structure, space group C2/c and the lattice parameters of a = 5.0623(5) Å, b = 8.7876(9) Å, c = 9.7533(15) Å, β = 100.212(11)°, and V = 427.01(9) Å³. The crystal structure was refined to the conventional values of R = 2.4% and wR=3.3% for 2187 independent observed reflections. The cationic arrangement of (LiTi₂) layers in Li₂TiO₃ was precisely revealed by the structure analysis.     

Controlling temperature coefficient of resistivity in La1−xSrxMnO3 ceramics

We propose La_1−xSr_xMnO₃ as a new lead-free and ruthenium-free conductive oxide used for thick film resistors. The temperature coefficient of resistivity (TCR) of the La_1−xSr_xMnO₃ was controlled systematically by changing the composition x. The TCR behavior depended on the change of the crystal symmetries and the average valence of Mn ions. The highest value of 9356 ppm/°C was obtained at the x = 0.35. Zero TCR was realized around 0.200 < x < 0.225 and 0.45 < x < 0.50, where the critical x values were related to the characteristic change from Mott-insulator to metallic behavior. The systematical controlling TCR and the zero TCR are the first to be demonstrated for conductive oxide.     

Crashworthiness characteristics investigation of silk/epoxy composite square tubes

This research concentrates on the evaluation of crashworthiness characteristics of natural silk/epoxy composite square tubes energy-absorbers. Composite laminate specimens were subjected to static axial compression load and experimental evaluation of the energy absorption capability of silk/epoxy composite. Specimens were in the form of square cross-sections with the dimension of 80 mm × 80 mm and a radius curvature of 5 mm. The variables in the experiment were the length of the tubes built 50 mm, 80 mm and 120 mm. Meanwhile, the thickness of the walls, consisting of laminates of silk/epoxy of 12, 24 and 30 plies, correspond to equivalent wall thickness of 1.7 mm, 3.4 mm and 4.2 mm, respectively. The parameters measured were the total absorbed energy (E_total), and the crash force efficiency (CFE). E_total is the measure of the amount of energy that the structure can withstand without failure and thus is a measure of its strength, while CFE gives a quantitative indication of the mode of failure of the composites. The mode of failure was observed using photography.     

Improved thermoelectric properties by adding Al for Zn in (ZnO)mIn2O3

The grain size and density of the sintered (Zn_1 − xAl_xO)_mIn₂O₃ bodies decreased with the small Al₂O₃ content (≤ 0.012), and then increased gradually by further increasing the Al₂O₃ content. The addition of Al for Zn in the (ZnO)_mIn₂O₃ led to an increase in both the electrical conductivity and the absolute value of the Seebeck coefficient. This indicates that the power factor was significantly enhanced by adding Al for Zn. The thermoelectric power factor was maximized to 1.67 × 10^− 3 W m^− 1 K^− 2 at 1073 K for the (Zn_0.992Al_0.008O)_mIn₂O₃ sample.     

Crack arrest testing of high strength structural steels for naval applications

The crack arrest fracture toughness of two high strength steel alloys used in naval construction, HSLA-100, Composition 3 and HY-100, was characterized in this investigation. A greatly scaled-down version of the wide-plate crack arrest test was developed to characterize the crack arrest performance of these tough steel alloys in the upper region of the ductile-brittle transition. The specimen is a single edge-notched, 152 mm wide by 19 mm thick by 910 mm long plate subjected to a strong thermal gradient and a tensile loading. The thermal gradient is required to arrest the crack at temperatures high in the transition region, close to the expected service temperature for crack arrest applications in surface ships. Strain gages were placed along the crack path to obtain crack position and crack velocity data, and this data, along with the applied loading is combined in a “generation mode” analysis using finite element analysis to obtain a dynamic analysis of the crack arrest event. Detailed finite element analyses were conducted to understand the effect of various modeling assumptions on the results and to validate the methodology compared with more conventional crack arrest tests.Brittle cracks initiation, significant cleavage crack propagation and subsequent crack arrest was achieved in all 15 of the tests conducted in this investigation. A crack arrest master curve approach was used to characterize and compare the crack arrest fracture toughness. The HSLA-100, Comp. 3 steel alloy had superior performance to the HY-100 steel alloy. The crack arrest reference temperature was T_KIA = −136 °C for the HSLA-100 plate and T_KIA = −64 °C for the HY-100 plate.     

Superconducting properties of internal-tin route Nb3Sn wires with radially arranged filaments : Development that realizes high Jc and low hysteresis loss

An internal-tin route Nb₃Sn superconducting wire that has both remarkably low hysteresis loss (Q_h) and high critical current density (J_c) was developed according to a new design idea. The wire was constructed by arranging the filaments in a radial layout, enlarging the outer filaments along the radial direction, narrowing the filament spacing in the radial direction intentionally and enlarging the filament spacing in tangential direction. Thus, the electromagnetic coupling among the filaments in tangential direction due to the bridging and/or proximity effect was suppressed without decreasing the volume fraction of Nb. As a result, excellent properties such as J_c(12 T) = 1.15 × 10³ A/mm² and Q_h = 301 mJ/cm³ (for 1 cycle of B = ±3 T) were obtained. We also evaluated the transition temperature (T_c) and upper critical field (B_c2) of the wire. The values for T_c and B_c2 were 17.3 K and 24.1 T, respectively, which were much better than those of usual internal-tin route wires. Moreover, electron probe micro-analyses confirmed that the good T_c and B_c2 were the result of the qualitative improvement of the Nb₃Sn compound based on the effects of arranging the Nb filaments radially, increasing the ratio of Sn-to-Nb and shortening the diffusion length for Sn. This wire is promising for use with conduction-cooled high-field magnets, in which there is a need to decrease the load of the cryocooler, and also for the strands of fusion coils.