Comparison of Different Approaches to Surface Functionalization of Biodegradable Polycaprolactone Scaffolds

Due to their good mechanical stability compared to gelatin, collagen or polyethylene glycol nanofibers and slow degradation rate, biodegradable poly-epsilon-caprolactone (PCL) nanofibers are promising material as scaffolds for bone and soft-tissue engineering. Here, PCL nanofibers were prepared by the electrospinning method and then subjected to surface functionalization aimed at improving their biocompatibility and bioactivity. For surface modification, two approaches were used: (i) COOH-containing polymer was deposited on the PCL surface using atmospheric pressure plasma copolymerization of CO2 and C2H4, and (ii) PCL nanofibers were coated with multifunctional bioactive nanostructured TiCaPCON film by magnetron sputtering of TiC-CaO-Ti3POx target. To evaluate bone regeneration ability in vitro, the surface-modified PCL nanofibers were immersed in simulated body fluid (SBF, 1x) for 21 days. The results obtained indicate different osteoblastic and epithelial cell response depending on the modification method. The TiCaPCON-coated PCL nanofibers exhibited enhanced adhesion and proliferation of MC3T3-E1 cells, promoted the formation of Ca-based mineralized layer in SBF and, therefore, can be considered as promising material for bone tissue regeneration. The PCL-COOH nanofibers demonstrated improved adhesion and proliferation of IAR-2 cells, which shows their high potential for skin reparation and wound dressing

Recent Progress in Fabrication and Application of BN Nanostructures and BN-Based Nanohybrids

Due to its unique physical, chemical, and mechanical properties, such as a low specific density, large specific surface area, excellent thermal stability, oxidation resistance, low friction, good dispersion stability, enhanced adsorbing capacity, large interlayer shear force, and wide bandgap, hexagonal boron nitride (h-BN) nanostructures are of great interest in many fields. These include, but are not limited to, (i) heterogeneous catalysts, (ii) promising nanocarriers for targeted drug delivery to tumor cells and nanoparticles containing therapeutic agents to fight bacterial and fungal infections, (iii) reinforcing phases in metal, ceramics, and polymer matrix composites, (iv) additives to liquid lubricants, (v) substrates for surface enhanced Raman spectroscopy, (vi) agents for boron neutron capture therapy, (vii) water purifiers, (viii) gas and biological sensors, and (ix) quantum dots, single photon emitters, and heterostructures for electronic, plasmonic, optical, optoelectronic, semiconductor, and magnetic devices. All of these areas are developing rapidly. Thus, the goal of this review is to analyze the critical mass of knowledge and the current state-of-the-art in the field of BN-based nanomaterial fabrication and application based on their amazing properties

Adhesion and Proliferation of Mesenchymal Stem Cells on Plasma-Coated Biodegradable Nanofibers

Various biomedical applications of biodegradable nanofibers are a hot topic, as evidenced by the ever-increasing number of publications in this field. However, as-prepared nanofibers suffer from poor cell adhesion, so their surface is often modified. In this work, active polymeric surface layers with different densities of COOH groups from 5.1 to 14.4% were successfully prepared by Ar/CO2/C2H4 plasma polymerization. It has been shown that adhesion and proliferation of mesenchymal stem cells (MSCs) seeded onto plasma-modified PCL nanofibers are controlled by the CO2:C2H4 ratio. At a high CO2:C2H4 ratio, a well-defined network of actin microfilaments is observed in the MSCs. Nanofibers produced at a low CO2:C2H4 ratio showed poor cell adhesion and very poor survival. There were significantly fewer cells on the surface, they had a small spreading area, a poorly developed network of actin filaments, and there were almost no stress fibrils. The maximum percentage of proliferating cells was recorded at a CO2:C2H4 ratio of 35:15 compared with gaseous environments of 25:20 and 20:25 (24.1 ± 1.5; 8.4 ± 0.9, and 4.1 ± 0.4%, respectively). Interestingly, no differences were observed between the number of cells on the untreated surface and the plasma-polymerized surface at CO2:C2H4 = 20:25 (4.9 ± 0.6 and 4.1 ± 0.4, respectively). Thus, Ar/CO2/C2H4 plasma polymerization can be an excellent tool for regulating the viability of MSCs by simply adjusting the CO2:C2H4 ratio

Effect of <i>h</i>-BN Support on Photoluminescence of ZnO Nanoparticles: Experimental and Theoretical Insight

Herein we report a simple and easily scalable method for fabricating ZnO/h-BN composites with tunable photoluminescence (PL) characteristics. The h-BN support significantly enhances the ultraviolet (UV) emission of ZnO nanoparticles (NPs), which is explained by the ZnO/h-BN interaction and the change in the electronic structure of the ZnO surface. When h-BN NPs are replaced with h-BN microparticles, the PL in the UV region increases, which is accompanied by a decrease in visible light emission. The dependence of the PL properties of ZnO NPs on the thickness of h-BN carriers, observed for the first time, is explained by a change in the dielectric constant of the support. A quantum chemical analysis of the influence of the h-BN thickness on the electron density redistribution at the wZnO/h-BN interface and on the optical properties of the wZnO/h-BN composites was carried out. Density functional theory (DFT) calculations show the appearance of hybridization at the h-BN/wZnO interface and an increase in the intensity of absorption peaks with an increase in the number of h-BN layers. The obtained results open new possibilities for controlling the properties of ZnO/h-BN heterostructures for various optical applications

Microstructure evolution during AlSi10Mg molten alloy/BN microflake interactions in metal matrix composites obtained through 3D printing

Utilization of metal/ceramic powders opens new possibilities for 3D printing of metal matrix composites of complex shape with high strength, but it is still a great challenge. In this work, an AlSi10Mg matrix composite embedded with 1 wt.% of hexagonal BN phase microflakes (h-BN) was obtained by means of 3D printing. Then the present study elucidated microstructure evolutions occurring at the h-BN/melt interface during selective laser melting (SLM) of an h-BN-AlSi10Mg powder mixture. During short-term (0.15 ms) high-temperature (∼2900 K) processing the BN inclusions partly dissolved in the Al-Si melt. This process was accompanied by the formation of an AlN phase at the BN surfaces. The AlN crystallites, 100-200 nm in size, had spherical/semispherical shape and formed a continuous layer along the BN/metal grain boundaries. The peculiar growth of AlN grains along the metal/BN interfaces was governed by the specific features of localized N diffusion in the vicinity of interfaces. By contrast, B atoms, released from the dissolved BN phase, were randomly distributed over the melt. AlB2 nanocrystallites (∼10 nm in size) precipitated from the supersaturated Al-Si melt during cooling stage. With the addition of h-BN microflakes, the composite hardness and tensile strength increased by 32% and 28%, respectivelly. The observed experimental results were supported by ab initio molecular dynamics simulations. Our study demonstrates the possibility and wide prospects of obtaining a dense BN/AlSi10Mg material reinforced with h-BN, AlN, and AlB2 phases via SLM 3D printing and sheds a new light on fine morphological and microstructural features of thus obtained new composites

Structure and superelasticity of novel Zr-rich Ti-Zr–Nb shape memory alloys

Two novel superelastic Ti-41Zr-8(10)Nb alloys were studied and compared to the reference Ti-18Zr-15Nb alloy (all in at. %) in terms of their microstructure and mechanical properties. A thermomechanical treatment consisting of cold rolling and post-deformation annealing was applied to all the alloys to create conditions for their superelastic behavior at room temperature. X-ray diffraction analysis demonstrated considerably larger lattice distortions of both parent and martensitic phases in Zr-rich alloys that resulted in significantly higher theoretical limits of recovery strain in these alloys (~ 8.0%) as compared to the reference alloy (~ 5.5%). However, during room temperature fatigue testing, the novel alloys accumulated considerable residual strains and showed a relatively weak fatigue resistance caused by the presence of notable quantities of α″-phase at this temperature. Conversely, the reference alloy containing only β-phase at the temperature of testing and therefore, a more favorable phase composition at the testing temperature manifested a better superelasticy, and therefore, a better fatigue resistance. Nonetheless, an excellent combined effect of shape memory and superelasticity in Zr-rich alloys indicates that their room temperature superelasticity could be improved via an additional adjustment of their chemical composition.</p

Electrospun Polycaprolactone/ZnO Nanocomposite Membranes with High Antipathogen Activity

The spread of bacterial, fungal, and viral diseases by airborne aerosol flows poses a serious threat to human health, so the development of highly effective antibacterial, antifungal and antiviral filters to protect the respiratory system is in great demand. In this study, we developed ZnO-modified polycaprolactone nanofibers (PCL-ZnO) by treating the nanofiber surface with plasma in a gaseous mixture of Ar/CO2/C2H4 followed by the deposition of ZnO nanoparticles (NPs). The structure and chemical composition of the composite fibers were characterized by SEM, TEM, EDX, FTIR, and XPS methods. We demonstrated high material stability. The mats were tested against Gram-positive and Gram-negative pathogenic bacteria and pathogenic fungi and demonstrated high antibacterial and antifungal activity

Synthesis and Characterization of Folate Conjugated Boron Nitride Nanocarriers for Targeted Drug Delivery

International audienceWe have developed advanced folate bonded to boron nitride (BN) nanocarriers with a high potential for targeted drug delivery. The folic acid (FA) molecules were successfully conjugated to BN nanoparticles (BNNPs) in three consecutive stages (i) FA preactivation by N,N'-dicyclohexylcarbodiimide (DCC), (ii) BNNP modification by AgNPs and their further NH2-functionalization with L-cysteine, and (iii) final conjugation of activated FA to modified BNNPs. To shed light on the FA-BNNPs binding mechanism, detailed energetic analysis of the atomic structure and stability of the FA-BNNPs system using density functional theory (DFT) calculations was carried out. The results indicated that the FA was successfully bonded with the BNNPs by a condensation reaction between amino groups of Cyst-Ag/BNNPs and carboxyl groups of FA using DCC. Theoretical analysis also demonstrated that the grafting of FA to the surface of BNNP does not affect FA targeting properties

Synergistic Catalytic Effect of Ag and MgO Nanoparticles Supported on Defective BN Surface in CO Oxidation Reaction

Micron-sized supports of catalytically active nanoparticles (NPs) can become a good alternative to nanocarriers if their structure is properly tuned. Here, we show that a combination of simple and easily scalable methods, such as defect engineering and polyol synthesis, makes it possible to obtain Ag and MgO nanoparticles supported on defective hexagonal BN (h-BN) support with high catalytic activity in the CO oxidation reaction. High-temperature annealing in air of Mg-containing (h-BN micropellets led to surface oxidation, the formation of hexagonal-shaped surface defects, and defect-related MgO NPs. The enhanced catalytic activity of Ag/MgO/h-BN materials is attributed to the synergistic effect of h-BN surface defects, ultrafine Ag and MgO NPs anchored at the defect edges, and MgO/Ag heterostructures. In addition, theoretical simulations show a shift in the electron density from metallic Ag towards MgO and the associated decrease in the negative charge of oxygen adsorbed on the Ag surface, which positively affects the catalytic activity of the Ag/MgO/h-BN material

New insights into synthesis of nanocrystalline hexagonal BN

Uncovering the mechanism behind nanocrystalline hexagonal boron nitride (h-BN) formation at relatively low temperatures is of great scientific and practical interest. Herein, the sequence of phase transformations occurring during the interaction of boric acid with ammonia in a temperature range of 25-1000 °C has been studied in detail by means of thermo-gravimetric analysis, X-ray diffraction, infrared spectroscopy, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. The results indicate that at room temperature boric acid reacts with ammonia to form an ammonium borate hydrate (NH4)2B4O7x4H2O. Its interaction with ammonia upon further heating at 550 °C for 1 h leads to the formation of turbostratic BN. Nanocrystalline h-BN is obtained either during heating in ammonia at 550 °C for 24 h or at 1000 °C for 1 h. This result is important for the development of novel cost-effective and scalable syntheses of h-BN nanostructures, such as nanosheets, nanoparticles, nanofibers, and nanofilms, as well as for sintering h-BN ceramic materials