•Porous fibers were prepared via electrospinning and calcination using silica nanospheres as building blocks.•The porous structure was derived from the inherent spaces between carbon-bound nanospheres.•Porosity could be regulated by controlling the content of the sacrificial polymer polymethylmethacrylate (PMMA).•The fibers demonstrated drug absorption and release capabilities in relating to their pore volumes.Porous silica fibers were fabricated aiming to broaden the applications of SiO2 nanosphere materials. The fibers were built with SiO2 nanospheres via electrospinning and calcinations. At first, SiO2 nanospheres (synthesized by Stober method) were surface-modified using γ-aminopropyltriethoxysilane to obtain SiO2-NH2 nanospheres, which dispersed homogeneously in the solvent. Then, polyacrylonitrile (PAN) and polymethylmethacrylate (PMMA) were introduced in different weight ratios into the suspension. Subsequently, PAN/PMMA/SiO2 composites were electrospun, followed by preoxidization and calcination to transfer PAN into carbon form and to remove PMMA component. Thus, porous silica fibers were fabricated with SiO2 nanospheres binding together during carbonization and porous structure was formed. The porosity, pore size and pore volume of porous silica fibers were controllable by adjusting the content of SiO2 nanospheres and the weight ratio of PAN/PMMA. Accordingly, the drug adsorption and release performance of these porous silica fibers depended on their micro-structural features. The thus-obtained porous silica fibers displayed great potentials in applications such as drug carriers and adsorbents.Download high-res image (158KB)Download full-size image

The effects of dopamine reduced graphene oxide (pDop-rGO) on the curing activity and mechanical properties of epoxy-based composites were evaluated. Taking advantage of self-polymerization of mussel-inspired dopamine, pDop-rGO was prepared through simultaneous functionalization and reduction of graphene oxide (GO) via polydopamine coating. Benefiting from the universal binding ability of polydopamine, good dispersion of pDop-rGO in epoxy matrix was able to be achieved as the content of pDop-rGO being below 0.2 wt %. Curing kinetics of epoxy composites with pDop-rGO were systematically studied by nonisothermal differential scanning calorimetry (DSC). Compared to the systems of neat epoxy or epoxy composites containing GO, epoxy composites loaded with pDop-rGO showed lower activation energy (Eα) over the range of cure (α). It revealed that the amino-bearing pDop-rGO was able to react with epoxy matrix and enhance the curing reactions as an amine-type curing agent. The nature of the interactions at GO-epoxy interface was further evaluated by Raman spectroscopy, confirming the occurrence of chemical bonding. The strengthened interfacial adhesion between pDop-rGO and epoxy matrix thus enhanced the effective stress transfer in the composites. Accordingly, the tensile and flexural properties of EP/pDop-rGO composites were enhanced due to both the well dispersion and strong interfacial bonding of pDop-rGO in epoxy matrix.Keywords: curing kinetics; dopamine; epoxy; graphene oxide; nonisothermal differential scanning

Bioactive glass (BG)-containing carbon nanofibers (CNFs) were prepared by combining the processes of sol–gel, polyacrylonitrile (PAN) electrospinning and heat treatment. Two types of BG, i.e. 45S and 68S, were incorporated. The crystalline structure evolution of the BG component during the formation of the CNFs was characterized by XRD, SEM, and TEM observations in relation to silicon content. Then the apatite-forming ability of the hybridized CNF/BG in simulated body fluid was evaluated in relation to the crystalline structure of the BG component. Interactions between functional groups in PAN and BG sol–gel precursors were identified in the steps of electrospinning and heat treatment. As a result, the 45S-type BG containing less silicon formed α-CaSiO3, while the 68S-type BG containing more silicon transformed to β-CaSiO3 in the final hybridized CNF/BG upon carbonization. This difference led to different dissolution rates and osteocompatibility activities of the BG component from the hybrids, which regulated their capacities in inducing apatite deposition, proliferation and osteogenic differentiation of bone mesenchymal stromal cells.

Composite carbon nanofibers (CNFs) containing bioglass (BG) nanoparticles displayed different morphology and microstructures depending on the sintering temperature (800, 1000 and 1200 °C) when they were produced from an electrospun polyacrylonitrile–BG precursor blend nanofibers. Biomineralization using simulated body fluid (SBF) and biological evaluation using an osteoblast culture were performed to investigate their relationship with sintering temperature. Characterization revealed that the BG nanoparticles on CNF/BG sintered at 1000 °C (CNF/BG-1000) possessed small particle size and uniform size distribution, and the crystallinity of the BG nanoparticles increased as the sintering temperature was increased from 800 to 1200 °C. The dissolution rate of the BG nanoparticles was thus different between the cases, which enhanced the biomineralization and cell proliferation/differentiation to varying degrees. Benefiting from the homogeneous distribution and large specific surface area of the BG nanoparticles on the CNFs, the results demonstrated that CNF/BG-1000 had the strongest ability in promoting apatite deposition, proliferation and osteogenic differentiation of MC3T3-E1 pre-osteoblasts in comparison with CNF/BG sintered at 800 or 1200 °C. The results demonstrate a flexible tool to regulate the physiochemical and biological properties of CNF/BG composites by controlling the sintering temperature, which could find promising applications in skeleton repairing.

The hybrids of bioactive glass-ceramic (BG) decorated carbon nanofibers (CNFs) have drawn wide interest as bone repairing materials. Herein, hybridized CNFs were produced from electrospinning the mixture solution of polyvinylpyrrolidone (PVP) and BG sol–gel precursors, followed by preoxidation and carbonization. Choosing 45S-type BG (mol%: 46.10% SiO2–41.48% CaO–12.42% P2O5) as the model, the interaction of BG precursors with PVP and the micro-structural evolution of CNF/BG composites were systematically evaluated in relation to aging times (1–7 days) of BG precursor solution. With aging time prolonging, BG precursors underwent morphological changes from small sol clusters with a loosely and randomly branched structure at 1 day, to a fully developed Si-network structure at 3 days, and finally to a dense Si-network at 7 days. On one hand, it showed continuous increase in network linking degree. On the other hand, the gel particles underwent the process of size increase and subsequently decrease. This directly influenced the miscibility between BG precursors and PVP in solution, and the surface morphology of CNF/BG composites. At short aging times, the sol–gel solution of BG precursors mixed uniformly with PVP and the resulting BG nanoparticles were less likely to migrate toward the fiber surface. With the aging time prolonging, the phase separation between BG precursors and PVP facilitated more BG nanoparticles to form on the fiber surface. Calcium ions were found to be able to interact with carbonyl groups in PVP, while phosphorus element would be lost gradually depending on aging time, which led the CaSiO3 formed in the final CNF/BG changing from a weak to strong crystal state along with longer aging time. By soaking in simulated body fluid, it was found that the CNF/BG composites prepared from BG precursor sol–gel solution with 7 day aging demonstrated the fastest apatite deposition, which was ascribed to those abundant BG nanoparticles on the fiber surface having exposed numerous nucleation sites for the apatite deposition. Promisingly, CNF/BG composites developed from electrospinning and carbonization of PVP/BG sol–gel mixtures were envisioned good choices for bone repairing.

•Different SiO2-PMMA nanospheres were prepared using Stober and ATRP methods.•SiO2-PMMA nanosphere composed nanofibers were directly fabricated by electrospinning.•One-dimensional necklace-like SiO2-PMMA nanofibers were successfully obtained.•The polymer-like characteristics of polymer-grafted inorganic particles was verified.The direct fabrication of hybrid nanofibres composed of poly(methyl methacrylate)-grafted SiO2 (SiO2-PMMA) nanospheres via electrospinning was investigated in detail. SiO2-PMMA nanospheres were successfully prepared, with the SiO2 nanospheres synthesized via the Stober method, followed by in situ surface-initiated atom transfer radical polymerization of methyl methacrylate (MMA). Electrospinning was carried out with N,N-dimethylformamide (DMF) as the solvent to disperse SiO2-PMMA nanospheres. The size of the SiO2 core, the molecular weight of the PMMA shell and the concentration of the SiO2-PMMA/DMF solution all had substantial effects on the morphology and structure of electrospun nanofibres composed of SiO2-PMMA nanospheres. When these determining factors were well-tailored, it was found that one-dimensional necklace-like nanofibres were obtained, with SiO2-PMMA nanospheres aligned one by one along the fibre. The successful fabrication of nanofibres by directly electrospinning the SiO2-PMMA/DMF solution verified that polymer-grafted particles possess polymer-like characteristics, which endowed them with the ability to be processed into desirable shapes and structures.Formation mechanism of electrospun SiO2-PMMA nanofibers under different conditions.

Bioactive glass (BG) decorated nanoporous composite carbon nanofibers (PCNF–BG) were prepared for the purpose of obtaining effective substrates for skeletal tissue regeneration. The preparation was conducted by electrospinning of polyacrylonitrile (PAN)–polymethylmethacrylate (PMMA) blends with the addition of sol–gel precursors of 58s-type (mol%: 58% SiO2–38% CaO–4% P2O5) BG, followed by high temperature thermal treatment. The removal of PMMA during the carbonization of PAN generated numerous slit-like nanoporous structures along CNFs, leading to a significant enhancement in the specific surface area, surface roughness and pore volume, which was confirmed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET) characterizations. PCNF–BG composites with different specific surface areas were biologically evaluated by experiments of biomineralization in simulated body fluid (SBF), in vitro MC3T3-E1 osteoblast proliferation and osteogenic differentiation. Compared to non-porous CNF/BG, the nanoporous structure distinctively enlarged the interfacial reaction area of the BG component with a medium environment and thus enhanced the bioactivity of CNFs by accelerating the dissolution of the BG component and providing abundant nucleation sites for hydroxyapatite depositions. The released ions displayed distinct promotion in proliferation and osteogenic differentiation of osteoblast cells, which promoted the osteocompatibility of carbon-based materials significantly.

We investigated the effect of structural factor and amide grafted multi-walled carbon nanotubes (MWNTs-NH2) on crushing characteristics of filament wound CFRP tube under quasi-static compression conditon. It was found that CFRP tubes sequentially showed the brittle fracturing mode, the local buckling fracturing mode and transverse shearing fracturing mode with increasing winding angle, respectively, with the characterizations by mechanical testing, SEM and optical microscopy. Moreover, crack propagation initiated by pre-crack and subsequent failure in the tube were strongly dependent on pre-crack angle due to deflection and penetration competition of crack evolution. The simulated compression failure behavior correlated well with the experimental results, revealing that the Chang-Chang failure criterion was effective in representing the quasistatic crushing characteristics of the tube. In addtion, the MWNTs-NH2 were sucessfully obtained by multistep functionization. The compressvie properties of the tubes were significantly improved by the addition of the MWNTs-NH2 due to their uniform dispersion and high interfacial chemical reactivity, whereas the as-received MWNTs and other functionalized MWNTs were not as effective.

Bioactive glass (BG) decorated nanoporous composite carbon nanofibers (PCNF–BG) were prepared for the purpose of obtaining effective substrates for skeletal tissue regeneration. The preparation was conducted by electrospinning of polyacrylonitrile (PAN)–polymethylmethacrylate (PMMA) blends with the addition of sol–gel precursors of 58s-type (mol%: 58% SiO2–38% CaO–4% P2O5) BG, followed by high temperature thermal treatment. The removal of PMMA during the carbonization of PAN generated numerous slit-like nanoporous structures along CNFs, leading to a significant enhancement in the specific surface area, surface roughness and pore volume, which was confirmed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET) characterizations. PCNF–BG composites with different specific surface areas were biologically evaluated by experiments of biomineralization in simulated body fluid (SBF), in vitro MC3T3-E1 osteoblast proliferation and osteogenic differentiation. Compared to non-porous CNF/BG, the nanoporous structure distinctively enlarged the interfacial reaction area of the BG component with a medium environment and thus enhanced the bioactivity of CNFs by accelerating the dissolution of the BG component and providing abundant nucleation sites for hydroxyapatite depositions. The released ions displayed distinct promotion in proliferation and osteogenic differentiation of osteoblast cells, which promoted the osteocompatibility of carbon-based materials significantly.