Electrospun Nanofibrous Composite Membranes for Long-Term Release of Celecoxib for Achilles Tendon Reconstruction Following Injury

Embedding multiple pharmaceutical drugs into poly(lactic-co-glycolic acid) (PLGA) nanofibers is known to improve the regeneration of the Achilles tendon upon implantation after injury and rapidly restore post-surgery activity. In this study, an implantable material comprising celecoxib, collagen, bupivacaine, and PLGA (CCBP) is prepared by electrospinning. Its in vitro/vivo drug discharge behaviors are evaluated, and its efficacy in tendon regeneration is investigated in a rat model. The regeneration capacity of the wounded tendon is also compared with that of a doxycycline-collagen-bupivacaine-PLGA (DCBP) combination. The results show that, relative to the primary PLGA nanofibers, the pharmaceutical-embedded nanofibers have thinner fiber diameters and higher hydrophilicity. The drug-eluting nanofibers also offer a sustained release of celecoxib for at least 30 d in vitro and 28 d in vivo. Achilles tendons regenerated using the CCBP combination nanofibers demonstrate a significantly higher maximum load-to-failure than normal tendons and those repaired using the DCBP combination. Additionally, the expression of growth factors and composition of collagen I induced by the CCBP combination are superior to those induced by the DCBP combination. The results suggest that the CCBP combination is a promising scaffold for the repair of ruptured Achilles tendons.     

Electrospun composite nanofibers of poly (vinylidene fluoride‐trifluoroethylene)/polyaniline‐polystyrene sulfonic acid

Nanofibers of poly(vinylidene fluoride‐trifluoroethylene)/polyaniline‐polystyrene sulfonic acid (PVDF‐TrFE/PANi‐PSSA) were fabricated in air at room temperature using electrospinning, with the thinnest fiber having a diameter of ～ 6 nm. This is a cheap, fast, and reliable process for generating PVDF‐TrFE/PANi‐PSSA composite nanofibers. The presence of conducting PANi‐PSSA increased the charge density of the solution and assisted in the fabrication of PVDF‐TrFE nanofibers at low polymer concentrations in dimethylformamide without the beading effect. Ultraviolet and visible spectroscopy showed that PANi‐PSSA was well incorporated into the PVDF‐TrFE solution with no polymer segregation or degradation. A scanning electron microscope was used for morphological characterization of the fibers and a profilometer used to determine the fiber diameter. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation of Composite Electrospun Membranes Containing Strontium‐Substituted Bioactive Glasses for Bone Tissue Regeneration

Barrier membranes used for the treatment of bone tissue defects caused by periodontitis lack the ability to promote new bone tissue regeneration. However, the addition of an osteogenic component to membranes may enhance their regenerative potential. Here the manufacturing of composite membranes made of poly(caprolactone) and strontium‐substituted bioactive glass is described using the solution‐electrospinning technique, with particles located both inside and on the surface of the fibers. All membranes are characterized using scanning electron microscopy and energy dispersive X‐ray spectroscopy, and glass dissolution from within the fibers is investigated in water. In vitro material cytotoxicity is determined using a rat osteosarcoma cell line. Electrospun fibers exhibit porous surfaces and regions of increased diameter where the particles are accumulated. The glass dissolves after immersion in water, releasing dissolution products that are associated with increased pH. Further evidence suggests accelerated polymer degradation due to interactions between both components, which may provide the additional benefit of reducing the pH changes associated with glass dissolution. All compositions are biocompatible in vitro, with the exception of membranes with >50 μg of glass on their surface. In conclusion, these membranes show great potential for bone healing applications, including guided bone regeneration and scaffolds for musculoskeletal tissue engineering.

     

Electrospun Bead‐On‐String Hierarchical Fibers for Fog Harvesting Application

Quest for efficient fog harvesting methods has drawn immense attention in recent times. In this study, electrospinning is used to fabricate three different sets of membranes that are based on pristine poly(N‐isopropylacrylamide) (PNIPAM) fibers, pristine polyvinylidene fluoride (PVDF) fibers, and PNIPAM‐PVDF bead‐on‐string fibers. The wettability of these membranes is investigated as a function of temperature and the effect of their wettability on the fog collection efficiency is determined. Membranes based on pristine PNIPAM and pristine PVDF fibers are fabricated using conventional electrospinning and are shown to have a smooth surface morphology. On the other hand, PNIPAM‐PVDF bead‐on‐string fibers are fabricated using core–shell electrospinning. Water collection efficiency of the membranes is compared to investigate the influence of microstructures and wettability gradient on fog harvesting ability of the samples. Among the three samples, the bead‐on‐string hierarchical fibrous membrane demonstrates the highest fog harvesting rate of 1150 ± 28 mg cm⁻² h⁻¹ at 25 °C and 909 ± 31 mg cm⁻² h⁻¹ at 40 °C. Furthermore, the results demonstrate that the presence of microstructures on the nanofibers improve the fog harvesting efficiency of PNIPAM‐PVDF bead‐on‐string fibers.

     

Electrospun Sandwich‐Structure Composite Membranes for Wound Dressing Scaffolds with High Antioxidant and Antibacterial Activity

In this study, the sandwich‐structured composite (SSC) membranes with well‐antibacterial and antioxidant properties, which have the promising application as wound dressing, are successfully fabricated by combining an electrospinning process. The SSC membranes are composed of three layers, including the bottom polyvinylidene fluoride fibrous layer, the middle curcumin/polylactic acid (PLA) microsphere layer, and the top enrofloxacin/PLA fibrous layer, respectively. The obtained SSC membranes are characterized in terms of morphology, component, and mechanical property using scanning electronic microscope, X‐ray diffractometer, Fourier transform infrared spectroscopy, and universal electronic testing machine, respectively. Moreover, in vitro drug release, antioxidant activity, antimicrobial activity, and biocompatibility of the SSC membranes are also evaluated. The results showed that the obtained composite membranes indeed possess the sandwich structure, where the middle microsphere layer is located between two fibrous surface layers. It is found that the drug‐loaded SSC membranes show excellent antioxidant activity against ^?OH and DPPH free radicals and antibacterial activity against Staphylococcus aureus, Escherichia coli, Streptococcus pneumoniae, Pseudomonas aeruginosa, and Candida albicans. The combination of electrospinning and electrospraying opens up a new way to fabricate a variety of composite membranes with a sandwich structure, which have promising potential application as wound dressing scaffolds.     

Electrospun gelatin/nylon‐6 composite nanofibers for biomedical applications

We describe the preparation and characterization of gelatin‐containing nylon‐6 electrospun fibers and their potential use as a bioactive scaffold for tissue engineering. The physicochemical properties of gelatin/nylon‐6 composite nanofibers were analyzed using field emission scanning electron microscopy (FE‐SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, TGA and contact angle and tensile measurements. FE‐SEM and TEM images revealed that the nanofibers were well oriented and showed a good incorporation of gelatin. FTIR spectroscopy and TGA also revealed that there was good interaction between the two polymers at the molecular level. The adhesion, viability and proliferation properties of osteoblast cells on the gelatin/nylon‐6 composite nanofibers were analyzed by an in vitro cell compatibility test. Our results suggest that the incorporation of gelatin can increase the cell compatibility of nylon‐6 and therefore the composite mat obtained has great potential in hard tissue engineering. © 2012 Society of Chemical Industry     

Low‐cost upscaling compatibility of five different ITO‐free architectures for polymer solar cells

Five different indium‐tin‐oxide free (ITO‐free) polymer solar cell architectures provided by four participating research institutions that all presented a laboratory cell performance sufficient for use in mobile and information and communication technology (ICT) were evaluated based on photovoltaic performance and lifetime tests according to the ISOS protocols. The comparison of the different device architectures was performed using the same active material (P3HT: PCBM) and tested against an ITO‐based reference device. The active area was 1 cm² and rigid glass or flexible polyester substrates were employed. The performance results were corroborated by use of a round robin methodology between the four participating laboratories (DTU/DK, ECN/NL, Frauenhofer ISE/DE, and the Holst Centre/NL), while the lifetime testing experiments were carried out in only one location (DTU). Five different lifetime testing experiments were carried out for a minimum of 1000 h: (1) shelf life (according to ISOS‐D‐1); (2–3) stability under continuous 1 sun illumination (1000 Wm^?2, AM1.5G) at low (37 ± 3°C) and high (80 ± 5°C) temperatures (according to ISOS‐L‐1 and ISOS‐L‐2); (4) stability under continuous low‐light conditions at 0.1 sun (100 Wm^?2, AM1.5G, 32°C) (according to ISOS‐LL); (5) continuous illumination (670 Wm^?2, AM1.5G) at high temperature (65°C) and high humidity (50% RH) (according to ISOS‐L‐3). Finally, the upscaling compatibility of these device architectures based on the device photovoltaic behavior, stability and scalability were identified and we confirm that an architecture that presents a high score in only one aspect of the solar cell performance is not sufficient to justify an investment in upscaling. Many will require further technical development. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 944‐954, 2013     

Direct Printing of Thermal Management Device Using Low‐Cost Composite Ink

This work presents a new method for fabricating thermal devices, such as heat sinks, using a 3D printing technique and lightweight composite ink. The method focuses on formulating composite inks with desired properties and direct ink writing for manufacturing. The ink undergoes two phases: phase one uses low viscosity epoxy to provide viscoelastic properties and phase two provides the fillers consisting of carbon fiber and graphite nanoplatelets to provide high thermal conductivity and structural properties. By combining these functional materials, 3D structures with a high thermal conductivity (≈2 W m⁻¹ K⁻¹) are printed for thermal management applications with the storage modulus of 3000 MPa and a density only 1.24 g cm⁻³. The results show that by carefully tailoring functional properties of the ink, net‐shape multifunctional structures can be directly printed for thermal management device applications, such as heat sinks.     

Composite Proton‐Conducting Membranes for PEMFCs

Composite membranes are of interest for PEMFCs and DMFCs. This paper describes a basic study of the influence of silica on the proton conductivity: (i) added as a filler to poly(vinylidene fluoride‐hexafluoropropylene) and poly(benzimidazole)‐based membranes activated with H₃PO₄, or (ii) included in the matrix of class II hybrids based on tetraethoxysilane and poly(ethylene glycol) and activated with phosphotungstic acid (PWA). The addition of acidic silica as a filler determines proton conductivity increases up to one order of magnitude for filler amounts which strongly depend on the proton transport mechanism, and on the nature (free or partially free) of the activating acid. The increase of the silica content in the hybrid matrix induces a more complex behaviour which also depends on the amount of PWA.     

Elaboration of Ultra‐High Molecular Weight Polyethylene/Carbon Nanotubes Electrospun Composite Fibers

Micron‐sized fibers of UHMWPE reinforced with CNT were fabricated by the electrospinning process. Conditions for a metastable mutual solution of UHMWPE and CNTs were found at elevated temperature. These solutions were used for electrospining using a device having controlled temperature and gaseous environment around the electrospun liquid jet. The fabricated micron‐sized fibers exhibited the reinforcing CNTs as self‐organized nano‐ropes embedded within them. A post‐spinning drawing process enhanced the mechanical properties of the composite fibers to the level of 6.6 GPa strength and elongation at break of 6%. The CNT nano‐ropes form spontaneously in the liquid jet during electrospinning, and provide the reinforcement framework which is amenable for post‐drawing of the fibers for subsequent utilization as composite nanofibers. The experimental results exhibit the highest strength value reported to date for electrospun fibers.

     

Temperature Effects on Concentration Polarization Thickness in Thin‐Film Composite Reverse Osmosis Membranes

Continuous research and development of reverse osmosis (RO) technologies has led to the production of membranes that are very effective with high salt rejection abilities. As temperature is one of the factors that affects salt rejection capabilities in membranes, this paper investigates the effect of temperature on the thickness of the concentration polarization layer (CPL) deposited on thin‐film composite seawater RO membranes. Two types of membranes were studied: those with ex situ macromolecules and those with in situ macromolecules. FilmTec's reverse osmosis system analysis design software was used to predict the variation of salt rejection and permeate flow rate with temperature. The impact of these variations on the thickness of the CPL was analyzed for different polyamide concentrations in the membrane.     

Electrospun nanofiber‐coated separator membranes for lithium‐ion rechargeable batteries

Nanofiber‐coated composite membranes were prepared by electrospinning polyvinylidene fluoride‐co‐chlorotrifluoroethylene (PVDF‐co‐CTFE) and PVDF‐co‐CTFE/polyvinylidene fluoride‐co‐hexafluoropropylene (PVDF‐co‐HFP) onto six different Celgard® microporous battery separator membranes. Application of a PVDF‐based copolymer nanofiber coating onto the surface of the battery separator membrane provides a method for improving the electrolyte absorption of the separator and the separator‐electrode adhesion. Peel tests showed that both PVDF‐co‐CTFE and PVDF‐co‐CTFE/PVDF‐co‐HFP nanofiber coatings have comparable adhesion to the membrane substrates. Electrolyte uptake capacity was investigated by soaking the nanofiber‐coated membranes in a liquid electrolyte solution. PVDF‐co‐CTFE and PVDF‐co‐CTFE/PVDF‐co‐HFP nanofiber‐coated membranes exhibited higher electrolyte uptake capacities than uncoated membranes. It was also found that PVDF‐co‐CTFE nanofiber‐coated membranes have higher electrolyte uptakes than PVDF‐co‐CTFE/PVDF‐co‐HFP nanofiber‐coated membranes due to the smaller diameters of PVDF‐co‐CTFE nanofibers and higher polarity of PVDF‐co‐CTFE. The separator–electrode adhesion properties were also investigated. Results showed PVDF‐co‐CTFE and PVDF‐co‐CTFE/PVDF‐co‐HFP nanofiber coatings improved the adhesion of all six membrane substrates to the electrode. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Preparation of Chamottes as a Raw Material for Low‐Cost Ceramic Membranes

Low‐cost ceramic membranes are usually prepared from a mixture of natural raw materials and some organic porogen agent such as starch. The fact that porogen must be completely eliminated during firing, leaving an interconnected porous structure, impose large firing times, increasing the final price. A study about the synthesis of porous chamottes as an alternative to organic pore formers was conducted to reduce firing costs. Chamottes were obtained from mixtures of clay and starch. Different starches were used and the influence of the composition and processing variables were studied. The viability of the porous chamottes was demonstrated.     

Electrospun Poly(l‐Lactic Acid) Nanofibers for Nanogenerator and Diagnostic Sensor Applications

This paper presents for the first time that poly(l ‐lactic acid) (PLLA) nanofibers can show the piezoelectricity along the fiber direction (d₃₃) by using an electrospinning method. First, the electrospun fiber bundles are characterized by scanning electron microscope, X‐ray, and piezoelectric coefficient measurements. The data show that the supercritical CO₂ treatment can greatly enhance the piezoelectricity of electrospun PLLA fibers, which can be resulting from the increased crystallinity of the fibers. Later, it is found that the electrospun PLLA fiber can generate a current of 8 pA and a voltage of 20 mV by a simple push–release process. Further, a single PLLA fiber‐based blood pulse sensor is also fabricated and tested and shows around a 2 pA output for blood pulse. Due to easy fabrication and relatively simple structure, this device enables a broad range of promising future applications in the medical sensor area.

     

Thrombin‐Loaded Poly(butylene succinate)‐Based Electrospun Membranes for Rapid Hemostatic Application

Poly(butylene succinate) (PBS) and gelatin‐coated PBS electrospun membranes are evaluated for use as support materials to immobilize thrombin, an effective hemostat for topical injury, and three methods differing in whether and when gelatin is included are envisaged to prepare thrombin‐loaded PBS‐based electrospun membranes for use as rapid hemostatic materials. Both PBS and gelatin‐coated PBS membranes have high porosity, excellent wettability, rapid water penetration rate, and high water uptake, and thus are suitable support materials for thrombin. The thrombin immobilized onto gelatin‐coated PBS membrane has both high initial enzyme activity and high storage stability ascribed to the stabilizing effect of gelatin on thrombin activity. The hemostasis performance of thrombin‐immobilized membrane is evaluated in a rat liver model, showing shorter hemostasis time and less blood loss than clinically used gelatin sponge. The hemostasis mechanism is attributed to combined effects of thrombin and porous structure of electrospun membrane.     

Low‐viscosity and soluble phthalonitrile resin with improved thermostability for organic wave‐transparent composites

High processing viscosity and poor solubility limit the application of heterocyclic polymers for fabricating organic wave‐transparent composites for aerospace applications. In this paper, a novel resin, poly(phthalazinone ether bisphenol fluorene) encapped with phthalonitrile (PPEBF‐Ph), was synthesized and used as the matrix. Biphenol‐based phthalonitrile monomer BP‐Ph was also synthesized and blended with PPEBF‐Ph to further lower the processing viscosity. Solubility tests showed that the resin was soluble in dimethylformamide, N,N‐dimethyl acetamide, N‐methylpyrrolidone, dimethyl sulfoxide, chloroform, and other solvents. Differential scanning calorimetry and rheological studies revealed that the mixed resins exhibited low processing viscosity and a wide processing window below the gel temperature. Thermogravimetric analysis indicated that the cured resins were stable below 510–530 °C under nitrogen atmosphere after 6 h of curing (decreased by 40–60% compared with previous reports on phthalonitrile resin). In air, the char yields of the resins reached 20–30% when heated at 800 °C. The composites were reinforced by a quartz fiber cloth and exhibited a dielectric constant of 2.94–3.27 in an electromagnetic field with frequency ranging from 8 to 18 GHz. Retention of the bending modulus exceeded 70% at 400 °C according to dynamic mechanical analysis, indicating excellent mechanical stability was obtained. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45976.     

Thermally stable interpenetrating polymer networks for second‐order nonlinear optical materials

We report several kinds of interpenetrating polymer networks (IPNs) with nonlinear optical (NLO) properties. DMA spectra show that the two components of the IPNs have good compatibility with each other. The NLO materials have good optical transparency. The thermal stability of alignment was improved and the poled order remained very high. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 7–9, 1999     

Fast response single‐ion transport light‐emitting electrochemical cell based on PPV derivative

We present the electrical and optical characteristics of a single‐ion transport light‐emitting electrochemical cell (SLEC) based on poly(p‐phenylene vinylene) (PPV) derivative containing aryl‐substituted oxadiazole in the backbone (MEH‐OPPV). Ionized polyurethane–poly(ethylene glycol) (PUI) used as polymer electrolyte is introduced into the active layer of the SLEC. The turn‐on voltage of the SLEC is about 3 V according to its current density–voltage (J–V) characteristics. The response time of the SLEC is less than 10 ms, lower than that of normal LECs by two orders of magnitudes roughly. The reasons of the quick response for the SLEC are discussed in the article. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4253–4255, 2006     

Generic Molding Platform for Simple,Low‐Cost Fabrication of Polymeric Microneedles

Micromolding technology is widely used for the fabrication of polymer microneedles for transdermal and intradermal drug delivery applications. Geometric features of microneedles in molding are solely determined by geometry of the master mold template. Fabrication of master mold template usually involves costly and cumbersome technologies due to small feature sizes typical of microneedles. In this research, a novel molding platform is designed that is fabricated using low‐cost and simple techniques with flexibility of producing large number of microneedle geometries. The proposed molding platform eliminates need for developing multiple mold templates for fabrication of various geometries of polymer microneedles. Utility of this molding platform is demonstrated in polylactic acid‐based solid thermoplastic microneedles and polyacrylic acid‐based dissolvable microneedles with various aspect ratio settings. Various microneedles fabricated at heights differing with resolution of as low as 100 µm are successfully achieved using specified settings in the molding platform. The suitability of fabricated microneedles for drug delivery applications is evaluated by in vitro and in vivo testing.