The processes used to create synthetic spider silk greatly affect the properties of the produced fibers. This paper investigates the effect of process variations during artificial spinning on the thermal and mechanical properties of the produced silk. Property values are also compared to the ones of the natural dragline silk of the Nephila clavipes spider, and to unprocessed (as‐spun) synthetic silk. Structural characterization by scanning pyroelectric microscopy is employed to provide insight into the axial orientation of the crystalline regions of the fiber and is supported by X‐ray diffraction data. The results show that stretching and passage through liquid baths induce crystal formation and axial alignment in synthetic fibers, but with different structural organization than natural silks. Furthermore, an increase in thermal diffusivity and elastic modulus is observed with decreasing fiber diameter, trending toward properties of natural fiber. This effect seems to be related to silk fibers being subjected to a radial gradient during production.
Polymer‐based electrospun fibers have been intensively studied as antimicrobial membranes, drug carriers, and energetic materials. Inorganic fillers or small molecules have been routinely added into polymer matrices in order to enhance product functions. However, the electrospinning process is kinetically controlled and solvent rapidly evaporates due to the large surface‐to‐volume ratio of spinning liquid jet. When electrospinning a multicomponent system, complex phase behavior may occur and give rise to interesting internal structures of resulting products. Such kinetically driven phenomena deserve more attention for optimizing product performance. Here, electrospun poly(ε‐caprolactone)(PCL)/aminopropyl‐heptaisobutyl‐polyhedral oligomeric silsesquioxane (AMPOSS) fibers with AMPOSS content up to 30 wt% are studied as a model system to understand the impact of kinetically controlled phase separation on the fibers' internal structure, properties, and thermal stability. With sufficient AMPOSS loading, the hybrid fibers are found to have an AMPOSS‐shell/PCL‐core structure. The thermal stability of the as‐spun PCL/AMPOSS fibers is therefore greatly enhanced.
Carbon nanofiber/polycaprolactone (CNF/PCL) composite fibers are fabricated using a microfluidic approach. The fibers are made with different content levels of CNFs and flow rate ratios between the core and sheath fluids. The electrical conductivity and tensile properties of these fibers are then investigated. It is found that at a CNF concentration of 3 wt%, the electrical conductivity of the composite fiber significantly increases to 1.11 S m−1. The yield strength, Young's modulus, and ultimate strength of the 3 wt% CNF increase relative to the pure PCL by factors of 1.72, 2.88, and 1.23, respectively. Additionally, the results show that a microfluidic approach can be considered as an effective method to align CNFs along the fibers in the longitudinal direction.
Electrospinning of sulfur‐free softwood lignin (SFSL) in N,N‐dimethylformamide (DMF) is reported as is and with poly(ethylene oxide) (PEO). SFSL macromolecules behave as rigid spheres, instead of free draining macromolecules in DMF. Hence they are investigated as colloids. Colloidal SFSL generates uniform fibers only at the volume fraction of 0.63. It is due to the sufficiently high longest mean relaxation time at the volume fraction of 0.63. Colloidal SFSL below the volume fraction of 0.63 does not exhibit any measurable viscoelasticity and also does not generate any uniform fibers. Bead‐free fibers are generated at volume fractions below 0.63 only by adding PEO. PEO presence brings elasticity to colloidal SFSL and produces bead‐free fibers only above the entanglement concentration of PEO in DMF. The presence of SFSL macromolecules does not cause any interactions with PEO molecules, except it reduces the available of free volume for PEO chains in DMF.
The assembly of natural and synthetic polymers into fibrous nanomaterials has applications ranging from textiles, tissue engineering, photonics, and catalysis. However, rapid manufacturing of these materials is challenging, as the state of the art in nanofiber assembly remains limited by factors such as solution polarity, production rate, applied electric fields, or temperature. Here, the design and development of a rapid nanofiber manufacturing system termed pull spinning is described. Pull spinning is compact and portable, consisting of a high‐speed rotating bristle that dips into a polymer or protein reservoir and pulls a droplet from solution into a nanofiber. When multiple layers of nanofibers are collected, they form a nonwoven network whose composition, orientation, and function can be adapted to multiple applications. The capability of pull spinning to function as a rapid, point‐of‐use fiber manufacturing platform is demonstrated for both muscle tissue engineering and textile design.
Electrospinning (e‐spinning) has been extensively explored as a simple, versatile, and cost‐effective method in preparing ultrathin fibers from a wide variety of materials. Electrospun (e‐spun) ultrathin fibers are now widely used in tissue scaffold, wound dressing, energy harvesting and storage, environment engineering, catalyst, and textile. However, compared with conventional fiber industry, one major challenge associated with e‐spinning technology is its production rate. Over the last decade, compared with conventional needle e‐spinning, needleless e‐spinning has emerged as the most efficient strategy for large‐scale production of ultrathin fibers. For example, rolling cylinder and stationary wire as spinnerets have been commercialized successfully for significantly improving throughput of e‐spun fibers. The significant advancements in needleless e‐spinning approaches, including spinneret structures, productivity, and fiber quality are reviewed. In addition, some striking examples of innovative device designs toward higher throughput, as well as available industrial‐scale equipment and commercial applications in the market are highlighted.
For major advances in microfabricated drug delivery systems (DDS), fabrication methods with high throughput using biocompatible polymers are required. Once these DDS are fabricated, loading of drug poses a significant challenge. Here, hot punching is presented as an innovative method for drug loading in microfabricated DDS. The microfabricated DDS are microcontainers fabricated in photoresist SU‐8 and biopolymer poly‐l ‐lactic‐acid (PLLA). Furosemide (F) drug is embedded in poly‐ε‐caprolactone (PCL) polymer matrix. This F‐PCL drug polymer matrix is loaded in SU‐8 and PLLA microcontainers using hot punching with >99% yield. Thus, it is illustrated that hot punching allows high‐throughput, parallel loading of 3D polymer microcontainers with drug‐polymer matrices in a single process step.
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.
The N‐containing conjugated microporous polymers (CMPs) are synthesized by 2,5‐dibromopyrazine or its isomeric pyridazine monomer and 1,3,5‐triethynylbenzene via the Pd(0)/Cu(I)‐catalyzed Sonogashira–Hagihara cross‐coupling polycondensation. The resulting CMPs exhibit diverse porosity and morphology, which reveals macroscopically porous 3D networks for BQCMP‐1, agglomerated and amorphous structure for DQCMP‐1, arising from the variation of isomeric monomer. In addition, metal ions adsorption capacity of Zn(II), Cr(VI), Ni(II) have been investigated due to the good porosity of CMPs. Compared with Zn(II) and Cr(VI), the adsorption capacity of Ni(II) for BQCMP‐1 and DQCMP‐1 is maximal, which is 272 mg g?1 and 559 mg g?1. Our study may provide a useful guidance to manipulate CMPs by varying the constitution of isomeric monomer.
The ability to fabricate high‐quality colloidal photonic crystal (CPC) films in large areas is critical in many applications, ranging from flexible displays, security devices to optical enhancement. Herein, a large‐scaled CPC film with crack‐free structure and uniform optical performance is prepared via a hydrogen‐bond‐assisted method. The crack‐free CPC film is ascribed to the intermolecular hydrogen bonds between carboxyl ( COOH) moieties of poly(styrene‐methyl methacrylate acrylic acid) microspheres and isocyanate ( NCO ) moieties of polyurethane. Furthermore, the as‐prepared CPC film is applied as a Bragg reflection mirror for fluorescence enhancement. It is demonstrated that a fourfold enhancement of fluorescence signal is achieved when the stopband of CPCs overlaps with the emission wavelength of quantum dots. This simple method of preparing large‐area and crack‐free CPC film is promising for developing efficient optical devices.
Collection of clean water from humid air has attracted immense attention in recent years due to the lack of access to pure drinking water among large section of population in several parts of the world. Hence, there is a persistent demand for the fabrication of robust, scalable membranes for efficient harvesting of pure water, especially in fog‐laden areas. Herein, three different membranes based on neat nanofibers, nanofibers with microparticles, and nanofibers with hierarchical structures (nanopillars) are successfully fabricated using poly(vinylidene fluoride‐co‐hexafluoropropylene) and fluorinated polyhedral oligomeric silsesquioxane composite mixture. Neat nanofibers and nanofibers with microparticles are fabricated by employing direct electrospinning and electrospinning combined with electrospraying process, respectively. Hierarchical structured fibers are fabricated by growing nanopillars on the surface of the fibers using electrospinning combined with template‐wetting method. The wettability properties including water contact angle and hysteresis of these membranes are investigated. Due to the increased surface roughness and low surface energy, the hierarchical fibers exhibit higher contact angle (153°) and lower hysteresis (3°) compared to the neat nanofibers and nanofibers with microparticles. Furthermore, the results demonstrate that the presence of nanopillars on the surface of the nanofibers improves the membrane's water collection efficiency when exposed to humid air.
Conductive textiles with exceptional electrical properties have been prepared by coating the conjugated polymer, poly(3,4‐ethylenedioxyphiophene)‐polystyrenesulfonate(PEDOT‐PSS), on polyethylene terephthalate (PET) nonwoven fabrics. Phase segregation from covalent bond formation to surface silica particles generates PEDOT‐PSS coated textiles that hold potential for wearable electronics due to the breathability of the fabric, low toxicity, easy processing and lightweight with high current carrying capacity. The conductive textiles were demonstrated for applications such as electrical connections and resistive heating.
Development of artificial soft materials that have good mechanical performances and autonomous healing ability is a longstanding pursuit but remains challenging. This work reports a kind of highly flexible, tough, and self‐healable poly(acrylic acid)/Fe(III) (PAA/Fe(III)) hydrogels. The hydrogels are dually cross‐linked by triblock copolymer micelles and ionic interaction between Fe(III) and carboxyl groups. Due to the coexistence of these two cross‐linking points, the resulting PAA/Fe(III) hydrogels are tough and can be flexibly stretched, bent, knotted, and twisted. The hydrogels can withstand a deformation of 600% and an ultimate stress as high as 250 kPa. Moreover, the dynamic ionic interaction also endows the hydrogels self‐healing properties. By varying the ratio of Fe(III)/AA, a compromised healing efficiency of 73% and an ultimate stress of 200 kPa are obtained.
Photo‐reversible polyurethane (PU) coatings based on coumarin diol (CD) are obtained. Initially, pre‐polymers based on different amounts of coumarin (5, 15, and 25 mol%) and 1,6‐hexamethylene diisocyanate are prepared to obtain PUs with a large incorporation of CD and high molecular weight. The pre‐polymer is posterior reacted with poly(ε‐caprolactone) diol (PCL‐diol), either with molecular weight = 530 or 2000 g mol–1. The thermal stabilities of the PUs are studied using thermogravimetric analysis. Polymers with a higher content of CD present higher stability. The thermal transitions and the mechanical response are analyzed using differential scanning calorimetry and strain‐stress tests, respectively. Moreover, the photo‐reversibility of CD‐based PUs is followed by UV absorption. In general, photo‐dimerization induces better mechanical properties of the final PUs. Materials obtained with short PCL‐diol ( = 530 g mol–1) and the highest amount of CD present higher reversibility processes. Therefore, these polymers are promising for application as coating systems.
To endow nanofibers with the desirable antibacterial and mechanical properties, a facile strategy using Pickering emulsion (PE) electrospinning is proposed to prepare functional nanofibers with core/shell structure for the first time. The water‐in‐oil (W/O) Pickering emulsion stabilized by oleic acid (OA)‐coated magnetite iron oxide nanoparticles (OA‐MIONs) is comprised of aqueous vancomycin hydrochloride (Van) solution and poly(lactic acid) (PLA) solution. The core/shell structure of the electrospun Van/OA‐MIONs‐PLA nanofibers is confirmed by scanning electron microscopy and transmission electron microscopy observation. Sustained release of Van from the PE electrospun nanofiber membrane is achieved within the time of 600 h. Compared with the neat PLA electrospun nanofiber membrane, 57% increase of tensile strength and 36% elevation of elongation at break are achieved on PE electrospun nanofiber membrane. In addition, the PE electrospun nanofiber membrane demonstrates excellent antibacterial property stemming from the combinational antibacterial activities of OA‐MIONs and Van. The Van‐loaded PE electrospinning nanofibers with sustained antibacterial performance possess potential applications in tissue engineering and drug delivery.
Three kinds of rigid‐rod copolyimide (co‐PI) fibers are prepared by wet‐spinning of their precursor poly(amic acid)s, which are copolymerized from 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA), p‐phenylenediamine (PDA), and the third asymmetric heterocyclic diamines, including 2‐(4‐aminophenyl)‐5‐aminobenzoxazole (BOA), 2‐(4‐aminophenyl)‐5‐aminobenzimidazole (PABZ), and 2,5‐bis(4‐aminophenyl)‐pyrimidine (PRM), respectively. The asymmetry is increasing in the order PRM < BOA ≈ PABZ. The introduction of asymmetric heterocyclic units results in mesomorphic order structure and decreases the size of microvoid of PI fiber, which apparently improves the toughness of PI fiber and shows positive effects on mechanical properties. The tensile strength and initial modulus of co‐PI fibers are in the ranges of 2.6–3.2 GPa and 91.8–133.5 GPa, respectively. The lowest asymmetry leads to the highest lateral order, crystal orientation, and initial modulus of BPDA/PDA/PRM co‐PI. Moreover, the introduction of asymmetric heterocyclic units can effectively improve compressive properties. BPDA/PDA/PABZ co‐PI fiber shows the highest loop strength and recoil compressive strength due to hydrogen bonding interactions. The highest orientation leads to the lowest transverse strength of BPDA/PDA/PRM co‐PI fibers, reducing the recoil compressive strength.
Visible light curing of photopolymers has gained increasing interest in recent years. Dental materials are one of the important areas of application, where the bimolecular camphorquinone/amine initiator system is currently state of the art initiator. In this study, the authors describe the synthesis and photochemistry of tetrakis(2,4,6‐trimethylbenzoyl)silane, as cleavable Type I visible light photoinitiator. Besides excellent photobleaching behavior, this photoinitiator can well compete with up to now used long wavelength initiators.
A multi‐wavelength light drivable bilayer actuator is fabricated by depositing a thin layer of reduced graphene oxide (RGO) onto a flexible poly(dimethyl siloxane) (PDMS) substrate. The RGO/PDMS bilayer film shows fast and reversible bending/unbending motions upon exposure to UV light, visible light, or near‐infrared light (NIR). The photo‐thermal effect of the pump lights is studied by measuring and comparing the light induced temperature rises on RGO/PDMS film. The results demonstrate that the RGO absorbs and converts the light into heat. Thus the bilayer film undergoes thermal expansion under light irradiation. The calculated thermal expansion of the RGO thin layer is smaller than that of the PDMS layer, which results in the bilayer actuator bending towards the layer on the RGO side. Oscillational motion on the bilayer film is successfully achieved using continuous light irradiation on an offset sandwiched RGO/PDMS bilayer cantilever. Light induced motion on the RGO based film provides a new strategy for absorbing light energy and outputting photomechanical work.
An extruded sheet having unique molecular orientation is developed using a miscible blend of isotactic polypropylene (PP) and isotactic polybutene‐1 (PB). Blends containing a small amount of N ,N′‐dicyclohexyl‐2,6‐naphthalenedicarboxamide are extruded from a ribbon‐shaped die onto a chill roll at various temperatures. It is found that form‐I crystals of PB become oriented in the flow direction, whereas β‐form crystals of PP become oriented perpendicular to the flow direction. The molecular orientation is the most obvious for the blend containing 60 wt% of PB extruded at a chill roll temperature of 80 °C. The anisotropy in the tensile modulus of the obtained extruded sheet is reduced by its extraordinary molecular orientation.
Poly(ethylene glycol) diacrylate (PEG‐DA) hydrogels have been widely utilized to investigate cell–material interactions and as scaffolds for tissue engineering. Traditionally, PEG‐DA hydrogels are prepared via the UV‐cure of aqueous precursor solutions, but afford a limited range of pore size and interconnectivity that is essential for cellular proliferation and neotissue formation. To overcome these limitations, macroporous PEG‐DA hydrogels are prepared in this study using a combination of solvent‐induced phase separation (SIPS) and a fused salt template. PEG‐DA concentration in the organized fabrication solvent (20, 30, and 40 wt%) and average salt particle size (≈180, ≈270, and ≈460 μm) are varied and the resulting hydrated hydrogel morphology, swelling, mechanical properties, and degradation are characterized. These templated SIPS PEG‐DA hydrogels broaden PEG‐DA hydrogel properties and, in some cases, afford a series of compositions whose properties are decoupled.
下载免费PDF全文