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.
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.
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.
A novel method of preparing skinned asymmetric membranes with two distinctive layers is described: a top layer composed of chemically cross‐linked polymer chains (dense layer) and a bottom layer of non‐cross‐linked polymer chains (porous substructure). The method consists of two simple steps that are compatible with industrial membrane fabrication facilities. Unlike conventional processes to prepare asymmetric membranes, with this approach it is possible to finely control the structure and functionalities of the final membrane. The thickness of the dense layer can be easily controlled over several orders of magnitude and targeted functional groups can be readily incorporated in it.
Polymerization shrinkage of dental composites remains a major concern. Free‐radically polymerizable cyclic monomers can be a conceivable alternative to methacrylates for the development of low‐shrinkage composites. In this study, the one‐step synthesis of the novel low viscosity difunctional vinylcyclopropanes 1 – 4 is described. Photopolymerization kinetics of these monomers are investigated by photo‐differential scanning calorimeter, using bis(4‐methoxybenzoyl)diethylgermane as photoinitiator. Real‐time near‐infrared photorheology measurements are performed to evaluate rheological behavior (i.e., time of gelation, polymerization‐induced shrinkage force) and chemical conversion (i.e., double bond conversion at the gel point, final double bond conversion) of the vinylcyclopropanes in situ. The potential of these monomers as reactive diluents in dental restorative materials is evaluated. Composites based on vinycyclopropanes 1 – 4 show good mechanical properties and exhibit significantly lower volumetric shrinkage and shrinkage stress than corresponding dimethacrylate‐based materials. The results indicate that such monomers are promising candidates for the replacement of commonly used low viscosity dimethacrylates such as triethylene glycol dimethacrylate in dental composites.
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.
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.
In this work, the authors report an effective one‐pot method to prepare poly(ε‐caprolactone) (PCL)‐incorporated bovine serum albumin (BSA)/calcium alginate/hydroxyapatite (HAp) nanocomposite (NC) scaffolds by templating oil‐in‐water high internal phase emulsion (HIPE), which includes alginate, BSA, and HAp in water phase and PCL in oil phase. The water phase of HIPEs is solidified to form hydrogels containing emulsion droplets via gelation of alginate induced by Ca2+ ions released from HAp. And the prepared hydrogels are freeze‐dried to obtain PCL‐incorporated porous scaffolds. The obtained scaffolds possess interconnected pore structures. Increasing PCL concentration clearly enhances the compressive property and BSA stability, decreases the swelling ratio of scaffolds, which assists in improving the scaffold stability. The anti‐inflammatory drug ibuprofen can be highly efficiently loaded into scaffolds and released in a sustained rate. Furthermore, mouse bone mesenchymal stem cells can successfully proliferate on the scaffolds, proving the biocompatibility of scaffolds. All results show that the PCL‐incorporated NC scaffolds possess promising potentials in tissue engineering application.
A fundamental study on the sterilization of thiol‐ene/acrylate polymers for biomedical applications is presented. These polymer networks belong to the emerging field of shape memory polymers and have the capability to undergo softening after insertion into the body. The impact of various sterilization methods, such as radiation, steam, and ethylene oxide on the thermomechanical properties of these stimuli responsive materials is investigated. Time and temperature dependent thermomechanical properties of sterilized and nonsterilized samples are determined by means of dynamic mechanical analysis in an aqueous environment to allow testing of polymers in phosphate buffered saline. The findings show that ethylene oxide sterilization is appropriate for thiol‐ene and thiol‐ene/acrylate based shape memory polymers. This method does not adversely affect thermomechanical and self‐softening properties and after sterilization, endotoxin levels remain below the thresholds recommended in the FDA Guidance.
A series of drawn melt‐crystallized linear polyethylenes (LPEs) with different molecular weight distributions (MWD = M w/M n) ranging from 2 to 25 are investigated with respect to the visible‐light transparency. The results indicate that the MWD of the LPEs significantly influences the visible‐light transparency of drawn melt‐crystallized LPEs. At a high MWD, drawn melt‐crystallized LPEs films are transparent and glass‐like, this in contrast to the LPEs with a low MWD. A mechanism behind the observed results is proposed based on differential scanning calorimetry (DSC) analysis, small‐angle X‐ray scattering, wide‐angle X‐ray scattering, and small‐angle light scattering experiments. A correlation between the molecular characteristics, especially the MWD, and the visible‐light transparency of the drawn melt‐crystallized LPEs is proposed.
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.
Proton exchange membranes for fuel cell applications are synthesized by surface‐initiated (SI) atom transfer radical polymerization (ATRP). Poly(vinylidene fluoride‐co‐chlorotrifluoroethylene) is electrospun into 50 µm thick mat, which is then employed as multifunctional initiator for copper‐mediated SI ATRP of 4‐styrene sulfonic acid sodium salt. Fine‐tuning of the ATRP conditions allows adjustment of the membrane's ion exchange capacity by varying the loading of the grafted ionomer. Structure and composition of the membranes are investigated by spectroscopic means and thermogravimetric analysis, respectively. The membrane morphology is probed by scanning electron microscopy. A membrane with proton conductivity as high as 100 mS cm−1 is obtained. Long‐term durability study in direct methanol fuel cells is conducted for over 1500 h demonstrating the viability of this novel facile approach.
Composites of ethylene‐vinyl acetate (EVA) reinforced with graphene platelets are fabricated. Morphological, thermal, mechanical, electrical properties as well as moisture absorption of the composites are characterized. Transmission electron microscopy shows a good dispersion of graphene platelets in the matrix. The unidirectional orientation of graphene platelets parallel to the surface of the composites is revealed by field emission scanning electron microscopy and is validated using the Halpin–Tsai model. Tensile strength and elongation of the composites are respectively improved by 109 and 83%, after the addition of 3 wt% graphene platelets. The incorporation of 5 wt% graphene platelets enhances the char residue of the composites from 0.544% for pure EVA to 6.63% for the composites. The electrical conductivity of the composite with 3 wt% graphene platelets is two orders of magnitude higher than that of pure EVA with 10−13 S cm–1 electrical conductivity.
Assembly of anisotropic nanoparticles on polymeric templates has attracted much attention recently because of the potential useful applications. In this work, 3D electrospun nanofiber membrane is used as template for the assembly of ex situ synthesized palladium nanocubes. The assembly process is achieved by simple immersion step, in which the electrostatic assembly of the nanocubes occurs. The dense nanocubes on the nanofibers as well as the fibrous nanostructure render the nanocomposite membrane excellent catalytic activity. Moreover, the catalytic membrane can be recycled for at least six times, which makes it possible for practical usage.
Epoxy coatings which can be healed via photothermal effect from focused sunlight are reported. The diamine of m‐xylylenediamine (MXDA) and monoamine of 4‐(heptadecafluorooctyl)aniline (HFOA) are reacted into the diglycidylether of bisphenol A (DGEBA) network. Via gradual replacement of MXDA with HFOA, the glass transition temperature and crosslinking density of the epoxy network are tuned to achieve the thermally induced healing based on chain diffusion and reentanglement. Aniline black (AB) with well absorptivity for sunlight is used subsequently as the organic photothermal compound, transferring the thermally induced healing into a sunlight responsive one. A common handheld magnifier, which can focus natural sunlight to the required power density (0.6–0.9 W cm−1), is used to successfully heal one cracked coating in outdoor circumstance. This study provides a potential approach to achieve the convenient, precise, and timely healing for outdoor epoxy coatings.
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.
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.
Additive manufacturing (AM) is still underutilized as an industrial process, but is quickly gaining momentum with the development of innovative techniques and materials for various applications. In particular, stereolithography (SLA) is now shifting from rapid prototyping to rapid manufacturing, but is facing challenges in parts performance and printing speed, among others. This review discusses the application of SLA for polymer nanocomposites fabrication to show the technology's potential in increasing the applicability of current SLA‐printed parts. Photopolymerization chemistry, nanocomposite preparation, and applications in various industries are also explained to provide a comprehensive picture of the current and future capabilities of the technique and materials involved.
Nanofiber production platforms commonly rely on volatile carrier solvents or high voltages. Production of nanofibers comprised of charged polymers or polymers requiring nonvolatile solvents thus typically requires customization of spinning setup and polymer dope. In severe cases, these challenges can hinder fiber formation entirely. Here, a versatile system is presented which addresses these challenges by employing centrifugal force to extrude polymer dope jet through an air gap, into a flowing precipitation bath. This voltage‐free approach ensures that nanofiber solidification occurs in liquid, minimizing surface tension instability that results in jet breakup and fiber defects. In addition, nanofibers of controlled size and morphology can be fabricated by tuning spinning parameters including air gap length, spinning speed, polymer concentration, and bath composition. To demonstrate the versatility of our platform, para‐aramid (e.g., Kevlar) and biopolymer (e.g., DNA, alginate) nanofibers are produced that cannot be readily produced using standard nanofiber production methods.
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.
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