Ultralight, Structurally Stable Electrospun Sponges with Tailored Hydrophilicity as a Novel Material Platform

Thoroughly Hydrophilized Electrospun Poly(L-Lactide)/ Poly(ε-Caprolactone) Sponges for Tissue Engineering Application

Biodegradable electrospun sponges are of interest for various applications including tissue engineering, drug release, dental therapy, plant protection, and plant fertilization. Biodegradable electrospun poly(l-lactide)/poly(ε-caprolactone) (PLLA/PCL) blend fiber-based sponge with hierarchical pore structure is inherently hydrophobic, which is disadvantageous for application in tissue engineering, fertilization, and drug delivery. Contact angles and model studies for staining with a hydrophilic dye for untreated, plasma-treated, and surfactant-treated PLLA/PCL sponges are reported. Thorough hydrophilization of PLLA/PCL sponges is found only with surfactant-treated sponges. The MTT assay on the leachates from the sponges does not indicate any cell incompatibility. Furthermore, the cell proliferation and penetration of the hydrophilized sponges are verified by in vitro cell culture studies using MG63 and human fibroblast cells.

Facile strategy to prepare polyimide nanofiber assembled aerogel for effective airborne particles filtration

Polyimide nanofiber (PINF) aerogel materials have received extensive attention as heat insulation, sensors and filtration media due to their excellent thermodynamic properties and unique porous structure. However, PINF must be difficult to disperse in organic solvents (dioxane or dimethyl sulfoxide) and dimensional instability has been regarded as issues that limits the preparation of PINF aerogels, especially in the water. So, it is of great significance to prepare polyimide aerogels with stable structure using water as a dispersant. In this work, the electrospun polyimide nanofiber precursor (polyamic acid (PAA) nanofiber (PAANF)) is uniformly dispersed in water, and triethylamine is added to terminated PAA oligomer as a binder. The resultant PINF aerogel has excellent mechanical properties with outstanding elasticity and a maximum compressive stress of 7.03 kpa at 50% strain. Furthermore, due to the extremely high porosity (98.4%) and hierarchical porous structure, the aerogel exhibits a high filtration efficiency (99.83%) for PM2.5, while the pressure drop is lower than that of the corresponding nanofiber membrane materials, which will facilitate its application in high temperature filtration and other fields.

3D PCL/Gelatin/Genipin Nanofiber Sponge as Scaffold for Regenerative Medicine

Recent advancements in tissue engineering and material science have radically improved in vitro culturing platforms to more accurately replicate human tissue. However, the transition to clinical relevance has been slow in part due to the lack of biologically compatible/relevant materials. In the present study, we marry the commonly used two-dimensional (2D) technique of electrospinning and a self-assembly process to construct easily reproducible, highly porous, three-dimensional (3D) nanofiber scaffolds for various tissue engineering applications. Specimens from biologically relevant polymers polycaprolactone (PCL) and gelatin were chemically cross-linked using the naturally occurring cross-linker genipin. Potential cytotoxic effects of the scaffolds were analyzed by culturing human dermal fibroblasts (HDF) up to 23 days. The 3D PCL/gelatin/genipin scaffolds produced here resemble the complex nanofibrous architecture found in naturally occurring extracellular matrix (ECM) and exhibit physiologically relevant mechanical properties as well as excellent cell cytocompatibility. Samples cross-linked with 0.5% genipin demonstrated the highest metabolic activity and proliferation rates for HDF. Scanning electron microscopy (SEM) images indicated excellent cell adhesion and the characteristic morphological features of fibroblasts in all tested samples. The three-dimensional (3D) PCL/gelatin/genipin scaffolds produced here show great potential for various 3D tissue-engineering applications such as ex vivo cell culturing platforms, wound healing, or tissue replacement.

Rapid In Situ Polymerization of Polyacrylonitrile/Graphene Oxide Nanocomposites as Precursors for High-Strength Carbon Nanofibers

Graphene oxide (GO) has been widely used as an additive of polyacrylonitrile (PAN)-based carbon nanofibers (CNFs) to optimize its crystal structure and improve the mechanical performances of nanofibers. However, the homogeneous dispersion of GO nanosheets among entangled PAN molecular chains is always challenging, and the poor dispersion of GO severely limits its positive effects on both the structure and performances of CNFs. Considering this issue, this paper provides for the first time an effective solution to achieve rapid and uniform introduction of GO in PAN-based nanofibers via in situ polymerization, and the optimization of the nanofiber structure by GO is systematically studied in three consecutive stages (polymerization, electrospinning, and carbonization) of the production process. During in situ polymerization, PAN is tightly attached on GO nanosheets to form PAN/GO nanocomposites, and this interaction is maintained throughout the spinning process. Not only the arrangement of PAN molecular chains but also the crystal size of the final turbostratic structure of CNFs is considerably improved by the interaction between PAN and GO. Besides, the direct proof that GO nanosheets promote the crystallization and orientation of the nanofiber matrix is presented. As a result, the tensile strength of CNFs is remarkably increased by 2.45 times with 0.5 wt % addition of GO. In summary, this paper provides a method for efficiently introducing nanoscale additives into PAN-based nanofibers and gives insights into the production of high-performance CNFs with the addition of GO.

Three-dimensional composite electrospun nanofibrous membrane by multi-jet electrospinning with sheath gas for high-efficiency antibiosis air filtration

Three-dimensional (3D) composite polyvinylidene fluoride (PVDF)/polyacrylonitrile (PAN) electrospun nanofibrous membranes combining both thick and thin nanofibers have been fabricated by the method of multi-jet electrospinning with sheath gas to realize high-efficiency air filtration under a low pressure drop. The thin PAN nanofibers form a dense membrane, with a strong capturing ability on the ultra-fine particles, while the thick PVDF nanofibers play a 3D supporting effect on the thin PAN nanofibers. In this case, the combination results in a fluffy membrane with higher porosity, which could achieve the airflow passing through the membrane without the air pressure drop. The effects of the composite manner of thick nanofibers and thin nanofibers are investigated, in order to optimize the air filtration performance of the 3D composite nanofibrous membrane. As a result, the maximum quality factor for air filtration could reach up to 0.398 Pa^-1. The particle-fiber interaction model was used to simulate the air filtration process as well, and the simulation results were fairly consistent with the experimental results, providing a guidance method for the optimization of composite nanofibrous membrane for high-efficiency air filtration. More interestingly, a cationic poly[2-(N,N-dimethyl amino) ethyl methacrylate] (PDMAEMA) was added in the PVDF solution to obtain a composite air filtration membrane with excellent antibiosis performance, which achieved the highest inhibition rate of approximately 90%. In short, this work provides an effective way to promote antibiosis air filtration performance by using an electrospun nanofibrous membrane, and might also effectively accelerate the biological protection application of current air filtration membranes.

Moisturizing effect of skin patches with hydrophobic and hydrophilic electrospun fibers for atopic dermatitis

Atopic dermatitis (eczema), one of the most common disease and also most difficult to treat, is seeking for novel development not only in medicine but also in bioengineering. Moisturization is the key in eczema treatment as dry skin triggers inflammation that damages the skin barrier. Thus, here we combine electrospun hydrophobic polystyrene (PS) and hydrophilic nylon 6 (PA6) with oils to create patches helping to moisturize atopic skin. The fibrous membranes manufactured using electrospinning: PS, PA6, composite PS - PA6 and sandwich system combining them were characterized by water vapor transmission rates (WVTR) and fluid uptake ability (FUA). To create the most effective moisturizing patches we use borage, black cumin seed and evening primrose oil and tested their spreading. We show a great potential of our designed patches, the oil release tests on a skin and their moisturizing effect were verified. Our results distinctly reveal that both fiber sizes and hydrophilicity/hydrophobicity of polymer influence oil spreading, release from membranes and WVTR measurements. Importantly, the direct skin test indicates the evident increase of hydration for both dry and normal skin after using the patches. The electrospun patches based on the hydrophobic and hydrophilic polymers have outstanding properties to be used as oil carriers for atopic dermatitis treatment.

Polyimide-Based Foams: Fabrication and Multifunctional Applications

Because of their unique three-dimensional cellular structure and intrinsic properties, polyimide foam materials have bright prospects for development in multiple functional equipment, which arouses extensive concern. In this Spotlight on Applications, several typical fabrication methods of polyimide foams and the related synthesis mechanism have been systematically described. The advantages and disadvantages of the preparation methods have been compared with each other. Representative functions and the corresponding mechanism models have been concluded, which involve thermal, mechanical, sensing, electromagnetic, environmental, and electrical fields. In the end, the severe tasks and challenges of polyimide foam materials have been summarized, and their promising future development is worth expecting.

Reaction-Spun Transparent Silica Aerogel Fibers

Aerogel fibers, the simultaneous embodiment of aerogel 3D network and fibrous geometry, have shown great advantages over natural and synthetic fibers in thermal insulation. However, as a fast gelation to ensure aerogel fiber spinning generally induces rapid local clustering of precursor particles (i.e., phase separation) and unavoidably results in nontransparency and nonuniformity in the gel state, a severe challenge remains in remedying the spinning to make transparent aerogel fibers come true. Herein, we report a reaction spinning toward highly porous silica aerogel fibers, where the Brownian motion (i.e., diffusion) of colloidal particles is hampered during spinning to allow the maintaining of the fiber shape, while a rapid gelation reaction is activated by concentrated ammonia to solidify the fiber. The aggregation degree of the primary particles can be precisely controlled by pH-dependent hydrolyzation, and thus, the final aerogel fiber can be either transparent or opaque, as dominated by Rayleigh or Mie scattering. The resulting transparent silica aerogel fibers with low density, high specific surface area, and flexibility can inherit advanced features including excellent thermal insulation, wide temperature stability, and optional hydrophobic functionalization and, thus, be suitable for wearable applications.