Superelastic and Ultralight Aerogel Assembled from Hemp Microfibers

Aerogels with both high elastic strain and fast shape recovery after compression have broad application potentials as thermal regulation, absorbents, and electrical devices. However, creating such aerogels from cellulosic materials requires complicated preparation processes. Herein, a simple strategy for scalable production of hemp microfibers using a top-down method is reported, which can further be assembled into aerogels with interconnected porous structures via ice-templating technique. With density as low as 2.1 mg cm⁻³, these aerogels demonstrate isotropic superelasticity, as exhibited by their fast shape restoration from over 80% compressive strain. Due to the high porosity (99.87%) and structural tortuosity, these aerogels show a low thermal conductivity of 0.0215 ± 0.0002 W m⁻¹ K⁻¹, suggesting their potential in thermal insulation application. Certain hydrophobic modification using silane derivative further endows these aerogels with reduced water affinity. Overall, the proposed strategy to prepare bio-based microfibers using scalable technology, as well as the assembled aerogels, provides new insights into the design and fabrication of multifunctional bio-based aerogels for value-added applications.     

Valorization of Gleditsia triacanthos Invasive Plant Cellulose Microfibers and Phenolic Compounds for Obtaining Multi-Functional Wound Dressings with Antimicrobial and Antioxidant Properties

Gleditsia triacanthos is an aggressive invasive species in Eastern Europe, producing a significant number of pods that could represent an inexhaustible resource of raw material for various applications. The aim of this study was to extract cellulose from the Gleditsia triacanthos pods, characterize it by spectrophotometric and UHPLC–DAD-ESI/MS analysis, and use it to fabricate a wound dressing that is multi-functionalized with phenolic compounds extracted from the leaves of the same species. The obtained cellulose microfibers (CM) were functionalized, lyophilized, and characterized by ATR-FTIR and SEM. The water absorption and retention capacity as well as the controlled release of phenolic compounds with antioxidant properties evaluated in temporal dynamics were also determined. The antimicrobial activity against reference and clinical multi-drug-resistant Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Acinetobacter baumannii, Enterobacter cloacae, Candida albicans, and Candida parapsilosis strains occurred immediately after the contact with the tested materials and was maintained for 24 h for all tested microbial strains. In conclusion, the multi-functionalized cellulose microfibers (MFCM) obtained from the reproductive organs of an invasive species can represent a promising alternative for the development of functional wound dressings with antioxidant and antimicrobial activity, as well as being a scalable example for designing cost-effective, circular bio-economy approaches to combat the accelerated spread of invasive species.     

热处理温度对M-Ba铁氧体微米纤维结构和磁性能的影响

以柠檬酸和金属盐为原料,采用有机凝胶先驱体转化法成功制备了直径为500～600nm的钡铁氧体(BaFe12O19)微米纤维。通过XRD、SEM和VSM等技术对所制备的目标纤维进行了表征。结果表明,经750℃焙烧2h后,可获得M-Ba铁氧体纯相。随着焙烧温度的升高,晶粒逐渐长大,经850℃焙烧2h后,纤维主要由比较规则的片状晶粒组成。钡铁氧体纤维的磁性能主要受晶粒尺寸和测试温度的影响。经950℃焙烧2h后,组成纤维的晶粒尺寸约为62nm,室温下测得的饱和磁化强度和矫顽力均取得最大值,分别约为67A.m2/kg和328kA/m。在液氮(77K)条件下,纤维的饱和磁化强度有显著提高,最大值约为87A.m2/kg,这主要是由于纳米晶的表面自旋有序程度提高造成的。     

Nano‐RuO2‐Decorated Holey Graphene Composite Fibers for Micro‐Supercapacitors with Ultrahigh Energy Density

Compactness and versatility of fiber‐based micro‐supercapacitors (FMSCs) make them promising for emerging wearable electronic devices as energy storage solutions. But, increasing the energy storage capacity of microscale fiber electrodes, while retaining their high power density, remains a significant challenge. Here, this issue is addressed by incorporating ultrahigh mass loading of ruthenium oxide (RuO₂) nanoparticles (up to 42.5 wt%) uniformly on nanocarbon‐based microfibers composed largely of holey reduced graphene oxide (HrGO) with a lower amount of single‐walled carbon nanotubes as nanospacers. This facile approach involes (1) space‐confined hydrothermal assembly of highly porous but 3D interconnected carbon structure, (2) impregnating wet carbon structures with aqueous Ru³⁺ ions, and (3) anchoring RuO₂ nanoparticles on HrGO surfaces. Solid‐state FMSCs assembled using those fibers demonstrate a specific volumetric capacitance of 199 F cm^?3 at 2 mV s^?1. Fabricated FMSCs also deliver an ultrahigh energy density of 27.3 mWh cm^?3, the highest among those reported for FMSCs to date. Furthermore, integrating 20 pieces of FMSCs with two commercial flexible solar cells as a self‐powering energy system, a light‐emitting diode panel can be lit up stably. The current work highlights the excellent potential of nano‐RuO₂‐decorated HrGO composite fibers for constructing micro‐supercapacitors with high energy density for wearable electronic devices.     

Conductive Polymer Hydrogel Microfibers from Multiflow Microfluidics

Conductive hydrogels are receiving increasing attention for their utility in electronic area applications requiring flexible conductors. Here, it is presented novel conductive hydrogel microfibers with alginate shells and poly (3, 4‐ethylenedioxythiophene): poly (4‐styrenesulfonate) (PEDOT: PSS) cores fabricated using a multiflow capillary microfluidic spinning approach. Based on multiflow microfluidics, alginate shells are formed immediately from the fast gelation reaction between sodium alginate (Na‐Alg) and sheath laminar calcium chloride flows, while PEDOT: PSS cores are solidified slowly in the hollow alginate hydrogel shell microreactors after their precursor solutions are injected in situ as the center fluids. The resultant PEDOT: PSS‐containing microfibers are with features of designed morphology and highly controllable package, because material compositions or the sizes of their shell hydrogels can be tailored by using different concentrations or flow rates of pregel solutions. Moreover, the practical values of these microfibers in stretch sensitivity and bending stability are explored based on various electrical characterizations of the compound materials. Thus, it is believed that these microfluidic spinning PEDOT: PSS conductive microfibers will find important utility in electronic applications requiring flexible electronic systems.     

Fabrication of micro‐meltblown filtration media using parallel plate die design

Meltblown fibers are typically produced using a die technology based on the slot concept, an extension of the sheet die technology with a series of holes substituting the center rectangular slot of the sheet die. While this prevalent technology has met with considerable success, an economical, facile design would be desirable. In this study a new parallel plate die concept to fabricate micro‐meltblown fibers that offers simplicity, ease of use, and low cost was examined. The new die concept had parallel plates forming channels for polymer melt to flow through with a set of air holes surrounding them. This die design produced meltblown fibrous media with fibers in the range of 3–10 μm with pore size between 20 and 60 microns. The underlying mechanisms leading to such large fiber size formation and its implication in air filtration performance has been discussed. While conventional meltblown die generates fibers of smaller diameter and webs with higher filtration efficiency than the parallel plate geometry, design modifications could enhance the parallel plate meltblown die performance and make it a viable alternative. These die adaptations that include reducing air flow resistance, increasing the number of air nozzles around the polymer nozzles, recessing the polymer spinnerets above the die face, and having inclined air channels to increase the drag force on the fibers has been discussed. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42998.     

Multiple Bio-Actives Loaded Gellan Gum Microfibers from Microfluidics for Wound Healing

Wound healing, known as a fundamental healthcare issue worldwide, has been attracting great attention from researchers. Here, novel bioactive gellan gum microfibers loaded with antibacterial peptides (ABPs) and vascular endothelial growth factor (VEGF) are proposed for wound healing by using microfluidic spinning. Benefitting from the high controllability of microfluidics, bioactive microfibers with uniform morphologies are obtained. The loaded ABPs are demonstrated to effectively act on bacteria at the wound site, reducing the risk of bacterial infection. Besides, sustained release of VEGF from microfibers helps to accelerate angiogenesis and further promote wound healing. The practical value of woven bioactive microfibers is demonstrated via animal experiments, where the wound healing process is greatly facilitated because of the excellent circulation of air and nutritious substances. Featured with the above properties, it is believed that the novel bioactive gellan gum microfibers would have a remarkable effect in the field of biomedical application, especially in promoting wound healing.     

Bioinspired Robust Helical-Groove Spindle-Knot Microfibers for Large-Scale Water Collection

Helical structure is ubiquitous in nature with high-order configuration, specific paths, large superficial areas, providing an approach to bioinspired wettability control. Owing to its special hydrophilic rough surfaces and periodic knot and joint structure, natural spider silk can catch tiny droplets in fog and transport them directionally, sparking scientific interest in bioinspired knotted microfibers to address the risk of water scarcity. To further enhance the water collection ability, a bioinspired helical-groove-modified spindle-knot (HSK) microfiber is continuously fabricated in this work by a simple coating method combined with crack regulation. The formation and morphology can be precisely manipulated by adjusting the drawing velocity and concentration of the coating solution. Compared with smooth spindle-knot microfibers, HSK exhibits greater performances of wetting speed, droplets growth rate, and hanging ability, which can be attributed to the unique helical paths that bring capillary force difference and offer extra three-phase contact line lengths for water collection behavior. The maximum droplet volume is almost 2114 times that of the microfiber knots, which is the highest compared with previous reports. Moreover, HSK microfibers are endowed with repairable wettability, long-term durability, excellent mechanical properties, and flexibility, showing great potential in the realm of applications for large-scale water collection.     

Flexible Asymmetric Encapsulation for Dehydration‐Responsive Hybrid Microfibers

A new class of smart alginate microfibers with asymmetric oil encapsulates is introduced. These fibers are produced by injecting an aqueous alginate solution into an outer aqueous calcium chloride solution to form alginate fibers, which are asymmetrically loaded with oil entities through eccentrically aligned inner capillaries. The fiber morphology and its degree of asymmetry can be tuned via altering the size, location, and frequency of the oil encapsulates. These asymmetric fibers reveal significant potential for applications where conventional symmetric fibers fail to perform. It is shown how asymmetric oil‐encapsulated fibers can become dehydration‐sensitive, and trigger the release of encapsulates if their hydration level drops below a critical value. It is also shown how the triggered response could be switched off on demand by stabilizing the oil encapsulates. The capability of asymmetric fibers to carry and release multiple cargos in parallel is demonstrated. The fibers loaded with equal‐sized spheres are more asymmetric than those containing unequal drops, have a higher tensile strength, and show better potential for a triggered response.