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Nature is an amazing source of inspiration for the design of thermal insulation strategies, which are key for saving energy. In nature, thermal insulation structures, such as penguin feather and polar bear hair, are well developed; enabling the animals' survival in frigid waters. The detailed microscopy investigations conducted in this study, allowed us to perform microstructural analysis of these thermally insulating materials, including statistical measurements of keratin fiber and pore dimensions directly from high resolution Scanning Electron Microscope (SEM) images. The microscopy study revealed many similarities in both materials, and showed the importance of their hierarchically-organized porous structure. Finally, we propose the schematic configuration of a thermally-insulating structure, based on the penguin feather and polar bear hair. These optimized thermal-insulator systems indicate the road maps for future development, and new approaches in the design of material properties. We present the first detailed comparison of microstructures of penguin feather and polar bear hair for designing optimum thermal insulation properties. This unique study involves the measurement of the sizes of pores and fibers of these two keratin-based materials, including the investigation of their 3D arrangements. We revealed porosity interconnection, especially in polar bear hair, which is one of the key designs exhibited by thermal insulation materials. [ABSTRACT FROM AUTHOR]

Abstract Triboelectric generators rely on contact-generated surface charge transfer between materials with different electron affinities to convert mechanical energy into useful electricity. The ability to modify the surface chemistry of polymeric materials can therefore lead to significant enhancement of the triboelectric performance. Poly(methyl methacrylate) (PMMA) is a biocompatible polymer commonly used in medical applications, but its central position on the triboelectric series, which empirically ranks materials according to their electron-donating or electron accepting tendencies, renders it unsuitable for application in triboelectric generators. Here, we show that the surface potential of PMMA fibers produced by electrospinning can be tailored through the polarity of the voltage used during the fabrication process, thereby improving its triboelectric performance, as compared to typically spin-coated PMMA films. The change in surface chemistry of the electrospun PMMA fibers is verified using X-ray photoelectron spectroscopy, and this is directly correlated to the changes in surface potential observed by Kelvin probe force microscopy. We demonstrate the enhancement of triboelectric energy harvesting capability of the electrospun PMMA fibers, suggesting that this surface potential modification approach can be more widely applied to other materials as well, for improved triboelectric performance. Graphical abstract fx1 Highlights • Surface chemistry of electrospun PMMA fibers can be tailored via the polarity of the applied voltage, as verified using XPS. • The resulting surface potential of the PMMA fibers is studied using KPFM, and compared with a spin-coated PMMA film. • Enhanced triboelectric performance is achieved in electrospun PMMA fibers, due to their modified surface charge properties. [ABSTRACT FROM AUTHOR]

Electrospinning is an increasingly common technique used to produce fibers with a range of diameters. These electrospun fibers are used extensively in applications that exploit the material’s high surface area to volume ratio, thus requiring detailed knowledge of the surface properties of the fibers. The surface free energy of individual free standing electrospun styrene-butadiene rubber (SBR) fibers was determined here from the time-dependent break-up of long fibers driven initially by Rayleigh-Plateau/Weber instabilities. Individual free standing electrospun rubber fibers were observed to change from a cylindrical fibrous geometry to semi-spherical droplets during a time period of several days when above the glass transition temperature of the polymer. A wave-like transition from fiber to droplet was attributed to a surface tension driven break-up process occurring over a time strongly influenced by the rubber's viscosity. The surface free energy for an electrospun rubber fiber was found using a Weber approach for the free standing fibers and Diez et al theory for dynamic fluid instability of fluid ridges. Both methods lead to similar values of fiber surface free energy and were confirmed from bulk measurements exploiting Owens-Wend theory. The approach presented here is powerful as the surface free energy, indicative of the physical and chemical behavior of the fiber surface, can be determined for any fiber diameter provided the geometric break-up of the fiber is observed. [ABSTRACT FROM AUTHOR]

The interaction between resident cells and electrospun nanofibers is critical in determining resultant osteoblast proliferation and activity in orthopedic tissue scaffolds. The use of techniques to evaluate cell–nanofiber interactions is critical in understanding scaffold function, with visualization promising unparalleled access to spatial information on such interactions. 3D tomography exploiting focused ion beam (FIB)–scanning electron microscopy (SEM) was used to examine electrospun nanofiber scaffolds to understand the features responsible for (osteoblast-like MC3T3-E1 and UMR106) cell behavior and resultant scaffold function. 3D imaging of cell–nanofiber interactions within a range of electrospun poly( d , l -lactide-co-glycolide acid) (PLGA) nanofiber scaffold architectures indicated a coherent interface between osteoblasts and nanofiber surfaces, promoting osteoblast filopodia formation for successful cell growth. Coherent cell–nanofiber interfaces were demonstrated throughout a randomly organized and aligned nanofiber network. Gene expression of UMR106 cells grown on PLGA fibers did not deviate significantly from those grown on plastic, suggesting maintenance of phenotype. However, considerably lower expression of Ibsp and Alpl on PLGA fibers might indicate that these cells are still in the proliferative phase compared with a more differentiated cell on plastic. This work demonstrates the synergy between designing electrospun tissue scaffolds and providing comprehensive evaluation through high resolution imaging of resultant 3-dimensional cell growth within the scaffold. Statement of Significance Membranes made from electrospun nanofibers are potentially excellent for promoting bone growth for next-generation tissue scaffolds. The effectiveness of an electrospun membrane is shown here using high resolution 3D imaging to visualize the interaction between cells and the nanofibers within the membrane. Nanofibers that are aligned in one direction control cell growth at the surface of the membrane whereas random nanofibers cause cell growth into the membrane. Such observations are important and indicate that lateral cell growth at the membrane surface using aligned nanofibers could be used for rapid tissue repair whereas slower but more extensive tissue production is promoted by membranes containing random nanofibers. [ABSTRACT FROM AUTHOR]

Abstract: The elastic modulus of individual electrospun polyvinyl-alcohol (PVA) fibers was measured using atomic force microscopy (AFM) based bending tests. Results indicated an increase in the elastic modulus as the fiber diameter decreased. Consideration of electrospun fibers as a composite structure consisting of a shell region of aligned polymer chains surrounding a bulk-like isotropic core was analytically modeled and showed good agreement with the experimental data. Phase contrast AFM imaging of focused ion beam (FIB) prepared PVA fiber cross-sections provided a method of observing the shell–core structure directly and supported the model proposed. These findings indicate the potential for considerable polymer chain alignment for the production of high performance fibers using electrospinning methods. [Copyright &y& Elsevier]

Abstract: Single event electrospraying (SEE) is a method for on-demand deposition of picoliter volumes of liquids. The steady electrospraying of water in the cone–jet mode is difficult under normal operating conditions. This paper shows that SEE can be used for water to deposit very small volumes (1pL) and spray water in a stable pulsed cone–jet mode. The stability regime for SEE of deionized water with regard to pulse time and frequency of applied voltage was determined and was explained by the analysis of the characteristic times involved in SEE. With our unique set-up it is possible to use a pulsed cone–jet mode for a stable ejection on-demand. The pulse time for stable SEE of water is limited due to the time of formation of a space charge in between the nozzle and the counter electrode. Moreover, the maximum pulse frequency is limited to two times the natural oscillation frequency of the liquid. Additionally, the volume of liquid deposited per SEE can be calculated using a theoretical consideration of the electrohydrodynamic displacement of water inside the capillary. [ABSTRACT FROM AUTHOR]

The most common injuries of the human musculoskeletal system are related to soft tissue structures such as tendons or ligaments. To repair torn structures, surgical intervention and application of a biological or synthetic graft may be required. A typical procedure for the processing, storage, and distribution of soft tissue grafts involves at least two freezing/thawing (F/T) cycles. Even though repeated F/T cycles decrease the mechanical performance and change the structure of tendons, it is unclear whether there exists a maximum number of F/T cycles above which tendons should not be approved for use as a tissue allograft. To fill this research gap, we present an ex vivo study on the effects of repetitive F/T cycles on the biomechanical stability of bovine superficial digital flexor tendon tissue. Using mechanical testing supported with scanning electron microscopy imaging, we show that multiple F/T cycles affect the viscoelastic and structural properties of tissue by significantly reducing its tensile modulus after the 3rd or 4th F/T cycle (depending on the strain range), stress drop during relaxation after the 8th F/T cycle (regardless the strain values), mechanical hysteresis after the 10th F/T cycle, and by causing a significant decrease in collagen fibril diameter. Our results provide a deeper insight into understanding the mechanisms responsible for tissue damage during multiple F/T cycles, and thus, may be useful for the future optimization of tissue storage protocols. [Display omitted] • Multiple freezing significantly affects the viscoelastic properties of tendon tissue. • Repeated formation of ice crystals causes a decrease in collagen fibril diameters. • Material properties of tendon are dependent on considered level of its hierarchy. [ABSTRACT FROM AUTHOR]

• Root resorption often starts at cement – enamel junction (CEJ) in teeth. • SEM study allows for understanding the initiation and propagation of the resorption process in teeth. • The gap CEJ and the dentin exposure cause the focal inflammation, ideal conditions for resorption. The cement – enamel junction (CEJ) gains a growing interest in clinical dentistry, due to an increasing number of idiopathic tooth resorption leading to the inevitable loss of permanent dentition. Therefore, in this research study, we investigated healthy and under resorption teeth to verify junctions' morphology in relation to the resorption process, its initiation, and propagation. Using light and scanning electron microscopy we examined the three types of CEJ: 1) coronal cementum, 2) abutment) and 3) the gap between cementum and enamel. With energy-dispersive X-ray spectroscopy (EDX) we analyzed the Ca and P concentration along the CEJ border. The study indicated the strict correlation between the gap junction and tooth resorption, due to the dentine exposure to the oral environment. [ABSTRACT FROM AUTHOR]

Scaffolds designed for tissue engineering must meet multiple criteria, including mechanical performance matching particular tissue properties. One of the strategies to improve electrospun scaffolds strength is the incorporation of ceramic nanoparticles. In this work, the effect of the addition of hydroxyapatite (HA) and titanium dioxide (TiO 2) nanoparticles on tensile strength, elongation and toughness of poly (3-hydroxybuty-rate-co-3-hydroxyvalerate (PHBV) based fibers was tested. Samples morphology along with chemical composition and particles distribution were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR). Mechanical properties of PHBV-based electrospun scaffolds were correlated with the nanoparticles' distributions examined via microscopy analysis to understand the failure mechanism of composite fibers. We observed a significant improvement of mechanical properties of composites containing HA nanoparticles compared with solely PHBV fibers. Notably, 3 times higher tensile strength and strain at failure, followed by 16 times improved toughness, was correlated with homogenous distribution of HA nanoparticles with an average area of aggregates reaching 0.11 μm2. At the same time, two times larger TiO 2 aggregates were irregularly formed along PHBV fibers and caused deterioration of their mechanical properties. We showed the relevant strategy of particle distribution in fibers that are able to tailor mechanical properties by controlling the size and distribution of ceramic fillers in hybrid scaffolds. [ABSTRACT FROM AUTHOR]

An understanding of the reinforcement mechanism in composites is crucial for the development of novel materials where the application is limited by their mechanical properties. One of the methods used to obtain high performance composites is reinforcement with short fibers. Polymeric materials, such as electrospun polymethyl methacrylate (PMMA) fibers, have a very high tendency to fragment into regular short fibers after applying very low stress. This phenomenon was used to reinforce a polycarbonate (PC) core-shell structure (PMMA-PC) by using fragmented short PMMA fibers for reinforcement in the critical length limits. Mechanical testing revealed an increase of maximum stress and Young's modulus of almost 260% and 630%, respectively, for PMMA-PC fiber meshes. The observation of core-shell fibers after mechanical testing was confirmed by using confocal microscopy, showing very regular short fragments of PMMA fibers inside the PC shell. This work demonstrates a hierarchical approach that can be taken for reinforcement of a single fiber on the nanoscale and a composite on the macroscale. [Display omitted] [ABSTRACT FROM AUTHOR]

The development of wearable electronics has spurred an increased interest in self-powered systems and triboelectric nanogenerators (TENGs). To enhance the output performance of TENGs, researchers have dedicated significant efforts toward finding effective ways to increase triboelectric and mechanical performance. This study examined how conductive carbon black (CB) affects the mechanical and triboelectric properties of electrospun fibers made of polyurethane (PU), polystyrene (PS), and polycarbonate (PC). The addition of CB affected their mechanical properties, including increased tensile strength and decreased elongation at break. Importantly, triboelectric testing revealed that incorporating CB decreased the triboelectric output of PU and PS by over 90%, while it increased the output of PC by 260%. These findings indicate that CB's effects on triboelectric properties depend on the material and its content, underscoring the importance of selecting CB content carefully for optimal mechanical and triboelectric performance in electrospun fibers and composites. This research validates the development of advanced composite materials for electrostatic discharge protection and energy harvesting applications. [Display omitted] • Mechanical properties and triboelectric performance of polymer/carbon black composites. • Triboelectric properties of fiber mesh with carbon black show stable output for >15k cycles. • Carbon black in electrospun PC fibers led to 260% power increase. • Carbon black, cheap and sustainable filler for designing composites applied in energy harvesting. [ABSTRACT FROM AUTHOR]

Chitosan-based films modified with synthesized (propylene glycol monoacetate, propylene glycol esters of fatty acids, and epoxidized propylene glycol esters) and commercial eco-friendly plasticizers (epoxidized soybean oil and epoxidized palm oil) were prepared by a casting technique, with the aim to obtain environmentally friendly materials for packaging applications. To assess the applicability of alternative plasticizers, their properties were compared to the two most common plasticizers, i.e. glycerol and sorbitol. The chemical structure of newly synthesized plasticizers was verified by gas chromatography with mass detector, infrared spectroscopy and 1H NMR; and their acid, epoxy, iodine, and saponification values were determined. Plasticized chitosan-based films were characterized in terms of hydrophilic, barrier, thermal, mechanical properties, zeta potential and morphology, confirming their flexibility and homogeneity. The research confirmed that the alternative plasticizers introduced by us are more effective than commercially available ones, exhibiting lower hydrophilicity and superior mechanical properties compared to samples plasticized with traditional plasticizers. Moreover, these properties were found to be even better after ageing for 10 months. [Display omitted] • Plasticizers based on esters and epoxidized esters as an alternative to glycerol and sorbitol • Comparison of the properties of films containing commercial plasticizers with alternative plasticizers • Improved mechanical and hydrophilic properties after addition of alternative plasticizers • Extension of the ageing process of the film thanks to the use of alternative plasticizers [ABSTRACT FROM AUTHOR]

[Display omitted] • Successful modification of PI patches with sodium hypochlorite (NaOCl). • Chlorination of the membranes changes their hydrophobic character to hydrophilic. • Decreased zeta potential of the patches is beneficial for antimicrobial activity. • Chlorinated PI patches inhibit bacteria growth, both gram-positive and gram-negative. Atopic dermatitis (AD) is a common andcomplex disorder caused by many inherently intractable factors. One of the symptoms is an increased amount of Staphylococcus aureus on the skin surface. These bacteria trigger, accelerate, and exacerbate AD. In order to reduce inflammation, we designed antimicrobial patches, which inhibit bacterial growth. Using electrospinning, we produced polyimide (PI) nanofibers collected in the form of porous membranes. These PI membranes were modified with sodium hypochlorite (NaOCl). The active chlorine content was confirmed with scanning electron microscopy (SEM) with secondary electrons (SE) mode, backscattered electrons (BSE) mode, and energy-dispersive X-ray (EDX) spectroscopy, with Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Moreover, we evaluated the wettability and zeta potential of the patches. Finally, we performed an antimicrobial efficacy assay against the Gram-positive model organism S. aureus and the Gram-negative model, Escherichia coli. We observed that the chlorinated PI patches demonstrate effective bacterial killing, making them excellent material for antimicrobial skin patches applications. [ABSTRACT FROM AUTHOR]

The release of industrial wastewater into the ecosystem prompted our research on the development of an efficient and biodegradable material that can be used for wastewater treatment. We optimized preparation of porous material from poly(lactic acid) (PLA) by variation in solvents and drying methods (air-drying vs. supercritical CO 2 -drying). In addition, we optimized the method of TiO 2 nanoparticles immobilization (in situ vs. ex situ) onto porous PLA. The material properties and functionality were verified by SEM, water displacement, gas adsorption-desorption, Hg-intrusion porosimetry, dye degradation, FTIR, TGA/DSC, and water contact angle analysis. We showed that the morphology of PLA material could be controlled by variation in process parameters resulting in porosity from 43% to 73%. The prepared material sustained floatability for longer than 4 weeks and provided complete discoloration of dye C.I. Acid Orange 7 after 240 min of illumination. The high photocatalytic activity was preserved within three repeated cycles. [Display omitted] • Porous material was obtained by air-drying and scCO 2 -drying of PLA alcogels. • Selection of the solvent and drying method significantly affected PLA material morphology. • ScCO 2 -drying enabled the preparation of material with porosity up to 73%. • Floating photocatalyst was obtained by immobilization of TiO 2 nanoparticles onto porous PLA. • Immobilization of TiO 2 nanoparticles affected the surface hydrophobicity of PLA material. [ABSTRACT FROM AUTHOR]

Microcapsules of customized shapes offer significant advantages over spherical ones, including enhanced internalization by host cells, improved flow characteristics, and higher packing capacity. In our work, we propose a method for defined-shape polymer capsules fabrication inspired by a traditional "pelmeni" (dumplings) making process. The proposed method is based on soft lithography technique. Two different approaches were demonstrated resulting in polyelectrolyte multilayer and poly(lactic acid) (PLA) capsules both showing monodisperse size and shape distribution with about 7 μm long torpedo-like shape. The PLA capsules are described in terms of their morphology, loading of model cargo molecules, cell cytotoxicity and cell uptake. Carboxyfluorescein, FeCl 2 ground crystals and Fe 3 O 4 nanopowder were used as model cargoes for microcapsules. Capsules demonstrate core-shell structure, high loading capacity, hydrophilic molecules retention and internalization by cells without causing toxic effects. The loading efficiency of model cargo in PLA capsules was more than 80 wt%, resulting in about 40 pg of carboxyfluorescein inside each capsule. Proposed method allows unique advantages compared with alternative microencapsulation techniques, such as precise control over capsules' geometry, flexibility for the choice of active cargoes, regardless of their solubility and molecular weight and potential for triggered release mechanism. [Display omitted] • Microencapsulation approach for printed polymer capsules fabrication based on soft lithography method was proposed. • Polyelectrolyte and polylactic capsules were fabricated to demonstrate the concept. • Both types of microcapsules have defined torpedo shape and monodispersed size distribution and high loading capacity. • Wide range of possible cargoes indifferent to its solubility could be encapsulated. [ABSTRACT FROM AUTHOR]

[Display omitted] • Electrospinning composite membranes with PS and PA6 fibers. • Oil spreading depends on the fiber dimeter and pore size in membranes. • Water vapor transmission rate is reduced with hydrophilic PA6 nanofibers. • Electropsun PS – PA6 fibers with borage oil are applied as atopic skin patches. 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. [ABSTRACT FROM AUTHOR]

Surface potential of biomaterials is a key factor regulating cell responses, driving their adhesion and signaling in tissue regeneration. In this study we compared the surface and zeta potential of smooth and porous electrospun polycaprolactone (PCL) fibers, as well as PCL films, to evaluate their significance in bone regeneration. The ' surface potential of the fibers was controlled by applying positive and negative voltage polarities during the electrospinning. The surface properties of the different PCL fibers and films were measured using X-ray photoelectron spectroscopy (XPS) and Kelvin probe force microscopy (KPFM), and the zeta potential was measured using the electrokinetic technique. The effect of surface potential on the morphology of bone cells was examined using advanced microcopy, including 3D reconstruction based on a scanning electron microscope with a focused ion beam (FIB-SEM). Initial cell adhesion and collagen formation were studied using fluorescence microscopy and Sirius Red assay respectively, while calcium mineralization was confirmed with energy-dispersive x-ray (EDX) and Alzarin Red staining. These studies revealed that cell adhesion is driven by both the surface potential and morphology of PCL fibers. Furthermore, the ability to tune the surface potential of electrospun PCL scaffolds provides an essential electrostatic handle to enhance cell-material interaction and cellular activity, leading to controllable morphological changes. Unlabelled Image • Applied voltage polarity in electrospinning tailors surface chemistry and potential of PCL fibers. • Surface potential was analyzed by KPFM and compared with zeta potential in liquid. • Cell adhesion, collagen formation and mineralization are controlled with surface potential. • Surface potential on PCL fibers can enhance the bone regeneration process. [ABSTRACT FROM AUTHOR]