Increased thickness uniformity of large-area nanofibrous layers by electrodynamic spinning

This paper studies the causes of thickness inhomogeneities in continuously deposited large-area nanofibrous layers, introduces a new method of their rapid analysis and suggests technical measures to ensure greater thickness uniformity of produced nanofibrous layers. The thickness uniformity of nanofibrous layers over large surface areas and its testing have recently appeared as very important issues following the scale up of the production of nanofibrous layers from laboratory to industrial levels, i.e. from point-to-plate arrangement to roll-to-roll processing. The basic electrostatic spinning method produces layers with thickness distribution corresponding to the bivariate Gaussian distribution. However, increasing production and scaling-up processes often results in variations in the thickness of deposited nanofibrous layers even up to the order of tens of percent. But for most applications, inhomogeneities in the thickness are a critical and even limiting factor. Our results show that by using the method of electrodynamic spinning with moving electrodes, we were able to achieve 30% greater thickness uniformity within the observed area (100 x 26) cm2 than with the electrostatic method. Electrodynamic spinning can therefore be considered a very promising technology for the industrial production. We also demonstrated the digital image analysis as a new and efficient tool to optically determine the thickness uniformity of electrospun layers by analyzing the intensity of transmitted light through the layer on 26 x 22 cm2 sample area. This unique approach brings benefits of non-destructive, rapid and reproducible evaluation of the thickness uniformity of the nanofibrous layers over decimeter-square surface areas at the same time

Electrospinning of fibrous layers containing an antibacterial chlorhexidine/kaolinite composite

The aim of this study was to prepare self-supporting homogeneous nano/microfibrous layers with a content of the clay mineral kaolinite and kaolinite modified with the antibacterial agent chlorhexidine (CH). Fibers were made of hydrophobic polymers-polyurethane and polycaprolactone. Polymer suspensions for electrospinning contained 2, 5, and 8 wt % (relative to the total weight of the suspension) of kaolinite or CH/kaolinite and were electrospun using 4SPIN LAB. The morphology of prepared fibrous layers was characterized using scanning electron microscopy; energy-dispersive X-ray spectroscopy mapping and Raman spectroscopy were used to confirm the presence and distribution of kaolinite in the layers. Fiber diameters decreased after adding kaolinite or CH/kaolinite and ranged from 600 nm to 5 mu m. Antibacterial CH was found in kaolinite itself as well as separately in the fibers (result of imperfect bonding of CH onto the surface of kaolinite). The encapsulation efficiency of all samples exceeded 64%, and the highest efficiency was observed in samples with 2 wt % CH/kaolinite. Samples containing CH exhibited good antibacterial activity against Staphylococcus aureus, and the effectiveness of which was affected by the concentration of the antibacterial agent. The release of CH was very slow, and there was no initial burst release. Overall, no more than 5% of the CH was released over a course of 168 h. The Korsmeyer-Peppas model revealed that CH is released by a diffusion mechanism.Web of Science353038302

Výroba nanovláken a technologické možnosti laboratorního přístroje 4SPIN®

4SPIN® je stolní laboratorní zařízení, které bylo vyvinuto pro depozici nanomateriálů pro lékařské aplikace, ale také pro další oblasti, jako jsou nanotechnologie, optika, filtrace a tak dále. Zařízení integruje různé metody pro umožnění přípravy nanostrukturovaných materiálů podle výzkumných požadavků. Devět zásadně odlišných emitorů (většina z nich je použitelná v metodě zvané „electroblowing“) a šest různých kolektorů dovoluje provádět různé druhy experimentů. Toto umožňuje přípravu nanovlákenných materiálů s různými mikroskopickými a makroskopickými strukturami. Laboratorní přístroj 4SPIN® byl vyvinut ve firmě Contipro Biotech s.r.o. a sedm použitých principů bylo patentováno. Zařízení získalo bezpečnostní certifikát podle norem CE a bylo uvedeno na trh od ledna 2013

Polymer lead pencil graphite as electrode material: Voltammetric, XPS and Raman study

Mechanical pencil leads were studied as disposable, low-cost electrodes. Lateral surfaces of mechanical pencil leads branded as “polymer” show high electron transfer rates for hexaamineruthenium chloride, potassium ferricyanide, ascorbate, ferric chloride and dopamine electrochemical probes, and are significantly better electrode materials than either classic woodcase clay–graphite pencil compositions or non-polymer mechanical pencil leads. Best polymer leads outperform glassy carbon, basal and edge graphite and boron-doped diamond electrodes. In addition to electrochemical experiments, the studied pencil leads were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy and Raman spectroscopy. High content of sp3 hybridized carbon (up to 80%) with a low degree of surface oxidation and occurrence of silicon monoxide (SiO) on the surfaces of the polymer pencil leads were found using X-ray photoelectron spectroscopy. Low double layer capacitance values of similar magnitude as that found for boron-doped diamond electrodes are at the origin of favourably low background currents on the polymer pencil lead electrodes. SiO containing polymer pencil lead electrodes allow electrochemical analysis that is more sensitive than common carbon electrodes, as demonstrated by voltammetry of adenine and xanthine. © 2016 Elsevier B.V

The Effects of Electric Field Dynamics on the Quality of Large-Area Nanofibrous Layers

This paper presents technological modifications of an electrostatic spinning device, which significantly increase the thickness homogeneity (i.e., quality) of produced layers by creating auxiliary dynamic electric fields in the vicinity of the spinning and collector electrodes. A moving body was installed above the needleless spinning electrode, which destabilized the standing wave occurring on the free surface of the spinning solution. Furthermore, an endless belt design was used for the collector electrode instead of a roll-to-roll design, which made it possible to substantially increase the surface speed of the substrate and, therefore, the dynamics of the electric field at the place of collection of the fibers being spun. As a result, the coefficient of variation of the area weight of 912 samples cut out from the deposited nanofibrous layer, which was (1000 × 500) mm2 in size and had an average area weight of (17.2 ± 0.8) g/m2, was less than 4.5%. These results were obtained only when the dynamics of both the spinning and collector electrodes were increased at the same time. These modifications resulted in a significant increase in the quality of deposited nanofibrous layers up to the standard required for their use in pharmaceutical applications

Nanofibrous material from hyaluronan derivatives preserving fibrous structure in aqueous environment

Nanofibrous materials produced from natural polymers have wide range of potential uses in regenerative medicine. This paper focuses on preparation of nanofibrous layers produced from intentionally hydrophobized derivatives of hyaluronan, which is known for its ability to promote wound healing. This structural modification of hyaluronan expands the range of potential uses of this promising material, which is otherwise limited due to the hydrophilic nature of hyaluronic acid. The aim of this research was preparation of nanofibrous material that would retain its fibrous structure and dimensional stability even after getting into contact with an aqueous medium, which is impossible to achieve with layers composed solely of native hyaluronan. As a result, such material would be able to retain its breathability and good mechanical properties when both dry and wet. Furthermore, all prepared materials were proved non-toxic for cells. This self-supporting nanofibrous matrix can be used as a scaffold, or porous wound dressing. © 2021 Elsevier Lt

Antimicrobial nanofibrous mats with controllable drug release produced from hydrophobized hyaluronan

Due to their large active surface, high loading efficiency, and tunable dissolution profiles, nanofibrous mats are often cited as promising drug carriers or antimicrobial membranes. Hyaluronic acid has outstanding biocompatibility, but it is hydrophilic. Nanofibrous structures made from hyaluronan dissolve immediately, making them unsuitable for controlled drug release and longer applications. We aimed to prepare a hyaluronan-based antimicrobial nanofibrous material, which would retain its integrity in aqueous environments. Self-supporting nanofibrous mats containing octenidine dihydrochloride or triclosan were produced by electrospinning from hydrophobized hyaluronan modified with a symmetric lauric acid anhydride. The nanofibrous mats required no cross-linking to be stable in PBS for 7 days. The encapsulation efficiency of antiseptics was nearly 100%. Minimal release of octenidine was observed, while up to 30% of triclosan was gradually released in 72 h. The nanofibrous materials exhibited antimicrobial activity, the fibroblast viability was directly dependent on the antiseptic content and its release.Web of Science267art. no. 11822