Marek Pokorný

Hyaluronic acid (HA), a natural polymer produced through biotechnological processes, is initially synthesized with a high molecular weight, which is subsequently reduced for specific applications. This work aims to develop an experimental laboratory device that enables the controlled depolymerization of HA to achieve a targeted molecular weight. This is accomplished by applying precisely regulated temperature and pressure conditions that facilitate the cleavage of HA polymer chains as they pass through a narrow capillary. The process also allows for a controlled exposure time to elevate the temperature and pressure, with the rapid transition between standard and elevated conditions ensuring temporal stability. A key innovation of this approach is the selective application of an elevated temperature to a designated capillary section, adjustable from 0.5 to 5 m in 0.5 m increments, allowing for a broad range of reaction times. Numerical simulations verified temperature distribution along the capillary during heating and cooling. The device’s effectiveness is demonstrated by cleaving HA chains (initial Mw = 2150 kDa) dissolved in an aqueous solution at a 0.1 mg/mL concentration. Results from a factorial experiment that evaluated the extremes of three main variables show cleavage across a wide molecular weight range, reaching values as low as 8 kDa, with a variance of less than 5%. This study presents a viable device for the selective depolymerization of HA via physical parameters alone, eliminating the need for additional substances such as acids, hydroxides, or enzymes.

In the realm of surgical and dental applications, hyaluronic acid (HA) braided threads show significant therapeutic potential due to their incorporation of pharmaceutical active ingredients. This study primarily focuses on resolving the crucial challenge of devising a deposition method that can ensure both precision and uniformity in the content of the active ingredient Octenidine dihydrochloride (OCT) within each segment of the threads. Our objective in this study was to develop a continuous deposition method for OCT onto a braided thread composed of 24 hyaluronic acid-based fibers, aiming for a specific OCT content of 0.125 µg/mm, while maintaining a maximum allowable deviation of ±15% in OCT content. The motivation behind designing this novel method stemmed from the necessity of employing a volatile solvent for the active agent. Conventional wetting methods proved unsuitable due to fluctuations in the solution’s concentration during deposition, and alternative methods known to us demanded intricate technical implementations. The newly introduced method offers distinct advantages, including its online processing speed, scalability potential, and cost-efficiency of the active agent solution. Additionally, it minimizes the impact on the natural polymer thread, preserving energy by obviating the need for complete thread saturation. Our research and precise apparatus development resulted in achieving the desired thread properties, with an OCT content of (1.51 ± 0.09) µg per 12 mm thread piece. These findings not only validate the suitability of this innovative method for depositing active agents but also extend its potential applicability beyond dental care.

Traditional filtration media composed of fibers with sizes on the micrometer scale have difficulty filtering particles a little smaller than 300 nm. Even though nanofibrous materials are able to capture these particles and can have excellent filtration efficiency, their widespread use continues to be inhibited by several obstacles, particularly an excessive pressure drop and the inability to form self-supporting filtration membranes. We have prepared two types of composite materials, namely an ultra-thin nanofibrous layer made of polyurethane or nylon with various fiber diameters and pore areas. Scanning electron microscopy was used for their characterization. The nanofibrous layer was deposited directly onto a traditional melt-blown polypropylene filtration fabric with a very low area weight of 30 g/m², which facilitates handling and bypasses the need for the layer to be self-supporting. Moreover, a fine polyethylene mesh was added as a separate layer to prevent humidity from passing through the filtration material as well as to cover fabrics. The filtration efficiency and the pressure drop of the prepared materials were determined. The results showed that the incorporation of a nylon nanofibrous layer with smaller fiber diameters and pore areas leads to a significant increase in the filtration efficiency (92%) against the most penetrating particles, the critical size of which decreased to 50 nm, while the pressure drop was comparable to the pressure drop of a commercially available FFP2 respirator. The prepared filtration material could be used to manufacture respirators.

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.

The aim of the study was to develop an orthopedic implant coating in the form of vancomycin-loaded collagen/hydroxyapatite layers (COLHA+V) that combine the ability to prevent bone infection with the ability to promote enhanced osseointegration. The ability to prevent bone infection was investigated employing a rat model that simulated the clinically relevant implant-related introduction of bacterial contamination to the bone during a surgical procedure using a clinical isolate of Staphylococcus epidermidis. The ability to enhance osseointegration was investigated employing a model of a minipig with terminated growth. Six weeks following implantation, the infected rat femurs treated with the implants without vancomycin (COLHA+S. epidermidis) exhibited the obvious destruction of cortical bone as evinced via a cortical bone porosity of up to 20% greater than that of the infected rat femurs treated with the implants containing vancomycin (COLHA+V+S. epidermidis) (3%) and the non-infected rat femurs (COLHA+V) (2%). The alteration of the bone structure of the infected COLHA+S. epidermidis group was further demonstrated by a 3% decrease in the average Ca/P molar ratio of the bone mineral. Finally, the determination of the concentration of vancomycin released into the blood stream indicated a negligible systemic load. Six months following implantation in the pigs, the quantified ratio of new bone indicated an improvement in osseointegration, with a two-fold bone ingrowth on the COLHA (47%) and COLHA+V (52%) compared to the control implants without a COLHA layer (27%). Therefore, it can be concluded that COLHA+V layers are able to significantly prevent the destruction of bone structure related to bacterial infection with a minimal systemic load and, simultaneously, enhance the rate of osseointegration.

A composite nanofibrous layer containing collagen and hydroxyapatite was deposited on selected surface areas of titanium acetabular cups. The layer was deposited on the irregular surface of these 3D objects using a specially developed electrospinning system designed to ensure the stability of the spinning process and to produce a layer approximately 100 micrometers thick with an adequate thickness uniformity. It was verified that the layer had the intended nanostructured morphology throughout its entire thickness and that the prepared layer sufficiently adhered to the smooth surface of the model titanium implants even after all the post-deposition sterilization and stabilization treatments were performed. The resulting layers had an average thickness of (110 ± 30) micrometers and an average fiber diameter of (170 ± 49) nanometers. They were produced using a relatively simple and cost-effective technology and yet they were verifiably biocompatible and structurally stable. Collagen- and hydroxyapatite-based composite nanostructured surface modifications represent promising surface treatment options for metal implants.

This contribution focuses on the effects of electrospinning process on the homogeneity of nanofibrous tubular structures caused by different emitters. Six types of emitters were used for the production of nanofibrous tubes. For all, the electric potential and the electric field were simulated. The quality of the produced tubes was verified by scanning electron microscopy, contact measurement of thickness and by a new digital image processing method based on transillumination. The analysis of the spun samples proved that the quality and therefore the parameters of the prepared tubes are significantly influenced by the choice of an emitter and its configuration. The use of the five-needle and needleless emitters resulted in a tenfold increase in production, however, image analysis revealed major thickness inhomogeneities. The highest thickness homogeneity and a high repeatability of the spinning process were achieved by using a moving double-needle emitter. The results will find use especially in the research of small-diameter vascular replacements and other applications in the field of tissue engineering requiring highly uniform tubular grafts.

Nanofibrous materials are currently widely used in many different areas. One of the technologies commonly used for their production is electrospinning. The mass distribution in a produced nanofibrous layer is a crucial factor especially for filtration applications and active ingredients or drug release applications. Image analysis is an efficient non-destructive method of a mass distribution determination, which has already been used in the evaluation of textiles and melt-blown webs, but so far only a few publications have dealt with its use in the field of electrospun materials. To facilitate the process of image analysis of deposited nanofibers, we developed a new collector electrode, which makes it possible to determine the optical mass distribution profile of the produced layer. A series of experiments proved that the developed collector allows an easy evaluation of the appearance of nanofibrous layers as well as the effects of many associated factors such as emitter configuration on the resulting sample. The results showed how the properties of nanofibrous layers (such as deposition zone dimensions, location of these zones, mass distribution profiles produced by different spinning nozzles) can change during the electrospinning process. The advantages of the method described in the present article are that it allows a contactless and non-destructive determination of mass distribution, detection of macroscopic defects, and investigation of causes behind layer thickness inhomogeneities. All in all, the presented method is a useful research and development tool for the field of electrospinning.

In this work, a hybrid copolymer consisting of poly(3-hydroxybutyrate) grafted to hyaluronic acid (HA) was synthesised and characterised. Once formed, the P(3HB)-g-HA copolymer was soluble in water allowing a green electrospinning process. The diameters of nanofibres can be tailored by simply varying the M_w of polymer. The optimization of the process allowed to produce fibres of average diameter in the range of 100–150 nm and low polydispersity. The hydrophobic modification has not only increased the fibre diameter, but also the obtained layers were homogenous. At the nanoscale, the hybrid copolymer exhibited an unusual hairy topography. Moreover, the hardness and tensile properties of the hybrid were found to be superior compared to fibres made of unmodified HA. Particularly, this reinforcement was achieved at the longitudinal direction. Additionally, this work reports the use in the composition of a water-soluble copolymer containing photo cross-linkable moieties to produce insoluble materials post-electrospinning. The derivatives as well as their nanofibrous mats retain the biocompatibility of the natural polymers used for the fabrication.