Electrospray is a promising method for fabricating semipermeable polytetrafluoroeth-ylene (PTFE) membranes. These membranes exhibit high hydrophobicity and a large specific surface area. They can be used in various sectors, including the chemical and energy industries, aerospace, and microelectronics manufacturing. In this study, we investigated the effect of different spray solution compositions, heat treatment re-gimes, and exposure to various media on the physicochemical properties of these membranes. We used scanning electron microscopy to determine the optimal range of spray solution compositions for electrospraying. We found that quenching the mem-branes after electrospraying reduced shrinkage, increased tensile strength, and in-creased relative elongation. This was attributed to a decrease in the degree of crystal-linity in the quenched membranes. We also investigated the effects of various aggres-sive media, including concentrated acids, alkalis, organic solvents, and mineral oil, on the tensile strength and relative elongation of the membranes. No significant changes in tensile strength or relative elongation were observed after immersion for 48 h at 100 °C, indicating the high chemical stability and operational reliability of the elec-trosprayed PTFE membranes.

Owing to their high strength characteristics, chemical stability, and piezoelectric activity, vinylidene fluoride (VDF) copolymers have become promising materials for creating implants to replace bone tissue defects. However, a significant drawback of these materials is the biological inertness of their surface, which leads to unsatisfactory integration with the patient’s bone tissue. In this study, we propose a single-step approach for immobilizing hydroxyapatite (HAp) on the surface of porous implants made of vinylidene fluoride and tetrafluoroethylene copolymer (P(VDF-TeFE)). This method consists of treating the surface of the product with a mixture of solvents while simultaneously capturing HAp microparticles. Using scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS), it was shown that the proposed method preserves the morphology of model implants (pore diameter and printed line thickness) and allows HAp to cover up to 63 ± 14% of their surface, reaching concentrations of calcium and phosphorus up to 6.0 ± 1.3 and 3.6 ± 0.7 at. %, respectively, imparting superhydrophilic properties to them. Optical profilometry revealed that the surface roughness of samples increased by more than seven times as a result of HAp immobilization. X-ray diffraction analysis (XRD) confirmed that the piezoelectric phase of P(VDF-TeFE) is preserved after treatment, as are the compressive strength characteristics of the samples. Hydroxyapatite immobilization significantly improved the adhesion and osteogenic differentiation of multipotent stem cells cultured with P(VDF-TeFE)-based samples. Thus, the proposed method can significantly enhance the biological activity of implants based on the piezoelectric VDF copolymer.

The study examines how well a nanomembrane reactor functions in the base catalyst transesterification process to produce biodiesel with rapeseed oil as the feedstock. The fabrication of a porous electrospun nanomembrane was achieved through the utilization of poly(vinylidene fluoride) and a copolymer of vinylidene fluoride with tetrafluoroethylene. The polymeric membrane's structure allowed it to passively filter the crude biodiesel produced while retaining the glycerol and byproducts. With the maximum fatty acid methyl esters (FAME) content of about 99% and high reproducibility, the ideal transesterification conditions were found at 65 degrees C and a 4:1 methanol/oil weight ratio for 65 min. The FAME produced satisfied the key requirements of EN 14214. After four preparation cycles, there was no glycerol in the product stream, indicating that the nanomembrane could hold the glycerol in the reaction medium.

Being biocompatible and extremely rigid polymer, polyetherketoneketone (PEKK) emerged as a promising material for the development of bone implants, but its inert surface limits bone-implant integration. Herein, we report a single-step approach for the immobilization of hydroxyapatite (HAp) particles on the surface of additively fabricated porous PEKK implants based on the swelling of the implant surface with subsequent entrapment of the HAp particles. By means of the scanning electron microscopy, it was established that this approach effectively preserved the morphology (pore diameter and printed line width) of the original implants. With that, up to 35.0 ± 14.0 % of the sample surface was covered with HAp particles, leading to improved hydrophilicity (<1° water contact angle). From the energy-dispersive spectroscopy results, calcium and phosphorus content on the surface of the modified samples reached 17.4 ± 4.1 wt% and 8.0 ± 1.7 wt%, respectively. Compression test revealed no changes in the samples strength. From the in vitro experiment with bone marrow multipotent stem cells (MSC) HAp immobilization improved cell adhesion (from 121 ± 40 cells/mm² to 234 ± 8 cells/mm²) and induced their osteogenic differentiation. Thus, the proposed method may be used for the development of PEKK-based implants for bone tissue restoration.

Electrospun polytetrafluoroethylene (PTFE)-based artificial pericardium represents a promising material for use in cardiovascular surgery, particularly in cases requiring repeated cardiac interventions. A key factor determining its clinical applicability is its structure. This study presents a comparative evaluation of an artificial pericardium made from polytetrafluoroethylene (PTFE) via electrospinning against a commercial analogue from Gore® (PRECLUDE®). Two morphologies were investigated: fibrous (porosity ~59 ± 2%, fiber diameter 1.25 ± 0.25 µm) and spherical (porosity 34 ± 3%, particle size 3.90 ± 0.75 µm). The commercial sample exhibited a characteristic node-fibril structure with a porosity of 45 ± 3%. The Gore® material was the strongest sample (23.4 ± 2.3 MPa), whereas the electrospun samples demonstrated significantly higher relative elongation (170 ± 20% and 370 ± 10% for the spherical and fibrous samples, respectively, versus 70 ± 20% for the control). In vitro investigation on mice dermal fibroblast culture revealed no cytotoxicity and demonstrated good cell adhesion and proliferation on all investigated materials. Histological analysis after implantation into the rat greater omentum showed that the sample with a spherical structure elicited the least inflammatory response and formed the thinnest fibrous capsule compared to both the fibrous sample and the commercial Gore® material. The results indicate that the electrospinning enables the creation of biocompatible materials for cardiovascular surgery, with the spherical surface morphology being the most promising due to its ability to minimize the inflammatory response in vivo.

The healing potential of individual polymer implants for the reconstruction of extensive craniofacial defects after cancer resection is largely determined by the internal architecture of the implant. The architecture of an implant during polymer crystallization could affect the structure and shape of the implant at the micro and macro levels. In this study, the relationship between the internal architecture (triply periodic minimum surface structure (gyroid), cube, grid, and honeycomb) and shape changes of individual implants by 3D printing with a vinylidene fluoride-tetrafluoroethylene copolymer after crystallization is examined at a filling density of 70%. Using the method of differential scanning calorimetry, it is established that crystallization leads to the rearrangement of the crystalline structure of the implant into electrically active (ferroelectric) crystalline phases. Moreover, the type of internal architecture affects the change in the shape of the implant after crystallization. The results of the computed tomography show that structures with a triply periodic minimum surface (gyroid) provide the minimal deformation of the implant during crystallization, which makes such structures optimal for manufacturing implants for replacing bone defects in the zygomatic-orbital complex.

Electrospinning is a unique technology based on the fabrication of polymer fibers from the solution under an applied electric field. Electrospun membranes are applied in various fields, starting from filter technologies to tissue engineering. Polyalyletherketones (PAEK) is a family of synthetic bioinert polymers characterized by outstanding mechanical performance, high chemical stability, and biocompatibility. In the present study, the effect of electrospinning parameters (collector-to-tip distance, applied voltage, spinning solution flow rate and polymer concentration in the spinning solution) on the morphology of the fabricated polyetherketoneketone (PEKK) membranes as well as their crystal structure, chemical stability and biocompatibility was investigated. Based on 108 combinations of the electrospinning parameters, it was found that minimum concentration of PEKK in the spinning solution in 1,1,1,3,3,3-hexafluoropropan-2-ol (HFP) required for the fibers' formation is 4 wt %, while the applied voltage providing fibers without defects was found at 20 kV. It was demonstrated that the tested electrospinning regimes allow to fabricate the membranes with average fiber diameter from 0.76 f 0.29 to 1.46 f 0.60 mu m and porosity from 87 f 1 to 92 f 1 %. It was found that electrospinning process has no effect on the chemical structure of PEKK macromolecules. Electrospinning parameters had no effect on crystal structure of PEKK in the fabricated membranes, which was found to be amorphous. The fabricated membranes demonstrated high Young modulus (above 150 MPa) and elongation over 170 %, were stable in strong alkali and acid solutions and biocompatible towards mouse embryonic fibroblasts.

The development of tissue engineering structures (scaffolds) for the reconstruction of bone tissue defects is the relevant task of modern biomedical materials science. Compared to metal-based structures, polymer constructs provide numerous advantages, among them - better processibility and metallosis avoidance. Owing to its high mechanical performance and biocompatibility, polyetherketoneketone (PEKK) became a promising material for the development of such structures. Previously, a method for the immobilization of hydroxyapatite (HAp) on PEKK surface was proposed by our group for the enhancement of stem cell adhesion. In the present study, we propose a single-step method of HAp immobilization on the surface of 3D-printed porous PEKK implants. The proposed approach allowed to preserve the morphology (pore diameter, width of the printed lines) of the pristine implants. With that, up to 35.0+-14.0 sample surface were coated with HAp particles, which resulted in improved hydrophilicity (0 degrees water contact angle). The calcium and phosphorus content on the surface of the modified samples was up to 17.4+-4.1 and 8.0+-1.7 wt. compressive strength of the 3D-printed porous PEKK implants. HAp immobilization provided better adhesion of stem cells (from 121+-40 cells/mm2 to 234+-8 cells/mm2) and induce their osteogenic differentiation.

Herein, we report a single-step immobilization of hydroxyapatite (HAp) on the surface of poly(vinylidene fluoride) copolymer. This method utilizes the ability of fluoropolymer to undergo a limited swelling in acetone/ water mixture followed by an entrapment of HAp on its surface. We found that while acetone/water ratio does not affect the thickness of HAp-containing layer, an increase in acetone content results in higher amounts of calcium and phosphorus found in modified area. HAp immobilization not only improved the hydrophilicity of the poly(vinylidene fluoride) copolymer surface but also contributed to enhanced cell adhesion (0.8 +/- 0.4 % for the fluoropolymer surface vs. 86.9 +/- 9.1 % for the modified fluoropolymer surface) and viability (increased by up to 30 %). Overall, this method represents a potent strategy for the modification of fluoropolymers which allows for the fabrication of bioactive implants using standard laboratory equipment.

Electrospun poly(ε-caprolactone) (PCL)-based scaffolds are widely used in tissue engineering. However, low cell adhesion remains the key drawback of PCL scaffolds. It is well known that nitrogen-doped diamond-like carbon (N-DLC) coatings deposited on the surface of various implants are able to enhance their biocompatibility and functional properties. Herein, we report the utilization of the pulsed vacuum arc deposition (PVAD) technique for the fabrication of thin N-DLC coatings on the surface of electrospun PCL scaffolds. The effect of N-DLC coating deposition under various nitrogen pressures on the morphological, mechanical, physico-chemical, and biological properties of PCL scaffolds was investigated. It was established that an increase in nitrogen pressure in the range from 5 × 10−3 to 5 × 10−1 Pa results in up to a 10-fold increase in the nitrogen content and a 2-fold increase in the roughness of the PCL fiber surface. These factors provided the conditions for the enhanced adhesion and proliferation of human mesenchymal stem cells (MMSCs) on the surface of the modified PCL scaffolds. Importantly, the preservation of N-DLC coating properties determines the shelf life of a coated medical device. The elemental composition, tensile strength, and surface human MMSC adhesion were studied immediately after fabrication and after 6 months of storage under normal conditions. The enhanced MMSC adhesion was preserved after 6 months of storage of the modified PCL-based scaffolds under normal conditions.

Prevention of fibrosis during the oral mucosal wound regeneration is a pressing issue of today’s surgical dentistry. The study was aimed to perform morphological assessment of the effects of biocompatible piezoelectric membranes on fibrous tissue formation during regeneration of the oral mucosal wounds. We assessed cell–cell interactions of macrophages and fibroblasts, along with changes in the CD68 and TGFβ1 marker expression and their effects on the development of fibrosis under conditions of using biocompatible polymeric membranes with piezoelectric properties at various stages of the oral mucosal wound defect regeneration. Comparative morphological assessment of the oral mucosal structures was conducted in animals having intact mucosa (n = 15), having open wound defects (n = 15), and having wounds covered with biocompatible piezoelectric membranes (n = 15). Biomaterial was collected from the wound defect site on days 3, 7, and 12 of the experiment; collection of biomaterial from intact animals was performed on the same days. In the group, where biocompatible membranes were used, signs of proliferation phase at the defect site were detected as early as on day 3 of the study; the faster shift from macrophage infiltration to fibroblast infiltration, the decline in inflammatory response were detected on day 7; restoration of the numerical density of macrophages and fibroblasts to the intact values was detected on day 12. The expression of CD68 and TGFβ1, the prognostic markers of fibrosis, was lower in the group, where no membranes were used. Reduction of the dense fibrous connective tissue specific area was observed at the microscopic level, severe soft tissue deformation was reported at the macroscopic level. In the group with no wound covering, extensive cell infiltration and increased CD68 and TGFβ1 expression persisted throughout the experiment, which resulted in the fact that specific area of dense fibrous connective tissue was larger, than that of loose connective tissue, on day 12 of the study, as well as in the cicatricial soft tissue deformities.

Wound healing of the oral mucosa is an urgent problem in modern dental surgical practice. This research article presents and compares the findings of the investigations of the structural, physicochemical, and biological characteristics of two types of polymeric membranes used for the regeneration of oral mucosa. The membranes were prepared from poly(tetrafluoroethylene) (PTFE) and a copolymer of vinylidene fluoride and tetrafluoroethylene (VDF-TeFE) and analyzed via scanning electron microscopy, atomic force microscopy, X-ray diffraction analysis, and Fourier transform infrared spectroscopy. Investigation results obtained indicate that both types of membranes are composed of thin fibers: (0.57 ± 0.25) μm for PTFE membranes and (0.43 ± 0.14) μm for VDF-TeFE membranes. Moreover, the fibers of VDF-TeFE membranes exhibit distinct piezoelectric properties, which are confirmed by piezoresponse force microscopy and X-ray diffraction. Both types of membranes are hydrophobic: (139.7 ± 2.5)° for PTFE membranes and (133.5 ± 2.0)° for VDF-TeFE membranes. In vitro assays verify that both membrane types did not affect the growth and division of mice fibroblasts of the 3T3-L1 cell line, with a cell viability in the range of 88-101%. Finally, in vivo comparative experiments carried out using Wistar rats demonstrate that the piezoelectric VDF-TeFE membranes have a high ability to regenerate oral mucosa.

Fabrication of tissue engineering scaffolds with tailored physicochemical and biological characteristics is a relevant task in biomedical engineering. The present work was focused at the evaluation of the effect of fabrication approach (single-channel or multi-channel electrospinning) on the properties of the fabricated poly(lactic acid)(PLA)/poly(epsilon-caprolactone)(PCL) scaffolds with various polymer mass ratios (1/0, 2/1, 1/1, 1/2, and 0/1). The scaffolds with same morphology (regardless of electrospinning variant) were fabricated and characterized using SEM, water contact angle measurement, FTIR, XRD, tensile testing and in vitro experiment with multipotent mesenchymal stem cells. It was demonstrated, that multi-channel electrospinning prevents intermolecular interactions between the polymer components of the scaffold, preserving their crystal structure, what affects the mechanical characteristics of the scaffold (particularly, leads to 2-fold difference in elongation). Better adhesion of multipotent mesenchymal stem cells on the surface of the scaffolds fabricated using multichannel electrospinning was demonstrated.

This study deals with the impact of a microgel particle-laden drop of the water-agar solution onto nanofiber mats of different wettability at Weber numbers in the range of 14-502 and initial velocities in the range of 0.32-1.83m/s. We examined the effects of inertia and the competition between the wetting and antiwetting pressures within the liquid impalement on the hydrodynamic behavior of drops in the spreading and contraction phases. Hydrophilic mat representing a full water absorption coating is manufactured by electrospinning from a mixture of polycaprolactone and polyvinylpyrrolidone; hydrophobic-from polytetrafluoroethylene. The micro- and nanoscale characteristics of nanofiber mats are analyzed by scanning electron microscopy and atomic force microscopy, respectively. A physical model of liquid flow under an impacting microgel particle-laden drop along and inside the micro- and nanostructures of nanofiber mats is proposed. Empirical expressions for the prediction of drop impact hydrodynamics are derived. By introducing the impalement factor, which is physically close to the Euler number, they take into account the difference between wetting and anti-wetting pressures in addition to inertia. Microgel particle-laden drop deposition accounting for the effect of liquid impalement inside nanofiber materials with different wettability is expected to enhance the efficiency of bioprinting polymer layers in tissue engineering.

Burst release, typical for the drug-loaded electrospun poly(ε-caprolactone) (PCL) scaffolds is unfavorable in case of cytostatics due to the toxic levels reached during the initial implantation period. In the present short communication, we report an unexpected ability of the composite scaffolds made of PCL and water-soluble polyvinylpyrrolidone (PVP) to provide long-term release of widely used anti-cancer drug doxorubicin hydrochloride (DOX-HCl). That effect was observed for electrospun DOX-HCl-loaded composite scaffolds based on PCL and PVP with various mass ratios (100/0, 95/5, 90/10, 75/25 and 50/50). After the morphology and water contact angle studies, it was concluded that PVP content has no effect on the average fiber diameter, while PVP content higher 10 wt. % changes the hydrophobic character of the scaffolds surface (water contact angle of 123.9 ± 3.5°) to superhydrophilic (water contact angle of 0°). Despite the dramatic change in water wettability, by high performance liquid chromatography (HPLC), it was revealed that the PVP content in the scaffolds reduces the DOX-HCl release rate under short (first hours) and long-term (during 1 month) exposure to phosphate buffer saline (PBS). These results are in good agreement with in vitro studies, in which the viability of HeLa cervical cancer cells was higher after 24 h of culture with scaffolds with high PVP content.

We studied restoration of microvessels in the oral mucosa wound defects under a polymer piezoelectric membrane (group 2) and without it (group 1). The control group included animals with intact mucosa. On day 3, the expression of the vascular endothelial growth factor (VEGF) increased in all experimental groups, while the expression of CD34 increased only in group 2, which attested to intensive neoangiogenesis. On day 7, we observed a decrease in VEGF expression and an increase in CD34 expression that was more pronounced in group 2, which reflected the beginning of blood vessels maturation. More rapid formation and maturation of blood vessels in group 2 was confirmed by electron microscopy: on day 7, endothelial cells with mature organelles and signs of active transcapillary exchange were seen. On day 12, the immature blood vessels still predominated in group 1, while in group 2, the expression of angiogenesis markers decreased though remained above the control, which created prerequisites for the complete restoration of wound area vascularization in group 2. In group 1, the expression of VEGF and CD34 was significantly below the control, which attested to the development of poorly vascularized scar tissue.

The impact of microgel particles onto a wall represents an elementary process that determines the one-stage production of a biopolymer layer on a nanofiber scaffold in the framework of tissue bioengineering. The formation of a microgel layer is experimentally examined on a hydrophobic uniform surface and a nonwoven polymer membrane made of vinylidene fluoride-tetrafluoroethylene copolymer. In-air microfluidics methods, namely, an external vibration disturbance on the microflow of a cross-linkable biopolymer, make it possible to form the microstructures of "beads-on-thread" with a uniform distance between microgel particles of identical size (340-480 μm, depending on the sample). The successive particle-surface and particle-particle collisions are explored to develop the concept of technology for depositing microgel particles on surfaces for mobile one-stage production of microgel layers with a thickness of one and two particles, respectively. A physical model of successive particle-surface and particle-particle interactions is proposed. Empirical expressions are derived for predicting the diameters of maximum spreading (deformation) and the minimum heights of microgel particles on smooth and nanofiber surfaces, as well as in particle-particle collisions using a dimensionless criterion of gelation degree. The effect of microgel viscosity and fluidity on the maximum particle spreading during successive particle-surface and particle-particle collisions is elucidated. The consistent findings have made it possible to develop a predictive method for determining the growth dynamics of microgel layer area with a thickness of one or two particles on a nanofiber scaffold within a few seconds. The specific behavior of a microgel with a given gelation degree is simulated to produce a layer.

Wound defects of the oral mucosa are a common pathology the treatment of which often involves synthetic membranes. Development of varieties of such membranes is an ongoing process. This study aimed to register morphological features of the oral mucosa regeneration process in the presence of one of the varieties, the polymer piezoelectric membranes. The study involved 45 Wistar rats divided into 3 groups: 1) animals with an open wound defect; 2) animals with a wound defect covered with a copper-coated polymer membrane; 3) intact animals. The samples for morphometric study were collected on the 3rd, 7th and 12th days. On the 3rd day, rats of group 1 had the specific area of granulation tissue 1.4 times greater than that in group 2 (p = 0.033). In group 1 rats, endotheliocytes expressed more VEGF than in the animals of group 2. In group 2, the defect was ultimately completely covered with the epithelial layer, which was not the case in group 1. On the 7th day, the epithelium in rats of group 2 was twice as thick as the layer registered in group 1 (p = 0.019). Granulation tissue was replaced by loose fibrous connective tissue. In group 1, the specific area of inflammatory infiltration was greater than that of loose fibrous connective tissue, and the VEGF expression level was lower than in group 2. On the 12th day, the predominant tissue in group 2 was the loose fibrous connective tissue, the VEGF expression level equaled that of group 3, and peripheral nerves began to grow. In group 1, the specific area of dense fibrous tissue was 3.9 times greater than that in group 2 (p = 0.012), the epithelium had pathological changes and the VEGF expression was below control values. Thus, a polymer piezoelectric membrane had a positive effect on the post-wound restoration of the oral mucosa tissues.