Investigation of the Mechanical and Dynamic-Mechanical Properties of Electrospun Polyvinylpyrrolidone Membranes: A Design of Experiment Approach

Effect of Citric Acid on Swelling Resistance and Physicochemical Properties of Post-Crosslinked Electrospun Polyvinyl Alcohol Fibrous Membrane

A series of electrospun polyvinyl alcohol (PVA) fiber membranes were crosslinked with citric acid (CA) at concentrations of 10, 20, and 30 wt.% (designated as CA10, CA20, and CA30). The effects of CA on the chemical structure, mechanical strength, swelling resistance, and cytotoxicity of the crosslinked PVA fibrous membranes were investigated. Infrared spectroscopy indicated the enhanced esterification of carboxyl and hydroxyl groups between CA and PVA. The modulus and strength of the electrospun PVA membrane increased due to the crosslinking between CA and PVA. The crosslinking of the PVA fiber matrix with CA increased the PVA binding point, thereby increasing the swelling resistance and modulus; however, the concentration of CA used was limited. Results showed that the water absorption of the PVA membranes decreased from 6.58 ± 0.04 g/g for CA10 to 3.56 ± 3.33 g/g for CA20 and 2.85 ± 0.40 g/g for CA30 with increasing CA. The water absorption remained unchanged after the membrane was soaked for a period of time, so no significant difference was found in the water absorption capacity of the same group after immersion from 1 h to 3 d. The tensile strength increased from 20.52 MPa of CA10 to 22.09 MPa of CA20. With an increased amount of CA used for crosslinking, the tensile strength and modulus of CA30 decreased to 11.48 and 13.94 MPa, respectively. Our study also showed that CA was not toxic to L929 cell viability when used for fiber crosslinking at less than 20 wt.% PVA, meaning it may be a good candidate as a support layer for guided tissue engineering.

Influence of Electrospinning Setup Parameters on Properties of Polymer-Perovskite Nanofibers

Optimizing the properties of electrospun polymer-perovskite nanofibers is considered essential for improving the performance of flexible optoelectronic devices. Here, the influence of electrospinning setup parameters (i.e., electrical voltage, collector type (planar or rotary), rotation speed, as well as process time) on the properties (i.e., external structure, perovskite crystallinity, optical properties, thermal properties, the shrinkage ratio, mechanical properties, and long-term stability) of electrospun polyvinylpyrrolidone nanofibers modified with cesium lead iodide nanocrystals has been studied. The results have shown that the structure of nanofibers is related to the electrical voltage, collector rotation speed, and process duration. Perovskite crystallinity and light absorption have improved by increasing the electrical voltage or/and the process time. The polymer's glass transition temperature is affected by the embedded perovskite and the collector's rotation speed. The shrinkage ratio and mechanical properties of nanofibers have been controlled by the rotation speed and the electrical voltage. The shrinkage is caused by the stress created in the nanofibers during the electrospinning process. The best mechanical properties can be noticed with the rotary collector at a rotational speed of 500--750 rpm. Nanofibers have shown good long-term stability and high thermal stability. The long-term stability is inversely proportional to the value of the electrical voltage.

3D Polycaprolactone/Gelatin-Oriented Electrospun Scaffolds Promote Periodontal Regeneration

Periodontitis is a worldwide chronic inflammatory disease, where surgical treatment still shows an uncertain prognosis. To break through the dilemma of periodontal treatment, we fabricated a three-dimensional (3D) multilayered scaffold by stacking and fixing electrospun polycaprolactone/gelatin (PCL/Gel) fibrous membranes. The biomaterial displayed good hydrophilic and mechanical properties. Besides, we found human periodontal ligament stem cell (hPDLSC) adhesion and proliferation on it. The following scanning electron microscopy (SEM) and cytoskeleton staining results proved the guiding function of fibers to hPDLSCs. Then, we further analyzed periodontal regeneration-related proteins and mRNA expression between groups. In vivo results in a rat acute periodontal defect model confirmed that the topographic cues of materials could directly guide cellular orientation and might provide the prerequisite for further differentiation. In the aligned scaffold group, besides new bone regeneration, we also observed that angular concentrated fiber regeneration in the root surface of the defect is similar to the normal periodontal tissue. To sum up, we have constructed electrospun membrane-based 3D biological scaffolds, which provided a new treatment strategy for patients undergoing periodontal surgery.

Polymer-free cyclodextrin and natural polymer-cyclodextrin electrospun nanofibers: A comprehensive review on current applications and future perspectives

The present review discusses the use of cyclodextrins and their derivatives to prepare electrospun nanofibers with specific features. Cyclodextrins, owing to their unique capability to form inclusion complexes with hydrophobic and volatile molecules, can indeed facilitate the encapsulation of bioactive compounds in electrospun nanofibers allowing fast-dissolving products for food, biomedical, and pharmaceutical purposes, filtering materials for wastewater and air purification, as well as a variety of other technological applications. Additionally, cyclodextrins can improve the processability of naturally occurring biopolymers helping the fabrication of "green" materials with a strong industrial relevance. Hence, this review provides a comprehensive state-of-the-art of different cyclodextrins-based nanofibers including those made of pure cyclodextrins, of polycyclodextrins, and those made of natural biopolymer functionalized with cyclodextrins. To this end, the advantages and disadvantages of such approaches and their possible applications are investigated along with the current limitations in the exploitation of electrospinning at the industrial level.

Effect of sodium alginate molecular structure on electrospun membrane cell adhesion

Alginate-based electrospun nanofibers prepared via electrospinning technique represent a class of materials with promising applications in the biomedical and pharmaceutical industries. However, to date, the effect of alginate molecular mass and block composition on the biological response of such systems remains to some extent unclear. As such, in the present work, three alginates (i.e., M.pyr, L.hyp, A.nod) with different molecular features are employed to prepare nanofibers whose ability to promote cell adhesion is explored by using both skin and bone cell lines. Initially, a preliminary investigation of the raw materials is carried out via rheological and zeta-potential measurements to determine the different grade of polyelectrolyte behaviour of the alginate samples. Specifically, both the molecular mass and block composition are found to be important factors affecting the alginate response, with long chains and a predominance of guluronic moieties leading to a marked polyelectrolyte nature (i.e., lower dependence of the solution viscosity upon the polymer concentration). Subsequently, physically crosslinked alginate nanofibrous mats are first morphologically characterized via both scanning electron and atomic force microscopy, which show a homogenous and defect-free structure, and their biological response is then evaluated. Noticeably, fibroblast and keratinocyte cell lines do not show significant differences in terms of cell adhesion on the three mats (i.e., 30-40% and 10-20% with respect to the seeded cells, respectively), with the formers presenting a greater affinity toward the alginate-based nanofibers. Conversely, both the investigated osteoblast cells are characterized by a distinct behaviour depending on the alginate type. Specifically, polysaccharide samples with an evident polyelectrolyte nature are found to better promote cell viability (i.e., cell adhesion in the range 15-36% with respect to seeded cells) compared to the ones displaying a nearly neutral behaviour (i.e., cell adhesion in the range 5-25% with respect to seeded cells). Therefore, the obtained results, despite being preliminary, suggest that the alginate type (i.e., molecular structure properties) may play a topical role in conditioning the efficiency of healing patches for bone reparation, but it has a negligible effect in the case of skin regeneration.

Effect of Crosslinking Type on the Physical-Chemical Properties and Biocompatibility of Chitosan-Based Electrospun Membranes

Chitosan nanofibrous membranes are prepared via an electrospinning technique and explored as potential wound healing patches. In particular, the effect of a physical or chemical crosslinking treatment on the mat morphological, mechanical, water-related, and biological properties is deeply evaluated. The use of phosphate ions (i.e., physical crosslinking) allows us to obtain smooth and highly homogenous nanofibers with an average size of 190 nm, whereas the use of ethylene glycol diglycidyl ether (i.e., chemical crosslinking) leads to rougher, partially coalesced, and bigger nanofibers with an average dimension of 270 nm. Additionally, the physically crosslinked mats show enhanced mechanical performances, as well as greater water vapour permeability and hydrophilicity, with respect to the chemically crosslinked ones. Above all, cell adhesion and cytotoxicity experiments demonstrate that the use of phosphate ions as crosslinkers significantly improves the capability of chitosan mats to promote cell viability owing to their higher biocompatibility. Moreover, tuneable drug delivery properties are achieved for the physically crosslinked mats by a simple post-processing impregnation methodology, thereby indicating the possibility to enrich the prepared membranes with unique features. The results prove that the proposed approach may lead to the preparation of cheap, biocompatible, and efficient chitosan-based nanofibers for biomedical and pharmaceutical applications.

Scale-up of Electrospinning: Market Overview of Products and Devices for Pharmaceutical and Biomedical Purposes

Recently, the electrospinning (ES) process has been extensively studied due to its potential applications in various fields, particularly pharmaceutical and biomedical purposes. The production rate using typical ES technology is usually around 0.01-1 g/h, which is lower than pharmaceutical industry production requirements. Therefore, different companies have worked to develop electrospinning equipment, technological solutions, and electrospun materials into large-scale production. Different approaches have been explored to scale-up the production mainly by increasing the nanofiber jet through multiple needles, free-surface technologies, and hybrid methods that use an additional energy source. Among them, needleless and centrifugal methods have gained the most attention and applications. Besides, the production rate reached (450 g/h in some cases) makes these methods feasible in the pharmaceutical industry. The present study overviews and compares the most recent ES approaches successfully developed for nanofibers' large-scale production and accompanying challenges with some examples of applied approaches in drug delivery systems. Besides, various types of commercial products and devices released to the markets have been mentioned.

Electrical Percolation Threshold and Size Effects in Polyvinylpyrrolidone-Oxidized Single-Wall Carbon Nanohorn Nanocomposite: The Impact for Relative Humidity Resistive Sensors Design

This paper reports, for the first time, on the electrical percolation threshold in oxidized carbon nanohorns (CNHox)-polyvinylpyrrolidone (PVP) films. We demonstrate-starting from the design and synthesis of the layers-how these films can be used as sensing layers for resistive relative humidity sensors. The morphology and the composition of the sensing layers are investigated through Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), and RAMAN spectroscopy. For establishing the electrical percolation thresholds of CNHox in PVP, these nanocomposite thin films were deposited on interdigitated transducer (IDT) dual-comb structures. The IDTs were processed both on a rigid Si/SiO2 substrate with a spacing of 10 µm between metal digits, and a flexible substrate (polyimide) with a spacing of 100 µm. The percolation thresholds of CNHox in the PVP matrix were equal to (0.05-0.1) wt% and 3.5 wt% when performed on 10 µm-IDT and 100 µm-IDT, respectively. The latter value agreed well with the percolation threshold value of about 4 wt% predicted by the aspect ratio of CNHox. In contrast, the former value was more than an order of magnitude lower than expected. We explained the percolation threshold value of (0.05-0.1) wt% by the increased probability of forming continuous conductive paths at much lower CNHox concentrations when the gap between electrodes is below a specific limit. The change in the nanocomposite's longitudinal Young modulus, as a function of the concentration of oxidized carbon nanohorns in the polymer matrix, is also evaluated. Based on these results, we identified a new parameter (i.e., the inter-electrode spacing) affecting the electrical percolation threshold in micro-nano electronic devices. The electrical percolation threshold's critical role in the resistive relative-humidity sensors' design and functioning is clearly emphasized.