Stimulus-Responsive Shrinkage in Electrospun Membranes: Fundamentals and Control

Electrospun polysuccinimide scaffolds containing different salts as potential wound dressing material

In this research, we applied electrospinning to create a two-component biodegradable polymeric scaffold containing polysuccinimide (PSI) and antibacterial salts. Antibacterial agents for therapeutical purposes mostly contain silver ions which are associated with high environmental impact and, in some cases, may cause undesired immune reactions. In our work, we prepared nanofibrous systems containing antibacterial and tissue-regenerating salts of zinc acetate or strontium nitrate in different concentrations, whose structures may be suitable for developing biomedical wound dressing systems in the future. Several experiments have been conducted to optimize the physicochemical, mechanical, and biological properties of the scaffolds developed for application as wound dressings. The scaffold systems obtained by PSI synthesis, salt addition, and fiber formation were first investigated by scanning electron microscopy. In almost all cases, different salts caused a decrease in the fiber diameter of PSI polymer-based systems (<500 nm). Fourier-transform infrared spectroscopy was applied to verify the presence of salts in the scaffolds and to determine the interaction between the salt and the polymer. Another analysis, energy-dispersive X-ray spectroscopy, was carried out to determine strontium and zinc atoms in the scaffolds. Our result showed that the salts influence the mechanical properties of the polymer scaffold, both in terms of specific load capacity and relative elongation values. According to the dissolution experiments, the whole amount of strontium nitrate was dissolved from the scaffold in 8 h; however, only 50% of the zinc acetate was dissolved. In addition, antibacterial activity tests were performed with four different bacterial strains relevant to skin surface injuries, leading to the appearance of inhibition zones around the scaffold discs in most cases. We also investigated the potential cytotoxicity of the scaffolds on human tumorous and healthy cells. Except for the ones containing zinc acetate salt, the scaffolds are not cytotoxic to either tumor or healthy cells.

4D Printing of Biocompatible Scaffolds via In Situ Photo-crosslinking from Shape Memory Copolyesters

The complexity of surgical treatments for large-area soft tissue injuries makes placing large implants into injury sites challenging. Aliphatic polyesters are often used for scaffold preparation in tissue engineering owing to their excellent biodegradability and biocompatibility. Scaffolds with shape-memory effect (SME) can also avoid large-volume trauma during the implantation. However, the complexity and diversity of diseases require more adaptable and precise processing methods. Four-dimensional (4D) printing, a booming smart material additive manufacturing technology, provides a new opportunity for developing shape memory scaffolds. With the aim of personalized or patient-adaptable soft tissues such as blood vessels, we developed a feasible strategy for fabricating scaffolds with fine architectures using 4D printing crosslinkable shape memory linear copolyesters using fused deposition modeling (FDM). To overcome the weak bonding strength of each printed layer during FDM, a catalyst-free photo-crosslinkable functional group derived from biocompatible cinnamic acid was embedded into the linear copolyesters as in situ crosslinking points during FDM printing. Under ultraviolet-assisted irradiation, the resulting 4D scaffold models demonstrated excellent SME, desirable mechanical performance, and good stability in a water environment owing to the chemical bonding between each layer. Moreover, the excellent biocompatibility of the scaffold was evaluated in vitro and in vivo. The developed composite scaffolds could be used for minimally invasive soft tissue repair.

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.

Shape-Memory Materials via Electrospinning: A Review

This review aims to point out the importance of the synergic effects of two relevant and appealing polymeric issues: electrospun fibers and shape-memory properties. The attention is focused specifically on the design and processing of electrospun polymeric fibers with shape-memory capabilities and their potential application fields. It is shown that this field needs to be explored more from both scientific and industrial points of view; however, very promising results have been obtained up to now in the biomedical field and also as sensors and actuators and in electronics.

Nanocomposite electrospun fibers of poly(ε-caprolactone)/bioactive glass with shape memory properties

Electrospun fibers of shape memory triethoxysilane-terminated poly(epsilon-caprolactone) (PCL-TES) loaded with bioactive glasses (BG) are here presented. Unloaded PCL-TES, as well as PCL/BG nanocomposite fibers, are also considered for comparison. It is proposed that hydrolysis and condensation reactions take place between triethoxysilane groups of the polymer and the silanol groups at the BG particle surface, thus generating additional crosslinking points with respect to those present in the PCL-TES system. The as-spun PCL-TES/BG fibers display excellent shape memory properties, in terms of shape fixity and shape recovery ratios, without the need of a thermal crosslinking treatment. BG particles confer in vitro bioactivity to PCL-based nanocomposite fibers and favor the precipitation of hydroxycarbonate apatite on the fiber surface. Preliminary cytocompatibility tests demonstrate that the addition of BG particles to PCL-based polymer does not inhibit ST-2 cell viability. This novel approach of using bioactive glasses not only for their biological properties, but also for the enhancement of shape memory properties of PCL-based polymers, widens the versatility and suitability of the obtained composite fibers for a huge portfolio of biomedical applications.