Electrospinning of biomedically relevant multi-region scaffolds: From honeycomb to randomly-oriented microstructure

Enhanced Electroactive Phases of Poly(vinylidene Fluoride) Fibers for Tissue Engineering Applications

Nanofibrous materials generated through electrospinning have gained significant attention in tissue regeneration, particularly in the domain of bone reconstruction. There is high interest in designing a material resembling bone tissue, and many scientists are trying to create materials applicable to bone tissue engineering with piezoelectricity similar to bone. One of the prospective candidates is highly piezoelectric poly(vinylidene fluoride) (PVDF), which was used for fibrous scaffold formation by electrospinning. In this study, we focused on the effect of PVDF molecular weight (180,000 g/mol and 530,000 g/mol) and process parameters, such as the rotational speed of the collector, applied voltage, and solution flow rate on the properties of the final scaffold. Fourier Transform Infrared Spectroscopy allows for determining the effect of molecular weight and processing parameters on the content of the electroactive phases. It can be concluded that the higher molecular weight of the PVDF and higher collector rotational speed increase nanofibers' diameter, electroactive phase content, and piezoelectric coefficient. Various electrospinning parameters showed changes in electroactive phase content with the maximum at the applied voltage of 22 kV and flow rate of 0.8 mL/h. Moreover, the cytocompatibility of the scaffolds was confirmed in the culture of human adipose-derived stromal cells with known potential for osteogenic differentiation. Based on the results obtained, it can be concluded that PVDF scaffolds may be taken into account as a tool in bone tissue engineering and are worth further investigation.

Electrical Stimulation Enabled via Electrospun Piezoelectric Polymeric Nanofibers for Tissue Regeneration

Electrical stimulation has demonstrated great effectiveness in the modulation of cell fate in vitro and regeneration therapy in vivo. Conventionally, the employment of electrical signal comes with the electrodes, battery, and connectors in an invasive fashion. This tedious procedure and possible infection hinder the translation of electrical stimulation technologies in regenerative therapy. Given electromechanical coupling and flexibility, piezoelectric polymers can overcome these limitations as they can serve as a self-powered stimulator via scavenging mechanical force from the organism and external stimuli wirelessly. Wireless electrical cue mediated by electrospun piezoelectric polymeric nanofibers constitutes a promising paradigm allowing the generation of localized electrical stimulation both in a noninvasive manner and at cell level. Recently, numerous studies based on electrospun piezoelectric nanofibers have been carried out in electrically regenerative therapy. In this review, brief introduction of piezoelectric polymer and electrospinning technology is elucidated first. Afterward, we highlight the activating strategies (e.g., cell traction, physiological activity, and ultrasound) of piezoelectric stimulation and the interaction of piezoelectric cue with nonelectrically/electrically excitable cells in regeneration medicine. Then, quantitative comparison of the electrical stimulation effects using various activating strategies on specific cell behavior and various cell types is outlined. Followingly, this review explores the present challenges in electrospun nanofiber-based piezoelectric stimulation for regeneration therapy and summarizes the methodologies which may be contributed to future efforts in this field for the reality of this technology in the clinical scene. In the end, a summary of this review and future perspectives toward electrospun nanofiber-based piezoelectric stimulation in tissue regeneration are elucidated.

Design of an electrospun tubular construct combining a mechanical and biological approach to improve tendon repair

Hand tendon injuries represent a major clinical problem and might dramatically diminish a patient's life quality. In this study, a targeted solution for flexor tendon repair was developed by combining a mechanical and biological approach. To this end, a novel acrylate-endcapped urethane-based polymer (AUP) was synthesized and its physico-chemical properties were characterized. Next, tubular repair constructs were developed using electrospinning of the AUP material with incorporated naproxen and hyaluronic acid (i.e. anti-inflammatory and anti-adhesion compounds, respectively), and with a tubular braid as mechanical reinforcement. Tensile testing of the repair constructs using ex vivo sheep tendons showed that the developed repair constructs fulfilled the required mechanical properties for tendon repair (i.e. minimal ultimate stress of 4 MPa), with an ultimate stress of 6.4 ± 0.6 MPa. Moreover, in vitro biological assays showed that the developed repair tubes and the incorporated bioactive components were non-cytotoxic. In addition, when equine tenocytes and mesenchymal stem cells were co-cultured with the repair tubes, an increased production of collagen and non-collagenous proteins was observed. In conclusion, this novel construct in which a mechanical approach (fulfilling the required mechanical properties) was combined with a biological approach (incorporation of bioactive compounds), shows potential as flexor tendon repair application. Graphical abstract.

Electrospun microstructured PLA-based scaffolds featuring relevant anisotropic, mechanical and degradation characteristics for soft tissue engineering

Electrospun scaffolds combine suitable structural characteristics that make them strong candidates for their use in tissue engineering. These features can be tailored to optimize other physiologically relevant attributes (e.g. mechanical anisotropy and cellular affinity) while ensuring adequate degradation rates of the biomaterial. Here, we present the fabrication of microstructured scaffolds by using a combination of micropatterned electrospinning collectors (honeycomb- or square-patterned) and poly(lactic acid) (PLA)-based copolymers (linear or star-shaped). The resulting materials showed appropriate macropore size and fiber alignment that were key parameters to enhance their anisotropic properties in protraction. Moreover, their elastic modulus, which was initially similar to that of soft tissues, gradually changed in hydrolytic conditions, matching the degradation profile in a 2- to 3-month period. Finally, honeycomb-structured scaffolds exhibited enhanced cellular proliferation compared to standard electrospun mats, while cell colonization was shown to be guided by the macropore contour. Taking together, these results provide new insight into the rational design of microstructured materials that can mimic the progressive evolution of properties in soft tissue regeneration.