Fabrication of Customizable and Reproducible 3D Chondrocyte-Laden Nanofibrous Architectures: Effect of Specific Fiber Alignments and Porosities on Chondrocyte Response under Cyclic Compression

Electrospinning has been widely employed to fabricate complex extracellular matrix-like microenvironments for tissue engineering due to its ability to replicate structurally biomimetic micro- and nanotopographic cues. Nevertheless, these nanofibrous structures are typically either confined to bidimensional systems or confined to three-dimensional ones that are unable to provide controlled multiscale patterns. Thus, an electrospinning modality was used in this work to fabricate chondrocyte-laden nanofibrous scaffolds with highly customizable three-dimensional (3D) architectures in an automated manner, with the ultimate goal of recreating a suitable 3D scaffold for articular cartilage tissue engineering. Three distinct architectures were designed and fabricated by combining multiple nanofibrous and chondrocyte-laden hydrogel layers and tested in vitro in a compression bioreactor system. Results demonstrated that it was possible to precisely control the placement and alignment of electrospun polycaprolactone and gelatin nanofibers, generating three unique architectures with distinctive macroscale porosity, water absorption capacity, and mechanical properties. The architecture organized in a lattice-like fashion was highly porous with substantial pore interconnectivity, resulting in a high-water absorption capacity but a poor compression modulus and relatively weaker energy dissipation capacity. The donut-like 3D geometry was the densest, with lower swelling, but the highest compression modulus and improved energy dissipation ability. The third architecture combined a lattice and donut-like fibrous arrangement, exhibiting intermediary behavior in terms of porosity, water absorption, compression modulus, and energy dissipation capacity. The properties of the donut-like 3D architecture demonstrated great potential for articular cartilage tissue engineering, as it mimicked key topographic, chemical, and mechanical characteristics of chondrocytes' surrounding environment. In fact, the combination of these architectural features with a dynamically compressive mechanical stimulus triggered the best in vitro results in terms of viability and biosynthetic production.

Comparative Analysis of Fiber Alignment Methods in Electrospinning

Fabrication of anisotropic materials is highly desirable in designing biomaterials and tissue engineered constructs. Electrospinning has been broadly adopted due to its versatility in producing non-woven fibrous meshes with tunable fiber diameters (from 10 nanometers to 10 microns), microarchitectures, and construct geometries. A myriad of approaches have been utilized to control fiber alignment of electrospun materials to achieve complex microarchitectures, improve mechanical properties, and provide topographical cellular cues. This review provides a comparative analysis of the techniques developed to generate fiber alignment in electrospun materials. A description of the underlying mechanisms that drive fiber alignment, setup variations for each technique, and the resulting impact on the aligned microarchitecture is provided. A critical analysis of the advantages and limitations of each approach is provided to guide researchers in method selection. Finally, future perspectives of advanced electrospinning methodologies are discussed in terms of developing a scalable method with precise control of microarchitecture.

Magnetic Properties of Electrospun Magnetic Nanofiber Mats after Stabilization and Carbonization

Magnetic nanofibers are of great interest in basic research, as well as for possible applications in spintronics and neuromorphic computing. Here we report on the preparation of magnetic nanofiber mats by electrospinning polyacrylonitrile (PAN)/nanoparticle solutions, creating a network of arbitrarily oriented nanofibers with a high aspect ratio. Since PAN is a typical precursor for carbon, the magnetic nanofiber mats were stabilized and carbonized after electrospinning. The magnetic properties of nanofiber mats containing magnetite or nickel ferrite nanoparticles were found to depend on the nanoparticle diameters and the potential after-treatment, as compared with raw nanofiber mats. Micromagnetic simulations underlined the different properties of both magnetic materials. Atomic force microscopy and scanning electron microscopy images revealed nearly unchanged morphologies after stabilization without mechanical fixation, which is in strong contrast to pure PAN nanofiber mats. While carbonization at 500 °C left the morphology unaltered, as compared with the stabilized samples, stronger connections between adjacent fibers were formed during carbonization at 800 °C, which may be supportive of magnetic data transmission.

Magnetic-Electrospinning Synthesis of γ-Fe2O3 Nanoparticle-Embedded Flexible Nanofibrous Films for Electromagnetic Shielding

The exploration of a new family of flexible and high-performance electromagnetic shielding materials is of great significance to the next generation of intelligent electronic products. In this paper, we report a simple magnetic-electrospinning (MES) method for the preparation of a magnetic flexible film, γ-Fe₂O₃ nanoparticle-embedded polymeric nanofibers. By introducing the extra magnetic field force on γ-Fe₂O₃ nanoparticles within composite fibers, the critical voltage for spinning has been reduced, along with decreased fiber diameters. The MES fibers showed increased strength for the magnetic field alignment of the micro magnets, and the attraction between them assisted the increase in fiber strength. The MES fibers show modifications of the magnetic properties and electrical conductivity, thus leading to better electromagnetic shielding performance.

Orientation of Electrospun Magnetic Nanofibers Near Conductive Areas

Electrospinning can be used to create nanofibers from diverse polymers in which also other materials can be embedded. Inclusion of magnetic nanoparticles, for example, results in preparation of magnetic nanofibers which are usually isotropically distributed on the substrate. One method to create a preferred direction is using a spinning cylinder as the substrate, which is not always possible, especially in commercial electrospinning machines. Here, another simple technique to partly align magnetic nanofibers is investigated. Since electrospinning works in a strong electric field and the fibers thus carry charges when landing on the substrate, using partly conductive substrates leads to a current flow through the conductive parts of the substrate which, according to Ampère's right-hand grip rule, creates a magnetic field around it. We observed that this magnetic field, on the other hand, can partly align magnetic nanofibers perpendicular to the borders of the current flow conductor. We report on the first observations of electrospinning magnetic nanofibers on partly conductive substrates with some of the conductive areas additionally being grounded, resulting in partly oriented magnetic nanofibers.