Sliding Fibers: Slidable, Injectable, and Gel-like Electrospun Nanofibers as Versatile Cell Carriers

Designing biomaterial systems that can mimic fibrous, natural extracellular matrix is crucial for enhancing the efficacy of various therapeutic tools. Herein, a smart technology of three-dimensional electrospun fibers that can be injected in a minimally invasive manner was developed. Open surgery is currently the only route of administration of conventional electrospun fibers into the body. Coordinating electrospun fibers with a lubricating hydrogel produced fibrous constructs referred to as <i>slid</i>able, <i>in</i>jectable, and <i>g</i>el-like (SLIDING) fibers. These SLIDING fibers could pass smoothly through a catheter and fill any cavity while maintaining their fibrous morphology. Their injectable features were derived from their distinctive rheological characteristics, which were presumably caused by the combinatorial effects of mobile electrospun fibers and lubricating hydrogels. The resulting injectable fibers fostered a highly favorable environment for human neural stem cell (hNSC) proliferation and neurosphere formation within the fibrous structures without compromising hNSC viability. SLIDING fibers demonstrated superior performance as cell carriers in animal stroke models subjected to the middle cerebral artery occlusion (MCAO) stroke model. In this model, SLIDING fiber application extended the survival rate of administered hNSCs by blocking microglial infiltration at the early, acute inflammatory stage. The development of SLIDING fibers will increase the clinical significance of fiber-based scaffolds in many biomedical fields and will broaden their applicability

Sliding Fibers: Slidable, Injectable, and Gel-like Electrospun Nanofibers as Versatile Cell Carriers

Designing biomaterial systems that can mimic fibrous, natural extracellular matrix is crucial for enhancing the efficacy of various therapeutic tools. Herein, a smart technology of three-dimensional electrospun fibers that can be injected in a minimally invasive manner was developed. Open surgery is currently the only route of administration of conventional electrospun fibers into the body. Coordinating electrospun fibers with a lubricating hydrogel produced fibrous constructs referred to as <i>slid</i>able, <i>in</i>jectable, and <i>g</i>el-like (SLIDING) fibers. These SLIDING fibers could pass smoothly through a catheter and fill any cavity while maintaining their fibrous morphology. Their injectable features were derived from their distinctive rheological characteristics, which were presumably caused by the combinatorial effects of mobile electrospun fibers and lubricating hydrogels. The resulting injectable fibers fostered a highly favorable environment for human neural stem cell (hNSC) proliferation and neurosphere formation within the fibrous structures without compromising hNSC viability. SLIDING fibers demonstrated superior performance as cell carriers in animal stroke models subjected to the middle cerebral artery occlusion (MCAO) stroke model. In this model, SLIDING fiber application extended the survival rate of administered hNSCs by blocking microglial infiltration at the early, acute inflammatory stage. The development of SLIDING fibers will increase the clinical significance of fiber-based scaffolds in many biomedical fields and will broaden their applicability

Integration of Adeno-Associated Virus-Derived Peptides into Nonviral Vectors to Synergistically Enhance Cellular Transfection

This study describes a simple, versatile approach for developing a nonviral gene carrier by adopting the highly efficient gene delivery properties of the adeno-associated virus (AAV). Specific viral peptides (r3.45_hepBD) extracted from AAV r3.45, which directly evolved to improve gene delivery capabilities in many cell types, were conjugated onto branched polyethylenimine (PEI) to form hybrid gene carriers. AAV r3.45 carries a sequence insertion (LATQVGQKTA; r3.45) within the heparin-binding domain (LQRGNRQA; hepBD), which ultimately comprises a novel sequence (LQRGNLATQVGQKTARQA; r3.45_hepBD) on the capsid. This sequence is hypothesized to be a crucial cue to enhance gene delivery efficiency. Consequently, the intimate interactions of the conjugated r3.45_hepBD with the glycosaminoglycans, including chondroitin sulfate, resulted in significantly enhanced cellular transfection of DNA/PEI-r3.45_hepBD complexes. The successful establishment of a nonviral system that is built with novel peptides will provide a powerful means for developing a substantial number of gene therapy applications

Tubing-Electrospinning: A One-Step Process for Fabricating Fibrous Matrices with Spatial, Chemical, and Mechanical Gradients

Guiding newly generated tissues in a gradient pattern, thereby precisely mimicking inherent tissue morphology and subsequently arranging the intimate networks between adjacent tissues, is essential to raise the technical levels of tissue engineering and facilitate its transition into the clinic. In this study, a straightforward electrospinning method (the tubing-electrospinning technique) was developed to create fibrous matrices readily with diverse gradient patterns and to induce patterned cellular responses. Gradient fibrous matrices can be produced simply by installing a series of polymer-containing lengths of tubing into an electrospinning circuit and sequentially processing polymers without a time lag. The loading of polymer samples with different characteristics, including concentration, wettability, and mechanical properties, into the tubing system enabled unique features in fibrous matrices, such as longitudinal gradients in fiber density, surface properties, and mechanical stiffness. The resulting fibrous gradients were shown to arrange cellular migration and residence in a gradient manner, thereby offering efficient cues to mediate patterned tissue formation. The one-step process using tubing-electrospinning apparatus can be used without significant modifications regardless of the type of fibrous gradient. Hence, the tubing-electrospinning system can serve as a platform that can be readily used by a wide-range of users to induce patterned tissue formation in a gradient manner, which will ultimately improve the functionality of tissue engineering scaffolds

BiFACIAL (<i>Bi</i>omimetic <i>F</i>reestanding <i>A</i>nisotropic <i>C</i>atechol‑<i>I</i>nterfaces with <i>A</i>symmetrically <i>L</i>ayered) Films as Versatile Extracellular Matrix Substitutes

Biological naïve extracellular matrices (ECMs) exhibit anisotropic functions in their physical, chemical, and morphological properties. Representative examples include anisotropic skin layers or blood vessels simultaneously facing multiphasic environments. Here, anisotropically multifunctional structures called BiFACIAL (<i>bi</i>omimetic <i>f</i>reestanding <i>a</i>nisotropic <i>c</i>atechol-<i>i</i>nterfaces with <i>a</i>symmetrically <i>l</i>ayered) films were developed simply by contacting two polysaccharide solutions of heparin-catechol (Hep-C) and chitosan-catechol (Chi-C). Such anisotropic characters were due to controlling catechol cross-linking by alkaline pH, resulting in a trimodular structure: a rigid yet porous Hep-C exterior, nonporous interfacial zone, and soft/highly porous Chi-C interior. The anisotropic features of each layer, including the porosity, rigidity, rheology, composition, and ionic strength, caused the BiFACIAL films to show spontaneously biased stimuli responses and differential behaviors against biological substances (e.g., blood plasma). The films could be created in situ in live animals and imitated the structural/functional aspects of the representative anisotropic tissues (e.g., skin and blood vessels), providing valuable ECM-like platforms for the creation of favorable environments or for tissue regeneration or disease treatment by effectively manipulating cellular behaviors

Highly Moldable Electrospun Clay-Like Fluffy Nanofibers for Three-Dimensional Scaffolds

The development of three-dimensional polymeric systems capable of mimicking the extracellular matrix is critical for advancing tissue engineering. To achieve these objectives, three-dimensional fibrous scaffolds with “clay”-like properties were successfully developed by coaxially electrospinning polystyrene (PS) and poly­(ε-caprolactone) (PCL) and selective leaching. As PS is known to be nonbiodegradable and vulnerable to mechanical stress, PS layers present at the outer surface were removed using a “selective leaching” process. The fibrous PCL scaffolds that remained after the leaching step exhibited highly advantageous characteristics as a tissue engineering scaffold, including moldability (i.e., clay-like), flexibility, and three-dimensional structure (i.e., cotton-like). More so, the “clay-like” PCL fibrous scaffolds could be shaped into any desired form, and the microenvironment within the clay scaffolds was highly favorable for cell expansion both in vitro and in vivo. These “electrospun-clay” scaffolds overcome the current limitations of conventional electrospun, sheet-like scaffolds, which are structurally inflexible. Therefore, this work extends the scope of electrospun fibrous scaffolds toward a variety of tissue engineering applications

Ultrawide Spectral Response of CIGS Solar Cells Integrated with Luminescent Down-Shifting Quantum Dots

Conventional Cu­(In_1–<i>x</i>,Ga<i>_x</i>)­Se₂ (CIGS) solar cells exhibit poor spectral response due to parasitic light absorption in the window and buffer layers at the short wavelength range between 300 and 520 nm. In this study, the CdSe/CdZnS core/shell quantum dots (QDs) acting as a luminescent down-shifting (LDS) layer were inserted between the MgF₂ antireflection coating and the window layer of the CIGS solar cell to improve light harvesting in the short wavelength range. The LDS layer absorbs photons in the short wavelength range and re-emits photons in the 609 nm range, which are transmitted through the window and buffer layer and absorbed in the CIGS layer. The average external quantum efficiency in the parasitic light absorption region (300–520 nm) was enhanced by 51%. The resulting short circuit current density of 34.04 mA/cm² and power conversion efficiency of 14.29% of the CIGS solar cell with the CdSe/CdZnS QDs were improved by 4.35 and 3.85%, respectively, compared with those of the conventional solar cells without QDs

Long-term integration of the transplanted neurons.

<p>Confocal microscopy images extracted from xyz-tile acquisitions showing GFP+ neuron implantation throughout the hippocampus 24 weeks post-transplantation. <b>a</b>) shows beads at the injection site carrying GFP+ neurons which are projecting their processes in the host hippocampus, <b>b</b>) shows neurons in Or -oriens layer of the hippocampus sending out processes through the radiatum layer, and <b>c</b>) shows cells in the stratum lucidum of the CA3. Brain slices were stained with CD11b a marker for microglia cells (<b>d</b>), and CD68 a marker for macrophages (<b>e</b>). Confocal microscopy images 4 xy frames extracted from xyz-tile acquisitions showing glass bead cluster were projected in z. Increase in microglia cells and macrophages was associated with the presence of GFP+ cells without processes (arrows). Beads without cells were free of microglia and macrophages, suggesting that these cells were there to clear non-integrated GFP+ neurons. All scale bars  =  100 µm.</p

Transplanted neurons in the adult rat hippocampus.

<p>DIV 5 GFP-neurons were injected unilaterally into the right hippocampus of 6 weeks old rats using 45 µm bead carriers. <b>a</b>) Schematic representation showing the injection location in the dentate gyrus (DG), and in the CA3 region (CA3). After a week the animals were sacrificed and their brains were sliced and immuno-stained with GFP antibody (green) and with Nissl (red) a nuclear cell marker. <b>b</b>) Fluorescence microscopy image of a brain slice taken at the injection site (scale bar  =  1 mm). Fields extracted from a XYZ-tile scan of the hippocampus, −3.7 mm A/P from the bregma, showing the extent of the transplanted neuron implantation in <b>c</b>) the CA3 stratum lucidum layer. <b>d</b>) Cross-section of a bead carrying two GFP+ neurons sending processes into the hippocampus in a 150 µm thick slice. <b>e</b>) A rare GFP+ neuron found in the brain section after dissociation from 2D support prior to injection. Scale bar  =  50 µm. Anterio-posterior GFP+ neuron distribution for injections made at [AP] = −3.5 in the CA3 (blue) and in the DG (red). <b>f</b>) shows the average number of GFP+ neuron (N_GFP-cell), and <b>g</b>) shows the average number of GFP-neuron (N_GFP-cell) per mm³. Error bars represent the standard deviations for series of 10 animals.</p

Influence of the injection position on the distribution of the implanted GFP-neurons.

<p><b>a)</b> Schematic representation of the different hippocampus sub-regions. CA1-field SLu- stratum lucidum, Rad- radiatum layer of the hippocampus, PoDG- polymorph layer of the dentate gyrus, GrDG- granular layer of the dentate gyrus, MoDG- molecular layer of the dentate gyrus, LMol- lacunosum moleculare layer of the hippocampus, Py - pyramidal cell layer of the hippocampus, and Or -oriens layer of the hippocampus. Confocal microscopy images extracted from xyz-tile acquisitions showing GFP+ neuron implantation through out the hippocampus: <b>b</b>) shows the radiatum layer, <b>c</b>) the stratum lucidum of the CA3, <b>d</b>) part of the dentate gyrus. <b>f</b>) Fraction of the total GFP+ cells found in each region for injections in the CA3 (blue) and in the DG (red). Error bars represent the standard deviations for series of 10 animals. Scale bars  =  100 µm.</p