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

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

Sticky “Delivering-From” Strategies Using Viral Vectors for Efficient Human Neural Stem Cell Infection by Bioinspired Catecholamines

Controlled release of biosuprastructures, such as viruses, from surfaces has been a challenging task in providing efficient ex vivo gene delivery. Conventional controlled viral release approaches have demonstrated low viral immobilization and burst release, inhibiting delivery efficiency. Here, a highly powerful substrate-mediated viral delivery system was designed by combining two key components that have demonstrated great potential in the fields of gene therapy and surface chemistry, respectively: adeno-associated viral (AAV) vectors and adhesive catecholamine surfaces. The introduction of a nanoscale thin coating of catecholamines, poly­(norepinephrine) (pNE) or poly­(dopamine) (pDA) to provide AAV adhesion followed by human neural stem cell (hNSC) culture on sticky solid surfaces exhibited unprecedented results: approximately 90% loading vs 25% (AAV_bare surface), no burst release, sustained release at constant rates, approximately 70% infection vs 20% (AAV_bare surface), and rapid internalization. Importantly, the sticky catecholamine-mediated AAV delivery system successfully induced a physiological response from hNSCs, cellular proliferation by a single-shot of AAV encoding fibroblast growth factor-2 (FGF-2), which is typically achieved by multiple treatments with expensive FGF-2 proteins. By combining the adhesive material-independent surface functionalization characters of pNE and pDA, this new sticky “delivering-from” gene delivery platform will make a significant contribution to numerous fields, including tissue engineering, gene therapy, and stem cell therapy