Near-Field Electrospinning for Three-Dimensional Stacked Nanoarchitectures with High Aspect Ratios

Abstract

Near-field electrospinning (NFES) was developed to overcome the intrinsic instability of traditional electrospinning processes and to facilitate the controllable deposition of nanofibers under a reduced electric field. This technique offers a straightforward and versatile method for the precision patterning of two-dimensional (2D) nanofibers. However, three-dimensional (3D) stacked structures built by NFES have been limited to either micron-scale sizes or special shapes. Herein, we report on a direct-write 3D NFES technique to construct self-aligned, template-free, 3D stacked nanoarchitectures by simply adding salt to the polymer solution. Numerical simulations suggested that the electric field could be tuned to achieve self-aligned nanofibers by adjusting the conductivity of the polymer solution. This was confirmed experimentally by using poly(ethylene oxide) (PEO) solutions containing 0.1−1.0 wt% NaCl. Using 0.1 wt% NaCl, nanowalls with a maximum of 80 layers could be built with a width of 92 ± 3 nm, height of 6.6 ± 0.1 μm, and aspect ratio (height/width) of 72. We demonstrate the 3D printing of nanoskyscrapers with various designs, such as curved "nanowall arrays", nano "jungle gyms," and "nanobridges". Further, we present an application of the 3D stacked nanofiber arrays by preparing transparent and flexible polydimethylsiloxane films embedded with Ag-sputtered nanowalls as 3D nanoelectrodes. The conductivity of the nanoelectrodes can be precisely tuned by adjusting the number of 3D printed layers, without sacrificing transmittance (98.5%). The current NFES approach provides a simple, reliable route to build 3D stacked nanoarchitectures with high-aspect ratios for potential application in smart materials, energy devices, and biomedical applications.

Processing variables of direct-write, near-field electrospinning impact size and morphology of gelatin fibers

“…This median is similar to the fiber diameters (~2 µm) and structures seen by collagen fibers in prior work as well as matching the extreme low end of typical PCL MEW fibers (2 µm) (26,34). They, however, do not reach the 92 nm fiber sizes see with prior work using polyethylene oxide solution (22). For our applications for musculoskeletal fibrous tissues, we believe our fibers are of an appropriate size for replicating the ECM environment of the cells as they are on the upper end of collagen fibers which is the domain where the fibroblast would reside (10).…”

“…This approach combines the advantages of the two previous methods allowing for the fabrication of a structure with fibers similar in size to the fibers of collagen (2-20µm) while also meeting the macroscopic requirements needed to replicate musculoskeletal fibrous tissue (17)(18)(19)(20)(21). The DWNFE system has even been shown to create 3D stacked fibrous scaffolds with 90-100nm fiber diameters from polyethylene oxide (22).…”

“…To date, DWNFE systems have largely been implemented using synthetic polymers or solutions combining synthetic polymers with alginate or cellulose (22)(23)(24). Synthetic polymers provide mechanical properties similar to musculoskeletal fibrous tissue and are often biodegradable; however, they have limited bioactivity (25,26).…”

Direct‐Printing of Functional Nanofibers on 3D Surfaces Using Self‐Aligning Nanojet in Near‐Field Electrospinning

“…To improve the pattern resolution to sub‐micrometer level, a nanopositioning stage should be equipped, but most importantly, both the droplet size and JTD as small as possible are desired. One route to reducing the size of the droplet size and JTD is the utilization of micropipette with a metal‐coated surface, as previously demonstrated by Park et al [ 43 ] By controlling the coiling radius by changing the applied voltage and TTCD, [ 20,33 ] the development of 3D electrodes [ 44,45 ] and 3D scaffolds [ 46 ] toward 3D surfaces using SA‐N can be further explored.…”

Recent Advances on Nanofiber Fabrications: Unconventional State-of-the-Art Spinning Techniques

“…Recently, Cho et al successfully fabricated nanofiber stacks built with high-resolution control using the NFES technique [ 87 ] ( Figure 9 a). In their method, a high aspect ratio in a variety of architectures such as curved nanowall, grid pattern, and nanobridge, was achieved without any pre- designed collector because of the self-alignment behavior of the nanofibers.…”