Pressure driven spinning: A multifaceted approach for preparing nanoscaled functionalized fibers, scaffolds, and membranes with advanced materials

Abstract

Electrospinning, a flexible jet-based fiber, scaffold, and membrane fabrication approach, has been elucidated as having significance to the heath sciences. Its capabilities have been most impressive as it possesses the ability to spin composite fibers ranging from the nanometer to the micrometer scale. Nonetheless, electrospinning has limitations and hazards, negating its wider exploration, for example, the inability to handle highly conducting suspensions, to its hazardous high voltage. Hence, to date electrospinning has undergone an exhaustive research regime to a point of cliché. Thus, in the work reported herein we unveil a competing technique to electrospinning, which has overcome the above limitations and hazards yet comparable in capabilities. The fiber preparation approach unearthed herein is referred to as "pressure driven spinning (PDS)." The driving mechanism exploited in this fiber spinning process is the pressurized by-pass flow. This mechanism allows the drawing of either micro- or nanosized fibers while processing polymeric suspensions containing a wide range of advanced materials spanning structural, functional, and biological entities. Similar to electrospinning if the collection time of these continuous formed fibers is varied, composite scaffolds and membranes are generated. In keeping with our interests, multicompositional structural entities such as these could have several applications in biology and medicine, for example, ranging from the development of three-dimensional cultures (including disease models) to the development of synthetic tissues and organ structures to advanced approaches for controlled and targeted therapeutics.

Figure 1

Representative digital images and optical micrographs of the pressure driven devices explored in these studies. (a) The single needle device and (b) the single needle exit, (c) the coaxial or concentric needle device, and (d) the concentric needle exit.

Figure 2

Representative high-speed digital images of the spinning process in action in the single needle device (a) in the unstable condition and stable spinning conditions at applied pressures of (b) ∼2, (c) ∼3, (d) ∼4, and (e) ∼5 bar, respectively, for a flow rate of ∼10⁻¹⁰ m³ s⁻¹. Panel (f) depicts the spinning process in the stable state while varying the flow rate to ∼10⁻⁷ m³ s⁻¹ for a constant applied pressure of ∼3 bar. Panel (g) depicts the media behavior at the exit of the needle, illustrating the convergence of media together with the nonwetting of the needle. Panel (h) demonstrates the coaxial or concentric needle device at an arbitrary stable operational condition while processing two immiscible nanomaterial-containing suspensions.

Figure 3

Characteristic high-resolution scanning electron micrographs illustrating residues collected in (a) the unstable condition and [(b)–(e)] in stable conditions at applied pressures of ∼2, ∼3, ∼4, and ∼5 bar for a flow rate of ∼10⁻¹⁰ m³ s⁻¹ generated by way of the single needle device. Panel (f) depicts a PLLA suspension spun forming a multicomponent porous and fibrous structure at an applied pressure and flow rate of ∼3 bar and ∼10⁻¹¹ m³ s⁻¹, respectively.

Figure 4

Panels (a) and (b) demonstrate an electron micrograph of the composite fibers and materials analysis carried out using energy-dispersive x rays, which illustrate the existence of SiO₂ nanoparticulates within the fibers. Panel (c) depicts the diffraction pattern of those nanoparticulate-bearing fibers demonstrating the amorphous nature of these SiO₂ nanoparticles. Transmission electron micrographs (d) and (e) depict characteristic fibers that contain bamboo-type multiwalled nanotubes, which were added into the polymer solution during its formulation. Panel (f) illustrates the nanocrystalline properties of these embedded nanotubes. Finally, the scanning electron micrograph (g) represents a multicomponent and multilayered scaffold/membrane generated by way of collecting the generated fibers via a single needle device over a long time span (∼1200 s).

Figure 5

Illustrative micrographs (a) fluorescence in combination with optical and (b) optical alone demonstrating the multicompositional structures that could be fabricated with the coaxial pressure driven device. (c) demonstrates a typical hollow and porous fibrous structure imaged via high-resolution scanning electron microscopy while processing a PLLA based concentrated nanosuspension. Panels (d) and (e) illustrate the effect of driving pressure on the morphology in surface porosity.

Figure 6

Typical (a) digital image of a cell-bearing living scaffold/membrane, (b) post-treated near-confluent cells, which were indistinguishable with those controls, and (c) fluorescent and optical image depicting the scaffold nesting living cells.