Design of Suspended Melt Electrowritten Fiber Arrays for Schwann Cell Migration and Neurite Outgrowth

Abstract

In this study, well-defined, 3D arrays of air-suspended melt electrowritten fibers are made from medical grade poly(ɛ-caprolactone) (PCL). Low processing temperatures, lower voltages, lower ambient temperature, increased collector distance, and high collector speeds all aid to direct-write suspended fibers that can span gaps of several millimeters between support structures. Such processing parameters are quantitatively determined using a "wedge-design" melt electrowritten test frame to identify the conditions that increase the suspension probability of long-distance fibers. All the measured parameters impact the probability that a fiber is suspended over multimillimeter distances. The height of the suspended fibers can be controlled by a concurrently fabricated fiber wall and the 3D suspended PCL fiber arrays investigated with early post-natal mouse dorsal root ganglion explants. The resulting Schwann cell and neurite outgrowth extends substantial distances by 21 d, following the orientation of the suspended fibers and the supporting walls, often generating circular whorls of high density Schwann cells between the suspended fibers. This research provides a design perspective and the fundamental parametric basis for suspending individual melt electrowritten fibers into a form that facilitates cell culture.

Assessing the response of human primary macrophages to defined fibrous architectures fabricated by melt electrowriting

“…These highly defined scaffolds with controlled microfiber diameters and fiber orientations provide uniquely engineered cellular niches to better study and control cell response within 3D environments. This includes the impact of precisely placed microfibers on cell response within a 3D environment, such as providing guidance cues for nerve growth and glial cell migration [ 40 ] or the biomechanical influence of overlapping fibers angles, where these small scale geometries have been shown to drive the osteogenic differentiation of mesenchymal stromal cells [ 30 ]. More relevant to the current study is a recent report on the impact of precisely fabricated pore sizes and shape on macrophage cell phenotype [ 31 ].…”

Melt electrowriting to produce microfiber fragments

“…Figure 1B is a photograph of the fragmented fibers on the microrelief substrate, while a top view perspective is provided in Figure S1. In a related study that suspended MEW fibers, a lower temperature of 19.7°C enabled multi‐millimeter spanning of fiber walls, while at 23.7°C fibers tended to sag and collapse across air gaps 3 . Here, we increase the ambient temperature to above 36°C, to the level that the molten jet breaks apart due to Plateau–Rayleigh instabilities in the air gap instead of sagging or spanning.…”

“…Even when the collector speed is increased to 165 mm/s, the direct‐written jet is only further stretched but rarely breaks 2 . Such fast speeds were recently taken advantage of to suspend MEW fibers over millimeter wide gaps without sagging 3 in order to form well‐defined oriented fiber arrays for neurons 4 …”

“…breaks. 2 Such fast speeds were recently taken advantage of to suspend MEW fibers over millimeter wide gaps without sagging 3 in order to form well-defined oriented fiber arrays for neurons. 4 However, there are several applications where discontinuous microfibers with defined morphology are relevant including the reinforcement of hydrogels in the field of bioprinting, or the use as injectables for drug delivery.…”

“…In a related study that suspended MEW fibers, a lower temperature of 19.7 C enabled multi-millimeter spanning of fiber walls, while at 23.7 C fibers tended to sag and collapse across air gaps. 3 Here, we increase the ambient temperature to above 36 C, to the level that the molten jet breaks apart due to Plateau-Rayleigh instabilities in the air gap instead of sagging or spanning. Figure 1C shows the approximate polymer melt and ambient temperatures that decide the jet breaking probability.…”