A Transparent and Flexible Graphene-Piezoelectric Fiber Generator.

Piezoelectric fiber-based generators are prepared by combining two distinctive materials - poly(vinlyidene fluoride) fibers and monolayer/bilayer graphene. Novelty lies in the replacement of opaque metal electrodes with transparent graphene electrodes which enable the graphene-piezoelectric fiber generator to exhibit high flexibility and transparency as well as a great performance with an achievable output of voltage/current about 2 V/200 nA.

Self-Powered Active Sensor with Concentric Topography of Piezoelectric Fibers.

In this study, we demonstrated a flexible and self-powered sensor based on piezoelectric fibers in the diameter range of nano- and micro-scales. Our work is distinctively different from previous electrospinning research; we fabricated this apparatus precisely via near-field electrospinning which has a spectacular performance to harvest mechanical deformation in arbitrary direction and a novel concentrically circular topography. There are many piezoelectric devices based on electrospinning polymeric fibers. However, the fibers were mostly patterned in parallel lines and they could be actuated in limited direction only. To overcome this predicament, we re-arranged the parallel alignment into concentric circle pattern which made it possible to collect the mechanical energy whenever the deformation is along same axis or not. Despite the change of topography, the output voltage and current could still reach to 5 V and 400 nA, respectively, despite the mechanical deformation was from different direction. This new arbitrarily directional piezoelectric generator with concentrically circular topography (PGCT) allowed the piezoelectric device to harvest more mechanical energy than the one-directional alignment fiber-based devices, and this PGCT could perform even better output which promised more versatile and efficient using as a wearable electronics or sensor.

The control of cell orientation using biodegradable alginate fibers fabricated by near-field electrospinning.

For spatially controlling cell alignment, near field electrospinning (NFES) was developed to direct-write alginate fiber patterns. Compared to randomly electrospun fibers, NFES fibers guided the extension of HEK 293T cells and the levels of cell alignment increased with decreasing fiber distances. However, these guiding fibers were unfavorable for cell adhesion and limited cell growth. To preserve cell alignment ability and improve biocompatibility, the stability of patterned alginate fibers was adjusted by regulating the level of ion crosslinking. These partially crosslinked NFES fibers demonstrated parallel line-patterns in the initial stage while gradually degraded with time. The reduction of fiber density increased the available area for cell growth and enhanced cell viability. On the other hand, aligned cells were still found on these degraded patterns, suggesting that cell morphologies were mainly guided during cell seeding. This dynamically controlled fiber pattern system fulfilled the need of controlling cell orientation and biocompatibility, thus was potential to modify scaffold surfaces for tissue engineering application.

Hybrid Energy Harvester Consisting of Piezoelectric Fibers with Largely Enhanced 20 V for Wearable and Muscle-Driven Applications.

We present a polyvinylidene fluoride (PVDF) nanogenerator (NG) with advantages of direct writing and in situ poling via near-field electrospinning (NFES), which is completely location addressable and substrate independent. The maximum output voltage reached 20 V from the three layers piled NGs with serial connections, and the maximum output current can exceed 390 nA with the parallel integration setup. Linear superposition and switching polarity of current and voltage tests were validated by the authentic piezoelectric output. Nanofiber (NF)-based devices with a length ∼5 cm can be easily attached on the human finger under folding-releasing at ∼45°, and the output voltage and current can reach 0.8 V and 30 nA, respectively. This work based on NFs can potentially have a huge impact on harvesting various external sources from mechanical energies.