Multiscale periodic assembly of striped nanocrystal superlattice films on a liquid surface.

Self-assembly of nanocrystals (NCs) into periodically ordered structures on multiple length scales and over large areas is crucial to the manufacture of NC-based devices. Here, we report an unusual yet universal approach to rapidly assembling hierarchically organized NC films that display highly periodic, tunable microscale stripe patterns over square centimeter areas while preserving the local superlattice structure. Our approach is based on a drying-driven dynamic assembly process occurring on a liquid surface with the stripe pattern formed by a new type of contact-line instability. Periodic ordering of NCs is realized on microscopic and nanoscopic scales simultaneously without the need of any specialized equipment or the application of external fields. The striped NC superlattice films obtained can be readily transferred to arbitrary substrates for device fabrication. The periodic structure imparts interesting modulation and anisotropy to the properties of such striped NC assemblies. This assembly approach is applicable to NCs with a variety of compositions, sizes, and shapes, offering a robust, inexpensive route for large-scale periodic patterning of NCs.

Durable and Fatigue-Resistant Soft Peripheral Neuroprosthetics for In Vivo Bidirectional Signaling.

Soft neuroprosthetics that monitor signals from sensory neurons and deliver motor information can potentially replace damaged nerves. However, achieving long-term stability of devices interfacing peripheral nerves is challenging, since dynamic mechanical deformations in peripheral nerves cause material degradation in devices. Here, a durable and fatigue-resistant soft neuroprosthetic device is reported for bidirectional signaling on peripheral nerves. The neuroprosthetic device is made of a nanocomposite of gold nanoshell (AuNS)-coated silver (Ag) flakes dispersed in a tough, stretchable, and self-healing polymer (SHP). The dynamic self-healing property of the nanocomposite allows the percolation network of AuNS-coated flakes to rebuild after degradation. Therefore, its degraded electrical and mechanical performance by repetitive, irregular, and intense deformations at the device-nerve interface can be spontaneously self-recovered. When the device is implanted on a rat sciatic nerve, stable bidirectional signaling is obtained for over 5 weeks. Neural signals collected from a live walking rat using these neuroprosthetics are analyzed by a deep neural network to predict the joint position precisely. This result demonstrates that durable soft neuroprosthetics can facilitate collection and analysis of large-sized in vivo data for solving challenges in neurological disorders.