Chen, S. W. | bioRxiv Science

bioRxiv2020

Flexible and transparent silver nanowire structures for multifunctional electrical and optical biointerfacing

Transparent microelectrodes have recently emerged as a promising approach to combine electrophysiology with optophysiology for multifunctional biointerfacing. High-performance flexible platforms that allow seamless integration with soft tissue systems for such applications are urgently needed. Here, silver nanowires (Ag NWs)-based transparent microelectrodes and interconnects are designed to meet this demand. The Ag NWs percolating networks are patterned on flexible polymer substrates using an innovative photolithography-based solution-processing technique. The resulting nanowire networks exhibit a high average optical transparency of 76.1-90.0% over the visible spectrum, low normalized electrochemical impedance of 3.4-15 {Omega} cm2 at 1 kHz which is even better than those of opaque solid Ag films, superior sheet resistance of 11-25 {Omega} sq-1, excellent mechanical stability up to 10,000 bending cycles, good biocompatibility and chemical stability. Studies on Langendorff-perfused mouse and rat hearts demonstrate that the Ag NWs microelectrodes enable high-fidelity real-time monitoring of heart rhythm during co-localized optogenetic pacing and optical mapping with negligible light-induced electrical artifacts. This proof-of-concept work illustrates that the solution-processed, transparent, and flexible Ag NWs networks are a promising candidate for the next-generation of large-area multifunctional biointerfaces for interrogating complex biological systems in basic and translational research.

bioengineering↗

bioRxiv2020

The extent of protein hydration dictates the preference for heterogeneous or homogeneous nucleation generating either parallel or antiparallel β-sheet α-synuclein aggregates

-Synuclein amyloid self-assembly is the hallmark of a number of neurodegenerative disorders, including Parkinsons disease, although there is still very limited understanding about the factors and mechanisms that trigger this process. Primary nucleation has been observed to be initiated in vitro at hydrophobic/hydrophilic interfaces by heterogeneous nucleation generating parallel {beta}-sheet aggregates, although no such interfaces have yet been identified in vivo. In this work, we have discovered that -synuclein can self-assemble into amyloid aggregates by homogeneous nucleation, without the need of an active surface, and with a preference for an antiparallel {beta}-sheet arrangement. This particular structure has been previously proposed to be distinctive of stable toxic oligomers and we here demonstrate that it indeed represents the most stable structure of the preferred amyloid pathway triggered by homogeneous nucleation under limited hydration conditions, including those encountered inside -synuclein droplets generated by liquid-liquid phase separation. In addition, our results highlight the key role that water plays not only in modulating the transition free energy of amyloid nucleation, and thus governing the initiation of the process, but also in dictating the type of preferred primary nucleation and the type of amyloid polymorph generated depending on the extent of protein hydration. These findings are particularly relevant in the context of in vivo -synuclein aggregation where the protein can encounter a variety of hydration conditions in different cellular microenvironments, including the vicinity of lipid membranes or the interior of membraneless compartments, which could lead to the formation of remarkably different amyloid polymorphs by either heterogeneous or homogeneous nucleation.

biophysics↗