Bimodal ionic photomemristor based on a high-temperature oxide superconductor/semiconductor junction

Memristors, a cornerstone for neuromorphic electronics, respond to the history of electrical stimuli by varying their electrical resistance across a continuum of states. Much effort has been recently devoted to developing an analogous response to optical excitation. Here we realize a novel tunnelling photo-memristor whose behaviour is bimodal: its resistance is determined by the dual electrical-optical history. This is obtained in a device of ultimate simplicity: an interface between a high-temperature superconductor and a transparent semiconductor. The exploited mechanism is a reversible nanoscale redox reaction between both materials, whose oxygen content determines the electron tunnelling rate across their interface. The redox reaction is optically driven via an interplay between electrochemistry, photovoltaic effects and photo-assisted ion migration. Besides their fundamental interest, the unveiled electro-optic memory effects have considerable technological potential. Especially in combination with high-temperature superconductivity which, in addition to facilitating low-dissipation connectivity, brings photo-memristive effects to the realm of superconducting electronics.

Tuneable microfibrillar collagen structures within dense chitosan hydrogels

Chitosan-type I collagen hydrogels are paradigms of polysaccharide-protein assemblies with applications as biomaterials. However, preparing physical hydrogels combining them at comparable, high concentrations (>20 mg mL-1) within interpenetrated networks remains challenging. Here, we could combine chitosan and collagen solutions at 25 mg mL-1 to prepare two different types of concentrated hydrogels. When neutralized under ammonia vapours, mixed solutions form composite hydrogels, where collagen fibers exhibiting an unusual, branched morphology occupy a chitosan network porosity. In contrast, neutralization by immersion in liquid ammonia yielded hybrid networks where collagen microfibrils were associated with chitosan nanoaggregates. Structural variations impacted the mechanical behaviour and biological properties, assessed by 2D cultures of fibroblasts, of these hydrogels. Differences in gelation kinetics between the two biomacromolecules in the two processes appeared as a key factor driving the mixed network structuration. This work discloses a new route to obtain dense hydrogels from binary biopolymer systems and offers additional insights into the underlying gelation process.