Inspired by the relatively simple morphological blueprint provided by batoid fish such as stingrays and skates, we create a biohybrid system that enables an artificial animal, a tissue-engineered ray, * Correspondence to: K.K.P. 29 Oxford Street, Pierce Hall Cambridge, MA 02130. kkparker@seas.harvard.edu. Phone: 617-495-2850, 617-835-5920. Fax: 617-496-1793 Bioinspired design, as applied to robotics, aims at implementing naturally occurring features such as soft materials, morphologies, gaits, and control mechanisms in artificial settings to improve performance (1-4). For example, recent soft-robotics studies raised awareness on the importance of material properties (3, 4), shifting the focus from rigid elements to soft materials, while other investigations report successful mimicry of gaits or morphological features inspired by insects (5, 6), fish (7,8), snake (9), salamanders (10) and cheetahs (11). While recent advances have the promise of bridging the performance gap with animals, the current soft-robotic actuators based on, for instance, electroactive polymers, shape memory alloys or pressurized fluids, are yet to mature to the point of replicating the high-resolution complex movements of biological muscles (3, 4).In this context, biosensors and bioactuators (12) are intriguing alternatives, since they can intrinsically respond to a number of control inputs (such as electric fields and optical stimulation). Thanks to recent advances in genetic tools (13) and tissue engineering (12), these responses can be altered and tuned across a wide range of time and length scales. Some pioneering studies have exploited these technologies for self-propulsion, developing miniaturized walking machines (14-16), and flagellar (17) or jellyfish inspired (18) swimming devices. These biohybrid systems operate at high energy efficiency and harvest power from energy dense, locally available nutrients, although at present they require specialized environments (physiological solutions) that may limit their applicability. Moreover and most importantly, these biohybrid locomotors lack of the reflexive control (9, 19) necessary to enable adaptive maneuvering and thus of the ability to respond to spatiotemporally varying external stimuli.Here, we design, build and test a tissue-engineered analog of a batoid fish such as stingrays and skates. By combining soft materials and tissue engineering with optogenetics, we created an integrated sensory-motor system that allowed for coordinated undulating fin movement and phototactically controlled locomotion, that is guided via light stimuli. We drew from fish morphology, neuromuscular dynamics and gait control to implement a living, bio-hybrid system that leads to robust and reproducible locomotion and turning maneuvers. Batoid fish are ideal biological models in robotics (8) because their nearly planar bauplan is characterized by a broad dorsoventral disk, with a flattened body and extended pectoral fins, that enhances stability against roll (20). They swim with high energy efficien...

This paper reviews the recent advances in experiment and theory of the induction of chiroptical effects, primarily circular dichroism (CD), at the plasmonic and excitonic resonances of achiral inorganic nanocrystals (NCs) capped and/or formed with chiral molecules. It also addresses stronger chiroptical effects obtained in intrinsically chiral inorganic nanostructures obtained from growing enantiomeric excess of intrinsically chiral NCs or arranging achiral plasmonic particles in chiral configurations. The accumulated experimental data and theory on various CD induction mechanisms provide an extended set of tools to properly analyze and understand the electromagnetic influence of chiral molecules on inorganic particles and obtain new general insights into the interaction of capping molecules with inorganic NCs. Among the field-induced CD mechanisms developed recently one can name the Coulomb (near-field, dipolar) mechanism for nanostructures much smaller than the wavelength, and for larger nanostructures, the electromagnetic (effective chiral medium), and intrinsically chiral plasmonic mechanisms.

The neurovascular unit (NVU) regulates metabolic homeostasis as well as drug pharmacokinetics and pharmacodynamics in the central nervous system. Metabolic fluxes and conversions over the NVU rely on interactions between brain microvascular endothelium, perivascular pericytes, astrocytes and neurons, making it difficult to identify the contributions of each cell type. Here we model the human NVU using microfluidic organ chips, allowing analysis of the roles of individual cell types in NVU functions. Three coupled chips model influx across the blood-brain barrier (BBB), the brain parenchymal compartment and efflux across the BBB. We used this linked system to mimic the effect of intravascular administration of the psychoactive drug methamphetamine and to identify previously unknown metabolic coupling between the BBB and neurons. Thus, the NVU system offers an in vitro approach for probing transport, efficacy, mechanism of action and toxicity of neuroactive drugs.