Optogenetic tools enable the causal examination of how specific cell types contribute to brain circuit functions. A long-standing question is whether it is possible to independently activate two distinct neural populations in mammalian brain tissue. Such a capability would enable the examination of how different synapses or pathways interact to support computation. Here we report two new channelrhodopsins, Chronos and Chrimson, obtained through the de novo sequencing and physiological characterization of opsins from over 100 species of algae. Chrimson is 45 nm red-shifted relative to any previous channelrhodopsin, important for scenarios where red light would be preferred; we show minimal visual system mediated behavioral artifact in optogenetically stimulated Drosophila. Chronos has faster kinetics than any previous channelrhodopsin, yet is effectively more light-sensitive. Together, these two reagents enable crosstalk-free two-color activation of neural spiking and downstream synaptic transmission in independent neural populations in mouse brain slice.

Soft continuum robots exhibit access and manipulation capabilities in constrained and cluttered environments not achievable by traditional robots. However, environmental contact can drastically alter the motion of continuum robots, complicating their control in these applications. Here we describe the design, modeling, and control of a soft continuum robot with a novel extension degree-of-freedom that enables movement in a direction that is always tangent to the robot's backbone, independent of environmental contacts. Steering occurs by inflating multiple Series Pneumatic Artificial Muscles (sPAMs) arranged radially around the backbone and extending along the robot's whole length. This design simplifies navigation of the robot by decoupling steering and extension. To navigate to a destination, the robot is steered to point at the destination, and the extension degree-of-freedom is used to reach it. We present models and experimentally verify the sPAMs and growing robot kinematics. The kinematic model has a mean position accuracy of 5.5 cm for predicting the tip position of a 42 cm long robot. Control of the growing robot is demonstrated using an eye-inhand visual servo control law that enables growth of the robot to designated locations.

We describe a new series pneumatic artificial muscle (sPAM) and its application as an actuator for a soft continuum robot. The robot consists of three sPAMs arranged radially round a tubular pneumatic backbone. Analogous to tendons, the sPAMs exert a tension force on the robot’s pneumatic backbone, causing bending that is approximately constant curvature. Unlike a traditional tendon driven continuum robot, the robot is entirely soft and contains no hard components, making it safer for human interaction. Models of both the sPAM and soft continuum robot kinematics are presented and experimentally verified. We found a mean position accuracy of 5.5 cm for predicting the end-effector position of a 42 cm long robot with the kinematic model. Finally, closed-loop control is demonstrated using an eye-in-hand visual servo control law which provides a simple interface for operation by a human. The soft continuum robot with closed-loop control was found to have a step-response rise time and settling time of less than two seconds.