Multi-modal vehicles by morphing metamaterials
The adaptive soft machine technology is focused on finding a structure that can reversibly morph in complex configurations and support loads with minimal power supply. The low melting point alloy (LMPA) embedded kirigami introduced in our study can rapidly morphs flat sheets into complex, load bearing shapes, with reversibility and self-healing through phase-change. Since this structure overcomes the trade-offs between extensibility and load bearing capacity in reconfigurable soft systems, they can be integrated with onboard power, control, motors, and embedded heaters to create a functional morphing drone. The device can achieve multiple remotely controlled locomotion modes by an autonomous morphing from a ground to air vehicle configuration.
The device consists of LMPA endoskeletons of kirigami embedded in an elastomer. The multi-layered composite also consists of heating layer to enable phase transition of the endoskeleton. The heating layer is localized at specific morphing points to enable the triggered transformation. These heaters are connected in series with two copper wires that can establish a close circuit with a power supply source. The shape transformation starts at the power station where the contact between copper wires on the drone and liquid metal layers deposited on the station. As a result, vehicle to drone transformation occurs by phase change of LMPA with no external intervention. The flat drone stiffens by solidification of the LMPA endoskeleton and recovers load bearing ability. At this stage, the drone can support the thrust of the propeller and fly by remote control triggers.
Prosthetic hand using micro-structured composite
Thermal conductivity of insulating polymers increases with material’s elastic modulus. So, natural soft elastomer have significantly low conductivity of < 1.0 Wm-1K-1. The aligned microstructure of LM programmed elastomer (LMPE) attains incongruent combination of high thermal conductivity and soft mechanical response. High thermal conductivity (> 10 Wm-1K-1 ) with modulus low modulus (<1.0 MPa) makes LMPEs suitable for thermal management of soft actuators and electronics.
We have incorporated LMPEs as mechanically invisible heat sinks to develop thermally activated artificial muscles. The muscles constructued by encapsulating shape memory alloy (SMA) between LMPE layers are mounted on 3D printed robotic hand. The robotic hand model (“phoenix hand” from Thingiverse) is chosen from e-NABLE which is an online global community that develops prosthetic limbs for musculoskeletal disability. Heat generated by SMA during actuation is quickly dissipated by LMPEs to protect underlying users or substrates from high temperatures for human-machine interaction. Functionality of the prosthetic hand to grip and release a plastic cup. The muscles are actuated by joule heating which contracts the SMA wire and bends the PIP and MCP joints for gripping an object. Then, the actuation is stopped by discontinuing the power supply and the elastic rubber bands elongate the SMA wire to release the cup. The temperature of the LMPE composite during gripping and lifting positions remains below body temperature (nearly 37 oC), while the embedded SMA reaches 70 oC to activate. Without the thermal management of LMPE, such a high temperature of the SMA wire would be discomforting for a user. The LMPE prevents heat accumulation without disrupting the functionality of the SMA.
Robotic actuators using multifunctional thin films
The free standing form of stretchable and conductive LM elastomeric thin films (LETs) can be transferred onto diverse substrates and materials. LETs can withstand stretching, twisting, and bending deformation modes and can still maintain conductivity. Multifunctionality of the films in the flexible actuator technologies are demonstrated by adopting LETs as compliant electrodes in dielectric elastomeric actuator (DEA) and as resistive heaters for liquid crystal elastomer (LCE).
Conductive LET electrodes are placed on opposite sides of dielectric elastomer to form compliant parallel plate capacitors of DEAs. VHB acrylic elastomers (1 mm thick) are used a are dielectric elastomers (DE) which are equibiaxially stretched in a frame to increase energy density. The DEA activation is achieved by a high voltage power supply to the electrodes. The LET electrodes can sustain a high voltage of 9.0 kV without breakdown with an areal stain of nearly 120 %. LETs can also act as resistive heater for thermal responsive actuators such as LCEs. The LCE is developed from nematic mesogen RM82 and thiol chain extender EDDT. which has nematic–isotropic transition temperature of 150 oC. The thin film is directly attached to a rectangular section of 1.0 cm x 0.5 cm LCE and connected to a power source using copper tapes. Joule heating is applied to the thin film at a constant voltage to enable efficient power consumption (<500 mW) during actuation. We can achieve a 15 % deformation of thermally stimulated LCE nearly in 10s to pull a 1 g mass. The large force-displacement of greater than 1×10-5 N.m of the actuator demonstrates the functionality of LM composite film for robust and flexible actuation.
Bio-inspired Sensorized Underwater Adhesive
Switchable underwater adhesion using synthetic adhesives have limited capacity due to lack of sensing function and slow adhesion-release mechanisms. We have developed octopus inspired sensorized adhesives that can detect object and activate adhesion. The embedded proximity sensors can trigger the adhesion to increase by a factor of 450 times from an off to on adhesion state. These conformal adhesives can be implemented is wearable system such as glove that allows us to develop sensor controlled adhesive skin to capture objects in aqueous environment.
The basic switchable adhesive element consists of a compliant, silicone suction cup (blue) capped with a soft, pneumatically actuated membrane (red). Pneumatically applied negative pressure creates a adhesive pull at the membrane which creates adhesive stresses as high as 64 kPa in water. This adhesion can immediately dropped by applying positive pressure to release an object.
By coupling micro-LIDAR optical sensors that detect proximity to submerged objects with the adhesive elements, we sense contact and autonomously activate the adhesive elements. This control loop for rapid attachment and controlled release is functionalized in a wearable adhesive glove which has the ability to pick and release a variety of items underwater including flat, curved, rigid, and soft objects.
