Science News

Self-healing soft pneumatic robots

Inspired by the compliance found in many organisms, soft robots are made almost entirely out of flexible, soft material, making them suitable for applications in uncertain, dynamic task environments, including safe human-robot interactions. Their intrinsic compliance absorbs shocks and protects them against mechanical impacts. However, the soft materials used for their construction are highly susceptible to damage, such as cuts and perforations caused by sharp objects present in the uncontrolled and unpredictable environments they operate in. In this research, we propose to construct soft robotics entirely out of self-healing elastomers. On the basis of healing capacities found in nature, these polymers are given the ability to heal microscopic and macroscopic damage. Diels-Alder polymers, being thermoreversible covalent networks, were used to develop three applications of self-healing soft pneumatic actuators (a soft gripper, a soft hand, and artificial muscles). Soft pneumatic actuators commonly experience perforations and leaks due to excessive pressures or wear during operation. All three prototypes were designed using finite element modeling and mechanically characterized. The manufacturing method of the actuators exploits the self-healing behavior of the materials, which can be recycled. Realistic macroscopic damage could be healed entirely using a mild heat treatment. At the location of the scar, no weak spots were created, and the full performance of the actuators was nearly completely recovered after healing.

Source: Sciencemag.org – Science Robotics Latest Content

Robot-driven downward pelvic pull to improve crouch gait in children with cerebral palsy

Children with cerebral palsy commonly exhibit an abnormality called crouch gait, which is characterized by excessive flexion of the hips/knees and weak plantar flexor muscles during the stance phase. One of the major reasons for this pathological gait is weakness in soleus muscles. During the mid-stance phase of gait when the toe and heel are both on the ground, the soleus keeps the shank upright and facilitates extension of the knee angle. It also provides propulsive forces on the body during the late stance phase of the gait cycle. We hypothesized that walking with downward pelvic pull will (i) strengthen extensor muscles, especially the soleus, against the applied downward force and (ii) improve muscle coordination during walking. We then tested a robotic training paradigm to improve both posture and gait of children with crouch gait. In this paradigm, participants with crouch gait were subjected to downward pelvic force when walking on a treadmill, provided by a cable-driven robot called Tethered Pelvic Assist Device. Electromyography of soleus and gastrocnemius muscles and walking kinematics of the participants showed the feasibility of this training, enhanced upright posture of the participants, and improved muscle coordination. In addition, walking features of these participants, such as increased step length, range of motion of the lower limb angles, toe clearance, and heel-to-toe pattern, improved. This robotic training method can be a promising intervention for children with cerebral palsy who have a crouch gait.

Source: Sciencemag.org – Science Robotics Latest Content

A soft robot that navigates its environment through growth

Across kingdoms and length scales, certain cells and organisms navigate their environments not through locomotion but through growth. This pattern of movement is found in fungal hyphae, developing neurons, and trailing plants, and is characterized by extension from the tip of the body, length change of hundreds of percent, and active control of growth direction. This results in the abilities to move through tightly constrained environments and form useful three-dimensional structures from the body. We report a class of soft pneumatic robot that is capable of a basic form of this behavior, growing substantially in length from the tip while actively controlling direction using onboard sensing of environmental stimuli; further, the peak rate of lengthening is comparable to rates of animal and robot locomotion. This is enabled by two principles: Pressurization of an inverted thin-walled vessel allows rapid and substantial lengthening of the tip of the robot body, and controlled asymmetric lengthening of the tip allows directional control. Further, we demonstrate the abilities to lengthen through constrained environments by exploiting passive deformations and form three-dimensional structures by lengthening the body of the robot along a path. Our study helps lay the foundation for engineered systems that grow to navigate the environment.

Source: Sciencemag.org – Science Robotics Latest Content