Soft robots can create complicated structures and functions for rehabilitation. The posture perception of soft actuators is critical for performing closed-loop control for a precise location. It is essential to have a sensor with both soft and flexible characteristics that does not affect the movement of a soft actuator. This paper presents a novel end-to-end posture perception method that employs flexible sensors with kirigami-inspired structures and long short-term memory (LSTM) neural networks. The sensors were developed with conductive sponge materials. With one-step calibration from the sensor output, the posture of the soft actuator could be calculated by the LSTM network. The method was validated by attaching the developed sensors to a soft fiber-reinforced bending actuator. The results showed the accuracy of posture prediction of sponge sensors with three kirigami-inspired structures ranged from 0.91 to 0.97 in terms of R2. The sponge sensors only generated a resistive torque value of 0.96 mNm at the maximum bending position when attached to a soft actuator, which would minimize the effect on actuator movement. The kirigami-inspired flexible sponge sensor could in future enhance soft robotic development.

Adolescent idiopathic scoliosis is a common condition that affects children between the age of 10 and young adulthood. Rigid brace treatment is an effective treatment to control the progression of spinal deformity. However, it limits mobility and causes discomfort, which leads to low treatment compliance. In this study, we developed and characterized a kirigami-inspired CT/MRI compatible spring that could be employed to modify our previously designed exoskeleton hinge vertebrae to provide immediate in-brace correction, good wear comfort, and one that does not inhibit mobility simultaneously. Additive manufacturing has drawn significant interest in academic and industrial terms due to its ability to produce geometrically complex structures. The structural design and dimension of the proposed 3D printed kirigami-inspired springs were optimized with the finite element method (FEM). The carbon-fiber-reinforced nylon material (PA-CF) was selected as the material of the kirigami-inspired spring with the balance of printing easiness and performance of the material. The stiffness of designed kirigami-inspired springs varied between 1.20 and 42.01 N/mm. A case series study with three scoliosis patients has been conducted to investigate the immediate in-brace effect on reducing the spinal curvature and asymmetry of the body contours using radiographic examination. The experiment results show that there are 4.6%–50.5% improvements in Cobb angle for different sections of spines. The X-ray images proved that our kirigami-inspired springs would not block views for Cobb angle measurements.