Wearable “robot-assisted training” is quickly emerging as a method that helps improve gait rehabilitation. (Reuters)

Scientists have designed a wearable lower-limb robot exoskeleton that features natural knee movement to help stroke and spinal cord injury patients regain ability to walk and strengthen their muscles.

Wearable “robot-assisted training” is quickly emerging as a method that helps improve gait rehabilitation.

Now, researchers from Beihang University in China and Aalborg University in Denmark have designed a lower-limb robot exoskeleton – a wearable robot – that features natural knee movement to greatly improve patients’ comfort and willingness to wear it for gait rehab.

The robotic exoskeleton is intended to help stroke patients strengthen their physical fitness, aid the rehabilitation training of paralysed patients, or to assist those who need help performing daily activities.

The team focused on the knee joint, one of the most complex mechanical systems within the human body and a critical player during gait.

The knee joint’s motion is actuated by several skeletal muscles along its articular surfaces, and its centre of rotation moves.

Researchers wondered if a parallel mechanism similar to skeletal muscles would be useful for designing a bionic knee joint.

“Our new design features a parallel knee joint to improve the bio-imitability and adaptability of the exoskeleton,” said Weihai Chen, a professor at Beihang University.

The exoskeleton taps a hybrid serial-parallel kinematic structure consisting of a 1-degree of freedom (DOF) hip joint module and a 2-DOF knee joint module in the sagittal plane.

A planar 2-DOF parallel mechanism helps to fully accommodate the motion of the human knee – enabling rotation and relative sliding.

Movement transparency is critical when wearing a robot for gait rehab. When wearing the exoskeleton, its movement should be synchronised and consistent with a patient’s natural movement.

“If not, it exerts extra forces on the human joint. And this extra force causes patient discomfort and unnatural movements,” Chen said.

“To improve the transparency of the robot, we studied the structure of the human body, then built our model based on a biometric design of the lower limb exoskeleton,” Chen said.

This design is the first known use of a parallel mechanism at the knee joint to imitate skeletal muscles.

“Our design goes beyond solving the transparency problem in the knee joint – and it’s a simple structure,” Chen added.

“Unlike most previous exoskeletons, which simplified the knee joint as a pin joint, ours provides 2-DOF to make the exoskeleton’s movement consistent with a patient’s natural movement,” said Chen.

The exoskeleton’s main role will be to help stroke or spinal cord injury patients with their rehab, researchers said.

The research was published in the journal Review of Scientific Instruments.