Soft robotics has been developed rapidly in recent years. Different from traditional robotics, soft robotics have the advantages of higher flexibility, safer operations, lightweight and simplified production, resulting in lower manufacturing cost. Soft robotics has been mainly applied in various industrial grippers and medical/rehabilitation devices. The core component of soft robots is made up of flexible material. But how can customers choose suitable materials and processing methods to allow it meeting both design and functional requirements? This article introduces a soft robotic glove for rehabilitation which was invented by Professor TONG Kai Yu and his team from The Chinese University of Hong Kong (CUHK). The soft elastomer-based actuator made with ACEO® 3D-printed silicone provides a new solution for soft robotics.
The Latest Development of Soft Robotics for Rehabilitation
Stroke is the leading cause of disability around the world. Globally, stroke claims a life every 6 seconds, while half of them happen in China. Hand disability is a common and intractable stoke sequela. The so-called “Golden period” with optimal recovery of hand function occurs typically within the first 3 months after a stroke. Several studies demonstrated the ability to improve hand motoric functions through identical and repetitive movements by the impaired hands, as the brain reorganizes (neuroplasticity) after stroke to recover motoric function. To support efforts by occupational therapists that can be labor-intensive, costly and inefficient, different mechanical devices for hand rehabilitation were developed. However, existing devices have disadvantages including heavy weight and large size. Most of them cannot provide aid to activities of daily living, such as hold and pick simple objects, which is a challenging task for stroke patients due to post-stroke spasticity.
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Recently, Professor TONG Kai Yu, Professor LI Zheng and their team from CUHK addressed this problem with a 3D-printed soft robotic glove. This light-weight soft robotic glove can be personalized for patients according to the size of their fingers and palms. Using WACKER’s ACEO® 3D-printed silicones, it has a design of a Soft Elastic Composite Actuator (SECA) to facilitate both flexion and extension of fingers with spasticity and assist patients to improve their hand function in activities of daily living, providing a personalized and affordable solution for stroke rehabilitation training. This novel soft robotic glove was awarded Silver Medal at the 47th International Exhibition of Inventions Geneva in April, 2019.
ACEO® 3D Printing with Silicones
The reasons to use 3D printing to fabricate SECA are complicated process steps and the long time needed in conventional molding. 3D printing offers a method to accelerate the fabrication process and reduce the number of steps required to make one SECA. In addition, 3D printing also provides freedom of design. The unique drop-on-demand technology from ACEO® allows parts and assemblies with complex geometries, for example cavities and overhangs, as well as ‘impossible products,’ which could not previously be produced. The 3D-printed part keeps all the advantages of silicones, such as high elasticity, temperature and UV stability, tensile strength and compression set. These properties are maintained throughout the ACEO® printing process so the performance of 3D-printed silicone parts are comparable with silicone parts that are manufactured using conventional processes such as injection molding or rapid prototyping.
HEUNG Ho Lam, a Ph.D student from CUHK, is the key member of the research team who designed the SECA. According to HEUNG, the requirements for the material of SECA are mainly elongation and durability when undergoing large deformations. Before HEUNG got to know ACEO® 3D-printed silicone, he had tried other rubber-like materials from other 3D printing service providers. But the low durability could not support larger deformations. “We need silicone elastomers to be able to withstand large pressure and deformation for a long time, and we found ACEO® 3D-printed silicone can meet these requirements.” HEUNG Ho Lam explained.
SECA and Future Development
The SECA contains a silicone elastomer chamber. At the bottom of the chamber, there is an inextensible layer for torque compensation. When the chamber is supplied with fluid/air pressure, the chamber will curl towards the inextensible layer and bend the fingers when the glove is worn on a hand. When the pressure releases, the chamber will facilitate finger extension, and thus assist the patient for a complete hand closing and opening.
A stroke patient has been recruited to test the robotic glove with SECA. The device facilitated hand flexion and extension by the patient, and successfully assisted with grasp of a Chinese chess piece and twisting of a towel.
“We are still improving the durability and flexibility during the bending motion. If the design is strong enough, we can apply larger pressure to the SECA and further increase its output force,” introduced HEUNG Ho Lam, “we also hope it is possible to 3D print a large amount of SECA at a time. Still, quality is the first priority when we start mass-production.”
