Pneumatic artificial muscles composed of 3D printed structures and able to stretch and contract according to the need: this is the innovative design of ‘Grace’ – acronym for GeometRy-based Actuators capable of contracting and stretching – actuators designed by the researchers of the Italian Institute of Technology (Iit) in Genoa and the Scuola Superiore Sant’Anna (Sssa) in Pisa. The work was demonstrated in Science Robotics and the researchers showed the versatility of the actuators in a first, a pneumatic hand made up of 18 different ‘Grace’, produced in a single printing process.
The realization of artificial muscles is a very ambitious goal in the field of robotics, as in nature muscle tissue has complex characteristics that allow for very versatile movements, from fast and powerful to small and precise deformations of the body such as those of human facial expressions. Although individual muscle fibers can only contract, in fact, it is their particular arrangement in a complex muscular architecture that makes joint deformations such as flexion, torsion and antagonistic movements possible. The research desire addressed the problem, starting with individual pneumatic actuators. Each actuator can simply expand, lengthen and shorten thanks to its geometric shape, a sort of spindle with folds, made up of a single body, 3D printable and achievable with different materials and in different sizes.

Various ‘Grace’ can be printed directly assembled together in complex architectures, so as to satisfy the needs of movement. “Their size is limited only by the manufacturing technology adopted”, comments Corrado De Pascali, first author of the study and doctoral student in the Iit Bioinspired Soft Robotics laboratory in Genoa and at the Institute of BioRobotics of the Sssa of Pisa.
“They can be built in different sizes, and we can vary their performance, both in terms of deformation and strength, and manufacture them with different materials and technologies, even directly integrated into the structures to be implemented”, he adds. The researchers demonstrated the characteristics of the ‘Grace’ in the printing of a pneumatic hand, made with a commercial 3D printer and in a single printing process. The material used is a soft resin and is composed of 18 ‘Grace’ of different sizes and shapes, so that with a pressure of a few tenths of a bar it is possible to bend the fingers, twist the palm and rotate the wrist. The hand weighs about 100 grams and is comparable in size to that of a human hand.
The actuators are designed in such a way that they can sometimes reach over 1000 times their weight depending on the material used to manufacture them. In fact, the forces they generate and the demands can be increased or adopted by adopting more or less rigid materials as well as by modifying the thickness of the membrane that composes these actuators while maintaining the performance of contraction and extension unchanged. The ‘Grace’ actuators have the ideal characteristics to be applied in different robotic solutions, in a simple way and with very low costs. Their simplicity of manufacture makes them replicable even outside research laboratories, such as in the fab labs available to makers. The result was obtained as part of the animal musculature studies envisaged by the European Fet Proboscis project coordinated by Lucia Beccai of Iit, and within the research of robotics inspired by living beings conducted by Iit’s Bioinspired Soft Robotics in Genoa coordinated by Barbara. Mazzolai, in collaboration with the SSSA BioRobotics Institute in Pisa.