Closed-loop control of 4D-printed hydrogel soft robots

Polyelectrolyte hydrogels consist of highly polar polymer chains, that form hydrophilic networks with desirable features such as biocompatibility, biodegradability, tunable mechanical, and electrical properties; hence, they could be promising materials for three-dimensional (3D)-printed biomedical applications. The progress in materials science and 3D printing can provide the platform to pursue innovative applications of polyelectrolytes in 4D printing and soft robotics where the shape-changing characteristics of such materials in response to external energy stimuli can be utilized in manufacturing specialized functional materials. This chapter presents a detailed report of design, fabrication, characterization, optimization, modeling, and control of a common polyelectrolyte hydrogel, chitosan in a 4D printing study with a soft robotic direction. The printing parameters are optimized for the actuation performance for a specified geometrical model. The performance of the 4D-printed polyelectrolyte is compared to the conventional cast film replica. A systematic approach to modeling and control methods including other 4D-printed polyelectrolyte gels soft robots is also presented.