Bio-inspired rigid-flexible coupled skin-scales system for enhanced protection in soft robotic fish

Abstract

Soft robotic fish have garnered attention for their compliance and adaptability. However, they remain vulnerable to mechanical damage, which limits their reliability. To address this vulnerability, we introduce a bio-inspired rigid–flexible coupled skin–scales system (BIS). The BIS integrates rigid scales with a flexible silicone substrate through a multi-stage molding process to enhance protection. Static compression tests demonstrate across five elastomers that the BIS enhances energy absorption capacity by at least 2.1 times compared to the purely flexible structure (PFS, silicone skin without scales). In robotic fish underwater experiments, BIS exhibits a tail-beat amplitude deviation of <10% relative to PFS and achieves 12.8 cm/s, retaining 87% of PFS’s peak speed. In addition, fluid dynamics simulations show BIS incurs only a minor drag in low-speed flow. By balancing protection and amplitude response, this research provides a practical approach for enhancing soft robotic fish in demanding aquatic environments.