Grand challenges for burrowing soft robots

Abstract

Robotic burrowing holds promise for applications in agriculture, resource extraction, and infrastructure development, but current approaches are ineffective, inefficient, or cause significant environmental disruption. In contrast, natural burrowers penetrate substrates with minimal disturbance, providing biomechanical principles that could inspire more efficient and sustainable mechanisms. A notable feature of many natural burrowers is their reliance on soft body compositions, raising the question of whether softness contributes to their burrowing success. This review explores the role of soft materials in biological burrowing and their implications for robotic design. We examine the mechanisms that soft-bodied organisms and soft robots employ for submerging and subterranean locomotion, focusing on how softness enhances efficiency and adaptability in granular media. We analyze the gaps between the capabilities of natural burrowers and soft robotic burrowers, identify grand challenges, and propose opportunities to enhance robotic burrowing performance. By bridging biological principles with engineering innovation, this review aims to inform the development of next-generation burrowing robots capable of operating with the efficiency and efficacy seen in nature.

Keywords: bioinspiration; burrowing; granular media; soft robotics; soil.

FIGURE 1

General flow of burrowing steps, which is composed of submerging (above-ground to below-ground) and subterranean locomotion (within-ground).

FIGURE 2

Burrowers with fully soft bodies and bodies made of both soft and rigid components reach similar depths. Worms can reach 1,000 mm (Cadman and Nelson-Smith, 1993), octopuses can reach 110 mm (Montana et al., 2015), bivalves can reach 750 mm (Holland and Dean, 1977), and sandfish skinks can reach 40 mm (Catena and Hembree, 2014).

FIGURE 3

Burrowing mechanisms used by biological organisms. Information for burrowing organism examples are from the following sources: Sharpe et al. (2015), Trueman (1975), Trueman (1966), Trueman (1967), Hodge et al. (2009), Merz and Woodin (2006).

FIGURE 4

Burrowing mechanisms used by soft robots. Example robot drawings are based from the following: Das et al. (2020), Sadeghi et al. (2013), Eken et al. (2023), Niiyama et al. (2022), Maladen et al. (2011a), Isaka et al. (2019), Tang et al. (2024), Chopra et al. (2023), Naclerio et al. (2021).

FIGURE 5

Comparison between burrowing methods employed by soft biological organisms and robots. Burrowing methods are divided into submerging mechanisms (vertical axis) and subterranean locomotion mechanisms (horizontal axis). Information for burrowing methods are from the following sources: Dorgan et al. (2013), Che and Dorgan (2010a), Trueman (1975), Murphy and Dorgan (2011), Dorgan et al. (2005), Volkenborn et al. (2010), Dorgan (2018), Lesanpezeshki et al. (2019), Trueman (1966), Trueman (1967), Aoyama et al. (2005), Hodge et al. (2009), Tatom-Naecker and Westneat (2018), Gidmark et al. (2011), Maladen et al. (2009), Sharpe et al. (2015), Atkinson et al. (1987), Montana et al. (2015), Du et al. (2022), Naclerio et al. (2021), Eken et al. (2023), Sadeghi et al. (2013), Han et al. (2024), Tang et al. (2024), Even et al. (2023), Maladen et al. (2011a), Chopra et al. (2023), Ortiz et al. (2019), Omori et al. (2009), Das et al. (2020), Niiyama et al. (2022), Isaka et al. (2019).

FIGURE 6

Summary of the discussed grand challenges soft burrowing robots face in granular media. In this illustration, the robots are in an environment with cohesionless granular media, but the represented challenges apply for cohesive media as well.