Abstract
Technologies that provide mechanical assistance are required in the medical field, such as implants that regenerate tissue through elongation and stimulation. One of the challenges is to develop actuators that combine the benefits of high axial extension at low pressures, modularity, multifunction, and load-bearing capabilities into one design while maintaining their shape and softness. Overcoming such a challenge will provide implants with enhanced capacity for mechanical assistance to induce tissue regeneration. We introduce two novel actuators (M2H) built of stacked Hyperelastic Ballooning Membrane Actuators (HBMAs) that can be realized using helical and toroidal configurations. By restraining the HBMA expansion deterministically using a semisoft exoskeleton, the actuators are endowed with axial extension and radial expansion capabilities. These actuators are thus built of modules that can be configured to different therapeutical needs and multifunctionality, to provide anatomically congruent stimulation. We present the design, fabrication, testing, and numerical and experimental validation of the M2H-HBMAs. They can axially extend up to 41% and 32% in their helical and toroidal configurations at input pressures as low as 26 and 24 kPa, respectively. If the axial extension module is used separately, its extension capacity reaches >170%. The M2H-HBMAs can perform independent and simultaneous expansion and extension motions with negligible intraluminal deformation as well as stand at least 1 kg of axial force without collapsing. The M2H-HBMAs overcome the limitations of hyperexpanding machines that show low resistance to load. We envisage M2H-HBMAs as promising tools to perform tissue regeneration procedures.
Highlights
Soft robots are highly compliant and conformable systems made of materials with similar mechanical properties to those of living tissues [1]
By encoding the capabilities provided by the compliance of the aforementioned requirements into the design of two novel Multimodal Hybrid (M2H) actuators, we introduce the following contributions to this area of research: (1) introduction of the concept of stacked Hyperelastic Ballooning Membrane Actuators (HBMAs) realized by 3D arrangements of ballooning membranes; (2) a series of numerical analyses to define the M2H-HBMA design features; (3) proposal of two modular and versatile tubular actuator designs, helical and toroidal, based on HBMAs, capable of hyperextensibility and load-bearing; and (4) experimental characterization and validation of the two types of soft actuators
All percentages of extension presented throughout this section were calculated using the formula ðL − L0Þ/L0 ∗ 100, where L is final length and L0 is the initial length of the actuators, comprising one Actuation Chambers (AACs) and two Radial Actuation Chambers (RACs)
Summary
Soft robots are highly compliant and conformable systems made of materials with similar mechanical properties to those of living tissues [1] They can perform different motions by combining hyperelastic materials with inextensible substrates or by preprogramming them into their geometries, such as axial extension [2], radial expansion [3], or twisting [4]. There has been an increasing interest in the development of medical robots and their components using hybrid soft- and semisoft (a combination of hyperelastic and elastic materials into one system)- [6] based approaches, for either outside of the human body as exosuits [7, 8] or inside, as implants [9] Most of these technologies have been focused on wearables [10] that work outside of the body [5] and devices for minimally invasive procedures [11], endoscopic tools [12] and catheters [13]. The majority of soft robotic implants have focused on treating heart failure [9, 14]; these types of devices have the potential to assist in the delivery of a number of therapies
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