Harnessing resonance with adjustable stiffness for persistent peak efficiency: design, fabrication, and characterization of a heart-inspired pulsatile pump

Abstract

Pulsatile flow is a fundamental mode of fluid transport in biological and environmental systems. This unsteady flow regime is exemplified in cardiovascular circulation, in the locomotion of cephalopods and jellyfish, in the roots of certain plants and many other natural phenomena. The temporal and spatial variations inherent in pulsatile flow not only regulates mass transport but can also support efficient energy usage, underscoring its importance in physiological functions.

In the field of mechatronics, the capability to produce highly unsteady flow regimes constitutes a critical asset for the actuation of pressure-driven soft robotic systems, the regulation of fluidic circuitry, and the propulsion of autonomous aquatic platforms. Notably, in biomedical engineering, the generation of controlled pulsatile flow patterns is of particular significance for the development of cardiac assist devices that more faithfully emulate the physiological dynamics of the native heart. By enabling flow characteristics more closely aligned with natural cardiovascular function, this technological approach offers a promising pathway for improving therapeutic outcomes and addressing the increasing prevalence of cardiovascular diseases in an aging global population.

Despite its significance, generating controlled and efficient pulsatile flow across a broad range of frequencies remains a challenge that current pumping technologies fail to meet. This thesis addresses this gap by investigating the physics underpinning optimal pulsatile pumping and by developing a novel pumping system capable of optimal operation over a wide frequency bandwidth.

Inspiration is drawn from biological shape-changing mechanisms such as the beating heart or the mantle-driven propulsion of cephalopods as they present four highly sought-after features: pulsatility, compactness, efficiency and preservation of fluid integrity. Specifically, pulsatile self-propelling systems have been shown to successfully exploit resonance to enhance propulsive efficiency, similarly to what certain sea-dwelling organisms do, hinting at the opportunity to exploit the same benefit in pumping systems. Although resonance has been widely exploited in mechanical systems, its potential in fluid pumping mechanisms, and particularly in pulsatile flows, has never been systematically investigated. This work introduces, for the first time, a resonance-based approach to pulsatile fluid pumping, demonstrating its efficacy in improving flow performance and system efficiency.

In order to leverage resonance across a broad range of pulsation frequencies, this work introduces variable stiffness as a means to actively tune the system’s natural frequency. Although stiffness modulation has been implemented in other engineering systems, its use for controlling transition to resonance is sparse and almost unheard of in the context of fluid displacement technology making this approach the first of its kind.

This thesis presents the design, development, and experimental validation of a variable-stiffness, heart-inspired, pulsatile pump.

We begin by designing a custom variable stiffness mechanism, specifically developed for seamless implementation within robotic artefacts that require adaptable mechanical properties. Building upon this, we engineer a pulsatile pump inspired by the heart’s dynamic pumping strategy, integrating the variable stiffness mechanism to actively modulate system compliance. The resulting device is experimentally tested, revealing how its flow patterns evolve as the pump approaches resonance. Characteristic features emerge in the pressure–flow rate relationship, including amplitude magnification and phase shifts, which collectively identify regions of maximum operational efficiency. Crucially, we demonstrate that the introduction of variable stiffness can enable the pump to transition smoothly across a range of pulsation frequencies while persistently maintaining peak performance. To our knowledge, this represents the first demonstration of a heart-inspired pumping system with the potential to sustain optimal efficiency across variable operating conditions through active stiffness modulation.

In summary, this thesis proposes and validates a novel approach to harnessing mechanical resonance in pulsatile pumping through stiffness modulation. This new technology lays the groundwork for advanced soft robotics actuation systems and, crucially, for the development of next-generation cardiac implants. By enabling a mode of operation more closely aligned with the physiological dynamics of the human heart, while offering enhanced performance and persistent autonomy, this approach addresses some of the most critical challenges in the treatment of cardiac diseases. Moreover, by combining higher operational efficiency with a nature-inspired pulsatile pumping strategy, it promises to enhance biocompatibility and extend device longevity, overcoming longstanding limitations of both commercial and state-of-the-art cardiac assist systems and advancing the design of durable, adaptive, and physiologically harmonious cardiovascular therapies.