Martin L. Culpepper

Biohybrid robots powered by tissue engineered skeletal muscle have historically relied on architectures in which muscle actuators are placed directly on skeletons, thus limiting the accessible design space for such machines. By contrast, native musculoskeletal architecture relies on tendons to bridge the interface between muscles and skeletons, enabling precise, space-efficient, and energy-efficient force transmission. In this study, a mathematical model of the muscle-tendon-skeleton interface is used to design a biohybrid muscle-tendon unit composed of tissue engineered muscle coupled to adhesive tough hydrogel tendons. It is demonstrated that tuning tendon stiffness and pre-tension optimizes actuator performance, and tuning skeleton stiffness modulates force transmission from muscles to skeletons, with fatigue characteristics measured over > 7000 cycles. Furthermore, an ≈11X improvement in power-to-weight ratio of muscle-tendon units is demonstrated compared to previous demonstrations of robots powered by muscles alone. This work validates a robust approach for designing, manufacturing, and deploying muscle-tendon actuators that promises to enhance the modularity and efficiency of biohybrid robots.

Makerspaces are used as a tool in higher education to support curricular, hands-on projects and encourage student extracurricular and personal projects.Because access to making is more self-driven, there is a gap between what makerspace trainings teach students and what students are expected to know by the time they reach capstone courses in engineering.To test the effects of introducing a technical makerspace training to

Abstract Biohybrid robots powered by tissue engineered skeletal muscle have historically relied on architectures in which muscle actuators are placed directly on skeletons, thus limiting the accessible design space for such machines. By contrast, native musculoskeletal architecture relies on tendons to bridge the interface between muscles and skeletons, enabling precise, space-efficient, and energy-efficient force transmission. In this study, we use a mathematical model of the muscle-tendon-skeleton interface to design a biohybrid muscle-tendon unit composed of tissue engineered muscle coupled to adhesive tough hydrogel tendons. We show how tuning tendon stiffness and pre-tension modulates actuator performance, measure fatigue characteristics of our actuators over >7000 cycles, and tune skeleton stiffness to increase force transmission muscles to skeletons by ∼29X. Furthermore, we demonstrate an ∼11X improvement in power-to-weight ratio of muscle-tendon units as compared to previous demonstrations of robots powered by muscles alone. This work validates a robust approach for designing, manufacturing, and deploying muscle-tendon actuators that promises to enhance the modularity and efficiency of biohybrid robots.

Muscle Actuators with Flexures Biohybrid robots require robust, reproducible, and predictable muscle actuators. Ritu Raman and co-workers have designed compliant mechanisms, termed “flexures”, that enhance the performance and decode the contractile dynamics of biological actuators with unprecedented accuracy and precision (see article number 2300834). The authors’ platform enables user-defined control of muscle contractile dynamics and fatigue behavior, enabling real-world applications of muscle as an actuator for adaptive machines. [Cover art by Ella Marushchenko.]

Leveraging living muscle as an efficient and adaptive actuator for soft robots has been of increasing interest over the past decade, with a focus on proof‐of‐concept demonstrations of function. Reproducible design and scalable manufacturing of biohybrid machines requires methods to increase the stroke output of strain‐limited muscle actuators and enable accurate and precise quality control and performance monitoring. Compliant mechanical elements, termed flexures, are designed to enhance muscle contractile stroke to ≈5× previously reported values and decode contraction dynamics with high spatiotemporal resolution. Combining rigid and flexible elements within a linear elastic flexure enables us to outperform the sensitivity of gold standard elastomeric beam‐based measurements of muscle contraction at both low‐ and high‐frequency stimulations. Flexures are leveraged to make quantitative comparisons of force, work, and power outputs in muscle actuators, driving us to discover a new observation of frequency‐dependent fatigue in muscle, and also develop a novel method for tuning muscle contractile dynamics in a frequency‐independent manner. By enhancing the contractile stroke of muscle actuators and precisely tuning contractile dynamics and endurance with unprecedented precision, this study sets the stage for leveraging flexures to improve robust, reproducible, and predictive design and manufacturing of next‐generation biohybrid robots.

With the current Artemis missions planned, by 2028, NASA and its international and commercial partners may be establishing a permanent presence at the lunar South pole. The Artemis Base Camp will be the locus of international and public-private collaboration under the Artemis Accords, helping to bootstrap a lunar economy. As the lunar economy grows, traffic of people and goods will grow with it. Thus, we envision that NASA and its international and commercial partners will have increasing long-term needs for producing metal from in situ resources such as lunar regolith. These metals can be used to produce many end products on the moon including large pressure vessels, both for spacious habitats and industrial-scale storage and operations. In this paper, as a part of the NASA 2023 BIG Idea Challenge ’Lunar Forge: Producing Metal Products on the Moon’, we design and manufacture a molten regolith electrolysis (MRE) reactor capable of producing various alloys of steel and other metal products from lunar regolith, with oxygen as a useful byproduct. We have built ARTEMIS Steelworks (Advancing Reactor Technologies for Electrolytic Manufacturing of In situ Steel), which consists of an electrolytic reactor, supporting the addition of alloying elements to produce molten steel from lunar regolith simulant. To prepare for a lunar technology demonstration, a preliminary test of the reaction on Earth was performed in a vacuum, a sonicator was tested to dislodge oxygen bubbles from the anode to increase electrode life, and an automated iron and slag collector was made to reduce the need for astronaut operation. The project’s technical objectives are to demonstrate steel-making capability while also quantifying energy efficiency, steel quality, and the expected useful life of the electrodes and vessel under different configurations relative to the state of the art. The comprehensive testing plan presented here includes functional subsystem and integrated testing in ambient conditions; automation capabilities; and validation of the main output, steel alloys, using tests and simulations to confirm their suitability for the intended primary end-use of large steel pressure vessels. Through the demonstration of the MRE reactor and the demonstration and characterization of alternative steel alloys, we aim to show the utility of the proposed technology to the lunar exploration goals of NASA and its international and commercial partners.