From the laboratories of the ETH Zurich, a new muscle-bone interface paves the way for soft, precise robots that can integrate with our bodies.

Contemporary robotics is undergoing a profound rethink. After decades dominated by rigid structures, electric motors, and mechanical mechanisms, there is growing interest in systems capable of approximating the behavior of living tissue. This is the context in which the most recent research by Soft Robotics Lab at ETH Zurich, which has developed a biohybrid system capable of replicating the biological interface between muscles, tendons, and bones, significantly improving force transmission. This achievement marks a concrete step towards musculoskeletal robots more efficient and towards new biomedical applications.

The work, published in July 2025 in the journal “Science Advances”, is the result of an interdisciplinary collaboration that also involves theInstitute for Bioengineering of Catalonia andUniversity of BarcelonaAt the centre of the study is the functional reconstruction of the so-called myotendinous junction, the critical point where the muscle transfers its force to the tendon and then to the bone. In natural biomechanics, this transition is essential to ensure precision, resilience, and fine control of movement.

When biology becomes functional architecture

Biological muscles combine characteristics that traditional robotics struggles to replicate: elevata densità di potenza, flexibility, micro-control capabilities, and, to some extent, self-repair. However, integrating living tissues with synthetic components poses a significant structural problem: the inefficient transmission of forces at the interface between soft and rigid materials, which generates energy losses and instability. The group led by Professor Robert Katzschmann he addressed this critical issue by taking direct inspiration from human anatomy.

“In nature, the tendon acts as a transition element, with an intermediate rigidity between muscle and bone,”

explains Miriam Filippi, first author of the study and a researcher at ETH Zurich.

“We reproduced this principle using a 3D-printed biohybrid actuator, in which muscle tissue and tendon tissue are integrated with a synthetic bone structure.”

The solution is based on the 3D bioprinting of muscle cells and connective tissue cells, organized in a geometry optimized through computational analysis. The result is a living muscle-tendon unit, capable of repeatable and stable contractions over time, anchored to a rigid segment that simulates bone. In laboratory tests, these actuators have demonstrated a transmission of force significantly higher than previous biohybrid solutions.

A step forward towards musculoskeletal robots

The impact of the research goes beyond the single prototype. According to Professor Katzschmann,

"This study lays the foundation for functional biohybrid systems that credibly connect biology and robotics. It's a key step toward robots equipped with real muscles and tendons, capable of interacting with their environment more naturally."

The statement reflects a paradigm shift: no longer just mimicking biology with synthetic materials, but integrate living tissues within technical systems.

From an engineering perspective, the presence of a bio-printed tendon with controlled stiffness allows for better management of variable loads and complex movements. This aspect is particularly relevant for the collaborative robotics and assistive, where safety and adaptability to human contact are key requirements. A robotic arm equipped with biohybrid actuators could, in the future, modulate force similarly to a human limb, grasping delicate objects or reacting to unexpected stimuli.

Experimental data show that the actuators maintain contractile capacity for extended periods, an essential element for any real-world application. Although the system still requires controlled laboratory conditions, the demonstrated stability represents an advancement over previous attempts. bioactuators based on cultivated muscles.

The road from robotics to regenerative medicine

The most immediate implications could emerge in the medical field. The possibility of reproducing functional muscle-tendon units in vitro opens new avenues for the regenerative medicine and for biomechanical modeling. One example cited by the researchers concerns the middle ear, where the interaction between the tiny stapes bone and the stapedius muscle plays a crucial role in protecting hearing.

“Our work demonstrates how engineered biological tissues can be used to reproduce the mechanics of natural musculoskeletal systems,”

the ETH academic further emphasizes.

“This is relevant not only for soft robotics and bio-inspired technology, but also for the development of biohybrid implants and lab-grown tissue replacements.”

Looking ahead, such models could reduce the need for animal testing and improve the design of adaptive prosthetics.

In the European context, research is part of a broader strategy of convergence between life sciences and advanced engineering, supported in recent years by funding programs oriented towards interdisciplinary innovation. Federal Polytechnic of Zurich, in particular, is confirmed as one of the main junctures of this transformation, with implications ranging from industrial robotics to health.

Future scenarios between ethics, scale and real-world applications

Despite progress, significant questions remain. The scalability of living tissue-based systems, their long-term maintenance, and the ethical implications of using biological cells in technical devices are topics that will require extensive discussion. Furthermore, the transition from the laboratory to operational settings will require solutions for powering, controlling, and protecting biological components.

Yet, the work of the Soft Robotics Lab suggests a clear direction: innovation in robotics does not only come from more sophisticated algorithms, but also from a deeper understanding of mechanics of living thingsIntegrating real muscles and tendons into artificial systems means moving closer to machines capable of moving, adapting, and interacting in ways more closely aligned with human experience. This horizon, spanning robotics and medicine, redefines the very boundary between natural and artificial.

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