Accelerating Musculoskeletal Robotics Through Parametric Design and 3D-Printed Flexible Structures

Shunnosuke Yoshimura; Kento Kawaharazuka; Kei Okada

doi:10.1002/aisy.70537

Accelerating Musculoskeletal Robotics Through Parametric Design and 3D-Printed Flexible Structures

Parametric design · Flexible 3D printing · Musculoskeletal robotics

Advanced Intelligent Systems · 2026 · e70537

Shunnosuke Yoshimura^*
Kento Kawaharazuka
Kei Okada

Graduate School of Information Science and Technology
The University of Tokyo, Japan

Paper (Wiley)Video BibTeX

Overview

Life-sized musculoskeletal robot, 3D lattice and 2D surface patterns, generated body parts, fabrication, and supported motion — Unified design and fabrication of a life-sized musculoskeletal system.

Abstract

The human body moves smoothly through coordinated soft elements including muscles, tendons, ligaments, and cushioning tissues. Conventional musculoskeletal robots often simplify these using wires or rigid joints, limiting biological flexibility and requiring extensive customization. Thus, a unified framework for designing biomimetic compliant elements remains lacking. Here, parametric design is integrated with flexible 3D printing to generate muscle-, tendon-, ligament-, and cushioning-inspired compliant components through a unified fabrication process using a single thermoplastic polyurethane (TPU) material. Tuning pattern parameters, like lattice density and branch thickness, tailors mechanical properties across body regions. Additionally, ligament-based joint constraints and integrated tendon-driven actuation enable continuous, coordinated multi-joint leg motions at life scale under external suspension, with partial body-weight support and torso roll, pitch, and yaw each constrained from minus 20 to plus 20 degrees. These results validate patterned flexible structures as a practical framework for musculoskeletal robot construction, simplifying design-to-fabrication workflows and enabling scalable biomimetic systems with potential extensions to whole-body humanoids and embedded sensing.

Video

Flexible pattern structures

Three-dimensional lattices fill anatomical volumes, while two-dimensional patterns are projected onto curved surfaces. Cell dimensions, strut thickness, and spatial gradients tune compliance within a single material.

Branching unit cell repeated into a volumetric lattice — Two pattern families share a single TPU fabrication workflow. Cropped from manuscript Figure 1.

Planar grid mapped to a curved surface — Two pattern families share a single TPU fabrication workflow. Cropped from manuscript Figure 1.

Muscles, tendons, and cushioning

Varying lattice geometry creates compliant muscles, stiffer tendons, and sole cushioning, including muscle–tendon gradients within one print. Motor-driven wires provide active contraction; printed ligament patterns constrain the hip, knee, and ankle without bearings.

Muscle–tendon module with enlarged views of sparse muscle and dense tendon lattices — Selected muscle–tendon and joint examples from manuscript Figures 4 and 2.

Ligament-patterned joint bending and twisting — Selected muscle–tendon and joint examples from manuscript Figures 4 and 2.

Coordinated joint motion

Coordinated muscle commands demonstrate approximately 90° hip flexion, 30° hip extension, 30° hip abduction, 105° knee flexion, and 15° ankle plantarflexion.

Leg at the start of the motion, t equals 0 seconds — One representative sequence: hip flexion followed by knee extension. Cropped from manuscript Figure 7A.

Hip flexed to approximately 90 degrees, t equals 8 seconds — One representative sequence: hip flexion followed by knee extension. Cropped from manuscript Figure 7A.

Stepping under external support

Alternating stepping was demonstrated with 0.4 m / 1.6 s and 0.8 m / 2.4 s stride / period conditions. External suspension provided partial body-weight support and constrained torso rotations to ±20°. Autonomous walking was not demonstrated.

Overlaid stepping sequence showing the robot and its overhead external suspension — 0.4 m stride, 1.6 s period; external suspension visible above the robot. Cropped from manuscript Figure 8.

Mechanical characterization

Tests with three specimens per condition characterized hysteresis, fatigue, creep, and joint behavior. The structures completed 999 loading cycles without rupture under the tested conditions, with changes in stiffness. Printing orientation and TPU viscoelasticity remain important design considerations.

BibTeX

@article{yoshimura2026musculoskeletal,
  author = {Yoshimura, Shunnosuke and Kawaharazuka, Kento and Okada, Kei},
  title = {Accelerating Musculoskeletal Robotics Through Parametric Design and {3D}-Printed Flexible Structures},
  journal = {Advanced Intelligent Systems},
  year = {2026},
  month = sep,
  pages = {e70537},
  doi = {10.1002/aisy.70537},
  url = {https://doi.org/10.1002/aisy.70537}
}

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