🌊 NUS Engineers Unveil OstraBot: The Fastest Muscle-Powered Swimmer

The National University of Singapore (NUS) has achieved a groundbreaking milestone in biohybrid robotics with OstraBot, a swimming robot propelled by lab-grown skeletal muscle tissues. This innovative device reached an astonishing speed of 467 millimetres per minute (mm/min), equivalent to 15.6 body lengths per minute, marking the fastest performance ever recorded for any skeletal muscle-driven biohybrid robot. Led by Assistant Professor Tan Yu Jun from the NUS Department of Mechanical Engineering in the College of Design and Engineering, the team published their findings in Nature Communications on March 18, 2026, detailing how self-trained muscles overcame longstanding limitations in force generation for these living-machine hybrids.

OstraBot's success stems from a novel self-training platform that harnesses the natural spontaneous contractions of maturing muscle cells, turning them into a continuous workout regimen without any external electrical stimulation. This approach not only boosted muscle strength to unprecedented levels but also demonstrated practical controllability, paving the way for real-world applications in challenging environments.

The Challenge of Biohybrid Robotics: Why Muscle Power Matters

Biohybrid robots integrate living biological components, such as lab-grown muscle tissues, with synthetic materials to create machines that mimic natural locomotion. Unlike traditional rigid robots powered by electric motors, biohybrids offer softness, adaptability, and energy efficiency at micro- and millimeter scales—ideal for navigating confined spaces like blood vessels or delicate ecosystems. However, a persistent hurdle has been the weak force output of cultured skeletal muscle, limiting speeds, thrust, and task performance.

Skeletal muscle tissue engineered from cell lines like C2C12 (mouse myoblasts commonly used in labs worldwide) typically generates forces in the microwatt range, far below what's needed for agile movement. Previous biohybrid swimmers topped out at speeds under 150 mm/min, often requiring complex setups for muscle stimulation and lacking reproducibility. The NUS breakthrough addresses this by enabling muscles to 'self-train' during their differentiation phase, when they naturally twitch as myotubes (muscle fiber precursors) form and mature.

Innovative Self-Training: Arm-Wrestling for Muscle Tissues

The core innovation is the Self-Training Muscle Platform (STMP), inspired by arm-wrestling. Two ring-shaped muscle tissues are mechanically coupled via a sliding block on a polydimethylsiloxane (PDMS) frame. As cells differentiate around day three, spontaneous contractions begin: one tissue shortens, stretching the other, which then contracts in response. This reciprocal cycle—lengthening followed by shortening—persists autonomously for up to a week, peaking around day five.

No batteries, controllers, or manual intervention are needed; the platform leverages biology's own rhythms. Immunofluorescence imaging confirmed enhanced myotube alignment and hypertrophy (cell enlargement), with diameters averaging 15-20 micrometers. Resulting actuators produced a twitch force of 4.21 millinewtons (mN) and tetanic (sustained) force of 7.05 mN, yielding a stress of 8.51 mN/mm²—the highest for C2C12-derived tissues and over 10 times prior benchmarks.

This method's simplicity and use of commercial cell lines ensure scalability, contrasting with primary cell cultures that vary donor-to-donor.

OstraBot's Design: Boxfish-Inspired Efficiency

OstraBot emulates the ostraciiform (boxfish) locomotion: a rigid 3D-printed polylactic acid (PLA) body houses a single STMP-trained muscle ring, connected to two polyimide tails via PDMS tendons of tunable stiffness. Electrical fields (0.25-0.50 V/mm, 3 Hz, 20 ms pulses) trigger contractions, oscillating the tails for propulsion while the body remains stable, minimizing drag.

A physiology-based model simulated the actuation chain—from stimulation-induced calcium release, through cross-bridge cycling, to force-velocity relationships—coupled with fluid dynamics. This predicted optimal tendon stiffness (intermediate levels) and frequency (3 Hz) maximized energy loops, guiding fabrication.

Record Performance: Quantified Speeds and Thrust

High-speed camera tracking revealed OstraBot's peak velocity at 7.78 mm/s (467 mm/min) under optimal conditions, over three times faster than counterparts with conventionally cultured (HMP: hanging muscle platform) muscles. Steady-state speeds hit 5.50 mm/s, with thrust exceeding 1.5 mN. Heatmap analyses confirmed stiffness-frequency sweet spots, where power output peaked due to matched impedance.

• Maximum speed: 467 mm/min (15.6 BL/min)
• Twitch stress: 5.08 mN/mm²
• Tetanic stress: 8.51 mN/mm²
• Control range: 0-100% via field strength

Comparisons: Prior skeletal muscle biohybrids (e.g., ray-like or jellyfish mimics) lagged at <200 mm/min, often in larger scales or with cardiac muscle.

Photo by Deepal Tamang on Unsplash

Controllability: Sound-Triggered Precision

Beyond speed, OstraBot responds to clapping via integrated microphones, starting/stopping within seconds—demonstrating neural-like command response. Speed tunes continuously with field strength (e.g., 0.50 V/mm max, 0.25 V/mm half-speed), robust to interference like water splashes. Tailbeat frequencies synchronized at 3 Hz for efficiency. This controllability bridges the gap from 'alive but erratic' to practical tools.

The Team Behind the Innovation at NUS

Assistant Professor Tan Yu Jun, who joined NUS in 2021 after her PhD at NTU, leads a lab focused on sustainable biomaterials and soft robotics. Her group built capabilities from scratch—no specialized equipment initially—emphasizing self-healing and bio-derived systems. First author Dr. Pengyu Chen (postdoc) earned Best Poster at MRS Fall 2025; co-authors Xuchen Wang and Jinrun Zhou (PhD students) contributed modeling and fabrication.

Tan's vision: "remove a fundamental bottleneck... high-performance biohybrid systems designed with sustainability." This aligns with NUS's push in bioengineering, supported by Singapore's Research, Innovation and Enterprise 2025 plan.

Singapore's Growing Biohybrid Ecosystem

NUS joins NTU's Biohybrid Robot Research Group, exploring insect hybrids for rescue, and SUTD's robotics for youth STEM. Singapore invests heavily: NRF's RIE2030 allocates S$800M for semiconductors and biohealth, fostering interdisciplinary hubs. This OstraBot work exemplifies how local universities drive global leadership in soft robotics amid Smart Nation initiatives.

Transformative Applications Ahead

Stronger muscles enable minimally invasive tools: e.g., swimming endoscopes for vessel inspection or drug delivery. Environmentally, biodegradable OstraBots could monitor reefs or wetlands, degrading post-mission via PLA hydrolysis. Read the full paper for technical depth: Fast-swimming biohybrid OstraBot.

Biomedical potential: temporary implants dissolve sans surgery; efficiency suits low-Re (Reynolds number) flows.

Overcoming Hurdles: Stability and Scalability

Challenges remain: muscle fatigue after hours, nutrient delivery. Future: multi-muscle arrays, ML-optimized nutrition, primary human cells. NUS eyes fully biodegradable frames for eco-responsible robots. More at NUS news: OstraBot details.

Photo by Kobe Kian Clata on Unsplash

Singapore's Research Leadership and Opportunities

This NUS feat underscores Singapore's ascent in robotics, with universities like NTU and SIT advancing hybrids. For aspiring researchers, NUS labs offer PhD/postdoc roles in biohybrids. The publication highlights Singapore's translational edge, from lab to application.