A team of researchers have introduced STAMP—Simple Templating of Actuators via Micro-Topographical Patterning—a low-cost, reusable method for aligning skeletal muscle fibers on hydrogels using 3D-printed stamps.
Study: Leveraging microtopography to pattern multi-oriented muscle actuators. Image Credit: MIT, Courtesy of the researchers
Designed to simplify fabrication, STAMP enables precise muscle alignment for soft robotics and engineered tissues without relying on complex microfabrication techniques. To demonstrate its potential, the researchers built an optogenetically controlled iris-like robot powered by muscle layers aligned through this approach.
Rethinking Muscle Alignment for Biohybrid Systems
Engineered skeletal muscle is a key component in applications like drug screening and soft robotics, where directional contraction is essential. While three-dimensional muscle constructs often rely on mechanical tension for fiber alignment, two-dimensional (2D) monolayers—ideal for high-throughput imaging and planar devices—require patterned substrates to guide fiber orientation.
Earlier solutions used rigid microfabricated grooves or substrates, but these often failed under long-term culture, lacked transparency, or were too stiff for soft robotics. Hydrogels offered a more tissue-like alternative, but aligning fibers on soft materials has traditionally depended on expensive equipment or time-intensive processes.
STAMP addresses these challenges directly. It allows researchers to generate consistent, microscale patterns on soft hydrogels in a single step, using affordable, reusable 3D-printed stamps. The method is compatible with live-cell imaging and scalable for both research and prototyping.
How STAMP Works: From Design to Muscle Patterning
To create the patterned stamps, the team used computer-aided design (CAD) software to model grooves ranging from 12.5 to 125 micrometers wide. The designs were printed using stereolithographic (SLA) or two-photon polymerization 3D printers, then cleaned, UV-cured, and sterilized for cell culture use.
For patterning, fibrin hydrogels were prepared in standard 24-well plates. Each stamp was coated with 1 % bovine serum albumin (BSA) to prevent sticking, then pressed into the gel as it polymerized at room temperature over 45 minutes. After use, stamps were cleaned with ethanol and UV-sterilized, retaining performance over at least four reuse cycles.
Mouse and human myoblasts were seeded onto the patterned gels and cultured for 12 days to promote differentiation. Contractility was evaluated using either electrical stimulation (1–4 Hz) or optogenetic activation with blue light (470 nm). The researchers measured movement using video-based tracking software and analyzed fiber development using immunostaining and confocal microscopy.
To visualize the groove structure and fiber alignment, the team used both confocal and scanning electron microscopy (SEM). Additionally, they created a computational model of iris contraction using Abaqus software, assigning thermal expansion properties to simulate radial and circular muscle strain.
Results: Muscle Alignment Without Trade-Offs
The stamps successfully transferred microgrooves to the hydrogels, enabling clear muscle alignment. Over 60 % of muscle fibers aligned within ±20° of the groove direction—compared to randomly oriented fibers in unstamped controls. Confocal and SEM imaging confirmed the pattern integrity, and contractility tests showed that function was not impaired by the patterning process.
Among the groove sizes tested, the narrowest (12.5 µm) produced the most pronounced directional contractions. Mouse muscle fibers on these grooves also showed greater width and higher nuclei density—markers of improved tissue maturation.
To highlight STAMP’s design flexibility, the team created a soft robotic iris using a stamp with concentric and radial grooves. The muscle-actuated device responded to optogenetic stimulation by constricting in a pupil-like fashion, with movement that closely matched computational predictions.
Why STAMP Matters
What sets STAMP apart is its simplicity and adaptability. Unlike traditional microfabrication, it doesn’t require cleanrooms, lithography tools, or multi-step processes. It works with standard lab equipment and is compatible with a variety of hydrogel materials and cell types.
STAMP enables centimeter-scale patterning on soft, transparent substrates—ideal for live imaging and long-term culture. Its successful application in both mouse and human cells and in a functional robotic system points to its broad utility in tissue engineering, disease modeling, and soft robotics.
Conclusion
STAMP offers a streamlined, cost-effective alternative to conventional muscle alignment techniques. By using reusable 3D-printed stamps, it bridges the gap between biofabrication and real-world applications—supporting the development of functional, precisely aligned muscle tissues for research and robotics.
The biohybrid iris robot is a compelling proof of concept, showcasing how this method can be used to create multi-directional muscle actuators capable of controlled motion. As interest grows in soft, biologically integrated machines, tools like STAMP will be essential for making these systems more accessible, reproducible, and scalable.
Journal Reference
Rossy, T., Schwendeman, L., Kohli, S., Bawa, M., Umashankar, P., Habba, R., Tchaicheeyan, O., Lesman, A., & Raman, R. (2025). Leveraging microtopography to pattern multi-oriented muscle actuators. Biomaterials Science. DOI:10.1039/d4bm01017e. https://pubs.rsc.org/en/content/articlelanding/2025/bm/d4bm01017e
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