The notion that the secret to creating artificial muscles could be found in a glass of water is subtly astounding. Not figuratively, but literally. Surprisingly, water content controls the transition between stiffness and flexibility in arthropod cuticle, according to researchers studying the structural mechanics of insect exoskeletons. A locust’s or beetle’s cuticle isn’t just hard or soft. Depending on how much water it can hold, it can be either. That seemingly straightforward discovery is actually having a significant impact on the direction of robotics and materials science.
For many years, some of the most fascinating engineering research being conducted worldwide has come from Harvard’s Wyss Institute for Biologically Inspired Engineering. It doesn’t always garner as much media attention as, say, a novel AI model. However, it may matter more in the long run.
Donald Ingber, a physician and professor of bioengineering who founded the institute, has characterized his entire career as a sort of “biased random walk”—moving constantly in the direction of a goal but never in a straight line. That is a pretty good description of the science itself. It’s not a clear path from researching insect wings to creating micro-aerial robots to creating biodegradable plastics. And yet, here we are.
| Key Information | Details |
|---|---|
| Topic | Muscles from Water — Bioinspired Materials & Soft Robotics |
| Lead Institution | Wyss Institute for Biologically Inspired Engineering |
| Key Material | Shrilk — composite of chitosan (from shrimp shells) and silk fibroin |
| Shrilk Strength | Twice as strong as nylon or PLA; comparable to aluminum alloy at half the weight |
| Core Concept | Biomimicry — replicating structural principles found in insect cuticle |
| Reference Project | Harvard RoboBee (X-Wing version) |
| RoboBee Weight | 259 milligrams — roughly a quarter of a paper clip |
| Key Researchers | Donald Ingber, Javier Fernandez, Robert Wood, Noah Jafferis, Elizabeth Helbling |
| Water’s Role | Water content alone can reversibly shift Shrilk between rigid and highly flexible states |
| Published In | Nature — Untethered Flight of Insect-Sized Flapping-Wing Vehicle |
| Potential Applications | Surgical devices, wearable sensors, assistive robots, biodegradable packaging, wound dressings |
| Field Category | Biomechanics, Soft Robotics, Bioengineering, Sustainable Materials |
| Reference Resource | PlasticsToday — Shrilk Biomaterial Overview |
It is worth pausing to appreciate the information that made Shrilk, a portmanteau of shrimp and silk, known to the larger scientific community. Prior attempts to replicate insect cuticle using chitin and protein had already failed, so researchers Javier Fernandez and Donald Ingber weren’t just attempting to combine existing substances. Instead of focusing solely on the components of the cuticle, they attempted to replicate its laminar, plywood-like layering. A thin, transparent film with the mechanical intricacy of the original was the end product. Shrilk reads less like a lab experiment and more like something that ought to be lining grocery store shelves because it is half the weight of aluminum, twice as strong as nylon, and completely biodegradable.
The reversibility is what elevates muscles from water above a mere poetic expression. When a sample of Shrilk is exposed to different moisture levels, it visibly and quantifiably changes from a rigid state to a highly flexible one. Heat is not necessary. No chemical interaction. Only water. It’s the type of thing that appears to be a misprint when you first read it. However, the underlying mechanism is not magical; the insect world has been using this same principle for hundreds of millions of years. Near a joint, the cuticle must flex. A wing case’s cuticle must be resistant. Moisture gradients are how nature resolved that issue, and it turns out we can as well.
It’s difficult to ignore how much of this research is related to Harvard SEAS’s RoboBee project. The tiny robotic insect, an engineering marvel in and of itself, was connected to an external power cord for almost ten years. The solar-powered RoboBee launched into a brief moment of mild chaos in August 2019 when graduate student Elizabeth Helbling counted down from three. It briefly raced toward the lights before the power was cut and it fell into its safety harness. Noah Jafferis, a coworker, remarked, “It went up,” while observing from the high-speed camera monitor. That’s all. The milestone is that. Weighing 259 milligrams and consuming less energy than an LED Christmas bulb, it is the lightest vehicle ever to achieve sustained untethered flight. The bioinspired thinking that produced Shrilk is directly related to the artificial muscles powering those wings, which are piezoelectric actuators designed to operate at millimeter scales.
The wider ramifications are still being worked out. According to Ingber, wearable sensors, haptic communication tools, and minimally invasive surgical devices are all using the underlying technologies created for the RoboBee project. Because of its biocompatibility, shrimp may serve as a scaffold for regenerative medicine, a field in which a substance that simply dissolves into the body after serving a purpose is a benefit rather than a drawback. In the same way that shrimp shells are technically a waste product, there is a philosophically fulfilling aspect to creating the medication of the future from something that the seafood industry discards.
Of course, there are practical limitations to all of this. The RoboBee is still unable to fly outside because it requires three Earth suns to power its wings, which are currently replicated in a lab using halogen lamps. Plastic packaging has not yet been replaced by Shrilk. There is still a huge gap between a research paper and a product on the shelf, and science coverage often ignores it completely. However, the work’s direction is obvious and deserving of attention. The materials of the future might not be synthetic at all, or they might be synthetic in the sense that they were created but natural in every way. Water-based muscles. Shrimp shells provide strength. A bee that weighs less than a coin takes off. Observing the accumulation of this research year after year gives me the impression that the most beneficial things we will create in the coming decades will resemble life much more than machines.
