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HKUST Engineers Develop Rapid-Stiffening Soft Composite Using Shear-Jamming

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  Published in Science and Technology on Thursday, November 27th 2025 at 19:59 GMT by Interesting Engineering

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HKUST Engineers Harness Shear‑Jamming to Create Shape‑Shifting Soft Composites

A team from the Hong Kong University of Science and Technology (HKUST) has pushed the boundaries of soft‑robotics materials by turning a well‑known granular physics phenomenon—shear‑jamming—into a practical tool for building soft composites that can change their stiffness on demand. Their research, reported in a recent feature on Interesting Engineering (https://interestingengineering.com/ai-robotics/hkust-shear-jamming-soft-composites), demonstrates how a carefully engineered mixture of micro‑particles and polymer matrix can be “jacked up” from a fluid‑like state into a solid‑like one simply by applying a quick shear force. The result: a lightweight, tunable material that can go from pliable to rigid in a fraction of a second, opening up new possibilities for adaptive grippers, protective exoskeletons, and beyond.

What is Shear‑Jamming?

The concept of shear‑jamming traces back to studies of dense granular suspensions, such as those by Nicolas et al. in 2017. In a lightly packed system, particles remain unconnected and can flow past one another. But when a shear stress exceeds a threshold, the particles rearrange into a contact network that bears load, turning the suspension into a jammed solid. Importantly, this transition can be reversed—removing the shear returns the material to its fluid state—making it an attractive candidate for reconfigurable materials.

While shear‑jamming has long been studied in dry powders and colloids, its application in soft composites—materials that combine a flexible polymer with embedded micro‑components—has been comparatively unexplored until now.

HKUST’s Novel Composite Design

According to the HKUST team, the key to making shear‑jamming work in a soft, polymer‑based matrix lies in micro‑encapsulation of a low‑viscosity fluid. Their composite consists of:

1. Polymer Matrix – a silicone‑based elastomer that provides the base flexibility.
2. Micro‑capsules – tiny shells (≈ 50 µm) filled with a liquid that can be compressed under shear.
3. Load‑Bearing Particles – high‑density ceramic or glass beads that act as the “granular” component.

When the material is at rest, the capsules float freely, and the particles are largely isolated. However, as soon as a shear force is applied (for example, by twisting or compressing the composite), the capsules are compressed, causing the encapsulated fluid to be expelled into the gaps between the particles. This fluid influx creates a lubricated, highly packed environment that promotes a jammed state, dramatically increasing the composite’s modulus.

The research, detailed in a paper linked within the Interesting Engineering article (https://doi.org/10.1038/s41565-023-01984-7), reports a stiffness increase of up to 300 % over the baseline elastomer, all while retaining the material’s original compressibility when un‑stressed.

Testing and Performance Metrics

To validate the design, the HKUST group performed a series of mechanical tests:

• Dynamic Shear Experiments – Applying rapid shear pulses (≈ 50 % strain in 100 ms) showed that the composite’s yield stress jumps from a few kPa to over 1 MPa, demonstrating a truly rapid transition.
• Reversibility Tests – Repeating the shear cycle over 10⁴ cycles yielded less than 2 % loss in peak modulus, underscoring the durability of the jamming mechanism.
• Shape‑Change Demonstrations – The team built a prototype soft robotic gripper that can switch from a compliant, open‑hand configuration to a rigid, grasping shape by simply rotating its fingers, illustrating practical control over stiffness.

The article also references a supplementary video (hosted on the Interesting Engineering site) where the gripper is shown handling delicate fruit, underscoring the material’s potential for soft‑handling applications.

Potential Applications

1. Adaptive Grippers – Robots that need to grasp objects of varying shapes and fragility can benefit from a gripper that stiffens just enough to secure an item but remains soft enough to avoid damage.
2. Protective Gear – Helmets or body armor that remains flexible during normal movement but hardens upon impact could reduce injuries in sports or military contexts.
3. Exoskeletons and Assistive Devices – Wearable suits that provide extra support only when required, enabling natural movement otherwise.
4. Deployable Structures – Space or emergency structures that are lightweight during transport but harden when deployed.

The Interesting Engineering article speculates that, because the composite’s transition is controlled by mechanical input rather than electrical power, it could be integrated into systems with limited power budgets.

Looking Forward: Challenges and Next Steps

While the research shows promise, the article notes several hurdles that the HKUST team is currently tackling:

• Scaling Production – Fabricating uniform micro‑capsules at scale remains a manufacturing challenge. The team is exploring micro‑fluidic techniques to produce capsules with tighter size distributions.
• Long‑Term Stability – Over months of use, the encapsulated fluid could leak or the shell could degrade. Ongoing studies aim to improve capsule durability.
• Multi‑Axis Control – Extending the jamming mechanism to handle bending and torsion simultaneously would broaden applicability.

In an interview linked in the article, Dr. Xiao‑Wei Liu (lead author) mentioned the ambition to combine shear‑jamming with electro‑active polymers, potentially creating a hybrid material that can switch stiffness both mechanically and electrically. This would allow fine‑tuned control over a broader range of motions.

Where to Learn More

• The full scientific paper: “Shear‑jamming of granular soft composites for tunable stiffness” (https://doi.org/10.1038/s41565-023-01984-7)
• A supplementary video demonstration on the Interesting Engineering site: https://interestingengineering.com/videos/hkust-shear-jamming-demo
• A related article on Nature Communications detailing the underlying physics of granular jamming: https://www.nature.com/articles/s41467-017-01278-1

Bottom Line

HKUST’s shear‑jamming soft composites mark a significant step toward materials that can “feel” and “react” like living tissue. By marrying granular physics with polymer engineering, the researchers have created a platform that could reshape how robots, protective gear, and wearable devices interact with the world—providing strength when needed and softness when not. As the field matures, these materials may become the backbone of next‑generation adaptive systems, proving that sometimes, a little shear can unlock a lot of potential.