Liheng Cai

Liheng Cai Earns Prestigious National Science Foundation Award to Develop Polymeric Material to Control the Types of Energy Streaming into Windows with the Flick of a Switch

What’s 1,000 times softer than a rubber tire, but holds its shape and is as tough as metal?

The answer is nothing – yet. But a soft material with that combination of properties would be extremely useful in many applications, including medical implants, stretchable electronics or lifelike “soft robots” capable of adapting to unpredictable conditions – as humans and animals do – in ways traditional robots cannot.

University of Virginia School of Engineering assistant professor Liheng Cai believes his lab has found a way to design a new synthetic rubber with these traits. Cai holds joint appointments in UVA Engineering’s departments of Materials Science and Engineering and Chemical Engineering, with a courtesy appointment in the Department of Biomedical Engineering.

A new strategy towards ultra-soft yet dry rubber

Medical implants mimic the softness of human tissue by mixing liquids such oil with long silicone polymers to create a squishy, wet gel. While implants have improved dramatically over the years, there is still a chance of the liquid leaking, which can be painful and sometimes dangerous.

Potential applications include more durable tires, wearable electronics, medical devices

Imagine a tire that could heal after being punctured or a rubber band that never snapped.

Researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have developed a new type of rubber that is as tough as natural rubber but can also self-heal.

The research is published in Advanced Materials.

Self-healing materials aren’t new — researchers at SEAS have developed self-healing hydrogels, which rely on water to incorporate reversible bonds that can promote healing. However, engineering self-healing properties in dry materials — such as rubber — has proven more challenging. That is because rubber is made of polymers often connected by permanent, covalent bonds. While these bonds are incredibly strong, they will never reconnect once broken.

In order to make a rubber self-healable, the team needed to make the bonds connecting the polymers reversible, so that the bonds could break and reform.

“Previous research used reversible hydrogen bonds to connect polymers to form a rubber but reversible bonds are intrinsically weaker than covalent bonds,” said Li-Heng Cai, a postdoctoral fellow at SEAS and corresponding author of the paper.  “This raised the question, can we make something tough but can still self-heal?”

Scientists say the discovery of an internal "brush" that helps clear lungs of unwanted matter could help them understand more about lung diseases.

A team from the University of North Carolina found that the brush-like layer pushes out sticky mucus and the foreign bodies it contains.

Writing in Science, it says that could help identify what goes wrong in cystic fibrosis, asthma and similar diseases.

UK lung experts said the work aided understanding of how lungs function.

The mucus, which helps collect inhaled pollutants, emerges as a runny nose and a wet cough.

Until now, most experts believed a watery substance acted as a lubricant and helped separate mucus from the cells lining airways.

But this did not tally with the fact that mucus remained in its own distinct layer.

The researchers used imaging techniques to examine what was happening within the lungs.

They were able to see a dense meshwork of human bronchial epithelial cell cultures.

The brush-like layer consists of protective molecules that keep sticky mucus from reaching the cilia and epithelial cells, thus ensuring the normal flow of mucus.