Okinawa Institute of Science and Technology Graduate University, Okinawa, Japan

Transforming liquids into gels plays an important role in many industries, including cosmetics, medicine, and energy. But the transformation process, called gelation, where manufacturers add chemical thickeners and either heat or cool the fluids to make them more viscous or elastic, is expensive and energy demanding.

Fig. 1 – This enlarged image shows microposts interspersed through the channel in a microfluidic platform. This setup can also be called a micropillar array.
Now, Okinawa Institute of Science and Technology Graduate University (OIST) Professor Amy Shen is experimenting with a new method of gelation. Shen leads the Micro/Bio/Nanofluidics Unit at OIST, where she changes the way that liquids behave using microfluidic platforms, which are flat, palm-sized trays with microscopic channels for the liquid to pass through. Researchers can add nanoparticles or biomolecules with useful pH, chemical, and temperature sensing properties into a liquid, but incorporating those liquids into existing technology proves difficult.

“A gel is easier to integrate into a device,” Shen explained, pointing to biomedical devices and sensors, “whereas liquid just evaporates.” Most recently, Shen and two PhD students created a glucose sensitive gel that more effectively stabilizes a glucose-sensing enzyme. This would make it possible to efficiently produce less invasive glucose testing devices for diabetics, who often have to check their blood sugar five times or more each day. This research was published in the Royal Society of Chemistry’s Lab on a Chip.

How It Works

To induce gelation, Shen’s lab first molds a microfluidic platform out of transparent rubber, creating grooved channels through which liquid can travel. Sometimes the platforms look like thin rivers snaking through a microscope slide; other times the researchers place posts in the middle of a wider channel to create gaps of just few microns in width. Then, they pump a watery and soapy mixture through the platform, and it emerges from the other side as a thick gel. “In this way, we are able to change phase from water to something more like hair gel,” Shen explained. She estimates that her method requires just half of the chemicals that traditional gelation processes require. (See Figure 1)

Fig. 2 – After passing through the microfluidic platform, the soapy molecules form Y-shaped structures and tangle together, as shown above, to form a viscous and elastic gel. Shen and colleagues produced this detailed image using a scanning electron microscope.
In previous research, Shen’s group suggested a mechanism for this method. The soapy mixtures she uses as starting materials tend to form tiny aggregates of soap molecules, which can be spherical or oblong depending on the soap concentration, temperature, and acidity. They manipulate the mixture recipe to adjust the number of oblong aggregates before passing through the microfluidic platform. The structure of the platform allows these aggregates to fuse and form Y-shaped junctions. The arms of these Yshaped aggregates can further tangle together, which gives the gel its stiffer, more viscous and elastic properties.

The research team determined that by adding more ingredients to the initial soapy mixture, they can create gels with unusual properties, which they call smartgels. (See Figure 2)

Shen and her lab created a gel that encapsulated glucose oxidase, or GOx, an enzyme that is frequently used in glucose test strips because it generates a measurable electric signal in response to glucose. They then showed that the gel could use a single gel scaffold to accurately sense blood glucose levels over a much wider range than current glucose sensing technology. The gel contains water, which prevents the GOx enzyme from drying out, thus stabilizing it better than current glucose test strips.

The team has been able to create the gel under room temperature and ambient pressure, both critical to maintaining GOx’s functionality. Shen also envisions that the gel could be incorporated into a patch that would sense blood glucose for days or weeks at a time. The gel has the potential to be more biocompatible than current implantable devices, which often provoke an immune response within five to seven days of use.