Could reusable ‘jelly ice’ cubes replace regular ice?_tio2 anatase materials project
2022-05-25 05:52:42

Chemistry

Could reusable ‘jelly ice’ cubes replace regular ice?

The new ‘ice’ may provide a moldable and eco-friendly new option for chilling food and more

University of California, Davis researchers say these innovative new cooling cubes are anti-microbial and could reduce food storage cross-contamination.

Gregory Urquiaga/UC Davis

Share this:

  • Email
  • Facebook
  • Twitter
  • Pinterest
  • Reddit
  • Google Classroom
  • Print

By Katie Grace Carpenter

“Jelly” ice may one day replace the cubes chilling your cold drink. These reusable cubes trap water inside their sponge-like structure. That water can freeze but it can’t escape. Researchers at the University of California, Davis, hope their innovation may open new frontiers in food-cooling tech.

Jelly ice cubes are made of hydrogel — meaning “water-gel.”  Hydrogel sounds technical. But you’ve probably eaten hydrogel before — Jell-O. You can even freeze that popular food. But there’s a problem. Once thawed, it turns to goop.

a petri dish full of cooling cubes
These new cooling cubes could cut down on cross-contamination from meltwater. They’re also compostable and plastic-free. Gregory Urquiaga/UC Davis

Not jelly ice cubes. They can be frozen and thawed, again and again. They’re also eco-friendly. Re-using them can save water. Plus, the hydrogel is biodegradable. Unlike plastic freezer packs, at the end of their useful life, they won’t leave behind long-lived plastic waste. They’re even compostable. After about 10 uses, you can use these cubes to boost garden growth.

Finally, they may make storage of frozen food cleaner. In fact, that’s where “the original idea started,” says Luxin Wang. She’s a microbiologist on the UC Davis team. As regular ice melts, bacteria can hitch a ride in that water to other foods stored in the same place. In this way, “it can cross-contaminate,” Wang says. But the hydrogel won’t turn liquid again. After use, it can even be rinsed clean with dilute bleach.

The team described its hydrogel ice cubes in a pair of papers on November 22. The research was published in ACS Sustainable Chemistry & Engineering.

Educators and Parents, Sign Up for The Cheat Sheet

Weekly updates to help you use Science News for Studentsin the learning environment

Thank you for signing up!

There was a problem signing you up.

Icy alternative

Just like ordinary ice, hydrogel’s cooling agent is water.

Ice absorbs heat, leaving things around it colder. Think of “cold” as just the absence of heat. When holding an ice cube, it feels like cold moves into your hand from the ice. But that cold feeling really comes from the heat moving outof your hand. When ice absorbs enough heat, it melts. But in the jelly ice cubes, Wang explains, the water is “trapped in the gel structure.”

Explainer: How heat moves

The team compared its hydrogel’s ability to chill food — its “cooling efficiency” — with normal ice. First, they packed food samples into foam-insulated containers and chilled the food with jelly ice cubes or regular ice. Sensors measured changes in the food’s temperature. Normal ice worked better, but not by much. For example, after 50 minutes, the temperature of an ice-cooled sample was 3.4º Celsius (38º Fahrenheit). The gel-cooled sample was 4.4 ºC (40 ºF).

They also tested the hydrogel’s strength. Its sponge structure is made mostly of a protein called gelatin (just as in Jell-O). Hydrogels with a higher gelatin percentage were stronger but showed lower cooling efficiency. Tests revealed that hydrogels with 10 percent gelatin showed the best balance of cooling and strength.

This video shows how researchers’ new jelly ice cubes may have some advantages over normal ice.

During manufacture, jelly ice cubes can be molded into any shape. And that’s what has research, medical and food companies interested.

“We’ve gotten emails from lab managers,” Wang says. “They say, ‘That’s cool. Maybe you can make it this shape?’ And they send us pictures.”

For example, small ball shapes could be used as a chilly shipping material. Or perhaps hydrogel could be used to hold test tubes. When scientists need test tubes to stay cold outside the freezer, they often put them into a tub of ice. But maybe, Wang says, the gel instead could be fashioned into “a shape where we could put the test tubes in it.”

A work in progress

Jelly ice cubes aren’t yet ready for prime time. “This is a prototype,” Wang says. “As we move forward, there will be additional improvements.”

Price may be one downside. Compared to regular ice, “mostly [the gel] will not be cheaper,” Wang says. At least not initially. But options for cutting costs exist — such as if it’s reused many times, for example. The team is already working on that. Wang says a new study is showing better gel stability due to different types of connections being created between proteins in the gel’s sponge structure.

Another problem may be the use of gelatin itself. It’s an animal product and some people, such as vegetarians, won’t eat gelatin, says Michael Hickner. He teaches materials science at Penn State University in University Park. With these cubes, he notes, “You could get gelatin on your food that you don’t want.”

a photo of a molded red-orange desert jello on a stand
Like the new jelly ice cubes, gelatin desserts (such as Jell-O) are another example of hydrogel. But if this gelatin dessert were frozen and then thawed, it would lose its shape and become a watery mess. Victoria Pearson/DigitalVision/Getty Images Plus

Polymer scientist Irina Savina at the University of Brighton in England also has concerns. “Probably it is good to have a cooling material that doesn’t leak; I will agree with that.” But cleaning with bleach could be a problem, she says. You don’t want to get bleach in your food, but the gelatin could adsorb bleach and release it when it touches your food. She has another concern. “Gelatin itself is a food for microbes.”

Vladimir Lozinsky is a polymer scientist at the Russian Academy of Sciences in Moscow. He echoes Savina’s point. “I worry the thawed cubes could be a nutritional source for microbes,” he says — including ones that can make you sick. Even without meltwater, the cubes might still contact food directly. And that, he worries, “could be a problem.”

Hickner agrees there are problems to work out. But he also imagines possibilities for far-future applications, like “food innovation.”

Freezing food can affect its texture. Especially when it comes to something like meat, which is made of intact cells. “Freezing destroys cells by making long, knifelike ice crystals,” says Hickner at Penn State. Working out ways out to reduce damage caused by the freezing process could open up new possibilities. And in this hydrogel study, “they’ve used polymers to control the size of the ice crystals. That makes all the difference,” he says. Using a gelatin hydrogel may be a “nice environmentally friendly way to do this without using really exotic preservatives.”

The eco-friendly potential of the cubes is the “big goal,” according to Wang. The hydrogel could promote a “circular economy,” she says. “When you use up something, such as these cubes, they could go to back to the environment, with minimal footprint on the Earth.”

This is one in a series presenting news on technology and innovation, made possible with generous support from the Lemelson Foundation.

Power Words

More About Power Words

agent: A person or thing (it can be a chemical or a form of energy) that plays some role in getting something done.

application: A particular use or function of something.

bacteria: (singular: bacterium) Single-celled organisms. These dwell nearly everywhere on Earth, from the bottom of the sea to inside other living organisms (such as plants and animals). Bacteria are one of the three domains of life on Earth.

bleach: A dilute form of the liquid, sodium hypochlorite, that is used around the home to lighten and brighten fabrics, to remove stains or to kill germs. Or it can mean to lighten something permanently, such as: Being in constant sunlight bleached most of the rich coloring out of the window drapes.

cell: (in biology) The smallest structural and functional unit of an organism. Typically too small to see with the unaided eye, it consists of a watery fluid surrounded by a membrane or wall.

crystal: (adj. crystalline) A solid consisting of a symmetrical, ordered, three-dimensional arrangement of atoms or molecules. It’s the organized structure taken by most minerals. Apatite, for example, forms six-sided crystals. The mineral crystals that make up rock are usually too small to be seen with the unaided eye.

exotic: An adjective to describe something that is highly unusual, strange or foreign (such as exotic plants).

gel: A gooey or viscous material that can flow like a thick liquid.

gelatin: A substance made from animal collagen, usually bones and cow or pig hides. It starts out as a pale colored, tasteless powder. It contains proteins and amino acids. It can make jiggly desserts (like those known as Jell-O). But this substance also is used in yogurt, soups, candies and more. It can even be used as the basis of the clear capsules used to hold single-serving amounts of dry medicines.

hydrogel: A “smart” material that can change its structure in response to its environment, such as the local temperature, pH, salt or water concentration. The material is made from a polymer — a chain made from links of identical units — that have free, water-attracting ends sticking out. So in the presence of water, it may hold (bond) those water molecules for quite a while. Some hydrogels are used in baby diapers to hold urine, in potting soils to hold water near to plants until they need it and in wound dressings to keep a sore from drying out.

materials science: The study of how the atomic and molecular structure of a material is related to its overall properties. Materials scientists can design new materials or analyze existing ones. Their analyses of a material’s overall properties (such as density, strength and melting point) can help engineers and other researchers select materials that are best suited to a new application. 

meltwater: The water that comes from melting ice. The quantities can be large and show up quickly when it comes from melting glaciers, ice sheets and snow-capped mountains.

microbe: Short for microorganism. A living thing that is too small to see with the unaided eye, including bacteria, some fungi and many other organisms such as amoebas. Most consist of a single cell.

microbiologist: Scientists who study microorganisms, the infections they might cause or ways that they can interact with their environment.

polymer: A substance made from long chains of repeating groups of atoms. Manufactured polymers include nylon, polyvinyl chloride (better known as PVC) and many types of plastics. Natural polymers include rubber, silk and cellulose (found in plants and used to make paper, for example).

protein: A compound made from one or more long chains of amino acids. Proteins are an essential part of all living organisms. They form the basis of living cells, muscle and tissues; they also do the work inside of cells. Among the better-known, stand-alone proteins are the hemoglobin (in blood) and the antibodies (also in blood) that attempt to fight infections. Medicines frequently work by latching onto proteins.

sensor: A device that picks up information on physical or chemical conditions — such as temperature, barometric pressure, salinity, humidity, pH, light intensity or radiation — and stores or broadcasts that information. Scientists and engineers often rely on sensors to inform them of conditions that may change over time or that exist far from where a researcher can measure them directly.

technology: The application of scientific knowledge for practical purposes, especially in industry — or the devices, processes and systems that result from those efforts.

United Kingdom: Land encompassing the four “countries” of England, Scotland, Wales and Northern Ireland. More than 80 percent of the United Kingdom’s inhabitants live in England. Many people — including U.K. residents — argue whether the United Kingdom is a country or instead a confederation of four separate countries. The United Nations and most foreign governments treat the United Kingdom as a single nation.

vegetarian: A person who does not eat red meat (such as beef, bison or pork), poultry (such as chicken or turkey) or fish. Some vegetarians will drink milk and eat cheese or eggs. Some will eat the flesh of fish only, not mammals or birds. Vegetarians get the vast majority of each day’s calories from plant-based foods.

waste: Any materials that are left over from biological or other systems that have no value, so they can be disposed of as trash or recycled for some new use.

Citations

Journal:​ ​​J. ​Zou​ ​et​ ​al.​ ​Sustainable and reusable gelatin-based hydrogel “jelly ice cubes” as food coolant. I: Feasibilities and challenges.​ ​​ACS Sustainable Chemistry & Engineering.​ ​​Vol.​ ​9, November 22, 2021, p. 15357​. doi:​​ 10.1021/acssuschemeng.1c02853.

Journal:​ ​​J. ​Zou​ ​et​ ​al.​ ​Sustainable and reusable gelatin-based hydrogel “jelly ice cubes” as food coolant. II: Ideal freeze–thaw conditions.​ ACS Sustainable Chemistry & Engineering.​ ​​Vol.​ ​9, ​November 22, 2021, p. 15365. doi:​ ​10.1021/acssuschemeng.1c06309.

()