The novel cellulose aerogels are nearly as light as air. Photo: Andrew Marais.
The novel cellulose aerogels are nearly as light as air. Photo: Andrew Marais.

A new low-cost and sustainable synthesis technique could expand the opportunities for hospitals and clinics to deliver therapeutics with aerogels, a foam-like material now found in high-tech applications such as insulation for spacesuits and breathable plasters.

With the help of an ordinary kitchen freezer, this newest form of aerogel was made from all-natural ingredients, including plant cellulose and algae, says Jowan Rostami, a researcher in fiber technology at KTH Royal Institute of Technology in Stockholm, Sweden. The aerogel's low density and favorable surface area make it ideal for a wide range of uses, including timed release of medication and wound dressing. Rostami, together with colleagues at KTH and Lund University in Sweden, reports this new aerogel in a paper in Materials Today.

The aerogel's density can be pushed down to as low as 2kg per cubic meter, which Rostami and her colleagues believe is among the lowest recorded densities for similar materials. "To give you an idea of how light that is – the density of air is 1.23kg per cubic meter," she says.

To demonstrate that the material can be used for controlled delivery of therapeutics, the researchers attached proteins to the aerogel via a water-based self-assembly process. "The aerogel is designed for biointeractivity, so it can for example be used to treat wounds or other medical problems," Rostami explains.

With an air volume of up to nearly 99.9%, aerogels are super-lightweight yet durable (the KTH aerogel is nearly 99% air). They have been used in a wide range of products since the mid-20th century, from skin care to paint, and numerous materials for building construction. Technical advances have recently allowed aerogels to be produced from the cellulose nanofibrils in plant cells, and these aerogels have generated interest for environmental applications such as water purification and home insulation.

The usual process for synthesizing nanocellulose-based aerogels involves dispersing the cellulose nanofibrils in water and then drying out the mixture. But the steps required to do this are energy-intensive and time-consuming, in part because they require freeze drying or critical-point drying with carbon dioxide gas.

"We use a sustainable approach instead," Rostami says. "It's simple yet sophisticated."

The nanofibrils are mixed in water with alginate – a naturally occurring polymer derived from seaweed – and then calcium carbonate is added. In the freezer, the water turns to ice and compresses these components together, producing a frozen hydrogel.

This frozen hydrogel is removed from the freezer and placed in acetone. Not only does the acetone remove the water and evaporate quickly, but by adding a bit of acid, it also dissolves the calcium carbonate particles, thereby releasing carbon dioxide bubbles that make the material more porous.

The dissolution of calcium carbonate produces yet another benefit: it releases calcium ions that crosslink with the alginate and cellulose nanofibrils, giving the aerogel wet-stability and the ability to recover its shape after being suffused with liquid.

Rostami says this quality further adds to the aerogel's usefulness in a greater range of applications, "without using costly, time and energy-consuming processes, toxic chemicals or complicated chemistry".

This story is adapted from material from KTH Royal Institute of Technology, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.