Researchers at Massachusetts Institute of Technology (MIT) and Brigham and Women's Hospital in the US loaded the gels with two antimalarial drugs.
The material could also be used to carry other types of drugs, said former MIT postdoc Angela DiCiccio, lead author of the research paper published in the journal Biomaterials. Drugs carried by this kind of material could be chewable or easier to swallow, the researchers said.
"It is really appealing for patient populations, especially children, who have difficulty with swallowing capsules and tablets," said Giovanni Traverso, a research affiliate at MIT.
Making polymer gels usually requires metal catalysts, which could be hazardous if any of the catalyst remains in the material after the gel is formed.
The MIT team wanted to come up with a new way to make gels using catalysts and starting materials that are based on food products and other materials that are safe to ingest.
"Our goal was to try to simplify the method of manufacturing and impart an improved safety profile from the beginning by using potentially safer catalysts," Traverso said.
Although caffeine has not been used for chemical synthesis before, it drew the researchers' attention because it is plant-derived and can act as a weak base, meaning that it gently removes protons from other molecules.
It also has a similar structure to some other organic weak bases that have been used to catalyse the type of chemical reaction needed to form these gels - the formation of ester bonds to create a polyester.
The researchers decided to use caffeine to induce citric acid, another edible material produced by plants, to form a polymer network along with polyethylene glycol (PEG), a biocompatible polymer that has been used in drugs and consumer products such as toothpaste for many decades.
When mixed with citric acid and PEG, and slightly heated, caffeine opens up an oxygen-containing ring in the PEG, allowing it to react with citric acid to form chains that consist of alternating molecules of PEG and citric acid.
If drug molecules are present in the mixture, they also become incorporated into the chains. The researchers showed that they could load two malaria drugs, artesunate and piperaquine, into these polymers.
They could also vary the chemical and mechanical properties of the gel by altering its composition.