Imma Perfetto
Cosmos science journalist
The humble loofah sponge is the ultimate bathroom body scrubber. The dried out fibrous skeletons of fruits in the genus Luffa are stiff and strong when dry, flexible when wet, and quick to dry which helps keep mould under control.
A new study shows that loofah-inspired materials could be just as useful out of the shower.
Chemists have developed a method to create a synthetic loofah-like membrane in the lab. The material is fine enough to filter out bacteria and viruses from liquid, and strong and light enough to form a rigid material for use in devices.
“We developed a lightweight yet mechanically robust porous polymer that resembles the fibre network of a natural loofah sponge,” says Associate Professor Yoshimitsu Itoh from the Department of Chemistry and Biotechnology at the University of Tokyo, Japan.
“Though we did not set out to create something with such an appearance, it was a pleasant surprise. So-called polymer materials like this already exist in nature, but we wanted to create something synthetic as it affords us control over its properties such that we can give it various useful functions.”
According to Itoh, one drawback of lightweight polymers is their mechanical weakness: “They tend to be very soft. Ours is low density, only half a gram of material per cubic centimetre, but has a stiffness of 11 gigapascals – for reference this is perhaps 4 times stronger than that of an ordinary polymer. This means it could be used to create devices where strength is key, without having to resort to denser, heavier and less-sustainable materials.”
He adds that producing the material is very cheap and easy.
The ingredients include pure water and a mixture of deprotonated resorcinol and an aldehyde. When a voltage is applied to the liquid the deprotonated resorcinol and aldehyde spontaneously react to form a thin layer of sponge-like, cross-linked membrane.
Applying acidic water to the polymer caused it to become more rigid, while alkaline water caused it to become less rigid. This property could be harnessed to allow a portion of material to become more, or less, porous.
“One big advantage of this membrane is that there is no need for post-processing,” says Itoh. “Usually, thin films are made by first synthesising the bulk polymer and then processing it into a film. Our method can directly give the product the form of a thin film and is, in principle, applicable to roll-to-roll processing.”
They found it was also possible to create a thin, porous carbon membrane by baking the material at 1,020°C under a vacuum.
“Thin carbon membranes are desirable for many applications; in particular, they play an important role in advanced electronics such as wearable devices, biosensors, and supercapacitors that take advantage of their potentially high flexibility, low-energy permeability, and high electronic conductivity,” the authors write in the study published in the journal Science.
Itoh says that the material could find many uses but adds that “there are many steps to take before contemplating industrial integration of any kind.”