A net of fibers within a novel synthetic gel.
Credit: Radboud University Nijmegen.
The innards of cells boast remarkable mechanical properties, and now researchers have constructed artificial gels that mimic those qualities.
The gels could be useful in treating wounds and could even help in the development of artificial cells and tissues. These could be more closely compatible with their counterparts in humans than are currently available materials, researchers said.
The cell parts in question provide structure to cells. Just as humans possess skeletons made of bones, cells possess cytoskeletons made of filaments of protein. The width and length of these filaments can vary, giving the scaffolds they form a wide range of mechanical abilities, such as stiffening in response to force.
"As a critical stress is applied, when it is stretched to about 110 percent of its original length, the stiffness increases, and it becomes progressively more difficult to further stretch the material," researcher Paul Kouwer, a materials chemist at Radboud University Nijmegen in the Netherlands, told TechNewsDaily, "This is a good mechanism to protect the cell."
Kouwer explained that when low levels of stress are applied to a cell, it makes sense that it would remain relatively pliable, in order help detect activity in its surroundings. "At larger stresses, however, the cell should protect itself from rupture," he said.
Usually, a material's stiffness is not related to how strongly the material gets stretched. Indeed, until now, stress stiffening was absent in synthetic polymer gels.
But scientists have now created synthetic polymers that, like cytoskeletal proteins, can assemble themselves into fibers or bundles and then mesh-like networks. These novel transparent gels can imitate the mechanical properties of gels prepared from intermediate filaments. One of the components of cytoskeletons, these filaments are necessary for stress stiffening.
"We really mimic a part of the cytoskeleton, something that nature developed a long time ago," Kouwer said.
The polymers are based on short, helical strings of amino acids, the building blocks of proteins. Scientists chemically modified these polymers with other organic compounds, creating bundles only 7.5 nanometers or billionths of a meter in diameter, a little under four times the width of a double helix of DNA.
The new gel not only stiffens in response to mechanical stress, but also in response to heat — exactly the opposite of how the gelatin in Jell-O behaves. This means the gel could help in treating wounds.
"Once applied, the gel protects the wound. The microscopic structure allows fluid to pass through, but keeps bacteria out," said researcher Alan Rowan, a chemist at Radboud University Nijmegen. "Once the wound has healed, the 'plaster' can be easily removed by cooling the gel."
The molecular characteristics of the polymers control how they bundle together, and thus the resulting mechanical properties of the networks they form. With small modifications to the structure and composition of the polymers, the researchers can tailor the mechanical properties of these networks. Thus, synthetic compounds may offer greater versatility in applications than can biopolymers from life.
"We patented the materials and gels, founded a spin-off company NovioTech that is trying to commercialize this," Kouwer said.
Kouwer noted that real cytoskeletons are composed of three different kinds of proteins, which helps them cover a wide range of mechanical properties. Future research may also incorporate multiple kinds of molecules to create hybrid gels, he said.
Kouwer, Rowan and their colleagues detailed their findings online Jan. 23 in the journal Nature.