Biomedical engineers at Texas A&M University developed a hydrogel made from nanoflakes of synthetic clay and sugar chains extracted from seaweed. The gel could act as an injectable bandage to stop internal bleeding on a battlefield, in a surgical suite, or at an accident site.
A hydrogel made from nanoflakes of synthetic clay and sugar chains extracted from seaweed could act as an injectable bandage to stop internal bleeding on a battlefield, in a surgical suite, or at an accident site.
Commercially available absorbant gauzes or gels prompt blood clotting and quickly stop bleeding when applied with pressure on external wounds. But few products can stop internal bleeding, since applying pressure is impossible when the bleeding is near vital organs.
Akhilesh Gaharwar, a biomedical engineer at Texas A&M University, and his colleagues wanted to make an injectable material that could be used to stop internal bleeding. The researchers created a hydrogel that behaves like toothpaste: it flows like a liquid when squeezed out of a syringe and solidifies once the pressure is removed.
To make this material, the researchers started with a solution of disk-shaped synthetic nanosilicates about 30 nm in diameter and 1-2 nm thick. The surface of the nanoflakes carries negative charges, while the outer edges are positively charged. These opposite charges attract each other, and the flakes self-assemble into a network that deforms under shear stress when injected through a syringe. The network reforms once the force is removed and the material exits the syringe.
By itself, this nanoflake network is too brittle on its own to be useful as a bandage near squishy organs. So the researchers added κ-carrageenan, a string of linear sulfated sugars extracted from seaweed and commonly used as a thickening or gelling agent in food. The combination of silicate nanoflakes and carragen produced a stretchy hydrogel.
“κ-Carrageenan acts as a glue to hold the nanoflake structure together,” Gaharwar says.
The researchers combined aqueous solutions of 1 percent κ-Carrageenan by weight and 2 percent nanosilicate by weight and injected the liquid into circular molds. The material recovered 80 percent of its storage modulus (which is related to the degree of crosslinking) after repeated cycles of high and low strain, indicating that shear thinning forces from a syringe would not affect its mechanical integrity and ability to form a gel. The material was strong enough to block an open wound because the stiffness of the hydrogel was five to eight times greater than human blood pressure. Its components also helped blood clot faster.
Both carrageenan and the silicate nanoflakes have highly negatively charged structures, which attracts positively charged blood proteins and platelets that form clots. Bovine blood clotted on the surface of the hydrogel in less than three minutes, about five minutes faster than its unassisted clotting time.
The hydrogel is biocompatible because it is made from materials that we already consume or are already found in our bodies, Gaharwar says. The components are also readily available and affordable. He says two companies are testing the material in large animals. If the tests go well, he hopes the material will be commercially available soon.
Gaharwar has targeted two applications for this material. Soliders, untrained in medical care, could inject this hydrogel to stop bleeding from shrapnel wounds long enough to transport someone to the hospital. Once at the hospital, doctors would remove the hydrogel and sew the wounds shut.
He also envisions adding therapeutic small molecules to the gel to speed healing after a wound is closed. The researchers tested the gel’s ability to release small molecules and speed wound healing by adding vascular endothelial growth factor (VEGF), a protein that helps stimulate blood vessel growth, to the gel. The protein sticks to the silicate nanoflakes and slowly leaches from the hydrogel.
Then they tested the ability of this molecule-loaded gel to speed wound healing. They soaked the gel in cell culture media for seven days to collect the leached protein. Then they scratched a layer of human umbilical vein endothelial cells and covered the cells with the hydrogel-soaked media. After 36 hours, the liquid from the hydrogel containing VEGF significantly increased the amount of the scratch that filled with new cells when compared to a hydrogel without VEGF.
Other experimental materials that deliver drugs to wounds release a burst of medicine, thus requiring multiple injections. This material could release the medicine more slowly. In fact, when Gaharwar tested it with a fluorescent protein, the clay-sugar gel released 40 percent of the molecules in 21 days compared to all 100 percent of the protein in four days with a conventional gel. Gaharwar pictures doctors injecting the material in an area of regenerating tissue. The blood-vessel boosting molecules would seep out of the gel, and then the hydrogel would biodegrade over time.
Melissae Fellet is an independent technology writer.
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