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Cross-Linking Elastomer with Metal Ions May Yield Biomedical Breakthroughs

Image: Cornell Chronicle Elastomer cross-linked with metal ion
Seeking to develop an elastic vascular graft incorporating copper that could help repair heart tissue, researchers at Cornell University have created a framework that allows cross-linking of different metals with a polymer, yielding a range of mechanical and biomedical properties.

Seeking to develop an elastic vascular graft incorporating copper that could help repair heart tissue, researchers at Cornell University have created a framework for turning a polymer into several different elastomers by incorporating metal ions. It’s the first time anyone has demonstrated a biodegradable metal-ion elastomer, according to an article in the Cornell Chronicle.

Yadong Wang, the McAdam Family Foundation Professor of Cardiac Assist Technology in the Meinig School of Biomedical Engineering, and postdoctoral associate Ying Chen were conducting research on incorporating copper into grafts to take advantage of its angiogenetic properties, the process by which new blood vessels grow from existing ones. Mixing copper and other metal ions with polymers is a niche area of chemistry, so there was no blueprint for Chen to follow, writes Syl Kacapyr in the Chronicle. “Instead, she set out to engineer a biocompatible and biodegradable elastomer from scratch.”

Elastomer cross-linked with metal ion
The metal-ion elastomer can be stretched hundreds of times without risk of rupturing. Image courtesy Cornell Chronicle.

Chen's key breakthrough was crosslinking the polymer with copper ions using chelating ligands, molecules that tightly bind a metal ion using two or more bonds. Chelation bonds are considered to be of moderate strength in chemistry. However, elastomers have many crosslinking molecules, resulting in multiple chelating ligands working together to form a strong molecule. Moreover, because one ligand can bind multiple metal ions, the material can yield a range of mechanical properties, such as stiffness and toughness, along with biomedical properties. The copper ions could be replaced in the polymer with zinc, other metal ions, or combinations of metal ions.

As proof of concept, Chen engineered six unique elastomers using one polymer and six different metals, and then made a seventh elastomer using a calcium-magnesium mix. “It was the first time anyone had demonstrated a biodegradable metal-ion elastomer, let alone seven of them,” writes Kacapyr.

The research team also performed mechanical stress and strain tests and biocompatibility experiments on the elastomers. Their durability and biocompatibility matched the properties of conventional biomaterials.

The research is detailed in "Chelation Crosslinking of Biodegradable Elastomers," which was published on Sept. 22, 2020, in Advanced Materials.

Chen is now focusing her research on the copper-elastomer graft’s ability to repair blood vessels and heart tissue. She has expressed the hope that other engineers will use her platform to create new materials for improving soft-tissue reconstruction and regeneration.

Meanwhile, Wang sees many other applications outside of the medical space, including the production of industrial elastomers to make, for example, eco-friendly tires that biodegrade.

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