This illustration highlights how two hydrogels (shown in blue) can be bonded in different ways by thin chitosan films (shown in orange). The bonds that form are extraordinarily strong and can resist high tensions. [Image courtesy of Peter Allen, Ryan Allen, and James C. Weaver]
Researchers say they created a method to bond layers made of the same or different types of hydrogels and other polymeric materials.
A team at the Wyss Institute for Biologically Inspired Engineering at Harvard University and Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) conducted this research. They created a simple, versatile method to instantly and effectively bond those layers using a thin film of chitosan. Chitosan, a fibrous, sugar-based material comes from the processed outer skeletons of shellfish.
The team successfully applied their new approach to a number of unsolved medical problems. They used it to protectively cool tissues, seal vascular injuries and prevent unwanted “surgical adhesions” of internal body surfaces that should not stick to each other. The team published their results in the Proceedings of the National Academy of Science (PNAS).
“Chitosan films with their abilities to effectively assemble, fine-tune, and protect hydrogels in the body and beyond, open numerous new opportunities to create devices for regenerative medicine and surgical care,” says senior author and founding Wyss Institute core faculty member David Mooney, “The speed, ease, and effectiveness with which they can be applied makes them highly versatile tools and components for in vivo assembly processes in often short time-windows during surgeries, and the simple fabrication of complex biomaterial structures in manufacturing facilities.”
Co-first author and former Wyss Research Associate Benjamin Freedman spearheaded “Tough Adhesives” development with Mooney. They aimed to develop a collection of regenerative medicine approaches using stretchable hydrogels. The team wanted to facilitate wound healing and tissue regeneration.
Freedman said they wanted to combine two or more hydrogels in complex assemblies in a fast, safe and simple process. Through a biomaterial screening approach, they came upon chitosan. They found that the films achieved rapid and strong bonding of hydrogels through chemical and physical interactions that are different from those involved in traditional hydrogel bonding methods.
Rather than create new chemical bonds, chitosan’s sugar strands rapidly absorb water between hydrogel layers. They entangle themselves with the polymer stands of hydrogels, forming multiple bonds. That creates adhesive forces between hydrogels that exceed those made by traditional approaches.
The researchers set out to test their method on different medical applications. They showed that the adhesives could be wrapped around cylindrical shapes like an injured finger as self-adhering bandages for improved wound care. This application also allowed the local cooling of the underlying human skin. Wyss says this could lead to alternative burn treatments.
Additionally, the team wrapped hydrogels whose surfaces were modified with thin chitosan films seamlessly around bowel, tendon and peripheral nerve tissue without bonding to the tissues themselves.
“This approach offers the possibility to effectively insulate tissues from each other during surgeries, which otherwise can form ‘fibrotic adhesions’ with sometimes devastating consequences. Their prevention is an unmet clinical need that commercial technologies cannot adequately address yet,” said Freedman.