Hydrogels are versatile biomaterials that are becoming increasingly prominent in the biomedical field. These water-swollen molecular networks are customizable, mimicking the physical and chemical characteristics of different organs and tissues. They are compatible with both internal and external human body applications, causing no harm to delicate anatomical parts. Currently, hydrogels are used clinically for various purposes, such as drug delivery to combat pathogens, intraocular and contact lenses, corneal prostheses in ophthalmology, bone cement, wound dressings, blood-coagulating bandages, and as 3D scaffolds in tissue engineering and regeneration. Despite these applications, a continued challenge has been the rapid and robust attachment of hydrogel polymers to each other. Traditional methods often provide weaker adhesion over extended periods and rely on complex procedures. Rapid polymer adhesion could unlock new applications like hydrogels with adjustable stiffness for better tissue conformity, encapsulation of flexible electronics for medical diagnostics, or self-adhesive wraps for challenging body parts. Now, a new bonding method that enables instant and effective adhesion of hydrogels has the potential to significantly advance new biomaterial solutions for various unmet clinical needs.

Scientists at the Wyss Institute for Biologically Inspired Engineering at Harvard (Boston, MA, USA) have developed a simple and effective technique for instant bonding of layers made of the same or different types of hydrogels and other polymeric materials. Their method uses a thin film of chitosan, a fibrous sugar-based material from shellfish outer skeletons. Chitosan films enable quick, strong hydrogel bonding through unique chemical and physical interactions, differing from traditional methods. Instead of forming covalent bonds through electron sharing, chitosan's sugar strands rapidly absorb water between hydrogel layers and intertwine with hydrogel polymers, creating multiple bonds via electrostatic interactions and hydrogen bonding (non-covalent bonds). This results in stronger adhesive forces than traditional bonding techniques.

The team applied this new method to solve several medical challenges, including localized tissue cooling, vascular injury sealing, and prevention of surgical adhesions between internal body surfaces. The range of applications emerging from this research adds a new dimension to the development of biomedical hydrogel devices, potentially offering innovative solutions for pressing challenges in regenerative and surgical medicine, and benefiting numerous patients.

“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,” said senior author and Founding Wyss Institute Core Faculty member David Mooney, Ph.D. “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.” 

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