Hydrogels are widely used in biomedical applications, but bonding them together or to other materials has been a major challenge. A new method using chitosan, a natural polymer derived from shellfish, can instantly and strongly bond hydrogels and other polymeric materials, opening new possibilities for medicine and surgery.
What are hydrogels and why are they important?
Hydrogels are three-dimensional networks of water-swollen polymers that can be tailored to mimic the mechanical and chemical features of various organs and tissues in the human body. They have many potential uses in medicine, such as delivering drugs to fight pathogens or cancer cells, healing wounds and burns, and building new tissues and organs from bio-printed cells or stem cells. Hydrogels are also safe and biocompatible, meaning they do not cause any harm or adverse reactions to the body.
However, attaching hydrogel polymers quickly and reliably to one another or to other materials, such as metals or plastics, has been difficult. Current methods are often slow, weak, or complex. For example, some methods rely on slow chemical reactions that require precise control of temperature, pH, or light. Other methods use potentially harmful substances, such as glue or sutures, that can damage the delicate hydrogels or cause inflammation or infection. These limitations have hindered the development and application of hydrogels in many biomedical areas.
How does chitosan solve this problem?
Chitosan is a fibrous sugar-based material derived from the processed outer skeletons of crustaceans, such as shrimp and crabs. Chitosan is biocompatible, biodegradable, and non-toxic, making it ideal for medical applications. Chitosan also has unique properties that allow it to bond hydrogels and other polymeric materials instantly and strongly.
The researchers at the Wyss Institute and Harvard SEAS developed a simple and effective method to bond layers of hydrogels and other polymeric materials using chitosan. They applied a thin layer of chitosan to the surfaces of the materials they wanted to connect. The chitosan layer quickly absorbed water from both materials, causing its sugar molecules to mix with the polymer molecules in the gels. This mixing created strong bonds through electrostatic forces and hydrogen bonding between different molecules. These bonds were surprisingly strong and could withstand extreme pulling forces up to 10 times higher than those achieved by conventional methods.
What are the advantages of this method?
The new method offers significant advantages over traditional methods:
- Speed: The chitosan-based approach works instantly, which is valuable in medical situations where timely intervention is crucial, such as during surgery. The researchers demonstrated that they could bond hydrogels in less than a second using this method.
- Strength: The resulting bonds are stronger than those achieved by conventional methods, which means greater reliability and durability of the bonded materials. The researchers showed that they could bond hydrogels with different stiffnesses and shapes without compromising their integrity or functionality.
- Simplicity: The process avoids the complexities of conventional methods, which often involve intricate chemical reactions or potentially harmful substances. The researchers used only water and chitosan to bond hydrogels and other polymeric materials without any additional catalysts or additives.
What are the applications of this method?
The researchers successfully applied their new approach to several unsolved medical problems, such as:
- Cooling tissues: The researchers used chitosan to bond hydrogels with embedded cooling agents to tissues that need local protection from heat damage during surgery or radiation therapy. They showed that they could cool tissues by up to 10°C using this method.
- Sealing vascular injuries: The researchers used chitosan to bond hydrogels with embedded hemostatic agents to blood vessels that need rapid sealing after injury or surgery. They showed that they could stop bleeding within seconds using this method.
- Preventing surgical adhesions: The researchers used chitosan to bond hydrogels with embedded anti-inflammatory agents to internal body surfaces that need prevention from unwanted adhesion after surgery. They showed that they could reduce adhesion formation by up to 90% using this method.
The researchers also demonstrated that they could bond different types of materials, such as hydrogels with metals or plastics, using chitosan. This could enable numerous new applications, such as:
- Tuning stiffness: The researchers showed that they could bond hydrogels with different stiffnesses to create composite materials with tunable mechanical properties. This could allow for better matching of hydrogels to specific tissues or organs.
- Encapsulating electronics: The researchers showed that they could bond hydrogels with flexible electronics to create encapsulated devices for medical diagnostics or monitoring. This could protect the electronics from water damage and the body from electrical interference.
- Creating self-adhesive wraps: The researchers showed that they could bond hydrogels with fabrics to create self-adhesive tissue wraps for hard-to-bandage parts of the body, such as fingers or toes. This could provide better wound coverage and healing.
The innovation could open new possibilities for medicine and surgery, as well as for manufacturing and engineering of complex biomaterial structures.
The findings are published in the Proceedings of the National Academy of Science .
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