Researchers at Harvard’s Wyss Institute have developed an ultra-strong hydrogel adhesive inspired by the glue secreted by a common slug.  The adhesive is biocompatible, flexible, and compared to the best available medical adhesives it;
     

      1) Binds to tissues with 3-times stronger tension
      2) Stretches 20-times its initial length
      3) Attaches to a variety of internal body wet and moving tissue surfaces

Adhesives for internal use in humans that can bond strongly to biological tissue and surfaces can have wide ranging biomedical applications, e.g., tissue repair, drug delivery, wound dressings, and biomedical devices. However, existing adhesives each present with their problems. For example, though cyanoacrylate (Super Glue) is the strongest class of tissue adhesive it(s):

     – Cytotoxic
     – Not effective in adhering to wet surfaces
     – Solidifies when its exposed to water
     – Forms into rigid plastic
     – Cannot accommodate dynamic movements of tissue

Also, nanoparticles with mussel-inspired adhesives do not adhere well to tissues, as their adhesion mainly relies on relatively weak physical interactions.  Other adhesives, such as the fibrin glue and polyethylene glycol–based adhesives can form covalent bonds with tissues. But their matrix toughness and adhesions’ capabilities remain weak.  Therefore, these brittle adhesives are vulnerable to debonding because of cohesive failure in the adhesive matrix.

Band-Aid® adhesive bandages are an effective tool for mitigating external bleeding from superficial skin wounds. But when surgeons need to stop internal bleeding, such a tool is yet to exist. Internal surgical glues and other materials are now often used instead of traditional wound closure techniques like stitches, staples, and clips as they reduce the patients’ time in hospital by lowering infection rates, and secondary injury/damage at the site of the internal wound.

An effective surgical glue material needs to be adaptable in diverse environments.  It needs be strong, flexible, non-toxic, and able to accommodate movement in the presence tissues, blood, organs, etc. Yet there are no such adhesives currently available that possesses all of these properties. But researchers at the Wyss Institute may have discovered one.  It’s this super-strong hydrogel adhesive that’s inspired by the glue secreted by a common slug.  Its biocompatible, flexible, and can adhere to moving tissues even in the presence of fluid, such as blood.

A team of researchers from the Wyss Institute for Biologically Inspired Engineering and the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) has created this super-strong “tough adhesive” that is biocompatible and binds to tissues with a strength comparable to the body’s own resilient cartilage, even when they’re wet. “The key feature of our material is the combination of a very strong adhesive force and the ability to transfer and dissipate stress, which have historically not been integrated into a single adhesive,” says corresponding author Dave Mooney, Ph.D., who is a founding Core Faculty member at the Wyss Institute and the Robert P. Pinkas Family Professor of Bioengineering at SEAS. 

Lead author Jianyu Li, Ph.D. (former Postdoctoral Fellow at the Wyss Institute and now an Assistant Professor at McGill University) thought of improving medical adhesives, he found a solution in an unlikely place: the Dusky Arion (Arion subfuscus) slug.  It’s common in Europe and parts of the United States, and secretes a special kind of tough sticky mucus.  When threatened, the slug secretes this glue-like mucus onto the predator.  The mucus is so strong and resilient it makes it difficult for the predator to pry itself away.

This super-strong adhesive’s predecessor utilized a single-layer polymer matrix with a positively charged surface.  This inspired Li and his colleagues to create a double-layered hydrogel instead. It consists of an alginate-polyacrylamide-chitosan polymer matrix supporting the adhesive inner adhesive layer.  that has positively-charged polymers on its surface.

The polymers bond to tissue via three mechanisms:

      1) Electrostatic attraction to negatively charged cell surfaces
      2) Covalent bonding
      3) Physical interpenetration

This added polymer matrix layer is thought to be as equally important to the functionality of the adhesive as inner layer.  Dr. Li says, “most prior material designs have focused only on the interface between the tissue and the adhesive. Our adhesive is able to dissipate energy through its matrix layer, which enables it to deform much more before it breaks.”  The design of the outer-layer matrix includes calcium ions that are bound to the hydrogel via ionic bonds. When stress is applied to the adhesive, the ionic bonds break, allowing the matrix to absorb a large amount of energy before its structure becomes compromised. In experiments, more than three-times the energy was needed to disrupt the tough adhesive’s bonding compared with other medical-grade adhesives.  When the material did break, it was the hydrogel itself, and not the bond between the adhesive and the tissue, demonstrating an unprecedented level of simultaneous high adhesion strength and matrix toughness.

Credit: Video – Wyss Institute at Harvard University