Nanoparticle Glue for Polymer Hydrogels and Soft Tissues

The instructions on most glues tell you to make sure the surfaces to be attached are clean and dry. But what if they are permanently wet? (Try to glue two jellyfish together!)

In many real-life situations we need to connect wet surfaces, such as polymer hydrogels and soft tissues. Polymer hydrogels consist mostly of water, with interpenetrating networks of polymer chains providing structural strength and flexibility. Although undoubtedly more complicated, human and animal tissues also have very high water content. In regenerative medicine, hydrogels are widely used as scaffolds to provide structural integrity, for drug delivery, and as barriers between tissues and material surfaces.

With a new nanoparticle glue described by a team of French scientists from École Supérieure de Physique et de Chimie Industrielles in Paris, it will be possible to reversibly connect hydrogels and soft tissues. Here is how their recent Letter to Nature, “Nanoparticle Solutions as Adhesives for Gels and Biological Tissues” describes it:

Here we show that strong, rapid adhesion between two hydrogels can be achieved at room temperature by spreading a droplet of a nanoparticle solution on one gel’s surface and then bringing the other gel into contact with it. The method relies on the nanoparticles’ ability to adsorb onto polymer gels and to act as connectors between polymer chains, and on the ability of polymer chains to reorganize and dissipate energy under stress when adsorbed onto nanoparticles […] The design principle is simple: to act as an efficient glue, the particles must be adsorbed onto the gel surface. The surface of the particles must therefore exhibit an affinity with network chains.

First, the scientists used commercially available TM-50 silica (silicon dioxide) nanoparticles solution to connect polydimethylacrylamide (PDMA) hydrogel pieces. PDMA gel has excellent affinity to silica, as was previously reported. The silica solution was applied between two strips of the gel, which were pressed together with a finger (equal to a contact pressure of 10 kPa for 30 s). Lap-shear tensile test was used to evaluate resulting adhesion (click for video). Using nanoparticles of the correct size was necessary to achieve the gluing effect:

For nanoparticles with diameters comparable with the network mesh size, several different network strands are adsorbed to the same particle. Thus, in the adhesive layer, nanoparticles act as connectors between gel pieces and gel-chains act as bridges between different particles.

As silica particles remained strongly bound to PDMA gel even in water (as was confirmed by confocal microscopy), the pieces of gel also remained strongly connected “when immersed in water and withstood a fivefold volume increase without failure.”

The adhesion created by the silica nanoparticles could be re-established after being disrupted, i.e., the pieces of the gel could be reconnected after they were peeled apart. Gels of different chemistries (such as PDMA and gelatin gel) could also be connected with silica nanoparticles.

Finally, the scientists glued strips of calf liver together using the same nanoparticle solution without any additional pretreatment or drying, which opens new perspectives for tissue engineering applications and medical products development. According to R&D Magazine:

This discovery opens up new applications and areas of research, particularly in the medical and veterinary fields and especially in surgery and regenerative medicine. It may for example be possible to use this method to glue together skin or organs having undergone an incision or a deep lesion. This method could moreover be of interest to the food processing and cosmetics industries as well as to manufacturers of prostheses and medical devices (bandages, patches, hydrogels, etc.)