16.01.2014

Nanoparticle solutions as adhesives for gels and biological tissues

Journal name:

Nature

Volume:

505,

Pages:

382–385

Date published:

(16 January 2014)

DOI:

doi:10.1038/nature12806

Received

06 May 2013

Accepted

24 October 2013

Published online

11 December 2013

Adhesives are made of polymers¹ because, unlike other materials, polymers ensure good contact between surfaces by covering asperities, and retard the fracture of adhesive joints by dissipating energy under stress^{2, 3}. But using polymers to ‘glue’ together polymer gels is difficult, requiring chemical reactions, heating, pH changes, ultraviolet irradiation or an electric field^{4, 5, 6, 7}. 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. We demonstrate this approach by pressing together pieces of hydrogels, for approximately 30 seconds, that have the same or different chemical properties or rigidities, using various solutions of silica nanoparticles, to achieve a strong bond. Furthermore, we show that carbon nanotubes and cellulose nanocrystals that do not bond hydrogels together become adhesive when their surface chemistry is modified. To illustrate the promise of the method for biological tissues, we also glued together two cut pieces of calf’s liver using a solution of silica nanoparticles. As a rapid, simple and efficient way to assemble gels or tissues, this method is desirable for many emerging technological and medical applications such as microfluidics, actuation, tissue engineering and surgery.

Figures

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Figure 1: Gluing gels by nanoparticle solutions.

a, Schematic illustration of the concept of gluing swollen polymer networks together using particles. The nanoparticle diameter is comparable with the gel network mesh size. Network chains are adsorbed on nanoparticles and anchor particles to gel pieces. Particles act as connectors between gel surfaces. Adsorbed chains also form bridges between particles. The black arrows indicate the pressure applied to squeeze the gel layers together. b, Particle adsorption is irreversible because particles are anchored to the gel networks by numerous attachments (red, light- and dark-blue strands). At equilibrium or under tension (indicated by black arrows) a monomer that detaches from a particle surface (red strand) can be replaced by a monomer belonging to the same or a different network strand (shown here as a dark-blue strand). Such exchange processes and rearrangements allow for large deformations and energy dissipation under stress.

Figure 2: Lap-shear adhesion tests.

a, Lightly crosslinked S0.1 gels stick to the table surface and to gloves but they do not stick to themselves. b, By spreading a drop of TM-50 silica solution on the gel surface, two gel pieces are glued together after being brought into contact for few seconds. c, The glued lap joint is able to sustain large deformations. d, The failure force measured by the lap-shear adhesion test for lap joints of various overlap length. Red circles indicate fracture outside the joint; blue squares indicate interfacial failure by peeling. e, Failure force, F, normalized by the width of the joint, w, for lap joints glued using solutions of various particles. Red bars indicate fracture outside the joint; blue bars indicate failure by peeling (mean; error bars are s.d.). f, Adhesion energy G_adh (in blue) measured by the lap-shear test and fracture energy G_c (in red) measured by the single-edge notch tensile test for PDMA gels of various crosslinking densities (mean; errors bars are s.d.).

Figure 3: Water-resistant and self-repairing glue.