Tailoring Hydrogel Adhesion to Polydimethylsiloxane Substrates Using Polysaccharide Glue

Strong Anchoring of Hydrogels through Superwetting-Assisted High-Density Interfacial Grafting

Strong adhesion of hydrogels on solids plays an important role in stable working for various practical applications. However, current hydrogel adhesion suffers from poor interfacial bonding with solid surfaces. Here, we propose a general superwetting-assisted interfacial polymerization (SAIP) strategy to robustly anchor hydrogels onto solids by forming high-density interfacial covalent bonds. The key of our strategy is to make the initiator fully contact solid surfaces via a superwetting way for enhancing the interfacial grafting efficiency. The designed anchored hydrogels show strong bulk failure with a high breaking strength of ≈1.37 MPa, different from weak interfacial failure that occurs in traditional strategies. The strong interfacial adhesion greatly enhances the stability of hydrogels against swelling destruction. This work opens up new inspirations for designing strongly anchored hydrogels from an interfacial chemistry perspective.

Electrochemical Bonding of Hydrogels at Rigid Surfaces

Flexible hydrogels can be chemically/physically bonded on soft surfaces. However, there is a lack of a facile method to build strong interfacial adhesion between hydrogel and various rigid surfaces. Herein, an electrochemical bonding protocol, which improves the interfacial adhesion energy of hydrogel from initial 8 to 3480 J m^-2 , ≈435 times enhancement at rigid glass surface, superior to the most of traditional methods, is proposed. A series of electrochemical bonding models to analyze the bonding mechanism, is demonstrated. The results indicate that the electrode reactions generate Fe³⁺ ions at the anode and OH^- ions at the cathode, which migrate and react to form nanoparticles of Fe(OH)₃ . These nanoparticles form hump-like physical structures at the interface and work as mechanical-bonding sites, enabling the strong interfacial adhesion. Upon applying acidic solution to decompose the nanoparticles, the strong adhesion can be weakened to easily remove hydrogel from the bonded surface. The electrochemically-bonded hydrogel can maintain its adhesion in water, which enables the electrochemical bonding of hydrogels for repairing various damaged surfaces such as plastic water tubes/bags, indicating promising potential for adhesive engineering applications.

Adaptive and multifunctional hydrogel hybrid probes for long-term sensing and modulation of neural activity

To understand the underlying mechanisms of progressive neurophysiological phenomena, neural interfaces should interact bi-directionally with brain circuits over extended periods of time. However, such interfaces remain limited by the foreign body response that stems from the chemo-mechanical mismatch between the probes and the neural tissues. To address this challenge, we developed a multifunctional sensing and actuation platform consisting of multimaterial fibers intimately integrated within a soft hydrogel matrix mimicking the brain tissue. These hybrid devices possess adaptive bending stiffness determined by the hydration states of the hydrogel matrix. This enables their direct insertion into the deep brain regions, while minimizing tissue damage associated with the brain micromotion after implantation. The hydrogel hybrid devices permit electrophysiological, optogenetic, and behavioral studies of neural circuits with minimal foreign body responses and tracking of stable isolated single neuron potentials in freely moving mice over 6 months following implantation.

Humidity- and Sunlight-Driven Motion of a Chemically Bonded Polymer Bilayer with Programmable Surface Patterns

We report a bilayer of sodium alginate/polyvinylidene fluoride (SA/PVDF) that is chemically bonded through a series of interfacial coupling reactions. The SA layer is hydrophilic in structure and is capable of strong interaction with water molecules, thus presenting high sensitivity to humidity, whereas the PVDF layer is hydrophobic, inert to humidity. This structural feature results in the bilayer having asymmetric humidity-responsive performances that can thus make its shape change with directionality, which cannot be achieved in an SA single layer. The responsive process to humidity can be adjusted by exposure of the bilayer to sunlight by means of a photothermal effect that accelerates dehydration of the bilayer to cause more rapid shape deformations. When the sunlight is removed, the bilayer adsorbs humidity again and returns to its original shape, indicating good reversibility. To exactly regulate the shape deformations of the bilayer with external stimuli, we employ Ca²⁺-treated filter paper to customize crosslinking reactions in the SA layer as desired patterns which are capable of causing different mechanical tensors and swellabilities in the bilayer so as to regulate and control the actuations for self-folding, curling, twisting, and coiling in response to sunlight and humidity.On the other hand, the chemically bonded bilayer has stronger interfacial toughness and is capable of reaching 300 J m^-2, which is around 12 times the interfacial toughness of the physically combined bilayer; as a result, the chemically bonded bilayer is capable of sustaining continuous shape deformations without interfacial failure. The directionally mechanical actuations can be utilized in designing an indicator to roughly indicate the range of intensity of sunlight by coupling the chemically bonded bilayer into a typical electric circuit, in which the range of intensity of sunlight can be easily estimated by visual observation of the light-emitting diodes.

A pH, glucose, and dopamine triple-responsive, self-healable adhesive hydrogel formed by phenylborate–catechol complexation

A pH, glucose, and dopamine triple-responsive, self-healable and adhesive polyethylene glycol hydrogel was developed via the formation of phenylborate–catechol complexation.