Strain-Stiffening Hydrogels with Dynamic, Secondary Cross-Linking.

Hydrogels are water-swollen, typically soft networks useful as biomaterials and in other fields of biotechnology. Hydrogel networks capable of sensing and responding to external perturbations, such as light, temperature, pH, or force, are useful across a wide range of applications requiring on-demand cross-linking or dynamic changes. Thus far, although mechanophores have been described as strain-sensitive reactive groups, embedding this type of force-responsiveness into hydrogels is unproven. Here, we synthesized multifunctional polymers that combine a hydrophilic zwitterion with permanently cross-linking alkenes, and dynamically cross-linking disulfides. From these polymers, we created hydrogels that contain irreversible and strong thiol-ene cross-links and reversible disulfide cross-links, and they stiffened in response to strain, increasing hundreds of kPa in modulus under compression. We examined variations in polymer composition and used a constitutive model to determine how to balance the number of thiol-ene vs disulfide cross-links to create maximally force-responsive networks. These strain-stiffening hydrogels represent potential biomaterials that benefit from the mechanoresponsive behavior needed for emerging applications in areas such as tissue engineering.

Heterostructures of polyaniline and Ce-ZnO nanomaterial coated flexible PET thin films for LPG gas sensing at standard environment.

The n-type Ce doped ZnO (Ce-ZnO) and p-type polyaniline (PANI) heterojunction were successfully synthesized via simple chemical solution method for sensing liquefied petroleum gas (LPG) at standard environment. The morphology and structures of as-prepared Ce-ZnO & PANI nanoparticles were analyzed by numerous kinds of techniques. Ce-ZnO & PANI nanoparticles were mixed with n-methylpyrrolidone (NMP) which is coated over the gold coated PET electrode by doctor blade method and dried overnight at 60 °C to form p-n junction. The as-formed p-n junction is to be driven with the help of 1.5 V potential at ambient temperature. X-ray photoelectron spectroscopy results of Ce-ZnO nanoparticles confirmed the existence of Ce4+ and the improved amount of both chemisorbed oxygen and oxygen vacancy after the formation of Ce-ZnO heterojunction. The maximum response of 80% was realized for hollow Ce-ZnO/PANI sensor at 100 ppm. The proposed material is a novel candidate to detect the LPG even at low (30) ppm and this study reveals the possibility of developing a potentially inexpensive hollow Ce-ZnO/PANI sensor for sensing LPG efficiently.

Bio-inspired temporal regulation of ion-transport in nanochannels.

Temporal regulation of mass transport across the membrane is a vital feature of biological systems. Such regulatory mechanisms rely on complex biochemical reaction networks, often operating far from equilibrium. Herein, we demonstrate biochemical reaction mediated temporal regulation of mass transport in nanochannels of mesoporous silica sphere. The rationally designed nanochannels with pH responsive electrostatic gating are fabricated through a hetero-functionalization approach utilizing propylamine and carboxylic acid moieties. At basic pH, cationic small molecules can diffuse into the nanochannels which release back to the solution at acidic pH. The transient ion transport is temporally controlled using a base as fuel along with esterase enzyme as the mediator. The slow enzymatic hydrolysis of a dormant deactivator (ethyl acetate) determines the lifetime of transient encapsulated state, which can be programmed easily by modulating the enzymatic activity of esterase. This system represents a unique approach to create autonomous artificial cellular models.

Supramolecular Switching of Ion-Transport in Nanochannels.

Noncovalent approaches to achieve smart ion-transport regulation in artificial nanochannels have garnered significant interest in the recent years because of their advantages over conventional covalent routes. Herein, we demonstrate a simple and generic approach to control the surface charge in mesoporous silica nanochannels by employing π-electron-rich charged motifs (pyranine-based donors) to interact with the surface of mesoporous silica modified with π-electron-deficient motifs (viologen-based acceptors) through a range of noncovalent forces, namely, charge-transfer, electrostatic, and hydrophobic interactions. The extent of each of these interactions was independently controlled by molecular design and pH, while employing them in a synergistic or antagonistic fashion to modulate the binding affinity of the charged motifs. This enabled the precise control of the surface charge of the nanochannels to achieve multiple ion-transport states.

Simple and Facile Approach To Create Charge Reversible Pores via Hydrophobic Anchoring of Ionic Amphiphiles.

Mesoporous silica-based charge reversal systems have gained significant attention in recent years due to a variety of applications such as drug delivery, dye adsorption, catalysis, chromatography, etc. Such systems often use covalent strategies to immobilize functional groups on the silica scaffold. However, lack of dynamism, modularity, and postsynthetic flexibility associated with covalent routes limit their wider applicability. Alternatively, supramolecular routes are gaining increased attention owing to their ability to overcome these limitations. Here, we introduce a simple and facile noncovalent design for a highly reversible assembly of charged amphiphiles within mesopores. Hexyl pendant groups were covalently attached to the surface to provide hydrophobic anchoring for charged amphiphiles to enable facile switching of surface charge of the mesoporous silica. These charge-switchable surfaces were used for fast and selective adsorption of dyes from aqueous solutions.