Hydrogels as potential drug-delivery systems: network design and applications

Hydrogels are 3D crosslinked polymer matrices having a colossal tendency to imbibe water and exhibit swelling under physiological conditions without deformation in their hydrophilic network. Hydrogels being biodegradable and biocompatible, gained consideration due to some unique characteristics: responsiveness to external stimuli (pH, temperature) and swelling in aqueous solutions. Hydrogels offer a promising option for various pharmaceutical and biomedical applications, including tissue-specific drug delivery at a predetermined, controlled rate. This article presents a brief review of the recent and fundamental advances to design hydrogels, the swelling and deswelling mechanism, various crosslinking methods and their use as an intelligent carrier in the pharmaceutical field. Recent applications of hydrogels are also briefly discussed and exemplified.

Self-Adhesive Hydrogels for Tissue Engineering

Hydrogels consisting of a three-dimensional hydrophilic network of biocompatible polymers have been widely used in tissue engineering. Owing to their tunable mechanical properties, hydrogels have been applied in both hard...

Oxidation Assisted Fabrication of Sterculia Gum/Protein Hybrid Hydrogel Networks through Schiff Base Formation: Characterization and Swelling Kinetic Studies

Polysaccharide/protein hybrid conjugate system becomes an emerging system with integrated characteristics of protein as well as polysaccharide to be exploited for recent advancements in biomedical sectors. Present study is an attempt to fabricate a sterculia gum/gelatin hybrid hydrophilic network system via Schiff base formation using oxidative route at ambient conditions. This route transforms hydrogel synthesis through green mode without employing any crosslinking systems so as to minimize the toxicity issues associated. Fabricated Schiff base based gel systems have been characterized by FT-IR, powdered XRD, FESEM and EDX to confirm the inclusion of new characteristics, morphological changes and functionalization. Oxidation of natural gum drastically alter the physico-chemical behaviour of the gum as confirmed by powdered XRD by incorporating crystalline nature of oxidized sterculia gum as compared to the native sterculia gum and the Schiff base formed. The changes observed are due to the chemical modification of sterculia gum during Schiff base formation. Further the swelling capacity of oxidized sterculia gum and crosslinked network formed is also modulated and was less as compared to native sterculia gum and gelatin. This article also elaborates the mechanistic changes which take place during oxidative route of hydrogel formation in various segments of sterculia gum during oxidation and Schiff base formation.

Poly(N,N′-Diethylacrylamide)-Based Thermoresponsive Hydrogels with Double Network Structure

Temperature response of double network (DN) hydrogels composed of thermoresponsive poly(N,N′-diethylacrylamide) (PDEAAm) and hydrophilic polyacrylamide (PAAm) or poly(N,N′-dimethylacrylamide) (PDMAAm) was studied by a combination of swelling measurements, differential scanning calorimetry (DSC) and 1H NMR and UV-Vis spectroscopies. Presence of the second hydrophilic network in DN hydrogels influenced their thermal sensitivity significantly. DN hydrogels show less intensive changes in deswelling, smaller enthalpy, and entropy changes connected with phase transition and broader temperature interval of the transition than the single network (SN) hydrogels. Above the transition, the DN hydrogels contain significantly more permanently bound water in comparison with SN hydrogels due to interaction of water with the hydrophilic component. Unlike swelling and DSC experiments, a rather abrupt transition was revealed from temperature-dependent NMR spectra. Release study showed that model methylene blue molecules are released from SN and DN hydrogels within different time scale. New thermodynamical model of deswelling behaviour based on the approach of the van’t Hoff analysis was developed. The model allows to determine thermodynamic parameters connected with temperature-induced volume transition, such as the standard change of enthalpy and entropy and critical temperatures and characterize the structurally different states of water.

A Modular and Practical Synthesis of Zwitterionic Hydrogels through Sequential Amine-Epoxy “Click” Chemistry and N-Alkylation Reaction

In this work, the amine-epoxy “click” reaction is shown to be a valuable general tool in the synthesis of reactive hydrogels. The practicality of this reaction arises due to its catalyst-free nature, its operation in water, and commercial availability of a large variety of amine and epoxide molecules that can serve as hydrophilic network precursors. Therefore, hydrogels can be prepared in a modular fashion through a simple mixing of the precursors in water and used as produced (without requiring any post-synthesis purification step). The gelation behavior and final hydrogel properties depend upon the molecular weight of the precursors and can be changed as per the requirement. A post-synthesis modification through alkylation at the nitrogen atom of the newly formed β-hydroxyl amine linkages allows for functionalizing the hydrogels. For example, ring-opening reaction of cyclic sulfonic ester gives rise to surfaces with a zwitterionic character. Finally, the established gelation chemistry can be combined with soft lithography techniques such as micromolding in capillaries (MIMIC) to obtain hydrogel microstructures.

Bio-inspired Ni2+-polyphenol hydrophilic network to achieve unconventional high-flux nanofiltration membranes for environmental remediation

A Ni2+-polyphenol network was synthesized as a hydrophilic coating to achieve highly efficient nanofiltration membranes with an unconventional high flux for dye wastewater remediation.

UF membrane with highly improved flux by hydrophilic network between graphene oxide and brominated poly(2,6-dimethyl-1,4-phenylene oxide)

PEI–GO/BPPO membranes with highly rough surfaces and hydrophilic cross-linking networks are formed by PEI–GO covalent bonded with BPPO.