Precipitation of Iron Oxide in Hydrogel with Superparamagnetic and Stimuli-Responsive Properties

In this work, we present a template-based preparation of iron oxide-containing hydrogels (ferrogels) with ionic sensitive and superparamagnetic properties. The influence of the cross-linked template polyacrylamide and the concentration of the iron salts and sodium hydroxide on the precipitation of the iron oxide particles is investigated with respect to the stability of the ferrogels. Scanning electron microscope images show cubic particles, which can be semiquantitatively classified in three groups of particle size with respect to the dilution level. Magnetic hysteresis curves reveal a sigmoidal shape without remanence and coercivity for all samples. The higher cross-linked ferrogels, in comparison with the lower cross-linked ferrogels, possess a steady-state degree of swelling in ultrapure water and a stimuli-sensitive deswelling over a wide range of varying ionic strengths. Thus, they are suitable candidates for applications in sensing and microfluidics.

Synthesis of chitosan and N-vinylimidazole graft-copolymers and the properties of their aqueous solutions

The aim of this work is to synthesise chitosan and N-vinylimidazole graft-copolymers of various compositions and to study the properties of their aqueous solutions.Chitosan and N-vinylimidazole graft-copolymers were obtained by solution polymerisation in the presence of a ceric ammonium nitrate redox initiator. The synthesised graft copolymers were characterised by FTIR to determine their compositions and the grafted side chains of poly-N-vinylimidazole were characterised by gel permeation chromatography to determine their molecular wights and polydispersity indices. It was established that the obtained products are characterised by high values of yield and grafting efficiency and low values of the polydispersity index. It was found that when the content of the N-vinylimidazole links is above 57 wt%, the synthesised graft copolymers are water-soluble. Aqueous solutions of the obtained copolymers were characterised using dynamic light scattering, transmission electron microscopy, and laserDoppler microelectrophoresis. The study showed that macromolecules of graft copolymers in aqueous solutions have stimuli-sensitive properties with respect to the medium reaction and at a concentration above 10–2 wt% are characterised by a tendency to self-association forming core-crown aggregates, the geometry of which depends on the molecular masses of the grafted chains. Associates of macromolecules in solutions are characterised by positive values of the electrokinetic potential, the values of which also depend on the medium reaction. Thus, it was found that the ceric ammonium nitrate initiator allows obtaining chitosan and N-vinylimidazole graft-copolymers showing stimuli-sensitive properties in aqueous solutions and prone to self-association at concentrations above 10–2 wt%.

Hydrogels: 3D Drug Delivery Systems for Nanoparticles and Extracellular Vesicles

Synthetic and naturally occurring nano-sized particles present versatile vehicles for the delivery of therapy in a range of clinical settings. Their small size and modifiable physicochemical properties support refinement of targeting capabilities, immune response, and therapeutic cargo, but rapid clearance from the body and limited efficacy remain a major challenge. This highlights the need for a local sustained delivery system for nanoparticles (NPs) and extracellular vesicles (EVs) at the target site that will ensure prolonged exposure, maximum efficacy and dose, and minimal toxicity. Biocompatible hydrogels loaded with therapeutic NPs/EVs hold immense promise as cell-free sustained and targeted delivery systems in a range of disease settings. These bioscaffolds ensure retention of the nano-sized particles at the target site and can also act as controlled release systems for therapeutics over a prolonged period of time. The encapsulation of stimuli sensitive components into hydrogels supports the release of the content on-demand. In this review, we highlight the prospect of the sustained and prolonged delivery of these nano-sized therapeutic entities from hydrogels for broad applications spanning tissue regeneration and cancer treatment. Further understanding of the parameters controlling the release rate of these particles and efficient transfer of cargo to target cells will be fundamental to success.

Hydrogels Classification According to the Physical or Chemical Interactions and as Stimuli-Sensitive Materials

Hydrogels are attractive biomaterials with favorable characteristics due to their water uptake capacity. However, hydrogel properties are determined by the cross-linking degree and nature, the tacticity, and the crystallinity of the polymer. These biomaterials can be sorted out according to the internal structure and by their response to external factors. In this case, the internal interaction can be reversible when the internal chains are led by physicochemical interactions. These physical hydrogels can be synthesized through several techniques such as crystallization, amphiphilic copolymers, charge interactions, hydrogen bonds, stereo-complexing, and protein interactions. In contrast, the internal interaction can be irreversible through covalent cross-linking. Synthesized hydrogels by chemical interactions present a high cross-linking density and are employed using graft copolymerization, reactive functional groups, and enzymatic methods. Moreover, specific smart hydrogels have also been denoted by their external response, pH, temperature, electric, light, and enzyme. This review deeply details the type of hydrogel, either the internal structure or the external response. Furthermore, we detail some of the main applications of these hydrogels in the biomedicine field, such as drug delivery systems, scaffolds for tissue engineering, actuators, biosensors, and many other applications.

The Impact of Bilayer Rigidity on the Release from Magnetoliposomes Vesicles Controlled by PEMFs

Stimuli-sensitive nanocarriers have recently been developed as a powerful tool in biomedical applications such as drug delivery, detection, and gene transfer techniques. Among the external triggers investigated, low intensity magnetic fields represent a non-invasive way to remotely control the release of compounds from a magneto-sensitive carrier. Magnetoliposomes (MLs), i.e., liposomes entrapping magnetic nanoparticles (MNPs), are studied due to their capacity to transport hydrophobic and hydrophilic agents, their easy production, and due to the ability of MNPs to respond to a magnetic actuation determining the triggered release of the encapsulated compounds. Here we investigated the design and optimization of the MLs to obtain an efficient on-demand release of the transported compounds, due to the magneto-mechanical actuation induced by applying low-intensity pulsed electromagnetic fields (PEMFs). In particular we studied the effect of the bilayer packing on the ability of MLs, with oleic acid-coated MNPs encapsulated in the bilayer, to respond to PEMFs application. Three kinds of MLs are produced with an increasing rigidity of the bilayer, defined as Liquid Disorder, Liquid Order, and Gel MLs and the delivery of a hydrophilic dye (as a model drug) is investigated. Results demonstrate the efficacy of the magnetic trigger on high-ordered bilayers, which are unable to dampen the perturbation produced by MNPs motion.