In this review, the importance of water in hydrogel (HG) properties and structure is analyzed. A variety of methods such as ¹H NMR (nuclear magnetic resonance), DSC (differential scanning calorimetry), XRD (X-ray powder diffraction), dielectric relaxation spectroscopy, thermally stimulated depolarization current, quasi-elastic neutron scattering, rheometry, diffusion, adsorption, infrared spectroscopy are used to study water in HG. The state of HG water is rather non-uniform. According to thermodynamic features of water in HG, some of it is non-freezing and strongly bound, another fraction is freezing and weakly bound, and the third fraction is non-bound, free water freezing at 0 °C. According to structural features of water in HG, it can be divided into two fractions with strongly associated and weakly associated waters. The properties of the water in HG depend also on the amounts and types of solutes, pH, salinity, structural features of HG functionalities.

Effective therapy lies in achieving a therapeutic amount of drug to the proper site in the body and then maintaining the desired drug concentration for a sufficient time interval to be clinically effective for treatment. The blood–brain barrier (BBB) hinders most drugs from entering the central nervous system (CNS) from the blood stream, leading to the difficulty of delivering drugs to the brain via the circulatory system for the treatment, diagnosis and prevention of brain diseases. Several brain drug delivery approaches have been developed, such as intracerebral and intracerebroventricular administration, intranasal delivery and blood-to-brain delivery, as a result of transient BBB disruption induced by biological, chemical or physical stimuli such as zonula occludens toxin, mannitol, magnetic heating and ultrasound, but these approaches showed disadvantages of being dangerous, high cost and unsuitability for most brain diseases and drugs. The strategy of vector-mediated blood-to-brain delivery, which involves improving BBB permeability of the drug–carrier conjugate, can minimize side effects, such as being submicrometre objects that behave as a whole unit in terms of their transport and properties, nanomaterials, are promising carrier vehicles for direct drug transport across the intact BBB as a result of their potential to enter the brain capillary endothelial cells by means of normal endocytosis and transcytosis due to their small size, as well as their possibility of being functionalized with multiple copies of the drug molecule of interest. This review provids a concise discussion of nano carriers for drug transport across the intact BBB, various forms of nanomaterials including inorganic/solid lipid/polymeric nanoparticles, nanoemulsions, quantum dots, nanogels, liposomes, micelles, dendrimers, polymersomes and exosomes are critically evaluated, their mechanisms for drug transport across the BBB are reviewed, and the future directions of this area are fully discussed.

Pore size and thickness of pore walls in macroporous polyacrylamide gels, so-called cryogels (pAAm-cryogels), were controlled by varying the content of monomers in the initial reaction mixture and the cross-linker used. The thickness of pore walls in pAAm-cryogels increased with increasing concentration of monomers in the initial reaction mixture. Pore volume in the supermacroporous pAAm-cryogels was in the range of 70–93% and decreased with increasing concentration of monomers in the reaction feed. The porous structure of the pAAm-cryogels was visualized using environmental scanning electron microscopy (ESEM) that allowed monitoring of the dehydration process in pAAm-cryogels. The accessibility of ligands covalently coupled to the polymer backbone for low molecular weight target, Cu(II) ions, and high molecular weight target, the protein lysozyme, was assessed for pAAm-cryogels produced from feeds with different monomer concentration. The amount of bound Cu(II) ions increased linearly with increasing monomer concentration in the reaction feed, suggesting that all ligands are equally accessible for small targets. On the contrary, lysozyme binding demonstrated a clear maximum at monomer concentration about 18% suggesting that only ligands present at the surface of pore walls are accessible for high molecular weight targets.