Hydrogels consist of three-dimensionally crosslinked polymeric chains, are hydrophilic, have the ability to absorb other molecules in their structure and are relatively easy to obtain. However, in order to improve some of their properties, usually mechanical, or to provide them with some physical, chemical or biological characteristics, hydrogels have been synthesized combined with other synthetic or natural polymers, filled with inorganic nanoparticles, metals, and even polymeric nanoparticles, giving rise to composite hydrogels. In general, different types of hydrogels have been synthesized; however, in this review, we refer to those obtained from the thermosensitive polymer poly(N-vinylcaprolactam) (PNVCL) and we focus on the definition, properties, synthesis techniques, nanomaterials used as fillers in composites and mainly applications of PNVCL-based hydrogels in the biomedical area. This type of material has great potential in biomedical applications such as drug delivery systems, tissue engineering, as antimicrobials and in diagnostic and bioimaging.

Changes in some polysaccharides during postharvest ripening of ‘Kent’ mangoes were evaluated in the present study. Fruit at physiologi-cal maturity stage were stored to simulate marketing conditions (20 ± 2 °C, 85 % relative humidity) until reaching the ripening stages 2, 3, 4 and 5 (according to the standards of Empacadoras de Mango de Exportación, A. C.). Changes in firmness, starch, pectin, hemicellulose and cellulose were determined. Polysaccharides were obtained from the alcohol-insoluble fractionof the mango flesh. Fruit showed a total firmness loss of 93 % from the ripening stage 2 to 5, which was progressively reduced in 40, 44 and 9 % when the fruit reached the stages 3, 4, and 5, respectively. In that order, the rate of softening was defined as initial, intermediate, and late. During the initial fruit softening, the content of starch was reduced by 90 % and the total sugars by 44 %, while the total uronic acids increased by 39 %. The total concen-tration of arabinose was maintained without significant changes in the different ripening stages at levels of 250 mg·100 g-1 fresh weight; however, a reduction of 50 % in glucose and galactose occurred during the initial softening. The water soluble-fraction was the prevalent pectin fraction with a composition near to 2:1 in the uronide:sugar ratio. During the softening of ‘Kent’ mangoes, changes in solubility and polymerization degree of pectin and hemicellulosic polysaccharides were observed.

Different synthetic strategies were tested for the incorporation of galactose molecules on thermoresponsive nanogels owing to their affinity for receptors expressed in cancer cells. Three families of galactose-functionalized poly(N-vinylcaprolactam) nanogels were prepared with the aim to control the introduction of galactose-moieties into the core, the core-shell interface and the shell. First and second of the above mentioned, were prepared via surfactant free emulsion polymerization (SFEP) by a free-radical mechanism and the third one, via SFEP/reversible addition-fragmentation chain transfer (RAFT) polymerization. Synthetic recipes for the SFEP/free radical method included besides N-vinylcaprolactam (NVCL), a shell forming poly(ethylene glycol) methyl ether methacrylate (PEGMA), while the galactose (GAL) moiety was introduced via 6-O-acryloyl-1,2,:3,4-bis-O-(1-methyl-ethylidene)-α-_D-galactopiranose (6-ABG, protected GAL-monomer): nanogels I, or 2-lactobionamidoethyl methacrylate (LAMA, GAL-monomer): nanogels II. For the SFEP/RAFT methodology poly(2-lactobionamidoethyl methacrylate) as GAL macro-chain transfer agent (PLAMA macro-CTA) was first prepared and on a following stage, the macro-CTA was copolymerized with PEGMA and NVCL, nanogels III. The crosslinker ethylene glycol dimethacrylate (EGDMA) was added in both methodologies for the polymer network construction. Nanogel’s sizes obtained resulted between 90 and 370 nm. With higher content of PLAMA macro-CTA or GAL monomer in nanogels, a higher the phase-transition temperature (T_VPT) was observed with values ranging from 28 to 46 °C. The ρ-parameter, calculated by the ratio of gyration and hydrodynamic radii from static (SLS) and dynamic (DLS) light scattering measurements, and transmission electron microscopy (TEM) micrographs suggest that core-shell nanogels of flexible chains were obtained; in either spherical (nanogels II and III) or hyperbranched (nanogels I) form.