The copolymer nanogels composed of two N-substituted acrylamides with different water solubility, N-isopropylacrylamide (NIPAM, water-soluble) and N-t-butylacrylamide (TBAM, water-insoluble), were prepared by free-radical polymerization in the presence of sodium dodecyl sulfate (SDS) as a dispersant and found to exhibit thermogelling ability at very low concentrations. To investigate the structure of the P(NIPAM-TBAM) nanogel and its formation mechanism in dispersion polymerization, we prepared the nanogels by changing the conditioning time, which is the time between the addition of SDS to the monomer solution and the start of polymerization, and compared the thermogelling properties of the resultant nanogels. As the conditioning time increased, (i) the hydrodynamic diameter of the nanogel decreased, (ii) the sol–gel and gel-syneresis transition temperatures of the nanogel dispersion decreased, and (iii) the storage moduli of the nanogel dispersion in a gel state increased. These results indicate that the P(NIPAM-TBAM) nanogel has a block-like structure composed of the TBAM-rich brushes and the NIPAM-rich core with three-dimensional polymer network, and that the TBAM ratio in the brushes increases with an increase in the conditioning time.

It should be noted that the critical gelation concentration of the P(NIPAM-TBAM) nanogel dispersion was very low (∼1.3 wt%), compared with other thermogelling polymers reported in literatures. This low gelation concentration can be attributed to the gel structure of the nanogel core because the NIPAM-rich core can retain water inside even when the TBAM-rich brushes are dehydrated and crosslink with each other to induce gelation of the system.Nanogels have gained great attention as delivery systems of drugs and bioactive food compounds due to their high surface area, swelling behavior, loading capacity, softness, and flexibility, that simulate the nature of most natural tissues. On its part, fucoidan is a marine polysaccharide obtained from brown seaweed, and it has a broad spectrum of biological activities, including anticancer effects. In this review, the theoretical framework of fucoidan, such as sources, extraction, and purification is described and discussed. Furthermore, the structural and bioactive roles of fucoidan in the preparation of these nanoplatforms are highlighted, and future opportunities for this polysaccharide in these innovative nanoplatforms are outlined in the concluding remarks.

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Jenny
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Journal of Nano Research & Applications