Temperature‐ and Redox‐Directed Multiple Self Assembly of Poly(N‐Isopropylacrylamide) Grafted Dextran Nanogels

Abstract

Poly(N-isopropylacrylamide) (PNIPAAm) grafted dextran nanogels with dodecyl and thiol end groups have been synthesized by RAFT process. Dodecyl-terminated polymers (DexPNI) can be readily dissolved in water and further self assemble into ordered stable nanostructures through direct noncovalent interactions at room temperature. SEM, AFM and DLS measurements confirm the formation of spherical nanogels at hundred-nanometer scales. The elevation of environment temperature will indirectly result in the formation of collapsed nanostructures due to the LCST phase transition of PNIPAAm side chains. Turbidimetry results show that the phase transition behaviors of DexPNI are greatly dependent on PNIPAAm chain length and polymer concentration: increasing PNIPAAm chain length and polymer concentration both lead to lower LCSTs and sharper phase transitions. Moreover, the dodecyl-terminated polymers can transform into thiol-terminated versions by aminolysis of trithiocarbonate groups, and further into chemical (disulfide) cross-linked versions (SS-DexPNI) by oxidation. SS-DexPNI nanogels have "doubled" chain length of PNIPAAm, and hence sharper phase transitions. In situ DLS measurements of the evolution of hydrodynamic radius attest that the self assembly of SS-DexPNI nanogels can be selectively directed by the change in either external temperature or redox potential. These nanogels thus are promising candidates for triggered intracellular delivery of encapsulated cargo. We can also expect that the polymer can be noncovalently (by dodecyl end groups) or covalently (by thiol end groups) coated on a series of nanomaterials (e.g., carbon nanotubes, graphene, gold nanomaterials) to build a variety of novel smart, and robust nanomaterials.

Recent Strategies to Develop Polysaccharide‐Based Nanomaterials for Biomedical Applications

“…A RAFT polymerization and following aminolysis has been examined. The RAFT polymerization allowed for the chain extension of PuL and DeX with poly( N ‐isopropylacrylamide) (PNIPAM), yielding PNIPAM‐grafted polysaccharides. The following aminolysis of terminal RAFT agents in the presence of a primary amine resulted in the synthesis of pendant HS‐terminated PNIPAM‐grafted polysaccharides.…”

Biohybrid nanogels

“…). Dual responsiveness of the Dex‐PNIPAM nanogels makes them useful for coating applications on different surfaces . Photoinitiated free radical polymerization of Dex‐2‐hydroxyethyl methacrylate (Dex‐HEMA) copolymerized with [2‐(methacryloyloxy) ethyl]‐trimethyl‐ammonium chloride (TMAEMA) yielded a stable crosslinked and cationic Dex‐based nanogels (Dex‐HEMA‐ co ‐TMAEMA) with a hydrodynamic diameter in the range of 200–300 nm.…”

Polymeric Nanogels with Tailorable Degradation Behavior

“…In addition to hydrogel properties such as high water content, good biocompatibility, and controlled release of payloads, the small particle size warrants the use of nanogels as an injectable colloidal drug delivery system for example intravenous therapy . Physically self‐assembled nanogels that are crosslinked exploiting hydrophobic interactions or/and hydrogen bonding have been developed, but nanogels prepared by chemical crosslinking usually have better stability . Furthermore, the use of stimulus‐sensitive crosslinks enables chemically crosslinked nanogels to respond to a certain external physical or a physiological trigger …”