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Self-assembled micro- and nanogels are frequently preparedby mixingtripolyphosphate (TPP) with dilute chitosan solutions. Upon its addition,the TPP ionically cross-links the chitosan molecules into gel-likecolloids that range from tens of nanometers to micrometers in diameter.These particles are biocompatible, mucoadhesive and, because theyare easy to prepare under very mild conditions, attract widespreadinterest in the encapsulation of drugs, neutraceuticals, and otherbioactive payloads. Despite their broad use, however, their formationmechanism has remained largely obscured by the very fast kineticsof their self-assembly. To this end, we have tuned the TPP and monovalentsalt (NaCl) concentrations to dramatically slow down this process(to occur on the time scale of days instead of milliseconds), andthen probed the evolution in the size and morphology of micro- andnanogels during their formation. This revealed that the micro- andnanogel formation rates are extremely sensitive to NaCl and TPP concentrations,and that the formation process occurs in two stages: (1) formationof small primary nanoparticles and (2) aggregation of primary particlesinto larger, higher-order colloids that are obtained at the end ofthe ionotropic gelation process. [ABSTRACT FROM AUTHOR]

Polymeric assemblies are used in many biomaterials applications, ranging from drug-bearing nanoparticles to macroscopic scaffolds. Control over their biodegradation rates is usually achieved through synthetic modification of their molecular structure. As a simpler alternative, we exploit the associative phase separation in mixtures of bioderived surfactants and polyelectrolytes. The gel fiber scaffolds are formed via phase inversion, using a homologous series of fatty acid salts-sodium caprate (NaC10), laurate (NaC12), and myristate (NaC14), and a water-soluble chitosan derivative, N-[(2-hydroxy-3-trimethylammonium)propyl] chitosan chloride (HTCC). Their dissolution times are modulated through the selection of the fatty acid molecule and vary in a predictable manner from minutes (for NaC10-HTCC), to hours (for NaC12-HTCC), to days (for NaC14-HTCC). These variations are linked to differences in surfactant-polyelectrolyte binding strength and scale with the equilibrium binding constants of their mixtures. These fibers were found to be both cytocompatible and cell-adhesive using neural stem/progenitor cells, suggesting their potential for utility in biomedical applications.