Preparation of polymeric micelles based on chitosan bearing a small amount of highly hydrophobic groups

Controlled Deposition of Structured Polymer Films: Chemical and Rheological Factors in Chitosan Film Formation

“…[1][2][3] Because of chitosan's demonstrated ability to immobilize enzymes in scaffold electrodes 1,2,4 and to provide enzyme stabilizing chemical microenvironments, 1,2,[4][5][6][7][8][9] new information regarding the utility of the spread-coating technique to fabricate micron thin chitosan biopolymer films, in terms of its ability to control film thickness and morphology, could prove of great benefit with regards to the field of enzyme immobilization and the production of chitosan-based biofuel cell electrodes and biosensors.…”

“…[5][6][7][8][9] Although the formation of micelles depends on entropy, the structure of the micellar regions of chitosan solutions depends on the relative amounts of intra-and intermolecular chemical/electronic interactions as well as key process variables, such as polymer concentration. 3,5,6,15,16 These chemical interactions include hydrogen bonding which occurs between the hydroxyl functional groups of the polymer backbone within a particular polymer strand, between neighboring strands, and with water molecules in the solution. Hydrogen bonding and electrostatic repulsions of the polyelectrolytic backbone, along with van der Waals dispersion forces that are present between all molecules, provides the attractive and repulsive interactions that are responsible for the differences in amounts of intra-and intermolecular aggregation of the hydrophobic side chains along the chitosan backbone.…”

“…5,9 Similarly, the degree of hydrophobic substitution can become too low to catalyze inter-or intramolecular hydrophobic aggregation, or it can become so large that hydrophobic properties will dominate the interactions and the polymer will become insoluble in aqueous solutions. 3 Although independently, these variables have the aforementioned effects, when combined, they can be carefully balanced to manipulate the resultant micellar structure. For example, with long alkyl chains and a low degree of substitution, or conversely, with short alkyl chains and a high degree of substitution it is still possible to see aggregation, though they will be very different in their relative degree of intra-vs. intermolecular interactions.…”

“…3,5,6,8,15,16,21,22 This is important from the perspective that for deacetylated chitosan, an enzyme is not immobilized while in solution and in the presence of the polymer (i.e., via encapsulation), but rather while the polymer condenses around the enzyme into a solid film either through freeze or air-drying (i.e., via entrapment). 7 However, upon phase separation, hydrophobically modified chitosan shows an increase in enzyme retention in the scaffold compared to deacetylated chitosan, suggesting that increased retention is related to an interaction between the enzymes and the hydrophobic groups in solution (i.e., via encapsulation).…”

“…One possible explanation could be that the polar units are on the outside and inside of the micellar regions, with the hydrophobic groups in between them, much like a lipid bilayer, and the enzyme is on the inside surrounded by a shell of polar moieties. Although it has been reported for low molecular weight polymers and copolymers that a collapse of the intermolecular micellar structure is induced by an ordering of the crystal structure during the evaporative drying process, 3,23 the relevance of these findings to larger molecular weight polymers, such as chitosan, remains poorly understood. Consequently, a characterization of how the presence and relative concentration of solution-based unimolecular micelles and/or micellar aggregates could impact the final thickness and morphology of air-dried films for medium molecular weight deacetylated or hydrophobically modified chitosan polymer is fundamental to the advancement of chitosan polymer as an immobilization material.…”