(63a) Development of a Coarse-Grained Model of Chitosan for Predicting Solution Behavior

Chitosan is a versatile biopolymer that has gained the attention of researchers in fields ranging from drug delivery and wound healing to water purification and oil spill remediation. It consists of a random sequence of glucosamine (GlcN) and N-acetylglucosamine (GlcNAc) monomers, which have drastically different properties in aqueous solution. GlcN monomers contain a primary amine that becomes protonated in solution, causing electrostatic repulsion between monomers, while GlcNAc monomers contain acetyl groups that introduce hydrophobic and hydrogen bonding interactions, leading to self-association between monomers. The amine group on GlcN can also be hydrophobically-modified to further influence its behavior in solution. We have developed a coarse-grained model of chitosan to use in designing self-assembled chitosan networks that can account for variation in the degree of acetylation (DA), charge density, and hydrophobic modification. Our results show that increasing the chitosan DA results in the formation of a percolated â??gel-likeâ? network in solution. Additionally, simulations of three different sequences of acetylated monomers (random, evenly spaced, and blocky) show that increasing the blockiness of the monomer sequence decreases the time required to form a network. The monomer sequence also affects the pore size distribution of the resulting chitosan networks, with blocky sequences leading to the largest pore sizes. We performed simulations of the diffusion of different sized particles within the chitosan networks, and showed that networks formed from evenly spaced monomer sequences (which result in the smallest pores) slow the diffusion of large particles but allow rapid diffusion of small particles. These results are being used to design chitosan hydrogels that could be used in the future to control the rate of drug release in the body. Our results also show that the addition of hydrophobic modification chains to chitosan leads to the formation of a â??gel-likeâ? network in the presence of hydrophobic particles. This indicates that hydrophobically-modified chitosan could be used as an effective additive for oil dispersants, causing oil to form a gel which could easily be removed from water following a spill.