Nanoparticle-induced assembly of hydrophobically modified chitosan

<p>Hydrophobically modified chitosan (HMC) self-assembles in solution to form gels, making it suitable for applications in oil dispersion, hydrogel design and wound dressing. The self-assembly of HMC is driven by the association of hydrophobic moieties that are attached to chitosan monomers along the polymer chain. We present the results of discontinuous molecular dynamics simulations aimed at understanding how the length and density of the hydrophobic modification chains attached to HMC affect self-assembly and the structure of the resulting network. Long modification chains are required to promote the formation of a stable network in solution at a modification density of 5%; the networks form more readily at a modification density of 10%. The pore size distribution of the resulting HMC network is relatively independent of the modification chain length and density. Insertion of different sized hydrophobic nanoparticles into HMC has a significant impact on network formation, with the particles acting as junction points that promote the association of several HMC chains. The networks form faster in the presence of many small nanoparticles than in the presence of few large nanoparticles. We conclude that HMC could be a viable candidate to form hydrogels in solution.</p

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

A new coarse-grained (CG) model of chitosan has been developed for predicting solution behavior as a function of degree of acetylation (DA). A multiscale modeling approach was used to derive the energetic and geometric parameters of this implicit-solvent, CG model from all-atom simulations of chitosan and chitin molecules in explicit water. The model includes representations of both protonated d-glucosamine (GlcN⁺) and <i>N</i>-acetyl-d-glucosamine (GlcNAc) monomers, where each monomer consists of three CG sites. Chitosan molecules of any molecular weight, DA, and monomer sequence can be built using this new CG model. Discontinuous molecular dynamics simulations of chitosan solutions show increased self-assembly in solution with increasing DA and chitosan concentration. The chitosan solutions form larger percolated networks earlier in time as DA and concentration increase, indicating “gel-like” behavior, which qualitatively matches experimental studies of chitosan gel formation. Increasing DA also results in a greater number of monomer–monomer associations, which has been predicted experimentally based on an increase in the storage modulus of chitosan gels with increasing DA. Our model also gives insight into how the monomer sequence affects self-assembly and the frequency of interaction between different pairs of monomers