Molecular Dynamics of a Water-Absorbent Nanoscale Material Based on Chitosan

Although
hydrogels have been widely investigated for their use
in materials science, nanotechnology, and novel pharmaceuticals, mechanistic
details explaining their water-absorbent features are not well understood.
We performed an all-atom molecular dynamics study of the structural
transformation of chitosan nanohydrogels due to water absorption.
We analyzed the conformation of dry, nanoscaled chitosan, the structural
modifications that emerge during the process of water inclusion, and
the dynamics of this biopolymer in the presence of nature’s
solvent. Two sets of nanoscaled, single-chained chitosan models were
simulated: one to study the swelling dependence upon the degree of
self-cross-linking and other to observe the response with respect
to the degree of protonation. We verified that nanohydrogels keep
their ability to absorb water and grow, regardless of their degree
of cross-linking. Noteworthy, we found that the swelling behavior
of nanoscaled chitosan is pH-dependent, and it is considerably more
limited than that of larger scale hydrogels. Thus, our study suggests
that properties of nanohydrogels are significantly different from
those of larger hydrogels. These findings might be important in the
design of novel controlled-release and targeted drug-delivery systems
based on chitosan.