Design of Novel Chitosan Nanoparticles for Antimicrobial Applications

Chitin and chitosan (de-acetylated chitin) are biopolymers derived mainly from langoustine shell waste and are considered potential candidates for novel antimicrobial applications. Chitosan is soluble in weakly acidic aqueous solutions and is polycationic, which gives rise to its antimicrobial properties. We have employed computational simulations to study the binding of chitosan to two different substrates to design new composite nanoparticles with antimicrobial properties. The model substrates studied are chitin nanocrystals and silica nanoparticles. Chitin nanocrystals are stable, biocompatible and biodegradable, and silica nanoparticles have been used for medical applications for a long time and are readily available. Using fully atomistic molecular dynamics and enhanced sampling methods, we evaluated the binding energies of chitosan to the substrates and studied the dynamics of the adsorption process. We show that the adsorption of chitosan to the chitin nanocrystal surface is driven by dispersion forces and hydrogen bonding, while the adsorption to the silica surface is driven by electrostatics. Furthermore, we have simulated the development of a biopolymer film with the substrates, providing insight into the loading capacity of the nanoparticles and the availability of the chitosan to interact with its environment. Our work therefore shows how computational simulations can be used to guide the design of novel composite materials for antimicrobial applications.