Design Principles of GSNO-Loaded Chitosan Nanogels Revealed by Coarse-Grained Molecular Dynamics
Autor
Neila Cristina Fonseca Machado
Co-autores
Roberta Albino dos Reis , Renan Silva Nunes , Nicolás A. García , Amedea Barozzi Seabra , Herculano da Silva Martinho
Resumo
Nitric oxide (NO) is a highly reactive signaling molecule involved in a wide range of physiological processes, including wound healing, antimicrobial activity, and vascular regulation. However, its short lifetime limits its direct application, requiring the development of efficient delivery systems. S-nitrosoglutathione (GSNO) is a biologically relevant NO donor, and chitosan–tripolyphosphate (CHT–TPP) nanogels have emerged as promising carriers. Despite extensive experimental use, the molecular mechanisms governing nanogel stability and GSNO encapsulation remain poorly understood.
In this work, we employ multi-stage coarse-grained molecular dynamics simulations within the Martini framework to investigate the structural organization, stability, and encapsulation behavior of GSNO-loaded CHT–TPP nanogels. The simulations reproduce the key stages of nanoparticle formation, including initial dispersion, ionotropic gelation, and post-assembly equilibration in aqueous media.
Our results demonstrate that multivalent TPP plays a central role in driving rapid nanoparticle formation through persistent NH3+–PO4- ionic crosslinking, leading to a dense and mechanically stable polymer network. This crosslinked scaffold remains intact upon dilution and undergoes moderate swelling, accompanied by interfacial smoothing while preserving structural integrity.
GSNO does not compete with TPP for ionic binding sites. Instead, it partitions into hydrated interstitial regions within the nanogel, where it exhibits transient and dynamically labile interactions with chitosan. Radial distribution functions and coordination analyses reveal that, although GSNO can approach protonated chitosan sites, its interactions are weaker and more diffuse compared to those of TPP. This behavior prevents GSNO from acting as a structural crosslinker and preserves its mobility within the nanogel interior.
Hydration analysis shows that the nanogel is not a collapsed hydrophobic aggregate, but rather a water-permeated, highly hydrated structure. Water molecules remain strongly associated with both chitosan and TPP, stabilizing protonation states and ionic interactions, while maintaining a polar environment around GSNO. This hydrated architecture is essential for preserving the chemical integrity of the S–NO bond and enabling controlled NO release.
Overall, this study provides a molecular-level framework linking multivalent crosslinking, hydration, and dynamic confinement to GSNO stabilization in chitosan nanogels. These findings offer mechanistic insights that complement experimental observations and establish design principles for the development of next-generation NO-delivery platforms across biomedical, dermocosmetic, and agricultural applications.
