New Patchy Particle Model with Anisotropic Patches for Molecular Dynamics Simulations: Application to a Coarse-Grained Model of Cellulose Nanocrystal

Current advances of nanocellulose application in biomedical field

Nanocellulose (NC) is a natural fiber that can be extracted in fibrils or crystals form from different natural sources, including plants, bacteria, and algae. In recent years, nanocellulose has emerged as a sustainable biomaterial for various medicinal applications including drug delivery systems, wound healing, tissue engineering, and antimicrobial treatment due to its biocompatibility, low cytotoxicity, and exceptional water holding capacity for cell immobilization. Many antimicrobial products can be produced due to the chemical functionality of nanocellulose, such disposable antibacterial smart masks for healthcare use. This article discusses comprehensively three types of nanocellulose: cellulose nanocrystals (CNC), cellulose nanofibrils (CNF), and bacterial nanocellulose (BNC) in view of their structural and functional properties, extraction methods, and the distinctive biomedical applications based on the recently published work. On top of that, the biosafety profile and the future perspectives of nanocellulose-based biomaterials have been further discussed in this review.

A study across scales to unveil microstructural regimes in the multivalent metal driven self-assembly of cellulose nanocrystals

Understanding the behaviour of self-assembled systems, from nanoscale building blocks to bulk materials, is a central theme for the rational design of high-performance materials. Herein, we revealed, at different length scales, how the self-assembly of TEMPO-oxidised cellulose nanocrystals (TOCNCs) into rod fractal gels is directed by the complexation of Fe3+ ions on the surface of colloidal particles. Different specificities in Fe3+ binding on the TOCNC surface and conformational changes of the nanocellulose chain were unveiled by paramagnetic NMR spectroscopy. The macroscopic properties of systems presenting different concentrations of TOCNCs and Fe3+ ions were investigated by rheology and microscopy, demonstrating the tunability of the self-assembly of cellulose nanorods driven by Fe3+ complexation. Near-atomistic coarse-grained molecular dynamics simulations were developed to gain microscopic insight into the behaviour of this colloidal system. We found that the formation of different self-assembled architectures is driven by metal-nanocellulose complexation combined with the attenuation of electrostatic repulsion and water structuration around cellulose, leading to different microstructural regimes, from isolated nanorods to disconnected rod fractal clusters and rod fractal gels. These findings lay the foundation to unlock the full potential of cellulose nanocrystals as sustainable building blocks to develop self-assembled materials with defined structural control for a range of advanced applications.

Flow and assembly of cellulose nanocrystals (CNC): A bottom-up perspective - A review

Cellulosic sources, such as lignocellulose-rich biomass, can be mechanically or acid degraded to produce inclusions called cellulose nanocrystals (CNCs). They have several uses in the sectors of biomedicine, photonics, and material engineering because of their biodegradability, renewability, sustainability, and mechanical qualities. The processing and design of CNC-based products are inextricably linked to the rheological behaviour of CNC suspension or in combination with other chemicals, such as surfactants or polymers; in this context, rheology offers a significant link between microstructure and macro scale flow behaviour that is intricately linked to material response in applications. The flow behaviour of CNC items must be properly specified in order to produce goods with value-added characteristics. In this review article, we provide new research on the shear rheology of CNC dispersion and CNC-based hydrogels in the linear and nonlinear regime, with storage modulus values reported to range from ~10^-3 to 10³ Pa. Applications in technology and material science are also covered simultaneously. We carefully examined the effects of charge density, aspect ratio, concentration, persistence length, alignment, liquid crystal formation, the cause of chirality in CNCs, interfacial behaviour and interfacial rheology, linear and nonlinear viscoelasticity of CNC suspension in bulk and at the interface using the currently available literature.

The stoichiometric interaction model for mesoscopic MD simulations of liquid-liquid phase separation

Liquid-liquid phase separation (LLPS) has received considerable attention in recent years for explaining the formation of cellular biomolecular condensates. The fluidity and the complexity of their components make molecular simulation approaches indispensable for gaining structural insights. Domain-resolution mesoscopic model simulations have been explored for cases in which condensates are formed by multivalent proteins with tandem domains. One problem with this approach is that interdomain pairwise interactions cannot regulate the valency of the binding domains. To overcome this problem, we propose a new potential, the stoichiometric interaction (SI) potential. First, we verified that the SI potential maintained the valency of the interacting domains for the test systems. We then examined a well-studied LLPS model system containing tandem repeats of SH3 domains and proline-rich motifs. We found that the SI potential alone cannot reproduce the phase diagram of LLPS quantitatively. We had to combine the SI and a pairwise interaction; the former and the latter represent the specific and nonspecific interactions, respectively. Biomolecular condensates with the mixed SI and pairwise interaction exhibited fluidity, whereas those with the pairwise interaction alone showed no detectable diffusion. We also compared the phase diagrams of the systems containing different numbers of tandem domains with those obtained from the experiments and found quantitative agreement in all but one case.

Cellulose nanocrystals produced using recyclable sulfuric acid as hydrolysis media and their wetting molecular dynamics simulation

Cellulose nanocrystals (CNCs) were successfully produced with good nanoscales and dispersibility, using a recycled sulfuric acid (H₂SO₄) hydrolysis process. This method, at the cost of an overall 25% increase in the hydrolysis time, could significantly reduce the dosage of H₂SO₄ by approximately 40% without affecting the per-batch yield and performance of CNCs. The obtained CNCs with an average diameter of 6.0-6.5 nm and an average length of 126-134 nm, were successfully applied in the preparation of oil-in-water (O/W) Pickering emulsions via high-pressure homogenization. The emulsions exhibited good storage stability when the concentration of CNC was 1.0 wt%. Further, understanding the wetting behaviors of surface modified CNCs with solvent is critical for the functional designing of Pickering emulsion. Hence, we gained insights into the wetting of hydrophobic and hydrophilic surfaces of sulfate modified CNCs with water and organic solvent (hexadecane) droplets, using molecular dynamic simulation. The results showed that both surfaces had hydrophilic as well as lipophilic properties. Although the sulfate-grafted surface was more hydrophilic than unmodified CNC, substantial local wetting heterogeneities appeared for both solvents. It provides a deeper understanding of the interfacial interactions between modified CNCs and solvent molecules at the molecular level.

Van der Waals force-driven indomethacin-ss-paclitaxel nanodrugs for reversing multidrug resistance and enhancing NSCLC therapy

The high expression of multidrug resistance-associated protein 1 (MRP1) in cancer cells caused serious multidrug resistance (MDR), which limited the effectiveness of paclitaxel (PTX) in non-small cell lung cancer (NSCLC) chemotherapy. Indomethacin (IND), a kind of non-steroidal anti-inflammatory drugs (NSAIDs), which has been confirmed to be a potential MRP1 inhibitor. Taking into account the advantages of old drugs without extra controversial biosafety issue, in this manuscript, the disulfide bond (-S-S-) was employed for connecting IND and PTX to construct conjugate IND-S-S-PTX, which was further self-assembled and formed nanodrug (IND-S-S-PTX NPs). The particle size of IND-S-S-PTX NPs was ~160 nm with a narrow PDI value of 0.099, which distributed well in water and also exhibited a stable characteristic. Moreover, due to the existence of disulfide bond, the NPs were sensitive to the high level of glutathione (GSH) in tumor microenvironment. Molecular dynamics (MD) simulation presented the process of self-assembly in detail. Density functional theory (DFT) calculations revealed that the main driving force in self-assembly process was originated from the van der waals force. In addition, this carrier-free nano drug delivery systems (nDDs) could reverse the MDR by downregulating the expression of MRP1 protein in A549/taxol.

A Review of Cellulose Coarse-Grained Models and Their Applications

Cellulose is the most common biopolymer and widely used in our daily life. Due to its unique properties and biodegradability, it has been attracting increased attention in the recent years and various new applications of cellulose and its derivatives are constantly being found. The development of new materials with improved properties, however, is not always an easy task, and theoretical models and computer simulations can often help in this process. In this review, we give an overview of different coarse-grained models of cellulose and their applications to various systems. Various coarse-grained models with different mapping schemes are presented, which can efficiently simulate systems from the single cellulose fibril/crystal to the assembly of many fibrils/crystals. We also discuss relevant applications of these models with a focus on the mechanical properties, self-assembly, chiral nematic phases, conversion between cellulose allomorphs, composite materials and interactions with other molecules.

Molecular Dynamics Simulation of Polyacrylamide Adsorption on Cellulose Nanocrystals

Classical molecular dynamics simulations of polyacrylamide (PAM) adsorption on cellulose nanocrystals (CNC) in a vacuum and a water environment are carried out to interpret the mechanism of the polymer interactions with CNC. The structural behavior of PAM is studied in terms of the radius of gyration, atom–atom radial distribution functions, and number of hydrogen bonds. The structural and dynamical characteristics of the polymer adsorption are investigated. It is established that in water the polymer macromolecules are mainly adsorbed in the form of a coil onto the CNC facets. It is found out that water and PAM sorption on CNC is a competitive process, and water weakens the interaction between the polymer and CNC.