Understanding Three Hydration-Dependent Transitions of Zwitterionic Carboxybetaine Hydrogel by Molecular Dynamics Simulations (original) (raw)

Water and Polymer Dynamics in Chemically Cross-Linked Hydrogels of Poly(vinyl alcohol): A Molecular Dynamics Simulation Study

The Journal of Physical Chemistry B, 2007

A topologically extended model of a chemically cross-linked hydrogel of poly(vinyl alcohol) (PVA) at high hydration degree has been developed for a molecular dynamics simulation with atomic detail at 323 K. The analysis of the 5 ns trajectory discloses structural and dynamic aspects of polymer solvation and elucidates the water hydrogen bonding and diffusion in the network. The features of local polymer dynamics indicate that PVA mobility is not affected by structural constraints of chemical junctions at the investigated crosslinking density, with a prevailing dumping effect due to water interaction. Simulation results are validated by a favorable comparison with findings of an incoherent quasi-elastic neutron scattering study of the same hydrogel system.

Molecular modeling using Molecular Dynamics and Coarse-grained models of hydrogel structural and transport properties

Chemical technology and engineering. Proceedings.2019.№1, 2019

Natural hydrogels are a specific group of functional materials, that are gaining more and more applicability in various fields. The most important ones include: medicine, tissue engineering, pharmacy, diagnostics, food industry, cosmetics as well as gardening and agriculture. In the study we show state-of-the-art molecular dynamics calculations of gelatine matrices and present methodology of relating the chemical comoposition of such structures with swelling, transport and mechanical properties. Кеуwordshydrogel, gelatin, molecular dynamics, solubility, diffusion, Young moduli.

Molecular dynamics simulation study of P (VP-co-HEMA) hydrogels: Effect of water content on equilibrium structures and mechanical properties

Biomaterials, 2009

Poly (N-vinyl-2-pyrrolidone-co-2-hydroxyethyl methacrylate) (P(VP-co-HEMA)) hydrogel system with a composition of VP:HEMA ¼ 37:13 was studied using molecular dynamics simulations in order to investigate the effect of the water content on the equilibrium structures and the mechanical properties. The degree of randomness of the monomer sequence for the random and the blocky copolymers, were 1.170 and 0.104, respectively, and the degree of polymerization was fixed at 50. The equilibrated density of the hydrogel was found to be larger for the random sequence than for the blocky sequence at low water contents (<40 wt%), but this density difference decreased with increasing water content. The pair correlation function analysis shows that VP is more hydrophilic than HEMA and that the random sequence hydrogel is solvated more than the blocky sequence hydrogel at low water content, which disappears with increasing water content. Correspondingly, the water structure is more disrupted by the random sequence hydrogel at low water content but eventually develops the expected bulk water-like structure with increasing water content. From mechanical deformation simulations, stress-strain analysis showed that the VP is found to relax more efficiently, especially in the blocky sequence, so that the blocky sequence hydrogel shows less stress levels compared to the random sequence hydrogel. As the water content increases, the stress level becomes identical for both sequences. The elastic moduli of the hydrogels calculated from the constant strain energy minimization show the same trend with the stressstrain analysis.

Probing the molecular connectivity of water confined in polymer hydrogels

The Journal of Chemical Physics, 2015

The molecular connectivity and the extent of hydrogen-bond patterns of water molecules confined in the polymer hydrogels, namely, cyclodextrin nanosponge hydrogels, are here investigated by using vibrational spectroscopy experiments. The proposed spectroscopic method exploits the combined analysis of the vibrational spectra of polymers hydrated with water and deuterated water, which allows us to separate and selectively investigate the temperature-evolution of the HOH bending mode of engaged water molecules and of the vibrational modes assigned to specific chemical groups of the polymer matrix involved in the physical interactions with water. As main results, we find a strong experimental evidence of a liquid-like behaviour of water molecules confined in the nano-cavities of hydrogel and we observe a characteristic destructuring effect on the hydrogen-bonds network of confined water induced by thermal motion. More interestingly, the extent of this temperaturedisruptive effect is found to be selectively triggered by the cross-linking degree of the hydrogel matrix. These results give a more clear picture of the molecular mechanism of water confinement in the pores of nanosponge hydrogel and open the possibility to exploit the spectroscopic method here proposed as investigating tools for water-retaining soft materials. C 2015 AIP Publishing LLC. [http://dx.

The Effect of Network Solvation on the Viscoelastic Response of Polymer Hydrogels

Polymers

The majority of investigations consider the deformation response of hydrogels, fully controlled by the deformation behavior of their polymer network, neglecting the contribution caused by the presence of water. Here, we use molecular dynamics simulation in an attempt to include the effect of physically bound water via polymer chain solvation on the viscoelastic response of hydrogels. Our model allows us to control the solvation of chains as an independent variable. The solvation of the chain is independent of other factors, mainly the effect (pH) which interferes significantly in experiments. The solvation of hydrophilic chains was controlled by setting a partial charge on the chains and quantified by the Bjerrum length (BL). The BL was calculated from the partial electric charge of the solvent and macromolecular network. When the BL is short, the repulsive Van der Waals interactions are predominant in the vicinity of macromolecules and solvation is not observed. For a long BL, the water molecules in the solvation zone of network are in the same range as attractive intermolecular forces and the solvation occurs. The model also allows the consideration of molecules of water attached to two chains simultaneously, forming a temporary bridging. By elucidating the relations between solvation of the network and structural changes during the network deformation, one may predict the viscoelastic properties of hydrogels knowing the molecular structure of its polymer chains.

Molecular dynamics in smart hydrogel systems

Journal of Non-Crystalline Solids, 2010

Intelligent hydrogels, particularly hydrolyzed polyacrylamide (PAAM) interact with their environment in a preprogrammed and intelligent manner. Since the dynamics property is critical to the applications of this material, we investigate in this study the ion exchange, between the hydrogel and its surrounding environment, induced by a chemical stimulation. Understanding the fundamental phenomena of PAAM contracting mechanisms is necessary in order to respond to emerging technology demands for high performance systems based on such materials.

Water and polymer dynamics in a model polysaccharide hydrogel: the role of hydrophobic/hydrophilic balance

Phys. Chem. Chem. Phys., 2015

The molecular dynamics of water and a polymer matrix is here explored in a paradigmatic model of a polysaccharide hydrogel, by the combined use of UV Raman scattering and infrared measurements. The case example of cyclodextrin nanosponges (CDNS)/hydrogel is chosen since the simultaneous presence in the structure of the polymer matrix of both hydrophilic and hydrophobic sites mimics the complexity of polysaccharide hydrogels. In this way, the contributions provided by the balance between the hydrophilicity/ hydrophobicity and the grade of entanglement of the polymer hydrogel to lead to the formation of the gel phase are separately accounted and evaluated. As main results, we found that the hydrophobic CH groups inserted on the aromatic ring of CDNS experience a more pronounced dynamic perturbation with respect to the carbonyl groups due to the collision between the solvent and vibrating atoms of the polymer. The overall results provide a detailed molecular picture of the swelling phenomena occurring when a chemically cross-linked polymer contacts with water or biological fluids and exploits the potentiality of UV Raman spectroscopy to retrieve dynamic information besides their structural counterpart obtained by the classical analysis of the basic features of vibrational spectra.

Rheological Properties and Solvent Structure of Polysaccharide Hydrogels Studied by Molecular Dynamics Simulations

2010

One important class of hydrogels based on natural polymers is the Glycosaminoglycan (GAG)-based hydrogels. In hydrogels biomaterial science, the mathematical modeling and computer simulation plays a complementary interpretative role in deciphering the complex physical/chemical and biological properties of this class of substances. Aim: the molecular modeling studies presented here aimed the information gathering regarding the particular molecular interactions responsible for rheological properties of this class of biomaterials. Methods: the methods included molecular dynamics simulations in t he NPT ensemble for polysaccharidic matrices, radial function analysis for the solvent and viscosity calculations using periodic strain non-equilibr ium molecular dynamics. All this methods were applied to models of 10 0%, 66% and 33% of maximum hydration compared to pure solvent simulations as control. Results and conclusions: decreasing the water content of the polymer matrix drastically affe...

Effect of monomeric sequence on transport properties of d-glucose and ascorbic acid in poly(VP-co-HEMA) hydrogels with various water contents: molecular dynamics simulation approach

Theoretical Chemistry Accounts, 2012

ABSTRACT We have used full-atomistic molecular dynamics (MD) simulations of both random and blocky sequence hydrogel networks of poly(N-vinyl-2-pyrrolidone-co-2-hydroxyethyl methacrylate) (P(VP-co-HEMA)) with a composition of VP/HEMA = 37:13 to investigate the effect of the monomeric sequence and the water content on the transport properties of ascorbic acid and d-glucose at 310.15 K. The degrees of randomness of the monomer sequence for the random and the blocky copolymers were 1.170 and 0.104, respectively, and the degree of polymerization was fixed at 50. By analyzing the pair correlation functions, it was found that for both monomeric sequences, the guest molecules (i.e., ascorbic acid and d-glucose) have greater accessibility to the VP units than to the HEMA units due to the higher hydrophilicity of VP compared to HEMA units. While the monomeric sequence effect on the P(VP-co-HEMA) hydrogel is clearly observed with 20 wt. % water content, the effect is significantly reduced with 40 wt. % water content and disappears completely with 80 wt. % water content. This is because the hydrophilic guest molecules are more likely to be associated with water molecules than with the polymer network at the high water content. By analyzing the diffusion of the guest molecules and the inner-surface area, it is also found that the guest molecules are confined in the system at 20 wt. % water content, resulting in highly anomalous sub-diffusion. Therefore, at low water content, the diffusion of the guest molecules in the hydrogel is directly affected by the monomeric sequence through the interaction of guest molecules with the monomeric units, whereas such monomeric sequence effects are significantly reduced with increasing water content.

Water–Polymer interactions in PVME hydrogels – Raman spectroscopy studies

Polymer, 2009

Raman spectroscopy was used to investigate molecular interactions and structure of water in PVME hydrogels of various crosslinking degrees. Analysis of polymer n(CH 3) and n(CH 2) stretching vibrations has allowed to monitor the changes of hydrophilic and hydrophobic polymer-water interactions in a course of water deswelling and volume phase transition. Formation of water-polymer hydrogen bonds has appeared to influence directly supramolecular structure of the absorbed water. It was found that the polymer network density determines an availability of the hydrophilic sites to water molecules and also influences the kinetics of volume phase transition of the hydrogels. Activation energy of the volume phase transition in the investigated systems was estimated to be ca.88 kJ/mol.