Molecular dynamics and experimental study of conformation change of poly(N-isopropylacrylamide) hydrogels in mixtures of water and methanol.

The conformation transition of poly(N-isopropylacrylamide) hydrogel as a function of the methanol mole fraction in water/methanol mixtures is studied both experimentally and by atomistic molecular dynamics simulation with explicit solvents. The composition range in which the conformation transition of the hydrogel occurs is determined experimentally at 268.15, 298.15, and 313.15 K. In these experiments, cononsolvency, i.e., collapse at intermediate methanol concentrations while the hydrogel is swollen in both pure solvents, is observed at 268.15 and 298.15 K. The composition range in which cononsolvency is present does not significantly depend on the amount of cross-linker. The conformation transition of the hydrogel is caused by the conformation transition of the polymer chains of its backbone. Therefore, conformation changes of single backbone polymer chains are studied by massively parallel molecular dynamics simulations. The hydrogel backbone polymer is described with the force field OPLS-AA, water with the SPC/E model, and methanol with the model of the GROMOS-96 force field. During simulation, the mean radius of gyration of the polymer chains is monitored. The conformation of the polymer chains is studied at 268, 298, and 330 K as a function of the methanol mole fraction. Cononsolvency is observed at 268 and 298 K, which is in agreement with the present experiments. The structure of the solvent around the hydrogel backbone polymer is analyzed using H-bond statistics and visualization. It is found that cononsolvency is caused by the fact that the methanol molecules strongly attach to the hydrogel's backbone polymer, mainly with their hydroxyl group. This leads to the effect that the hydrophobic methyl groups of methanol are oriented toward the bulk solvent. The hydrogel+solvent shell hence appears hydrophobic and collapses in water-rich solvents. As more methanol is present in the solvent, the effect disappears again.

[1]  H. A. El-Rehim,et al.  Swelling of radiation crosslinked acrylamide-based microgels and their potential applications , 2005 .

[2]  T. Straatsma,et al.  THE MISSING TERM IN EFFECTIVE PAIR POTENTIALS , 1987 .

[3]  T. Darden,et al.  A smooth particle mesh Ewald method , 1995 .

[4]  W. L. Jorgensen,et al.  The OPLS [optimized potentials for liquid simulations] potential functions for proteins, energy minimizations for crystals of cyclic peptides and crambin. , 1988, Journal of the American Chemical Society.

[5]  Hans Hasse,et al.  Molecular dynamics and experimental study of conformation change of poly(N-isopropylacrylamide) hydrogels in water , 2010 .

[6]  R. Hockney,et al.  Quiet high resolution computer models of a plasma , 1974 .

[7]  F. Tanaka,et al.  Temperature-responsive polymers in mixed solvents: competitive hydrogen bonds cause cononsolvency. , 2008, Physical review letters.

[8]  B. Vincent,et al.  Swelling behavior of poly- N-isopropylacrylamide microgel particles in alcoholic solutions , 1998 .

[9]  Hans Hasse,et al.  Hydrogen bonding of methanol in supercritical CO2: comparison between 1H NMR spectroscopic data and molecular simulation results. , 2007, The journal of physical chemistry. B.

[10]  S. Enders,et al.  Influence of different alcohols on the swelling behaviour of hydrogels , 2012 .

[11]  Carsten Kutzner,et al.  GROMACS 4:  Algorithms for Highly Efficient, Load-Balanced, and Scalable Molecular Simulation. , 2008, Journal of chemical theory and computation.

[12]  Wouter Olthuis,et al.  An efficient method for the fabrication of temperature-sensitive hydrogel microactuators. , 2004, Lab on a chip.

[13]  A. Khademhosseini,et al.  Hydrogels in Regenerative Medicine , 2009, Advanced materials.

[14]  K Schulten,et al.  VMD: visual molecular dynamics. , 1996, Journal of molecular graphics.

[15]  F. Tanaka,et al.  Temperature- and Tension-Induced Coil-Globule Transition of Poly(N-isopropylacrylamide) Chains in Water and Mixed Solvent of Water/Methanol , 2009 .

[16]  Howard G. Schild,et al.  Cononsolvency in mixed aqueous solutions of poly(N-isopropylacrylamide) , 1991 .

[17]  Chi Wu,et al.  LLS and FTIR Studies on the Hysteresis in Association and Dissociation of Poly(N-isopropylacrylamide) Chains in Water , 2006 .

[18]  Jing Ma,et al.  Solvation behaviors of N-isopropylacrylamide in water/methanol mixtures revealed by molecular dynamics simulations. , 2010, The journal of physical chemistry. B.

[19]  Thomas Ertl,et al.  Eurographics/ Ieee-vgtc Symposium on Visualization 2010 Coherent Culling and Shading for Large Molecular Dynamics Visualization , 2022 .

[20]  W. L. Jorgensen,et al.  Development and Testing of the OPLS All-Atom Force Field on Conformational Energetics and Properties of Organic Liquids , 1996 .

[21]  H. Berendsen,et al.  Molecular dynamics with coupling to an external bath , 1984 .

[22]  G. Demirel,et al.  Network parameters and volume phase transition behavior of poly(N-isopropylacrylamide) hydrogels , 2006 .

[23]  Sung Wan Kim,et al.  Swelling of poly(N-isopropylacrylamide) gels in water-alcohol (C1-C4) mixed solvents , 1993 .

[24]  K. Tobita,et al.  Synthesis, characterization and therapeutic efficacy of a biodegradable, thermoresponsive hydrogel designed for application in chronic infarcted myocardium. , 2009, Biomaterials.

[25]  H. Ringsdorf,et al.  Methanol-water as a co-nonsolvent system for poly(N-isopropylacrylamide) , 1990 .

[26]  G. Maurer,et al.  Phase equilibria of hydrogel systems , 2002 .

[27]  Toyoichi Tanaka,et al.  Reentrant phase transition of N‐isopropylacrylamide gels in mixed solvents , 1987 .

[28]  Thomas Ertl,et al.  Interactive Exploration of Polymer-Solvent Interactions , 2011, VMV.

[29]  M. Heskins,et al.  Solution Properties of Poly(N-isopropylacrylamide) , 1968 .

[30]  Erhan Pişkin,et al.  Functional copolymers of N-isopropylacrylamide for bioengineering applications , 2007 .

[31]  M. Parrinello,et al.  Canonical sampling through velocity rescaling. , 2007, The Journal of chemical physics.

[32]  Gerrit Groenhof,et al.  GROMACS: Fast, flexible, and free , 2005, J. Comput. Chem..

[33]  N. Peppas,et al.  Hydrogels in Pharmaceutical Formulations , 1999 .

[34]  Mauro Ferrario,et al.  Molecular-dynamics simulation of liquid methanol , 1987 .

[35]  E. A. Sosnov,et al.  New silicone hydrogels based on interpenetrating polymer networks comprising polysiloxane and poly(vinyl alcohol) networks , 2009 .

[36]  G. Maurer,et al.  Swelling of n-isopropyl acrylamide hydrogels in water and aqueous solutions of ethanol and acetone , 2004 .

[37]  G. Maurer,et al.  Swelling of N-isopropyl acrylamide hydrogels in aqueous solutions of poly(ethylene glycol) , 2004 .