Dissipative Particle Dynamics Simulations On Timuli-responsive Polymer Materials

Dissipative particle dynamics (DPD) simulations are performed to investigate the phasebehavior and the drug loading as well as releasing behaviors of thermo-responsive blockcopolymer (PCL-PNIPAM-PCL). Simulation results show that polymer concentration or drugcontent or the block length of the hydrophilic PNIPAM has significant effects on theself-assembled structures of the copolymer in aqueous solution. More importantly, thehydrophilic-to-hydrophobic change of PNIPAM via temperature leads to thecore-shell-to-multicompartment transition of the copolymer and also the drug-loaded micelles,which can significantly enhance the drug release.Then, DPD simulations are used to systematically explore the mechanisms and generalrules of core-shell or Janus nanoparticles formation via the self-assembly of polymer blends.Also studied are the mechanisms and dynamics of the reversible core-shell-to-Janus transitionof the thermo-sensitive polymer blend nanoparticles induced by temperature. The simulationsshow that, when the blended polymers are hydrophobic and incompatible, Janus nanoparticleswill form. When one polymer is relatively hydrophilic and the other is hydrophobic and theyare slightly incompatible, then core-shell nanoparticles will form with the relativelyhydrophilic polymer as the shell and the hydrophobic polymer as the core. When the blendedpolymers are hydrophobic and relatively compatible, core-shell type micelles can also begained, but at this time, the less hydrophobic polymer will encapsulate the more hydrophobicpolymer to form the shell, while the micelle core is mainly composed of the morehydrophobic polymer. Critical values of the DPD interaction parameters are defined whichcan act as criteria to predict core-shell or Janus nanoparticles formation. In addition, thehydrophilic-to-hydrophobic change of PNIPAM via temperature leads to thecore-shell-to-Janus transition of the thermo-responsive blend nanoparticles.After that, we employ DPD simulations to study the dynamics and general rules ofpolymer blend nanoparticles with desired structures (core-shell or Janus) via self-organizedprecipitation method. It is found that when the preparation conditions are good for water tobehave, then the hydrophobicity of the polymer will have effects on the shapes of thenanoparticles, while the polymer compatibility will affect the structures of the nanoparticles.Moreover, for different polymer blends, one can obtain polymer blend nanoparticles withdesired shapes by varying the content of the good solvent or poor solvent, or changing theaddition rate of the poor solvent, or the evaporation rate of the good solvent.DPD simulations are conducted to investigate the DNA loading and releasing behaviors of the pH-sensitive cationic polymer in aqueous solution. The simulations show that cationicpolymer concentration, the chain length of the cationic polymer and/or the DNA exertsignificant effects on the self-assembly of cationic polymer and DNA. Additionally, whetherthe DNA will be released to water after lowering the pH depends on the balance of theelectrostatic and hydrophobic attraction, and the electrostatic repulsion. However, whenlowering the pH, the structures of the cationic-DNA complex will be relaxed, which willenhance the DNA release no matter whether the DNA is released to the water.