Research on the Structures,Properties and Interaction Mechanisms of Matrix Materials for PVA/PAM Based Cartilage Scaffold
Author:Wei Qing Hua
Supervisor:zhang ying feng wang yan en
Comparing with other synthetic materials,Polyvinyl alcohol(PVA)based polymer blend is closer to human cartilage tissue,which is thanks to its excellent properties(e.g.,biocompatibility,mechanical properties,stable chemical properties and microstructure similar to the natural cartilage).So the PVA based polymer is considered to be one of the most promising cartilage scaffold materials.PVA,however,has some demerits,such as lack of biological activity,inability to withstand complex loads,and unfavorable properties for cell adhesion and growth.In the field of tissue engineering,there are lots of researches on the blending modification of PVA based cartilage scaffold and a series of remarkable achievements have been obtained.But there is little research involves the mechanism of micro and mesoscopic level.With the development of computer science and technology,molecular simulation plays an irreplaceable role in material design and development,which can reveal the micro mechanism and essence that cannot obtain by the traditional experiments.Therefore,taking the matrix materials of PVA/Polyacrylamide(PAM)blend hydrogels as the research objects,and in this research we have proposed a multi-scale research method which combines the micro/mesoscopic molecular simulations and macro experiments.Then the structure,properties and interaction mechanism of the matrix materials for PVA/PAM based cartilage scaffold can be calculated and analyzed by the multi-scale research method,which provides the theoretical predictions and scientific basis for the formula designs of the matrix materials for cartilage scaffold.The main works in this paper are as follows:(1)The micro structure,properties and interaction mechanism of PVA/PAM blend matrix materials were investigated.The structures,properties and interaction mechanisms of three different PVA/PAM polymer blends were studied at a micro atomic level by molecular dynamics(MD)simulation.The influence relationships between polymer composition ratio and properties were built and studied in terms of miscibility,mechanical properties,fractional free volume(FFV),and the diffusion of water molecules.The interaction mechanisms of molecular chains in blend systems were elaborated from the aspects of binding energy and pair correlation function(PCF),from which the hydrogen bond interaction between the polar functional groups and its surrounding hydrogen atoms of polymers is the inner root reason that determines the properties of PVA/PAM polymer blends.Moreover,some macro properties(e.g.,mechanical properties and surface morphology)were tested by some macro experiments,which verify the accuracy of the results and models in simulations.(2)The diffusion mechanism of water molecules in PVA/PAM blends was revealed.MD simulation method was applied to investigate the effects of composition ratios and temperatures on the diffusion behavior of water molecules in PVA/PAM blend systems from the aspects of the diffusion coefficient,free volume,and PCF,as well the diffusion mechanism of water molecules in blend system were revealed from the perspective of molecular interaction.Moreover,the diffusion trajectories of water molecules in PVA/PAM blend systems were reconstructed by capturing the coordinates of water molecules at different moments,which makes up the deficiency of the experiment and gives us a more intuitive understanding for the diffusion of water molecules.Finally,the hydrophilicity of blends with different composition ratios were studied based on the experiments of contact angle and equilibrium water content(EWC),which verifies some simulation results indirectly.Results show that the athletic ability of water molecules,the flexibility of polymer chains and the hydrophily of functional groups in polymers are the root reasons which affect the diffusion behavior of water molecules in polymer blends.Additionally,experimental results tell us the contact angle of water on membrane surface is mainly resulted by the hydrophilicity of materials,while the equilibrium water content of membrane is mainly caused by FFVs in blend composite membrane.(3)The interaction mechanism of nano-silica in PVA/PAM blends was explored.The PVA/PAM/silica blend systems with different concentrations of nano-silica(0~13%)and the friction models were constructed by varying the number of polymer molecular chains,the molecular dynamics(MD)simulation method was employed to study the effects of nano-silica on the properties of PVA/PAM blends at an atomic level in terms of concentration profile,mechanical properties,tribological properties,FFV,dynamic properties of polymers and X-ray diffraction patterns.Results show the incorporation of nano-silica into the PVA/PAM blends can significantly increase the mechanical properties,densities,semicrystalline character and tribological properties of polymer composites.The main reason for this phenomenon is the strong hydrogen bond interaction between polar functional groups of polymer molecular chains and the hydroxyl groups of the silica surface.Aditionally,comparing with the PVA molecular chain,a stronger hydrogen bond interaction exists between PAM molecular chain and interface of nano-silica,so the addition of nano-silica will greatly influence the distribution of polymers in the blend system to some extent.The above results are helpful for us to better understand the micro structures of the blends and the interaction mechanism of nano-silica in PVA/PAM blend systems.(4)The aggregation behavior of nano-silica in PVA/PAM blending hydrogel was studied,and the responding relationships between influencing factors and aggregation behavior of nano-silica were built.The dissipative particle dynamics(DPD)simulation method was applied to investigate the effects of influencing factors(nano-silica content,polymer component ratio,temperature,and shear rate)on the aggregation behavior of nano-silica in PVA/PAM/silica blend hydrogels.The influencing relationships between factors and the aggregation behavior of nano-silica were revealed in terms of the mesoscopic morphologies and the relative concentration distribution functions.Results show the aggregation of nano-silica becomes more obvious with the increase of nano-silica content in blend hydrogel,and the dispersion of nano-silica performs well while its content is below 1.5%,which agrees well with the SEM image results.Compared with PVA,a stronger interaction existing between PAM and nano-silica,which results in the dispersion of nano-silica becomes better with the increase of PAM content in blend hydrogel.Moreover,the dispersion of nano-silica also increase with the temperature,which is attribute to the compatibility of the beads in blend hydrogel system raising with the temperature.Finally,the analysis results of shear rate suggest when the shear rate is below 0.12,the dispersion of nano-silica in blend hydrogel firstly becomes worse with the increase of shear rate.While the shear rate is above 0.12,the dispersion of nano-silica performs better with the shear rate increasing.However,the initial uniformity of the polymers in blend hydrogel is also destroyed.