Complexation, dynamics and rheology of vesicles and polymers

COMPLEXATION, DYNAMICS AND RHEOLOGY OF VESICLES AND POLYMERS CHIENG YU YUAN NATIONAL UNIVERSITY OF SINGAPORE 2010 COMPLEXATION, DYNAMICS AND RHEOLOGY OF VESICLES AND POLYMERS CHIENG YU YUAN (B.Eng., M.Eng.(Hons.), Universiti Teknologi Malaysia) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF CHEMICAL AND BIOMOLECULAR ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2010 Acknowledgements ACKNOWLEDGEMENTS In the first place, I owe my deepest gratitude to my principal investigator, Professor Chen Shing Bor for his supervision, guidance and fruitful discussions that have been invaluable to me throughout my graduate study. His ideas, passions in research and constructive comments always have been of great value for me. This thesis would not have been possible without his tireless effort, encouragement and ongoing support. I am also grateful to my oral qualifying examiners, Professor Hong Liang and Professor Lanry Yung Lin Yue for their detailed reviews, constructive criticisms and excellent advices to this study. My warmest thanks go to my lab mates and friends for giving me such a pleasant time when working together with them as a postgraduate research student. My sincere appreciation also extends to all the lab technologists for their indispensable help and untiring technical assistance in this project. Furthermore, the financial support from the National University of Singapore is gratefully acknowledged. Last but not least, I would like to express my heartfelt gratitude to all my beloved family members (Chieng Sie Lung, Ho Lien Hsi, Ong Chin Kiat, Chieng Yu Ding, Chieng Yu Ling and Chieng Yu Siang) for their enduring love, concern and understanding. Their encouragement and moral support make me courageous enough to complete my research study. i Table of Contents TABLE OF CONTENTS Page ACKNOWLEDGEMENTS i TABLE OF CONTENTS ii SUMMARY v LIST OF TABLES vii LIST OF FIGURES viii NOMENCLATURE xiii CHAPTER Introduction to Phospholipid Vesicles and Polymers 1.1 Phospholipid Vesicles 1.2 Polymers 1.3 Objectives and Significance of the Study 1.4 Thesis Organization 10 CHAPTER Materials and Methods 2.1 Phospholipids 11 2.2 Polymers 12 2.2.1 Pluronic triblock copolymers 12 2.2.2 Poly(acrylic acid) 13 2.2.3 Hydrophobically modified hydroxyethyl cellulose 14 2.2.4 Poly(diallydimethylammonium chloride) 15 2.3 Others 16 2.4 Experimental Methods 16 2.4.1 Preparation of polymer solution 16 2.4.2 Preparation of phospholipid vesicles-polymer solution 18 ii Table of Contents 2.4.3 Dynamic light scattering (DLS) 19 2.4.4 Zeta potential 19 2.4.5 Differential scanning calorimetry (DSC) 20 2.4.6 Fluorescence microscopy 21 2.4.7 Rheometry 21 2.4.8 UV-visible spectrophotometer 22 CHAPTER Interactions and Complexation of Phospholipid Vesicles and Triblock Copolymers 3.1 Research Background 23 3.2 Results and Discussion 26 3.2.1 DLS for unilamellar vesicle-Pluronic F-127 system 26 3.2.2 DLS for unilamellar vesicle-Pluronic L-61 system 32 3.2.3 DSC and fluorescence microscopy for multilamellar vesiclePluronic F-127 system 34 3.2.4 DSC and fluorescence microscopy for multilamellar vesiclePluronic L-61 system 42 3.2.5 Rheological properties of multilamellar vesicle-Pluronic System 3.3 Conclusions CHAPTER 47 51 Interaction between Poly(acrylic acid) and Phospholipid Vesicles: Effect of pH, Concentration and Molecular Weight 4.1 Research Background 52 4.2 Results and Discussion 54 4.2.1 High molecular weight PAA (450,000 g/mol) 54 4.2.2 Low molecular weight PAA (2,000 g/mol) 65 iii Table of Contents 4.3 Conclusions CHAPTER 73 Rheological Study of Hydrophobically Modified Hydroxylethyl Cellulose and Phospholipid Vesicles 5.1 Research Background 75 5.2 Results and Discussion 78 5.2.1 Rheological behavior of HMHEC solution 78 5.2.2 Viscosity behavior of HMHEC-phospholipid vesicles solution 80 5.3 5.2.3 Dynamic behavior of HMHEC-phospholipid vesicles solution 94 Conclusions 100 CHAPTER Complexation of Cationic Polyelectrolyte with Anionic Phospholipid Vesicles: Concentration, Molecular Weight, and Salt Effects 6.1 Research Background 101 6.2 Results and Discussion 104 6.2.1 Effect of PDADMAC concentration and molecular weight 104 6.2.2 Effect of salt concentration 117 Conclusions 121 6.3 CHAPTER Conclusions and Recommendations 7.1 Conclusions 122 7.2 Recommendations 128 References 131 iv Summary SUMMARY To elucidate the complexation and interaction mechanism between phospholipid vesicle and four polymers of interest (Pluronic, poly(acrylic acid), hydrophobically modified hydroxyethyl cellulose and poly(diallyldimethylammonium chloride), we studied the physical, thermotropic, phase behavior and rheological properties of the mixture solutions using different methods of characterization. Firstly, interactions and complexation between phospholipid vesicle and triblock copolymers were investigated for a wide range of Pluronic concentrations (015wt%). At low concentrations, Pluronic F-127 and L-61 monomers were incorporated into the lipid bilayers. Results showed that Pluronic L-61 interacts more strongly with phospholipid vesicles than F-127. By further increasing the concentrations to the CMC, Pluronics solubilize parts of the vesicles into small bilayer disks and patches. For high concentrations, F-127 forms mixed micelles with solubilized lipid molecules in the form of bilayer patches. The presence of these bilayer patches within the F-127 gel at high enough temperature can considerably increase the F-127 viscosity and both storage and loss moduli properties. In contrast, more hydrophobic L-61 tends to precipitate with the solubilized lipids as large crewcut mixed aggregates. Secondly, we studied the interaction between poly(acrylic acid) and phospholipid vesicle by manipulating the polymer concentration, molecular weight and medium pH. Hydrogen bonding between PAA and vesicle is the major associative interaction under acidic conditions. PAA adsorbed on the vesicles surfaces and increased the cooperativity of the lipid acyl chains at very low concentrations. By increasing the PAA concentrations, high molecular weight PAA induced vesicles v Summary aggregation while low molecular weight PAA showed hydrophobic attraction with phospholipid vesicles. At high enough concentrations, high molecular weight PAA can completely disrupt the lipid bilayers. In contrast, low molecular weight PAA leads to vesicle aggregation without destroying the bilayers. At alkaline pH, complexation did not occur because of strong dissociation of carboxyl groups of PAA. Thirdly, we explored the rheological behavior of phospholipid vesicle and hydrophobically modified hydroxyethyl cellulose. Two HMHEC concentrations at 0.3wt% (semidilute) and 0.7wt% (concentrated) were investigated as a function of lipid species and concentration. Results demonstrated that HMHEC and phospholipid vesicle mixture viscosity could be enhanced by more than one order of magnitude for sonicated samples at certain lipid concentrations, compared to a pure HMHEC solution. The viscosity first increases with the lipid concentration and then decreases. Besides, the lipid addition increases the plateau modulus. Direct bridging and indirect linking associations interconnect the vesicles and contribute to the viscosity enhancement. Finally, the interaction behavior between cationic PDADMAC and anionic DPPG vesicle was examined. PDADMAC can bind electrostatically to the vesicle to compensate, neutralize and reverse the vesicular charge, depending on the molar ratio of cationic to anionic group, R. For R1, charge reversal took place, the complex size reduced. Although the thermal behavior was nearly independent of the polymer molecular weight, the complex morphology is different. vi List of Tables LIST OF TABLES Table Title Page Table 3.1 Thermal data for DPPC vesicles modified by F-127 35 Table 3.2 Thermal data for DPPC vesicles modified by L-61 44 Table 4.1 Thermal data and pH for DPPC and PAA (450,000g/mol) 55 Table 4.2 Thermal data and pH for DPPC and PAA (2,000g/mol) 67 Table 5.1 Effect of EPC concentrations on the viscoelastic properties of 0.7wt% HMHEC at 10C 98 Table 5.2 Rheological data of HMHEC with addition of phospholipid vesicles 99 Table 6.1 DSC thermal data for DPPG with high and very low molecular weight PDADMAC 107 vii List of Figures LIST OF FIGURES Figure Title Page Figure 2.1 Molecular structures of (a) EPC, (b) DPPC, and (c) DPPG phospholipids 12 Figure 2.2 Chemical structure of Pluronic (x, PEO portion; y, PPO portion) 13 Figure 2.3 Molecular structure of poly(acrylic acid) 14 Figure 2.4 Molecular structure of hydrophobically modified hydroxyethyl cellulose 15 Figure 2.5 Molecular structure of poly(diallyldimethylammonium chloride) 15 Figure 3.1 Hydrodynamic diameter of large unilamellar vesicles with addition of F-127 28 Figure 3.2 Size distribution of EPC vesicles with varying concentration of F-127 29 Figure 3.3 Hydrodynamic diameter of large unilamellar vesicles with addition of Triton X-100 31 Figure 3.4 Hydrodynamic diameter of large unilamellar vesicles with addition of L-61 33 Figure 3.5 DSC thermogram of DPPC vesicles at different F-127 concentrations: (a) 0.0, (b) 0.02, (c) 0.04, (d) 0.1, (e) 0.3, (f) 0.5, (g) 0.7, (h) 1.0, (i) 5.0, (j) 10.0, and (k) 15.0wt% 37 Figure 3.6 HHW of the main phase transition peak vs F-127 concentration (0-15wt%). 38 Figure 3.7 Schematic diagram of interaction mechanisms of low and high concentrations of Pluronic F-127 and L-61 with phospholipid vesicles 39 Figure 3.8 Fluorescence image of DPPC vesicles at different F-127 concentrations: (a) 0.0, (b) 0.02, (c) 0.3, (d) 0.7, (e) 5.0, and (f) 10.0wt%. 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Pharm., 126, pp.209-217. 1995 151 [...]... complexation and interaction between phospholipid vesicles and polymers The motivation, objectives and scopes of this research work have also been pointed out The materials and methods will be described in Chapter 2 Chapter 3 presents the results and discussion for the study of interaction between phospholipid vesicles and triblock copolymers Chapter 4 describes the effect of pH, concentration and molecular... DPPC and 0.7wt%HMHEC 88 x List of Figures Figure 5.8 Schematic network structure of HMHEC and phospholipid vesicles 90 Figure 5.9 Viscosity versus shear stress of pure HMHEC in 20mM NaCl buffer solution (control) and with addition of 5mg/ml EPC and DPPC vesicles at 10°C (a) 0.7wt% HMHEC and (b) 0.3wt%HMHEC 93 Figure 5.10 Storage modulus (closed symbols) and loss modulus (open symbols) as functions of. .. rheological properties of polymers, focusing on the effects of added vesicles concentration and system temperature Finally, the influence of cationic PDADMAC on the morphology and phase behavior of anionic phospholipid vesicles was investigated as a function of PDADMAC concentration, molecular weight and salt concentration 9 Chapter 1 Although the obtained results will be useful for the design of a phospholipidpolymer... focusing on charge compensation and neutralization of vesicles at relatively low concentration of polycation, charge reversal phenomenon at sufficiently high charge ratio of polycation is less studied and thus not well understood The motivation of this study is to have a good fundamental understanding of how these polymers interact with phospholipid vesicles over a wide range of 8 Chapter 1 concentration,... HMHEC at (c) 10°C and (d) 25°C 84 Figure 5.5 Zero-shear viscosity of (a) 0.7wt% HMHEC and (b) 0.3wt% HMHEC as a function of EPC concentration at 10 and 25°C 85 Figure 5.6 Flow curves of sonicated DPPC vesicles with 0.7 wt% HMHEC at (a) 10°C; (b) 25°C, and with 0.3wt% HMHEC at (c) 10°C and (d) 25°C 86 Figure 5.7 DSC thermogram of 5 mg/ml (a) unsonicated DPPC; (c) unsonicated DPPC and 0.7wt% HMHEC; (c)... symbol) and without (open symbol) 20 mM NaCl at 10°C and 25°C 80 Figure 5.2 Zero-shear viscosity as a function of EPC concentration for 0.7wt% HMHEC with sonicated vesicles at 10°C and 25°C 81 Figure 5.3 Shear viscosity (a) and moduli (b) of 1wt% HEC (720,000 g/mol) with sonicated EPC vesicles at 25 °C 82 Figure 5.4 Flow curve of sonicated EPC vesicles with 0.7 wt% HMHEC at (a) 10°C; (b) 25°C, and with... (magnification = 50) and schematic diagram depict the complex structure of 15wt%PDADMAC and DPPG bilayers 112 Figure 6.7 Effect of PDADMAC on the zeta potential of DPPG vesicles in 20 mM NaCl at pH 6.4, HMW=high molecular weight, VLMW=very low molecular weight 113 Figure 6.8 Effect of PDADMAC on the average hydrodynamic diameter of DPPG vesicles 115 xi List of Figures Figure 6.9 Turbidity of PDADMAC/DPPG... success Most of the previous studies overlooked the effect of important experimental parameters such as concentration, temperature, polymer molecular weight, salt and medium pH on the changes in physical and thermal behavior of phospholipid vesicles In brief, diverging findings were obtained for low concentration of Pluronic modified vesicles system While some studies reported the enhancement of vesicles. .. The effect of PAA concentration, molecular weight and pH on the structure of complexes formed has not been clearly elucidated To the best of our knowledge, there is yet no information about the rheological behavior of hydrophobically modified hydroxyethyl cellulose and phospholipid vesicles It remains questionable whether the insertion of HMHEC random hydrophobic side chains will interconnect and bridge... focused on studies concerning the interaction of different types of polymer with phospholipid vesicles to improve the performance of both systems such as stability, permeability and sensitivity properties The interaction between phospholipid vesicles and polymer in aqueous solution is complex, depending on the species and composition A good understanding of fundamental interaction mechanisms between . COMPLEXATION, DYNAMICS AND RHEOLOGY OF VESICLES AND POLYMERS CHIENG YU YUAN NATIONAL UNIVERSITY OF SINGAPORE 2010 COMPLEXATION, DYNAMICS AND RHEOLOGY. TABLE OF CONTENTS Page ACKNOWLEDGEMENTS i TABLE OF CONTENTS ii SUMMARY v LIST OF TABLES vii LIST OF FIGURES viii NOMENCLATURE xiii CHAPTER 1 Introduction to Phospholipid Vesicles and Polymers. diameter of large unilamellar vesicles with 28 addition of F-127 Figure 3.2 Size distribution of EPC vesicles with varying concentration 29 of F-127 Figure 3.3 Hydrodynamic diameter of large