The Level of Hydrophobic Substitution and the Molecular Weight of Amphiphilic Poly-L-lysine-Based Polymers Strongly Affects Their Assembly into Polymeric Bilayer Vesicles
✍ Scribed by Wei Wang; Laurence Tetley; Ijeoma F Uchegbu
- Book ID
- 102580770
- Publisher
- Elsevier Science
- Year
- 2001
- Tongue
- English
- Weight
- 435 KB
- Volume
- 237
- Category
- Article
- ISSN
- 0021-9797
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✦ Synopsis
With the aim of producing new materials for drug and gene delivery, the variables associated with the preparation of poly-L-lysine-based vesicles were investigated. Amphiphilic poly-Llysine graft copolymers with varying levels of grafted methoxypolyethylene glycol (mPEG) and palmitic acid were synthesized using two-step grafting reactions of the macromonomer, mPEG-pnitrophenyl carbonate (mPEG, MW = 5,000), and palmitic acid N-hydroxysuccinimide ester onto poly-L-lysine hydrobromide (MW = 4,000 and 19,600). Polymers were characterized by gel permeation chromatography/light scattering. 1 H NMR, and an assay for unreacted ε-amino groups. Polymeric unilamellar vesicles were produced by probe sonication of the amphiphilic poly-L-lysinebased polymers in the presence of cholesterol. Vesicles were characterized by electron microscopy and photon correlation spectroscopy. Vesicle formation was favored by a low molecular weight and a low level of palmitoyl substitution. A vesicle formation index has been derived, F ∝ H/L DP, where H is the %molar level of unreacted L-lysine units, L is the %molar level of substituted palmitoyl units, and DP is the square root of the degree of polymerization of the polymer. Additionally, the size of these vesicles may be controlled by controlling the initial molecular weight of the parent poly-Llysine/resulting amphiphilic polymer. Hence, amphiphilic poly-Llysine-based polymers of molecular weight = 89,000 and 25,000 produced polymeric vesicles of z-average mean diameter 570 nm and 252 nm, respectively. Vesicle encapsulation efficiency for the hydrophilic macromolecule, fluorescein isothiocyanate-dextran (MW = 4,400), increased with vesicle size.