2008 NSTI Nanotechnology Conference and Trade Show - Nanotech 2008 - 11th Annual

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TechConnect Summit
Clean Technology 2008

Multilamellar Stacks of Phospholipid Bilayers:Phase Transformation and Microstructure Evolution

M.A. Arunagirinathan, N. Dwivedi, J. Bellare
Indian Institute of Technology Bombay, IN

Keywords:
lipid, bilayer, lamellar, microstructure

Abstract:
Phase transformation and microstructure manifestation of self assembled phospholipid bilayers in the presence of anionic surfactant, sodium dodecylsulphate (SDS) was studied to understand the stability of multilamellar phospholipid bilayer stacks. Self assembly of phospholipids into various microstructures like vesicle, bilayer stacks, cylinder, tubule and perforated bilayer in the presence of sub-micellar and micellar concentration of surfactant is well known. However, solubilisation of multilamellar bilayer stacks that requires higher surfactant concentration has not been studied so far. Multibilayer stacks are known in applications like encapsulation, stabilization of particles and surfactant formulations. Dry phospholipid lamellar stacks on contact with water transform into swollen lamellar stacks by hydration of polar head groups followed by solubilisation of water within the lamellar bilayers. Cohesive attraction between phospholipid molecules and concomitant elasticity, transform swollen lamellar bilayer stacks into coaxially arranged concentric tube, myelin (Fig 1a). In this study, the electrostatic interactions between polar head groups and hydrophobic interactions among alkyl chains were tuned in the presence of surfactant and its effect on stability of phospholipid bilayer stacks was elucidated. Presence of SDS transforms the lamellar stacks of myelin microstructures into vesicles and cylinder like aggregates by adsorption, incorporation, saturation, and solubilisation mechanism. Transformation of bilayer stacks in myelin occur through peripheral thickening (as indicated by arrows in Fig. 1b,c), excessive swelling, followed by desquamation of bilayers from the lamellar stacks as vesicles (Fig. 1d). Formation of various microstructures depend on surfactant concentration (5 mM, 10 mM) used for solubilising the phospholipid bilayers. Interdigitation of SDS within the phospholipid bilayers increases the surfactant area head group thereby decreasing the critical packing parameter leading to phase transformation by destabilizing the lamellar stacks of bilayer. In addition, the domain formation by surfactant molecules within the phospholipid bilayers solubilises the lamellar stacks and splays the tubular microstructures into tiny aggregates. Optimisation of surfactant concentration and solubilisation of phospholipid bilayers by surfactant identified here will be of immense importance for pharmaceutical and personal care products. Dissolution of multilamellar stacks will shed light to understand the solubilisation of enteric coated tablets by bile surfactants in intestine. The stability of the lamellar stacks in the presence of SDS and water can be correlated to the maximum solubilisation of multiple components within the bilayers as in liquid detergents and shampoo formulations.


Nanotech 2008 Conference Program Abstract