Solubilization of Hydrophobic Guest Molecules in the Monoolein Discontinuous Q L Cubic Mesophase and Its Soft Nanoparticles Rivka Efrat, † Ellina Kesselman, ‡ Abraham Aserin, † Nissim Garti, † and Dganit Danino* ,‡ Casali Institute of Applied Chemistry, The Hebrew UniVersity of Jerusalem, Jerusalem 91904, Israel, and Department of Biotechnology and Food Engineering and the Russell Berrie Nanotechnology Institute, Technion;Israel Institute of Technology, Haifa 32000, Israel ReceiVed May 26, 2008. ReVised Manuscript ReceiVed July 22, 2008 Hydrophobic bioactive guest molecules were solubilized in the discontinuous cubic mesophase (Q L ) of monoolein. Their effects on the mesophase structure and thermal behavior, and on the formation of soft nanoparticles upon dispersion of the bulk mesophase were studied. Four additives were analyzed. They were classified into two types based on their presumed location within the lipid bilayer and their influence on the phase behavior and structure. Differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), polarized light microscopy, cryogenic- transmission electron microscopy (cryo-TEM), and dynamic light scattering (DLS) were used for the analysis. We found that carbamazepine and cholesterol (type I molecules) likely localize in the hydrophobic domains, but close to the hydrophobic-hydrophilic region. They induce strong perturbation to the mesophase packing by influencing both the order of the lipid acyl chains and interactions between lipid headgroups. This results in significant reduction of the phase transition enthalpy, and phase separation into lamellar and cubic mesophases above the maximum loading capacity. The inclusion of type I molecules in the mesophase also prevents the formation of soft nanoparticles with long-range internal order upon dispersion. In their presence, only vesicles or sponge-like nanoparticles form. Phytosterols and coenzyme Q 10 (type II molecules) present only moderate effects. These molecules reside in the hydrophobic domains, where they cannot alter the lipid curvature or transform the Q L mesophase into another phase. Therefore, above maximum loading, excess solubilizate precipitates in crystal forms. Moreover, when type II-loaded Q L is dispersed, nanoparticles with long-range order and cubic symmetry (i.e., cubosomes) do form. A model for the growth of the ordered nanoparticles was developed from a series of intermediate structures identified by cryo-TEM. It proposes the development of the internal structure by fusion events between bilayer segments. Introduction Lipid mesophases are potential sustained release vehicles for pharmaceuticals, cosmetic formulations, and food products because of their extensive capabilities of encapsulation of hydrophilic, hydrophobic, and amphiphilic bioactives, and the protection they provide to the encapsulated molecules. 1-4 However, the guest molecules may significantly influence the bulk liquid crystalline phase behavior by inducing structural transformations into other geometries and topologies or by separation into two phases. 5 The structural transitions depend on interactions between the lipid and the guest molecule, and the quantity entrapped. 5-9 Certain compounds reduce the bilayer curvature. This was demonstrated recently with sodium diclofenac (Na-DFC), where increasing quantities of the solubilized drug in the discontinuous cubic Q L mesophase induced transitions to a bicontinuous cubic phase and eventually to a lamellar phase. 10,11 The rate of release of the encapsulated bioactives depends on the mesophase and bioactive structures, and on physicochemical interactions between these components. 7,12-15 It can be modulated if sufficient knowledge is gained on the structure of the mesophase. 7,12,15 The high viscosity of hexagonal and cubic (glass-like) mesophases often limits their use to specific applications such as periodontal, mucosal, vaginal, and short-acting oral and parenteral drug delivery. 7 An attractive path to overcome this limitation is to disperse the bulk mesophases into small soft particles that keep the mesophase long-range order and retain some of the bulk material properties. 4,16-19 However, dispersing cubic and hexagonal lipid systems into nanoparticles often requires strong and prolonged shear, and results in the formation of particles in a wide range of sizes (1-100 µm). Recently it became possible to prepare low-viscosity mesophases, and consequently to form dispersed particles, at low shear rates and short application * Corresponding author. E-mail: dganitd@tx.technion.ac.il. Phone: +972- 4-829-2143. Fax: +972-4-829-3399. † The Hebrew University of Jerusalem. ‡ Technion;Israel Institute of Technology. (1) Fa, N.; Babak, V. G.; Stebe, M. J. Colloids Surf., A: Physicochem. Eng. Aspects 2004, 243(1-3), 117–125. (2) Yang, D.; Armitage, B.; Marder, S. R. Angew. Chem., Int. Ed. 2004, 43(34), 4402–4409. (3) Barauskas, J.; Johnsson, M.; Johnson, F.; Tiberg, F. Langmuir 2005, 21(6), 2569–2577. (4) Barauskas, J.; Johnsson, M.; Tiberg, F. Nano Lett. 2005, 5(8), 1615–1619. (5) Barauskas, J.; Misiunas, A.; Gunnarsson, T.; Tiberg, F.; Johnsson, M. Langmuir 2006, 22(14), 6328–6334. (6) Chang, C. M.; Bodmeier, R. Int. J. Pharm. 1997, 147(2), 135–142. (7) Shah, J. C.; Sadhale, Y.; Chilukuri, D. M. AdV. Drug DeliVery ReV. 2001, 47(2-3), 229–250. (8) Yaghmur, A.; de Campo, L.; Sagalowicz, L.; Leser, M. E.; Glatter, O. Langmuir 2006, 22(24), 9919–9927. (9) Li, S. J.; Yamashita, Y.; Yamazaki, M. Biophys. J. 2001, 81(2), 983–993. (10) Efrat, R.; Aserin, A.; Garti, N. J. Colloid Interface Sci. 2008, 321(1), 166–176. (11) Efrat, R.; Shalev, D. E.; Hoffman, R. E.; Aserin, A.; Garti, N. Langmuir 2008, 24, 7590–7595. (12) Clogston, J.; Craciun, G.; Hart, D. J.; Caffrey, M. J. Controlled Release 2005, 102(2), 441–461. (13) Kumar, K. M.; Shah, M. H.; Ketkar, A.; Mahadik, K. R.; Paradkar, A. Int. J. Pharm. 2004, 272(1-2), 151–160. (14) Welin-Berger, K.; Neelissen, J. A. M.; Engblom, J. J. Controlled Release 2002, 81(1-2), 33–43. (15) Clogston, J.; Caffrey, M. J. Controlled Release 2005, 107(1), 97–111. (16) Boyd, B. J. Int. J. Pharm. 2003, 260(2), 239–247. (17) Gustafsson, J.; Ljusberg-Wahren, H.; Almgren, M.; Larsson, K. Langmuir 1997, 13(26), 6964–6971. (18) Rosa, M.; Infante, M. R.; Miguel, M. D.; Lindman, B. Langmuir 2006, 22(13), 5588–5596. (19) Spicer, P. T.; Hayden, K. L.; Lynch, M. L.; Ofori-Boateng, A.; Burns, J. L. Langmuir 2001, 17(19), 5748–5756. 1316 Langmuir 2009, 25, 1316-1326 10.1021/la8016084 CCC: $40.75  2009 American Chemical Society Published on Web 09/10/2008