Controlling nanostructure and lattice parameter of the inverse bicontinuous cubic phases in functionalised phytantriol dispersions

doi:10.1016/j.jcis.2013.07.002

Journal of Colloid and Interface Science

Volume 408, 15 October 2013, Pages 117-124

https://doi.org/10.1016/j.jcis.2013.07.002 Get rights and content

Highlights

•
Functionalisation of inverse bicontinuous cubic phase lyotropic liquid crystalline dispersions is demonstrated.
•
Oleic acid and monosialoganglioside-G_M1 induce phase changes at room temperature.
•
Neutral, negatively and positively charged surfactants affect lattice parameter.
•
Bi-functionalisation of these dispersions is demonstrated.

Abstract

The preparation and phase behavior of dispersed liquid crystalline particles comprised of phytantriol and various functionalised lipids are reported. These inverse bicontinuous cubic phase colloidal dispersions have been sterically stabilized with a triblock copolymer, Pluronic F127. The influence of added negatively charged amphiphiles oleic acid and sodium dodecylsulfate, the positively charged hexadecyltrimethylammonium bromide, and monoolein a neutral amphiphile, on phase behavior and cubic phase structure was examined by synchrotron small angle X-ray scattering (SAXS). Functionality was also introduced through ligand specific lipids monosialoganglioside-G_M1 and 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[biotinyl(polyethylene glycol)-2000]. SAXS measurements showed that all of the additives affected the long-range order of the inverse cubic phase observed through either phase behavior changes or alteration in lattice parameter.

Graphical abstract

Introduction

The understanding of liquid crystalline amphiphile polymorphism and the range of ordered, complex nanostructures that can be formed has been growing over the last half-century [1], [2], [3], [4], [5]. This knowledge is being applied directly to develop technologies in several fields including drug delivery, biosensors and protein crystallization [6], [7], [8], [9], [10]. The technological application of advanced lipid systems often requires functionalisation of the mesophase. Functionalisation typically occurs at the lipid–water interface and is mediated through the addition of lipids with positively or negatively charged head-groups or ligand-specific groups which permit specific biological recognition.

Inverse bicontinuous cubic bulk phases are typically very viscous and thus difficult to manipulate. The most common methodology employed to reduce viscosity whilst retaining bulk material nanostructure is to disperse these materials into colloids; to prevent coalescence the dispersion is typically performed in the presence of steric stabilizers. The most commonly used stabilizer is the amphiphilic polymer Pluronic F127, a poly(ethylene oxide) poly(propylene oxide) poly(ethylene oxide) triblock copolymer, although new stabilizers have recently been established for the stabilization of mesophase dispersions [11], [12]. The propylene domain anchors the polymer to the nanoparticle whilst the ethylene oxide chains are highly water soluble and can be crudely described as acting as a flocculation barrier, giving the particles colloidal stability of months to years. The resultant particles are typically 200 nm in size, and are commonly referred to as cubosomes¹ [13]. The incorporation of additives to cubosomes leads to a change in the curvature of the system. The curvature change drives changes in the lipid bilayer thickness and/or the water channel size of the mesophase resulting in lattice parameter change. It may also induce an alteration in the mesophase structure itself. The influence of additives to the internal structure of the lipid nanoparticles can be assessed with synchrotron small angle X-ray scattering (Fig. 1).

For technological applications, such as drug delivery vehicles and biosensors, structure is integral to proper function of a material [14]. The extent of the change in curvature of the system is influenced by the molecular dimensions of the amphiphile which affects the type of phase observed under specific environmental conditions [15]. Thus the composition of the lyotropic phases must be considered to ensure that the desired structure is established and can be sustained within the operating environment of the materials.

The diterpenoid alcohol, phytantriol (3,7,11,15-tetramethyl-1,2,3-hexadecanetriol), is becoming increasingly employed as a building block of these self-assembling aggregates. The phase behavior of phytantriol has been well characterized in partial and excess hydration (Fig. 1) [16], [17]. Phytantriol is commonly used as it has a relatively high resistance to hydrolysis due to the lack of ester linkages and complete saturation of its aliphatic chain in comparison to a lipid such as monoolein. Depending on the purity of the material, it also typically retains its cubic phase in excess water between 22 and 56 °C [16]. The addition of functionalized lipids to phytantriol can have distinct effects on the nature and properties of the lipid mesophase. Phytantriol in excess water at 25 °C adopts a double diamond inverse bicontinuous cubic phase consisting of a lipid bilayer mapped over an infinite periodic minimal surface with two non-intersecting water pores (Fig. 1) [18]. The structure of this mesophase makes it ideal for applications where amphiphilicity and a high surface area are needed.

Few studies exist examining the effect of additives on the phase behavior of cubosome systems. A pioneering study, by Nakano and co-workers [19], examined the effect of the stabilizer Pluronic F127 on cubosome phase behavior, establishing an concentration range for F127 in cubosomes comprised of monoolein. The control of pore size via incorporation of a range of additives such as octylglucoside and proteins, and the subsequent determination of the aqueous channel size in cubic phases has been reported [6], [20], [21], [22], [23], [24]. Other groups have reported on addition of different stabilizers [25], lipids [26], [17] as well as small molecules [27], [28], with the latter studies focusing on small molecule diffusion and drug delivery from cubosomes. To the best of our knowledge, no studies have investigated the effect of several additives on the nanostructure of the phytantriol cubosome system using synchrotron small angle X-ray scattering. The SAXS data obtained herein consists of discrete Bragg reflections and a form factor component [29], [30]. This manuscript focuses on the nanostructure and the lattice parameters of the cubosome systems.

In this article we examine the effect of six different additives (Fig. 2), with distinct structural and electrostatic characteristics, on the phase behavior of the phytantriol/water/F127 ternary cubosome system using synchrotron small angle X-ray scattering (s-SAXS). The additives selected were the negatively charged oleic acid (OA), monoolein (MO), the cationic hexadecyltrimethylammonium bromide (cetyltrimethylammonium bromide, CTAB), anionic sodium dodecylsulfate (SDS), and the ligand specific lipids monosialoganglioside-G_M1 (G_M1) and 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[biotinyl(polyethylene glycol)-2000] (bDSPE). The first four lipids serve as references to determine the influence of molecular packing on the phase behavior of cubosomes. G_M1 and bDSPE are both membrane-based receptors for the biological ligands lectins (e.g cholera toxin) and avidin, respectively. Their effect on the inverse bicontinuous phase of the phytantriol/F127/water system was investigated at different loadings, up to 7.5 mol% for most formulations (with one exception). The effect of the presence of two lipids present in the bilayer (G_M1 and bDSPE) was also examined. Such studies are crucial to the potential use of lipidic systems as biosensors where it is necessary to understand the effect of functional additives such as bDSPE and G_M1 on the nanostructure of the materials. It may also be necessary to control pore size, membrane interface charge and the internal structure of materials to ensure system efficacy. Such control can be achieved through doping bilayers with the additives outlined herein.

Section snippets

Materials

Monosialoganglioside G_M1 (sodium salt, bovine brain, 95%), monoolein (1-oleoyl-rac-glycerol) (∼99%), oleic acid (⩾99%), hexadecyltrimethylammonium bromide (CTAB) (⩾99%), Pluronic F127, and sodium dodecylsulfate (SDS) (⩾98.5%) were purchased from Sigma Aldrich (St. Louis, USA). 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[biotinyl(polyethylene glycol)-2000] (ammonium salt, 100%) (bDSPE) was purchased from Avanti Polar Lipids Inc. (Alabaster, USA).

Effect of additives on particle size

Complex mixtures of cubosomes were prepared successfully according to the methods outlined earlier. Prior to the assessment of phase behavior, the average size and size distribution of the cubosomes was measured using DLS (Table 1). The cubosomes were categorized into two major classes: those containing a functional additive, and those containing a non-functional additive. The former class was comprised of G_M1/phytantriol/F127, bDSPE/phytantriol/F127, and G_M1/bDSPE/phytantriol/F127 cubosome

Conclusions

We have examined the effect of additives on the phase behavior of phytantriol/F127 cubosome systems. The different additives with diverse molecular geometry, charge state and functionality, affect the phytantriol/F127 system. As a result we observed that monoolein stabilized the Q_II phase of the phytantriol/F127 system, whereas all other non-functional formulations had greater effect on the system curvature. Oleic acid destabilized the Q_II phase and at high concentrations caused a phase change

Acknowledgments

This research was undertaken in part on the small angle X-ray scattering beamline at the Australian Synchrotron, Victoria, Australia. SJF would like to thank the CSIRO for funding of his studentship. SJF would also like to acknowledge the David Hay memorial fund for their generous support whilst writing up these findings.

References (42)

D. Libster et al.
J. Colloid Interface Sci.
(2011)
X. Mulet et al.
J. Colloid Interface Sci.
(2013)
A. Yaghmur et al.
Adv. Colloid Interface
(2009)
J.N. Israelachvili et al.
Biochim. Biophys. Acta
(1975)
X. Mulet et al.
Int. J. Pharm.
(2010)
J. Majewski et al.
Biophys. J.
(2001)
M. Corti et al.
J. Mol. Struct.
(1996)
K. Larsson
Z. Phys. Chem.-Frankfurt
(1967)
V. Luzzati et al.
Nature
(1968)
L.E. Scriven
Nature
(1976)

G. Lindblom et al.

J. Am. Chem. Soc.

(1979)

J.S. Patton et al.

Science

(1979)

C.E. Conn et al.

Soft Matter

(2010)

S.J. Fraser et al.

Aust. J. Chem.

(2011)

S.J. Fraser et al.

Soft Matter

(2011)

J.Y.T. Chong et al.

Soft Matter

(2011)

M. Dulle et al.

Langmuir

(2012)

E. Nazaruk et al.

Anal. Bioanal. Chem.

(2008)

J. Barauskas et al.

Langmuir

(2003)

Y.D. Dong et al.

Langmuir

(2006)

C. Fong et al.

Chem. Soc. Rev.

(2012)

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Controlling nanostructure and lattice parameter of the inverse bicontinuous cubic phases in functionalised phytantriol dispersions

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Materials

Effect of additives on particle size

Conclusions

Acknowledgments

J. Colloid Interface Sci.

J. Colloid Interface Sci.

Adv. Colloid Interface

Biochim. Biophys. Acta

Int. J. Pharm.

Biophys. J.

J. Mol. Struct.

Z. Phys. Chem.-Frankfurt

Nature

Nature

J. Am. Chem. Soc.

Science

Soft Matter

Aust. J. Chem.

Soft Matter

Soft Matter

Langmuir

Anal. Bioanal. Chem.

Langmuir

Langmuir

Chem. Soc. Rev.