Lyotropic liquid crystalline nanoparticles

Lyotropic liquid crystalline nanoparticles have also been described. Concentrated solutions of gold nanorods in water in the presence of a surfactant (cetyltrimethyl-ammonium bromide) display a nematic mesophase stable up to 200 °C [74[. The N mesophase was identified by optical microscopy by their typical nematic droplets texture. 

The particle size characteristics of lyotropic liquid crystalline nanoparticles can be evaluated by more pharmaceutically common methods. Submicron enhanced laser diffraction which is able... 

Pharmaceutical Applications of Lyotropic Liquid Crystalline Nanoparticles... 

Table 10.1 Examples for drug loading of lyotropic liquid crystalline nanoparticles. 

Using a y-irradiation technique, hexagonal PANI nanoparticles have been prepared in the hexagonal lyotropic liquid crystalline phases of a non-ionic and biodegradable surfactant alkyl polyglucoside (GP215 CS UP) in water and/or medium and long chain alkanes, used as a template [421]. 

Due to the distinct differences of the properties of the nanoparticle matrix (e.g. bicontinuous vs. homogeneous, polar vs. nonpolar), lyotropic and thermotropic liquid crystalline nanoparticles are discussed separately although methods of, e.g., physicochemical characterization are similar for both t)q3es of nanop>articles. 

The supramolecular assemblies that form the structural units of liquid crystalline phases lead to length scales of order in the nanometer range. Mesophases thus represent nanostructured materials already in the bulk state. Under certain circumstances, these materials can be dispersed into liquid crystalline nanoparticles (LCNP) which will be the focus of this chapter. Due to their specific properties, liquid crystalline phases offer interesting drug carrier properties which may be even more advantageous when used in the nanoparticulate dispersions. Hitherto, most investigations into this direction have been performed with lyotropic mesophases and this topic will be discussed in the first part of this chapter. In the second part, nanoparticulate carriers based on thermotropic mesophases will be introduced. 

In addition to nanoparticles, other precious metal catalyst structures have been investigated such as mesoporous nanostructured layers. In a series of publications Attard, Elliott, Bartlett, and co-workers described the formation of mesoporous Pt and PtRu films by lyotropic liquid crystalline phase templated electroless or electrochemical (faradaic) deposition [237-243]. Using non-ionic surfactants (e.g., polyethylene glycols such as C12EO8, CieEOs, and CisEOio) at concentrations above 30 wt% in order to assure the formation of a homogeneous liquid crystalline phase, the surfaetant moleeular aggregates in the bulk electrolyte could serve as templates for nanostruetured deposition of metal ions from the interstitial spaces. 

The term "lipid nanoparticles" includes all colloidal systems where the nanoparticles consist of a kind of lipid matrix whereas the matrix lipid can occur in different physicochemical states (Figure 9.1) isotropic liquid (e.g. conventional fat emulsions), liquid crystalline (e.g. lyotropic cubic and thermotropic smectic ) or solid crystalline (SLN). A further distinction can be made if the lipid matrix is continuous (emulsions, SLN) or presents a discontinuous network of e.g. lipid bilayers (e.g. cubic nanoparticles). However, it should be kept in mind that lipid nanoparticles in several physicochemical states may coexist in one formulation. Generally the mean size of the nanoparticles is in the mid to lower nm-range normally between 100 and 500 nm. 

Liquid crystalline phases, also called mesophases, bear a high potential in drug delivery which may be further extended by their use in nanoparticulate form. This chapter describes the different types of nanoparticles based on lyotropic and thermotropic mesophases, like cubosomes, hexosomes and supiercooled smectic nanoparticles. 

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