32 BF have also been useful to cover particles such as silica, latex or insoluble drug particles with lipids. Amphotericin B solubilized at the rim of DODAB BF provided a novel formulation with excellent activity against systemic candidiasis in mice at low drug dose 30, 31 with low nephrotoxicity. Lately, our group has been developing novel formulations for hydrophobic drugs or vaccines based on these structures.

28, 29 However, lipid BF or disks remained as a much less explored bilayer assembly. Bilayers were the preferential supramolecular assembly for several synthetic amphiphiles as dialkyldimethylammonium bromide or chloride, 20 sodium dihexadecylphosphate 22, 26, 27 and many other molecules. Structural and functional aspects of biological membranes were also copied in a variety of biomimetic systems. Since the major requirement to form a supramolecular assembly of the bilayer type was an approximately cylindrical amphiphilic molecule with a geometric parameter between 0.5 and 1.0, 25 not only natural phospholipids were prone to form bilayers. In addition, a variety of bilayer structures formed by dialkyldimethylammonium halides 20 and other synthetic amphiphiles 21 вЂ“ 24 were introduced to mimic membrane properties furnishing unique opportunities to investigate structure-function relationships. 19 The liposome вЂњmembraneвЂќ model prepared from phospholipids has lead to much of our present knowledge on membrane properties. Alec Bangham produced the first liposomes in 1965 in Cambridge UK. 18 Similarly, lipid assemblies such as liposomes, vesicles, solid lipid nanoparticles and lipidic bilayer fragments (BF) or disks are as versatile as particles. 6, 9 Polystyrene sulfate (PSS) nanoparticles covered with a dioctadecyldimethylammonium bromide (DODAB) bilayer 10 were used for adsorption of serum proteins, 11 cholera toxin, 11 Taenia crassiceps antigens, 12, 13 recombinant proteins, 13, 14 polysaccharides 15 вЂ“ 17 and giant DNA.

Properties of the intervening medium such as pH and ionic strength were systematically varied for achieving optimal lipid bilayer deposition and colloid stability. Silica, 6 latex, 7 or hydrophobic drug particles 8 have been coated with cationic lipids and characterized by means of adsorption isotherms, mean particle size from dynamic light scattering, surface potential analysis and colloidal stability. 4, 5 On the other hand, cationic lipids can be combined with negatively charged biomolecules or biological structures. They can mimic structural and functional aspects of viruses, bacteria and other biological assemblies and are currently being used in: imaging 1 biosensing 2 gene and drug delivery 3 and vaccines. Particles are important in pharmaceutical and biomedical research since their size scale can be similar to that of proteins or DNA. Biomolecular recognition between receptor and ligand can be reconstituted by means of receptor immobilization into supported lipidic bilayers allowing isolation and characterization of signal transduction steps. Thereby antigens can effectively be presented by tailored biomimetic particles for development of vaccines over a range of defined and controllable particle sizes. Cationic biomimetic particles offer suitable interfacial environment for adsorption, presentation and targeting of biomolecules in vivo. In other instances, hydrophobic drug molecules attach as monomers to borders of lipid bilayer fragments providing drug formulations that are effective in vivo at low drug-to-lipid-molar ratio. In certain cases, hydrophobic drug granules can be dispersed in aqueous solution via lipid adsorption surrounding the drug particles as nanocapsules. However, their self-assembly on a solid surface or at an interface remains poorly understood. In water, self-assembly of lipid molecules into supramolecular structures is fairly well understood. In this review, biomimetic assemblies based on natural or synthetic lipids by themselves or associated to silica, latex or drug particles will be discussed. Mimicking nature is a powerful approach for developing novel lipid-based devices for drug and vaccine delivery.

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