Colloids refer to dispersion of one phase in another of small particles with a size ranging from 1 nanometer, (nm) to 10 micrometers, providing flexibility, for example, in the development of drug delivery. The particles may be either dissolved macromolecules or macromolecular structures formed from smaller structural units. They may also constitute a separate phase, as in aerosols, powders, pigment dispersions, emulsions, micro-foams and finely pigmented plastics. As carriers, they can be classified as self-assembled lipid systems, polymer systems, nanoparticle systems, and pro-colloidal systems. Thus, colloids have evolved to be used in the enhancement of solubility and protection of labile substances, to reductions, for example, in the toxicity of drugs and improving their therapeutic performances. For all these reasons, the colloidal properties have opened new frontiers in the delivery of active ingredients, and/or in chemical and nano-micro biotechnological products leading to an increased surge of interest as bridge to nanoscience. For colloid particles, the kinetic effects are still important and for their small size, when dispersed in a medium (gas or liquid) they move by a process known as Brownian motion. However, the delivery of colloidal active ingredients provides the formulation scientist with an alternative formulation approach that could enhance solubility; ensure improved dissolution; and provide options for controlling or sustaining the active ingredient release, tailoring its surface properties to modify its kinetics and dynamics. In any way, the foundation of all the advances in colloidal delivery science has based on the widespread and versatile use of surfactants and polymers. Surfactants are amphiphilic molecules with a polar, ionic hydrophilic part and a non-polar, hydrophobic part, that usually comprises a hydrocarbon or fluorocarbon chain. The strong dipole interactions between the hydrophilic part and water render them water soluble, and the balance between the dual properties of hydrophilicity and hydrophobicity endows them with a unique characteristic of surface-active properties in solution. Thus, the amount of surfactant adsorption at the interface depends on its structure and nature of the two phases forming the interface, while the degradation pathway mainly depends on the alkyl chain length, its linearity and degree of branching, and branch distribution in the main alkyl chain of the surfactant.
展开▼
