What is nanotechnology?
A generally accepted definition is: The application of science that deals with elements in the range of 100 nano-metres to one tenth of a nano-metre in size’
Nanotechnology can be generally defined as fabrication and manipulation of structures that have at least one dimension or contain components with at least one dimension that is approximately 1-100 nm.
Various types nanomaterials used in nanotechnolog
Liposomes are vesicular structures with an aqueous core surrounded by a hydrophobic lipid bilayer, created by the extrusion of phospholipids. They are most widely known cosmetic delivery systems. Liposomes can vary in size, from 15 nm up to several μm and can have either a single layer or multi layer structure.
Liposomes have been formed that facilitate the continuous supply of agents into the cells over a sustained period of time, making them an ideal candidate for the delivery of vitamins and other molecules to regenerate the epidermis. They have also been used in the treatment of hair loss. Minoxidil, a vasodilator, is in the active ingredient in products like Reginae that claim to prevent or slow hair loss.
Cubosomes are discrete, sub-micron, nano structured particles of bi-continuous cubic liquid crystalline phase. It is formed by the self assembly of liquid crystalline particles of certain surface when mixed with water and a micro structure at a certain ratio. Cubosomes offer a large surface area, low viscosity and can exist at almost any dilution level. They have high heat stability and are capable of carrying hydrophilic and hydrophobic molecules. Combined with the low cost of the raw materials and the potential for controlled release through function, they are an attractive choice for cosmetic applications as well as for drug delivery.
They are 3D hydrophilic polymer networks that swell in water or biological fluids without dissolving as a result of chemical or physical cross-links. They can predict future changes and change their property accordingly to prevent the damage
Nano crystals are crystals having size less than 1μm. Typical sizes of these aggregates are between 10-400 nm . Nano crystals of poorly soluble drugs can also be incorporated in cosmetic products where they provide high penetration power through dermal application.
Dendrimers are uni molecular, mono disperse, mini nano structures, around 20 nm in size, with a well-defined, regularly branched symmetrical structure and a high density of functional end groups at their periphery. A dendrimer is typically symmetric around the core, and often adopts a spherical three-dimensional morphology
Niosomes are vesicles composed of non ionic surface, such as poly oxyethylene alkyl ethers or esters. The ultra structure of these vesicles is quite similar to that of mammalian milk, which contains nano-sized fat droplets surrounded by the milk fat globular membrane.The advantages of using niosomes in cosmetic and skin care applications include their ability to increase the stability of entrapped drugs, improved bio availability of poorly absorbed ingredients .
Methods for the preparation of nano particles:-
- The sol–gel method
- Vacuum deposition method
- Ball milling method
- Other methods like Arc (DC) plasma, Laser Processes, Wire electrical explosion, Sputtering, Droplet-to-Particle Conversion, Flame synthesis.
The sol–gel method:
Silver nano particles; for example, is prepared by mixing the AgNO3 solution with tetraethylorthosilicate, ethanol and water then with a few drops of HNO3 as a catalyst.
The mixed solution was dispersed and dried. The dried gels were reduced at a temperature of 400 0 C for 30 min in hydrogen gas. The Ag particles have a size of about 5-10 nm with a profile distribution in the form of log normal distribution. The nano particles are embedded in silica glass in well separated and protected matrix. The preparation of iron nano particles embedded in glass can be prepared with the same method by substituting FeCl3 for the silver salt.
Vacuum deposition method:-
The presence of inert gas in vacuum chamber and lowering down the substrate temperature to liquid nitrogen temperature during thermal evaporation can reduce the momentum of the evaporated metallic atoms or clusters by collision with gas to obviate their further aggregation on the substrate. The evaporated metal atoms condensed just at where they reached without migration to the potential minimum thereby lose Vander wall attraction between particles. The resulting smokes can be collected from the substrate or walls of the evaporation chamber with the particle sizes can be easily controlled between 30-1000 Å depending on the gas pressure, the evaporation speed, the type of gas used, and the substrate temperature. Direct (DC) or radio frequency (RF) sputtering with the structure of deposited films mostly to be amorphous without substrate heating can successfully deposit refractory metals and alloys.
Ball milling method:-
Hard and brittle ceramic materials can be ball-milled into nano particles to produce nano crystals, non crystals, and pseudo crystals. Powders of 500 nm sizes can be milled into several NM by strong vibrations when mixed with tungsten-carbide spheres.
In pyrolysis, a vaporous precursor (liquid or gas) is forced through an orifice at high pressure and burned. The resulting solid (a version of soot) is air classified to recover oxide particles from by-product gases. Pyrolysis often results in aggregates and agglomerates rather than single primary particles. The thermal plasma temperatures are in the order of 10,000 K, so that solid powder easily evaporates. Nano particles are formed upon cooling while exiting the plasma region. The main types of the thermal plasma torches used to produce nano particles are dc plasma jet, dc arc plasma and radio frequency (RF) induction plasmas.
Methods for preparation of Solid Lipid Nano particles
High shear homogenization and ultrasound
- High pressure homogenization
- Solvent emulsification /evaporation
- Micro emulsion based SLN preparations
- a) High shear homogenization and ultrasound
PROPERTIES OF NANO PARTICLES:-
- They are effectively a bridge between bulk materials and atomic or molecular structures.
- A bulk material should have constant physical properties regardless of its size, but at the nano-scale size-dependent properties are often observed.
- For bulk materials larger than one micrometer (or micron), the percentage of atoms at the surface is insignificant in relation to the number of atoms in the bulk of the material.
- The high surface area to volume ratio of nano particles provides a tremendous driving force for diffusion, especially at elevated temperatures. Sintering can take place at lower temperatures, over shorter time scales than for larger particles.
- Suspensions of nano particles are possible since the interaction of the particle surface with the solvent is strong enough to overcome density differences, which otherwise usually result in a material either sinking or floating in a liquid.