2010 TRI/PRINCETON CONFERENCE 255 impart shine, gloss, smoothness and silkiness to substrates such as a skin, fi bers (33) and hair nails. One requirement for handling/delivering these polymers is necessity of trans- porting them in form of micro/nano emulsion droplets (42) to the given substrates. Sili- cone emulsions for personal care appears either in the form of antiperspirant formulations or creams and lotions for skin care and sun protection34. These are mostly water-in-sili- cone-oil emulsions that possess the special properties of silicones: excellent spreading and fi lm-forming properties, gloss, dry nonsticky feel (35). Polish formulations in the form of water-in-silicone emulsions are obtained in a way similar to those described for antiper- spirants. Silicones in these applications create easily spreading fi lms and also facilitate the transport of other polishing oils and waxes. LIPOSOMES Liposomes are similar to nanogels but with different permeation properties, and are made up of phospholipids building blocks. Each phospholipid molecule has three major parts, one hydrophilic head and two hydrophobic tails. Liposomes, are self-assembled spherical colloidal vehicles of phospholipids bilayers with an aqueous cavity, which engulfs the water-soluble actives. They are proven to be very good carriers for cosmetics and drug attributes (18). Use of liposome in cosmetics can improve the permeation and availability of skin active components (19). The liposome particles have means for binding to microorganisms re- sponsible for skin disorders, scalp irritation, and underarm and foot odor and hence can be used to selectively treat these disorders (20). Though they are highly biocompatible, they suffer from the disadvantages of being leaky and of limited loading capacity (18). When a surfactant such as dodecyl sulfonate is added to a liposome made up of phospha- tidyl choline and phosphatidic acid, initially the size of the liposome increases and subse- quently it is solubilized (21). Electron spin resonance studies have shown the polarity and viscosity of liposomes change to that of micelles of dodecyl sulfonate at suffi ciently high concentrations of the surfactant. While the actual processes by which such disintegration takes place are not known, the process is very important from the release point of view. Recent experiments suggest that phosphatidic acid exits fi rst, leading to the weakening of the liposome structure and hence its dissolution. Furthermore, while the addition of cholesterol stabilizes liposomes, proteins destabilize them (22). GREENER SURFACTANTS FOR CLEANSING As discussed earlier, surfactant production from petroleum resources contributes to the release of atmospheric CO2 while there is a limit to the amount of palm and coconut oil that can be manufactured responsibly for natural derived surface active agents. There is a need for sustainable manufacturing of surfactants and development of greener surfactants will be important in cosmetic and personal care applications. Generally, the surface active reagents that are produced from renewable resources or bio- processes are considered to be green surfactants. For instance, sugar based polyglucosides and amino acid based lipopeptides, which have been studied toward many applications in industries. These green surfactants have many advantages, such as biodegradability, low

JOURNAL OF COSMETIC SCIENCE 256 toxicity and environmental compatibility. For further understanding on green surfac- tants, their interfacial properties have to be investigated in the comparison with conven- tional petroleum based surfactants. More importantly, the synergistic effect when mixed with other green surfactants or conventional ones is the key property towards higher effi - ciency at lower dosage. For e.g., acyl glutamate surfactants have shown unique interfacial properties such as high surface activity when mixed with conventional surfactants such as dodecyl maltoside (36). Acyl amino acid surfactants, such as myristoyl glutamate, are popular with consumers because these surfactants interact favorably with skin and hair (37), are hypoallergenic (38), do not cause eye irritation (39), and are readily biodegradable (40). In collaboration with modular genetics a new green surfactant was synthesized by using an engineered Bacillus strain. The engineered synthetase produces an acyl amino acid composed of a beta- hydroxy fatty acid linked to glutamate, referred to as FA-Glu (fatty acid-glutamate) (41). Due to the similarity in structure of FA-Glu to myristoyl glutamate, the water sol- ubility and CMC of these surfactants were measured (Figure 4). It was found that FA-Glu is more water soluble than myristoyl glutamate. In addition, FA-Glu has higher surface activity, as refl ected by its lower CMC (41) (1.3 mM for FA-Glu versus 14.1 mM for myristoyl glutamate). A lower relative CMC indicates that less FA-Glu should be re- quired in a formulation to achieve a particular desired reduction in surface tension. In addition, a lower CMC is correlated with an increased effectiveness in removing soils in cleaning formulation (39). CONCLUDING REMARKS Nanomaterials, such as nanogel particles, hybrid polymer nanodomains, nanoemulsions and liposomes have shown good applications in cosmetic science. The present article dis- cusses the mechanisms of development and understanding of these the nano-sized sys- tems. Hybrid polymers and their nanoemulsions can be used a delivery systems as well as for cosmetic effect (shine, glossiness, softness) on a given substrate. Figure 4. Comparison of critical micelle concentration for Fa-GLU (fi lled circle) and myristoyl glutamate (empty diamond), adapted from Gabriel O. Reznik et.al.