222 JOURNAL OF COSMETIC SCIENCE CLEANSING AND RELEASE BY NOVEL NANOGEL CARRIERS Ponisseril (Som) Somasundaran, Ph.D., F. Liu, D. Sarkar and C.C. Gryte National Science Foundation I/UR Center, Langmuir Center for Colloids and Interfaces Columbia University, New York, NY 10027 There is an ever-increasing need for environmentally benign cosmetic ingredients that can be released at slow rates. Design of personal care products for desired release of actives or removal of undesired secretions involves transport of the carrier onto the skin or the hair, deposition in response to dilution or changes in pH, temperature or salinity and release of the actives at a controlled rate. New polymer nanogels provide an efficient means to fulfill these requirements when appropriately modified to interact with the desired actives. Polyacrylamide nanogels, a type of nanosized, cross linked particles, have been synthesized towards this purpose using inverse microemulsion polymerization. These water-soluble, sponge-like nanogels are very small in size (50 nanometers) and have vast amounts of interstitial space between the polymer chains. To make them more specific and efficient, a series of chemical modifications were carried out by firstly copolymerizing ofN-acryloxysuccinimide into PAM structure and secondly using the activity ofsuccinimide to substitute various chemical functions into the nanogel structure. In addition, amide on the PAM was hydrolyzed to pendant carboxylic acid group, these methods permit the introduction of hexyl groups, ionic glycine and acrylic acid (anionic) and their combinations. The resultant functional nanogels and the unmodified nanogels were characterized in terms of swelling abilities, hydrophobicity and charge density. The physical properties of nanogel particles were changed significantly by the introduction of such functional groups. Active encapsulation experiments using 3-( 10, 11-dihydro-5H-dibenzo [ a,d] cycloheptene-5-ylidene )-N,N­ dimethyl-1-propanamine hydrochloride (C20H23N·HC1), a compound with hydrophobic and ionic groups and pyrene, that is hydrophobic, as target molecules were carried out with these nanogels. As can be seen from Figures 1 and 2, the nanogels chemically modified for hydrophobicity and/or electrostatic charge show markedly higher ability for active binding when compared to the unmodified nanogels. While Figure 1 shows the binding of the organic active as a function of crosslinking density, Figure 2 shows I/I 1 , a fluorescence parameter indicating the hydrophobicity around the pyrene molecules in the nanogels. 1/11 varies from 0.6 to 1 as a function of non-polarity. It can be seen that the nano gel is hydrophobic and the modification with hexyl groups increases the hydrophoibicity and thus the potential for uptake of organic materials. The polymeric repeat unit composition and the type of pendent groups on the polymer matrix of the nanogel are crucial for determining the degree of swelling and the capacity of the nanogels. Nanogels with different crosslinking densities were also prepared by inverse microemulsion polymerization and were modified by attaching hexyl and/or carboxylic acid groups to the polymer backbone. The effects of cross linking density on the structure of the polyacrylamide nano gel particles investigated by dynamic and static light scattering measurements, suggested that the swelling abilities of the nano gel particles strongly depend on the degree of the cross linking density. At high crosslinking density, the structure of the nanogel particle can be described as a rigid sphere. With the decrease in crosslinking density the nanogel particles tend to be flexible random networks. The crosslinking density proves to be important factor for active encapsulation abilities of nanogels, especially for large organic molecules. Active binding with nanogels to some extent, depends not only on the interaction between the organic molecules and the polymer backbone but also on the diffusion of the organic molecules inside the nano gel network. The highly crosslinked nano gels usually have compact structure with small particle size and might sterically exclude the large molecules. As the crosslinking density is decreased, the particles become less compact which makes the interior accessible for large molecules and thus the binding efficiency is increased.

2003 ANNUAL SCIENTIFIC MEETING 223 Release of tested absorbed organic species (C20H23N·HC1) was obtained by limited dilution and the results are plotted in Figure 3. When equilibrium is reached, 20% of the drug is released, indicating the nanogels to be good carriers to encapsulate small molecules and to have the potential for controlled release applications. In Figures 4 and 5, kinetics of small molecule binding and release processes was investigated using surface plasma resonance spectroscopy (SPR), a powerful technique for monitoring short-term and long-term changes. Results obtained are shown in Figures 4 and 5. Both processes are quick and the equilibrium is established within 20 minutes. These nanogels, as a type of carriers, exhibit flexibility for tailoring for different applications. By combining the effects of the crosslinking density and functional groups, nano gels can provide efficient delivery and release of active molecules. The build-up of structure-property relationships between functional nanogels and organic molecules provides a powerful means for designing carriers for uptake/release of fragrances as well as other types of active components with nano gels. 350 1, 300 i 250 � g 2 00 .. §] 150 i! � 100 1 50 a Nanogel Concentration = 5 mg/ml, In water \. C 20 H 13 N · HCI Concentration = 0.5 mg/ml 6-----.C6/Neg -·- -A._____________, C6 Neg l,_11---Un_m_o�dlfl_ed_····--·-·-··-··-t 0 +----,----.----.----,----,----1 0 10 12 Crosslinking Density,% Figure 1. C2oH23N·HCl binding with nanogels as a function of crosslinking densities 80 100 .. ::,7 80 t 60 ·a .. 60 � 40 40 "2 B 2 0 'a .. ' " · - · - •···II•,. - - II 20 � 0 0 0 100 2 00 300 400 500 Bound Active by N anogels, micromole Figure 3. CzoH23N·HCl release from nanogels C 20 H13N·HCI, Temp.= 25'C, pH= 6 .0.02 _____________ __, 20 40 60 80 100 110 1 Time, minutes Figure 5. Kinetics of C2oH23N·HCl release � '$. ii 1 � � � 0,82 0.78 0.74 0.7 0.66 0,62 0.58 C6nanogels ./_,. .,. , .,... Urmodffled 0.5 1.5 Nanogel Coo.centratim, wt% 2,5 Figure 2. Pyrene encapsulation with Nanogels 0.00� C 2 off23N·HC�25-C, pH= 6 20 40 60 80 100 120 140 Time,minute Figure 4. Kinetics of C2oH23N·HCl binding Acknowledgements We acknowledge the supports of National Science Foundation Engineering Research Center for Particle Science and Technology at University of Florida and National Science Foundation Industry/University Research Center for Advanced Surfactants at Columbia University