Industrial concentrates of hesperidin nanocrystals (5.0% nominal concentration) were produced applying the smartCrystal(®) combination technology of wet bead milling and subsequent high pressure homogenization. Stabilization was performed by Kolliphor(®) P 188, preservation by Euxyl PE 9010 and glycerol. Physical and chemical stability were monitored over 1.5 years of storage at 4-6 °C. The size of the bulk population stayed unchanged with about 250 nm (photon correlation spectroscopy). Absence of crystal growth by Ostwald ripening and absence of agglomerates were shown by laser diffraction (LD) and light microscopy. The LD diameter 90% was still 0.7 μm after 1.5 years. Despite the large surface of the nanosuspension in contact with the water phase, the chemical content proved also stable, only a reduction by 0.15% from 5.70% to 5.55% content was observed. The nanocrystals kept their crystalline state unchanged as shown by X-ray diffraction. The saturation solubility of the nanosuspension was more than triple compared to the raw drug powder in water. The data show the availability of a stable hesperidin concentrate as intermediate for industry to produce dermal formulations.

SUMMARY smartCrystal ® technology combining bead milling and subsequent high pressure homogenization was used and the process parameters for large scale production of hesperidin nanocrystals were established. A hesperidin concentrate was processed to make the process cost-effective (bead milling). For the final marketed product, this concentrate was diluted to 5%, and high pressure homogenized, yielding a product with PCS diameter of 265 nm. INTRODUCTION The potent antioxidative effect of flavonoids can be used in cosmetic products to prevent skin from aging and wrinkles – assumed a sufficient high skin penetration can be obtained by the dermal formulation. Cosmetic products can be gel, cream or lotion. However, the poor water solubility of this kind of actives limits the application due to the consequently low skin penetration and absorption. Nanocrystals increasing the oral bioavailability are meanwhile also dermally applied to improve the penetration into the skin. Cosmetic products are on the market since 2007. The improvement of the penetration of the poorly soluble actives into skin is caused by 3 effects: 1. The increased saturation solubility of the active (refers to Kelvin equation) generates a higher concentration of active in the formulation on the skin, subsequently a higher concentration gradient. 2. The nanosized particles have a high contact area to the skin, are adhesive and have a long residence time. 3. The small size leads to follicular accumulation of the nanocrystals promoting absorption and forming a depot. Two main methods, bead milling and high pressure homogenization, can be used in production of nanocrystals on large scale and industrial scale. Bead milling has been applied in pharmaceutical industry widely (e.g. Nanosystems/élan), being a low energy process. High pressure homogenization was developed as alternative process in the 1990ies to produce nanocrystals with high energy input allowing also aseptic production. The newly developed smartCrystal ® technology [1, 2] combines bead milling with high pressure homogenization. In this study hesperidin nanocrystals were produced on large scale as commercial nanocrystal concentrate for incorporation into cosmetic products. High concentrated nanosuspension was produced by bead milling first. This intermediate product was then diluted to the final market product concentration (5%) and processed by high pressure homogenization. EXPERIMENTAL METHODS Coarse suspension (batch weight 18 kg) of hesperidin (Table 1) as the intermediate concentrate was passed five times through a bead mill Bühler PML-2 (Bühler AG, Switzerland) with 1050 ml milling chamber. 0.4-0.6 mm Yttriumoxid stabilisiertes zirkon oxide beads (Hosokawa Alpine, Germany) were used as the milling medium. Milling rotator speed was 2000 rpm, pump capacity was 10%. During the production, the milling chamber was cooled at 5 o C. The size of nanocrystals was monitored during the milling after each passage. The milled product obtained after five passages was diluted (Table 1) and homogenized using an Avestin C50 (Avestin, Canada) applying 1 cycle at 500 bar to obtain the final market product. Content of active and preservative in the final product were measured by HPLC. Size analysis was carried out by photon correlation spectroscopy (PCS) (Zetasizer Nano ZS, Malvern Instruments, UK), laser diffractometry (LD) (Mastersizer 2000, Malvern Instruments, UK) and light microscopy (Ortophlan, Germany). Table 1. Compositions of nanocrystal concentrate and marketed dilution of the nanosuspension Formulation of concentrate (w/w) 18 kg batch