BONACUCINA, Giulia

CESPI, MARCO

PALMIERI, Giovanni Filippo

English

Archivio istituzionale della ricerca - Università di Camerino

 INTRODUCTION Poloxamers are block copolymers of ethylene oxide(EO) and propylene oxide (PO) used in differentindustrial areas such as detergents, foaming,lubrication, dispersion, stabilization, cosmetics, inks[1] and pharmaceutical field [2].  Their temperature-dependent self-assembling andthermogelling behaviour is well known. In fact, Poloxamers (above a certain concentration and at aspecific temperature) possess in water the ability tochange from individual block copolymer molecules(unimers) to self-assembling micelles. Moreover,some kind of Poloxamers are also characterized by aspecific temperature at which micelles organized(cmT, critical micelle temperature or gel point)generating the transition from a viscous solution to astrong gel. Both micellization and gelation dependon different factors: temperature, polymerconcentration, PEO block length [3] and presence ofseveral additives.  In this paper the thermogelling properties ofPoloxamer 407 have been analysed in order todetermine modification in samples behaviour afterthe addition of lactose. The work is part of larger project focussing on the development of a thermogelsystem able to work as a crystallization medium,being gelled at ambient temperature and liquid at alower temperature, so that the crystals can be easilyharvested. The effect of solute and Poloxamerconcentration have been very well characterized inorder to generate a system with the right conditionfor crystallization and gelation. Effect of Lactose on the thermogelation properties ofPoloxamer 407  Marco Cespi, Giulia Bonacucina, Giovanna Mencarelli, Giovanni Filippo Palmieri  Department of Chemical Sciences, University of Camerino, Italy  Mail: gianfilippo.palmieri@unicam.it  EXPERIMENTAL METHODS Materials Poloxamer 407 (Lutrol F127, Acef, Italy; molecular weight 12600 and PEO/POP ratio 2:1) and ά-Lactose monohydrate (Pharmatose 150M, DMV International, The Netherlands) were used as received. Deionised water was produced with a laboratory deionizer (Osmo Lab UPW 2, Gamma 3, Italy). Samples preparation Concentrated solutions of Poloxamer 407 (Poloxamer stock solutions, PSS) were prepared by dispersing the polymer in the required amount of degassed and deionised water using the “cold” procedure . PSS were stored at 4-5 °C for at least 48 hours before the use. Concentrated solutions of lactose (Lactose stock solutions, LSS) were instead prepared by dissolving the disaccharide in the required amount of degassed and deionised water at 70°C. Suddenly after the preparation, the LSS were left at room temperature until they reach the temperature of 25°C, and then added to the PSS stored in an ice bath. The final solutions were mixed for 10 minutes while is still in ice bath.  Rheological characterization Rheological analyses were performed using a stress control rheometer (Stress-Tech, Reologica) equipped with cone-plate geometry (4/40), automatic gap. All the systems were analysed suddenly after the preparation using a temperature sweep test (from 5 to 30 °C, 1°C/min, 1Hz, 1Pa)  7th World Meeting on Pharmaceutics, Biopharmaceutics and Pharmaceutical TechnologyMalta, 8th to 11th March 2010                                                                RESULT AND DISCUSSION The temperature sweep test allows the determinationof the gelation temperature and the quantification ofthe variation in samples elasticity. The sol/geltransition temperature is the temperature characterised by a drastic increase in the elastic and viscous modulus and by a drastic decrease of the phase angle (Fig. 1A). The gel point is representedby the temperature where the phase angle drop to avalue of 45° and the two moduli present similar values. Rheological tests showed that not all thecomposition analysed had the same behaviour interm of gelling performance and three different kindof systems have been observed: gelling, partiallygelling and no gelling (Fig. 1A, 1B and 1Crespectively). Similar results were evident also froma visual examination of the flow gel attitude.  020406080100120   Phase angle(degree) B Phase angle  A C5 10 15 20 25 300,010,1110100100010000 G',G" (Pa)Temperature (ºC)5 10 15 20 25 30  Elastic modulus G'Temperature (ºC)5 10 15 20 25 30 35 40 Viscous modulus G"Temperature (ºC)Figure 1. Effect of temperature on the rheologicalparameters G’,G” and phase angle for the A) gelling, B) partially gelling and C) no gelling systems.  The component ratio of the different gelling systemsand the influence of the system composition on thegel point (only for the gelling samples) are shown infig. 2. The gel point is strongly dependent on the Poloxamer and lactose concentration, particularly itdecreases as the concentration of the twocomponents increases. The results clearly indicatethat lactose interacts with the system Poloxamer/water altering its gelation properties, interm of gel point as well as rheological behaviour.   0 2 4 6 8 10 12 14 16 18 20 22 24 2610121416182022242628303234 gelation partial gelation no gelationPoloxamer (% w/w)Lactose (% w/w)10,0014,0016,0018,0020,0022,0026,0028,70Experimental data    Gel point (°C)        Figure 2. Effect of composition in rheological behaviour and gel point.  The same systems considered for gel point analysis were analysed also in term of complex viscosity in the temperature range below the gel point. As expected, results (not shown) showed an increase of the viscosity as the Poloxamer and lactose concentration increase, however the viscosity values were much less variable compared to gel point results. CONCLUSIONS Lactose interacts with poloxamer-water sysytems affecting the gelation temperature as well as their rheological behaviour. For a constant poloxamer concentration an increase of lactose amount decreases the gel point up to a threshold value over which it depress the gelling attitude until a complete inhibition of such process.  REFERENCES [1] P. Alexandridis, T. A. Hatton, Colloid Surf A-Physicochem Eng Asp 1995, 96, 1. [2] A. V. Kabanov, V. Y. Alakhov, Crit Rev Therap Drug Carrier Syst 2002, 19, 1. [3] N. K. Pandit, D. Wang, Int J Pharm 167 1998, 167, 183.    7th World Meeting on Pharmaceutics, Biopharmaceutics and Pharmaceutical TechnologyMalta, 8th to 11th March 2010

Effect of Lactose on the thermogelation properties of Poloxamer 407.

https://pubblicazioni.unicam.it/bitstream/11581/202400/1/Malta%202010%203.pdf

Effect of Lactose on the thermogelation properties of Poloxamer 407.

Abstract

Similar works

Full text

Available Versions

Archivio istituzionale della ricerca - Università di Camerino