Carbohydrate Polymers 88 (2012) 1033–1040 Contents lists available at SciVerse ScienceDirect Carbohydrate Polymers jo u rn al hom epa ge: www.elsevier.com/locate/carbpol Rheological characterization and release properties of inulin-based hydrogels Giovanna Pitarresi a,b,∗ , Daniela Giacomazza c , Daniela Triolo a , Gaetano Giammona a,c , Pier Luigi San Biagio c a Dipartimento di Scienze e Tecnologie Molecolari e Biomolecolari, Sezione di Chimica e Tecnologie Farmaceutiche, Università degli Studi di Palermo, Via Archirafi 32, 90123 Palermo, Italy b Istituto di Biomedicina e Immunologia Molecolare “Alberto Monroy”, Consiglio Nazionale delle Ricerche, Via U. La Malfa, 153, 90146 Palermo, Italy c Istituto di Biofisica (Palermo Unit), Consiglio Nazionale delle Ricerche, Via U. La Malfa, 153, 90146 Palermo, Italy a r t i c l e i n f o Article history: Received 26 October 2011 Received in revised form 12 January 2012 Accepted 19 January 2012 Available online 28 January 2012 Keywords: Inulin UV irradiation Chemical hydrogels Rheological measurements Drug release a b s t r a c t In the present study the rheological properties of hydrogels obtained through UV irradiation of an aque- ous solution of methacrylated inulin (INUMA) alone or in the presence of four different crosslinkers, have been recorded as a function of irradiation time, at two different wavelengths (320 and 365 nm) and fixed frequency and amplitude by oscillatory experiments. Each hydrogel has been analyzed by mea- surements of the frequency-dependency of the elastic modulus, G ′ , in the linear viscoelastic region. The amount of polymeric chains giving an elastic response has been correlated to the chemical nature of the crosslinker used together with INUMA. Finally the release properties of the hydrogel exhibiting the highest elastic modulus have been tested by using 5-Fluorouracil, as a model drug, and two different loading procedures. The rheological characterization allowed us to determine the most effective condi- tion (appropriate crosslinker, wavelength and irradiation time) to obtain a strong hydrogel that was able to give a modified drug release in simulated gastrointestinal fluids. © 2012 Elsevier Ltd. All rights reserved. 1. Introduction Inulin (INU) is a natural polysaccharide belonging to the fruc- tan group. It mainly, if not exclusively, consists of (2 → 1) fructyl fructose units (F m ) with normally, but not necessarily, one glucopy- ranose unit at the reducing end (GF n ) of the chain (De Leenheer, 1996; Hirst, McGilvray, & Percival, 1950; Stevens, Meriggi, & Booten, 2001; Van Loo, Coussement, De Leenheer, Hoebregs, & Smits, 1995). It is present in many plants, including onion, garlic, leek, chicory and artichoke. Its average chain length and molecular weight distribution depend on the plant species, the growth phase and preparation method. Average chain lengths of 30 fructose units are usual (Kunz & Begli, 1996). The growing interest in INU is due to its properties: it is non- toxic, biocompatible, water soluble, specifically degraded in the colon and very cheap polymer (Biedrzycka & Bielecka, 2004; Gibson & Roberfroid, 1995; Wang & Gibson, 1993). ∗ Corresponding author at: Dipartimento di Scienze e Tecnologie Molecolari e Biomolecolari, Sezione di Chimica e Tecnologie Farmaceutiche, Università degli Studi di Palermo, Via Archirafi 32, 90123 Palermo, Italy. Tel.: +39 09123891954; fax: +39 09123891960. E-mail address: giovanna.pitarresi@unipa.it (G. Pitarresi). Moreover, there are many beneficial effects of INU and oligosac- charides in general, for human health. It must be mentioned, particularly: (1) reduction of blood lipid levels; (2) selective stimulation of growth of bifidobacteria population in the intestine; (3) enhancement of the absorption of minerals in the colon. INU is also used in diagnostics for the determination of the renal clearance and in several foodstuffs as a dietary fiber (Knudsen & Hessov, 1995) and no significant inulin side effects have been noted in the medical literature except the case of very high concentra- tions. Series of animal studies demonstrate that inulin-type fructans affect the metabolism of lipids primarily by decreasing triglyc- eridaemia (Delzenne et al., 1993; Fiordaliso et al., 1995). Recent studies have shown that the effects on serum triglycerides are due to the reduced secretion of the very low density lipoprotein (VLDL) particles from the liver and associated with decreased activity and gene expression of the key regulatory enzyme, fatty acid synthetase (Kok, Roberfroid, & Delzenne, 1996a, 1996b). Although the data obtained from animal studies suggest convincing lipid-lowering properties of INU and oligofructose compounds in general, much less information is available from human studies, in which the 0144-8617/$ – see front matter © 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbpol.2012.01.059