Please cite this article in press as: Pedacchia, A., Adrover, A., Study of release kinetics and diffusion coefficients in swellable cellulosic thin films by means of a simple spectrophotometric technique. Chem. Eng. Res. Des. (2014), http://dx.doi.org/10.1016/j.cherd.2014.03.017 ARTICLE IN PRESS CHERD-1538; No. of Pages 7 chemical engineering research and design x x x ( 2 0 1 4 ) xxx–xxx Contents lists available at ScienceDirect Chemical Engineering Research and Design j ourna l h omepage: www.elsevier.com/locate/cherd Study of release kinetics and diffusion coefficients in swellable cellulosic thin films by means of a simple spectrophotometric technique Augusta Pedacchia, Alessandra Adrover ∗ La Sapienza Università di Roma, Dipartimento di Ingegneria Chimica, Materiali e Ambiente, Via Eudossiana 18, 00184 Rome, Italy a b s t r a c t Measurement of diffusion in gel is an essential task for pharmaceutic technology and biochemical engineering. In this work we investigate diffusion coefficients and release kinetics of colored substances loaded in polymeric thin strips, by extending a simple spectrophotometric technique from catalysis science to swellable polymer matrices. Absorbance can be a measure of the average solute concentration in the swollen gel so that the time decay of film absorbance can be a quantitative measure of the release kinetics and henceforth of the diffusion coefficient in the swollen gel. Thin film dissolution is carried out in a newly proposed microfluidic continuous flow-through device. Hydroxypropyl methylcellulose (HPMC) is used as filming polymer. Film thickness, uniformity of content and swelling time-scales are accounted for in the estimation of the effective diffusion coefficient. © 2014 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved. Keywords: Oral strips; Swelling; Diffusion coefficient; Drug release; UV–vis spectrophotometry 1. Introduction Polymeric thin films have recently appeared as a very promis- ing pharmaceutical dosage form (Murata et al., 2010; Nishigaki et al., 2012). In the last few years, they have attracted much attention, because of their substantial advantages on tra- ditional alternatives: enhanced bioavailability, high patient compliance, patent life extension of well-known active phar- maceutical ingredients (Hearnden et al., 2012). Oral strips are films with thicknesses less that 100 m, similar in size and shape to a postage stamp. They are usually composed of a hydrophilic polymer, drug, plasticizers and excipients (Dixit and Puthli, 2009). In contact with saliva, films rapidly hydrate and gel, adhere onto the site of application and disintegrate, without the need of water (Morales and McConville, 2011; Semalty et al., 2008). Drug transport through polymeric matri- ces is a key aspect to estimate the kinetics of drug release (Narasimhan, 2001; Gao and Fagerness, 1995). Gel from tablets and (rarely) films of bioerodible polymers have been studied in pharmaceutical science with this aim (Siepmann et al., ∗ Corresponding author. Tel.: +39 0644585609; fax: +39 0644585451. E-mail addresses: alessandra.adrover@uniroma1.it, ladrover@yahoo.it (A. Adrover). 1999). Diffusion of solute substances in gels has been object of extensive research. No single method can be considered valid in all situations, but different methods must be adopted for different solute/polymer systems (Andersson et al., 1997). A number of experimental techniques have been proposed at this purpose (Dickson et al., 2012; Westrin et al., 1994; am Ende and Peppas, 1997; Ye et al., 2012; Brandl et al., 2010; Garcia- Aparicio et al., 2012). Latest research tendencies are oriented towards diffusion studies which could give real-time informa- tion about drug release, as a potential alternative to traditional dissolution testing methods (Boetker et al., 2013; Gauno et al., 2013). In this work, we study diffusion coefficients and release of colored active ingredients initially loaded in glassy thin films, by extending a simple spectrophotometric technique known in catalysis science (Takahashi et al., 2000, 2001) to swellable gels. This technique has been originally applied to the mea- surement of the diffusion coefficient of nickel nitrate in wet silica gel, which is a non-swelling gel. We adopt this experi- mental method to determine the effective diffusion coefficient http://dx.doi.org/10.1016/j.cherd.2014.03.017 0263-8762/© 2014 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.