Journal of Pharmaceutical and Biomedical Analysis 49 (2009) 655–659 Contents lists available at ScienceDirect Journal of Pharmaceutical and Biomedical Analysis journal homepage: www.elsevier.com/locate/jpba Evaluation of surface and microstructure of differently plasticized chitosan films János Bajdik a , Marzia Marciello b , Carla Caramella b , Attila Domján c , Károly Süvegh d,e , Tamás Marek e , Klára Pintye-Hódi a,∗ a Department of Pharmaceutical Technology, University of Szeged, Eötvös u. 6, H-6720 Szeged, Hungary b Department of Pharmaceutical Chemistry, University of Pavia, Viale Taramelli 12, 27100 Pavia, Italy c Institute of Structural Chemistry, Chemical Research Center, Hungarian Academy of Sciences, P.O. Box 17, Budapest H-1525, Hungary d Laboratory of Nuclear Chemistry, Eötvös Loránd University, H-1518 Budapest 112, P.O. Box 32, Hungary e Laboratory of Nuclear Chemistry, Chemical Research Center, Hungarian Academy of Sciences, H-1117 Budapest, Pázmány P. s. 1/A, Hungary article info Article history: Received 21 August 2008 Received in revised form 14 November 2008 Accepted 12 December 2008 Available online 24 December 2008 Keywords: Chitosan Plasticizer Positronium lifetime measurement Solid-state NMR Surface free energy abstract Surface and structural investigations of natural biopolymer (chitosan) films containing various conven- tionally applied hydrophilic plasticizers (glycerol and poly(ethylene glycol) 400) were performed and the results were compared, with the aim of acquiring new information concerning the formation of these plasticized films. The surface tests revealed that the water uptake, the water-binding properties (mois- ture content) and the polarity were higher for the film containing glycerol as plasticizer. Positronium lifetime measurements and NMR studies performed to evaluate the effects of the plasticizer on the poly- mer structure demonstrated relevant differences in the effects of the plasticizers. The influence of glycerol on the structure of the film formed was more intensive than that of PEG 400. It can be concluded that the surface properties of the films, which are very important for their storage and application, cannot be established exactly by means of structural tests. Both surface and structural tests must be performed before the formulation of this type of plasticized mucoadhesive films. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Efforts are currently being made to acquire a more detailed understanding of all technological processes in pharmaceutical technology and hence in industry. Knowledge of film formation from aqueous solution of polymers is very important during the coating of solid dosage forms. This process and the structure of the film can be influenced by different additives [1,2]. An understanding of the formation of macromolecular films is very important, because the field of application of these films is constantly becoming wider. They are used not only as coatings and binders for granulation, but also as separate dosage forms (films for topical application), e.g. the buccal administration of different sensitive agents, such as proteins [3,4]. An exact knowledge of film-formation properties can be infor- mative in an evaluation of the surfaces of films. These are very relevant because the surface can determine the adhesion to the core or to biological membranes (bioadhesion for drug-loaded films) [5]. In spite of the importance of these surface tests, however, they are not frequently performed during optimization of fluids containing film-former agents. In studies conducted to evaluate the properties ∗ Corresponding author. Tel.: +36 62 545 576; fax: +36 62 545 571. E-mail address: klara.hodi@pharm.u-szeged.hu (K. Pintye-Hódi). of the surfaces of films, mainly films prepared from different solu- tions have been used [6,7]. It this case, the aqueous and organic solution of different types of cellulose ethers was evaluated. This can furnish a better understanding of the effects of different addi- tives. The changes in the surface properties of films due to the additives must not decrease the adhesion of the complex film to the surface. The adhesion between the particles can be calculated from the surface free energies of the components [8]. The levels of adhesion between solid materials and a single binder polymer for granulation have been evaluated [9,10]. In these studies, the work of adhesion and the work of cohesion were calculated and correlated with the pellet properties (friability, bulk and tapped density, and porosity). However, those publications did not deal with the films, but only with the solid components. In the event of the coating of films containing a large number of additives, it is not enough to determine the adhesion between the polymer and the core. Determination of the surface free energy of the com- plex film is therefore very important. It is well known from our previous results that the surface properties of film can not be pre- dicted from the parameters of the separate components [11]. In that study, taste-masking films were prepared from aqueous cit- ric acid solutions of a cationic polymer with various hydrophilic plasticizers. The wetting properties and surface free energy of the free films were studied. The direction of the change in polarity (a hydrophilic component caused a decrease in the polarity) was 0731-7085/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jpba.2008.12.020