Carbohydrate Polymers 93 (2013) 191–198 Contents lists available at SciVerse ScienceDirect Carbohydrate Polymers jo u rn al hom epa ge: www.elsevier.com/locate/carbpol Enzymatic digestion of partially and fully regenerated cellulose model films from trimethylsilyl cellulose Tamilselvan Mohan a , Rupert Kargl b,∗ , Aleˇ s Doliˇ ska a , Heike M.A. Ehmann a,b , Volker Ribitsch b,1 , Karin Stana-Kleinschek a,1 a Laboratory for Characterization and Processing of Polymers, Faculty of Mechanical Engineering, University of Maribor, Smetanova 17, SI-2000 Maribor, Slovenia b Institute of Chemistry, Karl-Franzens-University Graz, Heinrichstraße 28/III, AT-8010 Graz, Austria a r t i c l e i n f o Article history: Received 10 October 2011 Received in revised form 8 February 2012 Accepted 17 February 2012 Available online 25 February 2012 Keywords: Cellulase Cellulose model films Quartz crystal microbalance Capillary zone electrophoresis Wettability Attenuated total reflectance infrared spectroscopy a b s t r a c t Partially and fully regenerated cellulose model films from trimethylsilyl cellulose (TMSC) were prepared by a time dependent regeneration approach. These thin films were characterized with contact angle measurements and attenuated total reflectance infrared spectroscopy (ATR-IR). In order to get further insights into the completeness of the regeneration we studied the interaction of cellulase enzymes from Trichoderma viride with the cellulose films using a quartz crystal microbalance with dissipation (QCM-D). To support the results from the QCM-D experiments capillary zone electrophoresis (CZE) and atomic force microscopy (AFM) were applied. The changes in mass and energy dissipation due to the interaction of the enzymes with the substrates were correlated with the surface wettability and elemental composi- tion of the regenerated films. The highest interaction activity between the films and the enzyme, as well as the highest cellulose degradation, was observed on fully regenerated cellulose films, but some degra- dation also occurred on pure TMSC films. The enzymatic degradation rate correlated well with the rate of regeneration. It was demonstrated that CZE can be used to support QCM-D data via the detection of enzyme hydrolysis products in the eluates of the QCM-D cells. Glucose release peaked at the same time as the maximum mass loss was detected via QCM-D. It was shown that a combination of QCM-D and CZE together with enzymatic digestion is a reliable method to determine the conversion rate of TMSC to cellulose. In addition QCM-D and AFM revealed that cellulase is irreversibly bound to hydrophobic TMSC surfaces, while pure cellulose is digested almost completely in the course of hydrolysis. © 2012 Elsevier Ltd. All rights reserved. 1. Introduction The surface properties of cellulose can be studied using well defined model substrates in the form of nanometric thin films. Com- monly used methods for the preparation of these films are spin coating or Langmuir–Blodgett film forming of cellulose suspensions or derivatives (Ahola, Salmi, Johansson, Laine, & Österberg, 2008; Ahola, Turon, Österberg, Laine, & Rojas, 2008; Geffroy, Labeau, Wong, Cabane, & Cohen Stuart, 2000; Gunnars, Wågberg, & Cohen Stuart, 2002; Holmberg et al., 1997; Kontturi & Lankinen, 2010; Schaub, Wenz, Wegner, Stein, & Klemm, 1993; Wegner, Buchholz, Stemme, & Ödberg, 1996). As cellulose derivative, trimethylsilyl cellulose (TMSC) is often used for substrate coatings or surface interaction studies (Findenig et al., 2012; Spirk et al., 2010). These thin TMSC films can be partially or completely regenerated back to pure cellulose by hydrochloric acid vapours which cleave the ∗ Corresponding authors. E-mail addresses: rupert.kargl@uni-graz.at (R. Kargl), karin.stana@uni-mb.si (K. Stana-Kleinschek). 1 1 Member of the European Polysaccharide Network of Excellence (EPNOE). Si O bonds under formation of trimethylsilyl chloride and further hydrolysis to trimethylsilanol (Spirk, Nieger, Belaj, & Pietschnig, 2009). In this case films with different wettabilities and silicon contents can be obtained by adjusting the regeneration param- eters during the desilylation reaction (Mohan et al., 2011). The desilylation can conventionally be monitored using well estab- lished techniques such as attenuated total reflectance infrared spectroscopy (ATR-IR), X-ray photoelectron spectroscopy (XPS) (Kontturi, Thüne, & Niemantsverdriet, 2003a) or Raman spec- troscopy (Woods, Petkov, & Bain, 2011). Besides the investigations of surface properties such as wettabilities or elemental composi- tions, model films were also used to study the enzymatic digestion of cellulose or cellulose derivatives from different origins (Jausovec, Angelescu, Voncina, Nylander, & Lindman, 2008; Wang, Wang, & Ragauskas, 2010). In particular, the quartz crystal microbalance with dissipation monitoring (QCM-D) as a nanogram sensitive balance (Rodahl, Höök, Krozer, Brzezinski, & Kasemo, 1995) in com- bination with well defined model films of cellulose, was used to study the adsorption properties and digestion rates of cellulase enzymes systematically (Cheng et al., 2011; Eriksson et al., 2005; Esaki et al., 2009; Suchy et al., 2011). A significant contribution to this was the study of Ahola et al., who investigated cellulase 0144-8617/$ – see front matter © 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbpol.2012.02.033