Journal of Microencapsulation, 2012; 29(2): 147–155 ß 2012 Informa UK Ltd. ISSN 0265-2048 print/ISSN 1464-5246 online DOI: 10.3109/02652048.2011.635220 Sealing liquid-filled pectinate capsules with a shellac coating Stefan Henning 1 , Sabine Leick 2 , Maureen Kott 2 , Heinz Rehage 2 and Dieter Suter 1 1 Department of Experimental Physics III, TU Dortmund University, 44227 Dortmund, Otto-Hahn-Strasse 4, Germany, and 2 Department of Physical Chemistry II, TU Dortmund University, 44227 Dortmund, Otto-Hahn-Strasse 6, Germany Abstract Liquid-filled pectinate capsules have a large potential for the controlled and site-specific delivery of liquid drugs. Earlier studies have shown that pure pectinate capsules can store drugs only for a few minutes. Here, we show that the retention time can be extended to several hours by coating the capsules with the natural resin shellac. A bilberry extract containing anthocyanins with promising therapeutic properties was used as model drug to characterize the permeability of the capsules by in vitro drug release measurements. Characterizing the structure of the double-layered capsule membranes by NMR microscopy, we optimized the capsule production by adjusting the pH-value in the coating process and the gelation time of the pectinate hydrogel layer. A comparison of the layer thicknesses with drug release measurements reveals that capsules with the thinnest shellac layers provide the best entrapment. Additional squeezing experi- ments show that the shellac layer makes the capsules also mechanically more stable. Keywords: microencapsulation, coating, gastrointestinal, hydrogels, in vitro release, controlled release Introduction Capsules consisting of natural polysaccharide hydrogels such as alginates or pectins are frequently used for the encapsulation and transportation of drugs and for the transplantation of cells (Murano, 1998; De Vos et al., 2006; Champagne and Fustier, 2007). The encapsulation protects the content of the capsules against outer influ- ences like enzymes of the gastrointestinal (GI) tract and provides the possibility of controlled and site-specific release. The functionality crucially depends on the perme- ability of the capsules as well as on their mechanical and chemical stability. In order to decrease the permeability and to improve the stability of the capsules, they can be coated with additional layers. This study investigates the influence of an external shellac coating on liquid-filled pectinate capsules on their permeability and mechanical structure. The capsules were prepared in different ways and the relationship between the preparation, the structural composition of the capsule membrane, the mechanical stability and the permeability was observed by NMR microscopy, squeezing capsule experiments and drug release measurements, respectively. The inner membrane layer of the studied capsules con- sists of the polysaccharide pectin which can be extracted from the cell walls of higher plants (Sriamornsak, 2003). Because of its biodegradability, it has been used as thick- ening agent, gelling agent, colloidal stabilizer and transport matrix for drugs in the food and pharmaceutical industries. Low-esterified pectins form three-dimensional ionotropic gels with divalent cations. Here, we use this property to produce liquid-filled spherical capsules with a membrane of gelled pectinate. While these capsules have been shown to be useful (Liu et al., 2003; Leick et al., 2011), the perme- ability of these membranes is too high for many applica- tions (Ferreira et al., 2009). Here, we show how the permeability of these capsules can be reduced significantly by coating the polysaccharide membranes with an additional layer. Typically used coat- ings are chitosan, poly-l-lysine or shellac (Lim and Sun, 1980; Chiou et al., 2001; Ravi et al., 2008a). Shellac, a phys- iologically harmless and biodegradable resin secreted by Address for correspondence: Stefan Henning, Department of Experimental Physics III, TU Dortmund University, 44227 Dortmund, Otto-Hahn-Strasse 4, Germany. Tel: 0049 (0)231 7553562. Fax: 0049 (0)231 7553516. E-mail: stefan.henning@tu-dortmund.de (Received 1 Jun 2011; accepted 7 Oct 2011) http://www.informahealthcare.com/mnc 147