Enzymatic Degradation of Hyperbranched Polyesters Rajendar Reddy Mallepally, 1 Irina Smirnova, 1 Wolfgang Arlt, 1 Matthias Seiler, 2 Saskia K. Klee-Laquai, 3 Geoffrey Hills 3 1 Chair for Separation Science and Technology, University of Erlangen-Nuremberg, Egerlandstrasse 3, D-91058 Erlangen, Germany 2 Evonik Degussa GmbH, Process Technology and Engineering, Fluid Processing VT-F, Rodenbacher Chaussee 4, D-63457 Hanau, Germany 3 Evonik Goldschmidt GmbH, Goldschmidtstrasse 100, D-45127 Essen, Germany Received 30 May 2008; accepted 15 October 2008 DOI 10.1002/app.29524 Published online 11 February 2009 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: In this work, the enzyme-catalyzed degrada- tion of hyperbranched polyesters (HBPEs) was investigated. Enzymatic degradation experiments were performed in a phosphate buffer in the presence of the lipases Candida cylindracea, Pseudomonas cepacia, Novozym 388, Amano CE, Lipomod 34P, and Cal-B, whereas control experiments were performed in the same system without lipases. The extent of polymer degradation was determined by quantification of the released free fatty acids by gas chromatography. The influence of the alkane chain length and the number of alkane chain end groups on the lipase-catalyzed hydrolysis of esterified HBPEs was investigated systematically. It was found that the increase in the alkane chain length of the end groups diminished the enzymatic degradation of the poly- mer, whereas the number of end groups had no influence on the degradation rate. The effect of temperature on the rate of degradation was also described. Surface morphologi- cal changes that occurred during the degradation were assessed with reflected electron microscopy. The changes in the crystallinity of the polymers after they were subjected to degradation were qualitatively determined with differential scanning calorimetry through the quantification of the en- thalpy of melting. The enthalpy of melting of one HBPE sample increased from 79 to 90 and 94 J/g with and without the action of Lipomod 34P, respectively, in 7 days, showing the changes in the crystallinity of the polymer. The results prove that modified HBPEs are an important new class of biodegradable materials with a predictable degradation mechanism, and the degradation can be adjusted on the ba- sis of the molecular engineering. V V C 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 1873–1881, 2009 Key words: biodegradable; enzymes; hyperbranched; polyesters INTRODUCTION In view of the growing interest in biodegradable poly- mers in the field of life sciences, especially in phar- maceutical applications, it is important to know the degradation behavior of such polymers under differ- ent conditions. Among the existing polymers for pharmaceutical and biomedical applications, polyest- ers offer the advantage of being hydrolyzed in the presence of enzymes. 1–3 The biomedical and ecologi- cal applications of biodegradable linear synthetic polyesters, such as poly(lactic acid), poly(glycolic acid), polycaprolactone, and their copolyesters, have been intensively studied. 4–7 The enzymatic degrada- tion of these and other linear synthetic polyesters has also been reported. 8–14 In recent years, hyperbranched polymers, espe- cially hyperbranched polyesters (HBPEs), have been receiving increasing attention in the field of life scien- ces, particularly as drug delivery materials, because of their attractive properties, such as nontoxicity, bio- compatibility, and large numbers of functional groups. Hyperbranched polymers are highly branched, poly- disperse macromolecules with a treelike topology car- rying a large number of functional end groups. The biomedical applications of Boltorn H30, a commer- cially available HBPE, have been reported in the liter- ature. 15 It has been proved experimentally that the polymer contains 12 hydroxyl groups on its periphery and that they can be modified for the end use of the polymer. 16,17 The influence of the end groups on the properties of hyperbranched polymers has been investigated intensively by many authors. 18–24 Suttir- uengwong et al. 25 employed HBPEs and poly(ester amide)s for the controlled release of acetaminophen. Gao et al. 26 synthesized a water-soluble hyper- branched polymer for drug delivery applications. The use of HBPEs as dental composite materials was investigated by Klee. 27 Recently, hyperbranched poly(ester amide)s were synthesized with gallic acid Journal of Applied Polymer Science, Vol. 112, 1873–1881 (2009) V V C 2009 Wiley Periodicals, Inc. Correspondence to: I. Smirnova, Institute for Thermal Process Engineering, Technical University of Hamburg– Harburg, Eissendorfer Strasse 38, D-21073 Hamburg, Germany (irina.smirnova@tu-harburg.de).