Morphological Changes of Annealed Poly-e-caprolactone by Enzymatic Degradation with Lipase GABRIELA SEKOSAN, NADARAJAH VASANTHAN Department of Chemistry, Long Island University, One University Plaza, Brooklyn, New York 11201 Received 13 August 2009; revised 9 October 2009; accepted 9 October 2009 DOI: 10.1002/polb.21889 Published online in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: The effects of crystallinity and temperature on en- zymatic degradation of poly-e-caprolactone (PCL) films and structural changes after degradation have been studied using weight loss, differential scanning calorimetry, and optical mi- croscopy. The weight loss during the enzymatic degradation of PCL suggested that the extent of biodegradation and the rate of degradation strongly depend on the initial crystallinity. PCL films of lower crystallinity (24%) degraded much faster than films of higher crystallinity (45%). The crystallinity of low-crystalline PCL films increased with increasing degrada- tion time, whereas the crystallinity of high-crystalline PCL films decreased with time. The spherulite size increased with increasing degradation time for low-crystalline samples but decreased with time for high-crystalline samples. These results revealed that degradation occurs first in the amor- phous region where the degradation rate is much higher, and the crystalline region of the PCL film started to degrade simultaneously for those PCL with higher crystallinity. The en- zymatic degradation of PCL proceeded from the free amor- phous to restricted amorphous followed by lamellar edges, where PCL chains have higher mobility irrespective of hydro- lysis temperature. Caproic acid was identified as the primary product formed after degradation and confirmed by proton nuclear magnetic resonance spectroscopy, suggesting that degradation occurs through the depolymerization mechanism. V C 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 202–211, 2010 KEYWORDS: amorphous; biodegradable; crystallization; degra- dation; differential scanning calorimetry INTRODUCTION Poly-e-caprolactone (PCL) is one of the most promising biodegradable and biocompatible semicrystalline polymers with a low melting (approximately 60  C) and a glass transition temperature (approximately 60  C). 1 PCL has been used for limited applications such as drug delivery devices, commercial sutures, and scaffolds for tissue repair and regeneration. 2–6 Because of its slow degradation rate, PCL has not been used as frequently as other biodegradable aliphatic polyesters such as polyglycolides and polylactides for tissue engineering applications. 7,8 However, PCL has good biocompatibility and is able to form compatible blends with other polymers and copolymers with a wide range of other monomers. PCL copolymers and blends have better mechani- cal properties, processability, and higher permeability than PCL homopolymers because of their rubbery characteristics, and this has expanded the use of PCL greatly for various applications. 9,10 The degradation of polymers may be induced by thermal activation, hydrolysis, enzymes, oxidation, or photolysis. Depending on the mode of initiation, polymer degradation can be classified as thermal, mechanical, photochemical, bio- logical, or chemical. 4,11,12 Thermal degradation of PCL has been studied extensively, and several mechanisms have been proposed. 13–17 A single step unzipping depolymerization was proposed by Aoyagi et al. 15 for thermal degradation of PCL, whereas a different mechanism, random chain and specific chain end scission, was proposed for nonisothermal thermal degradation of PCL. 16 Like many other polyesters, PCL is sensitive to chemical hydrolysis. Two probable methods for chemical hydrolysis are hydrolytic degradation or solvolysis to 6-hydroxycaproic acid or 6-hydroxycaproic acid-based compounds and depolymerization of PCL to the cyclic mono- mer. 18 The biodegradation behavior, the mechanism associ- ated with degradation, and the structural changes during biodegradation are very important for biomedical applica- tions, 19,20 and biodegradation depends on initial morphology, degradation condition, pH, and temperature. 21,22 Enzymatic degradation of PCL fibers has been studied recently in solu- tion with different kinds of lipases. Three kinds of lipase were found to significantly accelerate the degradation of PCL: Rhizopus delemer , Rhizopus arrhizus, and Pseudomo- nas. 23 Hayashi et al. 24–26 have concluded, from a recent study conducted on PCL fibers, that degradation gradually takes place from the surface of the fibers and not in the bulk of the fibers. The rate of degradation was found to depend on the draw ratio and the crystallinity of the PCL fibers. It has been shown that, during enzymatic degradation, PCL fibers Correspondence to: N. Vasanthan (E-mail: nadarajah.vasanthan@liu.edu) Journal of Polymer Science: Part B: Polymer Physics, Vol. 48, 202–211 (2010) V C 2009 Wiley Periodicals, Inc. 202 INTERSCIENCE.WILEY.COM/JOURNAL/JPOLB