Compressive properties and degradability of poly(e-caprolatone)/hydroxyapatite composites under accelerated hydrolytic degradation K.C. Ang, 1 K.F. Leong, 1 C.K. Chua, 1 M. Chandrasekaran 2 1 School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore 2 Singapore Institute of Manufacturing Technology, A*Star, Singapore Received 21 June 2005; revised 1 June 2006; accepted 13 June 2006 Published online 18 October 2006 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/jbm.a.30996 Abstract: Hydroxyapatite (HA) was incorporated as filler into polycaprolactone (PCL) matrix to improve the bioactiv- ity as well as the compressive properties of the polymer composites that can be typically used in tissue engineering scaffolds. The compressive properties of five PCL/HA com- posites of different compositions were investigated in con- junction with the study of their rate of degradation. As PCL has a slow degradation rate, the experiment was conducted in a concentrated 5M sodium hydroxide medium to acceler- ate the degradation process. The compressive strength and modulus of all PCL/HA compositions were observed to de- crease as the degradation experiment progressed, with sam- ples having high HA content degraded most significantly as compared with samples with lower HA content. Pure PCL samples, however, were found to retain their mechanical properties comparatively well in the same degradation ex- periments. Although the addition of HA as filler into the PCL matrix was shown to have improved mechanical properties and bioactivity initially, these results do raise concerns of ma- terial properties being compromise during hydrolytic degra- dation. Ó 2006 Wiley Periodicals, Inc. J Biomed Mater Res 80A: 655–660, 2007 Key words: polycaprolactone; hydroxyapatite composite; accelerated degradation; sodium hydroxide; compressive properties INTRODUCTION Poly-e-caprolactone (PCL) is a semicrystalline poly- mer with a melting point of 608C and a glass transi- tion temperature of À608C. The presence of five non- polar methylene groups in the repeating molecular structure of PCL gives it unique properties that are similar to polyolefin, while the presence of hydrolyti- cally unstable aliphatic-ester linkage causes the poly- mer to be degradable. 1 PCL degrades hydrolytically via both bulk and surface erosion 2 with 5-hydroxy- hexanoic acids (caproic acids) being the degradation product. However, due to its hydrophobic nature, PCL degrades more slowly than either poly(glycolic acid) (PGA) or poly(L-latic acid) (PLLA), and gener- ally has a degradation time in the order of 2 years. The chemical structure of PCL has also given it the unusual property of being compatible with numerous other polymers. For instance, it has been reported that PCL is miscible with polymers such as poly(vinyl chlo- ride), chlorinated polyethylene, and polycarbonate. In addition, PCL is also considered to produce compati- ble, although phase-separated, blends with the ali- phatic polyesters and polyolefines. 3 As such, in order to produce novel materials with specifically tailored properties (in terms of surface chemistry, degradation rate, mechanical properties, and biocompatibility), PCL has been widely investigated by researchers as a co- polymer 4,5 or as a component in a polymer blend. 6–9 Generally, PCL is regarded as a nontoxic and tissue compatible polymer. 10,11 It has been used as a copoly- mer in the manufacture of a biodegradable suture under the trade name Monacryl. 12 PCL is also used in Capronor, a 1-year implantable subdermal contracep- tive device. 13 Extensive in vitro and in vivo biocompati- ble and efficacy studies have been performed leading to these FDA-approved products. More recently, PCL is being widely investigated as a potential tissue engi- neering material. Numerous investigations 7–9,14–16 have been carried out to examine its ability to support cell proliferation and differentiation. In most of these studies, PCL showed much promise as a potential bone tissue engineering material. However, it has been suggested that PCL alone may not be a satisfac- Correspondence to: K.F. Leong; e-mail: mkfleong@ntu.edu.sg ' 2006 Wiley Periodicals, Inc.