Biomaterials 25 (2004) 3939–3949 Processing, annealing and sterilisation of poly-l-lactide N.A. Weir a, *, F.J. Buchanan a , J.F. Orr a , D.F. Farrar b , A. Boyd c a School of Mechanical and Manufacturing Engineering, Queen’s University Belfast, Ashby Building, Stranmillis Road, Belfast BT9 5AH, UK b Smith & Nephew Group Research Centre, York Science Park, Heslington, York YO10 5DF, UK c Avalon Instruments, 97 Botanic Avenue, Belfast BT9 5BN, UK Received 21 February 2003; accepted 10 October 2003 Abstract Poly-l-lactide(PLLA)isoneofthemostsignificantmembersofagroupofpolymersregardedasbioabsorbable.Degradationof PLLA proceeds through hydrolysis of the ester bonds in the polymer chains and is influenced significantly by the polymer’s molecular weight and crystallinity. To evaluate the effects of processing and sterilisation on these properties, PLLA pellets were either compression moulded or extruded, subjected to annealing at 120  C for 4h and sterilised by ethylene oxide (EtO) gas. Procedureswereusedtoevaluatethemechanicalproperties,molecularweightandcrystallinity.Uponprocessing,thecrystallinityof thematerialfellfrom61%forthePLLApelletsto12%and20%forthecompressedandextrudedcomponents,respectively.After annealing, crystallinity increased to 43% for the compression-moulded material and 40% for the extruded material. Crystallinity further increased upon EtO sterilisation. A slight decrease in molecular weight was observed for the extruded material through processing, annealing and sterilisation. Young’s modulus generally increased with increasing crystallinity, and extension at break and tensile strength decreased. The results from this investigation suggest that PLLA is sensitive to processing and sterilisation, altering properties critical to its degradation rate. r 2003 Elsevier Ltd. All rights reserved. Keywords: Polylactic acid; Degradation; Crystallinity; Molecular weight; Mechanical properties; Sterilisation 1. Introduction In many tissue-fixation applications, the temporary presence of a biomaterial is often required, for support and to guide tissue regrowth. This has led to the development of bioabsorbable polymeric materials, which are not physiologically inert, and will absorb over time, through the natural mechanisms of the human body [1]. Synthetic bioabsorbable polymers first came into commercial medical use in 1970 with the introduction of a bioabsorbable suture material Dex- on s [2]. Such polymers have seen a steady progression intheirdevelopment,leading,inmorerecentyears,toa growth in experimental and clinical use in the field of orthopaedics and traumatology as fracture-fixation devices, and in the pharmaceutical industry as drug delivery devices. Recent advances have focused on developing bioabsorbable polymers as scaffolds in the field of tissue engineering [3,4]. Bioabsorbable polymers belonging to the aliphatic polyester family currently represent the most attractive group of polymers which meet the various medical and physical demands for safe clinical applications [5]. This is mainly due to their high level of biocompatibility, acceptable degradation rates and versatility regarding physical and chemical properties [5]. These polymers degrade in vivo by hydrolysis of their ester bonds. Due tothisunstablenature,theyaresensitivetoexposureto moisture and temperature during processing and ster- ilisation. Some of the factors which influence the absorption rate of these polymers relate to their microstructural properties and include chemical compo- sition, molecular weight and degree of crystallinity [6]. Undoubtedly, one of the most significant members of thealiphaticpolyesterfamilyisthepoly(a-hydroxyacid) polylactide (PLA) [7]. PLA has been the focus of significant research over the past 40 years and has found many applications in the biomedical field as a suture material and in various orthopaedic fixation ARTICLE IN PRESS *Correspondingauthor.Tel.:+44-28-9027-4509;fax:+44-28-9066- 1729. E-mail address: n.weir@qub.ac.uk (N.A. Weir). 0142-9612/$-see front matter r 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.biomaterials.2003.10.076