ELSEVIER zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA PII: SO142-9612 (97) 00098-7 Biomaterials 18 (1997) 1599-1607 0 1998 Elsevier Science Limited Printed in Great Britain. All rights reserved 014%9612/98/$19.00 zyxwvutsrqpon Erosion of biodegradable block copolymers made of poly(D,L-lactic acid) and poly(ethylene glycol) Friederike von Burkersroda” , Ruxandra Gref’ and Achim Giipferich” ‘Department of Pharmaceutical Technology, University of Regensburg, lJniver.Mitsstrasse 31, 93&O Regensburg, Germany; ilnstitut National Polytechnique de Lorraine, &o/e Nationale Superieure des lndustrfes Chimiques, Laboratoire de Chimie-Physique MacromolBculaire, LJRA CNRS 494, 1, rue Grandville, B.P. 451 54001 Nancy cedex, France Biodegradable block copolymers made of poly(ethylene glycol) monomethylether (Me.PEG) and poly(o,L-lactic acid) (PLA) were investigated for their erosion properties. Wide angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC) investigations prior to erosion revealed that despite the low content of crystallizable Me.PEG of lo%, Me.PEGsPLA45 is a partially crystalline polymer. The erosion of the polymer was investigated using cylindrical polymer matrix discs with a diameter of 8mm and a height of 1.5mm. WAXD and DSC spectra obtained from eroded polymer matrix discs suggest that both polymer blocks separate completely during erosion. The crystallinity of Me.PEG5-PLA45 was found to increase during erosion, which is probably due to the improved mobility of Me.PEG inside the polymer with a progressive degree of degradation. The erosion kinetics were found to be similar to that of PLA or poly(lactic-co-glycolic acid). During erosion the polymer matrix weight of dried samples remains constant for 11 weeks after which erosion sets in rapidly. From this observation one can conclude that the impact of the relatively small Me.PEG chains on Me.PEG5- PLA45 erosion is not pronounced. This is beneficial for all those applications that require the stability of the polymer matrix and in which the Me.PEG chain is intended to bring about other effects such as the modification of the surface properties of PLA polymers. 0 1998 Elsevier Science Limited. All rights reserved Keywords: Block copolymer, zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Me.PEG, PLA, Me.PEG-PLA, erosion Received 7 April 1997; accepted 3 June 1997 In recent years the needs of modern pharmacotherapy have spurred the interest in new biomaterials dramatically. As a result of this, an increasing number of problems in the field of drug delivery to the body can today be solved by tailoring the properties of biomaterials to fit the needs of a specific therapy. The undesired rapid uptake of intravenously administered nanoparticulate drug carriers by phagocytosing cells of the reticula endothelial system, for example, led to the development of polymers that suppress the rapid clearance of such systems from the blood stream. Block-copolymers made of poly(D,L-lactic acid) (PLA) and poly(ethylene glycol) monomethylether (Me.PEG) emerged thereby as suitable candidates to manufacture nanoparticles with increased plasma half-lifel. The core of these particles consists mainly of the degradable PLA chains, while the Me.PEG blocks are located mainly on the surface’. These Me.PEG chains on the surface suppress the adsorption of plasma proteins which is thought to be the initial step towards the uptake of the particles by cells of the reticula endothelial system. Especially block copolymers that Correspondence to Dr A. Giipferich. are composed of Me.PEG with M, 5000 and PLA with n/i, 45000 turned out to be suited for the manufacture of so-called stealth nanospheres3. Besides the manufacture of colloidal systems, Me.PEG-PLA block copolymers and related compounds have been used for a number of other drug delivery applications, such as the manufacture of microspheres or implants5. A common problem with such sophisticated materials is the time lag between their use for specific applications and the complete characterization of the material. While drug delivery systems, especially nanoparticles, made of these polymers have been characterized extensively so far” , 7, there is little information available on the internal structure of these polymers and the changes they undergo during erosion. Both properties have tremendous impact on our understanding of how these polymers function. The knowledge on the internal structure and the erosion properties are, therefore, decisive for the successful application of such biomaterials. It was the intention of this study to investigate how Me.PEG5- PLA45 erodes zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQP in vitro. For that purpose slabs of the material were investigated rather than the colloidal preparations, as these are much easier to handle and 1599 Biomaterials 1997, Vol. 18 No. 24