Preparation of porous structures with shape memory properties from biodegradable polymeric networks
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Preparation of porous structures with shape memory properties from biodegradable polymeric networks Shahriar Sharifi1, Sebastien Blanquer2, Dirk W. Grijpma1,2 1) Department of Biomedical Engineering, University Medical Centre Groningen, PO Box 196, 9700AD, Groningen, The Netherlands. 2) Department of Biomaterials Science and Technology, University of Twente, PO Box 217, 7500 AE, Enschede, The Netherlands.
ABSTRACT Preparing porous biodegradable structures from shape memory polymers can combine the structure-defining properties of porous structures with the minimally invasive implanting possibilities of shape memory polymers. In this study, porous biodegradable shape memory structures were prepared using photo-crosslinked networks based on poly(D,L-lactide-cotrimethylene carbonate). The characteristic shape memory properties of the structures, such as their shape fixity at a low temperature of 0 oC and their full shape recovery upon heating to physiological temperatures, were excellent. This makes these biodegradable and biocompatible structures very well-suited for use as self-deploying implants in medical applications like tissue engineering, drug delivery and the support of soft tissues. INTRODUCTION Shape memory polymers (SMPs) are smart materials that respond to an external stimulus such as temperature or light [1,2]. These materials return from a temporary fixed shape to their original permanent shape upon applying the stimulus. Biodegradable SMPs have high potential for application in medicine, especially regarding implantation of the device in a minimally-invasive manner [3,4]. A device prepared from a polymer that displays shape memory properties can be implanted in a temporary compressed from. Upon exposure to physiological conditions the implant will deploy to its permanent shape to perform as intended. For a variety of applications, porosity of the shape memory implant is a prerequisite. For example when used in tissue engineering, the porosity of the scaffold is essential to allow cell adhesion and tissue ingrowth, and to facilitate the transport of oxygen, nutrients and waste products. Porous shape memory structures can combine the structure-defining properties of porous implantable materials with the possibility of minimally invasive implantation of SMPs [5]. The literature on porous biodegradable SMPs is very limited [6,7]. Copolymers of D,L-lactide and trimethylene carbonate are well-known biocompatible and biodegradable polymers. By variation of their monomer composition, the glass transition temperatures, elastic moduli, tensile strengths and degradation rates of poly(D,L-lactide-cotrimethylene carbonate) polymers can be varied within wide ranges [8]. Networks prepared from macromers with a DLLA content of 0.4 to 0.6 have glass transition temperatures close to or below body temperature. These networks are especially interesting as at room temperature these materials are relatively rigid and can be implanted non-invasively in their temporary shape, while at body temperature they will return to thei
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