Amorphous Polymer Networks Combining Three Functionalities - Shape-Memory, Biodegradability, and Drug Release
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Amorphous Polymer Networks Combining Three Functionalities - Shape-Memory, Biodegradability, and Drug Release Christian Wischke1,2, Axel T. Neffe1, Susi Steuer3, Andreas Lendlein1,2 1
2 3
Center for Biomaterial Development, Institute for Polymer Research, GKSS Research Center Geesthacht GmbH, Kantstrasse 55, 14513 Teltow, Germany Berlin-Brandenburg Center for Regenerative Therapies, Berlin, Germany present address: Intervet Innovation GmbH, 55270 Schwabenheim, Germany
ABSTRACT Shape-memory polymers are of high scientific and technological interest in the biomedical field, e.g., as matrix for self-anchoring implantable devices. In this study, two different starshaped copolyester tetroles, semi-crystalline oligo[(H-caprolactone)-co-glycolide]tetrol (oCG) and amorphous oligo[(rac-lactide)-co-glycolide]tetrol (oLG), were synthesized and subsequently crosslinked by a low molecular weight diisocyanate resulting in copolyester urethane networks (N-CG, N-LG). Both networks could be loaded with model drugs and a diffusion controlled release of the drugs was observed without any effect on the mass loss as measure of hydrolytic degradation. However, the N-CG network’s capability of shape programming was disturbed as the crystallinity of the precursors got lost in the complex three dimensional architecture after crosslinking. By contrast, amorphous N-LG network showed an excellent shape-memory capability with a switching temperature around 36 °C corresponding to their glass transition temperature. This led to triple-functional materials combining biodegradability, shape-memory, and controlled drug release. INTRODUCTION Shape-memory polymers (SMP) [1] belong to the class of ‘actively moving’ polymers and possess the capability to recover from a temporarily fixed deformation (temporary shape) to their original shape. Different applications have been suggested for such SMP, either degradable or non-degradable materials, in the biomedical field including stents [2], as self-tightening sutures [3], intelligent electrodes [4], or thrombectomy devices [5]. In many cases, degradable SMP will be advantageous in order to avoid a second surgery for explantation. In order to initiate shape recovery, direct heating, indirect heating in a magnetic field [6,7], and light [8] have been described so far as suitable stimuli. The ability of a polymer to respond to such stimuli bases on the combination of the polymer’s molecular architecture and morphology combined with a thermomechanical process for creating the temporary shape, called programming. On a molecular level, entropy-elastic polymer networks are required having either covalent or physical netpoints that determine the permanent shape. Besides the netpoints, a switching segment must be present, forming either semi-crystalline or amorphous domains related to a characteristic melting point Tm or a glass transition Tg. Recently, semicrystalline polyester methacrylate networks [9] and amorphous copolyester urethane networks [10] were shown to beneficially combine controlled
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