Thermoemechanical Properties and Shape-Memory Capability of Drug Loaded Semi-Crystalline Polyestermethacrylate Networks
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Thermoemechanical Properties and Shape-Memory Capability of Drug Loaded SemiCrystalline Polyestermethacrylate Networks Axel T. Neffe1,2, Bui D. Hanh1, Susi Steuer3, Christian Wischke1,2 and Andreas Lendlein1,2; 1 Centre for Biomaterial Development, GKSS Forschungszentrum Geesthacht, Kantstrasse 55, 14513 Teltow, Germany 2 Berlin-Brandenburg Centre for Regenerative Therapies (BCRT), Berlin, Germany 3 Present address: Intervet Innovation GmbH, Zur Propstei, 55270 Schwabenheim, Germany. ABSTRACT Polymer networks synthesized by UV-curing of Oligo[(ε-caprolactone)-co-glycolide]dimethacrylates are hydolytically degradable. Their architecture with covalent netpoints and crystallizable domains is the molecular basis for a potential shape-memory capability. The molecular weight and glycolide content of the oligomeric precursors can be varied over a broad range of compositions to tailor the thermomechanical properties of the polymer network while having only a minor influence on the shape-memory effect. Recently, drug incorporation adding controlled drug release as further functionality to the polymer network was demonstrated [4]. Here, enoxacin and ethacridine lactate as test drugs were incorporated into the networks by soaking. Alternatively, defined amounts of ethacridine lactate were mixed with the precursors, which were subsequently crosslinked to the drug containing networks. The composition of the oligomeric precursors was varied in molecular weight between 3800 and 12800 g·mol-1 and in glycolide content χG between 0 and 30 mol-% to explore the influence of the drug incorporation on networks with varying compositions while retaining properties and functionalities. Polymer networks prepared from precursors with χG ≤ 14 mol-% and Mn ≥ 6900 g·mol-1 have a Tsw of 35-52 °C and sufficient crystallinity to ensure a high shape fixity in the programming step. These limits have to be kept to ensure the desired multifunctionality, otherwise drug incorporation can have an undesired influence on thermal, mechanical, and shape-memory properties.
INTRODUCTION Polymer systems are families of polymers in which slight changes of structural parameters allow the adjustment of the overall bulk properties of the material in a wide range [1]. This behavior can be used to tailor the desired properties to the specific application. Functionalities of polymers are different from properties as they are non-inherent, but are incorporated by a specific process. A typical example is the shape-memory effect; while being dependent on the molecular architecture/morphology of the polymer, a programming step is necessary to fix the deformation of a polymer as a temporary shape. Only an external trigger such as increased temperature leads to the recovery of the permanent shape [2]. Possible applications of shape-memory polymers include minimally invasive surgery [2] and intelligent suture material [3]. Biomaterials need to fulfill complex requirements, for which a combination of several functions has to be combined with tailored properties.
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