Multifunctional Dendritic Architectures: An Investigation of their Mechanical Properties
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Multifunctional Dendritic Architectures: An Investigation of their Mechanical Properties Haixia Zhou , 1 Marcel Richter, 2 Regine von Klitzing,2 and Rainer Haag*1 1 Organische Chemie, Institut für Chemie und Biochemie, Freie Universität Berlin, Takustr. 3, 14195 Berlin, Germany, E-mail: [email protected] 2 Stranski-Laboratorium für Physikalische und Theoretische Chemie, Institut für Chemie, Technische Universität Berlin, Straße des 17. Juni 124, 10623 Berlin, Germany ABSTRACT The paper deals with the synthesis and investigation of mechanical properties of multifunctional polyglycerol nanogels which consist of PEG with different chain lengths (glycerol, PEG 400, PEG 400-DGE, and PEG 1500). Their swelling behavior, elasticity, and stiffness are discussed in correlation with the PEG chain length. The nanogels built of PEG 400 exhibited most interesting and promising features and show the highest elasticity. INTRODUCTION Nanogels are nanosized hydrogel particles consisting of physically or chemically cross-linked networks. Over the last few years nanogels have gained widespread attention as a novel material for numerous applications, due to their high stability and excellent response to external parameters like ionic strength, pH, and temperature [1]. These applications focus on drug and gene delivery, micro container, and photodynamic therapy [2-4]. Hyperbranched aliphatic polyethers are especially suitable drug delivery candidates because of their excellent biocompatibility. The most promising one is hyperbranched polyglycerol (HPG) [5]. Unfortunately, efficiency in medical applications is limited especially by its size maxima of ~10 nm. Particles at this size rapidly leave the blood stream by extravasation and renal clearance [6]. In the past, we reported on glycerol based nanogels synthesized by a miniemulsion technique [7, 8]. These nanogels are a special case of high molecular weight polymers with characteristics of both HPG and cross-linked hydrogels. They exhibit low viscosity and have dense surface functionality very much like hyperbranched polyglycerol, at the same time, they have specific and tunable sizes between 20-200 nm resulting in "enhanced permeation and retention effect" (EPR effect) [9]. In relation to its gel-like features, such as swelling behavior, the internal architecture of nanogels is also of special interest. Polyethylene glycol (PEG) is popular as well as a building block for novel materials applied in medicine and pharmacology [10, 11]. As it is a commercially available product, its physical properties and biocompatibility are well investigated, which makes it an ideal alternative component of biocompatible nanogels. Glycerol based nanogel [8] shows a high Young's modulus, which is a sign of a rigid core structure. Long-chain components were used to obtain softer and more flexible gels with a porous structure. For this purpose, three nanogels based on long-chain components were synthesized and compared to glycerol based particles. This paper discusses the influence of polymer chain l
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