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GG3.09 - Customisation of Mechanical Properties and Porosity of Tissue Scaffold Materials via Layer-by-Layer Assembly of Polymer-Nanocomposite Coatings 
April 8, 2015   11:15am - 11:30am

Adequate strength, tailored stiffness, and an interconnected porous architecture are crucial requirements for engineered bone tissue scaffolds; however high porosity reduces mechanical properties, making it difficult to fabricate scaffolds with the required mechanical properties (1). A potential solution to this on-going problem is the deposition of a stiff and strong polymer-nanocomposite coating onto a porous template using layer-by-layer (LbL) assembly. This technique involves the alternate deposition of oppositely charged electrolyte complexes (e.g. polymer and nanoparticles) onto a substrate resulting in the formation of multilayer films, and is one of the most versatile means to control film properties and molecular architecture at the nanoscale (2). The aim of this study was to adapt LbL assembly to fabricate nanocomposite coatings onto porous substrate, enabling customisation of mechanical properties and porosity to obtain materials suitable for bone tissue scaffold applications. LbL deposition was conducted using aqueous solutions of polyethyleneimine (PEI), polyacrylic acid (PAA) and nanoclay (MTM) (Sigma Aldrich), prepared as previously described (3). Open-cell polyurethane (PU) foam substrates (30 PPI, EasyFoam Ltd.) were alternately subjected to cationic (PEI), and anionic (PAA and MTM) solutions using a custom-built apparatus. The deposition of a single PEI/PAA/PEI/MTM multilayer was repeated in intervals of 5 multilayers to obtain the desired number. The coated samples were dried for 24 h after each interval and the total mass of the coating was determined before deposition of subsequent multilayers. The mechanical properties of coated foams were determined by quasi-static mechanical testing in compression. The physical properties of the multilayer film can be tailored by changing certain process parameters (4): pH of solutions, drying and deposition times, and salt concentration. These variables were systematically altered and the effect on deposition rate and mechanical properties were measured. The mass and thickness of the multilayer coating were found to correlate directly with the number of layers deposited. The elastic modulus of coated substrates increased by over an order of magnitude with the deposition of 60 multilayers. A micromechanical model for open-cell foams (5) was adapted to predict the porosity and mechanical properties of coated open-cell foams. It is expected that these results will serve as a guide to the design of scaffold materials with tailored stiffness and porosity within a suitable range for bone tissue scaffold materials. References 1. Hutmacher, D. (et al.), J Tissue Eng Regen M, 1: 245-60, 2007 2. Yoo, D. (et al), Nano Lett, 8: 1762-70, 2008 3. Ziminska, M. (et al.), Proceedings of the 26th ESB Conference, Liverpool, UK, 2014 4. Dubas, S. (et al.), Macromolecules, 32: 8153-60, 1999 5. Ashby, M. (et al.), Phil. Trans. R. Soc. A, 364: 15-30, 2006

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