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Fabrication and Characterization of Organic Thin Films for Applications in Tissue Engineering: Emphasis on Cell-Surface Interactions Michael R. Wertheimer1, Amélie St-Georges-Robillard1, Sophie Lerouge2, Fackson Mwale3, Bentsian Elkin4, Christian Oehr4, Werner Wirges5, and Reimund Gerhard5 1

Department of Engineering Physics, École Polytechnique, Montréal, QC, H3C 3A7, Canada. 2 Department of Mechanical Engineering, École de Technologie Supérieure (ÉTS), Montréal, QC, H3C 1K3, Canada, and Centre de recherche du CHUM (CRCHUM). 3 Division of Orthopaedic Surgery, McGill University, and Lady Davis Institute for Medical Research, 3755, Chemin de la Cote Ste-Catherine, Montreal, QC H3T 1E2, Canada. 4 Fraunhofer Institute for Interfacial Engineering and Biotechnology, Nobelstrasse 12, 70569 Stuttgart, Germany. 5 Applied Condensed Matter Physics, University of Potsdam, 14476 Potsdam-Golm, Germany. ABSTRACT In several recent communications from these laboratories, we have described observations that thin organic layers which are rich in primary amine (R-NH2) groups are very efficient surfaces for the adhesion of mammalian cells, even for controlling the differentiation of stem cells. We prepare such deposits by plasma polymerization at low pressure (thin films designated “L-PPE:N”, for “Low-pressure Plasma Polymerized Ethylene containing Nitrogen”), at atmospheric (“High”) pressure (“H-PPE:N”), or by vacuum-ultraviolet photo-polymerization (“UV-PE:N”). More recently, we have also investigated a commercially available material, Parylene diX AM. In the present communication we shall, first, briefly introduce literature relating to electrostatic interactions between cells, proteins, and charged surfaces. Next, we discuss the comparative results of physico-chemical characterizations of the various organic deposits mentioned above, which deliberately contain varying concentrations of nitrogen, [N], and amine groups, [NH2]. Finally, we present certain selected cell-response results that pertain to applications in orthopedic medicine; we discuss the influence of surface properties on the observed behaviors of various cell lines, with particular emphasis on possible electrostatic attractive forces due to positively charged R-NH3+ groups and negatively charged proteins and cells, respectively.

INTRODUCTION In the well-known textbook “Biomaterials Science” [1], three main methods are listed (Table 6, page 227) for immobilizing bio-molecules: (i) physical adsorption, (ii) physical “entrapment”, and (iii) covalent attachment. The first of these includes van der Waals and electrostatic sub-categories, while the last includes one labelled “solid surfaces”. Clearly, there can be situations where sub-sets of these can coexist, for example, electrostatic attraction of a charged bio-molecule (or even a living cell) to an oppositely-charged surface: a conducting electrode or a polarized insulator, an electret. In this report, we deal specifically with such situations. This is by no means a “new” field; in the first edition of G. Sessler’s b