engleski

Novel Polyelectrolyte Multilayer-Calcium Phosphate Coatings for Bone Implants

Multilayer (ML) films formed by alternated adsorption of anionic and cationic polyelectrolytes (PE) have proven to be an efficient way to prepare functionalized surfaces (1). Recently, it has been indicated that crystalline calcium phosphate could grow on PE multilayers (2). These findings prompted us to attempt to develop novel organic-inorganic coatings for artificial bone implants consisting of PE multilayers and “ in-situ” grown calcium phosphate crystals (3) Coatings were prepared on titanium plates by a two-step procedure: (i) embedding several layers of amorphous calcium phosphate (ACP) particles between organic polyelectrolyte multilayers, obtained by alternate deposition of poly-L-lysine (PLL) and poly-L-glutamic acid (PGA). (ii) organic – inorganic coatings of the required thickness into a metastable calcifying solution to initiate “ in situ” crystal growth of nano-crystalline apatite within the organic matrix. With calcium phosphate as the top layer, SEM, EDS and thin layer X-ray diffraction revealed micron size octacalcium phosphate (OCP) crystals, growing perpendicularly to the substrate surface. Such crystals anchored the coatings to the metal surface but were not conducive to cell attachment. However, coatings containing final PLL-PGA-layers were true nanocomposites with smooth surfaces containing nanocrystalline apatite, as shown by thin layer XRD. Mechanical and biological tests showed that such coatings possess appropriate biomechanical stability with well adapted sites for cell adhesion and proliferation. Moreover, after two months of implantation into the hind legs of rabbits, bone bonding onto coated samples was two times stronger than onto chemically etched bare titanium plates. The good correlation of in-vitro and in-vivo tests clearly indicates that the organic-inorganic nanocomposite is a very promising surface coating with wide medical applications. References: 1. G. Decher, Science, 1997, 277:1232. 2. Cs. Gergely, P. Bar Yosef, R. Govrin-Lippman, F. Cuisinier, H. Füredi-Milhofer, Key Eng. Mater., 2003, 240-242: 287. 3. H. Füredi-Milhofer, M. Sikiric, P. Bar Yosef, F. Cuisinier, Cs. Gergely, Organic-inorganic Nanocomposite Coatings for Implant Materials. Provisional patent application to US patent office Nov. 25, 2002, patent # 60-428.725. Acknowledgement: The financial support of the European Commission through the SIMI project (GRDI-2000-26823) is gratefully acknowledged.

calciu phosphate; bone implants; polyelectrolytes

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