Porous Composites for Adhering Artificial Cartilage to Bone
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Porous Composites for Adhering Artificial Cartilage to Bone Kai Zhang, Mary E. Grimm1, Qiwei Lu, Theodore R. Oegema, Jr. 2, and Lorraine F. Francis Department of Chemical Engineering and Materials Science, 1 Department of Biomedical Engineering, 2 Departments of Orthopaedic Surgery and Biochemistry, University of Minnesota, Minneapolis, MN 55455, USA ABSTRACT Artificial cartilage can be grown from cultured chondrocytes, but adhering this tissue to bone presents a challenge. Porous polymer/bioactive glass composites are candidate materials for engineering the artificial cartilage/bone interface and possibly other soft-to-hard tissue (ligament/bone, tendon/bone) interfaces. A phase separation technique was used to make porous polymer/bioactive glass composites. The composites (thickness: 200-500 µm) have asymmetric structures with dense top layers and porous structures beneath. The porous structures consist of large pores (>100 µm) in a network of smaller (100 µm) pores and small (5-10 µm) interconnected pores would provide a means of biological bonding by cell attachment and ingrowth. The polymer matrix may also provide flexibility and toughness. Bioactive glass bonds well to both hard and soft tissues [3], so the incorporation of bioactive glass particles in the composite will enhance bonding ability. It is also possible to control mineralization in the composite by changing the glass content because the presence of bioactive glass particles enhances the composites’ apatite formation ability. Ceramic particles incorporated in the polymer matrix may also strengthen and stabilize the porous polymer matrix. This paper GG4.2.1
describes the preparation and morphologies of porous polymer (polysulfone, polyurethane and polylactide)/bioactive glass composites, and gives the two-week results for in vitro apatite formation in the simulated body fluid (SBF) and in vitro compatibility with rabbit chondrocytes. EXPERIMENTAL PROCEDURE Polysulfone powders (Mw = 35,000), tetrahydrofuran (THF), N, N-dimethylacetamide (DMAc), N,N-Dimethyl Formamide (DMF), 1,4-dioxane and ethanol were obtained from Aldrich Chemical Company. Polyurethane used in this research was industrial grade Avalon 92AE (from Huntsman Polyurethanes Co.). Polylactide (Mw ~ 80,000) was synthesized as previously reported [4]. Bioactive glass particles with an average particle size of about 10 µm and a composition of 4.6MgO, 44.7CaO, 34.0SiO2, 16.2P2O5 and 0.5CaF2 (wt%) was purchased from Specialty Glass, Inc. Some of the bioactive glass was further ground in an attrition mill to achieve an average particle size of approximately 2.0 µm. Porous polymer/bioactive glass composites prepared by the phase separation technique, which was originally designed for porous polymeric membranes [5], were made as reported before [6]. Briefly, homogeneous composite dispersions with different compositions were made by combining polymer, bioactive glass particles, solvents (THF and DMAc for polysulfone, DMF for polyurethane and dioxane for polylactide) and non-solvent (ethanol for p
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