Coenraad Jan Spaans

Solvent-free fabrication of micro-porous polyurethane amide and polyurethane-urea scaffolds for repair and replacement of the knee-joint meniscus

New porous polyurethane urea and polyurethane amide scaffolds for meniscal reconstruction have been developed in a solvent-free process. As soft segments, copolymers of 50/50 L-lactide/epsilon-caprolactone have been used. After terminating the soft segment with diisocyanates, chain extension was performed with adipic acid and water. Reaction between the isocyanate groups and adipic acid or water provides carbon dioxide and results in a porous polymer. Extra hydroxyl-terminated prepolymer was added in order to regulate the amount of carbon dioxide formed in the foaming reaction. Furthermore, salt crystals ranging in size from 150 to 355 microm were added in order to induce macroporosity. The pore size was regulated by addition of surfactant and by the use of ultrasonic waves. The resulting porous polymer scaffolds exhibit good mechanical properties like a high-compression modulus of 150 kPa. Chain extension with adipic acid results in better mechanical properties due to better defined hard segments. This results from the lower nucleophilicity of carboxylic acids compared to water and alcohols. By adjusting the reaction conditions, materials in which macropores are interconnected by micropores can be obtained. On degradation only non-toxic products will be released; importantly, the materials were obtained by a simple, reproducible and solvent-free procedure.

A NEW BIOMEDICAL POLYURETHANE WITH A HIGH MODULUS BASED ON 1,4-BUTANEDIISOCYANATE AND EPSILON -CAPROLACTONE

A new approach to the synthesis of biomedical polyurethanes based on ε-caprolactone and 1,4-butanediisocyanate with a high modulus, has been developed. By chain extending an ε-caprolactone prepolymer with a long uniform-size diisocyanate block, a segmented polyurethane with uniform-size hard segments was obtained. It shows excellent mechanical properties; an extremely high modulus of 105 MPa and a tensile strength of 35 MPa. The polymer is soluble at high concentrations in various volatile solvents such as chloroform and 1,4-dioxane. By a combination of salt-leaching and freeze-drying, porous materials have been obtained in which macropores ranging in size from 150–300 μm are highly interconnected by micropores. The material shows a sufficiently high compression modulus of 200 kPa and appears to be suitable for biomedical applications such as meniscal prostheses.