Bone tissue is a dynamic composite system that adapts itself, in response to the surrounding daily (cyclic) mechanical stimuli, through an equilibrium between growth and resorption processes. When there is need of synthetic bone grafts, the biggest issue is to support bone regeneration without causing mechanically–induced bone resorption. Apart from biological properties, such degradable materials should initially support and later leave room to bone formation. Further, dynamic mechanical properties comparable to those of bone are required. In this study we prepared composites comprising calcium phosphate and polylactide in various content ratios using extrusion method. We evaluated the effect of the inorganic filler amount on the polymer phase (i.e. on the post–extrusion intrinsic viscosity). We then studied the in vitro degradation and dynamic mechanical properties (in dry and humid conditions) of composites comprising nano–scaled calcium phosphate apatite and L–lactide/D–lactide copolymer. By increasing the filler content, we observed significant decrease of the intrinsic viscosity of the polymer phase during the extrusion process. Composites containing higher amounts of apatite had faster degradation, and were also mechanically stiffer. But, due to the lower intrinsic viscosity of their polymer phase, they had larger damping properties. Besides this, higher amounts of apatite also rendered the composites more hydrophilic letting them absorb more water causing then the largest decrease in stiffness. These results show the importance of filler content in controlling the properties of such composites. Further, in this study we observed that the viscoelastic properties of the composite containing 50%wt. apatite were comparable to those of dry human cortical bone.

Controlling dynamic mechanical properties and degradation of composites for bone regeneration by means of filler content

FARE', SILVIA;
2013-01-01

Abstract

Bone tissue is a dynamic composite system that adapts itself, in response to the surrounding daily (cyclic) mechanical stimuli, through an equilibrium between growth and resorption processes. When there is need of synthetic bone grafts, the biggest issue is to support bone regeneration without causing mechanically–induced bone resorption. Apart from biological properties, such degradable materials should initially support and later leave room to bone formation. Further, dynamic mechanical properties comparable to those of bone are required. In this study we prepared composites comprising calcium phosphate and polylactide in various content ratios using extrusion method. We evaluated the effect of the inorganic filler amount on the polymer phase (i.e. on the post–extrusion intrinsic viscosity). We then studied the in vitro degradation and dynamic mechanical properties (in dry and humid conditions) of composites comprising nano–scaled calcium phosphate apatite and L–lactide/D–lactide copolymer. By increasing the filler content, we observed significant decrease of the intrinsic viscosity of the polymer phase during the extrusion process. Composites containing higher amounts of apatite had faster degradation, and were also mechanically stiffer. But, due to the lower intrinsic viscosity of their polymer phase, they had larger damping properties. Besides this, higher amounts of apatite also rendered the composites more hydrophilic letting them absorb more water causing then the largest decrease in stiffness. These results show the importance of filler content in controlling the properties of such composites. Further, in this study we observed that the viscoelastic properties of the composite containing 50%wt. apatite were comparable to those of dry human cortical bone.
Composites, extrusion, dynamic mechanical properties, degradation, bone
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11311/707538
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