Biomechanical evaluation of cell-loaded and cell-free hydroxyapatite implants for the reconstruction of segmental bone defects

Porous hydroxyapatite (HA) scaffoldings are currently used in tissue engine ering for bone reconstruction. When this osteoconductive biomaterial is com bined with osteoprogenitor cells, it acquires osteoinductive features which accelerate and improve bone formation in vivo. The aim of our study was to assess the mechanical properties of HA-bone complexes undergoing indentati on tests, and relate stiffness to composition and structure as examined by micro X-ray. To this purpose, 35-mm tibia diaphyseal resections were perfor med in sheep. Gaps were filled using porous HA cylinders. Implants were loa ded with autologous bone marrow stromal cells (BMSC); cell-free cylinders w ere used as control. After 8 weeks, bone tissue was found within the intern al macropores of cell-loaded HA carriers, and in control implants, bone for mation was mostly limited to the outer surface. As assessed by indentation testing the stiffness values of bone-HA composites were halfway between tho se of HA scaffoldings and tibia bone. Cell-loaded implants were stiffer tha n cell-free ones. In a cell-loaded implant we also analyzed the variation o f stiffness along the main axis of the tibia. (C) 1999 Kluwer Academic Publ ishers.