RESUMO
Bone cements for treatment of fractures at weight-bearing sites are subjected to dynamic physiological loading from daily activities. An ideal bone cement rapidly sets after injection, exhibits bone-like strength, stimulates osteogenic differentiation of endogenous cells, and resorbs at a rate aligned with patient biology. However, currently available materials fall short of these targeted properties. Nanocrystalline hydroxyapatite (nHA) enhances osteogenic differentiation, new bone formation, and osteoclast differentiation activity compared to amorphous or micron-scale crystalline hydroxyapatite. However, the brittle mechanical properties of nHA precludes its use in treatment of weight-bearing bone defects. In this study, we report settable nHA-poly(ester urethane) (PEUR) nanocomposites synthesized from nHA, lysine triisocyanate (LTI), and poly(caprolactone) triol via a solvent-free process. The nanocomposites are easily mixed and injected using a double-barrel syringe, exhibit mechanical properties exceeding those of conventional bone cements, enhance mineralization of osteoprogenitor cells in vitro, and undergo osteoclast-mediated degradation in vitro. This combination of properties cannot be achieved using other technologies, which underscores the potential of nHA-PEUR nanocomposites as a new approach for promoting bone healing at weight-bearing sites.
RESUMO
Two- and three-dimensional structural models of the vertebral body have been used to estimate the mechanical importance of parameters that are difficult to quantify experimentally such as lattice disorder, trabecular thickness, trabecular spacing, connectivity, and fabric. Many of the models that investigate structure-function relationships of the vertebral body focus only on the trabecular architecture and neglect solid-fluid interactions. We developed a cellular solid model composed of two idealized unit cell geometries to investigate the continuum and micro-structural properties of human vertebral cancellous bone in a mathematically tractable model. Using existing histomorphological data we developed structure-function relationships for the mechanical properties of the solid phase, estimated the micro-structural strains, and predicted the fluid flow characteristics. We found that the micro-structural strains may be 1.7 to 2.2 times higher than the continuum level strains between the ages of 40 and 80. In addition, the predicted permeability agrees well with the experimental data.