Table 4.

Importance of mechanical stability in segmental bone defects.

Mechanical properties	Ultimate strength of cortical bone ranges between 100 and 230 MPa. Any scaffold that does not match this strength requires surgical fixation to prevent crushing/failure of the implant. Because bone is a mechanosensor organ, it is believed that a scaffold that is loaded cyclically will benefit from faster healing time.
Surgical fixation	Current bone tissue-engineered scaffolds require surgical fixation of the fractured extremities to prevent movement between the bone endings. This allows for callus formation and ossification to occur. Surgical fixation devices include screws, hardware, and intramedullary nails. They are often made of metals, specifically titanium or titanium alloys.
Stress shielding	Condition caused by the use of surgical fixation devices in load-bearing bones. Because metals have a higher modulus and compression strength, they support nearly all of the weight. In return, the fractured bone does not sense a significant change in mechanical activity, leading to a loss in bone density over time.