Influence of scaffold meso-scale features on bone tissue response

Creation of bone to restore form and function following disease, growth disorders, and trauma is possible with bone-replacement scaffolds by controlling the complex sequence of new bone formation at the scaffold interface with the surrounding biologic milieu. Much is known about the influence of scaffold nano-scale ( < 1 lm) features on biocompatibility and the influence of micro-scale (1–20 lm) features on the type of tissue that develops. Meso-scale (20–1000 lm) features have been less well characterized, in part because it was not possible to regulate this feature size until solid freeform fabrication techniques became available. Experimental results of animal studies of bone ingrowth into scaffolds fabricated using these technologies confirm that meso-scale features can have profound effects on the extent and pattern of bone formation. They also indicate that we do not yet have sufficient information to optimize the size of these features. Macro-scale features (>1 mm) provide anatomic form and delimit the extent of the scaffold, serving as a platform to integrate other length-scale features. Many of the main effects of features at each length scale are understood but interactions across length scales still need investigation. Major improvements in bone replacement are now possible— but optimization of the process remains an as-yet unrealized goal.