From benchtop to clinic: a translational analysis of the immune response to submicron topography and its relevance to bone healing.

Proper regulation of the innate immune response to bone biomaterials after implantation is pivotal for successful bone healing. Pro-inflammatory M1 and anti-inflammatory M2 macrophages are known to have an important role in regulating the healing response to biomaterials. Materials with defined structural and topographical features have recently been found to favourably modulate the innate immune response, leading to improved healing outcomes. Calcium phosphate bone grafts with submicron-sized needle-shaped surface features have been shown to trigger a pro-healing response through upregulation of M2 polarised macrophages, leading to accelerated and enhanced bone regeneration. The present review describes the recent research on these and other materials, all the way from benchtop to the clinic, including in vitro and in vivo fundamental studies, evaluation in clinically relevant spinal fusion models and clinical validation in a case series of 77 patients with posterolateral and/or interbody fusion in the lumbar and cervical spine. This research demonstrates the feasibility of enhancing biomaterial-directed bone formation by modulating the innate immune response through topographic surface features.