Vertical bone augmentation using additively manufactured scaffolds: an investigation into formation, resorption and implant osseointegration

Abstract

This study reports on the development of an additively manufactured polycaprolactone (PCL) biphasic scaffold for achieving vertical bone augmentation. The biphasic scaffold consisted of a space maintaining 3D-printed outer shell into which a highly porous melt electrospinning writing membrane was inserted. This emulated the architectural arrangement of the native jawbone composed by the cortical plate and alveolar bone. The biphasic scaffold was further functionalised with a heparinised hyaluronic acid/gelatine hydrogel containing Bone Morphogenetic Protein-2. Its performance with respect to vertical bone augmentation was assessed in an extraskeletal ovine model. For the purposes of comparison, 7 different groups were implanted for 8 weeks under a polymeric protective dome: Empty, Biphasic scaffold with the hydrogel (PCL-Gel), PCL-Gel with 75 or 150 μg of BMP-2 (PCL-BMP-75 and PCL-BMP-150), hydrogel (Gel), Gel containing 75 or 150 μg of BMP-2 (Gel-BMP-75 and Gel-BMP-150). This resulted in more bone formation in the elevated space in the BMP-2 containing groups, particularly the PCL-BMP specimens, whereby full height was achieved as measured by micro-computed tomography and histology. Interestingly, there was no significant bone volume increase with the higher dose of BMP-2. In a separate cohort of animals previously implanted with 2 samples of the Gel-BMP-150 and PCL-BMP-150 groups, a surgical re-entry at 8 weeks of healing was performed. The protective domes were removed, and one implant was placed on one specimen per group. Bone stability of the augmented bone structure was assessed at 8 weeks and demonstrated that the biphasic scaffold prevented bone resorption, whereas the hydrogel underwent extensive vertical bone loss. This was attributed to the space maintenance properties of the biphasic scaffold.