Mechanics Predicts Effective Critical-Size Bone Regeneration Using 3D-Printed Bioceramic Scaffolds

BACKGROUND: 3D-printed bioceramic scaffolds have gained popularity due to their controlled microarchitecture and
their proven biocompatibility. However, their high brittleness makes their surgical implementation complex for weightbearing
bone treatments. Thus, they would require difficult-to-instrument rigid internal fixations that limit a rigorous
evaluation of the regeneration progress through the analysis of mechanic-structural parameters.
METHODS: We investigated the compatibility of flexible fixations with fragile ceramic implants, and if mechanical
monitoring techniques are applicable to bone tissue engineering applications. Tissue engineering experiments were performed
on 8 ovine metatarsi. A 15 mm bone segment was directly replaced with a hydroxyapatite scaffold and stabilized by
an instrumented Ilizarov-type external fixator. Several in vivo monitoring techniques were employed to assess the
mechanical and structural progress of the tissue.
RESULTS: The applied surgical protocol succeeded in combining external fixators and subject-specific bioceramic
scaffolds without causing fatal fractures of the implant due to stress concentrator. The bearing capacity of the treated limb
was initially altered, quantifying a 28–56% reduction of the ground reaction force, which gradually normalized during the
consolidation phase. A faster recovery was reported in the bearing capacity, stiffening and bone mineral density of the
callus. It acquired a predominant mechanical role over the fixator in the distribution of internal forces after one postsurgical
month.
CONCLUSION: The bioceramic scaffold significantly accelerated in vivo the bone formation compared to other traditional
alternatives in the literature (e.g., distraction osteogenesis). In addition, the implemented assessment techniques
allowed an accurate quantitative evaluation of the bone regeneration through mechanical and imaging parameters.