Critical bone defects are considered one of the major clinical challenges in reconstructive bone surgery. The combination of 3D printed conductive scaffolds and exogenous electrical stimulation (ES) is a potential favorable approach for bone tissue repair. In this study, 3D conductive scaffolds made with biocompatible and biodegradable polycaprolactone (PCL) and multi-walled carbon nanotubes (MWCNTs) were produced using the extrusion-based additive manufacturing to treat large calvary bone defects in rats. Histology results show that the use of PCL/MWCNTs scaffolds and ES contributes to thicker and increased bone tissue formation within the bone defect. Angiogenesis and mineralization are also significantly promoted using high concentration of MWCNTs (3 wt%) and ES. Moreover, scaffolds favor the tartrate-resistant acid phosphatase (TRAP) positive cell formation, while the addition of MWCNTs seems to inhibit the osteoclastogenesis but present limited effects on the osteoclast functionalities (receptor activator of nuclear factor κβ ligand (RANKL) and osteoprotegerin (OPG) expressions). The use of ES promotes the osteoclastogenesis and RANKL expressions, showing a dominant effect in the bone remodeling process. These results indicate that the combination of 3D printed conductive PCL/MWCNTs scaffold and ES is a promising strategy to treat critical bone defects and provide a cue to establish an optimal protocol to use conductive scaffolds and ES for bone tissue engineering.

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Critical bone defects are a major clinical challenge in reconstructive bone surgery. Polycaprolactone (PCL) mixed with bioceramics, such as hydroxyapatite (HA) and tricalcium phosphate (TCP), create composite scaffolds with improved biological recognition and bioactivity. Electrical stimulation (ES) aims to compensate the compromised endogenous electrical signals and to stimulate cell proliferation and differentiation. We investigated the effects of composite scaffolds (PCL with HA; and PCL with β-TCP) and the use of ES on critical bone defects in Wistar rats using eight experimental groups: untreated, ES, PCL, PCL/ES, HA, HA/ES, TCP, and TCP/ES. The investigation was based on histomorphometry, immunohistochemistry, and gene expression analysis. The vascular area was greater in the HA/ES group on days 30 and 60. Tissue mineralization was greater in the HA, HA/ES, and TCP groups at day 30, and TCP/ES at day 60. Bmp-2 gene expression was higher in the HA, TCP, and TCP/ES groups at day 30, and in the TCP/ES and PCL/ES groups at day 60. Runx-2, Osterix, and Osteopontin gene expression were also higher in the TCP/ES group at day 60. These results suggest that scaffolds printed with PCL and TCP, when paired with electrical therapy application, improve bone regeneration.

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