Regional gene therapy with 3D printed scaffolds to heal critical sized bone defects in a rat model

Abstract

The objective of the present study was to assess the ability of transduced rat bone marrow cells (RBMCs) that overexpress BMP-2 loaded on a three-dimensionally (3D) printed scaffold to heal a critical sized rat femoral defect. Tricalcium phosphate (TCP) scaffolds were 3D printed to fit a critical sized rat femoral defect. The RBMCs were transduced with a lentiviral (LV) vector expressing BMP-2 or GFP. The rats were randomized into the following treatment groups: (1) RBMC/LV-BMP-2 + TCP,(2) RBMC/LV-GFP + TCP, (3) nontransduced RBMCs + TCP, (4) TCP scaffold alone.The animals were euthanized at 12 weeks and evaluated with plain radiographs, microcomputed tomography (micro-CT), histology, histomorphometry, and biomechanically.Each LV-BMP-2 + TCP treated specimen demonstrated complete healing of the femoral defect on plain radiographs and micro-CT. No femurs healed in the control groups.Micro-CT demonstrated that LV-BMP-2 + TCP treated femoral defects formed 197% more bone volume compared to control groups (p < 0.05). Histologic analysis demonstrated bone formation across the TCP scaffold, uniting the femoral defect on both ends in the LV-BMP-2 + TCP treated specimens. Biomechanical assessment demonstrated similar stiffness (p = 0.863), but lower total energy to failure, peak torque, and peak displacement (p < 0.001) of the femurs treated with LV-BMP-2 + TCP when compared to the contralateral control femur. Regional gene therapy induced overexpression of BMP-2 via transduced RBMCs combined with an osteoconductive 3D printed TCP scaffold can heal a critically sized femoral defect in an animal model. The combination of regional gene therapy and 3D printed osteoconductive scaffolds has significant clinical potential to enhance bone regeneration. K E Y W O R D S

BMP-2 Gene Delivery-Based Bone Regeneration in Dentistry

“…Indeed, Blum et al compared the osteogenic effects of adenoviral vectors and retroviruses for BMP-2 gene delivery, and adenoviral vectors were superior to retroviruses in terms of osteogenic differentiation and bone formation [68]. As a result, lentiviral BMP-2 gene delivery is utilized for the investigation of characteristics related to BMP-2 in bone healing or the development of innovative strategies for BMP-2 gene therapy [49,50,69,70,71]. Alaee et al suggested dual expression of a suicide gene and BMP-2 gene in a lentiviral vector due to safety concerns [72].…”

Reconstruction of critical‐size segmental defects in rat femurs using carbonate apatite honeycomb scaffolds

“…Researchers have attempted the reconstruction of critical‐size segmental defects in rat femurs using various scaffolds 9,15,18,23 . Kim et al 9 reported that very little bone had formed in the proximity of segment ends of native bone at 4 weeks post‐implantation when chitosan‐lactide‐fibrinogen hydrogel scaffolds alone were implanted into the segmental bone defects of rats.…”

“…Kim et al 9 reported that very little bone had formed in the proximity of segment ends of native bone at 4 weeks post‐implantation when chitosan‐lactide‐fibrinogen hydrogel scaffolds alone were implanted into the segmental bone defects of rats. Alluri et al 18 reported that when TCP scaffolds alone were implanted into the segmental bone defects of rats, little bone formed at the scaffold–defect interface and no bone had formed surrounding the scaffold, even at 12 weeks post‐implantation. Furthermore, even combined scaffolds and bone morphogenetic protein‐2 (BMP‐2) did not achieve complete recovery at 8 weeks post‐implantation, and 12 weeks were needed for complete recovery 18 .…”

“…Therefore, various scaffolds have been developed to overcome these limitations. At present, a large proportion of the scaffolds designed to address the reconstruction of segmental bone defects are composed of synthetic materials (e.g., ceramics, alloys, and polymers), which incorporate proteins (e.g., bone morphogenetic proteins, vascular endothelial growth factor, and stromal cell‐derived factor‐1α) and/or cells (e.g., mesenchymal stem cells and adipose‐derived stem cells) because the synthetic scaffold materials alone are inadequate to facilitate the reconstruction of critical‐sized bone defects 8‐24 . However, the use of either proteins or cells is accompanied by a higher cost and an increased likelihood of adverse effects, stemming from difficulties in controlling proteins and cells.…”

Bone Morphogenetic Protein‐2‐Activated 3D‐Printed Polylactic Acid Scaffolds to Promote Bone Regrowth and Repair

“…The narrow range of current treatment choices has generated a marked interest in improving translational bone regeneration policies to repair bone defects safely and effectively. [ 4 ]…”