Bone Tissue Engineering in the Growing Calvaria Using Dipyridamole-Coated, Three-Dimensionally–Printed Bioceramic Scaffolds: Construct Optimization and Effects on Cranial Suture Patency

Abstract

Background: Three-dimensionally-printed bioceramic scaffolds composed of β-tricalcium phosphate delivering the osteogenic agent dipyridamole can heal critically sized calvarial defects in skeletally mature translational models. However, this construct has yet to be applied to growing craniofacial models. In this study, the authors implanted three-dimensionally-printed bioceramic/ dipyridamole scaffolds in a growing calvaria animal model and evaluated bone growth as a function of geometric scaffold design and dipyridamole concentration. Potential adverse effects on the growing suture were also evaluated.Methods: Bilateral calvarial defects (10 mm) were created in 5-week-old (approximately 1.1 kg) New Zealand White rabbits (n = 16 analyzed). Three-dimensionally-printed bioceramic scaffolds were constructed in quadrant form composed of varying pore dimensions (220, 330, and 500 μm). Each scaffold was coated with collagen and soaked in varying concentrations of dipyridamole (100, 1000, and 10,000 μM). Controls consisted of empty defects. Animals were killed 8 weeks postoperatively. Calvariae were analyzed using micro-computed tomography, three-dimensional reconstruction, and nondecalcified histologic sectioning.Results: Scaffold-induced bone growth was statistically greater than bone growth in empty defects (p = 0.02). Large scaffold pores, 500 μm, coated in 1000 μM dipyridamole yielded the most bone growth and lowest degree of scaffold presence within the defect. Histology showed vascularized woven and lamellar bone along with initial formation of vascular canals within the scaffold lattice. Micro-computed tomographic and histologic analysis revealed patent calvarial sutures without evidence of ectopic bone formation across all dipyridamole concentrations.

Mesenchymal Stem Cells and Three-Dimensional-Osteoconductive Scaffold Regenerate Calvarial Bone in Critical Size Defects in Swine

“…Skull injury repair has primarily been investigated in small animal models such as rats [26][27][28][29] and rabbits. [30][31][32] These studies have made important contributions to the development of strategies for calvarial bone regeneration. However, rodent calvaria are very different from that of humans, and a large animal CSD model is ultimately necessary for enabling clinical translation.…”

Recent update on craniofacial tissue engineering

“…14 Bone regeneration is a popular research topic and numerous reports have been published on novel approaches to promote the best outcomes. [15][16][17] The investigation of such techniques in the craniofacial region has been reported clinically, but is still in its infancy due to the difficulty of developing a robust in vivo model of a craniofacial bone defect 18 (Figure 3).…”

“…These agents may enhance cellular recruitment and adhesion to the scaffold, promote proliferation then differentiation of specific cells important for bone regeneration and inhibit antagonistic activity (such as that of osteoclasts). [15][16][17][18]29,30 Calcium phosphates are widely used for bone reconstruction. 31,32 3D-printed β-tricalcium phosphate (β-TCP) scaffolds soaked in collagen and coated with dipyridamole have been investigated for bone regenerative purposes.…”

“…( Below , right ) Bone formation is guided by highly osteoconductive scaffold dimensions as new bone formation is directed from scaffold pore-to-pore ( green arrows ) while interacting with scaffold struts ( yellow arrows ). Adapted from Maliha et al 18…”

Personalized Bone Reconstruction and Regeneration in the Treatment of Craniosynostosis

“…Another group developed a new 3D-printed β-tricalcium phosphate (β-TCP) scaffold loaded with the osteogenic agent dipyridamole and evaluated the effects of this implants to support bone growing within bilateral calvarial defects in rabbit [120]. After the implantation, the Authors observed a volumetrically significant osteogenic regeneration of calvarial defects, with a favorable preservation of suture patency, at least in the short term [120]. The same group then reproduced the experiments in an immature rabbit model, evidencing a comparable responsiveness with respect to autologous bone grafts.…”