Background/Purpose Bone defects resulting from trauma or infection need timely and effective treatments to restore damaged bone. Using specialized three-dimensional (3-D) printing technology, combined with bioactive molecules, we can design custom 3-D scaffolds for bone repair. The Hydroxyapatite (HA)/Beta-Tri-Calcium Phosphate (B-TCP) scaffold components provide mechanical strength, conduct bone throughout the scaffold and remodel over time. Dipyridamole (DIPY) increases local adenosine levels by blocking cellular uptake of adenosine and stimulates bone regeneration. Because DIPY, adenosine and adenosine A2A receptor-specific agonists stimulate bone regeneration in mice as well as BMP-2, a growth factor currently used to promote bone regeneration, we tested the capacity of DIPY-coated matrices could promote successful bone regeneration

Methods 15% HA:85% B-TCP scaffolds were designed usingRobocad software, fabricated using a 3-D Robocasting system, and sintered at 1100°C for 4h. Scanning electron microscopy (SEM), micro-computed tomography (micro-CT), x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and inductive coupled plasma (ICP) were used for material characterization. Vehicle, BMP-2 and DIPY drug scaffolds (scaffold + PBS, scaffold + DIPY or BMP-2, scaffold+ collagen + DIPY or BMP-2) were implanted in C57B6 (wild type, WT) and A2AKO mice with 3mm critical size defect for 2, 4 and 8 weeks. DIPY release from scaffold was assayed spectrophotometrically over time. MicroCT and histological analysis were conducted to determine the degree of new bone formation and remodeling.  

Results Quantitative and qualitative results from microCT showed similar and significant bone formation and remodeling in HA/B-TCP- DIPY and HA/B-TCP-BMP-2 scaffolds when compared to vehicle at 2, 4 and 8 weeks in WT mice (55% bone formation for in HA/B-TCP- DIPY and HA/B-TCP-BMP-2  vs 41% for vehicle,  N=5 per group; P≤ 0.01). Dipyridamole did not enhance bone formation in A_2AKO mice 4 weeks after trephination (31% for HA/B-TCP- DIPY vs 27% for vehicle, N=5, p=ns). Histological analysis of WT mice showed increased bone formation and a trend toward increased remodeling in HA/B-TCP- DIPY and HA/B-TCP-BMP-2 scaffolds. Histologic examination of Dipyridamole treated scaffold in A2AKO mice showed no significant differences in bone formation when compare to vehicle treated scaffolds. Dipyridamole release from collagen coated scaffolds, maintain a constant concentration (10-6M) for up to 10 days.

Conclusion Dipyridanmole increases adenosine levels and targeting osteoblasts and osteoclasts via activation of the adenosine A2A receptor leads to increased bone regeneration in a murine model. Delivery of Dipyridamole in the 3-D ceramic scaffolds is a an effective approach for bone regeneration following orthopedic, dental and craniofacial procedures.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-use-of-three-dimensionally-printed-%ce%b2-tricalcium-phosphatehydroxyapatite-to-further-understand-the-regulation-of-adenosine-receptors-in-osteoclast-formation-and-promotion-in-bone-regeneration/