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Introduction: Even though conventionally prepared octacalcium phosphate and collagen composite (OCPcol) has exhibited excellent bone regeneration with angiogenesis (1, 2) and has already been commercialized for treating bone defects (3), reproducible appositional bone formation with OCPcol has never been achieved. Recently, it was developed double concentration of OCP/Col with applying liquid nitrogen during the preparation (OCPcol L2.0). And it demonstrated reproducible appositional bone formation in preclinical study (4). Because it was reported that bone formation in the implant would be enhanced by orderly arranged unidirectional macropores, the present study investigated whether appositional bone formation could be enhanced by different types of unidirectional macropores in OCPcol L2.0.
Methods: The prepared OCPcol L2.0 (diameter 9 mm, thickness 2 mm) were given parallel holes in the axial direction for adjusting cell invasion from outside of the disks, and divided four groups. They were OCPcol L2.0 disks with through hole (open hole: Open), blind holes from top to bottom (Top), blind holes from bottom to top (Bottom), and untreated (Unt). These disks were implanted into subperiosteal pockets in rodent calvaria (n = 5 x 4 groups). Radiomorphometric analysis was conducted at 4 and 12 weeks after implantation, and histological analysis was conducted at 12 weeks after implantation.
Results: In radiomorphometric analysis, the Open group indicated a greater degree of deformation than the other three groups, whereas all groups tended to retain their height and shape. In histomorphometric analysis, appositional bone formation was dominantly initiated from the surface of original bone towards inside of the implants, and the Open group demonstrated the lowest appositional bone formation compared with other three groups.
Conclusions: These results suggest that the addition of through holes in OCPcol L2.0 might be a subordinate factor for appositional bone formation compared with the increase of concentration of OCPcol or application of liquid nitrogen during the preparation.
References
1. Kamakura S, Sasaki K, Honda Y, Anada T, Suzuki O. Octacalcium phosphate (OCP) combined with collagen orthotopically enhances bone regeneration. J Biomed Mater Res B Appl Biomater 79, 210, 2006;
2. Kouketsu A, Matsui K, Kawai T, Ezoe Y, Yanagisawa T, Yasuda A, Takahashi T, Kamakura S. Octacalcium phosphate collagen composite stimulates the expression and activity of osteogenic factors to promote bone regeneration. J Tissue Eng Reger Med 14, 99, 2020;
3. Kawai T, Kamakura S, Matsui K, Fukuda M, Takano H, Iino M, Ishikawa S, Kawana H, Soma T, Imamura E, Kizu H, Michibata A, Asahina I, Miura K, Nakamura N, Kibe T, Suzuki O, Takahashi T. Clinical study of octacalcium phosphate and collagen composite in oral and maxillofacial surgery. J Tissue Eng 11, 2041731419896449, 2020;
4. Yanagisawa T, Yasuda A, Makkonen RI, Kamakura S. Influence of pre-freezing conditions of octacalcium phosphate and collagen composite for reproducible appositional bone formation. J Biomed Mater Res Part B 108, 2827, 2020;
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