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Bone Regeneration and Remodeling within a Unidirectional Porous Hydroxyapatite Bone Substitute at a Cortical Bone Defect Site: Histological Analysis at One and Two Years after Implantation.

ABSTRACT: Unidirectional porous hydroxyapatite (UDPHAp) is an artificial bone substitute with a unique microstructure consisting of 100-300-µm oval pores that present the material unidirectionally. UDPHAp has a compression strength of 14 MPa and a porosity of 75%, which promotes cell migration and capillary formation within the material. Despite these advantageous properties, bone remodeling and bone formation with UDPHAp remain unclear. To examine long-term remodeling and differences in bone formation based on the defect site, trapezoidal prism-shaped UDPHAp blocks were implanted into rectangular-shaped cortical bone defects in the proximal tibia of Japanese white rabbits. Histological analysis performed at 52 and 104 weeks after implantation revealed that bone and capillaries had formed within the implanted UDPHAp material. Bone formed within the UDPHAp implanted in the cortical defect of rabbit tibia and remodel up to two years. The percentage of new bone area within UDPHAp was larger in cortical lesions than that in medullary lesions. These findings suggest that UDPHAp is a promising material for the repair of non-critical-sized cortical bone defects.

SUBMITTER: Iwasashi M

PROVIDER: S-EPMC5455501 | biostudies-other | 2015 Jul

REPOSITORIES: biostudies-other

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Project description:BACKGROUND/AIM:The present study investigates the in vivo tissue reaction and the integration behavior of an injectable bone substitute material (IBS) composed of a water-based gel combined with nano hydroxyapatite particles and biphasic calcium phosphate granules. The results of the IBS were compared to biphasic bone substitute granules (BBSM) of the same chemical composition. MATERIALS AND METHODS:The subcutaneous implantation model in 40 female 5-week-old CD-1 mice up to 60 days after implantation was used for conduction of the in vivo experiments. Moreover, established histological, histopathological and histomorphometrical methods were applied. RESULTS:The results showed that the IBS was gradually invaded by cells and complex tissue elements. Thus, the implant bed could be distinguished in two areas, i.e. an outer and inner region. While the outer region started to interact with the peri-implant tissue by evoking multinucleated giant cells and at earlier time points by undergoing a continuous high vascularization, the inner part was free of peri-implant cells for at least 30 days, starting to undergo a similar tissue reaction at a later time point. The bone substitute granules allowed for a fast tissue influx between the interspaces of the granules starting at day 10. While the vessel density did not differ in both groups up to the end of the study, the amount of vascularization was significantly higher over the entire observation period in the BBSM group. Moreover, the amount of biomaterial-associated multinucleated giant cells (BMGCs) was significantly higher in the IBS group in the period of between 15 to 30 days after implantation, while comparable BMGC numbers were found in both groups towards the end of the study. CONCLUSION:IBS can build a barrier-like structure that is able to control the soft tissue influx into the central regions of the implantation bed, which could not be observed in other bone substitute granules of the same chemical composition. This directed integration behavior is assumed to be in accordance with the concept of Guided Bone Regeneration (GBR). Furthermore, BMGCs can significantly influence the process of angiogenesis within an implant bed of a biomaterial but not the maturity of blood vessels.

Project description:poly(l-lactic acid) (PLLA) has been approved for clinical use by the US Food and Drug Administration (FDA); however, their stronger hydrophobicity and relatively fast degradation rate restricted their widespread application. In consideration of the composition of bone, the inorganic-organic composite has a great application prospect in bone tissue engineering. Many inorganic-organic composite scaffolds were prepared by directly mixing the active ingredient, but this method is uncontrolled and will lead to lack of homogeneity in the polymer matrix. Strontium (Sr) is an admirable addition to improve the bioactivity and bone induction of hydroxyapatite (HA). To our knowledge, the application of biomimetic mineralized strontium-doped hydroxyapatite on porous poly(l-lactic acid) (Sr-HA/PLLA) scaffolds for bone defect repair has never been reported till date. Biomimetic mineralized Sr-HA/PLLA porous scaffold was developed in this study. The results indicated that the Sr-HA/PLLA porous scaffold could improve the surface hydrophobicity, reduce the acidic environment of the degradation, and enhance the osteoinductivity; moreover, the ability of protein adsorption and the modulus of compression were increased. The results also clearly showed the effectiveness of the Sr-HA/PLLA porous scaffold in promoting cell adhesion, proliferation, and alkaline phosphatase (ALP) activity. The micro computed tomography (micro-CT) results showed that more new bones were formed by Sr-HA/PLLA porous scaffold treatment. The histological results confirmed the osteoinductivity of the Sr-HA/PLLA porous scaffold. The results suggested that the Sr-HA/PLLA porous scaffold has a good application prospect in bone tissue engineering in the future.The purpose of this study was to promote the bone repair.Surgical operation of rabbits was carried out in this study.The results showed that formation of a large number of new bones by the Sr-HA/PLLA porous scaffold treatment is possible.Biomimetic mineralized Sr-HA/PLLA porous scaffold could effectively promote the restoration of bone defects in vivo.

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Bone Regeneration and Remodeling within a Unidirectional Porous Hydroxyapatite Bone Substitute at a Cortical Bone Defect Site: Histological Analysis at One and Two Years after Implantation.

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