Novel Development of Phosphate Treated Porous Hydroxyapatite.

Kazuya Doi,Yasuhiko Abe,Widyasri Prananingrum,Yoshifumi Oki,Reiko Kobatake,Yoshihito Naito,Yohei Okazaki,Kazuhiro Tsuga

doi:10.3390/ma10121405

Abstract

Phosphoric acid-etching treatment to the hydroxyapatite (HA) surface can modify the solubility calcium structure. The aim of the present study was to develop phosphate treated porous HA, and the characteristic structures and stimulation abilities of bone formation were evaluated to determine its suitability as a new type of bone graft material. Although the phosphoric acid-etching treatment did not alter the three-dimensional structure, a micrometer-scale rough surface topography was created on the porous HA surface. Compared to porous HA, the porosity of phosphate treated porous HA was slightly higher and the mechanical strength was lower. Two weeks after placement of the cylindrical porous or phosphate treated porous HA in a rabbit femur, newly formed bone was detected in both groups. At the central portion of the bone defect area, substantial bone formation was detected in the phosphate treated porous HA group, with a significantly higher bone formation ratio than detected in the porous HA group. These results indicate that phosphate treated porous HA has a superior surface topography and bone formation abilities in vivo owing to the capacity for both osteoconduction and stimulation abilities of bone formation conferred by phosphoric acid etching.

Highlights

Hydroxyapatite [Ca10 (PO4 )6 (OH)2 ] (HA) has been applied as an artificial bone graft material because of its excellent biocompatibility and osteoconduction ability [1]
Phosphoric acid etching reduced the Ca/P ratio of the HA surface from 1.67 to 1.50, which is consistent with the ratio for β-TCP, indicating that the material was conferred with stimulation abilities of bone. This was confirmed by an in vitro study demonstrating that the phosphoric acid-treated HA surface significantly promoted the adhesion, proliferation, and differentiation of osteoblastic cells. These results indicated that phosphoric acid treatment can modify a porous HA surface to achieve a biocompatible material with suitable stimulation abilities of bone formation to serve as a bone graft material
High magnification revealed that porous HA had a smooth inner pore surface, whereas phosphate treated HA showed micrometer-scale roughness on the inner surface of the pores

Summary

Introduction

Hydroxyapatite [Ca10 (PO4 ) (OH)2 ] (HA) has been applied as an artificial bone graft material because of its excellent biocompatibility and osteoconduction ability [1]. HA with a porous structure shows superior osteoconduction because it has an interconnected structure, which allows for the efficient migration of osteogenic cells and vascularization from surrounding bone [1,2]. Interconnected porous hydroxyapatite (IP-CHA), a type of porous HA, has a systematic arrangement of uniform pores with interconnections, and has been successfully used as a bone graft material for tissue engineering [3,4,5]. Despite the superior osteoconduction of porous HA, the ability of bone regeneration is not predictable, owing to the lack of stimulation abilities of bone formation.

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