Development of bioceramics with life functions by harnessing crystallographic anisotropy and their biological evaluations

Abstract

is a mineral component of vertebrate hard tissues, thus it assumes a pivot role as essential biomaterials for bone repair. The HAp crystal belongs to a hexagonal system, and has two types of crystal planes with different atomic arrangements: positively-charged calcium ions are packed mainly in the a(b)-plane, while negatively-charged phosphate ions and hydroxyl groups are packed mainly in the c-plane. In vertebrate long bone surfaces, HAp crystals have a c-axis orientation, which leads to the development of the a(b)-plane. On the other hand, in tooth enamel surface, HAp crystals have an a(b)-axis orientation, which results in the c-plane. However, the rationale behind the difference orientations between long bone and tooth enamel in different crystal planes remains poorly understood. Therefore, we would like to elucidate the effect of crystallographic anisotropy of HAp on its osteogenic functions. In particular, single-crystal HAp particles with preferred orientation to a(b)and c-axes were successfully synthesized as the models to mimic bone and tooth enamel and by investigating the specific adsorption of acidic and basic proteins onto these particles, key understanding of bone regeneration process could be made toward developing bioceramics with life function. In addition, porous HAp ceramics with osteoinductivity and enhanced osteoconductivity properties was also developed using a(b)-plane-exposed HAp fibers to further explore the relationship. In this review, we will describe the development of bioceramics with life functions by harnessing the crystallographic anisotropy of HAp to provide greater insight on the biological properties of the resulting bioceramics, such as cell behavior in vitro and bone formation in vivo.

Identification of Proteins Adsorbed on Hydroxyapatite Ceramics with a Preferred Orientation to a-Plane

“…This also indicates that aHAp ceramics can promote cell differentiation due to their high protein adsorption capability. The present findings corroborate our prior findings that aHAp has a high osteoblast differentiation-inducing ability [13].…”

“…Notably, these proteins specifically adsorb to aHAp. This finding may explain our previously reported high osteodifferentiation potential of aHAp [13]. Another notable protein is the vitamin K epoxide reductase complex subunit 1 (VKORC1) identified in aHAp-adsorbed proteins.…”

“…Hereafter, we refer to HAp ceramics with a-plane orientation preference as "aHAp ceramics" in the present study. Aizawa et al's culturing of MG-63 cells on densely packed aHAp ceramics to evaluate the cells' calcification potential using alizarin red S staining and the ceramics' ability to induce bone differentiation indicated that aHAp ceramics promoted osteoblast calcification [13].…”

Effect of wet‐jet milling on the c‐axis orientation of hydroxyapatite ceramics fabricated using a strong magnetic field

“…It is widely used as a biomaterial in artificial bones, bone fillers, and artificial tooth roots and nanofibrous membranes 1–7 . HA consists of a hexagonal crystal structure with a P 6 3 / m space group; its crystal unit cell is characterized by the dimensions a = b = 0.942 and c = 0.688 nm 8 . Moreover, its crystallites are oriented in hard tissues.…”

“…[1][2][3][4][5][6][7] HA consists of a hexagonal crystal structure with a P6 3 /m space group; its crystal unit cell is characterized by the dimensions a = b = 0.942 and c = 0.688 nm. 8 Moreover, its crystallites are oriented in hard tissues.…”