Porous alumina, zirconia and alumina/zirconia for bone repair: fabrication, mechanical and in vitro biological response

Abstract

Zirconia (ZrO2) and alumina (Al2O3) based ceramics are widely used for load-bearing applications in bone repair due to their excellent mechanical properties and biocompatibility. They are often regarded as bioinert since no direct bone-material interface is created unless a porous structure intercedes, leading to better bone bonding. In this regard, investigating interactions between cells and porous ceramics is of great interest. In the present study, we report on the successful fabrication of sintered alumina A-61, zirconia Z-50 and zirconia/alumina composite ZA-60 ceramics with medium porosities of 61, 50 and 60%, respectively, indicating a bimodal pore size distribution and good interconnectivity. They exhibit elastic moduli of 3-10 GPa and compressive strength values of 60-240 MPa, similar to those of human cortical bone.We performed in vitro cell-material investigations comparing the adhesion, proliferation and differentiation of mouse pre-osteoblasts MC3T3-E1 on the three porous materials. While all three ceramics demonstrate a strong cell attachment, better cell spreading is observed on zirconia-containing substrates. Significantly higher cell growth was quantified on the latter ceramics, revealing an increased alkaline phosphatase activity, higher collagen production and increased calcium biomineralization compared to A-61. Hence, these porous zirconia-containing ceramics elicit superior biological responses over porous alumina of similar porosity, promoting enhanced biological interaction, with potential use as non-degradable bone grafts or as implant coatings.

Effect of Porosity of Alumina and Zirconia Ceramics toward Pre-Osteoblast Response

“…In previous studies, we investigated the osteogenic potential of pre-osteoblasts on porous magnesia and yttria-stabilized zirconia ceramics (Hadjicharalambous et al, 2015b ), as well as the pre-osteoblastic cell response on zirconia, alumina, and zirconia/alumina composite (Hadjicharalambous et al, 2015a ). The objective of this study was to investigate the effect of zirconia and alumina ceramic substrate porosity on cellular adhesion and proliferation.…”

Porous alumina scaffolds chemically modified by calcium phosphate minerals and their application in bone grafts

“…Greater porosity of the material may be desirable for the growth of bone tissue, since the presence of interconnected pores allows cell migration and proliferation, as well as vascularization, effective fluid circulation, and transport of nutrients through the pores. However, excessively high porosity may compromise the mechanical properties of the scaffolds . Compared to porous scaffolds of alumina containing 5% nanometric zirconia inclusions, which showed the mechanical strength of 6.59 MPa, the alumina scaffold produced here showed lower mechanical resistance.…”

“…However, in porous form, this material is limited to application as bone grafts. Because it is bioinert, it is a strong candidate to replace metal in implants . Several studies have reported a greater efficacy of biodegradable synthetic substitutes, with non‐biodegradable alumina ceramics, supporting the use of this bioactive material in coatings .…”

Surface modification using the biomimetic method in alumina‐zirconia porous ceramics obtained by the replica method

“…3,4 The increased surface area of the porous structures leads to a better attachment to the host tissue. However, increased porosity compromises the mechanical properties of scaffolds, 28 as will be demonstrated below.…”