Porous Functional Graded Bioceramics with Integrated Interface Textures

Jonas Biggemann,Swantje Simon,David Köllner,Tobias Fey,Patrizia Hoffmann,Paula Heik

doi:10.3390/ceramics4040048

Jonas Biggemann, Swantje Simon + Show 4 more

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https://doi.org/10.3390/ceramics4040048

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Abstract

Porous functional graded ceramics (porous FGCs) offer immense potential to overcome the low mechanical strengths of homogeneously porous bioceramics used as bone grafts. The tailored manipulation of the graded pore structure including the interfaces in these materials is of particular interest to locally control the microstructural and mechanical properties, as well as the biological response of the potential implant. In this work, porous FGCs with integrated interface textures were fabricated by a novel two-step transfer micro-molding technique using alumina and hydroxyapatite feedstocks with varied amounts of spherical pore formers (0–40 Vol%) to generate well-defined porosities. Defect-free interfaces could be realized for various porosity pairings, leading to porous FGCs with continuous and discontinuous transition of porosity. The microstructure of three different periodic interface patterns (planar, 2D-linear waves and 3D-Gaussian hills) was investigated by SEM and µCT and showed a shape accurate replication of the CAD-designed model in the ceramic sample. The Young’s modulus and flexural strength of bi-layered bending bars with 0 and 30 Vol% of pore formers were determined and compared to homogeneous porous alumina and hydroxyapaite containing 0–40 Vol% of pore formers. A significant reduction of the Young’s modulus was observed for the porous FGCs, attributed to damping effects at the interface. Flexural 4-point-testing revealed that the failure did not occur at the interface, but rather in the porous 30 Vol% layer, proving that the interface does not represent a source of weakness in the microstructure.

Highlights

Porous bioceramics have been extensively investigated to satisfy the increasing demand of bone substitute materials induced by demographic change [1,2,3,4]
The density gradient ρi(x,y,z) induces location-dependent properties Mi(x,y,z) along the spatial directions (x,y,z) and perspective biomedical applications that cannot be achieved by common homogeneous porous ceramics, for which ρi and Mi are constant in volume [23,24,25]
Bi-layered bending bars were fabricated by joining two ceramic feedstocks containing varied amounts of 20 μm spherical pore formers (0–40 Vol%), which generated a well-defined porosity after the heat treatment inside each layer

Summary

Introduction

Porous bioceramics have been extensively investigated to satisfy the increasing demand of bone substitute materials induced by demographic change [1,2,3,4]. The tailored manipulation of the pore distribution throughout the entire sample volume, for instance, by generating highly anisotropic unidirectionally oriented pore architectures, provides the greatest potential for achieving high mechanical strengths [5,9]. In this context, porous ceramic FGCs gained recent interest as generation biomaterials to overcome the mechanical weaknesses of homogeneous porous ceramics by combining the advantageous of dense and porous ceramics in a single material [7,11,12,13,14]. Among the various mentioned processing routes, techniques utilizing computer-aided designing provide the highest potential to realize freely adjustable graded architectures with complex shapes [17,31], which are required for the fabrication of patient individual implants

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