Porous Functional Graded Bioceramics with Integrated Interface Textures

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.

Relation between Structure, Mechanical and Piezoelectric Properties in Cellular Ceramic Auxetic and Honeycomb Structures

“…This additional mechanical stress can generate more charges at the surface, which lead to an increased d 33 . To further investigate the influence of the surface stresses, additional surface structuring could be generated, [ 59 ] which could lead to a higher surface area and charge simultaneously.…”

Improved Mechanical Amplification of Monolithic PZT and PZT Composite via Optimized Honeycomb Macrostructures

“…The focus of this research was to analyze the mechanical amplification behavior and, most especially, the influence of the interface between building blocks and the PZT-filled resin on the fracture behavior. The results show that the processing caused a gradient structure [22][23][24][25][26][27] and a textured surface [22,23,[28][29][30][31][32].…”

“…Of particular interest is the influence of the manufacturing process on the interface. The PZT building blocks have a gradual porosity on the surface (5.92%, Figure 2a), which is caused by PbO evaporation and is desirable in this case and belongs to stochastic surface textures [22][23][24][25][26][27]. According to McBain et al [40], pores and gradient structures are the oldest and simplest way to create a mechanical interlock (Figure 2b).…”

“…A structured surface or roughness are parameters that affect the strength of bonded joints, as it increases adhesion by mechanical interlocking and leads to an increase in the contact area between the joining part (PZT building block) and the adhesive (PZT-filled silicone resin) [41][42][43]. In addition, due to the 3D printing of the positives for the silicone molds, the PZT building blocks have a textured surface [22,23,[28][29][30][31][32] with linear undulations analogous to [22,23,32]. The influence on the properties was investigated by Biggemann et al [23] and confirmed by Naat et al [32,44] The novel combination of the 3D printing process and injection molding leads to a significant enhancement of mechanical interlocking in the interface, which reduces the mechanical deformation behavior during compression tests.…”

Microporous Ceramics Based on β-Tricalcium Phosphate

“…Various methods can be used to achieve microporosity of ceramic materials. Among them are incomplete sintering [39], addition of small particles of sacrificial organic or inorganic components to the starting powder mixture [40,41], addition of components having the ability to release of sufficiently large volumes of gases when heated [42], using the sol-gel method of precursor preparation [43], or using a powder mixture containing columnar-like [44] or plate-like [45] particles restraining densification. Synthesized powders of dicalcium phosphate dihydrate CaHPO 4 •2H 2 O and/or dicalcium phosphate anhydrate CaHPO 4 (i.e., brushite and/or monetite) usually consist of plate-like or petal-like particles [46][47][48][49].…”