Abstract
Objective. To fabricate and characterise a biomimetic nacre-like ceramic/polymer composite material, comprising a highly aligned lamellar ceramic scaffold infiltrated with polymer, as a potential chairside CAD/CAM dental material.Method. Bi-directional freeze-casting was used to fabricate highly aligned Al2O3 ceramic scaffolds. Different lamellar microstructures were created by controlling processing parameters such as cooling rate, mould slope angle, solid loading, binder and MgO sintering aid concentrations. Once created, the green body scaffolds underwent two separate sintering steps, along with an intermediate uniaxial pressing stage, to produce densified ceramic scaffolds. These were then silanised with γ-MPS coupling agent before being infiltrated with UDMA/TEGDMA polymer to fabricate biomimetic composite materials with anisotropic microstructure and tuneable ceramic fractions. The mechanical properties (flexural strength, elastic modulus, hardness and fracture toughness) of the composite materials were characterised and compared to a commercial CAD/CAM composite material (Vita Enamic). Microstructural characterisation included optical microscopy, scanning electron microscopy (SEM) and micro-computerised tomography (micro-CT).
Results. Highly aligned lamellar ceramic scaffolds were produced by freezing under dual (bi-directional) temperature gradients. Ceramic scaffolds with a lamellar microstructure and different ceramic volume fractions were created by first-step sintering, followed by uniaxial pressing and then second-step sintering. Densified ceramic scaffolds with a brick-and-mortar structure were obtained similar to that seen in nacre. Silanisation of the final scaffold enabled good bonding between the ceramic and polymer phases, as confirmed by SEM. Biomimetic nacre-like ceramic/polymer composites (BCPCs) were fabricated with different ceramic volume fractions ranging from (70% to 76%). The flexural strength of the BCPCs ranged from 135.08 to 172.65 MPa, the elastic modulus from 57.75 to 105.4 GPa, hardness from 3.07 to 4.58 GPa and fracture toughness from 2.54 to 3.19 MPa.m1/2. These were all superior to that seen with commercially available Vita Enamic. The BCPCs also demonstrated good machinability.
Significance. Bi-directional freeze casting is a suitable method by which to fabricate highly aligned lamellar ceramic scaffolds. These scaffolds can be further engineered to produce a unique nacre-like ceramic preform capable of infiltration with a second phase of polymer. There was a correlation between the ceramic microstructure and the mechanical properties of the composite materials. These novel composite materials show potential as chairside CAD/CAM dental materials.
| Date of Award | 24 Mar 2020 |
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| Original language | English |
| Awarding Institution |
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| Sponsors | Jordan University of Science and Technology |
| Supervisor | Bo Su (Supervisor) & Anthony J Ireland (Supervisor) |