In this study ceramic scaffolds of the bioresorbable and osteoconductive bioceramic β-tricalcium phosphate (β-TCP) were impregnated with the bioresorbable and ductile polymer poly(ε-caprolactone) (PCL) to investigate the influence of the impregnation on the mechanical properties of the porous composites. The initial β-TCP scaffolds were fabricated by the ice-templating method and exhibit the typical morphology of aligned, open, and lamellar pores. This pore morphology seems to be appropriate for applications as bone replacement material. The macroporosity of the scaffolds is mostly preserved during the solution-mediated PCL impregnation as the polymer was added only in small amounts so that only the micropores of β-TCP lamellae were infiltrated and the surface of the lamellae were coated with a thin film. Composite scaffolds show a failure behavior with brittle and plastic contributions, which increase their damage tolerance, in contrast to the absolutely brittle behavior of pure β-TCP scaffolds. The energy consumption during bending and compression load was increased in the impregnated scaffolds by (a) elastic and plastic deformation of the introduced polymer, (b) drawing and formation of PCL fibrils which bridge micro- and macrocracks, and (c) friction of ceramic debris still glued together by PCL. PCL addition also increased the compressive and flexural strength of the scaffolds. An explanatory model for this strength enhancement was proposed that implicates the stiffening of cold-drawn PCL present in surface flaws and micropores.
Pure β-TCP scaffolds with an aligned, lamellar, open and interconnected porosity were fabricated by the ice-templating process. The morphology of the scaffold was analysed and the mechanical properties of the different scaffolds were tested by compression tests. The structural sizes of the scaffolds (pore width and ceramic cell wall thickness) were adjusted by the onset of a constant ice front velocity. For this purpose a freezing device was developed and a specific solution of the non-steady heat equation with a disturbing factor (phase transformation energy from water) was used to model the process parameters. It was found that increasing the ice front velocity decreases the structural sizes and consequently increases the compression strength of the scaffold.
An exponential cooling function for the directional solidification of liquids with constant ice front velocities is investigated with respect to an enhanced control over the ice-templating process. It is mathematically derived and set into relation to other cooling functions found in literature. A theoretical limit of applicability is discussed and a mathematical expression for the maximum sample size realizable with this new approach is derived. Experimental results from the time-resolved direct measurement of the ice front evolution during the directional solidification of pure water and a ceramic b-tricalcium phosphate (b-TCP) suspension in a cooling room environment are presented. These results are compared to the results of numerical simulations. Ice front velocities from 10 to 50 mm s -1 are realized.
Application and investigation of porous composite electrodes for organic batteries fabricated by an ice-templating method are reported for the first time. The possibility to produce polymer composite electrodes with highly aligned, parallel pores is demonstrated and electrochemical investigations are presented to examine their suitability for application in organic batteries. The performance of such ice-templated porous electrodes is experimentally compared with planar electrodes of similar composition against zinc and lithium counter electrodes, respectively. Fundamental properties limiting the performance of ice-templated porous electrodes are discussed and further means to overcome those limitations are proposed.
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