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Advances in the Processing and Fabrication of Bioinspired Materials and Implications by Way of Applications
Published in T. S. Srivatsan, T. S. Sudarshan, K. Manigandan, Manufacturing Techniques for Materials, 2018
Lakshminath Kundanati, Nicola M. Pugno
Casting process is a manufacturing process in which liquefied metals are poured in a mold to obtain a solid cast. Similarly, films were produced by mixing graphene oxide with polyvinylalcohol as a solution and casting on a polyethylene sheet. The graphene oxide is then reduced using hydroiodic acid to obtain the final nacre-like material (Li et al. 2012). Freeze casting is a variation in which ice formation direction is used to control the solidification direction. As shown in Figure 6.11, the freeze casting technique was used to assemble platelet-like particles to obtain directionally solidified and highly porous material similar to that of nacre (Hunger et al. 2013). Slip casting is a type of casting process that was traditionally used to manufacture ceramic materials. Recently, slip casting process was used to create bioinspired materials made of ceramic, metal, and polymers, in which particles are assembled using a magnetic field to tailor the microstructure (Le Ferrand et al. 2015).
Solution based freeze cast polymer derived ceramics for isothermal wicking - relationship between pore structure and imbibition
Published in Science and Technology of Advanced Materials, 2019
Daniel Schumacher, Dawid Zimnik, Michaela Wilhelm, Michael Dreyer, Kurosch Rezwan
The process of freeze casting, which is a templating method, allows to vary the properties of porous structures in a wide range. Hence, it has attracted considerable interest in recent years [22–25]. Though most research is carried out on dispersed particles (suspension-based freeze casting), solution-based freeze casting of preceramic polymers shows great potential in creating promising pore structures. Rather than rejection and entrapment of particles, thermally induced phase separation is the segregation mechanism in solution-based freeze casting [26]. Generally, pores are created by phase separation of a two-component system during freezing and the subsequent sublimation of the solvent crystals. At the beginning of solution-based freeze casting, a soluble phase (e.g. preceramic polymer) is dissolved in a liquid phase. Freezing of the solution results in crystallization of the liquid phase and depletion of liquid phase around growing crystals. Consequently, the volume between the solvent crystals depletes completely in the liquid phase and enriches in the solid phase. After completely frozen, sublimation removes the solidified liquid phase and thereby creates the porous structure which reflects the shape of the crystals. To a great extent, the liquid phase defines the pore morphology, ranging from cellular to lamellar, dendritic or prismatic [25,27–29].
Improvement of pore orientation and mechanical properties for hydroxyapatite – alumina composite porous scaffolds
Published in Advanced Composite Materials, 2023
As a recent trend in the development of ceramic artificial bones, the demand for porous artificial bones with high porosity for quicker integration with the surrounding bones at the implantation site has been increasing [1,8]. Various manufacturing approaches have been studied to achieve porous materials with high porosity and suitable mechanical properties, such as partial sintering [9], replica method [10,11], and the addition of pore-forming agents [12–26]. Table 1 lists the characteristics of porous HA reported in previous studies. With liquid pore-forming agents, a porous material is obtained by sublimating the crystals of the solvent formed when the ceramic slurry is frozen [21]. This method is also known as freeze-casting. Given that porous materials produced by the freeze-casting method have open pores with excellent connectivity, it is possible to produce porous materials with high fluid permeability suitable for artificial bones; many studies have been conducted to date on this topic [14–26]. By changing the size of the ceramic particles, type of solvent, freezing temperature, and freezing direction, porous materials with various pore forms can be produced. In particular, when the slurry is frozen in one direction, the pores can be oriented in the same direction. Compared to porous materials with non-oriented pores, better mechanical properties can be obtained in the oriented direction for the same porosity. Compared to the replica method, which can also provide orientation to the pores, the freeze-drying method does not require a separate mold or cutting machine for replica fabrication. In addition, solvent crystals can be easily removed by drying and sublimation of the frozen slurry, and there is no risk of producing toxic gases, particularly when water is used as the pore-forming agent. Furthermore, at the freezing front during the freezing process, HA particles are ejected as the ice crystals grow [27] and are pressed between the ice crystals. This has the advantage of increasing the strength of the green body prior to sintering.