Fabrication and characterization of highly porous calcium phosphate (CaP) ceramics by freezing foamed aqueous CaP suspensions

Abstract

Highly porous calcium phosphate (CaP) ceramics were fabricated by freezing foamed aqueous CaP suspensions with various CaP contents (15, 20, and 25 vol %) containing polyvinyl alcohol (PVA) as the binder and emulsifying agent. All the samples fabricated showed uniformly dispersed macropores, which were created by air bubbles introduced in the suspensions. In addition, aligned micropores were formed in the sintered CaP walls as a replica of the preferentially grown ice dendrites during freezing when CaP contents of 15 and 20 vol % were used. The overall porosity decreased from 83 to 73 vol % with increasing initial CaP content from 15 to 25 vol %, whereas the compressive strength and elastic modulus increased significantly from 1.2 « 0.2 to 4.7 « 0.9 MPa and from 20 « 11 to 163 « 42 MPa, respectively. The samples showed good biocompatibility, as assessed by the in vitro cell test using a pre-osteoblast cell line.

Freeze casting – A review of processing, microstructure and properties via the open data repository, FreezeCasting.net

“…. Plots of normalized compressive strength of freeze-cast ceramics as a function of relative density (1ϕ p ), categorized by pore structure, including: (a) lamellar (N=492[112, 117, 120, 149, 195, 219, 224, 239, 240, 282, 283, 285, 286, 295, 296, 302, 312, 336, 339, 379, 384, 386, 390, 405, 412, 414, 415, 446, 448, 460, 488, 505, 506, 514, 516, 563, 566, 569, 572, 579, 581, 624, 626-628, 633, 635, 637, 651, 655, 662, 667, 670, 682, 688, 689, 705, 711, 712, 721, 742, 747, 792, 795]), (b) dendritic (N=143[196, 224, 262, 296, 302, 320, 324, 379-381, 385, 388, 410, 461, 575, 576, 584, 606-608, 617-620, 623, 624, 640, 652, 665, 666, 668, 672, 675, 681, 683, 691, 692, 697, 723, 726]), (c) honeycomb (N=207[110, 224, 339, 341, 342, 351, 429-431, 492, 504, 569, 595, 647, 678, 690, 700, 703, 704, 737, 738, 750]), (d) cellular (N=145[38,39,226,285,379,391,590,615,617,619,629,634,668,671,674,677,708,712,720,721,745,754,795,809]), and (e) equiaxed (N=40[344,583,588,609,610,658,679,698,699]). All data in(a)-(c) correspond to anisotropic materials.…”

Influence of cryogenic drying conditions on hierarchical porous structure of aluminum oxide systems

“…The cryogel pore structures generally are columnar, lamellar or dendrite. The typical structure of inorganic oxide cryogels is the lamellar [7,13,24].…”

“…The typical synthesis route of cryogels is starting from aqueous suspensions, slurries [5][6][7][8][9][10][11][12][13]. The freezing of the aqueous suspension is followed by sublimation of the frozen phase and subsequent sintering yields ceramics granules.…”

“…According to the reported technique, the typical precursor material for the freeze drying is an aqueous suspension (slurry) of inorganic oxide powders. The 3D system of the cryogels is built up from open anisotropic macropores(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) µm Ø) and mesopores (7-9 nm Ø) closed in the pore walls. The macropores can be characterized with channel-like (columnar) pore architecture.…”

Inorganic Cryogels

“…The bimodal porosity with large longitudinal pores and numerous mesopores in the pore walls is very suitable for catalyst supports for gas phase reactions. Large oriented pores ensure rapid transport of gaseous reagents, while the mesopores in the pore walls are an ideal location for catalyst nanoparticles in order to ensure their maximum exposure to reagents [168][169][170][171]. Similarly to the cryogel synthesis of individual particles, the directed crystallization method also produces metal catalysts on oxide supports in the same synthesis run [172,173].…”