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Abstract

In the dentistry field, synthetic hydroxyapatite can be conveniently used as semiabsorbable alloplastic material to solve a number of clinical problems. The hydroxyapatite structure influences bone ingrowth as well as its resorption. In particular, pore size must exceed 100 microm to allow new bone ingrowth. Because of its brittleness, highly porous hydroxyapatite is difficult to handle without causing damage, and, therefore, its mechanical performance has to be improved placing the material on a dense hydroxyapatite substrate. Dense/porous hydroxyapatite laminates can be obtained by slip casting technology. The method starts with the preparation of a ceramic powder-binder-solvent system. This slurry produces, after solvent evaporation, a soft green tape, that is successively baked at 300 degrees C to remove all organic component, and finally sintered at high temperature (1200 degrees C). The material porosity cannot be significantly modified by changes in the slurry composition and sintering temperature; therefore, the macroporous hydroxyapatite layer must be obtained using a porous hydroxyapatite powder. The powder is prepared by grinding of green tape pieces and the resulting coarse material is successively baked at 300 degrees C. Such material is mixed with a polymer solution and cast on a green tape substrate. Layer fractures are not observed in both film bulks and interface, because during sintering the consolidation of two layers happens simultaneously. In the resulting material, the first layer consisted of macroporous hydroxyapatite with high osteoconductive properties, and the second layer was a dense hydroxyapatite substrate able to improve the laminate mechanical properties.

Calcium Orthophosphates as Bioceramics: State of the Art

“…Even so, the major limitations to use calcium orthophosphates as load-bearing bioceramics are their mechanical properties; namely, they are brittle with a poor fatigue resistance [46,47,48,63]. The poor mechanical behavior is even more evident for highly porous bioceramics and scaffolds because porosity greater than ~100 µm is considered as the requirement for proper vascularization and bone cell colonization [64,65,66]. Thus, for biomedical applications, calcium orthophosphates are used primarily as fillers and coatings, rendering it impossible to use them for repair of large osseous defects [57,58].…”

“…Furthermore, dimensions of open pores are directly related to bone formation, since such pores grant both the surface and space for cell adhesion and bone ingrowth. On the other hand, pore interconnection provides the way for cell distribution and migration, as well as allowing efficient in vivo blood vessel formation suitable for sustaining bone tissue neo-formation and possibly remodeling [64,65,66,122,347,348,349,350,351,352,66,122,347]. Namely, porous HA bioceramics can be colonized by bone tissues [349,353,354,355,356,357,358,359,360,361,362,363].…”

Calcium orthophosphate-based biocomposites and hybrid biomaterials

“…Even so, the major limitations to use calcium orthophosphates as load-bearing biomaterials are their mechanical properties; namely, they are brittle with poor fatigue resistance [26][27][28]. The poor mechanical behavior is even more evident for highly porous ceramics and scaffolds because porosity[100 lm is considered as the requirement for proper vascularization and bone cell colonization [84][85][86], i.e., why, in biomedical applications calcium orthophosphates are used primarily as fillers and coatings [23].…”

Production of tubular porous hydroxyapatite using electrophoretic deposition

“…7) Porous HA ceramics are used in many biomedical applications for repairing diseased tissues and organs. For the production of porous HA scaffolds, several methods have been used in literature, including; the polymeric sponge method, 8) slip casting, 9) gel casting, 10) starch consolidation, 11) electrophoretic deposition (EPD) 12) and 3D printing. 13) EPD is widely used because of its effectiveness in generating coatings and bulk materials.…”