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- Apatite (4) (entfernen)
Porous ceramics prepared by the foam replication technique have a high porosity and low mechanical stability. It has been reported that coating such porous ceramics with gelatin allows for an improved compressive strength. Little details regarding the influence of important gelatin parameters such as concentration, temperature and drying conditions as well as bloom number which is a measure of the gel rigidity, on this toughening effect are available. This paper investigates the influence of these parameters on compressive strength of gelatin coated porous hydroxyapatite ceramics. It was found that concentration in the gelatin sols has a marked impact whereas sol temperature, bloom number and differing conditions during subsequent drying have only little influence on the compressive strength of the coated ceramics.
The incorporation of ions in the lattice of hydroxyapatite alters significantly its structure.
Particularly, if anions such as trigonal borate units are accommodated in the lattice severe
distortions must occur around the substitution site because of different geometric shape, electric
charge and anion size. Solid-state NMR has been used to investigate this problem in detail for a
hydroxyapatite sample synthesized by high temperature solid state reaction. The results clearly
verify the existence of network distortions. Indeed, only about 1/3 of the total phosphate content
forms crystalline hydroxyapatite (also found in XRD) whereas the residual amount is contained in
two different phosphate sites with 31P chemical shifts of 5.5 ppm and 2.3 ppm, but broad resonances
lines suggesting disorder. Furthermore, a novel proton signal at -0.6 ppm was found which is
directly associated with the borate incorporation. No specific correlation of the two structurally
different borate units with the two phosphate groups is found.