Biomedical Engineering Reference
In-Depth Information
Other constructions, e.g., to study calcification of biological heart
valve prostheses [875], are also possible. In addition, one should
keep in mind that the potential of the standard CC technique has not
reached its limit yet: for example, recently a good mimicking of the
self-organized microstructure of tooth enamel has been achieved
[876].
The third major difference between the
in vivo
and
in vitro
crystallization conditions might be overcome by using the
appropriate crystallization solutions [860]. The presence of calcium
and orthophosphate ions in some biological fluids has been known,
at least, since 1921 [877, 878]. Therefore, the best way would be
to perform experiments using natural liquids (blood serum, saliva,
lymph, etc.), but this is not easy due to great variability of the chemical
and biochemical compositions of natural liquids and problems with
their collection and storage. As stated before, using supersaturated
aqueous solutions containing only the ions of calcium and
orthophosphate appears to be unable to mimic the crystallization
of biological apatite; therefore, more advanced solutions have been
elaborated. To the best of my knowledge, Hanks' balanced salt
solution (HBSS) [879] was the first successful simulating medium,
containing the ions of calcium and orthophosphate together with
other inorganic ions and glucose. HBSS is commercially available
and still used in biomimetic experiments [880-882]; its chemical
composition might be taken, e.g., from Refs. [883, 884]. Other
popular physiological solutions include α-modified Eagle's [885]
medium (α-mEm) and its variation Dulbecco's [886] modified Eagle's
medium (DMEM), which contain numerous bioorganic (alanine,
aspartic acid, glycine, biotin, vitamin C, folic acid, riboflavin) and
inorganic (CaCl
) components [887-891],
phosphate buffered saline (PBS) that contains only inorganic
(CaCl
, KCl, NaCl, NaH
PO
2
2
4
) components [892, 893].
Furthermore, artificial saliva [894-896], synthetic urine [838, 897]
and simulated milk ultrafiltrate (SmuF) [898-901] solutions are
available. They contain both bioorganic (e.g., xantan gum or sodium
carboxymethylcellulose, sorbitol, etc.) and inorganic (e.g., CaCl
, mgCl
, KCl, KH
PO
, NaCl, NaH
PO
2
2
2
4
2
4
,
2
mgCl
) compounds. Additional media
used for mineralization studies are listed in Table 3 of ref. [578]. All
these simulating solutions are commercially available.
However, the most popular biomimetic solution is a protein-free
acellular simulated body fluid (SBF). It was introduced by Kokubo et
, KCl, KH
PO
, NaCl, KH
PO
2
2
4
2
4
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