Biomedical Engineering Reference
In-Depth Information
PFCs are another kind of commonly used oxygen carriers. PFCs
are fluorine-substituted linear, cyclic, or polycyclic anthropogenic
hydrocarbons that have total chemical, biological, and enzymatic
inertness, low toxicity toward biological systems, thermostability,
and very strong hydrophobicity and lipophobicity.
23
,
29
Uniquely,
PFC liquids can dissolve large volumes of respiratory and other
nonpolar gases, having the solubility decreasing in the order
CO
2
>
O
2
>
>
N
2
. PFCs have the solubility of oxygen typically in the
range of 1,000-1,400 mg L
−
1
compared to just around 8.0 mg L
−
1
for water.
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-
32
All these factors make it suitable to be employed as
anoxygencarrierforbiomedicalapplications.Inaerobiccellculture
studies, PFCs have been used to substitute the limitations caused by
conventional aeration systems, a method where air or a mixture of
gases is forced through the volume of a bioreactor.
33
By abolishing
the aeration system, the intensive physical interference caused by
airmovementanditsmixingwiththeculturemediumiseliminated,
thusavoidingthegenerationofshearforcesthatcantriggerthephe-
nomenonknown as hydrodynamic (turbulent) shear cell stress.
34
CO
32.2.2
Induction and Enhancement of Vascularization
In nature, tissues rely on blood vessels for the supply of oxy-
gen and nutrients. The formation of new blood vessels is required
when tissue grows beyond the diffusion limit of oxygen, and this is
also applicable for tissue-engineered constructs. Experiences have
shownthat
invitro
cultureofalarger-volumeconstructisstillpossi-
ble with the aid of specially designed bioreactors, but after implan-
tation, the supply of oxygen and nutrients to the implant is often
limited by diffusion processes. The spontaneous invasion of blood
vessels from the host will occur in response to signals that are
secretedbytheimplantedcellsduetohypoxia.
35
However,therateis
oftentooslow,andnormally,spontaneousvasculargrowthisaround
several tenths of micrometers per day, indicating that complete vas-
cularizationofanimplantofseveralmillimetersneedsweeks.
36
This
could not support the need required by the implant, leading to fail-
ure inthe tissue regeneration effort.
Having this understanding, an approach has been taken to
induce, enhance, and speed up the formation of blood vessels
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