Biomedical Engineering Reference
In-Depth Information
zonal function (PRG4 expression)
in vitro
43
and can be mechani-
cally induced to form various shapes.
44
However, these constructs
rapidly lost their organization when implanted in femoral defects
of minipigs,
45
likely due to insu
cient mechanical properties upon
implantation.
36.2.2
Agarose
Agarose is a neutral linear polysaccharide with repeating units of
(1
→
3)-
β
-D-galactopyranose-1(1
→
4)-3,6-anhydro-
α
-L-galactoypy-
ranose (Fig. 36.4a)
46
derived from agar, which is extracted from
several species of
Rhodophyceae
(red seaweed). Compared with
agar, which is widely consumed throughout the world, agarose is
much more highly purified and more expensive. Agarose forms a
thermopolymerizing physical hydrogel and is commonly used for
electrophoresis, microbiology, plant tissue culture, and tissue engi-
neering applications. Agarose powder is not soluble in cold water
but must be heated above the gelatinization point, which ranges
between50
◦
C-95
◦
Cforcommerciallyavailablevarieties(SigmaCat-
alog, 2009), to form a solution. After being fully hydrated, agarose
willremainfluidicuntilitisnearitssettingtemperature(Fig.36.4b).
Theviscosityofhydratedagarosevariesdependingonitsmolecular
weight, which can vary between batches. Low-viscosity agarose is
easier to mix with a cell suspension and to be molded into specific
shapes. Also, it is easier to make gel with a higher concentration of
agarose. High-viscosity agarose is prone to entrap air bubbles dur-
ing heating and may require degassing for several hours at 98
◦
C.
46
Uponcoolingtothesettingtemperature(8
◦
C-42
◦
Cforvariouscom-
mercial varieties), the hydrogel forms.
Agaroseiswidelystudiedinthecartilagetissueengineeringfield,
as cells remain viable and express chondrotypic genes in a three-
dimensional system that allows for mechanical stimulation.
47
,
48
For
cartilage tissue engineering applications, a low setting temperature
is beneficial to ensure homogenous mixing with the cell suspen-
sion and to reduce cell death due to contact with high tempera-
ture.However,agarosewithalowsettingtemperaturetendstohave
low mechanical strength as well. A potential agarose for tissue engi-
neering purpose, from
Gracilaria dura
, has a setting temperature of
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