Biomedical Engineering Reference
In-Depth Information
Polymer molecules must penetrate through membranes into cells in order to
become subject to direct consumption. The rate of the penetration decreases, as
the molecular size increases. Therefore, the rate of direct consumption must also
decrease as molecular size increases. In addition, there must be a limit of penetra-
tion with respect to molecular size. It follows that
M
ρ
>
0 such that
0
for
ρ
()
M
=
MM
>
. Note that
ρ
α
()
MM
=
β
()
for
MM
>
(12.5)
ρ
. The weight distribution of PEG with respect to the
molecular weight
M
introduced in the following sections is given in the range
31
since
α
() () ()
MMM
=
ρ
+
β
.
≤
l g
M
≤
42
.
. The molecular weight in this range should be greater than
M
ρ
.
12.2.2
Biodegradation of PEG
Polyethers are utilized for constituents in a number of products including lubri-
cants, antifreeze agents, inks, cosmetics, etc. They are also used as raw materials
to synthesize detergents or polyurethanes. Those polymers are either water soluble
or oily liquid, and eventually discharged into the environment [6]. Since they are
not tractable to incineration or recycling, their biodegradability is an important
factor of environmental protection against their undesirable accumulation [7].
Polyethers include PEG, polypropylene glycol, and polytetramethylene glycol, and
they are polymers whose chemical structures are represented by the expression
HO(R - O)
n
H, for example, PEG: R
=
CH
2
CH
2
, polypropylene glycol: R
=
CH
3
CHCH
2
, polytetramethylene glycol: R
(CH
2
)
4
[23] .
PEG is produced in the largest quantity among polyethers. Its major part is
consumed in production of nonionic surfactants. Metabolism of PEG has been
well documented. PEG is depolymerized by liberating C
2
compounds, either aero-
bically or anaerobically [6, 7] (Figure 12.1 ).
=
12.3
Materials and Methods
12.3.1
Chemicals
All reagents used were of reagent grade.
12.3.2
Microorganisms and Cultivation
Microbial consortium E-1 was used as a PEG degrader, which was cultivated as
described previously. The culture was centrifuged to remove cells and the resultant
supernatant was subjected for HPLC analysis.
