Biomedical Engineering Reference
In-Depth Information
TABLE 11.4
Parameters Used in Model Validation [89]
Parameters
Values
N
3
K
30% total-receptor concentration
10 5 mg/mL/sec
β
3.8
×
Initial aggrecan content
16 mg/mL
1.0
0.8
1 day
0.6
3 days
0.4
5 days
0.2
6 h
10 h
2 h
0.0
0
0.2
0.4 0.6
Radial distance from center of the cartilage (mm)
0.8
1
1.2
1.4
FIGURE 11.18
Normalized IGF-I mediated aggrecan production rate, as a function of radial
distance from the center of cartilage undergoing free diffusion. The calculated
aggrecan production rate is normalized to the value of parameter β .( K =
0 . 3 c RT , β = 3.8
= 16 mg/mL, and c I 0 =
10 5 mg/mL/sec, n =3, c a 0
×
40 nM.)
stimulation extends into the inner region of the domain at an intermediate
frequency (i.e., 0.01 Hz).
Figure 11.18 shows predictions of the spatial dependence of IGF-I induced
aggrecan synthesis rate in the presence of 300 ng/mL bath IGF-I concentra-
tion undergoing free diffusion. It can be seen that a strong spatially dependent
aggrecan production develops at early times (i.e., time < 1 day) when IGF-I
initially diffuses into the cartilage with a steep concentration gradient from the
outer edge of the cartilage. Over time, as IGF-I gradually saturates the carti-
lage disc, aggrecan production rate becomes uniform throughout the disc and
reaches its maximum level. Eventually aggrecan production is “switched off”
 
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