Biomedical Engineering Reference
In-Depth Information
Similarly, the unknown parameters
Π
actOBA
NO
,
,
Π
rep OBP
NO
,
, and
Π
actOBU
P
2
can be
,
written as [3]
NO
NO
Π=
( 7. 31)
actOBA
,
K
+
O
DNO
9,
1
NO
Π=
( 7. 3 2)
rep OBP
,
1
+
NO K
DNO
10,
P
2
P
2
Π=
( 7. 3 3)
actOBU
,
K
+
P
2
DP
11,2
which relate directly to the concentrations of NO and PGE
2
caused by
mechanical loading. Here,
K
D
9,
NO
is the activation coefficient for OPG produc-
tion on OBA related to NO,
K
D
10,
NO
is the repression coefficient for RANKL
production on OBP related to NO, and
K
D
11,
P
2
is the activation coefficient for
OBU differentiation related to PGE
2
.
Here, a loading regime is defined as Equation (7.34) (this equation is also
widely used in animal tests [12,58]): The number of loading cycles during a
training day is
N,
T
rest
(h) is the rest time between loading bouts, and
n
is the
number of loading bouts per day. The amplitude
A
(Pa) and frequency (
f
[Hz])
of the interstitial fluid shear stress (
IFSS
) caused by the loading can be mea-
sured using the method in Bergmann, Graichen, and Rohlmann [59], and
therefore the peak fluid shear stress rate
R
IFSS
(Pa-Hz) can be defined as [46]
R
IFSS
= 2π
·
A
·
f
( 7. 3 4)
In Qin and Wang [2], the interstitial fluid flow is formulated only in terms
of load, as can be observed in Equation (7.34); this means that as an inter-
mediate variable it is not actually modeled. However, it is still worth stating
that the interstitial flow is the physical mediator of mechanotransduction by
osteocytes. This completes the crucial transduction from mechanical stimuli
to biochemical signals, which is now concluded for the first time in the field
after an extended literature review. This conclusion will help other research-
ers in the field to understand the mechanism of mechanotransduction of
bone remodeling under mechanical stimulus and to propose other possible
models in the future.
To study the sensitivity of bone remodeling to mechanical loading, the
mechanosensitivity of osteocytes (
MS
OST
) is defined with the frequency (
f
),
number of loads per day (
N
), the rest time between bouts (
T
rest
), and the length
of loading period (
t
). Experimental results indicate that loading has no effect
on bone formation if its frequency is less than 0.5 Hz [60], and the sensi-
tivity of bone changes little when the loading frequency exceeds 10 Hz [61]
