272
6 Growth
in a certain tissue, this could tell us something about how the tissue grows. Residual
stress also may serve other important functions in biological systems. For example,
studies suggest that residual stress enables load-bearing structures, such as arteries,
to carry loads more efficiently (Fung 1991). Civil and mechanical engineers long
have known that incorporating residual stress into their designs can make man-made
structures better able to withstand loads. A case in point is prestressed concrete.
Concrete is stronger in compression than in tension, and one way to improve
performance is to embed stretched steel bars in the concrete as it hardens. When
released, the bars shorten and compress the concrete, making the composite material
better able to withstand tensile loads without failure.
This section takes a more in-depth look at residual stress in biological structures.
The focus here again is on soft tissue. The role of residual stress in making the
skeleton a more efficient load-bearing structure should not be overlooked, however.
Like concrete, the compressive strength of bone is generally stronger than its tensile
strength.
6.5.1 Historical Background
Researchers have known for decades that soft tissues contain residual stress. Its
presence in blood vessels has been known at least since 1960, when Bergel (1960)
found that an isolated section of an artery opens following a longitudinal cut. As
discussed below, dissection is a common method used to study residual stress in
soft tissue. For example, if skin is cut, the wound opens by an amount that depends
on the tension in the tissue. 3 If an artery is stress-free, it would not open when cut.
The significance of Bergel’s study was largely overlooked for more than two
decades, until Vaishnav and Vossoughi (1983, 1987) confirmed his results. At
about the same time, Y.C. Fung and coworkers found residual stress in the heart
(Fung 1984; Omens and Fung 1990). Afterwards, with Fung leading the way, the
phenomenon of residual stress virtually exploded in popularity. Researchers found
residual stress nearly everywhere they looked, including the trachea (Han and Fung
1991), esophagus (Gregersen et al. 2000), and brain (Henderson et al. 2005; Xu et al.
2009), as well as in embryos (Beloussov et al. 1975) and plants (Goriely 2017).
In a series of landmark papers, Fung and colleagues explored the purpose of
residual stress in biology, as well as how it is created. Using theoretical models,
they showed that residual stress tends to homogenize wall stress in arteries subjected
to normal physiological pressure loads (Chuong and Fung 1986; Chuong et al.
1986). A more uniform stress distribution makes the artery more efficient in bearing
loads and may play a role in regulating blood flow, as all smooth muscle fibers
contribute almost equally to the contractile force that changes vessel radius (Fung
3 Skin loses elasticity with age, so the amount that a cut opens generally decreases as you grow
older (unless you have work done).
6 Growth
in a certain tissue, this could tell us something about how the tissue grows. Residual
stress also may serve other important functions in biological systems. For example,
studies suggest that residual stress enables load-bearing structures, such as arteries,
to carry loads more efficiently (Fung 1991). Civil and mechanical engineers long
have known that incorporating residual stress into their designs can make man-made
structures better able to withstand loads. A case in point is prestressed concrete.
Concrete is stronger in compression than in tension, and one way to improve
performance is to embed stretched steel bars in the concrete as it hardens. When
released, the bars shorten and compress the concrete, making the composite material
better able to withstand tensile loads without failure.
This section takes a more in-depth look at residual stress in biological structures.
The focus here again is on soft tissue. The role of residual stress in making the
skeleton a more efficient load-bearing structure should not be overlooked, however.
Like concrete, the compressive strength of bone is generally stronger than its tensile
strength.
6.5.1 Historical Background
Researchers have known for decades that soft tissues contain residual stress. Its
presence in blood vessels has been known at least since 1960, when Bergel (1960)
found that an isolated section of an artery opens following a longitudinal cut. As
discussed below, dissection is a common method used to study residual stress in
soft tissue. For example, if skin is cut, the wound opens by an amount that depends
on the tension in the tissue. 3 If an artery is stress-free, it would not open when cut.
The significance of Bergel’s study was largely overlooked for more than two
decades, until Vaishnav and Vossoughi (1983, 1987) confirmed his results. At
about the same time, Y.C. Fung and coworkers found residual stress in the heart
(Fung 1984; Omens and Fung 1990). Afterwards, with Fung leading the way, the
phenomenon of residual stress virtually exploded in popularity. Researchers found
residual stress nearly everywhere they looked, including the trachea (Han and Fung
1991), esophagus (Gregersen et al. 2000), and brain (Henderson et al. 2005; Xu et al.
2009), as well as in embryos (Beloussov et al. 1975) and plants (Goriely 2017).
In a series of landmark papers, Fung and colleagues explored the purpose of
residual stress in biology, as well as how it is created. Using theoretical models,
they showed that residual stress tends to homogenize wall stress in arteries subjected
to normal physiological pressure loads (Chuong and Fung 1986; Chuong et al.
1986). A more uniform stress distribution makes the artery more efficient in bearing
loads and may play a role in regulating blood flow, as all smooth muscle fibers
contribute almost equally to the contractile force that changes vessel radius (Fung
3 Skin loses elasticity with age, so the amount that a cut opens generally decreases as you grow
older (unless you have work done).