Biomedical Engineering Reference
In-Depth Information
5 mm
(a) Conventional suture
(b) Fixator parent shape
5 mm
Open fixator
(c) Deformed shape
2.5 mm
(d) Application to tissue
+
−
(e) Electric current heating
of backbone
(f ) Closure after heating
Closed fixator
FIGURE 9.3
Prototype and working principle of a self-closing clip for MIS. (From Song et al.,
Smart Mater. Struct.
, 11, 1-5,
2002, reproduced with permission from Springer.)
ability to recover large transformation stress and strain upon heating, SME, peudoelastic-
ity (or SE), and biocompatibility (Miyazaki and Ishida, 1999; Wolf and Heuer, 1995; Khan
et al., 1998). The work output per volume of SMA exceeds those of other microactuation
mechanisms. The phase transformation in SMA thin film is accompanied by significant
changes in mechanical, physical, chemical, electrical, and optical properties, such as yield
stress, elastic modulus, hardness, damping, shape recovery, electrical resistivity, thermal
conductivity, thermal expansion coefficient, surface roughness, vapor permeability, dielec-
tric constant, and so on (Fu et al., 2001; Fu et al., 2004). These changes can be fully uti-
lized in design and fabrication of microsensors and microactuators (Winzek et al., 2004;
Miyazaki, 1990).
In the early 1990s, several trials were made to fabricate TiNi thin films by sputter deposi-
tion (Walker et al., 1990). Some of these results showed that conventional micromachining
processes are applicable for making microstructures consisting of a silicon substrate and
a TiNi thin film. If the films contain microdefects, which are characteristic in sputter-
FIGURE 9.4
Over-the-scope clip system for gastrointestinal bleeding control. Left, atraumatic; right, traumatic versions.
(From Kirschniak et al.,
Gastrointest. Endosc.
, 66, 162-167, 2007, reproduced with permission from Elsevier.)
