Biomedical Engineering Reference
In-Depth Information
Table 4.2
General specifications of durometer types A and OO
Scale of Durometer
Material to be used
Main spring force
Indenter shape
Flat cone point, 35
◦
A
Soft elastometric materials, rubber,
and rubber-like
822 gf (8.06 N)
Sphere, 3/32
OO
Light foams, sponge rubber, and
animal tissue
113 gf (1.11 N)
Durometer
Type OO
Indenter
Presser Foot
Figure 4.36
Durometer type OO
As shown in Figure 4.36, a commercially available durometer test consists of four com-
ponents according to ASTM D 2240: the presser foot, indenter extension, indicating device
(e.g., dial), and calibrated spring. The scale reading is proportional to the indenter move-
ment. The soft material samples were measured using standard durometer types OO and A.
The successful application of the durometer in mechanical property evaluation of soft
tissue such as skin is reported by Falanga and Bucalo [20]. The measurement of elasticity
of tumors surrounded by soft tissue is reported in [21] and the range of elasticity of breast
tumors was found to be between 150 and 990 kPa.
In addition to the softness measurements, the compressive Young's modulus of the
objects for small strains (
<
10%) was measured using a conventional compression test.
The relationship between the durometer dial reading and Young's modulus of the objects
is shown in Figure 4.37. The Young's modulus of the harder object was measured as
6 MPa. The objects were then used to test the microfabricated sensor for softness sens-
ing. Figure 4.38 shows the MEMS sensor during test with an electrodynamic shaker for
applying dynamic loads. The soft objects were placed on the first beam. A compressive
load was then applied to the top surface of the objects using a rigid plate at the end of a
probe in order to mimic the grasping conditions.
The output of the PVDF films attached to all the three beams were recorded and
compared. Four samples were tested. Three of them were considered as soft objects and
