Biomedical Engineering Reference
In-Depth Information
et al. (2001) have studied the shear strength and moduli of PAMPS for reasonable
soft engineering applications. In their study, the shear modulus of two polyelectrolyte
gels—namely, poly(acrylic acid), a weak acid with small side groups, and PAMPS
gel, a strong acid with large side groups—has been measured with and without
application of an electric field across gel samples fully swollen with water.
In the absence of an electric field, the shear modulus of PAMPS gels is shown to
be inversely proportional to the swelling degree, in accord with their theoretical pre-
dictions. Under a steady electric field, the measured modulus of these gels was observed
to reduce with time. They explain that this is due to migration of the free counter-ions
and associated hydration and added mass water towards the cathode, resulting in
reduced contact between gel and rheometer due to exuded water. Theoretical prediction
of
G
in the presence of a thin slip layer is in good quantitative agreement with
experimental observations. Preliminary measurements of the reduction of shear mod-
ulus under pulsed electric field have also been obtained and they observed an unex-
pected recovery of the initial modulus on all subsequent applications of the field before
the continued reduction to successively lower values. When roughened platens were
used, a stepwise variation in measured modulus was observed, with a slightly lower
modulus being recorded in the presence of an applied electric field.
Yasuda et al. (2005) have studied the biomechanical properties of high-toughness
double-network (DN) hydrogels. Using pin-on-flat wear testing, they have evaluated
the wear property of four novel DN hydrogels composed of two kinds of hydrophilic
polymers. The gels involved PAMPS-PAAm gel, which consists of poly(2-acryla-
mide-2-metyl-propane sulfonic acid) and polyacrylamide; PAMPS-PDAAAm gel,
which consists of poly(2-acrylamide-2-metyl-propane sulfonic acid) and poly(N,N
′
and
G
″
-
dimetyl acrylamide); cellulose-PDMAAm gel, which consists of bacterial cellulose
and polydimetyl-acrylamide; and cellulose-gelatin gel, which consists of bacterial
cellulose and gelatin. Ultrahigh molecular weight polyethylene (UHMWPE) was
used as a control of a clinically available material.
Using a reciprocating apparatus, a million cycles of friction between a flat spec-
imen and ceramic pin were repeated in water under a contact pressure of 0.1 MPa.
To determine the depth and the roughness of the concave lesion created by wear, a
confocal laser microscope was used. As a result, the maximum wear depth of the
PAMPS-PDMAAm gel (3.20
′
m) was minimal in the five materials, while there was
no significant difference compared to UHMWPE. There were significant differences
between UHMWPE and one of the other three gels, namely the PAMPS-PAAm gel
(9.50
µ
µ
m), the cellulose-PDMAAm gel (7.80
µ
m), and the cellulose-gelatin gel
(1302.40
m). This study demonstrated that the PAMPS-PDMAAm DN gel has an
amazing wear property as a hydrogel that is comparable to the UHMWPE. In addition,
the PAMPS-PAAm and cellulose-PDMAAm DN gels are also resistant to wear to
greater degrees than conventionally reported hydrogels. On the other hand, this study
showed that the cellulose-gelatin DN gel was not resistant to wear.
µ
5.7
GEL ROBOTICS
There has been some development on gel robotics by the University of Tokyo and
Hokkhaido University researchers (Otake, et al., 1999, 2000a, 2000b, 2002, 2002a,
