Introduction to In Situ Forming Hydrogels for Biomedical Applications - In-Situ Gelling Polymers: For Biomedical Applications - page 21

Fig. 11 a Phase diagram
of the poly(alanine-co-
leucine)-poloxamer-
poly(alanine-co-leucine)
aqueous thermogelling
solutions determined by the
test tube inverting method.
b Storage modulus (G′) and
loss modulus (G″) of the
poly(alanine-co-leucine)-
poloxamer-poly(alanine-
co-leucine) aqueous
thermogelling solutions as a
function of temperature and
concentration. The legends
are the concentrations of
the polymers in water.
Reproduced with permission
from [ 62 ]
solution was investigated by the test tube inverting method. The aqueous polymer
solution (1.0 mL) was put in the test tube with an inner diameter of 11 mm. The
transition temperatures were determined by a flow (sol)-no flow (gel) criterion
with a temperature increment of 1 °C per step. Each data point is an average of
three measurements. Changes in modulus of the polymer aqueous solutions were
investigated by dynamic rheometry. The aqueous polymer solution was placed
between parallel plates of 25 mm diameter and a gap of 0.5 mm. To minimize the
water evaporation during the experiment, the plates were enclosed in a water-satu-
rated chamber. The data were collected under a controlled stress (4.0 dyn/cm 2 ) and
a frequency of 1.0 rad s -1 . The heating rate was 0.5 °C/min.
The phase diagram of PAL-PLX-PAL aqueous solutions determined by the test
tube inverting method is shown in Fig. 11 . Aqueous solutions of PAL-PLX-PAL
undergo sol-to-gel transition as the temperature increases in a concentration range
of 3.0-10.0 wt%. The sol-to-gel transition temperature decreased from 38 to 23 °C
as the concentration increased from 3.0 to 10.0 wt%. At concentrations lower than
3.0 wt%, the viscosity of the polymer aqueous solution increased as the tempera-
ture increased; however, it was not large enough to resist the flow when the test
tube was inverted, and thus they were regarded as a sol state. At polymer concen-
trations higher than 10.0 wt%, the polymer aqueous system formed a gel in a tem-
perature range of 0-60 °C.