Introduction to In Situ Forming Hydrogels for Biomedical Applications - In-Situ Gelling Polymers: For Biomedical Applications - page 15

Fig. 5 Sample creep curves under different stresses
compliance is compared to reciprocal shear modulus measured in small amplitude
oscillatory shear tests in order to judge if the sample displays pure elastic behav-
ior. Figure 5 shows a typical example of creep strain curves and creep compliance
curves of polystyrene at various stresses. In the linear viscoelasticity region, under
different stresses of A and B, the creep compliance curves overlap each other. The
curve induced by Stress C does not overlap as shown in Fig. 5 , indicating that the
linear viscoelasticity region has been exceeded.
In addition to the above-mentioned measurements, the flow properties of the
hydrogels as well as their abilities to retain or recover their original form after
experiencing shear flow or large strain are important factors to understand. Shear-
thinning and self-healing hydrogels are excellent candidates for injectable thera-
peutic delivery vehicles. Monitoring rheological behavior and structural evolution
of these gels during and after flow can help evaluate encapsulated therapy reten-
tion and delivery during syringe injection and the ability of the material to stay
localized after injection against possible biological forces in vivo (Fig. 6 ).
Inspired by our bodies' ability to heal, self-healing materials have the ability
to repair themselves when they are damaged. In the literature discussed in other
chapters in this topic, supramolecular chemistry as well as sample conditions
were varied in order to examine whether gel rheological behavior is dependent on
factors like polymer functionality sequence, polymer concentration, temperature
and pH.
There could be situations where a test material has not been rheologically
evaluated. This section focuses on the assessment of an unknown material. As a
Fig. 6 Graph illustrating
shear thickening and shear
thinning