Characterization and degradation behavior of agar-carbomer based hydrogels for drug delivery applications: solute effect

Abstract

In this study hydrogels synthesized from agarose and carbomer 974P macromers were selected for their potential application in spinal cord injury (SCI) repair strategies following their ability to carry cells and drugs. Indeed, in drug delivery applications, one of the most important issues to be addressed concerns hydrogel ability to provide a finely controlled delivery of loaded drugs, together with a coherent degradation kinetic. Nevertheless, solute effects on drug delivery system are often neglected in the large body of literature, focusing only on the characterization of unloaded matrices. For this reason, in this work, hydrogels were loaded with a chromophoric salt able to mimic, in terms of steric hindrance, many steroids commonly used in SCI repair, and its effects were investigated both from a structural and a rheological point of view, considering the pH-sensitivity of the material. Additionally, degradation chemistry was assessed by means of infrared bond response (FT-IR) and mass loss.

Keywords: FT-IR; degradation; drug effect; hydrogels; rheology.

Figure 1

SF release profile from AC1 (M_t) expressed as unitary fraction with respect to total loaded mass (M_∞).

Figure 2

Swelling kinetics of AC1 (a) and AC1_SF loaded hydrogel (b) in different pH solvent values (pH = 0.5 (red); pH = 7.4 (black); and pH = 14 (blue)).

Figure 3

Fourier transform infrared (FT-IR) spectra for both AC1 and AC1_SF gel samples. In red are highlighted peaks showing the presence of SF within the three-dimensional polymeric network.

Figure 4

(a) Mechanical spectra of AC1 and AC1_SF gels at room temperature with small oscillatory shear in the linear viscoelastic regime: G′ (■ AC1, ♦AC1_SF ) and G″ (□ AC1, ⋄ AC1_SF ) are frequency independent, indicating dominant viscoelastic relaxations at lower frequencies; (b) Dynamic strain sweep experiments of AC1 (G′ (■) and tan(δ) (□)) and AC1_SF (G′ (♦) and tan(δ) (⋄)) at constant frequency; (c) Measure of yield stress of AC1 (■) and AC1_SF (♦) by oscillatory experiments.

Figure 5

(a) FT-IR spectra of AC1_SF before and after 2 and 4 weeks of degradation in PBS; (b) FT-IR spectra of AC1 before and after 2 and 4 weeks of degradation in PBS.

Figure 6

Degradation of AC1 (■) and AC1_SF (♦) hydrogels in PBS at 37 °C with respect to weight loss.