Crosslinked Graft Copolymer of Methacrylic Acid and Gelatin as a Novel Hydrogel with pH-Responsiveness Properties

Abstract

In this paper, a novel gelatin-based hydrogel was synthesized through crosslinking graft copolymerization of methacrylic acid (MAA) onto gelatin, using ammonium persulfate (APS) as a free radical initiator in the presence of methylenebisacrylamide (MBA) as a crosslinker. A proposed mechanism for hydrogel formation was suggested and the structure of the product was established using FTIR spectroscopy and gravimetric analysis of the products. Moreover, morphology of the samples was examined by scanning electron microscopy (SEM) and thermogravimetric analysis (TGA/DTG). The effect of reaction variables such as concentration of APS and MBA were systematically optimized to achieve a hydrogel with swelling capacity as high as possible. The gelatin-g-PMAA hydrogel exhibited a pH-responsiveness character so that a swelling-deswelling pulsatile behavior was recorded at pHs 2 and 8. This on-off switching behavior makes the hydrogel as a good candidate for controlled delivery of bioactive agents.

Keywords: gelatin; graft copolymers; methacrylic acid.

Scheme 1

Proposed mechanistic pathway for synthesis of the gelatin-g-PMAA hydrogel.

Figure 1

Effect of crosslinker concentration on swelling capacity.

Figure 2

Effect of initiator concentration on swelling capacity.

Figure 3

FTIR spectra of hydrolyzed gelatin (a) and gelatin-g-PMAA hydrogel (b).

Figure 4

SEM photograph of the optimized hydrogel (gelatin 1.5 g, MBA 0.043 mol/L, APS 0.02 mol/L, 55 °C, 60 min). (A) Surface of porous hydrogel; (B) Cross-sectional area of porous hydrogel.

Figure 5

TGA curves of (a) gelatin and (b) gelatin-g-PMAA.

Figure 6

DTG curve of optimized hydrogel.

Figure 7

On-off switching behavior as reversible pulsatile swelling (pH 8.0) and deswelling (pH 2.0) of the gelatin-g-PMAA hydrogel.