Properties and Potential Applications of Carboxymethyl-kappa-carrageenan Hydrogels Crosslinked by Gamma Radiation

Abstract

Carboxymethyl κ-carrageenan (CMKC), with different degrees of substitution (DSs), were gamma-irradiated in viscous or paste solutions. Successfully synthezised chemically crosslinked hydrogels showed dependence on the DS, concentration, and radiation dose. The highest gel fraction was 76% exhibited by CMkC-3s hydrogel with a DS of 1.58. The hydrogels showed different swelling degrees in water and saline. Swelling behavior vs. time, in both solvents, corresponded to 2nd-order kinetics. The CMkC-3s at 20% concentration irradiated at 15 kGy had the highest water absorption of 334 g water/g dry gel. Selected hydrogels were evaluated for applications as wound dressing, as water retainer in sandy soil, and as metal adsorbent. As a wound dressing, CMkC-2s and CMkC-3s hydrogels exhibited considerable tensile strengths, abilities to absorb pseudo extracellular fluid, and extractables with pH/conductivity conducive for healing promotion. Also, the CMkC-3s hydrogel had no cytotoxic potential based on the MTT test. As water retainer in sandy soil, test samples with 0.1, 0.3, and 0.5% CMkC-3s granules initially retained 25.1%, 32.2%, and 42.6% water, respectively, compared to 19.2% of the sandy soil alone. On Day 7, the three sandy soil-CMkC groups still had 13.7–29.3% water, while the control had only 3.85%. In the batch adsorption studies, the hydrogels adsorbed Cu2+, Zn2+, Cd2+, and Pb2+ heavy metals in the solution at different capacities, with Cd2+ as the highly adsorbed and Pb2+ as the least. The CMkC-3s hydrogel showed the highest metal uptake and adsorption efficiency, followed by CMkC-2s, then CMkC-1s. The CMkC-3s hydrogel, further tested on pH effect, exhibited optimum metal uptake at neutral pH.