Super-Macroporous Pulluan Cryogels as Controlled Active Delivery Systems with Controlled Degradability

Abstract

Here, super-macroporous cryogel from a natural polysaccharide, pullulan was synthesized using a cryo-crosslinking technique with divinyl sulfone (DVS) as a crosslinker. The hydrolytic degradation of the pullulan cryogel in various simulated body fluids (pH 1.0, 7.4, and 9.0 buffer solutions) was evaluated. It was observed that the pullulan cryogel degradation was much faster in the pH 9 buffer solution than the pH 1.0 and 7.4 buffer solutions in the same time period. The weight loss of the pullulan cryogel at pH 9.0 within 28 days was determined as 31% ± 2%. To demonstrate the controllable drug delivery potential of pullulan cryogels via degradation, an antibiotic, ciprofloxacin, was loaded into pullulan cryogels (pullulan-cipro), and the loading amount of drug was calculated as 105.40 ± 2.6 µg/mg. The release of ciprofloxacin from the pullulan-cipro cryogel was investigated in vitro at 37.5 °C in physiological conditions (pH 7.4). The amount of drug released within 24 h was determined as 39.26 ± 3.78 µg/mg, which is equal to 41.38% ± 3.58% of the loaded drug. Only 0.1 mg of pullulan-cipro cryogel was found to inhibit half of the growing Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) colonies for 10 min and totally eradicated within 2 h by the release of the loaded antibiotic. No significant toxicity was determined on L929 fibroblast cells for 0.1 mg drug-loaded pullulan cryogel. In contrast, even 1 mg of drug-loaded pullulan cryogel revealed slight toxicity (e.g., 66% ± 9% cell viability) because of the high concentration of released drug.

Keywords: biocompatible/degradable polysaccharide cryogel; ciprofloxacin release; natural polymeric cryogel drug carrier; pullulan cryogel.

Figure 1

Schematic representation of synthesis (left); SEM images of pullulan cryogels (right).

Figure 2

(a) FT-IR spectra and (b) thermal degradation curves of pullulan biopolymer and pullulan cryogel.

Figure 3

Hydrolytic degradation behavior of pullulan cryogel in various buffer solutions: (a) weight loss (%) versus time; (b) cumulative weight loss (%) at 37.5 °C. The statistical analysis of cumulative weight loss (%) in different pH conditions was compared with the cumulative weight loss (%) at pH 7.4, and no significant statistical difference was detected.

Figure 4

(a) Schematic representation of ciprofloxacin drug loading into pullulan cryogel; (b) drug release profile of pullulan-cipro cryogel. Drug release conditions: pH 7.4 buffer solution, 37.5 °C.

Figure 5

Bacterial viability (%) of Gram-negative E. coli and Gram-positive S. aureus in the presence of 0.1 mg of drug-loaded pullulan-cipro cryogel over time. * p < 0.05, ** p < 0.01, and *** p < 0.001 compared with control group.

Figure 6

Cell viability of L929 fibroblast cells in the presence of (a) pullulan polysaccharide and ciprofloxacin antibiotic at concentrations ranging from 0.05 to 1 mg/mL and (b) bare pullulan cryogel and drug loaded pullulan-cipro cryogel at concentrations ranging from 0.1 to 1 mg over 24 h of incubation time. * p < 0.05, ** p < 0.01, and *** p < 0.001 compared with control group.