Controllable Release of Povidone-Iodine from Networked Pectin@Carboxymethyl Pullulan Hydrogel

Povidone-iodine (PI) is a common antiseptic reagent which is used for skin infections and wound healing. The control release of PI is quite important to heal the deep and intense wounds. Herein, the preparation of biodegradable pectin@carboxymethyl pullulan (Pe@CMP) hydrogel was carried out and applied for controllable release of PI. CMP was synthesized by interaction of monochloroacetic acid with pullulan at different ratios. The Pe@CMP hydrogel was then prepared by crosslinking of pectin with CMP in presence of glutaraldehyde as cross linker. After carboxymethylation, COOH contents were enlarged to be 24.2–51.2 mmol/kg and degree of substitution was 0.44–0.93. The rheological properties of Pe@CMP hydrogel were enlarged by increment of pectin ratio. Swelling ratio in water (16.0–18.0%) was higher than that of artificial sweat (11.7–13.2%). Pe@CMP hydrogel containing 20% pectin, exhibited the lowest release and 57.7% from PI was released within 360 min. The biological activity of the released PI was monitored to be highly efficient. The kinetic of release was fitted well to the first ordered reaction and Higuchi models. The mechanism of release was explained by the swelling of hydrogel. The networked structure of hydrogel was opened by swelling and PI was released from the outer pores followed by inner pores, achieving the controllable release.

Thermosensitive Poloxamer-graft-Carboxymethyl Pullulan: A Potential Injectable Hydrogel for Drug Delivery

A thermosensitive copolymer composed of amphiphilic triblock copolymer, poloxamer 407, grafted on hydrophilic pullulan with pendant carboxymethyl groups (CMP) was prepared and characterized. The structure of the new copolymer was assessed by Fourier transform infrared (FT-IR) and 1H nuclear magnetic resonance (1H NMR) spectroscopy. The content of the poloxamer in the grafted copolymer was 83.8% (w/w). The effect of the copolymer concentration on the gelation behavior was analyzed by the vertical method and rheological tests; the gel phase of the copolymer occurred at a lower concentration (11%, w/v) as compared with poloxamer (18%, w/v). The starting gelation time under the simulated physiological conditions (phosphate buffer with a pH of 7.4, at 37 °C) was sensitive on the rest temperature before the test, this being 990 s and 280 s after 24 h rest at 4 °C and 20 °C, respectively. The rheological tests evidenced a high elasticity and excellent ability of the copolymer to recover the initial structure after the removal of the applied force or external stimuli. Moreover, the hydrogel has proved a sustained release of amoxicillin (taken as a model drug) over 168 h. Taken together, the results clearly indicate that this copolymer can be used as an injectable hydrogel.

Chemically modified pullulans II. New hydrophobically substituted derivatives

New hydrophobically substituted pullulans were synthesized, such as (i) neutral derivatives obtained by direct esterification of pullulan with adenine and thymine butyric acid and (ii) ionic derivatives obtained by amidation of carboxymethyl pullulan with aromatic amines (aminopyrene and adenine). Rheological measurements in dilute solutions allowed us to test the influence of the hydrophobic aromatic substituents and of the ionicity of the parent support on the nature of the hydrophobic associations in dilute solutions. The rheological studies on the pullulan derivatives revealed mainly intramolecular hydrophobic associations for both ionic and non-ionic derivatives, suggesting a more compact conformation than that of the precursor. Keywords: hydrophobically modified pullulans, esterification, amidation, condensed aromatic ring, size exclusion chromatography, multi-angle laser light scattering.