Preparation of the Cationic Dendrimer-Based Hydrogels for Controlled Heparin Release

We introduce a cationic polyamidoamine (PAMAM) dendrimers and tetronic (Te) based hydrogels in which precursor copolymers were prepared with simple methods. In the synthetic process, tyramine-conjugated tetronic (TTe) was prepared via activation of its four terminal hydroxyl groups by nitrophenyl chloroformate (NPC) and then substitution of tyramine (TA) into the activated product to obtain TTe. Cationic PAMAM dendrimers G3.0 functionalized with p-hydroxyphenyl acetic acid (HPA) by use of carbodiimide coupling agent (EDC) to obtain Den-HPA. ¹H-NMR confirmed the amount of HPA and TA conjugations. The aqueous TTe and Den-HPA copolymer solution rapidly formed the cationic hydrogels in the presence of horseradish peroxidase enzyme (HRP) and hydrogen peroxide (H₂O₂) at physiological conditions. The gelation time of the hydrogels could be modulated ranging from 7 to 73 secs, when the concentrations of HRP and H₂O₂ varied. The hydrogels exhibited minimal swelling degree and low degradation under physical condition. In vitro cytotoxicity study indicated that the hydrogels were highly cytocompatible as prepared at 0.15 mg/mL HRP and 0.063 wt% of H₂O₂ concentration. Heparin release profiles show that the cationic hydrogels can sustainably release the anionic anticoagulant drug. The obtained results demonstrated a great potential of the cationic hydrogels for coating medical devices or delivering anionic drugs.