Highly water-dispersible and antibacterial magnetic clay nanotubes functionalized with polyelectrolyte brushes: high adsorption capacity and selectivity toward heparin in batch and continuous system†
Heparin sodium, a widely used anticoagulant, is commercially extracted from porcine intestinal mucosa in a partially-purified form. The difficulty in selective isolation and purification of heparin at high concentration from the digestion mixture is currently a major challenge in the production of this important drug. In this work, we report a novel highly water-dispersible macromolecular architecture of polymeric quaternary ammonium polyelectrolyte grafted from magnetic halloysite nanotubes (HNTs) as a low-cost, biocompatible, widely available, and tubular support with chemically active external and internal surfaces for selective and efficient heparin capture with linear structure. Polymer brushes of (3-acrylamidopropyl) trimethylammonium chloride (APTMAC), a striking cationic acrylamido monomer, were grafted in three different lengths from the surface of modified HNTs with Fe3O4 nanoparticles (HNTs@Fe). A higher recovery efficiency of heparin, both in terms of the recovery rate and the capacity, was found for HNTs@Fe–PAPTMAC compared to the Amberlite as a commercially available resin that is widely used for heparin recovery in industries. The mechanism of heparin adsorption onto the functional quaternary ammonium groups of APTMAC was considered by X-ray photoelectron spectroscopy and zeta potential techniques, and the results confirmed the strong electrostatic interaction between the sulfate groups of heparin and the functional groups of PAPTMAC. The HNTs@Fe–PAPTMAC could be successfully recovered utilizing saturated NaCl and reprocessed for recovery of heparin without considerable loss in adsorption capacity after six cycles. HNTs@Fe–PAPTMAC can selectively adsorb heparin from a real sample consisting of heparin digested from porcine intestinal mucosa. Examination of the effect of HNTs@Fe–PAPTMAC in aqueous suspension on bacterial culture reveals that HAPTMAC exerts dose-dependent inhibition upon a Gram positive strain at relatively low concentrations, with complete inhibition seen as low as 20 μg mL−1. The results confirmed that HNTs@Fe–PAPTMAC have the potential to be utilized as a low-cost, environmentally friendly, efficient, and selective adsorbent towards recovery of heparin from porcine intestinal mucosa.