Antibacterial activity of therapeutic agent-immobilized nanostructured TiCaPCON films against antibiotic-sensitive and antibiotic-resistant Escherichia coli strains

Abstract The development of flexible and low-cost methods of surface functionalization to fight infection at the early stage is an urgent scientific task. Herein, polymerization in low-pressure plasma rich in COOH species and carbodiimide chemistry methods were utilized to immobilize four different therapeutic agents (antibiotic (gentamicin), antimicrobial peptide (indolicidin), anti-adhesive molecules (heparin) and nitroxide radicals (2,2,5,5-tetramethyl-3-carboxyl-pyrrolidine-1-oxyl)) on the surface of nanostructured biocompatible TiCaPCON films to impart antibacterial characteristics. The polymers deposited from COOH-rich plasma showed decent stability in phosphate-buffered saline solution and were successfully used for the immobilization of different therapeutic agents via ionic or covalent bond. The bactericide attachment was proved by FTIR spectroscopy and XPS analysis. All samples with grafted therapeutic agents were hydrophilic with water contact angle values in the range of 26–56°. Bactericide release tests indicated the maximum concentration of therapeutic agents in the case of ionic immobilization. In case of covalent immobilization, fast initial release observed over 24 h was followed by slower leaching in the next 24 h (indolicidin), 48 h (heparin), and 96 h (gentamicin). The pH-sensitive COOH plasma polymer degradation and gentamicin release were demonstrated. The bactericide-linked films showed noticeable reduction of the antibiotic-sensitive E. coli U20 strain and, except indolicidin-immobilized samples, effectively inhibited growth of the antibiotic-resistant E. coli K261 strain at their initial concentration of 104 CFU/mL. The films with nitroxide radicals not only exhibited the highest antibacterial activity against E. coli K261 cells (100% after 8 h), but also prevented the biofilm formation.