Gas-phase surface engineering of polystyrene beads used to challenge automated particle inspection systems

Container challenge sets, used in the qualification and validation of automated visible particle inspection systems in the parenteral drug industry, are prepared by seeding a single standardized polystyrene-divinylbenzene (PS-DVB) bead inside the commercial product to mimic foreign particulates. Because of its low surface energy and wettability, the bead adheres to container walls, hindering its detection by the motion-based inspection system. The aim of this research is to modify the surface properties of the bead in such a way that it repulses the inner walls and stays in suspension inside the liquid product. The surface treatment consists of a photoinduced chemical vapor deposition (PICVD) process using syngas and ultraviolet (UVC) light. Following treatment, newly grafted C–OH, C–O–C, C═O, and COOH functional groups on the bead's surface are observed by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy, leading to an increase in the surface energy from 31 ± 1 to 65 ± 2 mJ/m2 and a corresponding zeta potential decrease from −38 to −61 mV. Finally, treated 100, 200, and 500 μm PS-DVB beads suspended in water exhibit dispersion stability over time that is higher than that of untreated beads. These results show the potential of syngas PICVD to provide an effective solution to the stability issue of container challenge sets for the validation of automated particle inspection systems, enabling significant savings of time and money to the parenteral drug industry.