A quality-by-design inspired approach to develop PET and PP nanoplastic test materials for use in in vitro and in vivo biological assays

Abstract

Micro- and nanoplastics have become environmental pollutants of concern, receiving increased attention from consumers, scientists, and policymakers. The lack of knowledge about possible impacts on wildlife and human health requires further research, for which well-characterized test materials are needed. A quality-by-design (QbD) driven approach was used to produce sterile, endotoxin monitored nanoplastics of polyethylene terephthalate (PET) and polypropylene (PP) with a size fraction of >90% below 1 μm and high yield of >90%. Glycerol was used as a versatile and biocompatible liquid storage medium which requires no further exogenous dispersing agent and maintained colloidal stability, sterility (0 CFU mL⁻¹), and low endotoxin levels (<0.1 EU mL⁻¹) for more than one year of storage at room temperature. Further, the glycerol vehicle showed no biological effect on the tested human bronchial cell line Calu-3 up to 0.8% (w/v). Given the concentration of 40 mg g⁻¹ nanoplastics in the glycerol stock, this corresponds to a nanoplastic concentration of 320 μg mL⁻¹. The surfactant-free nanoplastics are dispersible in bio-relevant media from the glycerol stock without changing size characteristics and are suitable for in vitro and in vivo research.