During the twenty-first century, engineered nanomaterials (ENMs) have attracted rising interest, globally revolutionizing all industrial sectors. The expanding world population and the implementation of new global policies are increasingly pushing society toward a bioeconomy, focused on fostering the adoption of bio-based nanomaterials that are functional, cost-effective, and potentially secure to be implied in different areas, the medical field included. This research was focused on silica nanoparticles (SiO₂-NPs) of bio-based and synthetic origin. SiO₂-NPs are composed of silicon dioxide, the most abundant compound on Earth. Due to their characteristics and biocompatibility, they are widely used in many applications, including the food industry, synthetic processes, medical diagnosis, and drug delivery. Using zebrafish embryos as in vivo models, we evaluated the effects of amorphous silica bio-based NPs from rice husk (SiO₂-RHSK NPs) compared to commercial hydrophilic fumed silica NPs (SiO₂-Aerosil200). We evaluated the outcomes of embryo exposure to both nanoparticles (NPs) at the histochemical and molecular levels to assess their safety profile, including developmental toxicity, neurotoxicity, and pro-inflammatory potential. The results showed differences between the two silica NPs, highlighting that bio-based SiO₂-RHSK NPs do not significantly affect neutrophils, macrophages, or other innate immune system cells.

In this work, polyurethane (PUR) aerogels doped with different SiO₂ particles, derived from a renewable source, were successfully synthesized, and the effects of SiO₂ content on the properties of PUR aerogels were investigated. Specifically, three types of SiO₂-based particles obtained from rice husk through different procedures were evaluated to enhance the thermal stability of the composites with special attention given to flame-retardant properties. With the optimal SiO₂ particles, obtained through acid digestion, the influence of their content between 0.5 and 3 wt.% on the physicochemical characteristics of the synthesized aerogels was thoroughly examined. The results showed that increasing the doping agent content improved the lightness, thermal stability, and flame-retardant properties of the resulting PUR aerogels, with the best performance observed at a 2 wt.% doping level. The doped aerogel samples with non-modified SiO₂ particles significantly enhanced the fire safety performance of the material, exhibiting up to an eightfold increase in flame retardancy. However, modification of the SiO₂ particles with phytic acid did not slow down the combustion velocity when filling the aerogels. This research highlights the promising potential of doped PUR/SiO₂ aerogels in advancing materials science and engineering applications for withstanding high temperatures and improving fire safety.

Bio-based nanomaterials (B-NMs), such as silica oxide (SiO₂)- and lignin (Lig)- based nanoparticles (NPs) derived from biomass waste, have gained attention in the last few years in the view of promoting the sustainability principles in several applications. However, scarce data are available about their safety. Thus, a hazard-testing strategy was designed considering as a reference the safe-and-sustainable-by-design (SSbD) framework for chemicals and materials, prioritizing the use of new approach methodologies (NAMs), such as in vitro and adverse outcome pathways (AOPs) approaches, for generating data about the potential hazard of B-NMs. Literature research was performed to identify the adverse outcomes (AOs) related to the selected B-NMs. All the AOPs investigated shared at least oxidative stress, inflammation and cytotoxicity as key events (KEs) that were investigated in lung and immune cells. The tested B-NMs resulted either non-toxic or moderately toxic towards human cells, validating their biocompatibility when compared to reference NMs of similar composition, but not of bio-origin. However, attention should be given to possible AOs deriving after specific functionalization of the B-NMs. Considering the lack of knowledge in this field, the studies performed represent a step forward in the state of the art of the safety assessment of B-NMs.

In modern industry, interest in nanomaterials has grown significantly over the decades, and nanotechnology stands as a cutting-edge approach that has revolutionized industries worldwide. However, the current challenges related to nanomaterials synthesis revolve around replacing existing raw materials and processes with more sustainable alternatives while also addressing the need for scaling up production. One widely used compound is titanium dioxide (TiO2), known for its chemical inertness, low cost, and high availability. It exhibits remarkable catalytic and distinctive semiconducting properties. This chapter will address the main physicochemical properties of TiO2, which form the basis for its utilization across various fields, spanning a wide range of current and emerging applications. The case study will compare and discuss both conventional and sustainable preparation methods, considering material characterization and techniques to upscale production.