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Hypothesis Iron oxide and other ferrite nanoparticles have not yet found widespread application in the medical field since the translation process faces several big hurdles. The incomplete knowledge of the interactions between nanoparticles and living organisms is an unfavorable factor. This complex subject should be made simpler by synthesizing magnetic nanoparticles with good physical (relaxivity) and chemical (colloidal stability, anti-fouling) properties and no biological activity (no immune-related effects, minimal internalization, fast clearance). Such an innocent scaffold is the main aim of the present paper. We systematically searched for it within the class of small-to-medium size ferrite nanoparticles coated by small (zwitter)ionic ligands. Once established, it can be functionalized to achieve targeting, drug delivery, etc. and the observed biological effects will be traced back to the functional molecules only, as the nanosized scaffold is innocent. Experiments We synthesized nine types of magnetic nanoparticles by systematic variation of core composition, size, coating. We investigated their physico-chemical properties and interaction with serum proteins, phagocytic microglial cells, and a human model of inflammation and studied their biodistribution and clearance in healthy mice. The nanoparticles have good magnetic properties and their surface charge is determined by the preferential adsorption of anions. All nanoparticle types can be considered as immunologically safe, an indispensable pre-requisite for medical applications in humans. All but one type display low internalization by microglial BV2 cells, a process strongly affected by the nanoparticle size. Both small (3 nm) and medium size (11 nm) zwitterionic nanoparticles are in part captured by the mononuclear phagocyte system (liver and spleen) and in part rapidly (≈1 h) excreted through the urinary system of mice. Findings The latter result questions the universality of the accepted size threshold for the renal clearance of nanoparticles (5.5 nm). We suggest that it depends on the nature of the circulating particles. Renal filterability of medium-size magnetic nanoparticles is appealing because they share with small nanoparticles the decreased accumulation-related toxicity while performing better as magnetic diagnostic/therapeutic agents thanks to their larger magnetic moment. In conclusion, many of our nanoparticle types are a bio-compatible innocent scaffold with unexpectedly favorable clearance.

Background Silica-based microspheres encapsulating aqueous glycerol are promising curing agents affording the formation of better one-component polyurethane foams, namely thermoset polymers cured by atmospheric moisture that are widely and increasingly utilized in the construction industry. The use of renewable, non toxic glycerol from biodiesel and oleochemicals industry to cure PU foams in place of traditionally employed oil-derived mono and diethylene glycols is both technically and environmentally beneficial. The higher amount of hydroxyl groups in glycerol compared to both mono- and diethylene glycol results in considerably lower percentage of free monomeric methylene diphenyl diisocyanate (MDI) and higher crosslinking density of the cured foam. Results We investigate by thermogravimetric analysis the nature and amount of the microencapsulated species in sol–gel silica and organosilica microspheres encapsulating aqueous glycerol. Along with a percentage of glycerol in weight up to 35%, the microspheres contain about 5 wt% water and 4 wt% entrapped surfactant. Conclusions The investigation shows the efficacy of the surfactant-assisted sol–gel microencapsulation aqueous glycerol in silica as well as in methyl-silica particles at least until 10% degree of methylation. The results are relevant to the practical development of functional materials that can be used to cure better and greener polyurethane foams largely employed as coatings, adhesives and sealants in many industrial sectors.