Biodegradable and fluorescent polylactide nanospheres loaded with iron oxide particles of different sizes (either 10 or 25 nm) were prepared by the combination of miniemulsion and emulsion/solvent evaporation techniques. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) studies indicate that the obtained particles have uniform and spherical shape with an average size between 80–120 nm. The size of the particles mainly depends on the molecular weight of the used polylactide. The iron oxide content and the encapsulation homogeneity were determined from the thermogravimetric analysis and preparative ultracentrifugation, respectively. The obtained particles displayed superparamagnetic properties. Additional incorporation of the hydrophobic fluorescent dye gives the possibility to employ the obtained composite particles as model markers in order to study, for example, cellular uptake mechanism.

Background aims. Mesenchymal stromal cells (MSC) are the focus of research in regenerative medicine aiming at the regulatory approval of these cells for specific indications. To cope with the regulatory requirements for somatic cell therapy, novel approaches that do not interfere with the natural behavior of the cells are necessary. In this context in vivo magnetic resonance imaging (MRI) of labeled MSC could be an appropriate tool. Cell labeling for MRI with a variety of different iron oxide preparations is frequently published. However, most publications lack a comprehensive assessment of the noninterference of the contrast agent with the functionality of the labeled MSC, which is a prerequisite for the validity of cell-tracking via MRI. Methods.We studied the effects of iron oxide-poly(L-lactide) nanoparticles in MSC with flow cytom-etry, transmission electron microscopy (TEM), confocal laser scanning microscopy (CLSM), Prussian blue staining, CyQuant® proliferation testing, colony-forming unit-fibroblast (CFU-F) assays, flow chamber adhesion testing, immuno-logic tests and differentiation tests. Furthermore iron-labeled MSC were studied by MRI in agarose phantoms and Wistar rats. Results. It could be demonstrated that MSC show rapid uptake of nanoparticles and long-lasting intracellular persistence in the endosomal compartment. Labeling of the MSC with these particles has no influence on viability, differentiation, clonogenicity, proliferation, adhesion, phenotype and immunosuppressive properties. They show excellent MRI properties in agarose phantoms and after subcutaneous implantation in rats over several weeks. Conclusions. These particles qualify for studying MSC homing and trafficking via MRI.

Janus nanoparticles with a poly(L-lactide) face and a polystyrene-based face functionalized with amine or carboxylic acid groups were synthesized via two different approaches. In the first approach, the poly(styrene-co-methacrylic acid) or poly-(styrene-co-2-aminoethyl methacrylate) copolymers were generated in situ in miniemulsion droplets before phase separation between the copolymers and the poly(L-lactide) occurred. In the second approach, the copolymers were prepared before the emulsification step. A solution containing the poly(L-lactide) and one of the copolymers was then emulsified, and the solvent was subsequently removed to induce a phase separation between the polymers, yielding a Janus morphology. The density of functional groups (amine or carboxylic acid) could be varied between 0 and 5 groups per nm 2 . Finally, we demonstrated that one face of the Janus nanoparticle could be selectively employed for a chemical reaction. Indeed, silver nanoparticles could be nucleated selectively on the poly(L-lactide) face.

SummaryIn recent years, the development of smart drug delivery systems based on biodegradable polymeric nanoparticles has become of great interest. Drug-loaded nanoparticles can be introduced into the cell interior via endocytotic processes followed by the slow release of the drug due to degradation of the nanoparticle. In this work, poly(L-lactic acid) (PLLA) was chosen as the biodegradable polymer. Although common degradation of PLLA has been studied in various biological environments, intracellular degradation processes have been examined only to a very limited extent. PLLA nanoparticles with an average diameter of approximately 120 nm were decorated with magnetite nanocrystals and introduced into mesenchymal stem cells (MSCs). The release of the magnetite particles from the surface of the PLLA nanoparticles during the intracellular residence was monitored by transmission electron microscopy (TEM) over a period of 14 days. It was demonstrated by the release of the magnetite nanocrystals from the PLLA surface that the PLLA nanoparticles do in fact undergo degradation within the cell. Furthermore, even after 14 days of residence, the PLLA nanoparticles were found in the MSCs. Additionally, the ultrastructural TEM examinations yield insight into the long term intercellular fate of these nanoparticles. From the statistical analysis of ultrastructural details (e.g., number of detached magnetite crystals, and the number of nanoparticles in one endosome), we demonstrate the importance of TEM studies for such applications in addition to fluorescence studies (flow cytometry and confocal laser scanning microscopy).