The interaction of particles with cells is of considerable interest in biomedicine, particle toxicology, and occupational health and safety [1], [2], [3]. Many studies have been devoted to nanoparticles, where size [4,5], shape [6], rigidity [7], [8], [9], surface charge [10,11], and surface functionalization [12] play key roles for cellular uptake. However, much less is known about the interaction of microparticles with cells, an area that is of considerable interest in nanomedicine [13] and even more in particle and fiber toxicology [14], [15], [16], [17], [18], [19], [20], e.g. concerning inhaled particles [21], [22], [23]. It is also of high interest in biomaterials science where particles (usually polyethylene or metals [24]) from abrasion or degradation are found in the vicinity of endoprostheses where they may induce aseptic loosening [25,26], sometimes also as carriers of bacteria [27]. Such particles have a typical diameter of 0.2 µm [28] to 0.5 µm [28]. In general, wear particles have a broad size distribution that ranges from about 0.05 µm to 10 µm and more with shapes from spherical to highly irregular [24,29,30].

Barium sulphate particles are chemically stable and insoluble at any pH, therefore they are well suited as inert model particles [31] to study the particle uptake by cells [32,33]. Generally, it is assumed that the uptake of particles occurs by endocytosis that is usually restricted to nanoparticles with an upper size limit of 200 to 300 nm [34], [35], [36], [37], [38], [39], [40], [41]. Here, we extend our earlier studies on barium sulphate nano-, submicro- and microparticles [32,33]. We have demonstrated that phagocytosing cells (rat alveolar macrophages NR8383 [32] and bone marrow-derived macrophages [33]) take up barium sulphate particles of all sizes. This is not surprising because phagocytosis can easily lead to the uptake of large particles [42], [43], [44], [45], [46]. Much less is known on the interaction of microparticles with non-phagocytosing cells which are, however, much more prominent in tissue, e.g. around endoprostheses. Here, we demonstrate that non-phagocytosing cells can take up microparticles with a size of about 1 µm as well. The uptake by three different cell lines was assessed in three different cell types (HeLa, THP-1, hMSC), including the usually non-phagocytosing HeLa and hMSCs cells.