When analysing the morphology of composites containing HAp nanoparticles, it is evident that unlike µHAp, nHAp particles tend to agglomerate. This phenomenon is characteristic of HAp nanoparticles, especially at high filler concentrations and in the absence of any dispersing agent . The presence of agglomerates may result from insufficient disruption of particle clusters in the starting powder (see Figure ) during the twin-screw extrusion process, or from secondary interactions between individual particles. In the case of PLA-based composites, two levels of nHAp particle distribution can be observed: a uniform dispersion of single nanoparticles at the 'micro' scale and a uniform dispersion of agglomerates at the 'macro' scale. Analysing the SEM images for the PLA/40nHAp composite, similar to µHAp, it is possible to observe the saturation of the polymer with ceramic filler, forming a kind of polymer-ceramic network. In the case of the PCL/20nHAp composite, despite the presence of agglomerates, their uniform dispersion is not observed.