Figures and show images of the PLA/20µHAp and PLA/40µHAp samples respectively, with the corresponding higher magnification images labelled A' and B'. The first thing to note when analysing these images is that the processing method used has resulted in a uniform distribution of µHAP particles throughout the material. There is no evidence of agglomeration. At higher magnifications, examination of individual HAp particles, and in particular the interface, reveals very good adhesion of the filler microparticles to the PLA matrix. This is evidenced by the presence of just a few tiny spaces on the interface and the absence of any broad spaces between the ceramic particles and the polymer matrix. In addition, the presence of polymer can be observed inside some HAp particles (it has got there through the holes visible on the surface -see Figure ), which further indicate an effective wetting of the HAp ceramic by the polymer. The good adhesion between PLA and HAp is justified in the literature . In their article, Shaobing Zhou et al. carried out a comprehensive analysis of the interactions at the PLA-HAp interface and demonstrated the formation of hydrogen bonds between the carbonyl group (C=O) in PLA and the P-OH groups on the surface of HAp particles. They also showed that the number of hydrogen bonds increases proportionally with the amount of HAp in the system. The latter may explain why the BSE detector image for the sample with 40% HAp addition is less contrasted than for 20%. At such high fill levels, the polymer-filler interaction network is so strong that it is difficult to distinguish individual particles from the matrix background using the SE detector (Figure ).