## 4 Conclusions  
The present work shows the measurement of printable thermoplastics (PLA, ABS, Carbon fiber, Nylon, PETG, HIPS, TPU, and PP) nanoparticles distributions in the additive manufacturing process. The technique used to carry out this inspection was through DHM. Despite the lateral limitations of the microscope, the measurement of the thickness of the film deposited on a glass substrate in the case of PLA and ABS were between 11.5 nm to 96.72 nm, presenting slight variations with the results previously reported [13]; also presenting a relative error of \(-\)54.63% and 41.54%, respectively. However, it is important to mention that the differences between the results may be due to the fact that [PERSON] et al. perform the measurement of the dimensions of the particles in the free state, while this work focuses on the measurement of film, in which the shape of the particle was altered as a result of the adhesion process to the glass substrate. For this reason, we can conclude that the proposed procedure is reliable for the measurement of nanostructures, supporting the area of nanotechnology as an alternative measurement tool. In addition, DHM presents some advantages in comparison with the chromatography equipment [13] or scanning mobility particle sizer coupled with an optical particle spectrometer [14]. The proposal by DHM is a simpler optical setup, is cheaper implementation, and is more compact size system than used in references [13; 14].  
Additionally, the importance of conducting research related to nanoparticles' presence in the FDM lies in the effects produced when they enter the human body. This is due to their ease of lodgment into the lungs, alveoli, and respiratory tract [14; 15]. Thus, causing health conditions as translocation of these thin materials to the brain through the olfactory nerve, cardiorespiratory problems, cardiovascular accidents, asthma symptoms, and even death [21; 43; 44].  
Finally, regarding the health issue, there are specific measures which can significantly mitigate the dangers derived from the exposure of nanoparticles and gases derived from thermal processing of plastics, as has been proven in industrial activities such as plastic injection. Being in the first place, the control of the temperatures for plastic handling; as well as the presence of proper ventilation in the thermal processes which materials are subjected, implementing local exhaust ventilation (LEV) for those areas where high emissions occur [43; 44].  
Conceptualization, M.L.-R., P.Y.-C., I.M.-A. and J.A.P.-M.; formal analysis, D.A.G.-E.; investigation, M.L.-R.; methodology, D.A.G.-E., M.L.-R. and P.I.-T.; resources, P.I.-T.; software, D.A.G.-E.; supervision, M.L.-R. and I.M.-A.; validation, D.A.G.-E.; writing--original draft, D.A.G.-E.; writing--review and editing, M.L.-R., P.Y.-C., I.M.-A., J.A.P.-M., A.C.-B. and P.I.-T. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Data underlying the results presented in this letter are not publicly available but may be obtained from the authors upon reasonable request.  
The corresponding author thanks [PERSON] from the Centro de Investigaciones en Optica A.C., Leon, Guanajuato, Mexico, for the valuable suggestions and advice to this work. In addition, authors thank the PRODEP program and CONACYT for its partial support.  
The authors declare no conflict of interest.