# Additive Manufacturing in Underwater Applications
## 7 Conclusions  
The main findings show that the usage of AM in underwater applications can bring a number of advantages--for instance, increasing the safety of the work, limiting the environmental burden, and high efficiency. Currently, polymers are the most important materials used in underwater applications; however, other groups of materials are also being intensively developed. Despite the widespread interest in this technology's application in the marine industry, thus far, only a few prototype products have been developed. Only two technologies find real underwater application (titanium alloys and concrete) for scientific purposes. However, some tests also show the possibility of the 3D printing of polymer materials in this environment.  
Moreover, underwater AM is a promising tool to develop new, effective applications on a larger scale; nonetheless, the technology itself, as well as the materials used, still require development and optimization. This article identifies the following areas as the most promising for future development:  
* The development of knowledge about the used materials--for example, there are no washout tests for 3D-printed materials described in the literature;
* The improvement of 3D printing technologies in situ according to the efficiency and quality of the obtained products;
* The development of underwater 3D printing in situ and the application of the technology, especially for deep-sea works, including the maintenance of infrastructure or possible restoration in situ of so-called mezzo reefs (the deepest reef formations);
* The design and modification of AM technologies for the 3D printing of multi-material compositions in one process for underwater applications;
* The employment of technologies such as ROVs and AUVs for underwater 3D printing applications, including process automatization;
* The development of 3D printing for advanced solutions, including 4D printing utilized for the fabrication of smart devices for underwater applications;
* The enhancement of data-based environmental analysis to confirm the real burden of this technology.  
Conceptualization, K.K., S.G. and T.G.; methodology, K.K.; validation, P.D., D.H.T. and S.P.; formal analysis, S.P. and M.R.; investigation, K.K., S.G. and S.P.; writing--original draft preparation, K.K. and S.G.; writing--review and editing, P.D., D.H.T. and M.R.; supervision, K.K. and T.G.; project administration, K.K. and T.G. All authors have read and agreed to the published version of the manuscript.  
This work was financed by the Polish National Agency for Academic Exchange in the framework of joint research projects between the Republic of Poland and the Federal Republic of Germany under the grant \"Underwater eco-monitoring\" (PPN/BDE/2021/1/00003/U/00001). And was supported by the Polish National Agency for Academic Exchange under the Exchange program for students and scientists as part of a bilateral cooperation offer for incoming students and scientists, grant no. BPN/BIL/2021/1/00159/U/00001.  
Not applicable.  
The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.