## 5 Conclusions  
This study demonstrates the feasibility of fabricating a low-cost strain sensor by employing additive manufacturing technology using a commercially available 3D desktop printer and filaments. The building materials employed were Carbon Nanotube (CNT)-enriched Polylactic Acid (PLA) and Acrylonitrile Styrene Acrylate (ASA). The key advantage of the proposed sensor is its ability to be manufactured onsite aboard a ship without the need for external facilities. This on-demand production capability is particularly beneficial in remote or maritime environments, where access to specialized manufacturing services is limited. By enabling the on-site production of spare parts and sensors in general, downtime is reduced, enhancing operational efficiency, which results in a reduction in the need for extensive inventories and long supply chains, extending the lifecycle of equipment, and decreasing the overall environmental impact.  
Preliminary characterization of the prototype demonstrated reliable piezoresistive properties, which are essential for accurate strain measurements. This characterization included the determination of the gauge factor, sensor linearity, hysteresis, and cyclic alternate bending response measurements. The deduced experimental results show a clear correlation between the thermal treatment of the device and the aforementioned characteristics, which can be attributed to previous research; overall, reliable and consistent characteristics of the prototype sensor were deduced, indicating the effectiveness of the sensor in measuring the strain.  
The sensor design is both robust and simple, rendering it advantageous for practical applications, whereas the developed one-step manufacturing process, in which the piezoresistive element, substrate, and contact pads are fabricated simultaneously, enhances the reliability and durability of the sensor. The deduced gauge factor for the optimum fabrication parameters investigated (0.95) is comparable to those of typical commercial resistive strain gauge sensors [42]. Moreover, direct communication with the necessary readout circuitry can be easily achieved through standard soldering using the integrated contact pads of the device which can be applied directly to the working structural component. This has immediate benefits in terms of the device's complexity, mechanical reliability, process time, and cost. In addition, its simple design and manufacturing enhances its durability under harsh conditions often encountered in marine environments.  
In summary, the successful development of the proposed 3D printed strain sensor demonstrates a viable and effective alternative for fabricating measuring devices for the marine industry, offering numerous benefits, including low-cost, on-demand, remote rapid production, robustness, and environmental sustainability. Its performance in preliminary characterization suggests that it can reliably measure strain, making it promising for applications, such as structural health monitoring and maintenance. Future work will focus on optimizing the design of the prototype and exploring other 3D printing materials with enhanced physical properties (such as low resistivity and hydrophilicity) that can be employed for the development of novel 3D printed sensing devices.  
Conceptualization, D.N.P.; Methodology, T.K., D.N.P., I.I. and G.K.; Validation, D.N.P., I.I. and G.K.; Formal analysis, T.K.; Investigation, T.K., D.N.P., I.I. and G.K.; Resources, D.N.P. and G.K.; Data curation, T.K., D.N.P., I.I. and G.K.; Writing--original draft, T.K. and D.N.P.; Writing--review & editing, D.N.P. and I.I.; Visualization, T.K.; Supervision, D.N.P. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.  
The authors declare no conflict of interest.