# Smart Infrastructure and Additive Manufacturing: Synergies, Advantages, and Limitations
## 3 Key Applications of 3D Printing in Smart Infrastructure
### 3D-Printed Sensors and IoT Devices  
The evolution of 3D printing technology has had a considerable impact on sensor fabrication, allowing for the quick production of complex, high-precision structures designed for Internet of Things (IoT) applications. Additive printing offers unprecedented design flexibility, enabling the development of customized sensors that may be incorporated directly into smart infrastructure components [76]. These sensors play an important role in a variety of fields, including healthcare, environmental monitoring, industrial automation, and smart cities, since they provide real-time data collecting and analysis capabilities [77; 78; 79]. Unlike conventionally manufactured sensors, which frequently require assembly from several components, 3D-printed sensors can be manufactured as monolithic structures, increasing reliability and lowering production costs. Three-dimensional printing makes it easier to fabricate a variety of sensor types, including temperature, pressure, chemical, optical, and electromechanical sensors, by using functional materials including conductive polymers, piezoresistive composites, and thermoresponsive inks [80; 81]. These developments help to miniaturize and optimize sensor systems, making them more efficient and adaptable to a wide range of IoT applications. One of the primary benefits of 3D-printed sensors in IoT applications is their ability to integrate easily into smart environments, increasing functionality and responsiveness. Wearable and implantable biosensors made using 3D printing allow for continuous physiological monitoring, which improves patient care and early diagnosis [82]. Environmental sensors in smart cities monitor air quality, garbage levels, and energy consumption to promote sustainable urban growth and effective resource management [83; 84; 85; 86; 87]. Predictive maintenance systems in industrial automation use embedded 3D-printed sensors to optimize operations, reduce downtime, and increase workplace safety [88; 89]. Similarly, in precision agriculture, 3D-printed sensors monitor soil moisture, temperature, and nutrient levels, allowing for data-driven decision-making that improves crop output and resource efficiency [90; 91; 92]. Furthermore, the aerospace and automotive industries use 3D-printed structural health monitoring sensors, which allow for real-time assessment of material integrity and operating safety [93; 94; 95]. These examples demonstrate the increasing reliance on 3D-printed IoT devices to improve connectivity, automation, and decision-making across a variety of industries. One particularly transformational feature of additive manufacturing is the ability to integrate sensors directly into components during creation, removing the requirement for post-production installation. This connection increases sensor durability by insulating them from environmental harm while also allowing for real-time data collection from important sites within smart infrastructure [96]. Furthermore, additive manufacturing enables the production of sensors with complicated geometries that were previously unachievable using standard manufacturing processes [97]. The combination of 3D printing and energy-harvesting materials has also resulted in the development of self-contained sensor systems that can function without external power sources. These developments are consistent with Industry 4.0 goals, which emphasize real-time monitoring and automation as key drivers of efficiency [98]. The ISO/ASTM 52900:2021 standard describes additive manufacturing as a layer-by-layer fabrication technique that provides a consistent foundation for producing these next-generation sensors [99]. To address the growing demands of smart infrastructure,researchers in this sector are continuing to focus on improving material characteristics, multi-material printing capabilities, and sensor functionality. Despite the promising advantages of 3D-printed sensors in IoT applications, a number of difficulties must be overcome before they can be widely adopted.