Material extrusion additive manufacturing (MEAM) has emerged as a versatile and widely adopted 3D printing technology due to its cost-effectiveness and ability to process a diverse range of materials. However, achieving consistent part quality and repeatability remains a challenge, mainly due to variations in process parameters and material behavior during fabrication. In-situ monitoring and advanced process control systems have been increasingly integrated into MEAM to address these issues, enabling real-time detection of defects, optimization of printing conditions, reliability of fabricated parts, and enhanced control over mechanical properties. This review examines the state-of-the-art in-situ monitoring techniques, including thermal imaging, vibrational sensing, rheological monitoring, printhead positioning, acoustic sensing, image recognition, and optical scanning, and their integration with process control strategies, such as closed-loop feedback systems and machine learning algorithms. Key challenges, including sensor accuracy, data processing complexity, and scalability, are discussed alongside recent advancements and their implications for industrial applications. By synthesizing current research, this work highlights the critical role of in-situ monitoring and process control in advancing the reliability and precision of MEAM, paving the way for its broader adoption in high-performance manufacturing.

Significant efforts have explored the field of Phase Change Materials (PCMs) for various applications. Research and real-world applications explore length scales that range from infrastructure to micro systems. A commonality of these efforts is the desire to utilize the phase change capability of the PCM to provide a steady temperature heat sink for thermal storage. Smaller scale efforts and materials are presented in this present review. A general challenge to the use of these PCMs regardless of application is the low thermal conductivity present as a baseline material property. Efforts to improve thermal conductivity have included the addition of underlying metal foam structures, heat pipes, or metallic fins inserted into the base PCM. Other efforts have investigated alterations to the base materials themselves by employing additives such as graphite to supplement thermal performance. Other additives are used to obtain form stability in the PCM as it melts. While the field of PCM research has been well established, the use of new materials and approaches that employ the use of natural materials continues to move research forward. This review captures significant efforts and presents a thoughtful comparison of common themes across centimeter and smaller-scale PCM use.