Advances in functional metamaterials: bridging mechanical, acoustic innovations with multifunctionality and adaptive responses

• Summarize current advancements in the development and use of functional metamaterials. • Combining flexible and multipurpose features of metamaterials • Artificial intelligence (AI) facilitated modelling, in enhancing the design and optimization procedures for metamaterials. • The range of uses for metamaterials and the new problems they face. Functional metamaterials have emerged as a class of engineered materials exhibiting properties not found in nature, enabling unprecedented control over electromagnetic, acoustic, thermal, and mechanical wave propagation. Their multifunctional characteristics position them as critical enablers for aerospace, automotive, biomedical, and energy applications. However, despite rapid academic progress, practical adoption remains limited due to unresolved challenges. This review systematically synthesizes recent advances (2020–2025) in functional and adaptive metamaterials, emphasizing structural innovations such as functionally graded materials, honeycomb/cellular architectures, and bio-inspired designs. The analysis draws on comparative evaluation of reported studies, tabulated literature summaries, and classification of physical phenomena governing metamaterial responses. Key findings highlight progress in additive manufacturing for scalable fabrication, AI/ML-driven design for performance optimization, and the integration of multifunctional properties, including energy absorption, acoustic damping, and tunable stiffness. Case studies demonstrate applications in lightweight aerospace components, vibration control systems, biomedical scaffolds, and sustainable material solutions. A clear identification of research gaps, limitations, and practical constraints is provided, supported by comparative tables and schematic figures. While significant progress has been achieved, challenges persist in scalability, durability, sustainability, and data-driven design reliability. This review outlines practical and industrial implications, recommends hybrid manufacturing strategies, circular-material approaches, and collaborative frameworks, and emphasizes the transition of metamaterials from laboratory concepts to real-world engineering solutions.