4D printing has emerged as a transformative technology in the field of biomedical engineering, offering the potential for dynamic, stimuli-responsive structures with applications in tissue engineering, drug delivery, medical devices, and diagnostics. This review paper provides a comprehensive analysis of the advancements, challenges, and future directions of 4D printing in biomedical engineering. We discuss the development of smart materials, including stimuli-responsive polymers, shape-memory materials, and bio-inks, as well as the various fabrication techniques employed, such as direct-write assembly, stereolithography, and multi-material jetting. Despite the promising advances, several challenges persist, including material limitations related to biocompatibility, mechanical properties, and degradation rates; fabrication complexities arising from the integration of multiple materials, resolution and accuracy, and scalability; and regulatory and ethical considerations surrounding safety and efficacy. As we explore the future directions for 4D printing, we emphasise the need for material innovations, fabrication advancements, and emerging applications such as personalised medicine, nanomedicine, and bioelectronic devices. Interdisciplinary research and collaboration between material science, biology, engineering, regulatory agencies, and industry are essential for overcoming challenges and realising the full potential of 4D printing in the biomedical engineering landscape.

This paper presents a comprehensive review of recent advancements in surface engineering of metals, encompassing techniques, characterization methods and applications. The study emphasizes the significance of surface engineering in enhancing the performance and functionality of metallic materials in various industries. The paper discusses the different techniques employed in surface engineering, including physical techniques such as thermal spray coatings and chemical techniques such as electroplating. It also explores characterization methods used to assess the microstructural, topographical, and mechanical properties of engineered surfaces. Furthermore, the paper highlights recent advancements in the field, focusing on nanostructured coatings, surface modification for corrosion protection, biomedical applications, and energy-related surface functionalization. It discusses the improved mechanical and tribological properties of nanostructured coatings, as well as the development of corrosion-resistant coatings and bioactive surface treatments for medical implants. The applications of surface engineering in industries such as aerospace, automotive, electronics, and healthcare are presented, showcasing the use of surface engineering techniques to enhance components, provide wear resistance, and improve corrosion protection. The paper concludes by discussing the challenges and future directions in surface engineering, highlighting the need for further research and development to address limitations and exploit emerging trends. The findings of this review contribute to advancing the understanding of surface engineering and its applications in various sectors, paving the way for future innovations and advancements.