Advancements in the material design of smart hydrogels have transformed the way therapeutic agents are encapsulated and released in biological environments. On the other hand, the expeditious development of 3D printing technologies has revolutionized the fabrication of hydrogel systems for biomedical applications. By combining these two aspects, 4D printing (i.e., 3D printing of smart hydrogels) has emerged as a new promising platform for the development of novel controlled drug delivery systems that can adapt and mimic natural physio-mechanical changes over time. This allows printed objects to transform from static to dynamic in response to various physiological and chemical interactions, meeting the needs of the healthcare industry. In this review, we provide an overview of innovation in material design for smart hydrogel systems, current technical approaches toward 4D printing, and emerging 4D printed novel structures for drug delivery applications. Finally, we discuss the existing challenges in 4D printing hydrogels for drug delivery and their prospects.

A scalable method to produce high-quality graphene by shear-exfoliation of graphite is presented. High shear mixing of graphite in the Taylor vortex flow regime allows for the bulk production of few-layer graphene with low content of defects.

Carbon nanodots (CNDs) derived from a green precursor, kidney beans, was synthesized with high yield via a facile pyrolysis technique. The CND material was easily modified through simple oxidative treatment with nitric acid, leading to a high density “self-passivated” water soluble form (wsCNDs). The synthesized wsCNDs have been extensively characterized by using various microscopic and spectroscopic techniques and were crystalline in nature. The highly carboxylated wsCNDs possessed tunable-photoluminescence emission behavior throughout the visible region of the spectrum, demonstrating their application for multicolor cellular imaging of HeLa cells. The tunable-photoluminescence properties of “self-passivated” wsCNDs make them a promising candidate as a probe in biological cell-imaging applications.

Micro-supercapacitors have recently emerged as promising microscale power sources for portable and wearable microelectronics. However, most reported planar micro-supercapacitors suffer from low energy density and the complexity of fabrication, which calls for their further development. In recent years, the fortification of graphene has enabled the dramatic improvement of planar micro-supercapacitors by taking full advantage of in-plane interdigital architecture and the unique features of graphene. The development of viable printing technologies has also provided better means for manufacturing, bringing micro-supercapacitors closer to practical applications. This review summarizes the latest advances in graphene-based planar micro-supercapacitors, with specific emphasis placed on formulation of graphene-based inks and their fabrication routes onto interdigital electrodes. Prospects and challenges in this field are also discussed towards the realization of graphene-based planar micro-supercapacitors in the world of microelectronics.