Conventional computed tomography (CT) remains the workhorse of cross-sectional medical imaging. But dual- and multi-energy CT allows for more specific material decomposition, enabling distinct advantages in the clinical setting. In this review, we describe the basic principles behind material decomposition in dual- and multi-energy CT, outline the techniques used to acquire images, and explore how enhanced material decomposition leads to improved patient care. We also explore areas of active research and future directions, including photon-counting CT, that have the potential to revolutionize CT in clinical use.

From the 1918 influenza pandemic (H1N1) until the recent 2019 severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic, no efficient diagnostic tools have been developed for sensitive identification of viral pathogens. Rigorous, early, and accurate detection of viral pathogens is not only linked to preventing transmission but also to timely treatment and monitoring of drug resistance. Reverse transcription-polymerase chain reaction (RT-PCR), the gold standard method for microbiology and virology testing, suffers from both false-negative and false-positive results arising from the detection limit, contamination of samples/templates, exponential DNA amplification, and variation of viral ribonucleic acid sequences within a single individual during the course of the infection. Rapid, sensitive, and label-free detection of SARS-CoV-2 can provide a first line of defense against the current pandemic. A promising technique is non-linear coherent anti-Stokes Raman scattering (CARS) microscopy, which has the ability to capture rich spatiotemporal structural and functional information at a high acquisition speed in a label-free manner from a biological system. Raman scattering is a process in which the distinctive spectral signatures associated with light-sample interaction provide information on the chemical composition of the sample. In this prospective, we briefly discuss the development and future prospects of CARS for real-time multiplexed label-free detection of SARS-CoV-2 pathogens.

Recent applications require vertical chip stacking to increase the performance of many devices without the need of advanced node components. Image sensors and vision systems will embed more and more smart functions, for instance, image processing, object recognition, and movement detection. In this perspective, the combination of Cu-to-Cu direct hybrid bonding technology with Through-Silicon-Via (TSV) will allow 3D interconnection between pixels and the associated computing and memory structures, each function fabricated on a separate wafer. Wafer-to-wafer hybrid bonding was achieved with multi-pitch design—1–4 μm—of single levels of Cu damascene patterned on 300 mm silicon substrates. Defect-free bonding, as far as the extreme edge of the wafer, was demonstrated on a stack with three wafers. Middle wafers thinning was done with grinding only and with a thickness uniformity (TTV) <2 μm to an ultimate thinning as low as 3 μm. Alignment performance was characterized by post-bonding for two superposed hybrid bonding interfaces. In our set of wafers, modeling the alignment with translation, rotation, and scaling components enables us to optimize the residuals down to 3σ < 100 nm. A process flow of thin TSV with a fine pitch of 2 μm for high-density vertical interconnect through a three-wafer stack was developed. Via-last TSV architecture was adopted with 1 μm TSV diameter and 10 μm thickness. Lithography, etching solutions, Ti/TiN barrier deposition, and void-free Cu filling solutions were demonstrated. TSV cross sections after CMP and connections with top and bottom Cu damascene lines show good profile control. Process developments are matured and can be reliably used in the fabrication of an electrical test vehicle including vertical interconnects associating multi-wafers stacking with a hybrid bonding process and high-density thin TSV applicable to low pitches (<5 μm).

Recent discovery of ferroelectricity in doped HfO2 has reignited research interest in the ferroelectric field-effect transistor (FeFET) as emerging embedded nonvolatile memory with the potential for neuro-inspired computing. This paper reviews two major aspects for its application in neuro-inspired computing: ferroelectric devices as multilevel synaptic devices and the circuit primitive design with FeFET for in-memory computing. First, the authors survey representative FeFET-based synaptic devices. Then, the authors introduce 2T-1FeFET synaptic cell design that improves its in situ training accuracy to approach software baseline. Then, the authors introduce the FeFET drain–erase scheme for array-level operations, which makes the in situ training feasible for FeFET-based hardware accelerator. Finally, the authors give an outlook on the future 3D-integrated 2T-1FeFET design.

From thin film solar cells to metal–oxide–semiconductor (MOS) devices in leading edge integrated circuits, the electronic structure at and near the interfaces between component materials determines the most important fundamental operating characteristics of those devices such as turn-on voltage, power dissipation, and off-state current leakage. Fermi level location at buried interfaces, semiconductor (SC) band bending, charge transfer, oxide defects, and work functions of the constituent materials all contribute to device performance. This paper describes how these important parameters can be determined by employing femtosecond photovoltage spectroscopy, an extension of ultraviolet photoelectron spectroscopy (UPS) using ultrafast lasers. While standard UPS is fundamentally a surface-sensitive spectroscopy, pump/probe techniques add a new dimension to this venerable spectroscopy, permitting the accurate extraction of the underlying band bending in SCs. When combined with the valence band edge location of the SC and oxide, and determination of the system Fermi level, full characterization of the electronic structure of a MOS stack can be obtained providing key insights on device operating properties. This approach can be extended to study key device materials in emerging areas of artificial intelligence and quantum computing. In each case, surprising new details were uncovered that led to performance optimization of these technologically important devices.

The deeper comprehension of biological phenomena has led to the pursuit of designing and architecting complex biological systems. This has been incorporated through the advances in bioprinting of artificial organs and implants even at the microscale. In addition, tissue modeling has been employed to understand and prevent malfunctional and detrimental mechanisms that lead to fatal diseases. Furthermore, the endeavor to convey the mechanical properties of both scaffolds and cells has enabled the unveiling of disease modeling and regenerative medicine. This paper aims to provide a brief review of the design, modeling and characterization of conventional and architected structures employed in bioengineering.

Bioelectronics aims to design electronic devices which can be fully integrated within tissues to monitor or stimulate specific cell functions. The main challenge is the engineering of the cell–chip interface and diverse materials, and devices have been developed to recapitulate biological architectures and functionalities. In this Prospective article, the authors give an overview on how the bioelectronics community has exploited biomimetic approaches to emulate cell morphologies, interactions, and functions to design optimal electrical platforms to be coupled to living cells.

The current COVID-19 pandemic has caused the shortage of personal protective equipment (PPE) where improvised manufacturing in particular 3D printing has addressed many needs. This prospective discusses the current global crisis, then follows the wide interest in addressing the shortage of medical devices and PPEs used for treatment and protection against pathogens. An overview of the 3D printing process with polymer materials is given followed by the different 3D printing projects of PPEs and medical devices that emerged for the pandemic (including validation/testing). The potential for rapid prototyping with different polymer materials and eventual high-throughput production is emphasized.

This article presents a comprehensive overview of currently available research on bioimplantable energy harvesters, with a specific focus on their fabrication and issue of biocompatibility. Both the achievements and limitations of the field are pointed out from the standpoint of materials science and engineering as directions for future research. Particular attention is paid to the controversy over the use of lead-based or lead-free piezoelectric ceramics in biomedical applications, which is closely related to different temporalities of research on biological conditions. This report is intended to serve as a reference guide for developing the next generation of piezoelectric biomedical devices.

Because of their structural versatility, fast redox reactivity, high storage capacity, sustainability, and environmental friendliness, soluble organic redox molecules have emerged as materials that have potential for use in energy-storage systems. Considering these advantages, this paper reviews recent progress in implementing such materials in aqueous soluble organic redox flow batteries and organic alkali metal/air batteries. We identify and discuss major challenges associated with molecular structures, cell configurations, and electrochemical parameters. Hopefully, we provide a general guidance for the future development of soluble organic redox materials for emerging energy-storage devices used in the electricity grid.

This report is on the synthesis by electrospinning of multiferroic core-shell nanofibers of strontium hexaferrite and lead zirconate titanate or barium titanate and studies on magneto-electric (ME) coupling. Fibers with well-defined core–shell structures showed the order parameters in agreement with values for nanostructures. The strength of ME coupling measured by the magnetic field-induced polarization showed the fractional change in the remnant polarization as high as 21%. The ME voltage coefficient in H-assembled films showed the strong ME response for the zero magnetic bias field. Follow-up studies and potential avenues for enhancing the strength of ME coupling in the core–shell nanofibers are discussed.

Natural systems displaying optical properties have for long been an inspiration for new classes of optical constructs. Using the same families of materials employed by Nature in combination with their directed assembly allows access to n-dimensions of control to, ultimately, generate optical systems with multiple coexisting functions. This review provides an overview of lab-made optical systems made of protein and polysaccharide-derived materials found in naturally occurring optical systems. Recent advances in optical biomimicry and bioinspired, polyfunctional optical structures are presented, addressing attributes such as sensing, edible devices, biologically activity, and resorbable optical formats.

Molecular semiconductors synergize a variety of uniquely advantageous properties such as excellent absorption and emission properties, soft and deformable mechanical properties, and mixed ionic and electrical conduction. Over the past two decades, this outstanding set of features has put molecular semiconductors in the spotlight for a variety of optoelectronics and sensing applications. When it comes to mass-market adaptation, however, a challenge in these soft and van der Waals-bonded materials remains their electrical as well as environmental stability and degradation. This Prospective will summarize some of our current understanding of why organic semiconductors degrade with a strong emphasis put on the quintessential role played by water in this process. Furthermore, it will be revisited by which mechanisms water-related stability shortcomings might be addressed in the future and how these lessons can be translated to relevant hybrid systems such as perovskites and carbon nanotubes. Throughout this discussion, some parallels and key differences between organic and hybrid materials will be highlighted, and it will be elaborated on how this affects the associated device stability.

Planet–satellite-type supracolloidal clusters represent a comparably young class of nanomaterials, which are unique with regard to structural order. In this prospective article, different approaches for their synthesis are discussed and compared. These synthetic methods enable the engineering of supracolloidal structural and adaptive properties, which in turn enables different emerging applications, such as in sensing and catalysis. These possibilities are explored on the basis of selected recent examples. A perspective about possible future developments is given at the end of this article.

The development of flexible, stretchable, conformal electronics, and smart textiles for wearables and other applications by now lacks a guidance toward environmentally benign product concepts. This article facilitates understanding of environmental implications of material choices and design decisions to help material scientists and product developers alike to consider sustainability implications of their research, innovation, and development. The more such electronics enter the market, the more these composite products will emerge as an ecological problem, unless appropriate measures are taken at the early research stage.

Inflammation is facilitated largely by macrophages and other white blood cells, which recognize and respond to evolutionarily conserved damage-associated molecular patterns that are released upon tissue injury and cell stress. Damage-associated molecular patterns are known to bind Toll-like receptors (TLRs) and initiate inflammatory responses through MyD88-dependent NF-κB signaling. Biomaterial implantation activates the innate immune system, resulting in a chronic inflammatory response known as a foreign body reaction (FBR). In this review, the authors discuss the current understanding of damage-initiated TLR signaling in the FBR and the significance of this response in the success of implanted devices.

The authors design six alumina hybrid structures consisting of stretching-dominated plates and different space-filling lattices comprised of hollow tubes and perform finite element simulations to study mechanical and failure behaviors of such hybrid structures. The authors investigate the effects of three geometrical parameters on the stiffness and failure of these hybrid structures and further compare their advantages and disadvantages. The authors find that the failure modes of these hybrid structures can be tuned by altering cell unit type and geometrical parameters. Among these hybrid structures, the ones with effective support from the lattice unit cells in the stretching direction exhibit better specific stiffness and strength. By varying the lattice and plate thickness, the authors find that the relations between stiffness/failure strength and density follow a power law. When intrinsic material failure occurs, the power law exponent is 1; when buckling failure arises, the power law exponent is 3. However, by varying tube thickness, their relations follow unusual power relations with the exponent changing from nearly 0 to nearly infinity. In addition, the hybrid structures also exhibit defect insensitivity. This study shows that such hybrid structures are able to greatly expand the design space of architectured cellular materials for engineering applications.

Periodic lattice materials have been studied extensively in numerous science and engineering fields. Despite the vast knowledge that has emerged, the activities have been stove-piped within individual research communities, often in isolation from those in related fields. To bring this work into a holistic framework, the present article considers the elements needed to integrate the study of lattice materials into the processing–structure–properties paradigm that underpins materials science as an academic discipline. The emphasis is on concepts of structure involving topology, morphology, and defects of lattice materials, with illustrations of structure–property relations in the context of lattice strength.

From being an unfavorable consequence to finding itself as the intended imaginary part of a non-Hermitian system, loss has truly emerged as more of a friend than a foe in the context of acoustic metasurfaces. With the promising features of sub-wavelength geometries and the rapid advances in manufacturing techniques that can enable their realization, loss becomes a central topic of discussion. Further, the capability of introducing and tailoring loss allows it to serve as a new degree of freedom in passive wavefront shaping devices. In this review, the authors look back at the recent progress in the field of lossy acoustic metasurfaces. The background behind loss in deep sub-wavelength geometries and the instinctive responses to treat them and exploit them are overviewed, followed by more recent works that embrace and tailor their behavior for unconventional applications. The forthcoming years for acoustic metasurfaces thus hold several promising avenues for exploration, with loss as the protagonist.

This Prospective covers an overview of the injection molding process and the importance of mold design and tooling considerations, important material requirements and thermal properties for molds, polymer material requirements for injection molding, mold flow analysis, and the promise of using the 3D printing process for mold fabrication. The second part demonstrates the injection molding process using 3D-printed polymer molds and its suitability for low-run productions. 3D-printed molds using stereolithography and fused filament fabrication have been injected with polylactic acid, and the quality of the injected parts was assessed in terms of dimensional accuracy and the damage mechanisms during fabrication.