Mechanical Engineering

Young Scholar TechTalk – Customizable Acoustic Metamaterials on Frequency and Spatial Dimensions

March 12 2024 (Tuesday) 4:30-5:30pm
Acoustic metamaterials are artificially designed structured ‘atoms’. Initially, scientists discovered that these meta-atoms can exhibit extraordinary properties beyond those found in natural materials, such as negative density and negative modulus, through localized resonance, which sparked significant interest in the academic community. Subsequently, it was confirmed that these unique narrow-band frequency responses can be extended to broadband impedance designs, leading directly to the emergence of absorption metamaterials and opening up large-scale applications in noise reduction. In recent years, the potential of customizable metamaterials has gradually been realized. We will present our latest works from two complementary perspectives: customized frequencies and spatial non-uniformity, which may open up new applications such as directional emission, stealth cloaking and automotive acoustics.

TechTalk – Nature-Inspired Fluidics

February 29 2024 (Thursday) 4:30-5:30pm
Fluids are ubiquitous in nature and transport of fluids plays an essential role in sustaining many activities across multiple scales. The mode of fluidic transport therefore also spans multiple length scales. Moreover, despite largely aqueous in nature, natural fluids exhibit complexity, dynamics and structures that have yet to be replicated synthetically. In this talk, I will share our works in designing approaches to form, manipulate and direct aqueous solutions. In particular, I will focus on unique properties of aqueous multiphase systems that may serve as model systems for understanding their natural counterparts. I will conclude by discussing how these systems can potentially inspire biomimetic and biomedical applications.

TechTalk – Biomimetic Soft Materials for Bio-Integrated Smart Devices

Biological tissues are soft, dynamic, and water-rich, while abiotic tools are typically rigid, static, and dry. These differences in physical properties have presented challenges for the development of advanced biomedical systems that require interfacing with the human body. In this presentation, I will introduce our recent work on biomimetic soft composites as a platform for engineering bio-integrated devices that can potentially bridge this gap. These synthetic materials capture important structural features of natural soft tissues and exhibit tissue-mimetic reconfigurability, robustness, and functionality, making them advantageous for constructing bio-interfaces. Soft electronic components were also integrated into the biomimetic materials platform, enabling multifunctional systems for physiological sensing and targeted stimulation. Examples of these smart biomedical tools include artificial cartilage and tendons, electroconductive hydrogels, and organ-integrated 3D electronics, which create exciting opportunities in advanced biomedicine.

TechTalk – A “Programmable” Cell Niche Engineering Platform – Multiphoton Microfabrication and Micropatterning (MMM) Technology

In native tissues, cells reside in a complex microenvironment (niche) consisting of factors including neighbor cells, soluble factors, extracellular matrices, topological and mechanical signals. Cell niche is critical in maintaining their phenotype and determining their fates and functions. Reconstituting complex cell niche factors in vitro, either individually or in combinations, in a quantitatively and spatially controllable manner, is critical for investigating the interactions between cells and their niches and hence deriving designing strategies for optimal conditions during cell culture applications and optimal scaffolds for tissue engineering applications. Our lab has developed a multiphoton microfabrication and micropatterning (MMM) technology. Here, the technical capability of the MMM platform in fabricating complex protein microstructures and micropatterns with pre-designed topological features, mechanical properties, extracellular matrix, cell interaction molecules and soluble factors, and biomedical applications including cell niche factor screening for phenotype maintenance and engineering cell niche for cell fate determination will be discussed.

Young Scholar TechTalk – High-throughput Cell Mechanics Characterization with Microfluidics

Cells can sense mechanical stimuli and convert them to biochemical signals for various specific cellular responses, such as stem cells differentiation, initiation of transcriptional programs, and cell migration. Cell mechanics focuses on the mechanical properties and behaviours of living cells and how cell mechanics relates to various cell functions. Currently, traditional cell mechanics measurement methods are cumbersome, low-throughput, and expensive to deploy. By exploiting microfluidic technology, Dr. Johnson Cui is investigating the cancer cell mechanics and developing an accurate, easy-to-use cell mechanics measurement platform for cell mechanics research and also for cancer diagnosis and therapeutics in the future.

TechTalk – Scalable Nanoprinting for Nanophotonics Computing Platform

Photonic platforms with multiplexing capabilities are of profound importance for high-dimensional information processing. In this talk, Professor Nicholas X. Fang will present their recent effort on advancing scalable nanoprinting methods compatible with nanophotonic computing platforms. In the first part, Professor Nicholas X. Fang will discuss an efficient and cost-effective grayscale stencil lithography method to achieve material deposition with spatial thickness variation, for spatially resolved amplitude and phase modulation suitable for flat optics and metasurfaces. The design of stencil shadow masks and deposition strategy offers arbitrarily 2D thickness patterning with low surface roughness. The method is applied to fabricate multispectral reflective filter arrays based on lossy Fabry–Perot-type optical stacks with dielectric layers of variable thickness, which generate a wide color spectrum with high customizability. Grayscale stencil lithography offers a feasible and efficient solution to overcome the thickness-step and material limitations in fabricating spatially thickness-varying structures. In the second part, they show that selective ion doping of oxide electrolyte with electronegative metals shows promise to reproducible resistive switching that are critical for reliable hardware neuromorphic circuits. Based on density functional theory calculations, the underlying mechanism is hypothesized to be the ease of creating oxygen vacancies in the vicinity of electronegative dopants due to the capture of the associated electrons by dopant midgap states and the weakening of Al-O bonds. These oxygen vacancies and vacancy clusters also bind significantly to the dopant, thereby serving as preferential sites and building blocks in the formation of conducting paths. They validate this theory experimentally by implanting different dopants over a range of electronegativities in devices made of multiple alternating layers of alumina and WN and find superior repeatability and yield with highly electronegative metals, Au, Pt, and Pd. These devices also exhibit a gradual SET transition, enabling multibit switching that is desirable for analog computing.

TechTalk – Meta-materials for Sustainability

Micro/nanostructured materials offer significantly new opportunities for high-efficiency devices and systems for energy harvesting, conversion and storage. There is, however, a tremendous gap between the proof-of-principle demonstrations at the small scale and the intrinsically large-scale real-world energy systems and sustainable applications. In this talk, Professor Yin will give an overview of our research and, more specifically, present our recent development on how structured photonic materials address the challenge of the tremendous power hungry for space cooling and promote photosynthesis and crop yield in greenhouses.

TechTalk – Micro-robots Powered by Stimuli-responsive Materials

Conventional mechatronic, hydraulic and pneumatic motors and actuators are used for large-scale robots from ≥10 cm to the human size. At the other, nanometric end of the length scale, nano-robots are powered by molecular motors. However, a number of applications in compact environments require robotic devices in the size range of 10 µm to 10 mm, but these are too small to be powered by the conventional mechatronic systems, and too large for molecular motors. Such a length scale ideally suits a few types of high-performance stimuli-responsive actuating materials that are emerging out of a very active research field in the past two decades, with examples including shape-memory polymers and metals, nanoporous noble metals, reactive polymers and liquid-crystal elastomers, carbon-based materials and transitional metal oxides. In addition to high actuating power densities, some of these materials also offer built-in sensory functions such as resistivity responses to mechanical, heat and humidity changes in the environment, and even energy generation capabilities. Integration of these materials and their signal flows in compact designs thus poses a novel strategy for robotics at the micro length scale. This talk will review some recent progress in this field.

Tech Talk – Anti-Covid-19 stainless steel

Stainless steel (SS) is one of the most extensively used materials in many public areas and hygiene facilities but has no inherent antimicrobial properties. Additionally, the SARS-CoV-2 exhibits strong stability on regular SS surfaces, with viable viruses detected even after three days. Undoubtedly, this has created a high possibility of virus transmission among people using these areas and facilities. Here, this talk presents the inactivation of pathogen microbes (especially the SARS-CoV-2) on SS surface by tuning the chemical composition and microstructure of regular SS. It is discovered that Pathogen viruses like H1N1 and SARS-CoV-2 exhibit good stability on the surface of pure Ag and Cu-contained SS of low Cu content, but are rapidly inactivated on the surface of pure Cu and Cu-contained SS of high Cu content. Significantly, the developed anti-pathogen SS with 20 wt% Cu can distinctly reduce 99.75% and 99.99% of viable SARS-CoV-2 on its surface within 3 and 6 h, respectively. Lift buttons made of the present anti-pathogen SS are produced using mature powder metallurgy technique, demonstrating its potential applications in public areas and fighting the transmission of SARS-CoV-2 and other pathogens via surface touching.

Tech Talk – Short-range exposure during close contact and the environmental interaction

Debate and scientific inquiries regarding airborne transmission of respiratory infections such as COVID-19 and influenza continue. Exposure was investigated under a face-to-face scenario, where people experience the highest risk of respiratory infection. The short-range airborne route was found to dominate exposure during close contact. Based on the fact that most of the outbreaks occurred in indoor environments, we built the link between long-range airborne transmission and short-range airborne route. Results suggest that effective environmental prevention strategies for respiratory infections require appropriate increases in the ventilation rate while maintaining a sufficiently low occupancy.