Fluidic technologies play a vital role in our society. The capability to accurately capture and discharge various chemical and biological fluids is essential across various domains. A major challenge has been to create a system that can switch between capturing and releasing these liquids with exact spatial and temporal control, as well as precise volume measurements. Recently, a team of researchers at The Polytechnic University of Hong Kong (PolyU) has developed an innovative method to tackle this issue.
Under the guidance of Prof. WANG Liqiu, who holds the Otto Poon Charitable Foundation Professorship in Smart and Sustainable Energy and serves as Chair Professor of Thermal-Fluid and Energy Engineering in the PolyU Department of Mechanical Engineering, the research team has crafted a novel fluidic processor dubbed “Connected Polyhedral Frames” (CPFs). With CPFs, the process of switching between liquid capture and release becomes reversible, programmable, and non-dependent on the polyhedral frames or the liquids being processed, thus classifying the processor as a meta-metamaterial. This work has been recently detailed in the journal Nature Chemical Engineering, with Dr. ZHANG Yiyuan, a Research Assistant Professor in the department, serving as the lead author.
While manipulation of solids has seen significant advancements, managing fluids remains a complicated endeavor, even though fluids are ubiquitous in sectors such as healthcare, pharmaceuticals, biology, and chemistry. The interaction between fluids and tools often leads to wetting and spreading on solid surfaces, which hampers complete liquid transfer, reduces volumetric precision, and increases the risk of cross-contamination between samples. To avoid contamination, single-use plastics like pipettes and microtubes are commonly used, exacerbating the global issue of plastic waste.
The ability to reversibly switch between capturing and releasing is essential to the effectiveness of CPFs in processing liquids. This functionality allows the liquid to be held or drained in a controlled, reversible manner. In the CPFs, frames positioned above a single-rod connection trap and hold liquids, functioning as capturers. In contrast, frames above a double-rod connection absorb and release liquids, acting as releasers. This occurs because lifting the CPFs from the liquid generates a liquid film between the double-rod connections, forming channels that facilitate the release of liquid.
Achieving reversible switching involves using existing tools to either create or break the continuity of liquid between frames. CPFs offer a flexible platform that supports a range of unique applications, including the three-dimensional (3D) programmable arrangement of liquids, spatiotemporal control of various material concentrations, and the packaging of 3D liquid arrays. The system can work with a wide variety of liquids, from aqueous solutions and biofluids to hydrogels, organic solvents, polymer solutions, and oils. This gives CPFs the versatility to incorporate numerous biomaterials and chemicals for a multitude of applications.
To illustrate the practical applications of CPFs for controlled multidrug release, Prof. Wang’s team created a CPF network that patterned vitamins B2 and B12 in 3D. These vitamins, representing different drug molecules, were encapsulated within sodium alginate hydrogel and gellan gum, respectively, and released in water. By adjusting the thickness of the gel membrane, the team could precisely manage the respective release rates of the two “drugs.”
Conventional cotton and flocking swabs often struggle with residue left behind during sample release. CPFs address this issue effectively due to their frame structure, which provides free liquid-liquid interfaces that enhance release efficiency. For example, when testing for the influenza virus, CPFs demonstrated superior sampling capabilities, successfully detecting the virus at low concentrations where both flocking swabs and cotton swabs failed.
The research team also showcased the potential of CPFs in encapsulating biomaterials. In a demonstration using Acetobacterium, the CPFs proved advantageous compared to traditional devices by aiding in the separation of bacteria and reaction products, simplifying microbial processes, and increasing bacterial utilization rates. It is likely that CPFs could also be used to encapsulate other biological materials for the efficient production of valuable products.
Besides applications in medicine and microbiology, Prof. Wang’s team has also highlighted the feasibility of CPFs in air conditioning systems. They developed a commercial-scale humidifier prototype that boasts greater water storage capacity and reduced water flow requirements, potentially improving energy efficiency. Additionally, CPFs facilitate large-scale 3D liquid dispersion, increasing surface area and enhancing gas absorption efficiency. This resulted in the successful implementation of an ideal CO2 cycle process using CPFs, covering carbon capture, storage, and CO2 recycling strategies.
Crucially, each frame in CPFs operates independently concerning the capturing or releasing of liquids, irrespective of their base materials, structures, or the fluids involved, positioning them as innovative meta-metamaterials. The creation of such a fluidic processor establishes a new benchmark for liquid handling that emphasizes controllability, versatility, and high performance. This not only inspires a new area of meta-metamaterials research, but also paves the way for groundbreaking advancements in various scientific and technological fields.
