Micro mould tools fabrication
Mould tools are critical for the fabrication of polymer micro/nano devices, as they are essential for micro feature replication and largely determine the feature size and surface roughness. Dr Zhang studied the micro/nano mould tool fabrication in his PhD with the development of multi-scale mould tools using Bulk Metallic Glasses, where the minimum feature size can be down to 80nm with large feature size in tens of microns.
In 2017, Dr Zhang proposed a novel high-performance tooling technology, 2D Materials nanocomposite moulds. Since then, the team has developed formulations of nanomaterial electrolytes, nanomaterial electroforming systems. Tremendous work has been carried out to understand 2D materials, formulation, and electroforming conditions on nanocomposite mechanical, tribological properties and surface chemistry. The micro-structured mould has been validated using micro hot embossing to significantly reduce friction and adhesion between the mould and moulded polymer materials. The mechanistic understanding of their high performance was studied. We are developing a wafer scale 2D materials electroforming system for large-area high-performance micro mould fabrication for mass production of polymeric micro/nano devices.
Meanwhile, our team has developed a rotation cathode electroforming system for 4in and 6 in-wafer scale electroforming. We have made much effort to understand the impact of the process, electrolyte composition and coating on flatness and microfeature electrodeposition. Process know-how on electroforming thick mould tools based on UV-LIGA has been established. We have used it for many microfluidic mould fabrication with features from 20 microns to 300 microns with wafer thicknesses up to 1.2mm. We are so proud that all our microfluidic devices in our lab are made using our own moulds, which save budget and also much faster, enabling us for fast development of microfluidic systems.
Submicron arrays mould made by BMG
Nickel moulds with 300um height inverted channels
Precision machined stainless steel mould with multi-step features from 80um to 500um
Nickel mould with inverted channel size 60 um
Nickel mould with minimum channel size 80micron, aspect ratio ~3
Large-area nanostructured aluminium mould
Micro/nano replication technologies
Following mould fabrication, replication technologies are important to translate the features from moulds to polymer surfaces. Our group focuses our effort, particularly on mass production technologies, such as micro injection moulding and nanoimprinting. Microinjection moulding is one of the most used production processes for fabricating plastic micro/nano components with low cost, high efficiency and complex 3D geometry. Microinjection moulded products can be categorized into two groups: miniature products and surface micro/nanostructures.
Our research on micro components focuses on extreme processing on morphology and properties of micro components, which leads to an important understanding of flow-induced crystallization control of properties of micro components from both processing and materials. This is critically important for medical devices, such as microneedles and stents.
Our research on surface micro/nanostructures focuses on the developmen of precision micro/nano mould tools and precision replication of micro/nanostructures and free forms. We are developing novel processes for precision replications, including variotherm-assisted micro injecting moulding, in-mould micro compression and mould tools shaping & rounding.
We aim to understand more about polymer replication process feature design, process, materials and interfacial effects through experimental study and numerical simulation.
Numerical simulation of microstructure replication for Microfluidic devices
Precision injection moulding of microfluidic
Microinjection moulding of miniature tensile specimen
Precision injection moulding of micro arrays and high aspect ratio features
Precision injection moulding of microfluidics
Microinjection moulding of sub 100nm structures
Precision 3D printing using Digital Light Processing (DLP)
Since 2021, Dr Zhang's team has started to work on micro additive manufacturing of polymer structures. We have done a systemic investigation on the polymer micro additive processes and found that DLP combines both efficiency and precision. Upto date, we have developed a customized DLP 3D printer with high resolution. Currently the machine can print features down to 6um with a layer thickness down using commercially available photopolymer. Additionally, this machine is currently the highest precision DLP 3D printer in Ireland. Our team will explore precision 3D printing, biomaterial 3D printing and functional nanomaterials printing by targeting medical devices and healthcare.
Functional structures for anti-Covid and antimicrobial surfaces and medical stent
Except for our effort in polymer micro fabrication, Dr Zhang also works on nanoimprinting for the fabrication of functional surface nanostructures with nanoparticles for anti-Covid virus and antimicrobial surfaces. Direct contact with contaminated surfaces in frequently accessed areas is a confirmed transmission mode of SARS-CoV-2. To address this challenge, we have developed novel plastic films with enhanced effectiveness for deactivating the SARS-CoV-2 by means of nanomaterials combined with nanopatterns. This is particularly meaningful at the beginning of the pandemic when the Vaccine is not available. It can help to prevent the transmission of infectious diseases.
Microbial transmissions via membrane surface and single-use plastic-induced pollution are two urgent societal problems. Using the same strategy, Dr Zhang's stem introduces a scalable fabrication strategy for fully biobased antibacterial and ultraviolet-B block polylactic acid (PLA) films integrating natural coatings and nanopatterns via ultrasonic atomization spray coating and thermal nanoimprinting lithography (TNIL) techniques, respectively. The integration of a TA or GA coating with nanopatterns further promotes the antibacterial rate up to 98%. We provide a scalable strategy for the sustainable development of eco-benign and functional films. based on roll-to-roll nanoimprinting.