Nan Zhang

University College Dublin | UCD · School of Mechanical and Materials Engineering

Compared with traditional drug delivery systems, stimuli-responsive injectable hydrogels exhibit sol–gel transition in response to external stimuli, thus showing significant advantages in the on-demand release of drug molecules. Among them, chitosan-based stimuli-responsive injectable hydrogels have attracted considerable attention due to their exc...

WE43 is a biodegradable magnesium alloy with a high potential for cardiovascular stent applications. Although it has many adequate properties, there are barriers to using it as a drug-eluting stent vehicle. Corrosion and hydrogen gas formation have an adverse effect on the surface, causing attached drug carriers to separate, which limits its functi...

Integrating nucleic acid extraction in amplification-based point-of-care diagnostics will be a significant feature for next-generation point-of-care virus detection devices. However, extracting DNA efficiently on a microfluidic chip poses many technological and commercialization challenges, including manual steps, multiple instruments, pretreatment...

Wound infections slow down the healing process and lead to complications such as septicemia, osteomyelitis, and even death. Although traditional methods relying on antibiotics are effective in controlling infection, they have led to the emergence of antibiotic-resistant bacteria. Hydrogels with antimicrobial function become a viable option for redu...

To explore the potential applicability of chitosan (CTS), we prepared aldehyde chitosan (CTS-CHO) with chitosan and sodium periodate via oxidation reaction and then a chitosan-based hydrophilic and antibacterial coating on the surface of poly (lactic acid) (PLA) film was developed and characterized. The oxidation degree was determined by Elemental...

Microbial transmissions via membrane surface and single-use plastic-induced pollution are two urgent societal problems. This research 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 a...

Polymeric micro devices are gaining huge market potential in broad areas of medical devices, diagnostic devices, drug delivery, and optical applications. Current research is focusing on developing functional polymeric micro devices on a mass-production scale. Microinjection moulding is a promising technique suitable for fabricating polymeric micro...

Abstract—In this study, the effect of anodization on the WE43 surface was investigated. The primary purpose was to achieve a corrosion-resistant surface that can be firmly bonded to polymers to design bioresorbable drug-eluting stents. WE43 samples were anodized at 4,5,6 volts and at different times after finding the best potential region for anodi...

Polymeric micro and nano surface structures are used widely in microfluidics, micro-optics and functional surfaces. Replication processes for these structures, e.g. micro injection moulding, hot embossing, are critical, but constricted by demoulding. Demoulding defects caused by friction, adhesion and thermal stresses, can cause microstructure dist...

The potentiodynamic polarization behaviour of nickel was examined in an electrolyte solution of nickel sulfamate to identify the etching, passivation, current limiting/polishing plateau and gas evolution regions for electropolishing and shaping of micro-mould features. Such features can be created either by means of 3D printing or direct machining...

In this study, an oxide layer is used to increase the bonding strength between a Multifunctional 3-layered polymer coating (PCL-PLLA-PLGA) and WE43 as well as protect the WE43 against degradation. The hydrophobic nature of polycaprolactone (PCL) acts as an anti-corrosion barrier as it prevents water uptake. Poly-L-lactic acid (PLLA) acts as a bridg...

Electropolishing (EP) is most widely used as a metal finishing process. It is a non-contact electrochemical process that can clean, passivate, deburr, brighten, and improve the biocompatibility of surfaces. However, there is clear potential for it to be used to shape and form the topology of micro-scale surface features, such as those found on the...

To reduce the adhesion and friction between polymer and mould surfaces during polymeric micro/nano structures replication, we have used tungsten disulfide (WS2) nanosheets to fabricate high-performance nickel/WS2 nanocomposite mould using electroforming. However, the aggregation of WS2 nanosheets in the electroforming solution is a critical issue t...

Transforming lab research into a sustainable business is becoming a trend in the microfluidic field. However, there are various challenges during the translation process due to the gaps between academia and industry, especially from laboratory prototyping to industrial scale-up production, which is critical for potential commercialization. In this...

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. Results prove that these functionalized films are ab...

In the replication of polymeric micro/nano structures, adhesion and friction between mould tool and polymer cause significant feature failure. For the first time, this work developed a novel strategy for the fabrication of high-hardness and self-lubricating 2D material-reinforced nickel mould tools using electroforming to achieve high precision rep...

As a combination of conventional injection moulding and compression moulding, injection compression moulding is expected to deliver a more uniform distribution of cavity pressure and more precise replication of surface structures. However, processing defects such as flash and design constraints such as thin edges of a product can cause non-uniform...

The integration of cleaner production technology and bio-based materials is welcomed to achieve a sustainable textile processing. This study introduces a one-step high efficiency and low temperature ultrasonic-assisted strategy for fully bio-based coloristic and functional cashmere using grape seed proanthocyanidins (GSPs) - a considerably generate...

A new approach to precision electroforming of a wafer-scale nickel shim with rotating cathode using an auxiliary cathode mask is developed to improve thickness uniformity and flatness. The effects of critical process parameters, including cathode rotating speed, cathode mask size, and current density, on the thickness uniformity and flatness of ele...

Microstructural replication accuracy in precision micro electroforming process is related to ions transportation inside the micro structure and microstructural feature width and aspect ratio. In this study, a novel star pattern having a varying feature width of 20∼320 μm with a corresponding aspect ratio of 5∼0.3125 is proposed to characterize ion...

Microfluidic chips have found many advanced applications in the areas of life science, analytical chemistry, agro-food analysis, and environmental detection. This chapter focuses on investigating the commonly used manufacturing technologies and process chain for the prototyping and mass production of microfluidic chips. The rapid prototyping techno...

Injection moulding has shown its advantages and prevalence in the production of plastic optical components, the performance and functionality of which rely on the precision replication of surface forms and on minimizing residual stress. The present work constitutes a systematic and comprehensive analysis of practical microlens arrays that are desig...

Micro electroforming is a promising electrodeposition-based precision replication technique for the fabrication of microstructured moulds. In this process, a poor mass transfer inside the micro structure with a high aspect ratio significantly affects the replication accuracy of the mould. In this paper, a novel star pattern with a continuously chan...

Injection moulding is ubiquitous in the production of plastic optical components, the functionality of which depends on minimising residual stress and on precisely replicating surface forms. In this study, variotherm-assisted microinjection moulding is used to manufacture a practical microlens array designed for light-field applications in order to...

Polymer microfabrication, as a simple and cost-effective way to achieve the miniaturization of the polymer parts, has become an efficient technique applied in life science, such as lab-on-a-chip (LOC) devices and micro-electromechanical system (MEMS). Polymer microfabrication mainly includes micro/nano forming, micro subtractive manufacturing, and...

Polymeric micro structures and micro components, as typically found on miniature medical devices and microfluidic chips, are mainly produced by the micro injection molding process, is a prevalent technology for mass production of polymer micro components and products with complex geometry and high precision surface micro structures. Because of high...

The dispersibility of graphene oxide particles (GOs) in nickel electrolytes is critical for its uniform incorporation in the nickel matrix during the electrodeposition process. In this study, we study the fundamental interaction of surfactants and nickel ionic strength for uniform and stable incorporation of GOs in nickel electrolytes and their eff...

Homogeneous dispersion of graphene oxide (GO) in nickel sulfamate solution is a significant challenge for electrodepositing high-performance nickel/GO composite coatings. In the present work, three typical surfactants, including anionic surfactant Sodium dodecyl sulfate (SDS), cationic surfactant Cetyltrimethylammonium bromide (CTAB), and non-ionic...

Ultrasonic-assisted electrodeposition was used to fabricate the nickel/graphene oxide composite coatings with high hardness, low friction coefficient, and high wear resistance. In the present study, the effects of ultrasonic power and concentration of graphene oxide on the mechanical and tribological properties of the electrodeposited nickel/graphe...

A new method, a 3D printing technique, in particular, selective laser melting (SLM), has been used to fabricate moulds for the injection moulding of thermoplastic microfluidic chips that are suitable for prototyping and early stage scale-up. The micro metallic patterns are printed on to a pre-finished substrate to form a microstructured mould. The...

Commercial software for injection moulding is available to optimise the mould design for macroscale products, but such software cannot accurately simulate the moulding process and defects for micro features, which are critical for the performance of polymeric micro/nano devices. In the present work, essential micro features with an aspect ratio of...

Human beings have witnessed unprecedented developments since the 1760s using precision tools and manufacturing methods that have led to ever-increasing precision, from millimeter to micrometer, to single nanometer, and to atomic levels. The modes of manufacturing have also advanced from craft-based manufacturing in the Stone, Bronze, and Iron Ages...

Micro features on surfaces are critical for the functionality of a product, such as micro channels for a microfluidic chip and micro lens arrays for an artificial compound eye lens. In the present work, we design a series of microfluidic and microstructured surface patterns to evaluate the influence of variotherm and vacuum venting on replication i...

Metallic-based microneedles (MNs) offer a robust platform for minimally invasive drug delivery and biosensing applications due to their mechanical strength and proven tissue and drug compatibility. However, current designs suffer from limited functional surface area or challenges in manufacturing scalability. Here, porous 316L stainless steel MN pa...

Micro injection moulding has been demonstrated as one of the most efficient mass production technologies for manufacturing polymeric microfluidic devices, which have been widely used in life sciences, environmental and analytical fields and agro-food industries. However, the filling of micro features for typical microfluidic devices is complicated...

The geometric surface integrity of micro patterns is critical for functionality of polymeric micro devices, e.g. replication accuracy for micro channels and individual lens for the element of a compound eye lens. Micro injection moulding has been used widely for mass production of these devices. However, achieving high replication integrity is a cr...

Piezoelectric properties of rat tail tendons, sectioned at angles of 0°, 59°, and 90° relative to the plane orthogonal to the major axis, were measured using piezoresponse force microscopy. The piezoelectric tensor at the length scale of an individual fibril was determined from angle-dependent in-plane and out-of-plane piezoelectric measurements. T...

Four physical parameters, namely cavity pressure close to the gate, filling time, part mass, and flow front pattern, have been used in a comparison between experiments and simulations to validate the accuracy with which the filling of micro ridges can be predicted using commercial software.

Experiments and simulations on micro injection moulding (μIM) of a thin wall micro part have been conducted. Simulations of μIM have been carried out using Moldex3D considering actual injection molding process. Factors influencing simulation accuracy were considered specifically: flow rate profile, packing pressure and time, injection machine param...

Two polymers, polymethylmethacrylate (PMMA) and cyclic olefin copolymer (COC), containing a range of nano- to micron- roughness surfaces (Ra 0.01, 0.1, 0.4, 1.0, 2.0, 3.2 and 5.0μm) were fabricated using electrical discharge machining (EDM) and replicated using micro injection moulding (μIM). Polymer samples were characterized using optical profilo...

Vacuum venting is a method proposed to improve feature replication in microparts that are fabricated using micro-injection molding (MIM). A qualitative and quantitative study has been carried out to investigate the effect of vacuum venting on the nano/microfeature replication in MIM. Anodized aluminum oxide (AAO) containing nanofeatures and a bulk...

Precision injection molding is the most efficient mass production technology for manufacturing plastic optics. Applications of plastic optics in field of imaging, illumination, and concentration demonstrate a variety of complex surface forms, developing from conventional plano and spherical surfaces to aspheric and freeform surfaces. It requires hi...

Microinjection molding (μIM) is a fast-developing technology which is used to produce polymeric microcomponents or components with micro/nanoscale features, such as are used in many fields including microfluidic diagnostics, microneedle drug delivery devices, microgears, and microswitches. The capabilities and performance of the microinjection mold...

Tooling is critical in defining multi-scale patterns for mass production of polymeric microfluidic devices using the microinjection molding process. In the present work, fabrication of various microstructured tool inserts using stainless steel, nickel and bulk metallic glasses (BMGs) is discussed based on die-sinking EDM (electrical discharge machi...

Product miniaturization and high shear/cooling rates during microinjection molding increase the volume of the highly oriented skin layer, thereby modifying the mechanical properties of the fabricated product.

Crystallization during microinjection molding is investigated relative to process conditions. Modulus and hardness of the skin layer are higher than the core layer, regardless of core structure. Young's modulus, strain at break and yield stress all increase with an increase of skin ratio. The relationship between process, morphology and mechanical...

Injection molding small milligram components requires precise metering and high-speed injection. Industrially, metering can be maintained either by using small injection screws (≤14 mm in diameter) or plungers as small as 3 mm diameter and/or by having very large sprues and runners. Although large sprues and runners increase metering volume, they h...

Polymer melts under micro injection molding process experience high shear rates and high thermal gradients, resulting in some unique morphology features. This paper examined the morphology of Pebax 7233 SA01 under designed experimental conditions. With measurement by cavity pressure and temperature (PT) sensors, shear rates and thermal gradients we...

Microsytems are motivating the development of complex, net-shape products weighing a few milligrams or having micro/nano features. Such small components or micro/nano features are subject to extreme shear rates and thermal gradients in the micro injection molding process due to their large surface to volume ratio. Detailed process monitoring and ch...

This study demonstrates a mass production method using nanoporous Anodized Aluminum Oxide (AAO) templates as mould insert tools that are used to structure large area polymer surfaces by a micro injection moulding process. SEM and water contact angle measurements served to evaluate the effect of nanostructures on surface properties. Human umbilical...

This study demonstrates a mass production method using nanoporous Anodized Aluminum Oxide (AAO) templates as mould insert tools that are used to structure large area polymer surfaces by a micro injection moulding process. SEM and water contact angle measurements served to evaluate the effect of nanostructures on surface properties. Human umbilical...

In-line process monitoring and rheological characterization can help to understand the behaviour of polymer melt flows during manufacture and to make injection moulding a measurable process for manufacturing high quality parts. This work developed an in-line rheology measurement system using a slit die attached to a micro injection moulding machine...

The development of MEMS and microsystems needs a reliable mass production process to fabricate micro components with micro/nano-scale features. In our study, we used the micro injection molding process to replicate micro/nano-scale channels and ridges from a bulk metallic glass (BMG) cavity insert. High-density polyethylene was used as the molding...

Micro-injection molding is widely used to form plastic components rapidly and precisely. Current tools for injection molding rely largely on steels for their strength and durability. The finite grain size in traditional crystalline metals means it is challenging to produce tools with features < 10 μm (Fig. 1b). However, the need for plastic compone...

The replication of micro/nano scale features is of great interest for MEMS and Microsystems. However, the flow behaviour of melts into a micro/nano cavity is still not well understood. In this work, we used the micro injection moulding process to replicate micro/nano scale channels and ridges from a Bulk Metallic Glass (BMG) cavity insert. High den...

Based on reciprocating micro injection molding machine, this paper characterizes the influence of machine process parameters and its transition response from velocity control to pressure control (V-P transition) on the micro cavity filling process. The method of Design of Experiment was employed to systematically and statistically investigate the e...

The replication of micro/nano scale features is of great interest for MEMS and Microsystems. However, the flow behaviour of melts into a micro/nano cavity is still not well understood. In this work, we used the micro injection moulding process to replicate micro/nano scale channels and ridges from a Bulk Metallic Glass (BMG) cavity insert. High den...