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Producing sustainable microfluidic devices on a large scale has become a trend in the biomedical field. However, the transition from laboratory prototyping to large-scale industrial production poses several challenges due to the gap between academia and industry. In this context, prototyping with a mass production approach could be the novel strategy necessary to bridge academic research to the market. Here, the performance of polymer inserts to produce PMMA microfluidic devices using the microinjection moulding process is presented. Inserts were fabricated with an additive manufacturing process: material jetting technology. The importance of the inserts' orientation on the printing plate in order to produce samples with more uniform thickness and lower roughness has been demonstrated using a flat cavity insert. In addition, preliminary tests were carried out on microstructured inserts with inverted channels of various cross-section shapes (semi-circular or trapezoidal) and widths (200 or 300 µm) in order to investigate the microstructures' resistance during the moulding cycles. The best geometry was found in the channel with the trapezoidal cross-section with a width equal to 300 µm. Finally, a preliminary microfluidic test was performed to demonstrate the devices' workability. [ABSTRACT FROM AUTHOR]

Producing sustainable microfluidic devices on a large scale has become a trend in the biomedical field. However, the transition from laboratory prototyping to large-scale industrial production poses several challenges due to the gap between academia and industry. In this context, prototyping with a mass production approach could be the novel strategy necessary to bridge academic research to the market. Here, the performance of polymer inserts to produce PMMA microfluidic devices using the microinjection moulding process is presented. Inserts were fabricated with an additive manufacturing process: material jetting technology. The importance of the inserts’ orientation on the printing plate in order to produce samples with more uniform thickness and lower roughness has been demonstrated using a flat cavity insert. In addition, preliminary tests were carried out on microstructured inserts with inverted channels of various cross-section shapes (semi-circular or trapezoidal) and widths (200 or 300 µm) in order to investigate the microstructures’ resistance during the moulding cycles. The best geometry was found in the channel with the trapezoidal cross-section with a width equal to 300 µm. Finally, a preliminary microfluidic test was performed to demonstrate the devices’ workability.

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 devices. This review aims to summarise the primary achievements that have been achieved in various aspects of microinjection moulding of polymer micro devices, consisting of micro parts and micro surface structures. The relationships of the machine, process, rheology, tooling, micro/nanoscale replication, morphology, properties, and typical applications are reviewed in detail. Finally, a conclusion and challenges are highlighted. [ABSTRACT FROM AUTHOR]

This paper suggests an original numerical investigation through a two-phase filling-stage model of microinjection moulding (μIM) of thermoplastics. An unsymmetrical stepped-part decreasing thickness was considered to perform our modelling attempts. The transient equations of mass, momentum, energy conservation, and crystallization kinetics are solved simultaneously using the Finite Element Method (FEM). Flow front advancement is tracked through the Level-set method (LSM), employing the penalty approach to deal with the mass loss problems. The significant role of the interfacial thermal contact resistance (TCR) is introduced by the thermal joint resistances approach to predict the strenuous heat transfer phenomenon along the melt–mould interface, with the presence of gap conductance. The numerical code predicted the V-shapes of the flow Fountain effect and the distinguishing flow marks due to the trapped air between the melt front and the mould. The high accuracy of the thermal joint interfacial heat transfer (htc) model and the consideration of the micro-scale features are necessary for capturing such relevant details. Model validation was performed using simulation of predicted spherulite diameters, shear rates, and layer thickness measurements. Aspects of the present work are beyond the capability of the current commercial software. [ABSTRACT FROM AUTHOR]

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 devices. This review aims to summarise the primary achievements that have been achieved in various aspects of microinjection moulding of polymer micro devices, consisting of micro parts and micro surface structures. The relationships of the machine, process, rheology, tooling, micro/nanoscale replication, morphology, properties, and typical applications are reviewed in detail. Finally, a conclusion and challenges are highlighted.

Diffractive microstructured surfaces are nowadays increasingly applied to polymeric parts for aesthetic, security and optical functionalities. However, both the machining of the mould blaze-grating and its replication on plastic are still representing challenging issues, from both the technical and economical points of view. In this work, an innovative process chain based on carbide tools micromilling of mould gratings was developed for mass production of diffractive patterns on injection moulded parts. A micromilling experimental campaign was conducted on a nickel-phosphorus (NiP) thick coating to machine a blaze-grating on the mould surface, evaluating the influence of the cutting parameters on the diffractive surface quality. Subsequently, the microstructures were replicated on ABS, PC and PMMA by injection moulding. The roughness parameters Sk, Spk and Svk were added with the idea that their sum is representative of the polymer replication of regular diffraction grating pattern. Moreover, the effect of the moulded grating surface quality on the optical performance was preliminarily assessed. The obtained results show that the proposed process chain is suitable for low-cost mass production of polymeric parts with diffractive microstructures. [ABSTRACT FROM AUTHOR]

Microinjection moulding has been developed to fulfil the needs of mass production of micro components in different fields. A challenge of this technology lies in the downscaling of micro components, which leads to faster solidification of the polymeric material and a narrower process window. Moreover, the small cavity dimensions represent a limit for process monitoring due to the inability to install in-cavity sensors. Therefore, new solutions must be found. In this study, the downscaling effect was investigated by means of three spiral geometries with different cross sections, considering the achievable flow length as a response variable. Process indicators, called “process fingerprints”, were defined to monitor the process in-line. In the first stage, a relationship between the achievable flow length and the process parameters, as well as between the process fingerprints and the process parameters, was established. Subsequently, a correlation analysis was carried out to find the process indicators that are mostly related to the achievable flow length.

Microinjection moulding combined with the use of removable inserts is one of the most promising manufacturing processes for microfluidic devices, such as lab-on-chip, that have the potential to revolutionize the healthcare and diagnosis systems. In this work, we have designed, fabricated and tested a compact and disposable plastic optical stretcher. To produce the mould inserts, two micro manufacturing technologies have been used. Micro electro discharge machining (µEDM) was used to reproduce the inverse of the capillary tube connection characterized by elevated aspect ratio. The high accuracy of femtosecond laser micromachining (FLM) was exploited to manufacture the insert with perfectly aligned microfluidic channels and fibre slots, facilitating the final composition of the optical manipulation device. The optical stretcher operation was tested using microbeads and red blood cells solutions. The prototype presented in this work demonstrates the feasibility of this approach, which should guarantee real mass production of ready-to-use lab-on-chip devices.

Thermoplastic polyurethane (TPU)/multiwalled carbon nanotubes (MWCNTs) composites were prepared through twin extrusion and microinjection moulding. The effect of processing temperature on the structure and properties of composites were studied. Scanning electron microscopy and rheological test reveal the realisation of well dispersion and network formation of carbon nanotube (CNT) in TPU. Enhanced electrical conductivity has been found with the increasing mould temperature from 25 to 150°C, post-moulding thermal treatment under 180°C for 1 h leads to a significant increase in the electrical conductivity by over three orders of magnitude for 5 wt-%MWCNT filled TPU composites. Images (SEM and TEM) characterise the morphology of CNT network under low and high temperatures and the microcontact reconstruction of CNT network is proposed to explain the enhancement of electrical conductivity. The increased crystallinity of TPU leads to the enhancement of tensile strength and Young's modulus of composites after thermal treatment. [ABSTRACT FROM AUTHOR]

The fabrication and experimental characterization of a microinjection molded piezoresistive polymer accelerometer is presented here. The simplicity and low-cost of the fabrication process are a major advantage of the proposed alternative for the fabrication of microaccelerometers. Also, the compatibility with injection molded technologies enables direct integration of the devices into complex structures. Accelerometers have been fabricated using thermoplastic material (POM). The main structure of the accelerometer consists of a proof mass connected to an external structure by four arms. At the end of each arm, a pizoresisistive material is used for transduction. A Wheatstone bridge and an amplifier are used to measure the accelerometer output. Fabricated devices show a sensitivity of 56 mV/g, a resonance frequency of 270 Hz and a dynamic range of ±37 g. [ABSTRACT FROM AUTHOR]

In this paper we present the benefits of combining microinjection moulding technology with flexible elements for the realization of 3D microdevices with added functionality. Microinjection moulding technology enables the fabrication of low-weight micro-parts with great design flexibility. Polyimide is a known flexible material for its electrical and thermal insulation and mechanical strength that can easily be processed for microelectronic applications. Although widely used, silicon microdevices have limitations on their configuration (typical silicon devices have a planar geometry) and therefore, are not suitable for some applications requiring complex and small tridimensional geometries. Placement of smart elements within polymeric micro-parts adds functionality and enables an increased integration and 3D configurations. In this work, integrated 3DOF (degrees-of-freedom) and 1DOF thermal accelerometers are fabricated using the proposed fabrication technology demonstrating the viability of the concept. Experimental measurements using the 1DOF devices show a sensitivity of 15 mV/g (at 10 Hz), a bandwidth of 14 Hz and a power consumption of 28.7mW. [ABSTRACT FROM AUTHOR]

The focus of this study was to investigate the dispersion state of pure and functionalized carbon nanotubes in polyamide 6, on composites prepared by twin-screw extrusion and then processed by microinjection moulding. Nanocomposites were prepared with different carbon nanotube compositions, with and without functionalization. The nanotubes were functionalized by the 1,3-dipolar cycloaddition reaction. The dispersion of the carbon nanotube agglomerates was quantified using optical microscopy and image analysis. The effect of functionalization on the polyamide 6/carbon nanotube interface, the nanocomposite morphology and the mechanical and electrical properties were studied. It was observed that the microinjected composites with functionalized carbon nanotubes presented improved dispersion, with smaller carbon nanotube agglomerate area ratio compared to the composites with pure nanotubes. The functionalized nanotubes showed better adhesion to polyamide 6 compared to pure nanotubes, as observed by scanning electron microscopy. The incorporation of carbon nanotubes considerably improved the mechanical properties. The effect of high polymer shear rate on carbon nanotube alignment during microinjection moulding was assessed by comparing the electrical resistivity of the composite after extrusion and after microinjection moulding, through the thickness and along the flow direction. The experiments showed that the mould design and processing conditions significantly affected electrical resistivity. [ABSTRACT FROM AUTHOR]

Abstract: The melt flow dynamics of acrylonitrile-butadiene-styrene (ABS) and polypropylene (PP) in a variable thickness microimpression was assessed by monitoring cavity temperature and pressure as relevant process parameters. A micromoulding block with a variable thickness cavity was designed, manufactured and instrumented with pressure and temperature sensors, acting as monitoring devices as well as flow position markers during filling. A full factorial design of experiment (DOE) was carried to optimize the filling of the microimpression. This study with ABS and PP suggests that mould temperature is the more important parameter for the entire micromoulding thickness range under analysis. Nevertheless, the influence of the melt temperature and the injection speed were found to depend on the micromoulding thickness and the polymer type. [Copyright &y& Elsevier]

Layer-based manufacture of three-dimensional functional models and concept prototypes play a crucial role in the early assessment and verification of product designs. Any change of design, which is frequently needed during product development, causes the development costs to rise significantly. However, there is a limited set of materials available for layer-based manufacturing, especially for producing polymer microcomponents. Therefore, for fabricating small batches of microcomponents in the required material it is necessary to develop rapid tooling process chains, e.g. for low-pressure injection moulding. This paper investigates the moulding performance of µSL inserts as a function of tool geometry in combination with the effects of process factors. Condition monitoring techniques applied to the µ-IM process have been carried out to provide information that can be used to optimize the process. It was found that small batches of parts with fine details and relatively high aspect ratio structures can be produced and that reduced pressure loads and in particular the decrease of the µSL inserts layer thickness can extend the tool life. [ABSTRACT FROM AUTHOR]

Process monitoring of microinjection moulding (µlM) is of crucial importance when analysing the effect of different parameter settings on the process and then in assessing its quality. Quality factors related to cavity pressure can provide valuable information about the process dynamics and also about the filling behavior of different polymer melts. In this paper, a pressure sensor mounted inside a tool cavity was employed to analyse maximum cavity pressure, pressure increase rate during filling and pressure work. The influence of four µlM parameters, melt temperature, mould temperature, injection speed, and packing pressure on these three pressure-related process parameters was investigated. A design of experiment study was conducted by moulding a test part, a microfluidic component, in three different polymer materials, PP, ABS, and PC. The results show a similar process behavior for all three polymers, in particular a higher injection speed led to a reduction of the pressure work while a lower mould temperature reduces the pressure rate. [ABSTRACT FROM AUTHOR]

Today, microinjection moulding represents an established special variant among the different replication techniques strongly promoted by the growing market demand for microcomponents. Spearheading progress towards more sophisticated technologies, micro powder injection moulding offers a large scale fabrication process for metal/ceramic microparts. Minimal details in the range of 10 μm and replication accuracy down to ±0·3% (in special cases, ±0·1%) can be reached. With a twofold aim of reducing mounting costs and enabling the production of highly integrated devices two-component microinjection moulding is under development. Interesting examples are immovable or movable ceramic shaft wheel components. [ABSTRACT FROM AUTHOR]

Achieving perfect replication of micro- and nanostructured surfaces without creating sink marks in the parts is challenging. Therefore, gas assisted injection moulding (GAIM) was investigated as a method to enhance moulding quality in polypropylene, polymethylmethacrylate (PMMA) and thermoplastic polyurethane (TPU) parts. For all three polymers, the GAIM did not improve replication (depth ratios) of low aspect ratio microfeatures moulded using tooling with positive features, but did significantly enhance replication of higher aspect ratio trenches and tapered holes. The enhanced replication was attributed to better filling, and with the semicrystalline polymer, significantly less shrinkage. GAIM sometimes enhanced the edge definition of the features, and as expected, reduced sink marks in the polypropylene surfaces. [ABSTRACT FROM AUTHOR]

The microinjection moulding process is subject to microspecific phenomena, such as rapid cooling or high shear rates, which greatly affect part properties. While the correlations between morphology, crystallinity and the mechanical properties are well known for parts of usual macroscopic dimensions, there is less information available for microparts. In this paper, these correlations are discussed, related to the dimensions of semicrystalline thermoplastic parts. Results indicate that, if submitted to rapid cooling, microparts exhibit a fine structure, with low crystallinity, low yield strength and low elastic modulus. Experimental investigations have shown the influence of process parameters to be negligible. More important are the material's rate and ability to crystallise, which allow for properties to be significantly enhanced. Another possibility to considerably improve the performance of microparts independent of the used polymer is processing with slow cooling in thermally conductive moulds. [ABSTRACT FROM AUTHOR]

Three-dimensional finite element method simulation was performed to clarify the mechanism on surface replication in microinjection moulding and thermal nanoimprinting. In particular, the filling flow behaviour into micro- and nanosurface features was discussed in comparison with the experimental results. The simulation results and the experimental results of injection moulding show possibility of the generation of air traps in the filling stage and it is considered that those air traps have a strong relation with replication shape and replication rate. The simulation results of thermal imprinting revealed the penetration behaviour of polymer melt into nanosurface features and showed that the aspect ratio of the surface features and imprinting pressure and temperature influenced flow behaviour in thermal imprinting. [ABSTRACT FROM AUTHOR]

A microinjection moulding machine was used to obtain micromouldings of polyoxymethylene, in order to study morphology development during the process. The method of design of experiments was used to investigate statistically the effects of processing variables on the microstructural features of the mouldings. The morphological features were identified by microtoming the samples in both transverse and longitudinal (flow) directions and observing the microtomed sections under a polarised light microscope. Morphology evolution along the flow direction was followed by microtoming the specimens along the centre plane longitudinally and sequentially. A five-layer skin core structure was identified for micromoulded polyoxymethylene. The development of the structure was explained, based on mechanisms which were similar to those proposed for conventional injection moulding. Injection speed was found to be the most significant factor affecting morphological features of the final moulding. Moreover, the average plunger velocity, which is directly related to the cavity filling flow rate, was found to have good correlation with skin layer thickness. The distributions of crystalline polymorphs were observed and explained, in light of the distributions of the flow and thermal patterns in the mould. Morphology evolution along the flow direction reflected the distribution of pressure, temperature and velocity of the polymer melt during the microinjection moulding process. The results provided some indications regarding micromoulding mould design. [ABSTRACT FROM AUTHOR]

With standard microinjection moulding becoming more and more established in practical manufacturing, special variants are attracting increasing attention. Especially, the approaches on multi-component microinjection moulding are worth mentioning: As handling and assembly are difficult procedures especially in microtechnology, methods to reduce mounting efforts are of high economic importance. By merging of shaping and mounting procedures in one step, economic progress as well as new material combinations can be obtained. An interesting approach for the fabrication of metal (or in principal, ceramic) microcomponents is the combination of insert injection moulding and metal deposition by electroforming. First, an electrically conductive base plate is produced by injection moulding of conductively filled polymers. In a second injection moulding step, microstructures consisting of insulating plastics are mounted on these plates. The quasi-infinite conductivity gradient allows controlled electroplating starting at the base plate only so that defect-free metal microcomponents can be achieved. As a further variant of microinjection moulding, the development of the so-called MicroPIM process facilitates a large-scale series fabrication technology for metal and ceramic microcomponents. Combined with multi-component technology, an interesting new approach for micromanufacturing is obtained, i.e. the realisation of magnetic/non-magnetic or conductive/non-conductive material combinations by two-component MicroPIM. But, also the combination of different mechanical properties like hard/tough pairings is possible. [ABSTRACT FROM AUTHOR]

In this paper, we present the rheology of a high-density polyethylene for microinjection moulding. At high flow rate, pressure becomes high enough so that shear heating and pressure-dependence of the viscosity cannot be neglected. Moreover, spurt and chaotic defects related to wall slip were encountered. Nevertheless, we used classical data processing. We obtained viscosity at high shear rate which is lower than the viscosity obtained with the Carreau-Yasuda extrapolation of the moderate shear rate data. In order to discuss the origin of this difference, we developed a flow numerical simulation in the capillary where we take into account pressure and temperature dependent viscosity. The relative importance of these phenomena and their coupling is presented. Then, injection moulding experiments were carried out in a plaque mould. Different moulding parameters were tested. A three dimensional injection moulding numerical simulation, using Rem3D software, was carried out. The quality of the different sets of rheological data is assessed by comparing computed and measured pressure. [ABSTRACT FROM AUTHOR]

Owing to the higher requirements on dosage accuracy and material strength for products with microfeatures, the analysis of the solid conveying process in a microinjection moulding machine becomes more important. A discrete element modelling method discrete element modelling (DEM) for simulating polymer particles moving in an inclined narrow screw channel is developed. Adhesion and its effects on normal contact force and rolling friction are taken into account in the modelling, allowing considerations of more influencing factors on the solid conveying process, such as temperature. The straight gravity field in the real world is transformed into the twisted time dependent gravity field in an unfolded straight channel, avoiding the calculation expensiveness induced by the complex geometry of the screw channel, which is important for DEM simulations. These have not been carried out previously. Using the developed programmes, effects of screw axis inclination on the specific throughput of the solid pellets are investigated. It is found that a larger inclination angle can induce higher specific throughput, especially when the screw rotational speed is lower. However, a smaller inclination angle is beneficial for easier throughput control. The results can be used to optimise the design of the plasticating unit as well as the operation parameters of the microinjection moulding machine. In addition, experimental studies are also carried out in this approach. Results of simulations are compared with those of experiments for verifying the accuracy of the simulation model. [ABSTRACT FROM AUTHOR]

Abstract: The implementation of replication techniques for mass production of microcomponents relies on the availability of tooling technologies for manufacturing of tools and moulds. Micromilling is a suitable technique for manufacturing of microstructures characterized by high aspect ratios and complex geometries as those characterizing injection moulding moulds. The realization of the micromilling process in connection with hardened tool steel as workpiece material is particularly challenging. The low strength of the miniaturized end mills implies reduction and accurate control of the chip load, which requires high positioning accuracy. Size effects, mainly related to the microstructure of the workpiece material and to the limited scalability of tool geometry and surface topography, critically influence the performance of the process in terms of part accuracy, surface roughness, cutting forces and tool wear. This paper presents the micromilling process applied to the manufacturing of microinjection moulding moulds in hardened tool steel, presenting experimental evidence and possible solutions to the above-mentioned issues. [Copyright &y& Elsevier]

Microinjection moulding has been developed to fulfil the needs of mass production of micro components in different fields. A challenge of this technology lies in the downscaling of micro components, which leads to faster solidification of the polymeric material and a narrower process window. Moreover, the small cavity dimensions represent a limit for process monitoring due to the inability to install in-cavity sensors. Therefore, new solutions must be found. In this study, the downscaling effect was investigated by means of three spiral geometries with different cross sections, considering the achievable flow length as a response variable. Process indicators, called "process fingerprints", were defined to monitor the process in-line. In the first stage, a relationship between the achievable flow length and the process parameters, as well as between the process fingerprints and the process parameters, was established. Subsequently, a correlation analysis was carried out to find the process indicators that are mostly related to the achievable flow length. [ABSTRACT FROM AUTHOR]

Microinjection moulding combined with the use of removable inserts is one of the most promising manufacturing processes for microfluidic devices, such as lab-on-chip, that have the potential to revolutionize the healthcare and diagnosis systems. In this work, we have designed, fabricated and tested a compact and disposable plastic optical stretcher. To produce the mould inserts, two micro manufacturing technologies have been used. Micro electro discharge machining (µEDM) was used to reproduce the inverse of the capillary tube connection characterized by elevated aspect ratio. The high accuracy of femtosecond laser micromachining (FLM) was exploited to manufacture the insert with perfectly aligned microfluidic channels and fibre slots, facilitating the final composition of the optical manipulation device. The optical stretcher operation was tested using microbeads and red blood cells solutions. The prototype presented in this work demonstrates the feasibility of this approach, which should guarantee real mass production of ready-to-use lab-on-chip devices. [ABSTRACT FROM AUTHOR]