Since the late 1980s a small number of research groups have been attracted with the idea of using induction heating technology for the processing of fibre reinforced polymer composites. Induction technology is suitable for the processing of thermoplastic and thermoset polymer materials but requires special susceptor additives (conductive materials) either in the form of structured fibres and fabric or particulate that can transform the electromagnetic energy into heat. This paper aims to summarize the principles of induction heating with respect to polymer composites processing taking a look first at material and equipment based process influences. State of the art applications and research activities are then reviewed, from thermoplastic composite welding, thermoset curing, selective material heating and fast mould heating technologies. Current simulation possibilities and available software tools have also been covered. Finally, some new ideas and possibilities for future developments in the field of polymer composites processing have been discussed.

The heating of polymer composites by electromagnetic induction – A review

Recent advances in microfluidic technology for manipulation and analysis of biological cells (2007-2017).

Drug development is a long process whose main content includes drug synthesis, drug delivery, and drug evaluation. Compared with conventional drug development procedures, microfluidics has emerged as a revolutionary technology in that it offers a miniaturized and highly controllable environment for bio(chemical) reactions to take place. It is also compatible with analytical strategies to implement integrated and high-throughput screening and evaluations. In this review, we provide a comprehensive summary of the entire microfluidics-based drug development system, from drug synthesis to drug evaluation. The challenges in the current status and the prospects for future development are also discussed. We believe that this review will promote communications throughout diversified scientific and engineering communities that will continue contributing to this burgeoning field.

Microfluidics for Drug Development: From Synthesis to Evaluation.

Finite element modeling of continuous induction welding of thermoplastic matrix composites

A low-cost, polymer-based microfluidic platform is described that not only includes passive microfluidic parts, but also pumps based on an on-chip electrochemical gas generation by electrolysis. A hydrogel is used as electrolyte material, which allows a simple fabrication process by screen printing or stencil printing. Test structures were designed and fabricated to illustrate the feasibility of the approach for batch processing. Microfluidic chips including reservoirs and channel structures were fabricated by microinjection molding and used to demonstrate the movement of liquids inside microchannels by the proposed micropumps. The channel system was furthermore functionalized by a plasma surface treatment to form hydrophobic and hydrophilic areas. For sealing of the channel system, as well as for bonding the microfluidic part to glass-like sensor parts, laser-cut adhesive tapes were applied.

Polymer Lab-on-Chip systems with integrated electrochemical pumps

Microfluidic systems are being used in many applications and the demand for such systems has been phenomenal in past decades. To meet such high volume market needs, a cheap and rapid method for sealing these microfluidic platforms which is viable for mass manufacture is highly desirable. Low frequency induction heating has been introduced as potential basis of a cost-effective, rapid production method for polymer microfluidic device sealing in preceding publications. Through this technique excellent bond strength was achieved, withstanding an air-pressure of up to 590 kPa. However, it has been found that during the bonding process it is important to effectively manage the heat dissipation to prevent distortion of the microfluidic platform. The heat affected zone, and the localised melted area, must be controlled to avoid blockage of the microfluidic channels or altering the channels’ wall characteristics. This work presents an analytical approach to address the issues and provide a basis for process optimisation and design rules.

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Low frequency induction heating for the sealing of plastic microfluidic systems

Purpose – Microfluidic or “lab‐on‐a‐chip” technology is seen as a key enabler in the rapidly expanding market for medical point‐of‐care and other kinds of portable diagnostic device. The purpose of this paper is to discuss two proposed packaging processes for large‐scale manufacture of microfluidic systems.Design/methodology/approach – In the first packaging process, polymer overmoulding of a microfluidic chip is used to form a fluidic manifold integrated with the device in a single step. The anticipated advantages of the proposed method of packaging are ease of assembly and low part count. The second process involves the use of low‐frequency induction heating (LFIH) for the sealing of polymer microfluidics. The method requires no chamber, and provides fast and selective heating to the interface to be joined.Findings – Initial work with glass microfluidics demonstrates feasibility for overmoulding through two separate sealing principles. One uses the overmould as a physical support structure and providing...

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Productionisation issues for commercialisation of microfluidic based devices

Microfluidic systems are being used in more and more areas and the demand for such systems is growing every day. Hence, a cheap and rapid method for sealing these microfluidic platforms which can be used for mass manufacture is needed. In this paper low frequency induction heating (LFIH) is presented as technique for the packaging of polymer based microfluidic systems. Thin metal layers serving as susceptors are introduced between a stack of polymer slides and heated inductively. The generated heat melts the surrounding polymer and creates a bond. Preliminary work reported here has demonstrated such bonds are able to withstand a pressure of up to 590 kPa, that both ferro- and paramagnetic susceptors are suitable for the bonding process, and that even small metal features can be rapidly heated to a temperature of 200 °C. In addition simulations and validating experiments have been carried out to understand control of the heat dissipation in the workpiece.

Plastic Packaging Using Low Frequency Induction Heating (LFIH) For Microsystems

Microfluidic systems are being used in more and more areas and the demand for such systems is growing every day. Hence, a cheap and rapid method for sealing these microfluidic platforms which can be used for mass manufacture is needed. In this paper low frequency induction heating (LFIH) is presented as technique for the packaging of polymer based microfluidic systems. Thin metal layers serving as susceptors are introduced between a stack of polymer slides and heated inductively. The generated heat melts the surrounding polymer and creates a bond. Preliminary work reported here has demonstrated such bonds are able to withstand a pressure of up to 590 kPa, that both ferro- and paramagnetic susceptors are suitable for the bonding process, and that even small metal features can be rapidly heated to a temperature of 200 °C.

Packaging of polymer based microfluidic systems using low frequency induction heating (LFIH)

Microfluidic systems are being used in many applications and the demand for such systems has been phenomenal in past decades. To meet such high volume market needs, a cheap and rapid method for sealing these microfluidic platforms which is viable for mass manufacture is highly desirable. The packaging must protect the system against dirt, humidity, stresses, etc and, depending on the application, provide electrical, fluidic or optical interconnection and thermal management. Most of the existing sealing and interconnecting techniques are cost-intensive and slow compared to the other manufacturing steps of the microfluidic system, so that they form a bottleneck in mass production. Low frequency induction heating (LFIH) has been introduced as potential basis of a cost-effective, rapid production method for polymer microfluidic device sealing in preceding publications. Induction heating is well established in the steel industry for hardening, melting, soldering, welding, and annealing, but increasingly is finding application in other areas like heating fillings in dental medicine, and cap sealing. Through this technique excellent bond strength was achieved, withstanding an air-pressure of up to 590 kPa. However, it has been found that during the bonding process it is important to effectively manage the heat dissipation to prevent distortion of the microfluidic platform. The heat affected zone, and the localised melted area, must be controlled to avoid blockage of the microfluidic channels or altering the channels' wall characteristics. This work sums up the results of experiments, simulations and analytical approaches to provide a basis for process optimisation. The effects of susceptor area and bond parameters like bond pressure and heating time on the heating rate are discussed. Heat affected zone and bond strength of pulse heated samples are compared to those of continuously heated systems and rules for susceptor design are provided. Based on the knowledge gained a microfluidic device is designed and manufactured.

Benedikt J. Knauf

Papers

Low frequency induction heating for the sealing of plastic microfluidic systems

Productionisation issues for commercialisation of microfluidic based devices

Plastic Packaging Using Low Frequency Induction Heating (LFIH) For Microsystems

Packaging of polymer based microfluidic systems using low frequency induction heating (LFIH)

Polymer bonding by induction heating for microfluidic applications