Microchannel Deformation Research Articles

A numerical study on thermal bonding with preheating technique for polypropylene microfluidic device

Abstract This study presents a method for producing microfluidic chips from polypropylene using a pre-heated bonding area and thermal bonding technology. ANSYS was utilized to investigate the effects of bonding parameters and microchannel deformation and predict the bonding strength. Results show that careful control of these parameters is critical to achieve a strong and durable bond between the microfluidic chip layers. Higher bonding temperatures were found to lead to greater microchannel deformation, with deformation increasing significantly, as the temperature approached the material’s melting point. Increased bonding pressure after 1 MPa and a time of 300 s also led to greater microchannel deformation. The study’s analysis of stresses revealed that the maximum principle compressive stress on the edges of the bonding area increased significantly with pressure. Tensile testing showed that bonding strength was near failure at a tensile force of 5,500 N, indicating a bonding strength close to 1.5 MPa.

Passive control of flow rate change due to the input pressure fluctuation based on microchannel deformation

Precise and controlled drug delivery is crucial in continuous infusion systems used for drug treatment, anesthesia, cancer chemotherapy, and pain management. Elastometric pumps are commonly utilized in continuous infusion systems for their ease of use and cost-effectiveness. However, the infusion accuracy is often compromised due to the fluctuating supply pressure of elastomeric pumps, requiring an additional flow regulator to stabilize the output flow rate. We, here, present a novel approach to passively control a flow rate even under the fluctuating pressure environment based on a channel deformation. The flow rate control is enabled by a flow regulator consisting of an open-end microchannel, a closed-end microchannel, and a flexible membrane in the middle. The pressure within an open-end microchannel decreases in the downstream direction, while the pressure within a closed-end microchannel remains equal to the input pressure, creating the pressure difference between the two channels. The membrane deforms in response to this pressure difference, allowing for adjustment of the output flow rate by decreasing the flow path area with the increase in the input pressure. It is found that this concept successfully works by maintaining a steady output flow rate over a target pressure range of 40–50 kPa. Fluid–structure interaction numerical simulations and theoretical analysis are used to explain the flow rate control mechanism of the device. The results show that the present approach offers a promising solution for achieving stable drug delivery in continuous drug infusion systems, addressing the limitations of conventional elastomeric pumps.

Deformation patterns and coordination mechanisms of cross-size microchannels during thermocompression bonding process

High-quality bonding of microfluidic chips is essential for driving the rapid marketization of microfluidic devices. While thermocompression bonding is known for its simplicity, challenges such as high deformation and low bond strength persist. In this paper, we conducted micro-scale compression creep experiments to address the coexistence problem between low deformation and high bond strength during the thermocompression bonding process. Accurate creep models were constructed based on the experimental results, achieving an improved simulation accuracy of 95% for microchannel deformation in thermocompression bonding. Additionally, a finite element simulation model was developed to simulate microchannel deformation during the thermocompression process. To enhance bond strength and minimize microchannel deformation, we propose two methods: microchannel height compensation and cross-size microchannel coordination. Results demonstrate a remarkable 200% improvement in bond strength with reduced microchannel deformation under the same bonding conditions. The findings of this study offer valuable insights and serve as a process reference and design basis for enhancing the quality of microfluidic chip products.

Highly dynamic tempered in-mold thermocompression bonding of microfluidic chips: process characteristics and bonding performances

Thermoplastic microfluidic chips show broad development prospects in biomedicine, point-of-care testing, healthcare, environmental monitoring, etc. However, improving the production efficiency of microfluidic chips remains a key industrial challenge to promote rapid popularization. In this work, we proposed a novel method for rapid and mass production of microfluidic chips based on a highly dynamic tempered in-mold thermocompression bonding (HD-IMTCB) process. The bonding temperature was tuned by a highly dynamic local variotherm technology based on thick film heaters. The results show that bonding temperature was the most significant factor for the bonding strength, and bonding time was the lowest one, which can be primarily optimized. With the bonding temperature reaching Vicat Softening Temperature and Glass Transition Temperature, the micro-channel deformation and bonding strength increased exponentially successively. The stable bonding strength reached 560–640 kPa with a microchannel deformation of less than 15%. The well-bonded thermoplastic microfluidic chips have been manufactured by the HD-IMTCB process from raw materials within 5 min, which not only improves the thermocompression bonding from a low-scale to a high-scale production model but also provides a blueprint for commercialization.

Effect of manufacturing deviations on the thermohydraulic performance of printed circuit heat exchangers with zigzag channels

• The etching-induced deformations have subtle effects on thermo-hydraulics; • The bonding-induced deformations is closely related to PCHE thickness; • An estimation model for bonding-induced deformation is proposed and validated; • The semicircular microchannel deformation mechanism is proposed and validated. A printed circuit heat exchanger (PCHE) is an essential component of the supercritical carbon dioxide Brayton cycle ( sCO 2 -BC ), but the effect of manufacturing deviations of PCHEs on thermohydraulic performance is seldom reported. To quantitatively analyse the etching-induced and bonding-induced deformations, 19 test plates/blocks are manufactured for measurement. Numerical simulations are performed to investigate the effects of these geometric deformations. The results indicate that the influences of etching-induced deformations are relatively small, the effect of the channel cross-section shape is more significant than the zigzag angle, and the longitudinal pitch is the weakest contributor. For the oval-shaped channel, the channel width plays a leading role in influencing the heat transfer, while the pressure drop is affected more severely by the channel depth. The channels tend to be narrower and shallower after diffusion bonding, and the bonding-induced channel cross-section deformation can cause large deviations in thermal-hydraulic characteristics, especially for those with thin blocks and few layers. Based on the measurement data, an estimation model for the relative deviation of the channel hydraulic diameter after bonding is proposed for the present manufacturing process.

Investigation of Solvent-Assisted In-Mold Bonding of Cyclic Olefin Copolymer (COC) Microfluidic Chips.

The bonding of microfluidic chips is an essential process to enclose microchannels or microchambers in a lab-on-a-chip. In order to improve the bonding quality while reducing the fabrication time, a solvent-assisted bonding strategy was proposed to seal the microchannels immediately after the cover sheet and substrate chip was injection molded in a single mold. Proper organic solvents were selected and the influences of solvent ratios on the surface roughness, microchannel morphology, and contact angle of microfluidic chips were investigated. When the solvent bonding was integrated in the mold, the influences of solvent volume fraction, solvent dosage, bonding pressure, and bonding time on the bonding quality were analyzed. Results show that the solvent cyclohexane needs to be mixed with isopropanol to reduce the dissolution effect. Solvent treatment is suggested to be performed on the cover sheet with a cyclohexane volume fraction of 70% and a dose of 1.5 mL, a bonding pressure of 2 MPa, and a bonding time of 240 s. The bonding strength reaches 913 kPa with the optimized parameters, while the microchannel deformation was controlled below 8%.

Study aspect ratio of microchannel on different polymer substrates with CO2 laser and hot bonding for microfluidic chip

The paper demonstrates four different polymer substrates including Polymethyl-methacrylate (PMMA), Polycarbonate (PC), Polystyene (PS) and Polyethylene Terephthalate (PET) for fabricating microfluidic chips using CO2 laser and hot bonding machine. The experimental methods are very simple and convenient. The work aims to obtain combination of optimal polymer for hot bonding through comparing the influence of different polymer cover plates on aspect ratio of different polymer microchannels at the same hot bonding parameters. There are three microchannels in each polymer substrate. And three microchannels are processed at three different laser parameters. The hot bonding parameters include bonding temperature of 95°C, pressure of 1Mpa for time of 9min. The results show PS cover plate with the basic plate of other substrates is the best due to stability of microfluidic chip and the ignored microchannel deformation. Next, a fluid mixing experiment in microfluidic chip with PMMA basic plate and PS cover plate is successfully performed. The microchannel in PMMA is processed with laser speed of 10mm/s, laser power of 12W, distance between the sheet surface and the lens of 7.5mm.

Uncovering the Contribution of Microchannel Deformation to Impedance-Based Flow Rate Measurements

Changes in electrical impedance have previously been used to measure fluid flow rate in microfluidic channels. Ionic redistribution within the electrical double layer by fluid flow has been considered to be the primary mechanism underlying such impedance based microflow sensors. Here we describe a previously unappreciated contribution of microchannel deformation to such measurements. We found that flow-induced microchannel deformation contributes significantly to the change in electrical impedance of solutions, in particular to those solutions producing an electrical double layer in the order of a few tens of nanometers (i.e., containing relatively high ionic strength). Since the flow velocity at the measurement surface is near zero, due to the laminar nature of the flow, the contribution of the double layer under the conditions mentioned above should be negligible. In contrast, an increase in the fluid flow rate results in an increase in the microchannel cross-sectional area (because of higher local pressure), therefore, producing a decrease in solution resistance between the two electrodes. Our results suggest that microflow sensors based on the concept of elastic deformation could be designed for in situ monitoring and fine control of fluid flow in flexible microfluidics. Finally, we show that purposefully engineering a larger deformability of the microchannel, by changing the geometry and the Young's modulus of the microchannel, enhances the sensitivity of this flow rate measurement.

A process analysis for microchannel deformation and bonding strength by in-mold bonding of microfluidic chips

Abstract A novel combination of thermal bonding and in-mold assembly technology was created to produce microfluidic chips out of polymethylmethacrylate (PMMA), which is named “in-mold bonding technology”. In-mold bonding experiments of microfluidic chips were carried out to investigate the influences of bonding process parameters on the deformation and bonding strength of microchannels. The results show that bonding temperature has the greatest impact on the deformation of microchannels, while bonding pressure and bonding time have more influence on deformation in height than in top width. Considering the bonding strength, the bonding temperature and the bonding pressure have more impact than the bonding time. The time is crucial for the sealing of the chips. By setting the bonding parameters reasonably, the microchannel deformation is <10%, while the bonding strength of the chips is 350 kPa. The production cycle of the chip is reduced to <5 min.

Numerical Simulation of Microchannel Deformation in Enhanced Insulation for Nb–Ti Superconducting Accelerator Magnets

A new insulation scheme for the Nb-Ti superconducting magnets to better extract heat from the coil was proposed in 2007, and several experiments were done to validate this novel concept, including the construction of a large aperture quadrupole. An essential parameter of this scheme is the size of the microchannels provided by a new topology of the insulation wrapping, allowing a direct helium path from the helium bath to the strands. The main question is whether these channels are still open under the large pressures induced during assembly and by electromagnetic forces. In this paper, one shows that a thermal model of the insulation scheme can be used to interpret the experimental data. The model suggests that the microchannels are significantly reduced with respect to their nominal values but are still well open. To validate this result, a finite-element model of the insulation and strands under pressure is done, and the behavior of this complex topology is estimated. The mechanical model confirms that the microchannels are open even under pressures of 100 MPa, with a cross-sectional reduction on the order of 50%. A parametric analysis of the microchannel deformation versus pressure is carried out, showing a good agreement with the experiments.

Rapid bonding enhancement by auxiliary ultrasonic actuation for the fabrication of cyclic olefin copolymer (COC) microfluidic devices

Thermal compression bonding is a straightforward, inexpensive and widely used method for enclosing open microchannels in thermoplastic microfluidic devices. It is advantageous over adhesive, solvent and grafting bonding methods in retaining material homogeneity. However, the trade-off between high bond strength and low microchannel deformation is always a crucial consideration in thermal compression bonding. In this study, an effective method for improving bond strength while retaining the microchannel integrity with negligible distortion is proposed and analyzed. Longitudinal ultrasonic actuation was applied to the preheated cyclic olefin copolymer (COC) substrates to achieve accelerated and enhanced bonding with an ultrasonic welding system. Intimate contact between the bonding surfaces before the ultrasonic actuation was found to be an important prior condition. With improper contact, several bonding defects would occur, such as voids, localized spot melting and edge melting. Under auxiliary ultrasonic vibration, within 10 s, the bond strength developed at the bonding interface could be dramatically improved compared with those achieved without ultrasonic actuation. The enhanced bond strength obtained at a preheating temperature of 20 °C lower than its Tg could be comparable to the strength for pure thermal compression at 5 °C higher than its Tg. It is believed that the ultrasonic energy introduced could elevate the interfacial temperature and facilitate the interdiffusion of molecular chain segments at the interface, consequently resulting in rapidly enhanced bonding. Also, the microchannel distortion after ultrasonic actuation was found to be satisfactory—another important requirement. From dynamic mechanical analysis, the glass transition temperature of COC was found to increase with increasing frequency, and the temperature of the bulk polymer under ultrasonic actuation was still well under Tg; therefore the deformation is minor under ultrasonic actuation.

Soft Tactile Sensor Arrays for Force Feedback in Micromanipulation

This paper describes the design, fabrication, and experimental validation of a soft tactile sensor array for submillimeter contact localization and contact force measurement in micromanipulation. The geometry and placement of conductive liquid microchannels embedded within the elastic sensor body are optimized to provide high sensitivity for representative micromanipulation tasks and to overcome functional limitations seen in previous soft tactile sensor research. Mechanical testing of the numerically optimized sensor prototype demonstrates sensitivity to normal contact forces of and submillimeter contact localization resolution. Tactile sensing experiments demonstrate the ability to infer the abstract geometries and motions of objects imparting force on the sensor surface by analyzing microchannel deformation patterns.

Microchannel Deformation of Polymer Chip in In-Mold Bonding

Abstract Microchannel deformation is a problem which often occurs in the thermal bonding of polymer microfluidic chip, and which is significantly determined by bonding parameters. In this paper, numerical analysis of the microchannel deformation in the process of in-mold bonding polymer chip was conducted, using Young's modulus and shear relaxation modulus of polymethylmethacrylate (PMMA) obtained in creep tests. Adhesion between the top and two lateral walls of microchannel was observed in the results, which can be attributed mainly to the viscoelastic deformation of PMMA. It was also revealed that the maximum percent deformation of microchannel is in height, and that bonding temperature had greater effect on the deformation of microchannel than bonding pressure and bonding time. The deformation of microchannel in simulation were consistent with those of experiment under the optimized parameters of 105 °C, 2 MPa and 240 s.

Deformation properties between fluid and periodic circular obstacles in polydimethylsiloxane microchannels: Experimental and numerical investigations under various conditions

Understanding the mechanical properties of optically transparent polydimethylsiloxane (PDMS) microchannels was essential to the design of polymer-based microdevices. In this experiment, PDMS microchannels were filled with a 100 μM solution of rhodamine 6G dye at very low Reynolds numbers (∼10(-3)). The deformation of PDMS microchannels created by pressure-driven flow was investigated by fluorescence microscopy and quantified the deformation by the linear relationship between dye layer thickness and intensity. A line scan across the channel determined the microchannel deformation at several channel positions. Scaling analysis widely used to justify PDMS bulging approximation was allowed when the applied flow rate was as high as 2.0 μl/min. The three physical parameters (i.e., flow rate, PDMS wall thickness, and mixing ratio) and the design parameter (i.e., channel aspect ratio = channel height/channel width) were considered as critical parameters and provided the different features of pressure distributions within polymer-based microchannel devices. The investigations of the four parameters performed on flexible materials were carried out by comparison of experiment and finite element method (FEM) results. The measured Young's modulus from PDMS tensile test specimens at various circumstances provided reliable results for the finite element method. A thin channel wall, less cross-linker, high flow rate, and low aspect ratio microchannel were inclined to have a significant PDMS bulging. Among them, various mixing ratios related to material property and aspect ratios were one of the significant factors to determine PDMS bulging properties. The measured deformations were larger than the numerical simulation but were within corresponding values predicted by the finite element method in most cases.

Effect of injection-molding-induced residual stress on microchannel deformation irregularity during thermal bonding

Micro injection molding offers a promising approach to rapidly produce thermoplastic microfluidic substrates in large volumes. Many research works have been focused on the replication fidelity of microstructures by injection molding. However, there has not been any investigation on the effect of molded-in residual stress on microchannel deformation during the subsequent thermal bonding process. These effects could be important, because the residual stress developed due to anisotropic polymer flow orientation and inhomogeneous cooling may lead to abnormal microchannel distortion. In the direct thermal bonding process, asymmetric cross-sectional distortion was observed in well-formed microchannels aligned perpendicular to the polymer melt injection direction. This asymmetric distortion is attributed to the residual stress introduced into the substrates during molding, particularly in the surface region where microchannels are molded. Design of experiment on injection molding was carried out to reduce the residual stress in order to achieve the lowest microchannel deformation irregularity, which is a new term defined in this study. The direct thermal bonding was utilized as a feasible non-destructive indirectly quantitative method to evaluate the effect of residual stress around microchannel regarding deformation irregularity. The dominant molding parameters with positive effects were found to be melt temperature, mold temperature as well as cooling time after packing. The presence of the residual stress was also demonstrated through photoelastic stress analysis in terms of phase retardation. With improved molding condition, the absolute retardation difference around microchannels aligned parallel and perpendicular to the molding direction could be tuned to the same level, which indicates that the molded-in residual stresses have been moderated.

Flame aerosol deposition of TiO2 nanoparticle films on polymers and polymeric microfluidic devices for on-chip phosphopeptide enrichment

Direct and fast (10s of seconds) deposition of flame-made, high surface-area aerosol films on polymers and polymeric microfluidic devices is demonstrated. Uniform TiO2 nanoparticle films were deposited on cooled Poly(methyl methacrylate) (PMMA) substrates by combustion of titanium(IV) isopropoxide (TTIP) - xylene solution sprays. Films were mechanically stabilized by in-situ annealing with a xylene spray flame. Plasma-etched microfluidic chromatography columns, comprising parallel microchannels were also coated with such nanoparticle films without any microchannel deformation. These microcolumns were successfully used in metal-oxide affinity chromatography (MOAC) to selectively trap phosphopeptides on these high surface-area nanostructured films. The chips had a high capacity retaining 1.2 μg of standard phosphopeptide. A new extremely fast method is developed for MOAC microchip stationary phase fabrication with applications in proteomics.

Research on Bonding of PMMA Microfluidic Chip with Precisely Controlled Bonding Pressure

Microfluidic chips have a great prospect in the field of biochemical analysis with advantages of fast processes, high flux and low consumption. Molding and bonding are separated by the conventional procedure of hot embossing and bonding, resulting in low automation and long production cycle. In order to reduce cycle time and achieve mass production, this paper proposed In-mold Bonding technology with precisely controlled bonding pressure by injection molding machine’s movement of core-pulling. So simulation analysis for bonding process of PMMA microfluidic chip was carried out using finite element software to study microchannel distortion at different bonding temperature and pressure. The results show that, at a certain bonding pressure, when bonding temperature was lower than glass transition temperature(Tg), microchannel distortion didn’t change significantly, when bonding temperature was higher than Tg, microchannel deformation increases with increasing temperature. Small microchannel distortion was obtained at a temperature of 108°C,which was recommended as the suitable bonding temperature.

The deformation of flexible PDMS microchannels under a pressure driven flow

Poly(dimethylsiloxane) (PDMS) microchannels are commonly used microfluidic structures that have a wide variety of biological testing applications, including the simulation of blood vessels to study the mechanics of vascular disease. In these studies in particular, the deformation of the channel due to the pressure inside is a critical parameter. We describe a method for using fluorescence microscopy to quantify the deformation of such channels under pressure driven flow. Additionally, the relationship between wall thickness and channel deformation is investigated. PDMS microchannels of varying top wall thickness were created using a soft lithography process. A solution of fluorescent dye is pumped through the channels at constant volume flow rates and illuminated. Pressure and fluorescence intensity are measured at five positions along the length of the channel. Fluorescence measurements are then used to determine deformation, using the linear relationship of dye layer thickness and intensity. A linear relationship between pressure and microchannel deformation is measured. Pressure drops and deformations closely correspond to values predicted by the model in most cases. Additionally, measured pressure drops are found to be up to 35% less than the pressure drop in a rigid-walled channel, and channel wall thickness is found to have an increasing effect as the channel wall thickness decreases.