Optimized SU-8 processing for low-cost microstructures fabrication without cleanroom facilities

The study and optimization of epoxy-based negative photoresist (SU-8) microstructures through a low-cost process and without the need for cleanroom facility is presented in this paper. It is demonstrated that the Ultraviolet Rays (UV) exposure equipment, commonly used in the Printed Circuit Board (PCB) industry, can replace the more expensive and less available equipment, as the Mask Aligner that has been used in the last 15 years for SU-8 patterning. Moreover, high transparency masks, printed in a photomask, are used, instead of expensive chromium masks. The fabrication of well-defined SU-8 microstructures with aspect ratios more than 20 is successfully demonstrated with those facilities. The viability of using the gray-scale technology in the photomasks for the fabrication of 3D microstructures is also reported. Moreover, SU-8 microstructures for different applications are shown throughout the paper.Work supported by FEDER funds through the Eixo I do Programa Operacional Fatores de Competitividade (POFC) QREN, project reference COMPETE: FCOMP-01-0124-FEDER-020241, and by FCT- Fundação para a Ciência e a Tecnologia, project reference PTDC/EBB-EBI/120334/2010. Vânia C. Pinto thanks the FCT for the SFRH/BD/81526/2011 grant. Paulo J. Sousa thanks the FCT for the SFRH/BD/81562/2011 grant. Vanessa F. Cardoso thanks the FCT for the SFRH/BPD/98109/2013 gran

Embolias gasosas em microcanais e técnica de focagem de fluxo na produção de micropartículas de PDMS

Este projeto de mestrado em Tecnologia Biomédica, de natureza essencialmente experimental, foi desenvolvido no Instituto Politécnico de Bragança (IPB) e na Universidade de Extremadura, Espanha. Foram dois os objetivos principais do trabalho realizado: um consistiu em estudar a formação e o transporte de microbolhas capazes de gerar embolias gasosas, desenvolvido no IPB, outro consistiu na fabricação e estudo do comportamento de micropartículas de polidimetilsiloxano (PDMS), que simulam os glóbulos vermelhos, através de uma técnica desenvolvida na Universidade de Extremadura, designada por focagem de fluxo. Para realizar o escoamento das microbolhas, foram fabricados pelo método de xurografia, microdispositivos de focagem de fluxo. Efetuaram-se escoamentos bifásicos de Dextrano (Dx40) com 2,5% hematócrito (Hct) e ar, a vários caudais. Nestes escoamentos foi possível visualizar a formação de microbolhas na zona de contração do microcanal. Foram analisados vários parâmetros: dimensão das bolhas, distância entre pares de bolhas, índice de deformação, velocidade das bolhas e espessura da camada livre de células em três zonas do microcanal. O estudo das microbolhas ao longo dos vasos sanguíneos, torna-se relevante visto que podem obstruir estes vasos e assim promover a deterioração dos tecidos e, em determinados casos, causar a morte dos mesmos. Na técnica de focagem de fluxo, utilizou-se polidimetilsiloxano (PDMS), glicerina e surfactante Brij 30, o que permitiu a produção de microgotas de PDMS com diâmetros entre os 10 e 11 μm. Após um processo de cura, obtiveram-se micropartículas com diâmetros inferiores, na ordem dos 4,4 μm. Foi analisado o índice de deformação médio das micropartículas em glicerina e Brij 30, e dos glóbulos vermelhos em Dx40, num canal com uma contração hiperbólica. Este trabalho possibilitou, pela primeira vez, a produção de micropartículas com diâmetros próximos dos glóbulos vermelhos (GVs).Estas micropartículas podem vir a ser utilizadas na produção de fluidos análogos ao sangue, simulando os GVs. Os fluidos análogos ao sangue são cada vez mais relevantes nos estudos in vitro. A utilização destes fluidos permite ultrapassar questões de natureza ética e de segurança.This master's project in Biomedical Technology, was developed at the Polytechnic Institute of Bragança (IPB) and at the University of Extremadura, Spain. This research work has two main objectives: to study the formation and transport of microbubbles capable of generating air embolism (work performed in IPB) and to fabricate and study the behaviour of microparticles of polydimethylsiloxane (PDMS), which simulate the red blood cells, through a technique developed at the University of Extremadura known as flow focusing. By using the xurography method, microchannels with a flow focusing geometries were fabricated. A two phase fluid flow having Dx40 with 2.5% Hct and air, was tested at various flow rates. At the tested flows it was possible to visualize the formation of microbubbles at the contraction region of the microchannel. In this study, several parameters were analysed such as dimension of the bubbles, the distance between pairs of bubbles, deformation index, velocity of the bubbles and the thickness of the cell free layer in three different zones of microchannel, i. e., contraction, intermediate and expansion zone. The study of microbubbles along the blood vessels, became relevant as it may obstruct the vessels thereby promoting deterioration of the tissues and, in certain cases, cause the death thereof. By means of a flow focusing technique, PDMS, glycerine and surfactant Brij 30 was used to produce PDMS droplets with diameters between 10 and 11 μm. However, after the curing process, microparticles with lower diameters of about 4 μm were obtained. It was also analysed the average deformation index of the microparticles in glycerine and Brij 30, and red blood cells (RBCs) in Dx40, flowing in a microchannel having a hyperbolic contraction. Hence, for the first time. Generated microdroplets had diameters dimensions close to RBCs. These generated microparticles can simulate RBCs and produce blood analogous fluids. The blood analogous fluids are increasingly important in vitro blood studies as the use of these fluids can overcomes both ethical and safety issues

Simple, Cost-Effective Fabrication, and Flow Dynamics Analysis of a Passive Microfluidic Mixer Using 3D Printing and Soft Lithography

Simple and low-cost fabrication of microfluidic devices has attracted considerable attention among researchers. The traditional soft lithography fabrication method requires expensive equipment like a UV exposure system and mask fabrication facility. In this work, an alternative and low-cost UV exposure system was introduced along with an alternative mask fabrication system. A previously reported passive microfluidic mixer was fabricated successfully using this modified soft lithography method. Challenges were presented during this modified fabrication method. Another emerging potential alternative for the fabrication of microfluidic mixers is 3D printing. It was also used in this experiment to fabricate a passive micromixer. This method is well known for rapid prototyping and the creations of complex structures. However, this method has several disadvantages like optical transparency, lower resolution fabrication, difficulties in flow characterization, etc. These problems were addressed, and the solutions were discussed in this work. Comparative analysis between 3D printing and soft lithography fabrication was presented. Flow characterization inside the 3D printed micromixer was carried out using the microparticulate image velocimetry (micro-PIV) system. It explains how the geometrical shape of the micromixer accelerates the natural diffusion process to mix the different fluid streams. Finally, a 3D numerical simulation of the passive micromixer was carried out to visualize the flow dynamics inside the micromixer. The flow pattern found from the numerical simulation and the experimental flow characterization is analogous. These observations could play an important role to design and fabricate cost-effective micromixers for lab-on-a-chip devices

A Passive Microfluidic Device Based on Crossflow Filtration for Cell Separation Measurements: A Spectrophotometric Characterization

Microfluidic devices have been widely used as a valuable research tool for diagnostic applications. Particularly, they have been related to the successful detection of different diseases and conditions by assessing the mechanical properties of red blood cells (RBCs). Detecting deformability changes in the cells and being able to separate those cells may be a key factor in assuring the success of detection of some blood diseases with diagnostic devices. To detect and separate the chemically modified RBCs (mimicking disease-infected RBCs) from healthy RBCs, the present work proposes a microfluidic device comprising a sequence of pillars with different gaps and nine different outlets used to evaluate the efficiency of the device by measuring the optical absorption of the collected samples. This latter measurement technique was tested to distinguish between healthy RBCs and RBCs chemically modified with glutaraldehyde. The present study indicates that it was possible to detect a slight differences between the samples using an optical absorption spectrophotometric setup. Hence, the proposed microfluidic device has the potential to perform in one single step a partial passive separation of RBCs based on their deformability.Research supported by FCT with the reference projects POCI-01-0145-FEDER-016861 (PTDC/QEQ-FTT/4287/2014), NORTE-01-0145-FEDER-029394 (PTDC/EMD-EMD/29394/2017), NORTE-01-0145-FEDER-030171 (PTDC/EME-SIS/30171/2017), UID/EEA/04436/2013, by FEDER funds through the COMPETE 2020, NORTE2020, PORTUGAL2020-Programa Operacional Competitividade e Internacionalizacao (POCI) with the reference project POCI-01-0145-FEDER-006941 and by the NORTE-01-0145-FEDER-028178 (PTDC/EEI-EEE/28178/2017) project, funded 85% from Programa Operacional Regional do Norte and 15% from FCT.info:eu-repo/semantics/publishedVersio

Label-free multi-step microfluidic device for mechanical characterization of blood cells: diabetes type II

The increasing interest to establish significant correlations between blood cell mechanical measurements and blood diseases, has led to the promotion of microfluidic devices as attractive clinical tools for potential use in diagnosis. A multi-step microfluidic device able to separate red and white blood cells (RBCs and WBCs) from plasma and simultaneously measure blood cells deformability (5 and 20% of hematocrit) is presented in this paper. The device employs passive separation based on the cross-flow filtration principle, introduced at each daughter channel. At the outlets, hyperbolic geometries allow single-cell deformability analysis. The device was tested with blood from five healthy and fifteen diabetic type II voluntary donors. The results have shown that WBCs have lower deformability than RBCs, and no significant differences were observed in WBCs from healthy and pathological blood samples. In contrast, RBCs have shown significant differences, with pathological cells exhibiting lower deformability. Shear rheology has shown that blood from patients with type II diabetes has higher viscosity than blood from healthy donors. This microfluidic device has demonstrated the ability to reduce cell concentration at the outlets down to 1%, an ideal cell concentration for assessing the blood cells deformability, under healthy and pathological conditions. The results provide new insights and quantitative information about the hemodynamics of in vitro type II diabetes mellitus RBCs. Thus, such device can be a promising complement in clinical diagnosis and biological research as part of an integrated blood-on-a-chip system.This work was supported by Projects NORTE-01-0145-FEDER-028178, NORTE-01-0145-FEDER-029394, NORTE-01-0145-FEDER-030171 funded by COMPETE2020, NORTE2020, PORTUGAL2020, and FEDER. This work was also supported by Fundacao para a Ciencia e a Tecnologia (FCT) under the strategic grants UIDB/04077/2020 and UIDB/00532/2020. D. Pinho and V. Faustino acknowledge the Ph.D. scholarships SFRH/BD/89077/2012 and SFRH/BD/99696/2014, respectively, both provided by FCT. Susana Catarino thanks FCT for her contract funding provided through 2020.00215.CEECIND. F. T. Pinho is thankful to FCT for financial support through projects LA/P/0045/2020 of the Associate Laboratory in Chemical Engineering (ALiCE) and pro-jects UIDB/00532/2020 and UIDP/00532/2020 of Centro de Estudos de Fenomenos de Transporte

Label-free multi-step microfluidic device for mechanical characterization of blood cells: Diabetes type II

The increasing interest to establish significant correlations between blood cell mechanical measurements and blood diseases, has led to the promotion of microfluidic devices as attractive clinical tools for potential use in diagnosis. A multi-step microfluidic device able to separate red and white blood cells (RBCs and WBCs) from plasma and simultaneously measure blood cells deformability (5 and 20% of hematocrit) is presented in this paper. The device employs passive separation based on the cross-flow filtration principle, introduced at each daughter channel. At the outlets, hyperbolic geometries allow single-cell deformability analysis. The device was tested with blood from five healthy and fifteen diabetic type II voluntary donors. The results have shown that WBCs have lower deformability than RBCs, and no significant differences were observed in WBCs from healthy and pathological blood samples. In contrast, RBCs have shown significant differences, with pathological cells exhibiting lower deformability. Shear rheology has shown that blood from patients with type II diabetes has higher viscosity than blood from healthy donors. This microfluidic device has demonstrated the ability to reduce cell concentration at the outlets down to 1%, an ideal cell concentration for assessing the blood cells deformability, under healthy and pathological conditions. The results provide new insights and quantitative information about the hemodynamics of in vitro type II diabetes mellitus RBCs. Thus, such device can be a promising complement in clinical diagnosis and biological research as part of an integrated blood-on-a-chip system.This work was supported by Projects NORTE-01-0145-FEDER- 028178, NORTE-01-0145-FEDER-029394, NORTE-01-0145-FEDER- 030171 funded by COMPETE2020, NORTE2020, PORTUGAL2020, and FEDER. This work was also supported by Fundação para a Ciência e a Tecnologia (FCT) under the strategic grants UIDB/04077/2020 and UIDB/00532/2020. D. Pinho and V. Faustino acknowledge the Ph.D. scholarships SFRH/BD/89077/2012 and SFRH/BD/99696/2014, respectively, both provided by FCT. Susana Catarino thanks FCT for her contract funding provided through 2020.00215.CEECIND. F. T. Pinho is thankful to FCT for financial support through projects LA/P/0045/2020 of the Associate Laboratory in Chemical Engineering (ALiCE) and projects UIDB/00532/2020 and UIDP/00532/2020 of Centro de Estudos de Fenómenos de Transporte.info:eu-repo/semantics/publishedVersio

Diseño e implementación de un sistema de fotolitografía para fabricar microdispositivos a partir de películas delgadas

Este artículo presenta el diseño e implementación de un sistema de fotolitografía para fabricar microdispositivos basados en películas delgadas. El sistema trabaja con una fuente ultravioleta (UV) de 380nm y permite obtener microestructuras de 10-200 μm. La implementación se hizo con el proceso de diseño y desarrollo de productos, donde se determinó las especificaciones técnicas, generación, selección y prueba de conceptos de los módulos de equipo del sistema. Se implementó un spincoater con rango de operación de 500-6000 rpm y una fuente de radiación UV basada en LEDs UV, con potencia de radiación de 1-20mW/cm2 y tiempo de exposición de 1-60s. Se obtuvo micropuentes (mPs) de 30-105μm sobre películas delgadas de cobre. Con microscopía óptica y procesamiento digital de imágenes, se determinó que el error relativo porcentual en sus áreas es menor al 4% y la variabilidad en sus anchos es menor a dos veces la desviación estándar.This article presents the design and implementation of a photolithography system to manufacture microdevices based on thin films. The system works with ultraviolet (UV) source of 380nm and allows to obtain 10-200 μm microstructures. The implementation was made with the product design and development process, where the technical specifications, generation, selection and proof of concepts of the system equipment modules were determined. A spincoater with an operating range of 500-6000 rpm and UV radiation source, based on LEDs, with ranges in power of 1-20mW/cm2 and time of exposure 1-60s, were implemented. With optical microscopy and digital image processing, it was determined that the percentage relative error in their areas is less than 4% and the variability in their widths is less than two times the standard deviation

Use of SU8 as a stable and biocompatible adhesion layer for gold bioelectrodes.

Gold is the most widely used electrode material for bioelectronic applications due to its high electrical conductivity, good chemical stability and proven biocompatibility. However, it adheres only weakly to widely used substrate materials such as glass and silicon oxide, typically requiring the use of a thin layer of chromium between the substrate and the metal to achieve adequate adhesion. Unfortunately, this approach can reduce biocompatibility relative to pure gold films due to the risk of the underlying layer of chromium becoming exposed. Here we report on an alternative adhesion layer for gold and other metals formed from a thin layer of the negative-tone photoresist SU-8, which we find to be significantly less cytotoxic than chromium, being broadly comparable to bare glass in terms of its biocompatibility. Various treatment protocols for SU-8 were investigated, with a view to attaining high transparency and good mechanical and biochemical stability. Thermal annealing to induce partial cross-linking of the SU-8 film prior to gold deposition, with further annealing after deposition to complete cross-linking, was found to yield the best electrode properties. The optimized glass/SU8-Au electrodes were highly transparent, resilient to delamination, stable in biological culture medium, and exhibited similar biocompatibility to glass

Diseño, fabricación y evaluación de circuitos microfluídicos para el movimiento de bacterias magnetotácticas

[ES] Este trabajo está dirigido hacia el ámbito biomédico, entorno que se centra en buscar nuevos métodos para combatir enfermedades a partir del estudio de aspectos biológicos relacionados con la medicina. El objetivo principal de este TFG es construir sistemas microfluídicos que puedan simular venas y arterias, dotando al equipo investigador de una plataforma para estudiar el comportamiento de las bacterias magnetotácticas (MTB) como bio-robots. La función que tienen estos microorganismos es la de transportar medicamentos y realizar tratamientos de hipertermia en zonas concretas del cuerpo. Se han fabricado tres tipos de microcanales simples, de una recta, con diferentes dimensiones, 1.5, 1 y 0.5 mm de ancho, 3 cm de largo y 100 µm de alto con reservorios de 8 mm de diámetro. Del mismo modo se han creado otros canales más complejos, con mayor dificultad para guiar las bacterias. Estos circuitos han sido creados en polidimetilsiloxano (PDMS), un polímero cada vez más utilizado en este tipo de investigaciones debido a sus propiedades de transparencia y biocompatibilidad. Asimismo, para la elaboración de los canales en PDMS se han utilizado moldes de SU-8 patronados por fotolitografía. A pesar de las dificultades surgidas a lo largo del proceso los resultados obtenidos son buenos. Se ha podido comprobar que es posible la creación de sistemas microfluídicos para el estudio del movimiento de las bacterias magnetotácticas, aunque se puede mejorar y avanzar más en la fabricación de estos dispositivos

Diseño, fabricación y evaluación de circuitos microfluídicos para el movimiento de bacterias magnetotácticas

[ES] Este trabajo está dirigido hacia el ámbito biomédico, entorno que se centra en buscar nuevos métodos para combatir enfermedades a partir del estudio de aspectos biológicos relacionados con la medicina. El objetivo principal de este TFG es construir sistemas microfluídicos que puedan simular venas y arterias, dotando al equipo investigador de una plataforma para estudiar el comportamiento de las bacterias magnetotácticas (MTB) como bio-robots. La función que tienen estos microorganismos es la de transportar medicamentos y realizar tratamientos de hipertermia en zonas concretas del cuerpo. Se han fabricado tres tipos de microcanales simples, de una recta, con diferentes dimensiones, 1.5, 1 y 0.5 mm de ancho, 3 cm de largo y 100 µm de alto con reservorios de 8 mm de diámetro. Del mismo modo se han creado otros canales más complejos, con mayor dificultad para guiar las bacterias. Estos circuitos han sido creados en polidimetilsiloxano (PDMS), un polímero cada vez más utilizado en este tipo de investigaciones debido a sus propiedades de transparencia y biocompatibilidad. Asimismo, para la elaboración de los canales en PDMS se han utilizado moldes de SU-8 patronados por fotolitografía. A pesar de las dificultades surgidas a lo largo del proceso los resultados obtenidos son buenos. Se ha podido comprobar que es posible la creación de sistemas microfluídicos para el estudio del movimiento de las bacterias magnetotácticas, aunque se puede mejorar y avanzar más en la fabricación de estos dispositivos