Ultra-low-cost fabrication of polymer-based microfluidic devices with diode laser ablation

Polymeric and Paper-Based Lab-on-a-Chip Devices in Food Safety: A Review

Food quality and safety are important to protect consumers from foodborne illnesses. Currently, laboratory scale analysis, which takes several days to complete, is the main way to ensure the absence of pathogenic microorganisms in a wide range of food products. However, new methods such as PCR, ELISA, or even accelerated plate culture tests have been proposed for the rapid detection of pathogens. Lab-on-chip (LOC) devices and microfluidics are miniaturized devices that can enable faster, easier, and at the point of interest analysis. Nowadays, methods such as PCR are often coupled with microfluidics, providing new LOC devices that can replace or complement the standard methods by offering highly sensitive, fast, and on-site analysis. This review's objective is to present an overview of recent advances in LOCs used for the identification of the most prevalent foodborne and waterborne pathogens that put consumer health at risk. In particular, the paper is organized as follows: first, we discuss the main fabrication methods of microfluidics as well as the most popular materials used, and then we present recent literature examples for LOCs used for the detection of pathogenic bacteria found in water and other food samples. In the final section, we summarize our findings and also provide our point of view on the challenges and opportunities in the field.

Basic Guide to Multilayer Microfluidic Fabrication with Polyimide Tape and Diode Laser

For normal operations, microfluidic devices typically require an external source of pressure to deliver fluid flow through the microchannel. This requirement limits their use for benchtop research activities in a controlled static environment. To exploit the full potential of the miniaturization and portability of microfluidic platforms, passively driven capillary microfluidic devices have been developed to completely remove the need for an external pressure source. Capillary microfluidics can be designed to perform complex tasks by designing individual components of the device. These components, such as the stop valve and trigger valve, operate through changes in microchannel dimensions and aspect ratios. A direct, maskless fabrication protocol that allows the precise fabrication of microchannels and other microfluidic components is introduced here. A diode laser and polyimide tape on a PMMA substrate are the only components needed to start fabrication. By varying the laser power used and the number of laser repetitions, various depths and widths of the microchannel can be quickly created to meet specific needs. As an example of a functional unit, a trigger valve was fabricated and tested, as proof of the validity of the fabrication protocol.

Breaking the clean room barrier: exploring low-cost alternatives for microfluidic devices

Microfluidics is an interdisciplinary field that encompasses both science and engineering, which aims to design and fabricate devices capable of manipulating extremely low volumes of fluids on a microscale level. The central objective of microfluidics is to provide high precision and accuracy while using minimal reagents and equipment. The benefits of this approach include greater control over experimental conditions, faster analysis, and improved experimental reproducibility. Microfluidic devices, also known as labs-on-a-chip (LOCs), have emerged as potential instruments for optimizing operations and decreasing costs in various of industries, including pharmaceutical, medical, food, and cosmetics. However, the high price of conventional prototypes for LOCs devices, generated in clean room facilities, has increased the demand for inexpensive alternatives. Polymers, paper, and hydrogels are some of the materials that can be utilized to create the inexpensive microfluidic devices covered in this article. In addition, we highlighted different manufacturing techniques, such as soft lithography, laser plotting, and 3D printing, that are suitable for creating LOCs. The selection of materials and fabrication techniques will depend on the specific requirements and applications of each individual LOC. This article aims to provide a comprehensive overview of the numerous alternatives for the development of low-cost LOCs to service industries such as pharmaceuticals, chemicals, food, and biomedicine.

Diode Laser and Polyimide Tape Enables Cheap and Fast Fabrication of Flexible Microfluidic Sensing Devices

Wearable devices are a new class of healthcare monitoring devices designed for use in close contact with the patient's body. Such devices must be flexible to follow the contours of human anatomy. With numerous potential applications, a wide variety of flexible wearable devices have been created, taking various forms and functions. Therefore, different fabrication techniques and materials are employed, resulting in fragmentation of the list of equipment and materials needed to make different devices. This study attempted to simplify and streamline the fabrication process of all key components, including microfluidic chip and flexible electrode units. A combination of diode laser CNC machine and polyimide tape is used to fabricate flexible microfluidic chip and laser-induced graphene (LIG) electrodes, to create flexible microfluidic sensing devices. Laser ablation on polyimide tape can directly create microfluidic features on either PDMS substrates or LIG electrodes. The two components can be assembled to form a flexible microfluidic sensing device that can perform basic electrochemical analysis and conform to curved surfaces while undergoing microfluidic flow. This study has shown that simple, commonly available equipment and materials can be used to fabricate flexible microfluidic sensing devices quickly and easily, which is highly suitable for rapid prototyping of wearable devices.

Merits and advances of microfluidics in the pharmaceutical field: design technologies and future prospects

Microfluidics is used to manipulate fluid flow in micro-channels to fabricate drug delivery vesicles in a uniform tunable size. Thanks to their designs, microfluidic technology provides an alternative and versatile platform over traditional formulation methods of nanoparticles. Understanding the factors that affect the formulation of nanoparticles can guide the proper selection of microfluidic design and the operating parameters aiming at producing nanoparticles with reproducible properties. This review introduces the microfluidic systems' continuous flow (single-phase) and segmented flow (multiphase) and their different mixing parameters and mechanisms. Furthermore, microfluidic approaches for efficient production of nanoparticles as surface modification, anti-fouling, and post-microfluidic treatment are summarized. The review sheds light on the used microfluidic systems and operation parameters applied to prepare and fine-tune nanoparticles like lipid, poly(lactic-co-glycolic acid) (PLGA)-based nanoparticles as well as cross-linked nanoparticles. The approaches for scale-up production using microfluidics for clinical or industrial use are also highlighted. Furthermore, the use of microfluidics in preparing novel micro/nanofluidic drug delivery systems is presented. In conclusion, the characteristic vital features of microfluidics offer the ability to develop precise and efficient drug delivery nanoparticles.

Fabrication of Polymer Microfluidics: An Overview

Microfluidic platform technology has presented a new strategy to detect and analyze analytes and biological entities thanks to its reduced dimensions, which results in lower reagent consumption, fast reaction, multiplex, simplified procedure, and high portability. In addition, various forces, such as hydrodynamic force, electrokinetic force, and acoustic force, become available to manipulate particles to be focused and aligned, sorted, trapped, patterned, etc. To fabricate microfluidic chips, silicon was the first to be used as a substrate material because its processing is highly correlated to semiconductor fabrication techniques. Nevertheless, other materials, such as glass, polymers, ceramics, and metals, were also adopted during the emergence of microfluidics. Among numerous applications of microfluidics, where repeated short-time monitoring and one-time usage at an affordable price is required, polymer microfluidics has stood out to fulfill demand by making good use of its variety in material properties and processing techniques. In this paper, the primary fabrication techniques for polymer microfluidics were reviewed and classified into two categories, e.g., mold-based and non-mold-based approaches. For the mold-based approaches, micro-embossing, micro-injection molding, and casting were discussed. As for the non-mold-based approaches, CNC micromachining, laser micromachining, and 3D printing were discussed. This review provides researchers and the general audience with an overview of the fabrication techniques of polymer microfluidic devices, which could serve as a reference when one embarks on studies in this field and deals with polymer microfluidics.

CO2 laser fabrication of hydrogel-based open-channel microfluidic devices

This study proposed a rapid and low-cost fabrication method for open-channel hydrogel-based microfluidic devices using CO₂ laser ablation. The agarose hydrogel substrate was prepared with agarose gelation in DI water upon microwave heating, then a commercial CO₂ laser system was used for the direct laser ablation of microchannels on the surface of agarose hydrogel substrate, the hydrophilic nature of the microchannels fabricated on hydrogel substrate enables the self-driven of the liquid inside the microchannels with capillary force. The profiles of the laser ablated microchannels on agarose hydrogel substrate with various laser power and scan speed were studied in detail. Due to the loss of water when exposed to the atmosphere, significant deformation of the fabricated microchannels was observed, and the profile change was recorded for 48 h for comparison. An easy-to-access storage method of hydrogel-based microfluidic device in DI water was also proposed in this study. Unlike compact silicon or polymer-based microfluidic devices, the hydrogel is formed by cross-linked polymer chains filled with water, for a better understanding of the diffusion of small molecules into the bulk hydrogel material during fluid propagation inside the microchannel, the Nile red fluorescent was added into the liquid and the diffusion across the hydrogel-based microchannels with time was measured and discussed in this study. Several open-channel agarose hydrogel-based microfluidic devices were fabricated in this study for the demonstration of the proposed fabrication method. The CO₂ laser ablation approach for agarose hydrogel-based microfluidic devices has the advantages of rapid processing time, low-cost, highly biocompatible, and self-driven without pumps and could have wide application potentials in biological and medical fields.

Toward Developing Immunocompetent Diabetic Foot Ulcer-on-a-Chip Models for Drug Testing

Bioengineering of skin has been significantly explored, ranging from the use of traditional cell culture systems to the most recent organ-on-a-chip (OoC) technology that permits skin modeling on physiological scales among other benefits. This article presents key considerations for developing physiologically relevant immunocompetent diabetic foot ulcer (DFU) models. Diabetic foot ulceration affects hundreds of millions of individuals globally, especially the elderly, and constitutes a major socioeconomic burden. When DFUs are not treated and managed in a timely manner, 15-50% of patients tend to undergo partial or complete amputation of the affected limb. Consequently, at least 40% of such patients die within 5 years postamputation. Currently, therapeutic strategies are actively sought and developed. However, present-day preclinical platforms (animals and in vitro models) are not robust enough to provide reliable data for clinical trials. Insights from published works on immunocompetent skin-on-a-chip models and bioengineering considerations, presented in this article, can inform researchers on how to develop robust OoC models for testing topical therapies such as growth factor-based therapies for DFUs. We propose that immunocompetent DFU-on-a-chip models should be bioengineered using diseased cells derived from individuals; in particular, the pathophysiological contribution of macrophages in diabetic wound healing, along with the typical fibroblasts and keratinocytes, needs to be recapitulated. The ideal model should consist of the following components: diseased cells embedded in reproducible scaffolds, which permit endogenous "diseased" extracellular matrix deposition, and the integration of the derived immunocompetent DFU model onto a microfluidic platform. The proposed DFU platforms will eventually facilitate reliable and robust drug testing of wound healing therapeutics, coupled with reduced clinical trial failure rates. Impact statement Current animal and cell-based systems are not physiologically relevant enough to retrieve reliable results for clinical translation of diabetic foot ulcer (DFU) therapies. Organ-on-a-chip (OoC) technology offers desirable features that could finally enable the vision of modeling DFU for pathophysiological studies and drug testing at a microscale. This article brings together the significant recent findings relevant to developing a minimally functional immunocompetent DFU-on-a-chip model, as wound healing cannot occur without a proper functioning immune response. It looks feasible in the future to recapitulate the stagnant inflammation in DFU (thought to impede wound healing) using OoC, diseased cells, and an endogenously produced extracellular matrix.