Laser Inscription of Microfluidic Devices for Biological Assays

Formation of a Controllable Diffusion Barrier Layer on the Surface of Polydimethylsiloxane Films by Infrared Laser Irradiation

Developing a diffusion barrier layer on material interfaces has potential applications in various fields such as in packaging materials, pharmaceuticals, chemical filtration, microelectronics, and medical devices. Although numerous physical and chemical methods have been proposed to generate the diffusion barrier layer, the complexity of fabrication techniques and the high manufacturing costs limit their practical utility. Here, we propose an innovative approach to fabricate the diffusion barrier layer by irradiating poly(dimethylsiloxane) (PDMS) with a mid-infrared (λ = 10.6 μm) CO2 laser. This process directly creates a diffusion barrier layer on the PDMS surface by forming a heavily cross-linked network in the polymer matrix. The optimal irradiation conditions were investigated by modulating the defocusing distance, laser power, and number of scanning passes. The barrier thickness can reach up to 70 μm as observed by the scanning electron microscope (SEM). The attenuated total reflectance (ATR), electron dispersive X-ray (EDX), and X-ray photoelectron spectroscopy (XPS) analyses collectively confirmed the formation of the SiOx structure on the modified surface based on the decreased methyl group signal and the increased oxygen/silicon ratio. The diffusion test with the model drugs (rhodamine B and donepezil) demonstrated that the modified surface exhibits effective diffusion barrier properties and the rate of drug diffusion through the modified barrier layer can be controlled by the optimization of the irradiation parameters. This novel approach provides the possibility to develop a controllable diffusion barrier layer in a biocompatible polymer with prospective applications in the fields of pharmaceuticals, packing materials, and medical devices.

Microfluidic Gradient Culture Arrays for Cell Pro-oxidation Analysis Using Bipolar Electrochemiluminescence

A microfluidic gradient array is a widely used screening and analysis device, which has characteristics of high efficiency, high automation, and low consumption. Bipolar electrode electrochemiluminescence (BPE-ECL) has special value in microfluidic array chips. The combination of the microfluidic gradient and BPE arrays has potential for high-throughput screening. In this article, a microfluidic BPE array chip for gradient culture and conditional screening of cancer cells was designed. The generation of concentration gradients, continuous culture of cancer cells with high throughput, and drug screening through BPE-ECL of the Ru(bpy)₃²⁺/TPrA system can be performed in one chip. We tested gradient pro-oxidation of MCF-7 by ascorbic acid and the synergistic effect of pro-oxidation on doxorubicin. The method achieves high analysis efficiency through a BPE array while simplifying the tedious procedures required by cell culture methods.

Microfluidic Systems with Embedded Cell Culture Chambers for High-Throughput Biological Assays

The ability to generate chemical and mechanical gradients on chips is important for either creating biomimetic designs or enabling high-throughput assays. However, there is still a significant knowledge gap in the generation of mechanical and chemical gradients in a single device. In this study, we developed gradient-generating microfluidic circuits with integrated microchambers to allow cell culture and to introduce chemical and mechanical gradients to cultured cells. A chemical gradient is generated across the microchambers, exposing cells to a uniform concentration of drugs. The embedded microchamber also produces a mechanical gradient in the form of varied shear stresses induced upon cells among different chambers as well as within the same chamber. Cells seeded within the chambers remain viable and show a normal morphology throughout the culture time. To validate the effect of different drug concentrations and shear stresses, doxorubicin is flowed into chambers seeded with skin cancer cells at different flow rates (from 0 to 0.2 μL/min). The experimental results show that increasing doxorubicin concentration (from 0 to 30 μg/mL) within chambers not only prohibits cell growth but also induces cell death. In addition, the increased shear stress (0.005 Pa) at high flow rates poses a synergistic effect on cell viability by inducing cell damage and detachment. Moreover, the ability of the device to seed cells in a 3D microenvironment was also examined and confirmed. Collectively, the study demonstrates the potential of microchamber-embedded microfluidic gradient generators in 3D cell culture and high-throughput drug screening.

Laser-Engraved Textiles for Engineering Capillary Flow and Application in Microfluidics

Steering capillary flow in textiles is of great significance in developing affordable and portable microfluidics devices. However, owing to the complex fibrous network, it remains a great challenge to achieve capillary flows with precise filling fronts. Here, an in situ laser engraving route is reported to accurately and rapidly etch textiles for manipulating capillary flow. The heterogeneity of the textile structure is enhanced because of the directional spreading of molten fibers polymer under the control of surface energy minimization. The principle of achieved anisotropic wicking of a water droplet in laser-engraved textiles is proposed. This understanding enables patterning the filling front of a fluid in different shapes, including arrow, straight line, diamond, and annulus. Precise capillary flow in textile-based microfluidics can benefit application in many fields, such as chemical analysis, biological detection, materials synthesis, multiliquid delivery. The laser engraving strategy has the advantages of simplicity, full scalability, and time rapidity, which provides an efficient avenue to steer capillary flow in diverse textiles for manufacturing customized microfluidic devices.

Air Plasma-Enhanced Covalent Functionalization of Poly(methyl methacrylate): High-Throughput Protein Immobilization for Miniaturized Bioassays

Miniaturized systems, such as integrated microarray and microfluidic devices, are constantly being developed to satisfy the growing demand for sensitive and high-throughput biochemical screening platforms. Owing to its recyclability, and robust mechanical and optical properties, poly(methyl methacrylate) (PMMA) has become the most sought after material for the large-scale fabrication of these platforms. However, the chemical inertness of PMMA entails the use of complex chemical surface treatments for covalent immobilization of proteins. In addition to being hazardous and incompatible for large-scale operations, conventional biofunctionalization strategies pose high risks of compromising the biomolecular conformations, as well as the stability of PMMA. By exploiting radio frequency (RF) air plasma and standard 1-ethyl-3-(3-(dimethylamino)propyl) carbodiimide (EDC) and N-hydroxysuccinimide (NHS) chemistry in tandem, we demonstrate a simple yet scalable PMMA functionalization strategy for covalent immobilization (chemisorption) of proteins, such as green fluorescent protein (GFP), while preserving the structural integrities of the proteins and PMMA. The surface density of chemisorbed GFP is shown to be highly dependent on the air plasma energy, initial GFP concentration, and buffer pH, where a maximum GFP surface density of 4 × 10^-7 mol/m² is obtained, when chemisorbed on EDC-NHS-activated PMMA exposed to 27 kJ of air plasma, at pH 7.4. Furthermore, antibody-binding studies validate the preserved biofunctionality of the chemisorbed GFP molecules. Finally, the coupled air plasma and EDC-NHS PMMA biofunctionalization strategy is used to fabricate microfluidic antibody assay devices to detect clinically significant concentrations of Chlamydia trachomatis specific antibodies. By coupling our scalable and tailored air plasma-enhanced PMMA biofunctionalization strategy with microfluidics, we elucidate the potential of fabricating sensitive, reproducible, and sustainable high-throughput protein screening systems, without the need for harsh chemicals and complex instrumentation.

Highly Flexible, Stretchable, and Tunable Optical Diffusers with Mechanically Switchable Wettability Surfaces

Highly stretchable and super-hydrophobic photonics provides a new geometric degree of freedom for photonic system design and self-cleaning applications. Here, we describe the design and experimental realization of mechanically stretchable and tunable photonic diffusers. These intrinsically designed diffusers (based on periodic arrays of cylindrical lenslets and microtip) were made directly on elastomer material using laser ablation. The dimensions of both the tips and the lenslet arrays play a critical role in the distribution of illumination and wettability resistance. By stretching the diffusers mechanically along the lenslet arrays, diffusion angle tuning was achieved and also a reversible change between hydrophilic to super-hydrophobic states. These multifunctional diffusers constitute an important step toward integration with flexible materials or devices such as stretchable organic light-emitting diodes and polymer light-emitting diodes.