Using Micromachined Molds, Partial-curing PDMS Bonding Technique, and Multiple Casting to Create Hybrid Microfluidic Chip for Microlens Array

Research on Integrated 3D Printing of Microfluidic Chips

Microfluidic chips have the advantages of miniaturization, integration, and portability, and are widely used in the early diagnosis of major diseases, personalized medical treatment, environmental detection, health quarantine, and other fields. The existing microfluidic chip manufacturing process is difficult to operate because of complex three-dimensional channels, complicated manufacturing steps, limited printing materials, the difficulty of operating the bonding process, and the need to purchase expensive new equipment. In this paper, an integrated molding method for microfluidic chips that integrates 3D printing and polymer dissolution technology is proposed. First, the channel mold of poly(vinyl alcohol) (PVA) or high impact polystyrene (HIPS) is dissolved to complete the manufacturing of the microfluidic chip channel. The integrated 3D-forming method of microfluidic chips proposed in this paper can manufacture microchannels inside the microfluidic chip, avoid the bonding process, and eliminate the need for rapid alignment of microchannels, material modification, and other operations, thus improving the stability of the process. Finally, by comparing the microchannels made by PVA and HIPS, it is concluded that the quality of the microchannels made by HIPS is obviously better than that made by PVA. This paper provides a new idea for the fabrication of microfluidic chips and the application of HIPS.

3D OPC method for controlling the morphology of micro structures in laser direct writing

A 3D optical proximity correction (OPC) method for controlling the morphology of micro-structures in laser direct writing is proposed, considering both the optical proximity effect and nonlinear response of a thick-film photoresist. This method can improve the manufacturability and optical performance of devices, and can be used for most 3D micro\nano structures. Its application in the fabrication of a quadratic curvature microlens array shows that the shape of the lens is well controlled; that is, when the height of the lens is 5.25 µm, the average height error of the lens shape is less than 5.22%.

Study of PDMS Microchannels for Liquid Crystalline Optofluidic Devices in Waveguiding Photonic Systems

Microchannels in LC:PDMS structures must be of good quality and suitable geometry to achieve the desired orientation of the liquid crystalline molecules inside. When applying a casting technique, with the molds obtained even by the most accurate method, i.e., photolithography, it is still crucial to inspect the cross-section of the structure and the surface roughness of the PDMS material. This paper presents a study of PDMS microchannels using a Scanning Electron Microscope (SEM) to make such a characterization as accurate as possible. By comparing images of the samples taken using standard polarized light microscopy and SEM, it is likely to understand the mechanism of the liquid crystal molecular orientation occurring in the samples. The results obtained in this work may be used for numerical simulations and further development of LC:PDMS structures.

A Systematic Approach for Developing 3D High-Quality PDMS Microfluidic Chips Based on Micromilling Technology

In recent years, there has been an increased interest in exploring the potential of micro-and mesoscale milling technologies for developing cost-effective microfluidic systems with high design flexibility and a rapid microfabrication process that does not require a cleanroom. Nevertheless, the number of current studies aiming to fully understand and establish the benefits of this technique in developing high-quality microsystems with simple integrability is still limited. In the first part of this study, we define a systematic and adaptable strategy for developing high-quality poly(methyl methacrylate) (PMMA)-based micromilled structures. A case study of the average surface roughness (Ra) minimization of a cuboid column is presented to better illustrate some of the developed strategies. In this example, the Ra of a cuboid column was reduced from 1.68 μm to 0.223 μm by implementing milling optimization and postprocessing steps. In the second part of this paper, new strategies for developing a 3D microsystem were introduced by using a specifically designed negative PMMA master mold for polydimethylsiloxane (PDMS) double-casting prototyping. The reported results in this study demonstrate the robustness of the proposed approach for developing microfluidic structures with high surface quality and structural integrability in a reasonable amount of time.

Development of intensified flat-plate packed-bed solar reactors for heterogeneous photocatalysis

Solar-driven photocatalysis is a promising water-cleaning and energy-producing technology that addresses some of the most urgent engineering problems of the twenty-first century: universal access to potable water, use of renewable energy, and mitigation of CO₂ emissions. In this work, we aim at improving the efficiency of solar-driven photocatalysis by studying a novel reactor design based on microfluidic principles using 3D-printable geometries. The printed reactors had a dimensional accuracy of 97%, at a cost of less than $1 per piece. They were packed with 1.0-mm glass and steel beads coated with ZnO synthesised by a sol-gel routine, resulting in a bed with 46.6% void fraction (reaction volume of ca. 840 μL and equivalent flow diameter of 580 μm) and a specific surface area of 3200 m² m^-3. Photocatalytic experiments, under sunlight-level UV-A irradiation, showed that reactors packed with steel supports had apparent reaction rates ca. 75% higher than those packed with glass supports for the degradation of an aqueous solution of acetaminophen; however, they were strongly deactivated after the first use suggesting poor fixation. Glass supports showed no measurable deactivation after three consecutive uses. The apparent first-order reaction rate constants were between 1.9 and 9.5 × 10^-4 s^-1, ca. ten times faster than observed for conventional slurry reactors. The mass transfer was shown to be efficient (Sh > 7.7) despite the catalyst being immobilised onto fixed substrates. Finally, the proposed reactor design has the merit of a straightforward scaling out by sizing the irradiation window according to design specifications, as exemplified in the paper.

Polymer Microchannel and Micromold Surface Polishing for Rapid, Low-Quantity Polydimethylsiloxane and Thermoplastic Microfluidic Device Fabrication

Polymer-based micromolding has been proposed as an alternative to SU-8 micromolding for microfluidic chip fabrication. However, surface defects such as milling marks may result in rough microchannels and micromolds, limiting microfluidic device performance. Therefore, we use chemical and mechanical methods for polishing polymer microchannels and micromolds. In addition, we evaluated their performance in terms of removing the machining (milling) marks on polymer microchannel and micromold surfaces. For chemical polishing, we use solvent evaporation to polish the sample surfaces. For mechanical polishing, wool felt polishing bits with an abrasive agent were employed to polish the sample surfaces. Chemical polishing reduced surface roughness from 0.38 μm (0 min, after milling) to 0.13 μm after 6 min of evaporation time. Mechanical polishing reduced surface roughness from 0.38 to 0.165 μm (optimal pressing length: 0.3 mm). As polishing causes abrasion, we evaluated sample geometry loss after polishing. Mechanically and chemically polished micromolds had optimal micromold distortion percentages of 1.01% ± 0.76% and 1.10% ± 0.80%, respectively. Compared to chemical polishing, mechanical polishing could better maintain the geometric integrity since it is locally polished by computer numerical control (CNC) miller. Using these surface polishing methods with optimized parameters, polymer micromolds and microchannels can be rapidly produced for polydimethylsiloxane (PDMS) casting and thermoplastic hot embossing. In addition, low-quantity (15 times) polymer microchannel replication is demonstrated in this paper.

Tunable microlens array fabricated by a silicone oil-induced swelled polydimethylsiloxane (PDMS) membrane bonded to a micro-milled microfluidic chip

Microlens arrays (MLAs) nowadays are critical micro-optical components and they can be applied in many application fields, such as optical communication systems and flat panel display modules. This article describes a novel approach to the fabrication of tunable, highly reliable, and uniform polydimethylsiloxane (PDMS) MLAs. A polydimethylsiloxane (PDMS) membrane is bonded to a micro-milled poly(methyl methacrylate) (PMMA) microfluidic chip and exposed to silicone oil of a specific viscosity. Molecules in the oil insert themselves into the molecular structure of the PDMS membrane, causing it to swell and subsequently form dome-shaped MLAs. From our experiments, we derived the following conclusions. First, the homogeneous swelling of the PDMS resulted in MLAs with a high numerical aperture (0.5), high uniformity illumination (CV of the illumination intensity is between 2.5%∼5.1%), and high uniformity (CV of sag height of MLAs is less than 0.05). Second, the shorter molecular chains in low-viscosity oils diffused more readily into the PDMS membrane, which increased the effects on swelling, resulting in MLAs with higher sag height and higher numerical aperture. For example, the 5 cst silicone oil resulted in sag height of 191 µm with NA of 0.50, whereas the 100 cst silicone oil resulted in sag height of 86 µm with numerical aperture of 0.33. Finally, the integrated mixer module enabled the simultaneous tuning of the 7 × 7 MLAs simply by adjusting the injection flow rates of the constituent silicone oils.