Biology subjects

Akhtar, M. U.

Publications and source records attributed to Akhtar, M. U..

4 recordsLinked to original sources

bioRxiv2026

Stop-Flow Lithography Using Hydrodynamic Flow Resistance Regulation and Hydraulic Compliance Minimization for Size-Tunable Anisotropic Multilayered Microparticles Fabrication

Stop-flow lithography (SFL) enables the fabrication of microparticles with designed geometries and material compositions, but its performance relies on rapid flow stopping, which remains particularly challenging in multi-inlet systems with high hydrodynamic flow resistance and hydraulic compliance. Here, we develop a pneumatic-controlled SFL platform with a framework based on flow resistance regulation and hydraulic compliance minimization for fabricating size-tunable anisotropic multilayered microparticles. Our analysis indicates that flow-stopping behavior is governed by the release of extra fluid volume stored in the system due to hydraulic compliance, which arises from the deformation of microfluidic components and the compressibility of the fluid within them. Through numerical modeling and analysis, we identify deformation in the PDMS inlet port region as the dominant contributor to the stored extra fluid volume. By regulating the flow resistance of the tubing relative to that of the outlet channel, the stored extra fluid volume can be preferentially released forward through the outlet or backward through the inlet tubing, enabling rapid flow stopping across configurations with 500, 250, and 100 m outlets. Furthermore, by supporting the PDMS membrane beneath the inlet region with a rigid glass substrate and reducing its dimensions, the hydraulic compliance and consequently the stored extra fluid volume are significantly reduced. With these strategies, microparticles with well-defined boundaries can be fabricated at short, flow-stopping, delay times, and the flow profiles obtained in multi-inlet systems can be preserved during flow stopping and transferred into particle patterns.

bioengineering↗

bioRxiv2026

Lab on a Capillary: Instrument-Free Compartmentalization Using Photopatterned Hydrogel Rings Embedded inside a Glass Capillary for Amplified Bioassays

Sensitive and low-cost protein biomarker detection is critical for disease diagnosis. Advanced microfluidic systems can generate miniature reaction compartments for a high-sensitivity assay. However, these platforms often require external instruments, skilled operators, and complex setups. Here, we develop a Lab on a Capillary (LabCap) platform that integrates photopatterned hydrogel rings within a glass capillary using a reconfigurable stop-flow lithography system. During sample loading and unloading steps, nanoliter-scale aqueous droplets (torodrops) are spontaneously formed around the hydrogel rings, creating isolated reaction compartments without the need for external instruments or an immiscible oil phase. The LabCap platform enables quantitative detection of clinically relevant biomarkers, including C-reactive protein (CRP) and N-terminal pro-B-type natriuretic peptide (NT-proBNP). By adjusting the incubation protocol, assay speed and sensitivity can be tuned to meet different analytical requirements. A periodic medium exchange protocol enables biomarker detection at concentrations as low as 1 ng/mL, whereas prolonged static incubation extends detection to 0.1 ng/mL. In addition, LabCap offers practical advantages, including low fabrication cost (<{euro}1 per device), low reagent consumption (<100 L per assay step), and minimal wash-buffer usage (1 mL). These results demonstrate that LabCap is a simple, cost-effective, and versatile platform for biomarker detection.

bioengineering↗

bioRxiv2025

3D Hydrodynamic Flow Lithography

Continuous- and stop-flow lithography has been widely used for the fabrication of ingenious multi-dimensional microstructures, including fibers and microparticles. The flow profile of multiple co-flowing streams during the process, as one of the dimensions, dictates the cross-sectional morphology of the microstructures. Here, we introduce a three-dimensional hydrodynamic flow lithography (3D HFL) approach that enables rapid and programmable generation of desired flow profiles and their conversion into solid microstructures. By strategically combining multiple flow sculpting strategies, including variable inlet configurations, intra-channel pillar configurations, and outlet configurations, we achieved precise and versatile control over flow sculpting, as validated by computational fluid dynamics simulations and experimental production of microparticles and fibers, offering unparalleled design flexibility. Importantly, the flow sculpting device is fabricated using low-cost 3D-printed molds to cast PDMS channels with precisely aligned inlets and complex geometries that are difficult or impossible to achieve using conventional soft lithography. Our 3D HFL approach effectively overcomes the limitations of existing microfabrication techniques in device complexity, structural diversity, multi-material integration, and production throughput. Furthermore, we demonstrated the capability of this platform to produce anisotropic multi-material microparticles and fibers tailored for specific applications, such as amphiphilic particles for uniform microdroplet capture, biocompatible patterned hydrogels for controlled cell adhesion, and dual-layer fibers for temperature sensing. The simplicity of device fabrication, combined with the broad design flexibility, establishes this platform as a scalable, high-throughput, and versatile solution for engineering anisotropic microparticles and fibers with tailored functionalities, providing powerful tools for a wide range of downstream fields.

bioengineering↗

bioRxiv2023

Fabrication of size-coded amphiphilic particles with a configurable 3D-printed microfluidic device for the formation of particle-templated droplets

Compartmentalizing an aqueous media into numerous nanoliter-scale droplets has substantially improved the performance of amplification assays. Particle-templated droplets or dropicles offer a user-friendly workflow for creating uniform volume compartments upon simple mixing of reagents and particles by using common laboratory apparatus. Amphiphilic shape-coded particles have been demonstrated to spontaneously hold aqueous droplets within hydrophilic cavities for multiplexed diagnostic assays. Here, we have proposed a configurable 3D-printed microfluidic device for the tunable fabrication of amphiphilic size-coded particles. The device was configured with multiple outlet tubings of different diameters and photomasks of variable slit lengths to fabricate a wide range of size-coded particles. We have fabricated >10 unique particle codes using a single reconfigurable device. The cross-sectional profile of the particles was further engineered by tuning the flow rate ratios of precursor streams to vary the inner and outer diameters of the particles and the thicknesses of the inner hydrophilic and outer hydrophobic layers. A range of cavity diameters and particle lengths enabled dropicle volumes of [~]1nL to [~]30nL. The fabricated particles were characterized by their ability to hold uniform droplet volumes and to orient themselves facing upwards or sideways in a well plate based on their aspect ratios.

bioengineering↗