Structural Attacks and Defenses for Flow-Based Microfluidic Biochips.

Flow-based microfluidic biochips (FMBs) have seen rapid commercialization and deployment in recent years for point-of-care and clinical diagnostics. However, the outsourcing of FMB design and manufacturing makes them susceptible to susceptible to malicious physical level and intellectual property (IP)-theft attacks. This work demonstrates the first structure-based (SB) attack on representative commercial FMBs. The SB attacks maliciously decrease the heights of the FMB reaction chambers to produce false-negative results. We validate this attack experimentally using fluorescence microscopy, which showed a high correlation ( R2 = 0.987) between chamber height and related fluorescence intensity of the DNA amplified by polymerase chain reaction. To detect SB attacks, we adopt two existing deep learning-based anomaly detection algorithms with  âˆ¼ 96% validation accuracy in recognizing such deliberately introduced microstructural anomalies. To safeguard FMBs against intellectual property (IP)-theft, we propose a novel device-level watermarking scheme for FMBs using intensity-height correlation. The countermeasures can be used to proactively safeguard FMBs against SB and IP-theft attacks in the era of global pandemics and personalized medicine.

Biomimetic fracture model of lizard tail autotomy.

Lizard tail autotomy is an antipredator strategy consisting of sturdy attachment at regular times but quick detachment during need. We propose a biomimetic fracture model of lizard tail autotomy using multiscale hierarchical structures. The structures consist of uniformly distributed micropillars with nanoporous tops, which recapitulate the high-density mushroom-shaped microstructures found on the lizard tail's muscle fracture plane. The biomimetic experiments showed adhesion enhancement when combining nanoporous interfacial surfaces with flexible micropillars in tensile and peel modes. The fracture modeling identified micro- and nanostructure-based toughening mechanisms as the critical factor. Under wet conditions, capillarity-assisted energy dissipation pertaining to liquid-filled microgaps and nanopores further increased the adhesion performance. This research presents insights on lizard tail autotomy and provides new biomimetic ideas to solve adhesion problems.

Biomimicking interfacial fracture behavior of lizard tail autotomy with soft microinterlocking structures.

Biological soft interfaces often exhibit complex microscale interlocking geometries to ensure sturdy and flexible connections. If needed, the interlocking can rapidly be released on demand leading to an abrupt decrease of interfacial adhesion. Here, inspired by lizard tail autotomy where such apparently tunable interfacial fracture behavior can be observed, we hypothesized an interlocking mechanism between the tail and body based on the muscle-actuated mushroom-shaped microinterlocks along the fracture planes. To mimic the fracture behavior of the lizard tail, we developed a soft bilayer patch that consisted of a dense array of soft hemispherical microstructures in the upper layer acting as mechanical interlocks with the counter body part. The bottom control layer contained a microchannel that allowed to deflect the upper layer when applying the negative pressure, thus mimicking muscle contraction. In the microinterlocked condition, the biomimetic tail demonstrated a 2.7-fold and a three-fold increase in adhesion strength and toughness, respectively, compared to the pneumatically released microinterlocks. Furthermore, as per the computational analysis, the subsurface microchannel in the control layer enabled augmented adhesion by rendering the interface more compliant as a dissipative matrix, decreasing contact opening and strain energy dissipation by 50%. The contrasting features between the microinterlocked and released cases demonstrated a highly tunable adhesion of our biomimetic soft patch. The potential applications of our study are expected in soft robotics and prosthetics.

Understanding interfacial fracture behavior between microinterlocked soft layers using physics-based cohesive zone modeling.

We examine the underlying fracture mechanics of the human skin dermal-epidermal layer's microinterlocks using a physics-based cohesive zone finite-element model. Using microfabrication techniques, we fabricated highly dense arrays of spherical microstructures of radius ≈50µm without and with undercuts, which occur in an open spherical cavity whose centroid lies below the microstructure surface to create microinterlocks in polydimethylsiloxane layers. From experimental peel tests, we find that the maximum density microinterlocks without and with undercuts enable the respective ≈4-fold and ≈5-fold increase in adhesion strength as compared to the plain layers. Critical visualization of the single microinterlock fracture from the cohesive zone model reveals a contact interaction-based phenomena where the primary propagating crack is arrested and the secondary crack is initiated in the microinterlocked area. Strain energy energetics confirmed significantly lower strain energy dissipation for the microinterlock with the undercut as compared to its nonundercut counterpart. These phenomena are completely absent in a plain interface fracture where the fracture propagates catastrophically without any arrests. These events confirm the difference in the experimental results corroborated by the Cook-Gordon mechanism. The findings from the cohesive zone simulation provide deeper insights into soft microinterlock fracture mechanics that could prominently help in the rational designing of sutureless skin grafts and electronic skin.

Phenotyping of the thrashing forces exerted by partially immobilized C. elegans using elastomeric micropillar arrays.

As a simple model organism, C. elegans plays an important role in gaining insight into the relationship between bodily thrashing forces and biological effects, such as disease and aging, or physical stimuli, like touch and light. Due to their similar length scale, microfluidic chips have been extensively explored for use in various biological studies involving C. elegans. However, a formidable challenge still exists due to the complexity of integrating external stimuli (chemical, mechanical or optical) with free-moving worms and subsequent imaging on the chip. In this report, we use a microfluidic device to partially immobilize a worm, which allows for measurements of the relative changes in the thrashing force under different assay conditions. Using a device adapted to the natural escape-like coiling response of a worm to immobilization, we have quantified the relative changes in the thrashing force during different developmental stages (L1, L3, L4, and young adult) and in response to various glucose concentrations and drug treatment. Our findings showed a loss of thrashing force following the introduction of glucose into a wild type worm culture that could be reversed upon treatment with the type 2 diabetes drug metformin. A morphological study of the actin filament structures in the body wall muscles provided supporting evidence for the force measurement data. Finally, we demonstrated the multiplexing capabilities of our device through recording the thrashing activities of eight worms simultaneously. The multiplexing capabilities and facile imaging available using our device open the door for high-throughput neuromuscular studies using C. elegans.

Rapid Detection and Trapping of Extracellular Vesicles by Electrokinetic Concentration for Liquid Biopsy on Chip.

Exosomes have gained immense importance since their proteomic and genetic contents could potentially be used for disease diagnostics, monitoring of cancer progression, metastasis, and drug efficacy. However, establishing the clinical utility of exosomes has been restricted due to small sizes and high sample loss from extensive sample preparation. Sample loss is particularly critical for body fluids limited in volume and difficult to access, e.g., cerebrospinal fluid. We present a microfluidic technique that locally enhances the concentration of extracellular vesicles extracted from MDA-MB-231 human breast cancer cell lines by using an ion concentration polarization (ICP)-based electrokinetic concentrator. Our design incorporates a trapping mechanism near the conductive polymer membrane; therefore, we can preconcentrate and capture extracellular vesicles simultaneously. Compared with standard fluorescence detection, our method increased the limit of detection (LOD) of extracellular vesicles by two orders of magnitude in 30 min. Our concentrator increased the extracellular vesicle concentration for 5.0 × 107 particles/1 mL (LOD), 5.0 × 108 particles/1 mL, and 5.0 × 108 particles/1 mL by ~100-fold each within 30 min using 45 V. This study demonstrates an alternative platform to simultaneously preconcentrate and capture extracellular vesicles that can be incorporated as part of a liquid biopsy-on-a-chip system for the detection of exosomal biomarkers and analysis of their contents for early cancer diagnosis.

Detecting and Trapping of a Single C. elegans Worm in a Microfluidic Chip for Automated Microplate Dispensing.

Microfluidic devices offer new technical possibilities for a precise manipulation of Caenorhabditis elegans due to the comparable length scale. C. elegans is a small, free-living nematode worm that is a popular model system for genetic, genomic, and high-throughput experimental studies of animal development and neurobiology. In this paper, we demonstrate a microfluidic system in polydimethylsiloxane (PDMS) for dispensing of a single C. elegans worm into a 96-well plate. It consists of two PDMS layers, a flow and a control layer. Using five microfluidic pneumatic valves in the control layer, a single worm is trapped upon optical detection with a pair of optical fibers integrated perpendicular to the constriction channel and then dispensed into a microplate well with a dispensing tip attached to a robotic handling system. Due to its simple design and facile fabrication, we expect that our microfluidic chip can be expanded to a multiplexed dispensation system of C. elegans worms for high-throughput drug screening.