Development of Microfluidic Dilution Network-Based System for Lab-on-a-Chip Microalgal Bioassays

Microfluidic chemostatic bioreactor for high-throughput screening and sustainable co-harvesting of biomass and biodiesel in microalgae

As a renewable and sustainable source for energy, environment, and biomedical applications, microalgae and microalgal biodiesel have attracted great attention. However, their applications are confined due to the cost-efficiency of microalgal mass production. One-step strategy and continuous culturing systems could be solutions. However, current studies for optimization throughout microalgae-based biofuel production pipelines are generally derived from the batch culture process. Better tools are needed to study algal growth kinetics in continuous systems. A microfluidic chemostatic bioreactor was presented here, providing low-bioadhesive cultivations for algae in a cooperative environment of gas, nutrition, and temperature (GNT) involved with high throughput. The chip was used to mimic the continuous culture environment of bioreactors. It allowed simultaneously studying of 8 × 8 different chemostatic conditions on algal growth and oil production in parallel on a 7 × 7 cm2 footprint. On-chip experiments of batch and continuous cultures of Chlorella. sp. were performed to study growth and lipid accumulation under different nitrogen concentrations. The results demonstrated that microalgal cultures can be regulated to grow and accumulate lipids concurrently, thus enhancing lipid productivity in one step. The developed on-chip culturing condition screening, which was more suitable for continuous bioreactor, was achieved at a half shorter time, 64-times higher throughput, and less reagent consumption. It could be used to establish chemostat cultures in continuous bioreactors which can dramatically accelerate the development of renewable and sustainable algal for CO2 fixation and biosynthesis and related systems for advanced sustainable energy, food, pharmacy, and agriculture with enormous social and ecological benefits.

Field-portable seawater toxicity monitoring platform using lens-free shadow imaging technology

The accidental spill of hazardous and noxious substances (HNSs) in the ocean has serious environmental and human health consequences. Assessing the ecotoxicity of seawater exposed to various HNS is challenging due to the constant development of new HNS or mixtures, and assessment methods are also limited. Microalgae viability tests are often used among the various biological indicators for ecotoxicity testing, as they are the primary producers in aquatic ecosystems. However, since the conventional cell growth rate test measures cell viability over three to four days using manual inspection under a conventional optical microscope, it is labor- and time-intensive and prone to subjective errors. In this study, we propose a rapid and automated method to evaluate seawater ecotoxicity by quantification of the morphological changes of microalgae exposed to more than 30 HNSs. This method was further validated using conventional growth rate test results. Dunaliella tertiolecta, a microalgae species without rigid cell walls, was selected as the test organism. Its morphological changes in response to HNS exposure were measured at the single cell level using a custom-developed device that uses lens-free shadow imaging technology. The ecotoxicity evaluation induced by the morphological change could be available in as little as 5 min using the proposed method and device, and it could be effective for 20 HNSs out of 30 HNSs tested. Moreover, the test results of six selected HNSs with high marine transport volume and toxicity revealed that the sensitivity of the proposed method extends to half the maximum effective concentration (EC50) and even to the lowest observed effective concentration (LOEC). Furthermore, the average correlation index between the growth inhibition test (three to four days) and the proposed morphology changes test (5 min) for the six selected HNSs was 0.84, indicating great promise in the field of various point-of-care water quality monitoring. Thus, the proposed equipment and technology may provide a viable alternative to traditional on-site toxicity testing, and the potential of rapid morphological analysis may replace traditional growth inhibition testing.

Construction and Manipulation of Serial Gradient Dilution Array on a Microfluidic Slipchip for Screening and Characterizing Inhibitors against Human Pancreatic Lipase

Obesity is one of the foremost public health concerns. Human pancreatic lipase (hPL), a crucial digestive enzyme responsible for the digestion of dietary lipids in humans, has been validated as an important therapeutic target for preventing and treating obesity. The serial dilution technique is commonly used to generate solutions with different concentrations and can be easily modified for drug screening. Conventional serial gradient dilution is often performed with tedious multiple manual pipetting steps, where it is difficult to precisely control fluidic volumes at low microliter levels. Herein, we presented a microfluidic SlipChip that enabled formation and manipulation of serial dilution array in an instrument-free manner. With simple slipping steps, the compound solution could be diluted to seven gradients with the dilution ratio of 1:1 and co-incubated with the enzyme (hPL)-substrate system for screening the anti-hPL potentials. To ensure complete mixing of solution and diluent during continuous dilution, we established a numerical simulation model and conducted an ink mixing experiment to determine the mixing time. Furthermore, we also demonstrated the serial dilution ability of the proposed SlipChip using standard fluorescent dye. As a proof of concept, we tested this microfluidic SlipChip using one marketed anti-obesity drug (Orlistat) and two natural products (1,2,3,4,6-penta-O-galloyl-β-D-glucopyranose (PGG) and sciadopitysin) with anti-hPL potentials. The IC₅₀ values of these agents were calculated as 11.69 nM, 8.22 nM and 0.80 μM, for Orlistat, PGG and sciadopitysin, respectively, which were consistent with the results obtained by conventional biochemical assay.

The Impact of Metal-Based Nanoparticles Produced by Different Types of Underwater Welding on Marine Microalgae

Underwater wet welding is commonly used in joining pipelines and in underwater construction. Harmful and hazardous compounds are added to many flux-cored wires for underwater welding and cutting, and can have a negative impact on marine life. The specific objective of this study was to evaluate the aquatic toxicity of two suspension samples obtained using welding electrode and flux-cored wire in marine microalgae Attheya ussuriensis and Porphyridium purpureum. Growth rate inhibition, cell size, and biochemical changes in microalgae were evaluated by flow cytometry. The results of the bioassay demonstrated that the suspension obtained after welding with electrode had an acute toxic impact on diatomic microalgae A. ussuriensis, and both tested suspensions revealed chronic toxicity in this microalga with a 40% growth rate inhibition after exposure to 40-50% of prepared suspensions for 7 days. Red algae P. purpureum revealed tolerance to both suspensions caused by exopolysaccharide covering, which prevents the toxic impact of metal cations such as Al, Ti, Mn, Fe, and Zn, which are considered the main toxic components of underwater welding emissions.

Bioresource Upgrade for Sustainable Energy, Environment, and Biomedicine

We conceptualize bioresource upgrade for sustainable energy, environment, and biomedicine with a focus on circular economy, sustainability, and carbon neutrality using high availability and low utilization biomass (HALUB). We acme energy-efficient technologies for sustainable energy and material recovery and applications. The technologies of thermochemical conversion (TC), biochemical conversion (BC), electrochemical conversion (EC), and photochemical conversion (PTC) are summarized for HALUB. Microalgal biomass could contribute to a biofuel HHV of 35.72 MJ Kg-1 and total benefit of 749 $/ton biomass via TC. Specific surface area of biochar reached 3000 m2 g-1 via pyrolytic carbonization of waste bean dregs. Lignocellulosic biomass can be effectively converted into bio-stimulants and biofertilizers via BC with a high conversion efficiency of more than 90%. Besides, lignocellulosic biomass can contribute to a current density of 672 mA m-2 via EC. Bioresource can be 100% selectively synthesized via electrocatalysis through EC and PTC. Machine learning, techno-economic analysis, and life cycle analysis are essential to various upgrading approaches of HALUB. Sustainable biomaterials, sustainable living materials and technologies for biomedical and multifunctional applications like nano-catalysis, microfluidic and micro/nanomotors beyond are also highlighted. New techniques and systems for the complete conversion and utilization of HALUB for new energy and materials are further discussed.

Generation of Dynamic Concentration Profile Using A Microfluidic Device Integrating Pneumatic Microvalves

Generating and maintaining the concentration dilutions of diffusible molecules in microchannels is critical for high-throughput chemical and biological analysis. Conventional serial network microfluidic technologies can generate high orders of arbitrary concentrations by a predefined microchannel network. However, a previous design requires a large occupancy area and is unable to dynamically generate different profiles in the same chip, limiting its applications. This study developed a microfluidic device enabling dynamic variations of both the concentration in the same channel and the concentration distribution in multiple channels by adjusting the flow resistance using programmable pneumatic microvalves. The key component (the pneumatic microvalve) allowed dynamic adjustment of the concentration profile but occupied a tiny space. Additionally, a Matlab program was developed to calculate the flow rates and flow resistance of various sections of the device, which provided theoretical guidance for dimension design. In silico investigations were conducted to evaluate the microvalve deformation with widths from 100 to 300 µm and membrane thicknesses of 20 and 30 µm under the activation pressures between 0 and 2000 mbar. The flow resistance of the deformed valve was studied both numerically and experimentally and an empirical model for valve flow resistance with the form of Rh=aebP was proposed. Afterward, the fluid flow in the valve region was characterized using Micro PIV to further demonstrate the adjustment mechanism of the flow resistance. Then, the herringbone structures were employed for fast mixing to allow both quick variation of concentration and minor space usage of the channel network. Finally, an empirical formula-supported computational program was developed to provide the activation pressures required for the specific concentration profile. Both linear (Ck = -0.2k + 1) and nonlinear (Ck = (110)k) concentration distribution in four channels were varied using the same device by adjusting microvalves. The device demonstrated the capability to control the concentration profile dynamically in a small space, offering superior application potentials in analytical chemistry, drug screening, and cell biology research.

Complete experimental and theoretical characterization of nonlinear concentration gradient generator microfluidic device for analytical purposes

Microfluidic devices that generate stable concentration gradients are efficient instruments for automated calibration for analytical and bioanalytical systems. However, little attention has been paid to the development of reusable microfluidic concentration gradient generators, which can be useful for a range of species through mathematical characterization. In this work, we develop a microfluidic device based on three steps of serial dilution that were able to generate nonlinear concentration gradient for dyes and biomolecules. The microfluidic device was described mathematically, statistically and was suitable for reusable analytical and bioanalytical analysis. The device reproducibility was assessed by experimental tests, which have shown the same gradient concentration profile for different dyes and statistical reproducibility with 95% confidence interval for bovine serum albumin (BSA). Moreover, the experimental data converged well with those  obtained by computational fluid dynamics simulation. Applicability was verified by coupling the microfluidic device to a surface plasmon resonance (SPR) biosensor, based on nanohole arrays with sensitivity of 358.7 nm RIU^-1 determined by white-light SPR excitation exposed to different D-(+)-glucose aqueous solutions with 1.3361-1.4035 refractive index interval. The transmission light intensities obtained by the array of images allowed to quantify a pseudo-unknown BSA sample (160 µg mL^-1) at 138 µg mL^-1. The SPR analysis has been validated in parallel by fluorescence emissions, which showed a concentration of 154.8 ± 16.6 µg mL^-1.

Integrating Engineering, Automation, and Intelligence to Catalyze the Biomedical Translation of Organoids

Organoid technology has developed at an impressive speed during the past decade. Still, organoids are not widely used in practical applications as expected. It is believed that this translation can be greatly accelerated with the integration of engineering and artificial intelligence into current research practices. It is proposed that this approach is the missing link to realize key milestones in organoid technology, namely, high-throughput, homogeneous, and standardized production, automated manipulation, and intelligent monitoring, evaluation, and control via integrated on-chip instrumentation and artificial intelligence. It is suggested that organoids-on-a-chip are the ideal platform to achieve these feats. Once these techniques are established and adopted by the scientific community, the rapid translation of organoids may be seen from laboratories to the clinics and pharmaceutical industry.

Aquatic toxicity of particulate matter emitted by five electroplating processes in two marine microalgae species

Electroplating is a widely used group of industrial processes that make a metal coating on a solid substrate. Our previous research studied the concentrations, characteristics, and chemical composition of nano- and microparticles emitted during different electroplating processes. The objective of this study was to evaluate the environmental toxicity of particulate matter obtained from five different electrochemical processes. We collected airborne particle samples formed during aluminum cleaning, aluminum etching, chemical degreasing, nonferrous metals etching, and nickel plating. The toxicity of the particles was evaluated by the standard microalgae growth rate inhibition test. Additionally, we evaluated membrane potential and cell size changes in the microalgae H. akashiwo and P. purpureum exposed to the obtained suspensions of electroplating particles. The findings of this research demonstrate that the aquatic toxicity of electroplating emissions significantly varies between different industrial processes and mostly depends on particle chemical composition and solubility rather than the number of insoluble particles. The sample from an aluminum cleaning workshop was significantly more toxic for both microalgae species compared to the other samples and demonstrated dose and time-dependent toxicity. The samples obtained during chemical degreasing and nonferrous metals etching processes induced depolarization of microalgal cell membranes, demonstrated the potential of chronic toxicity, and stimulated the growth rate of microalgae after 72 h of exposure. Moreover, the sample from a nonferrous metals etching workshop revealed hormetic dose-response toxicity in H. akashiwo, which can lead to harmful algal blooms in the environment.

Nonlinear microfluidics: device physics, functions, and applications

The microfluidic flow is typically laminar due to the dominant viscous effects. At Reynolds numbers far below 1 (Re ≪ 1), the fluid inertia can be neglected. For the steady flow of incompressible Newtonian fluids, it approaches linear Stokes flow. At intermediate Re, there exists a weak-inertia flow regime where secondary flows such as Dean vortices are accessible for microfluidic manipulations. Apart from the fluid inertia, other nonlinear factors such as the non-Newtonian fluid properties, concurrent flow of dissimilar fluids, compliant fluidic structures and stimuli-responsive materials can also cause intriguing flow behaviours. Through proper designs, they can be applied for a variety of microfluidic components including mixers, valves, oscillators, stabilizers and auto-regulators etc., greatly enriching the microfluidic flow control and manipulation strategies. Due to its unique working characteristics and advantages, nonlinear microfluidics has increasingly attracted extensive attention. This review presents a systematic survey on this subject. The designs of typical nonlinear microfluidic devices, their working mechanisms, key applications, and the perspective of their future developments will be discussed. The nonlinear microfluidic techniques are believed to play an essential role in the next generation of highly-integrated, automated, and intelligent microfluidics.

Microfluidics for microalgal biotechnology

Microalgae have expanded their roles as renewable and sustainable feedstocks for biofuel, smart nutrition, biopharmaceutical, cosmeceutical, biosensing, and space technologies. They accumulate valuable biochemical compounds from protein, carbohydrate, and lipid groups, including pigments and carotenoids. Microalgal biomass, which can be adopted for multivalorization under biorefinery settings, allows not only the production of various biofuels but also other value-added biotechnological products. However, state-of-the-art technologies are required to optimize yield, quality, and the economical aspects of both upstream and downstream processes. As such, the need to use microfluidic-based devices for both fundamental research and industrial applications of microalgae, arises due to their microscale sizes and dilute cultures. Microfluidics-based devices are superior to their competitors through their ability to perform multiple functions such as sorting and analyzing small amounts of samples (nanoliter to picoliter) with higher sensitivities. Here, we review emerging applications of microfluidic technologies on microalgal processes in cell sorting, cultivation, harvesting, and applications in biofuels, biosensing, drug delivery, and nutrition.

Microenvironment-Controlled Micropatterned Microfluidic Model (MMMM) for Biomimetic In Situ Studies

Attachment of trophozoites to the intestine is an indispensable step for Giardia's survival and pathogenicity in almost 280 million infections worldwide each year. However, the analysis of the attachment mechanism is difficult due to the lack of methods that can create a favorable microaerobic atmosphere. Herein, we developed an osmotic-pressure, pH, excretion, nutrition, gas, ionic-strength, flow-rate, and temperature microenvironment-controlled micropatterned microfluidic model to simulate the in vivo microenvironment to study in situ the stress applied to Giardia in the intestinal tract. We designed three nonbiological surfaces with stagger arrangement manners and integrated them with a resistance microfluidic network to split Giardia-attaching forces ingeniously and developed the term "attaching contribution rate" (ACR) to describe their corresponding contributions. Our study shows that the total attaching force measured is 49.58 Pa, with three components being 22.66 Pa (suction force), 12.52 Pa (clutching force), and 14.4 Pa (combined electrostatic and van der Waals force), respectively, with ACRs being 46%, 25%, and 29%, respectively. By decomposing the attaching force and analyzing each force component and their structure and composition basis, whole profiles of the attachment mechanisms were revealed. Our method enables the analysis of the surface attachment mechanisms and their ACRs for Giardia.

Toxicity assessment of particulate matter emitted from different types of vehicles on marine microalgae

Air pollution caused by vehicle emissions remains a serious environmental threat in urban areas. Sedimentation of atmospheric aerosols, surface wash, drainage water, and urbane wastewater can bring vehicle particle emissions into the aquatic environment. However, the level of toxicity and mode of toxic action for this kind of particles are not fully understood. Here we explored the aquatic toxic effects of particulate matter emitted from different types of vehicles on marine microalgae Porphyridium purpureum and Heterosigma akashiwo. We used flow cytometry to evaluate growth rate inhibition, changes in the level of esterase activity, changes in membrane potential and size changes of microalgae cells under the influence of particulate matter emitted by motorcycles, cars and specialized vehicles with different types of engines and powered by different types of fuel. Both microalgae species were highly influenced by the particles emitted by diesel-powered vehicles. These particle samples had the highest impact on survival, esterase activity, and membrane potential of microalgae and caused the most significant increase in microalgae cell size compared to the particles produced by gasoline-powered vehicles. The results of the algae-bioassay strongly correlate with the data of laser granulometry analyses, which indicate that the most toxic samples had a significantly higher percentage of particles in the size range less than 1 μm. Visual observation with an optical microscope showed intensive agglomeration of the particles emitted by diesel-powered vehicles with microalgae cells. Moreover, within the scope of this research, we did not observe the direct influence of metal content in the particles to the level of their aquatic toxicity, and we can conclude that physical damage is the most probable mechanism of toxicity for vehicle emitted particles.

Biotechnological Advances in the Design of Algae-Based Biosensors

In addition to their use in biomass production and bioremediation, algae have been extensively exploited in biosensing applications. Algae-based biosensors have demonstrated potential for sensitive, sustainable, and multiplexed detection of analytes of agroenvironmental and security interest. Their advantages include the availability of different algal bioreceptors including whole cells and their photosynthetic subcomponents, their potential to be integrated into dual transduction miniaturized devices, and the opportunity for continuous environmental monitoring. Despite obstacles including limited stability and selectivity, algae-based biosensing is a realistic prospect that has some recent effective applications. Strategic exploitation of cutting-edge technologies including materials science, nanotechnology, microfluidics, and genome editing will help to achieve the full potential of algae-based sensors.