Bioinspired Microfluidic Device by Integrating a Porous Membrane and Heterostructured Nanoporous Particles for Biomolecule Cleaning

Integration of 2D Nanoporous Membranes in Microfluidic Devices

2D material-based membranes have emerged as promising candidates for next-generation separation technology due to their exceptional permeability and selectivity. Integration of these membranes into microfluidic devices has offered significant potential for improving the efficiency, throughput, and precision. However, designing compact and reliable microfluidic devices with membranes has many challenges, including complexities in membrane integration, analyte measurement, and contamination issues. Addressing these challenges is critical for unlocking the full potential of membrane-integrated devices. This paper proposes a systematic procedure for integrating membranes into a microfluidic device by creating a pore in the middle layer. Furthermore, an ion transport experiment is carried out across various stacked graphene and poly carbonate track etch membranes in an Ostemer-based device. The resulting device is capable of facilitating the concurrent measurement, a task that is cumbersome in standard macroscopic diffusion cells. The transparency and compactness of the microfluidic device allowed for the in situ and real-time optical characterization of analytes. The integration of microfluidic devices with 2D nanoporous membranes has enabled the incorporation of several analytical modalities, resulting in a highly versatile platform with numerous applications.

Bioinspired Gradient Covalent Organic Framework Membranes for Ultrafast and Asymmetric Solvent Transport

Gradients play a pivotal role in membrane technologies, e.g., osmotic energy conversion, desalination, biomimetic actuation, selective separation, and more. In these applications, the compositional gradients are of great relevance for successful function implementation, ranging from solvent separation to smart devices; However, the construction of functional gradient in membranes is still challenging both in scale and directions. Inspired by the specific function-related, graded porous structures in glomerular filtration membranes, a general approach for constructing gradient covalent organic framework membranes (GCOMx) applying poly (ionic liquid)s (PILs) as template is reported here. With graded distribution of highly porous covalent organic framework (COF) crystals along the membrane, GCOMx exhibts an unprecedented asymmetric solvent transport when applying different membrane sides as the solvent feed surface during filtration, leading to a much-enhanced flux (10-18 times) of the "large-to-small" pore flow comparing to the reverse direction, verified by hydromechanical theoretical calculations. Upon systematic experiments, GCOMx achieves superior permeance in nonpolar (hexane ≈260.45 LMH bar-1) and polar (methanol ≈175.93 LMH bar-1) solvents, together with narrow molecular weight cut-off (MWCO, 472 g mol-1) and molecular weight retention onset (MWRO, <182 g mol-1). Interestingly, GCOMx shows significant filtration performance in simulated kidney dialysis, revealing great potential of GCOMx in bionic applications.

Dialysis-functionalized microfluidic platform for in situ formation of purified liposomes

Continuous-flow microfluidic devices have been extensively used for producing liposomes due to their high controllability and efficient synthesis processes. However, traditional methods for liposome purification, such as dialysis, gel chromatography, and ultrafiltration, are incompatible with microfluidic devices, which would dramatically restrict the efficiency of liposome synthesis. In this study, we developed a dialysis-functionalized microfluidic platform (DFMP) for in situ formation of purified drug-loaded liposomes. The device was successfully fabricated by using a high-resolution projection micro stereolithography (PμSL) 3D printer. The integrated DFMP consists of a microfluidic mixing unit, a microfluidic dialysis unit, and a dialysis membrane, enabling the liposome preparation and purification in one device. The purified ICG-loaded liposomes prepared by DFMP had a smaller size (264.01±5.34 nm to 173.93±10.71 nm) and a higher encapsulation efficiency (EE) (43.53±0.07% to 46.07±0.67%). In vivo photoacoustic (PA) imaging experiment demonstrated that ICG-loaded liposomes purified with microfluidic dialysis exhibited a stronger penetration and accumulation (2-3 folds) in tumor sites. This work provides a new strategy for one-step production of purified drug-loaded liposomes.

Specific Clearance of Lipopolysaccharide from Blood Based on Peptide Bottlebrush Polymer for Sepsis Therapy

Lipopolysaccharide (LPS) is the primary bacterial toxin that is vital to the pathogenesis and progression of sepsis associated with extremely high morbidity and mortality worldwide. However, specific clearance of LPS from circulating blood is highly challenging because of the structural complexity and its variation between/within bacterial species. Herein, a robust strategy based on phage display screening and hemocompatible peptide bottlebrush polymer design for specific clearance of targeted LPS from circulating blood is proposed. Using LPS extracted from Escherichia coli as an example, a novel peptide (HWKAVNWLKPWT) with high affinity (KD < 1.0 nм), specificity, and neutralization activity (95.9 ± 0.1%) against the targeted LPS is discovered via iterative affinity selection coupled with endotoxin detoxification screening. A hemocompatible bottlebrush polymer bearing the short peptide [poly(PEGMEA-co-PEP-1)] exhibits high LPS selectivity to reduce circulating LPS level from 2.63 ± 0.01 to 0.78 ± 0.05 EU mL-1 in sepsis rabbits via extracorporeal hemoperfusion (LPS clearance ratio > 70%), reversing the LPS-induced leukocytopenia and multiple organ damages significantly. This work provides a universal paradigm for developing a highly selective hemoadsorbent library fully covering the LPS family, which is promising to create a new era of precision medicine in sepsis therapy.

Bio-inspired self-pumping microfluidic device for cleaning of urea using reduced graphene oxide (rGO) modified polymeric nanohybrid membrane

In vitro technology facilitates the replication of in vivo tissues more accurately than conventional cell-based artificial organs, enabling researchers to mimic both the structural and functional characteristics of natural systems. Here, we demonstrate a novel spiral-shaped self-pumping microfluidic device for the cleaning of urea by incorporating reduced graphene oxide (rGO) modified a Polyethersulfone (PES) nanohybrid membrane for efficient filtration capacity. The spiral-shaped microfluidic chip is a two-layer configuration of polymethyl methacrylate (PMMA) integrated with the modified filtration membrane. In essence, the device replicates the main features of the kidney (Glomerulus), i.e., a nano-porous membrane modified with reduced graphene oxide to separate the sample fluid from the upper layer and collect the biomolecule-free fluid through the bottom of the device. We have achieved a cleaning efficiency of 97.94 ± 0.6 % using this spiral shaped microfluidic system. The spiral-shaped microfluidic device integrated with nanohybrid membrane has potential for organ-on-a-chips applications.

DNA-Polyelectrolyte Composite Responsive Microparticles for Versatile Chemotherapeutics Cleaning

Drug therapy is among the most widely used methods in disease treatment. However, there remains a trade-off problem between drug dosage and toxicity. Blood purification by adsorption of excessive drugs during clinical treatment could be a solution for enhancing therapeutic efficacy while maintaining normal body function. Here, inspired by the intrinsic action mechanism of chemotherapeutic agents in targeting DNA in the cell nucleus, we present DNA-polyelectrolyte composite responsive microparticles for chemotherapeutics cleaning. The presence of DNA in the microparticles enabled the adsorption of multiple common chemotherapy drugs. Moreover, the microparticles are endowed with a porous structure and a photothermal-responsive ability, both of which contribute to improved adsorption by enhancing the contact of the microparticles with the drug solution. On the basis of that, the microparticles are integrated into a herringbone-structured microfluidic chip. The fluid mixing capacity and the enhanced drug cleaning efficiency of the microfluidic platform are validated on-chip. These results indicate the value of the DNA-polyelectrolyte composite responsive microparticles for drug capture and blood purification. We believe the microparticle-integrated microfluidic platform could provide a solution for settling the dosage-toxicity trade-off problems in chemotherapy.

Thermodynamic and Kinetic Modulation of Microfluidic Interfaces by DNA Nanoassembly Mediated Merit-Complementary Heteromultivalency

The multivalent effect is often used to engineer microfluidic affinity interfaces to improve the target separation efficiency. Currently, no design rules exist for thermodynamic and kinetic tuning of properly joining multiple ligands. Herein, we developed a thermodynamic and kinetic modulating strategy of the microfluidic affinity interface via a merit-complementary-heteromultivalent aptamers functionalized DNA nanoassembly. Our strategy is built on the two types of identified aptamers that bind to distinct sites of EpCAM. The aptamer binding of one type is more rapid but less tight, while the other is opposite. By assembling the two types of aptamers together with a tetrahedral DNA framework, we fully exploited these aptamers' merits for tight and rapid recognition of EpCAM, leading to target cell capture with high efficiency and throughput. Our strategy provides a perspective on engineering multivalent recognition molecules through thermodynamic and kinetic tuning.

Rapid Microchip Electrophoretic Separation of Novel Transcriptomic Body Fluid Markers for Forensic Fluid Profiling

Initial screening of criminal evidence often involves serological testing of stains of unknown composition and/or origin discovered at a crime scene to determine the tissue of origin. This testing is presumptive but critical for contextualizing the scene. Here, we describe a microfluidic approach for body fluid profiling via fluorescent electrophoretic separation of a published mRNA panel that provides unparalleled specificity and sensitivity. This centrifugal microfluidic approach expedites and automates the electrophoresis process by allowing for simple, rotationally driven flow and polymer loading through a 5 cm separation channel; with each disc containing three identical domains, multi-sample analysis is possible with a single disc and multi-sample detection per disc. The centrifugal platform enables a series of sequential unit operations (metering, mixing, aliquoting, heating, storage) to execute automated electrophoretic separation. Results show on-disc fluorescent detection and sizing of amplicons to perform comparably with a commercial 'gold standard' benchtop instrument and permitted sensitive, empirical discrimination between five distinct body fluids in less than 10 min. Notably, our microfluidic platform represents a faster, simpler method for separation of a transcriptomic panel to be used for forensically relevant body fluid identification.

Pervaporation-assisted in situ formation of nanoporous microchannels with various material and structural properties

Nanoporous structures are crucial for developing mixed-scale micro-/nanofluidic devices because they facilitate the manipulation of molecule transport along the microfluidic channel networks. Particularly, self-assembled particles have been used for fabricating various nanoporous membranes. However, previous self-assembly mechanisms relied on the material and structural homogeneities of the nanopores. Here, we present a pervaporation-assisted in situ fabrication method that integrates nanoporous membrane structures into microfluidic devices. The microfluidic devices contain a control-channel layer at the top, which induces local and addressable pervaporation, and the main-channel layer, which is present at the bottom with pre-designated locations for nanoporous microchannels; the layers are separated using a gas-permeable film. The target particle suspensions are loaded into the main channels, and their pervaporation is controlled through the gas-permeable film, which successfully assembles the particles at the pre-designated locations. This method yields nanoporous microchannels with various material and structural properties by fabricating heterogeneous nanopore arrays/junctions in series and other diverse structures along the microchannels. We validate the basic working principle of microfluidic devices containing nanoporous microchannels. Furthermore, we theoretically analyze the fundamental experimental results, which suggest the remarkable potential of our strategy to fabricate nanopore networks without using conventional nanofabrication methods.

Controllable Fabrication of Molecularly Imprinted Microspheres with Nanoporous and Multilayered Structure for Dialysate Regeneration

Adsorption of urea from dialysate is essential for wearable artificial kidneys (WRK). Molecularly imprinted microspheres with nanoporous and multilayered structures are prepared based on liquid–liquid phase separation (LLPS), which can selectively adsorb urea. In addition, we combine the microspheres with a designed polydimethylsiloxane (PDMS) chip to propose an efficient urea adsorption platform. In this work, we propose a formulation of LLPS including Tripropylene glycol diacrylate (TPGDA), ethanol, and acrylic acid (30% v/v), to prepare urea molecularly imprinted microspheres in a simple and highly controllable method. These microspheres have urea molecular imprinting sites on the surface and inside, allowing selective adsorption of urea and preservation of other essential constituents. Previous static studies on urea adsorption have not considered the combination between urea adsorbent and WRK. Therefore, we design the platform embedded with urea molecular imprinted microspheres, which can disturb the fluid motion and improve the efficiency of urea adsorption. These advantages enable the urea absorption platform to be highly promising for dialysate regeneration in WRK.

Unusual Nanofractal Microparticles for Rapid Protein Capture and Release

Ion exchange porous microparticles are widely used for protein separation, but their totally porous structure often leads to slow diffusion rate and long separation time. Here unusual nanofractal microparticles synthesized by a strategy of electrostatic interaction regulated emulsion interfacial polymerization are demonstrated that exhibit excellent capability of rapid protein capture, release, and separation. The growth of nanostructures at nanofractal microparticle surface can be controlled by changing electrostatic repulsion between ion groups from weak to strong. The nanofractal microparticles provide a 3D contact model between ion groups and proteins, enable fast protein diffusion rate at initial capture and release stage, and realize rapid and efficient separation of similarly sized proteins as a proof of concept, superior to porous microparticles. This strategy offers an effective and general way for the synthesis of microparticles towards rapid and efficient separation in various fields of biomedicine, environment, and food.

Membrane Fouling Phenomena in Microfluidic Systems: From Technical Challenges to Scientific Opportunities

The almost ubiquitous, though undesired, deposition and accumulation of suspended/dissolved matter on solid surfaces, known as fouling, represents a crucial issue strongly affecting the efficiency and sustainability of micro-scale reactors. Fouling becomes even more detrimental for all the applications that require the use of membrane separation units. As a matter of fact, membrane technology is a key route towards process intensification, having the potential to replace conventional separation procedures, with significant energy savings and reduced environmental impact, in a broad range of applications, from water purification to food and pharmaceutical industries. Despite all the research efforts so far, fouling still represents an unsolved problem. The complex interplay of physical and chemical mechanisms governing its evolution is indeed yet to be fully unraveled and the role played by foulants' properties or operating conditions is an area of active research where microfluidics can play a fundamental role. The aim of this review is to explore fouling through microfluidic systems, assessing the fundamental interactions involved and how microfluidics enables the comprehension of the mechanisms characterizing the process. The main mathematical models describing the fouling stages will also be reviewed and their limitations discussed. Finally, the principal dynamic investigation techniques in which microfluidics represents a key tool will be discussed, analyzing their employment to study fouling.

Aptamer-decorated porous microneedles arrays for extraction and detection of skin interstitial fluid biomarkers

The detection of biomarkers in body fluids plays a great role in the diagnosis, treatment, and prognosis of diseases. Here, we present novel aptamer-decorated porous microneedles (MNs) arrays to realize the extraction and detection of biomarkers in skin interstitial fluid (ISF) in situ. The porous MNs arrays are fabricated by replicating the negative molds comprising glass microspheres with a UV-curable ethoxylated trimethylolpropane triacrylate (ETPTA). As the MNs arrays combine the superiorities of porous structure and aptamers, their specific surface area increased significantly to 6.694 m²/g, thus vast of stable aptamer probes with a concentration of 0.9459 μM could be immobilized. In addition, the MNs arrays could extract skin ISF into their porous structure on the basis of the capillarity principle, and subsequently capture and detect skin ISF biomarkers without sample post-process. Taking advantage of these features, we further demonstrated a highly sensitive and rapid detection of ISF endotoxin in the concentration ranges of 0.0342 EU/mL to 8.2082 EU/mL from rats model injected with endotoxin via tail vein by using such aptamer-decorated porous MNs arrays, with the limit of detection (LOD) of 0.0064 EU/mL. These results indicated that the aptamer-decorated porous MNs arrays possess great potential for non-invasive extraction and detection of biomarkers in clinical applications.

Targeted perfusion adsorption for hyperphosphatemia using mixed matrix microspheres (MMMs) encapsulated NH2-MIL-101(Fe)

Hyperphosphatemia, a common complication of chronic renal failure patients, is described as an excess amount of serum phosphate >4.5 mg dL-1. Current therapy for hyperphosphatemia is limited by low removal efficiency, secondary hyperparathyroidism, uremic bone disease, and the promotion of vascular and visceral calcifications. Metal organic frameworks (MOFs) have aroused great interest in the field of blood purification because of their strong specific adsorption. Herein, we prepared mixed matrix microspheres (MMMs) encapsulated NH2-MIL-101(Fe) with specific adsorption to blood phosphate. Simultaneously, a heparinoid copolymer poly (acrylic acid-sodium 4-vinylbenzenssulfonate) (P(AA-SSNa)) was incorporated to improve the hemocompatibility. The proposed MMMs exhibited excellent phosphate adsorption capacity both in aqueous and human plasma environments. They also showed comprehensive hemocompatibility e.g. low tendency of protein adsorption, low hemolysis rate and extended blood coagulation time. In general, we envision that the MMMs are potentially suitable as highly efficient hemoperfusion adsorbents for hyperphosphatemia treatment.

Pollens derived magnetic porous particles for adsorption of low-density lipoprotein from plasma

Adsorption of low-density lipoprotein from plasma is vital for the treatment of dyslipidemia. Appropriate adsorbent material for efficient and selective adsorption of low-density lipoprotein is highly desired. In this work, we developed pollens-derived magnetic porous particles as adsorbents for this purpose. The natural pollen grains were modified to obtain high surface porosity, a large inner cavity, magnet responsiveness, and specific wettability. The resultant particles exhibited satisfying performance in the adsorption of a series of oils and organic solvents out of water. Besides, the particles were directly utilized to the adsorption of low-density lipoprotein in plasma, which showed high selectivity, and achieved an outstanding adsorption capacity as high as 34.9% within 2 h. Moreover, their salient biocompatibility was demonstrated through simulative hemoperfusion experiments. These features, together with its abundant source and facile fabrication, makes the pollens-derived magnetic porous particles excellent candidate for low-density lipoprotein -apheresis and water treatment applications.

Artificial Leaf for Switchable Droplet Manipulation

Droplet manipulation plays an important role in scientific research, daily life, and practical production such as biological and chemical analysis. Inspired by the structure and function of three typical leaf veins, the bionic texture was replicated by the template method, and the artificial leaf was selectively treated by nanoparticles to obtain a quasi-three-dimensional hybrid superhydrophobic-hydrophilic surface. When the droplet touches the surface of the leaf, it will be attracted to the bottom of the main vein from different directions even in horizontal conditions due to the Laplace pressure gradient and energy gradient. The simulation analysis demonstrates that the reason for directional transportation is the energy gradient of the droplets on the different levels of veins, including the thin veins, lateral veins, and main vein. Meanwhile, the experimental result of water collection also showed an outstanding directional transportation effect and excellent water collection efficiency. In addition, when the sample is tilted upside down, the droplet will flow back to the main vein along the lateral vein and then flow down the main vein, showing a good droplet pumping effect. Therefore, the directional and polydirectional transportation of droplets on the same sample is successfully realized, and the conversion between executing single and multiple tasks simultaneously can be realized only by upright and inverted samples. This work provided a new strategy for directional and polydirectional water manipulation, water collection, directional drainage, and microfluidic devices.

Responsive Hydrogel Microcarrier-Integrated Microneedles for Versatile and Controllable Drug Delivery

Stratagems of drug delivery are important for disease treatment and other biomedical areas. In this study, a novel stratagem is presented for versatile and controllable drug delivery by integrating photoresponsive drug delivery microspheres (PDDMs) into pyramid microneedle (MN) arrays. The PDDMs, containing black-phosphorus (BP) and poly (N-isopropylacrylamide) (pNIPAM), are generated by a flexible capillary microfluidic method. Benefiting from the high water content of the pNIPAM hydrogel, various bioactive substances can be loaded and maintain biological activity. Furthermore, due to the near-infrared (NIR) absorption and conversion capabilities of the contained BP, the PDDMs can increase temperature, shrink volume, and release their encapsulated bioactives under the trigger of biocompatible NIR. In addition, as the PDDMs are stuffed into the solid MN arrays of porous ethoxylated trimethylolpropane triacrylate (ETPTA), the composited PDDMs-MNs system has enough mechanical strength to penetrate into the skin and can deliver drugs underneath the skin uniformly. Based on the resultant PDDMs-MNs, it is demonstrated that insulin can be controllably released to adjust blood glucose levels of streptozotocin (STZ)-induced diabetic mice. Thus, it is believed that the PDDMs-MNs can act as an excellent drugs delivery system and will find many practical values in clinical medicine.

Cheerios Effect Inspired Microbubbles as Suspended and Adhered Oral Delivery Systems

Oral drug administration has an important role in medical treatment. Attempts to develop drug microcarriers with desired features for extended duration and improved absorption is highly sought. Herein, inspired by the physical phenomenon of the Cheerios effect, a novel microfluidic electrospray microbubble carrier is presented that can suspend and actively adhere to the stomach for durable oral delivery. Compared with conventional fabrication methods, the present strategy shows stability and controllability of the product. Benefiting from their uniform hollow structure, the resultant microbubbles present the same behavior of the Cheerios and can float in the gastric juice, adhere and remain to the stomach wall, which thus enhance the duration and absorption of the loaded drugs. Based on these, it is demonstrated as a proof of concept that the dexamethasone-loaded hollow microbubbles can be applied to oral administration and remain suspended and adhered to the stomach of murine for more than 1 d, showing good therapeutic effect in treating lupus erythematosus. Thus, it is believed that the microbubbles floating system will find important values in long-term oral administration.

Advances in Micro/Nanoporous Membranes for Biomedical Engineering

Porous membrane materials at the micro/nanoscale have exhibited practical and potential value for extensive biological and medical applications associated with filtration and isolation, cell separation and sorting, micro-arrangement, in-vitro tissue reconstruction, high-throughput manipulation and analysis, and real-time sensing. Herein, an overview of technological development of micro/nanoporous membranes (M/N-PMs) is provided. Various membrane types and the progress documented in membrane fabrication techniques, including the electrochemical-etching, laser-based technology, microcontact printing, electron beam lithography, imprinting, capillary force lithography, spin coating, and microfluidic molding are described. Their key features, achievements, and limitations associated with micro/nanoporous membrane (M/N-PM) preparation are discussed. The recently popularized applications of M/N-PMs in biomedical engineering involving the separation of cells and biomolecules, bioparticle operations, biomimicking, micropatterning, bioassay, and biosensing are explored too. Finally, the challenges that need to be overcome for M/N-PM fabrication and future applications are highlighted.

Hierarchically Molecular Imprinted Porous Particles for Biomimetic Kidney Cleaning

Blood purification by adsorption of excessive biomolecules is vital for maintaining human health. Here, inspired by kidney self-purification, which removes a number of biomolecules with different sizes simultaneously, hierarchical molecular-imprinted inverse opal particles integrated with a herringbone microfluidic chip for efficient biomolecules cleaning are presented. The particle possesses combinative porous structure with both surface and interior imprints for the specific recognition of small molecules and biomacromolecules. Additionally, the presence of the herringbone mixer largely improve the adsorption efficiency due to enhanced mixing. Moreover, the inverse opal framework of the particles give rise to optical sensing ability for self-reporting of the adsorption states. These features, together with its reusability, biosafety, and biocompatibility, make the platform highly promising for clinical blood purification and artificial kidney construction.

Recent Progress of Microfluidic Devices for Hemodialysis

Microfluidic hemodialysis techniques have recently attracted great attention in the treatment of kidney disease due to their advantages of portability and wearability as well as their great potential for replacing clinical hospital-centered blood purification with continuous in-home hemodialysis. This Review summarizes the recent progress in microfluidic devices for hemodialysis. First, the history of kidney-inspired hemodialysis is introduced. Then, recent achievements in the preparation of microfluidic devices and hemodialysis nanoporous membrane materials are presented and categorized. Subsequently, attention is drawn to the recent progress of nanoporous membrane-based microfluidic devices for hemodialysis. Finally, the challenges and opportunities of hemodialysis microfluidic devices in the future are also discussed. This Review is expected to provide a comprehensive guide for the design of hemodialysis microfluidic devices that are closely related to clinical applications.