Use of electrospinning and dynamic air focusing to create three-dimensional cell culture scaffolds in microfluidic devices

Micro- and Nanostructured Fibrous Composites via Electro-Fluid Dynamics: Design and Applications for Brain

The brain consists of an interconnected network of neurons tightly packed in the extracellular matrix (ECM) to form complex and heterogeneous composite tissue. According to recent biomimicry approaches that consider biological features as active components of biomaterials, designing a highly reproducible microenvironment for brain cells can represent a key tool for tissue repair and regeneration. Indeed, this is crucial to support cell growth, mitigate inflammation phenomena and provide adequate structural properties needed to support the damaged tissue, corroborating the activity of the vascular network and ultimately the functionality of neurons. In this context, electro-fluid dynamic techniques (EFDTs), i.e., electrospinning, electrospraying and related techniques, offer the opportunity to engineer a wide variety of composite substrates by integrating fibers, particles, and hydrogels at different scales-from several hundred microns down to tens of nanometers-for the generation of countless patterns of physical and biochemical cues suitable for influencing the in vitro response of coexistent brain cell populations mediated by the surrounding microenvironment. In this review, an overview of the different technological approaches-based on EFDTs-for engineering fibrous and/or particle-loaded composite substrates will be proposed. The second section of this review will primarily focus on describing current and future approaches to the use of composites for brain applications, ranging from therapeutic to diagnostic/theranostic use and from repair to regeneration, with the ultimate goal of providing insightful information to guide future research efforts toward the development of more efficient and reliable solutions.

Cancer-on-chip: a 3D model for the study of the tumor microenvironment

The approval of anticancer therapeutic strategies is still slowed down by the lack of models able to faithfully reproduce in vivo cancer physiology. On one hand, the conventional in vitro models fail to recapitulate the organ and tissue structures, the fluid flows, and the mechanical stimuli characterizing the human body compartments. On the other hand, in vivo animal models cannot reproduce the typical human tumor microenvironment, essential to study cancer behavior and progression. This study reviews the cancer-on-chips as one of the most promising tools to model and investigate the tumor microenvironment and metastasis. We also described how cancer-on-chip devices have been developed and implemented to study the most common primary cancers and their metastatic sites. Pros and cons of this technology are then discussed highlighting the future challenges to close the gap between the pre-clinical and clinical studies and accelerate the approval of new anticancer therapies in humans.

Biomaterials based on hyaluronic acid, collagen and peptides for three-dimensional cell culture and their application in stem cell differentiation

In recent decades, three-dimensional (3D) cell culture technologies have been developed rapidly in the field of tissue engineering and regeneration, and have shown unique advantages and great prospects in the differentiation of stem cells. Herein, the article reviews the progress and advantages of 3D cell culture technologies in the field of stem cell differentiation. Firstly, 3D cell culture technologies are divided into two main categories: scaffoldless and scaffolds. Secondly, the effects of hydrogels scaffolds and porous scaffolds on stem cell differentiation in the scaffold category were mainly reviewed. Among them, hydrogels scaffolds are divided into natural hydrogels and synthetic hydrogels. Natural materials include polysaccharides, proteins, and their derivatives, focusing on hyaluronic acid, collagen and polypeptides. Synthetic materials mainly include polyethylene glycol (PEG), polyacrylic acid (PAA), polyvinyl alcohol (PVA), etc. In addition, since the preparation techniques have a large impact on the properties of porous scaffolds, several techniques for preparing porous scaffolds based on different macromolecular materials are reviewed. Finally, the future prospects and challenges of 3D cell culture in the field of stem cell differentiation are reviewed. This review will provide a useful guideline for the selection of materials and techniques for 3D cell culture in stem cell differentiation.

Electrospun hybrid nanofibers: Fabrication, characterization, and biomedical applications

Nanotechnology is one of the most promising technologies available today, holding tremendous potential for biomedical and healthcare applications. In this field, there is an increasing interest in the use of polymeric micro/nanofibers for the construction of biomedical structures. Due to its potential applications in various fields like pharmaceutics and biomedicine, the electrospinning process has gained considerable attention for producing nano-sized fibers. Electrospun nanofiber membranes have been used in drug delivery, controlled drug release, regenerative medicine, tissue engineering, biosensing, stent coating, implants, cosmetics, facial masks, and theranostics. Various natural and synthetic polymers have been successfully electrospun into ultrafine fibers. Although biopolymers demonstrate exciting properties such as good biocompatibility, non-toxicity, and biodegradability, they possess poor mechanical properties. Hybrid nanofibers from bio and synthetic nanofibers combine the characteristics of biopolymers with those of synthetic polymers, such as high mechanical strength and stability. In addition, a variety of functional agents, such as nanoparticles and biomolecules, can be incorporated into nanofibers to create multifunctional hybrid nanofibers. Due to the remarkable properties of hybrid nanofibers, the latest research on the unique properties of hybrid nanofibers is highlighted in this study. Moreover, various established hybrid nanofiber fabrication techniques, especially the electrospinning-based methods, as well as emerging strategies for the characterization of hybrid nanofibers, are summarized. Finally, the development and application of electrospun hybrid nanofibers in biomedical applications are discussed.

3D printed devices with integrated collagen scaffolds for cell culture studies including transepithelial/transendothelial electrical resistance (TEER) measurements

In this paper, we describe the use of 3D printed devices for both static and flow studies that contain electrospun collagen scaffolds and can accommodate transepithelial/transendothelial electrical resistance (TEER) measurements. Electrospinning was used to create the collagen scaffold, followed by an optimized 1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide/N-Hydroxysuccinimide (EDC/NHS) cross-linking procedure to produce stable collagen fibers that are similar in size to fibers in vivo. LC/MS was used to study the leaching of solvent and NHS from the scaffold, with several rinsing steps being shown to eliminate the leaching and promote the culture of Madin-Darby Canine Kidney (MDCK) epithelial cells on the scaffold. Both static and flow 2-part devices were successfully fabricated by 3D printing using either VeroClear or MED610 material (PolyJet printing) and assembling the scaffold between laser cut Teflon gaskets. The devices were designed to easily accommodate commonly used STX2 chopstick electrodes for TEER measurements. A detailed comparison was made between the use of collagen scaffolds vs other electrospun materials for cell culture. The collagen extracellular matrix model displayed a high barrier functionality for up to 7 days. In addition, a different 3D printed device with a collagen scaffold is described to incorporate continuous flow and replenishment of media under the cell layer in a manner that also enables periodic recording of TEER measurements. Overall, this work shows that the combination of biological ECM materials such as collagen into microfluidic devices that incorporate flow have great potential to form more realistic cell culture models in areas such as blood brain barrier research.

Evaluation and optimization of PolyJet 3D-printed materials for cell culture studies

Use of 3D printing for microfluidics is a rapidly growing area, with applications involving cell culture in these devices also becoming of interest. 3D printing can be used to create custom-designed devices that have complex features and integrate different material types in one device; however, there are fewer studies studying the ability to culture cells on the various substrates that are available. This work describes the effect of PolyJet 3D-printing technology on cell culture of two cell lines, bovine pulmonary artery endothelial cells (BPAECs) and Madin-Darby Canine Kidney (MDCK) cells, on two different types of printed materials (VeroClear or MED610). It was found that untreated devices, when used for studies of 1 day or more, led to unsuccessful culture. A variety of device treatment methodologies were investigated, with the most success coming from the use of sodium hydroxide/sodium metasilicate solution. Devices treated with this cleaning step resulted in culture of BPAECs and MDCK cells that were more similar to what is obtained in traditional culture flasks (in terms of cell morphology, viability, and cell density). LC-MS/MS analysis (via Orbitrap MS) was used to determine potential leachates from untreated devices. Finally, the use of a fiber scaffold in the devices was utilized to further evaluate the treatment methodology and to also demonstrate the ability to perform 3D culture in such devices. This study will be of use for researchers wanting to utilize these or other cell types in PolyJet-based 3D-printed devices.

Versatile membrane-based microfluidic platform for in vitro drug diffusion testing mimicking in vivo environments

Mimicking the diffusion that drugs suffer through different body tissues before reaching their target is a challenge. In this work, a versatile membrane-based microfluidic platform was developed to allow for the identification of drugs that would keep their cytotoxic properties after diffusing through such a barrier. As an application case, this paper reports on a microfluidic device capable of mimicking the diffusion that free or encapsulated anticancer drugs would suffer in the intestine before reaching the bloodstream. It not only presents the successful fabrication results for the platform but also demonstrates the significant effect that the analyzed drugs have over the viability of osteosarcoma cells. This intestine-like microfluidic platform works as a tool to allow for the identification of drugs whose cytotoxic performance remains effective enough once they enter the bloodstream. Therefore, it allows for the prediction of the best treatment available for each patient in the battle against cancer.

A Hybrid Nanofiber/Paper Cell Culture Platform for Building a 3D Blood-brain Barrier Model

The blood brain barrier (BBB) protects the central nervous system from toxins and pathogens in the blood by regulating permeation of molecules through the barrier interface. In vitro BBB models described to date reproduce some aspects of BBB functionality, but also suffer from incomplete phenotypic expression of brain endothelial traits, difficulty in reproducibility and fabrication, or overall cost. To address these limitations, we describe a three-dimensional (3D) BBB model based on a hybrid paper/nanofiber scaffold. The cell culture platform utilizes lens paper as a framework to accommodate 3D culture of astrocytes. An electrospun nanofiber layer is coated onto one face of the paper to mimic the basement membrane and support growth of an organized two-dimensional layer of endothelial cells (ECs). Human induced pluripotent stem cell-derived ECs and astrocytes are co-cultured to develop a human BBB model. Morphological and spatial organization of model are validated with confocal microscopy. Measurements of transendothelial resistance and permeability demonstrate the BBB model develops a high-quality barrier and responds to hyperosmolar treatments. RNA-sequencing shows introduction of astrocytes both regulates EC tight junction proteins and improves endothelial phenotypes related to vasculogenesis. This model shows promise as a model platform for future in vitro studies of the BBB.

A Review of Biomaterials and Scaffold Fabrication for Organ-on-a-Chip (OOAC) Systems

Drug and chemical development along with safety tests rely on the use of numerous clinical models. This is a lengthy process where animal testing is used as a standard for pre-clinical trials. However, these models often fail to represent human physiopathology. This may lead to poor correlation with results from later human clinical trials. Organ-on-a-Chip (OOAC) systems are engineered microfluidic systems, which recapitulate the physiochemical environment of a specific organ by emulating the perfusion and shear stress cellular tissue undergoes in vivo and could replace current animal models. The success of culturing cells and cell-derived tissues within these systems is dependent on the scaffold chosen; hence, scaffolds are critical for the success of OOACs in research. A literature review was conducted looking at current OOAC systems to assess the advantages and disadvantages of different materials and manufacturing techniques used for scaffold production; and the alternatives that could be tailored from the macro tissue engineering research field.

Electrospun Microfibers Modulate Intracellular Amino Acids in Liver Cells via Integrin β1

Although numerous recent studies have shown the importance of polymeric microfibrous extracellular matrices (ECMs) in maintaining cell behaviors and functions, the mechanistic nexus between ECMs and intracellular activities is largely unknown. Nevertheless, this knowledge will be critical in understanding and treating diseases with ECM remodeling. Therefore, we present our findings that ECM microstructures could regulate intracellular amino acid levels in liver cells mechanistically through integrin β1. Amino acids were studied because they are the fundamental blocks for protein synthesis and metabolism, two vital functions of liver cells. Two ECM conditions, flat and microfibrous, were prepared and studied. In addition to characterizing cell growth, albumin production, urea synthesis, and cytochrome p450 activity, we found that the microfibrous ECM generally upregulated the intracellular amino acid levels. Further explorations showed that cells on the flat substrate expressed more integrin β1 than cells on the microfibers. Moreover, after partially blocking integrin β1 in cells on the flat substrate, the intracellular amino acid levels were restored, strongly supporting integrin β1 as the linking mechanism. This is the first study to report that a non-biological polymer matrix could regulate intracellular amino acid patterns through integrin. The results will help with future therapy development for liver diseases with ECM changes (e.g., fibrosis).

Making quantitative biomicrofluidics from microbore tubing and 3D-printed adapters

Microfluidic technology has tremendously facilitated the development of in vitro cell cultures and studies. Conventionally, microfluidic devices are fabricated with extensive facilities by well-trained researchers, which hinder the widespread adoption of the technology for broader applications. Enlightened by the fact that low-cost microbore tubing is a natural microfluidic channel, we developed a series of adaptors in a toolkit that can twine, connect, organize, and configure the tubing to produce functional microfluidic units. Three subsets of the toolkit were thoroughly developed: the tubing and scoring tools, the flow adaptors, and the 3D cell culture suite. To demonstrate the usefulness and versatility of the toolkit, we assembled a microfluidic device and successfully applied it for 3D macrophage cultures, flow-based stimulation, and automated near real-time quantitation with new knowledge generated. Overall, we present a new technology that allows simple, fast, and robust assembly of customizable and scalable microfluidic devices with minimal facilities, which is broadly applicable to research that needs or could be enhanced by microfluidics.

3D-Printed, Modular, and Parallelized Microfluidic System with Customizable Scaffold Integration to Investigate the Roles of Basement Membrane Topography on Endothelial Cells

Because dysfunctions of endothelial cells are involved in many pathologies, in vitro endothelial cell models for pathophysiological and pharmaceutical studies have been a valuable research tool. Although numerous microfluidic-based endothelial models have been reported, they had the cells cultured on a flat surface without considering the possible three-dimensional (3D) structure of the native extracellular matrix (ECM). Endothelial cells rest on the basement membrane in vivo, which contains an aligned microfibrous topography. To better understand and model the cells, it is necessary to know if and how the fibrous topography can affect endothelial functions. With conventional fully integrated microfluidic apparatus, it is difficult to include additional topographies in a microchannel. Therefore, we developed a modular microfluidic system by 3D-printing and electrospinning, which enabled easy integration and switching of desired ECM topographies. Also, with standardized designs, the system allowed for high flow rates up to 4000 μL/min, which encompassed the full shear stress range for endothelial studies. We found that the aligned fibrous topography on the ECM altered arginine metabolism in endothelial cells and thus increased nitric oxide production. There has not been an endothelial model like this, and the new knowledge generated thereby lays a groundwork for future endothelial research and modeling.

From cells-on-a-chip to organs-on-a-chip: scaffolding materials for 3D cell culture in microfluidics

It is an emerging research area to integrate scaffolding materials in microfluidic devices for 3D cell culture (organs-on-a-chip). The technology of organs-on-a-chip holds the potential to obviate the gaps between pre-clinical and clinical studies. As accumulating evidence shows the importance of extracellular matrix in in vitro cell culture, significant efforts have been made to integrate 3D ECM/scaffolding materials in microfluidics. There are two families of materials that are commonly used for this purpose: hydrogels and electrospun fibers. In this review, we briefly discuss the properties of the materials, and focus on the various technologies to obtain the materials (e.g. extraction of collagen from animal tissues) and to include the materials in microfluidic devices. Challenges and potential solutions of the current materials and technologies were also thoroughly discussed. At the end, we provide a perspective on future efforts to make these technologies more translational to broadly benefit pharmaceutical and pathophysiological research.

Microfibrous Extracellular Matrix Changes the Liver Hepatocyte Energy Metabolism via Integrins

Cell line-based liver models are critical tools for liver-related studies. However, the conventional monolayer culture of hepatocytes, the most widely used in vitro model, does not have the extracellular matrix (ECM), which contributes to the three-dimensional (3D) arrangement of the hepatocytes in the liver. As a result, the metabolic properties of the hepatocytes in the monolayer tissue culture may not accurately reflect those of the hepatocytes in the liver. Here, we developed a modular platform for 3D hepatocyte cultures on fibrous ECMs produced by electrospinning, a technique that can turn a polymer solution to the micro/nanofibers and has been widely used to produce scaffolds for 3D cell cultures. Metabolomics quantitation by liquid chromatography-mass spectrometry (LC-MS) indicated that Huh7 hepatocytes grown in microfibers electrospun from silk fibroin exhibited reduced glycolysis and tricarboxylic acid (TCA) cycle, as compared to the cells cultured as a monolayer. Further mechanistic studies suggested that integrins were correlated to the ECM's effects. This is the first time to report how an ECM scaffold could affect the fundamental metabolism of the hepatocytes via integrins.

Microphysiological Systems: Design, Fabrication, and Applications

Microphysiological systems, including organoids, 3-D printed tissue constructs and organ-on-a-chips (organ chips), are physiologically relevant in vitro models and have experienced explosive growth in the past decades. Different from conventional, tissue culture plastic-based in vitro models or animal models, microphysiological systems recapitulate key microenvironmental characteristics of human organs and mimic their primary functions. The advent of microphysiological systems is attributed to evolving biomaterials, micro-/nanotechnologies and stem cell biology, which enable the precise control over the matrix properties and the interactions between cells, tissues and organs in physiological conditions. As such, microphysiological systems have been developed to model a broad spectrum of organs from microvasculature, eye, to lung and many others to understand human organ development and disease pathology and facilitate drug discovery. Multiorgans-on-a-chip systems have also been developed by integrating multiple associated organ chips in a single platform, which allows to study and employ the organ function in a systematic approach. Here we first discuss the design principles of microphysiological systems with a focus on the anatomy and physiology of organs, and then review the commonly used fabrication techniques and biomaterials for microphysiological systems. Subsequently, we discuss the recent development of microphysiological systems, and provide our perspectives on advancing microphysiological systems for preclinical investigation and drug discovery of human disease.

Review of 3D Cell Culture with Analysis in Microfluidic Systems

A review with 105 references that analyzes the emerging research area of 3D cell culture in microfluidic platforms with integrated detection schemes. Over the last several decades a central focus of cell culture has been the development of better in vivo mimics. This has led to the evolution from planar cell culture to cell culture on 3D scaffolds, and the incorporation of cell scaffolds into microfluidic devices. Specifically, this review explores the incorporation of suspension culture, hydrogels scaffolds, paper-based scaffolds, and fiber-based scaffolds into microfluidic platforms. In order to decrease analysis time, simplify sample preparation, monitor key signaling pathways involved in cell-to-cell communication or cell growth, and combat the limitations of sample volume/ dilution seen in traditional assays, researchers have also started to focus on integrating detection schemes into the cell culture devices. This review will highlight the work that has been performed towards combining these techniques and will discuss potential future directions. It is clear that microfluidic-based 3D cell culture coupled with quantitative analysis can greatly improve our ability to mimic and understand in vivo systems.

Flat and microstructured polymeric membranes in organs-on-chips

In recent years, organs-on-chips (OOCs) have been developed to meet the desire for more realistic in vitro cell culture models. These systems introduce microfluidics, mechanical stretch and other physiological stimuli to in vitro models, thereby significantly enhancing their descriptive power. In most OOCs, porous polymeric membranes are used as substrates for cell culture. The polymeric material, morphology and shape of these membranes are often suboptimal, despite their importance for achieving ideal cell functionality such as cell-cell interaction and differentiation. The currently used membranes are flat and thus do not account for the shape and surface morphology of a tissue. Moreover, the polymers used for fabrication of these membranes often lack relevant characteristics, such as mechanical properties matching the tissue to be developed and/or cytocompatibility. Recently, innovative techniques have been reported for fabrication of porous membranes with suitable porosity, shape and surface morphology matching the requirements of OOCs. In this paper, we review the state of the art for developing these membranes and discuss their application in OOCs.

The Effect of Endothelial Cells on UVB-induced DNA Damage and Transformation of Keratinocytes In 3D Polycaprolactone Scaffold Co-culture System

Nitric oxide ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup><mml:mrow><mml:mi>NO</mml:mi></mml:mrow> <mml:mo>·</mml:mo></mml:msup> </mml:math> ) plays an important role in the regulation of redox balance in keratinocytes post-UVB exposure. Since endothelial cells releases <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup><mml:mrow><mml:mi>NO</mml:mi></mml:mrow> <mml:mo>·</mml:mo></mml:msup> </mml:math> for a prolonged time post-UVB, we determined whether human umbilical vein endothelial cells (HUVEC) could have an effect on UVB-induced DNA damage and transformation of their adjacent keratinocytes (HaCaT) using a 3D cell co-culturing system. Our data show that the levels of DNA breaks and/or cyclobutane pyrimidine dimer (CPD) along with γH2AX are higher in the co-cultured than in the mono-cultured keratinocytes post-UVB. The <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup><mml:mrow><mml:mi>NO</mml:mi></mml:mrow> <mml:mo>·</mml:mo></mml:msup> </mml:math> level in the co-cultured cells is increased approximately 3-fold more than in mono-cultured HaCaT cells within 1-hour post-UVB but then is reduced quickly in co-cultured HaCaT cells comparing to mono-cultured cells from 6 to 24 h post-UVB. However, the peroxynitrite (ONOO^- ) level is higher in the co-cultured than in the mono-cultured HaCaT cells in whole period post-UVB. Furthermore, while expression level of inducible nitric oxide synthase (iNOS) is increased, the ratio of coupled/uncoupled eNOS is reduced in co-cultured HaCaT cells compared to mono-cultured HaCaT cells. Finally, the co-cultured cells have a significantly increased transformation efficiency after repeating UVB exposure compared to mono-culture HaCaT cells. Our results suggest that endothelial cells could enhance <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msup><mml:mrow><mml:mi>NO</mml:mi></mml:mrow> <mml:mo>·</mml:mo></mml:msup> </mml:math> /ONOO^- imbalance and promote transformation of adjacent keratinocytes.

Electrospinning: An enabling nanotechnology platform for drug delivery and regenerative medicine

Electrospinning provides an enabling nanotechnology platform for generating a rich variety of novel structured materials in many biomedical applications including drug delivery, biosensing, tissue engineering, and regenerative medicine. In this review article, we begin with a thorough discussion on the method of producing 1D, 2D, and 3D electrospun nanofiber materials. In particular, we emphasize on how the 3D printing technology can contribute to the improvement of traditional electrospinning technology for the fabrication of 3D electrospun nanofiber materials as drug delivery devices/implants, scaffolds or living tissue constructs. We then highlight several notable examples of electrospun nanofiber materials in specific biomedical applications including cancer therapy, guiding cellular responses, engineering in vitro 3D tissue models, and tissue regeneration. Finally, we finish with conclusions and future perspectives of electrospun nanofiber materials for drug delivery and regenerative medicine.

Insert-based microfluidics for 3D cell culture with analysis

We present an insert-based approach to fabricate scalable and multiplexable microfluidic devices for 3D cell culture and integration with downstream detection modules. Laser-cut inserts with a layer of electrospun fibers are used as a scaffold for 3D cell culture, with the inserts being easily assembled in a 3D-printed fluidic device for flow-based studies. With this approach, the number and types of cells (on the inserts) in one fluidic device can be customized. Moreover, after an investigation (i.e., stimulation) under flowing conditions, the cell-laden inserts can be removed easily for subsequent studies including imaging and cell lysis. In this paper, we first discuss the fabrication of the device and characterization of the fibrous inserts. Two device designs containing two (channel width = 260 μm) and four (channel width = 180 μm) inserts, respectively, were used for different experiments in this study. Cell adhesion on the inserts with flowing media through the device was tested by culturing endothelial cells. Macrophages were cultured and stimulated under different conditions, the results of which indicate that the fibrous scaffolds under flow conditions result in dramatic effects on the amount and kinetics of TNF-α production (after LPS stimulation). Finally, we show that the cell module can be integrated with a downstream absorbance detection scheme. Overall, this technology represents a new and versatile way to culture cells in a more in vivo fashion for in vitro studies with online detection modules. Graphical abstract This paper describes an insert-based microfluidic device for 3D cell culture that can be easily scaled, multiplexed, and integrated with downstream analytical modules.

A review of electrospinning manipulation techniques to direct fiber deposition and maximize pore size

Electrospinning has been widely accepted for several decades by the tissue engineering and regenerative medicine community as a technique for nanofiber production. Owing to the inherent flexibility of the electrospinning process, a number of techniques can be easily implemented to control fiber deposition (i.e. electric/ magnetic field manipulation, use of alternating current, or air-based fiber focusing) and/or porosity (i.e. air impedance, sacrificial porogen/sacrificial fiber incorporation, cryo-electrospinning, or alternative techniques). The purpose of this review is to highlight some of the recent work using these techniques to create electrospun scaffolds appropriate for mimicking the structure of the native extracellular matrix, and to enhance the applicability of advanced electrospinning techniques in the field of tissue engineering.

A Printed Equilibrium Dialysis Device with Integrated Membranes for Improved Binding Affinity Measurements

Equilibrium dialysis is a simple and effective technique used for investigating the binding of small molecules and ions to proteins. A three-dimensional (3D) printer was used to create a device capable of measuring binding constants between a protein and a small ion based on equilibrium dialysis. Specifically, the technology described here enables the user to customize an equilibrium dialysis device to fit their own experiments by choosing membranes of various material and molecular-weight cutoff values. The device has dimensions similar to that of a standard 96-well plate, thus being amenable to automated sample handlers and multichannel pipettes. The device consists of a printed base that hosts multiple windows containing a porous regenerated-cellulose membrane with a molecular-weight cutoff of ∼3500 Da. A key step in the fabrication process is a print-pause-print approach for integrating membranes directly into the windows subsequently inserted into the base. The integrated membranes display no leaking upon placement into the base. After characterizing the system's requirements for reaching equilibrium, the device was used to successfully measure an equilibrium dissociation constant for Zn²⁺ and human serum albumin (K_d = (5.62 ± 0.93) × 10^-7 M) under physiological conditions that is statistically equal to the constants reported in the literature.

Microchip-based 3D-Cell Culture Using Polymer Nanofibers Generated by Solution Blow Spinning

Polymer nano/micro fibers have found many applications including 3D cell culture and the creation of wound dressings. The fibers can be produced by a variety of techniques that include electrospinning, the primary disadvantage of which include the requirement for a high voltage supply (which may cause issues such as polymer denaturation) and lack of portability. More recently, solution blow spinning, where a high velocity sheath gas is used instead of high voltage, has been used to generate polymer fibers. In this work, we used blow spinning to create nano/microfibers for microchip-based 3D cell culture. First, we thoroughly investigated fiber generation from a 3D printed gas sheath device using two polymers that are amenable to cell culture (polycaprolactone, PCL and polystyrene, PS) as well as the parameters that can affect PCL and PS fiber quality. Using the 3D printed sheath device, it was found that the pressure of the sheath N2 and the concentration of polymer solutions determine if fibers can be produced as well as the resulting fiber morphology. In addition, we showed how these fibers can be used for 3D cell culture by directly depositing PCL fibers in petri dishes and well plates. It is shown the fibers have good compatibility with RAW 264.7 macrophages and the PCL fiber scaffold can be as thick as 178 ± 14 μm. PCL fibers created from solution blow spinning (with the 3D printed sheath device) were then integrated with a microfluidic device for the first time to fabricate a 3D cell culture scaffold with a flow component. After culturing and stimulating macrophages on the fluidic device, it was found that the integrated 3D fibrous scaffold is a better mimic of the extracellular matrix (as opposed to a flat, 2D substrate), with enhanced nitrite accumulation (product of nitric oxide release) from macrophages stimulated with lipopolysaccharide. PS fibers were also made and integrated in a microfluidic device for 3D culture of endothelial cells, which stayed viable for at least 72 hours (48 hours under the flowing conditions). This approach will be useful for future studies involving more realistic microchip-based culture models for studying cell-to-cell communication.