Selection, Enrichment, and Maintenance of Self-Renewal Liver Stem/Progenitor Cells Utilizing Polypeptide Polyelectrolyte Multilayer Films

Microfluidic array chip based on excimer laser processing technology for the construction of in vitro graphical neuronal network

To construct a graphical neural network in vitro and explore the morphological effects of neural network structural changes on neurons, this study aimed to introduce a method for fabricating microfluidic array chips with different graphical structures based on 248-nm excimer laser one-step etching. Through the comparative analysis of the graphical neural network cultured on our microfluidic array chip with the one on the glass slide, the morphological effects of the neural network on the morphology of the neurons were studied. First, the design of the chip was completed according to the specific structure of the neurons and the simulation of the flow field. The chips were fabricated by excimer laser processing combined with the casting technology. Neurons were cultured on the chip, and a graphical neural network was formed. The growth status of the neural network was analyzed by microscopy and immunofluorescence technology, and compared with the random neural network cultured on glass slides. The results showed that the neurons on the array chips grew in microchannels, and neurites grew along the direction of the channel, interlacing to form a neural network. Furthermore, when the structure of the neural network was graphically changed, the internal neuron morphology changed: on the same culture days, the maximum length of the neurites of the graphical neural network was higher than the average length of the neurites of the random neural network. This research can provide the foundation for the exploration of the neural network mechanism of neurological diseases.

A self-assembled layer-by-layer surface modification to fabricate the neuron-rich model from neural stem/precursor cells

BACKGROUND/PURPOSE

In vitro neural cell-based models have been widely used to mimic the in vivo neural tissue environments and quantitatively understand the effects of pharmaceutical molecules on neural diseases. Recently, several biomimetic neural tissue models have been widely developed by using biomaterials or surface modification. However, the complex protocols of material synthesis or surface modification lack an easy execution to fabricate the neuron favorite environment.

METHODS

In this study, we utilized a layer-by-layer technique as a surface modification method for regulating the behaviors of neural stem/precursor cells (NSPCs) on material surfaces. Polyelectrolyte multilayers (PEMs) via alternate deposition of poly (allylamine hydrochloride) (PAH) and poly (sodium-4-styrenesulfonate) (PSS) were used to culture NSPCs. After incubation for 7 days, the neuronal differentiation of NSPCs and synapse function of differentiated neurons were identified by immunocytochemistry for lineage specific markers.

RESULTS

Compared with the only PAH film, the PSS-ending film (neuron-rich model) was shown to significantly promote differentiation of NSPCs into neurons (more than 50%), form a neuronal network structure; and differentiated neurons exhibiting functional synaptic activity.

CONCLUSION

This study shows that the PEMs provided an easily alternative approach to modify the surface properties; and might be a method to obtain a neuron-rich model for the biological/pharmaceutical applications.

Layers and Multilayers of Self-Assembled Polymers: Tunable Engineered Extracellular Matrix Coatings for Neural Cell Growth

Growing primary cells and tissue in long-term cultures, such as primary neural cell culture, presents many challenges. A critical component of any environment that supports neural cell growth in vivo is an appropriate 2-D surface or 3-D scaffold, typically in the form of a thin polymer layer that coats an underlying plastic or glass substrate and aims to mimic critical aspects of the extracellular matrix. A fundamental challenge to mimicking a hydrophilic, soft natural cell environment is that materials with these properties are typically fragile and are difficult to adhere to and stabilize on an underlying plastic or glass cell culture substrate. In this review, we highlight the current state of the art and overview recent developments of new artificial extracellular matrix (ECM) surfaces for in vitro neural cell culture. Notably, these materials aim to strike a balance between being hydrophilic and soft while also being thick, stable, robust, and bound well to the underlying surface to provide an effective surface to support long-term cell growth. We focus on improved surface and scaffold coating systems that can mimic the natural physicochemical properties that enhance neuronal survival and growth, applied as soft hydrophilic polymer coatings for both in vitro cell culture and for implantable neural probes and 3-D matrixes that aim to enhance stability and longevity to promote neural biocompatibility in vivo. With respect to future developments, we outline four emerging principles that serve to guide the development of polymer assemblies that function well as artificial ECMs: (a) design inspired by biological systems and (b) the employment of principles of aqueous soft bonding and self-assembly to achieve (c) a high-water-content gel-like coating that is stable over time in a biological environment and possesses (d) a low modulus to more closely mimic soft, compliant real biological tissue. We then highlight two emerging classes of thick material coatings that have successfully captured these guiding principles: layer-by-layer deposited water-soluble polymers (LbL) and silk fibroin (SF) materials. Both materials can be deposited from aqueous solution yet transition to a water-insoluble coating for long-term stability while retaining a softness and water content similar to those of biological materials. These materials hold great promise as next-generation biocompatible coatings for tissue engineers and for chemists and biologists within the biomedical field.

Toward the Development of an Artificial Brain on a Micropatterned and Material-Regulated Biochip by Guiding and Promoting the Differentiation and Neurite Outgrowth of Neural Stem/Progenitor Cells

An in vitro model mimicking the in vivo environment of the brain must be developed to study neural communication and regeneration and to obtain an understanding of cellular and molecular responses. In this work, a multilayered neural network was successfully constructed on a biochip by guiding and promoting neural stem/progenitor cell differentiation and network formation. The biochip consisted of 3 × 3 arrays of cultured wells connected with channels. Neurospheroids were cultured on polyelectrolyte multilayer (PEM) films in the culture wells. Neurite outgrowth and neural differentiation were guided and promoted by the micropatterns and the PEM films. After 5 days in culture, a 3 × 3 neural network was constructed on the biochip. The function and the connections of the network were evaluated by immunocytochemistry and impedance measurements. Neurons were generated and produced functional and recyclable synaptic vesicles. Moreover, the electrical connections of the neural network were confirmed by measuring the impedance across the neurospheroids. The current work facilitates the development of an artificial brain on a chip for investigations of electrical stimulations and recordings of multilayered neural communication and regeneration.

Promotion and guidance of neural network formation on SU-8 photoresist microchannels adjusted with multilayer films

Induction of neural stem/progenitor cells (NSPCs) and establishment of neural network are important issues on neural engineering. In this work, a platform was designed to control and evaluate the differentiation of NSPCs, neurite direction, and to promote the neurite outgrowth. Polyelectrolyte multilayer (PEM) films provide surface properties by and have been used to regulate NSPCs differentiation in our previous study. Herein, a culture platform composed of SU-8 microchannel and PEM films was designed to achieve the goal of promoting NSPCs differentiation and to evaluate the effect of PEM films on the guidance of neural network formation. In this culture platform, NSPCs were induced into functional neurons, and neural network formation was accomplished on ITO glass-PEM films successfully.

Biomimetic Extracellular Environment Based on Natural Origin Polyelectrolyte Multilayers

Surface modification of biomaterials is a well-known approach to enable an adequate biointerface between the implant and the surrounding tissue, dictating the initial acceptance or rejection of the implantable device. Since its discovery in early 1990s layer-by-layer (LbL) approaches have become a popular and attractive technique to functionalize the biomaterials surface and also engineering various types of objects such as capsules, hollow tubes, and freestanding membranes in a controllable and versatile manner. Such versatility enables the incorporation of different nanostructured building blocks, including natural biopolymers, which appear as promising biomimetic multilayered systems due to their similarity to human tissues. In this review, the potential of natural origin polymer-based multilayers is highlighted in hopes of a better understanding of the mechanisms behind its use as building blocks of LbL assembly. A deep overview on the recent progresses achieved in the design, fabrication, and applications of natural origin multilayered films is provided. Such films may lead to novel biomimetic approaches for various biomedical applications, such as tissue engineering, regenerative medicine, implantable devices, cell-based biosensors, diagnostic systems, and basic cell biology.

Niche Mimicking for Selection and Enrichment of Liver Cancer Stem Cells by Hyaluronic Acid-Based Multilayer Films

Cancer stem cells (CSCs) represent a subpopulation of tumor cells that exhibit capacities for self-renewal, tumor initiation, disease relapse or metastasis, and resistance to chemotherapy and radiotherapy. However, the major obstacle associated with the use of CSCs is the difficulty in their isolation and enrichment. According to recent studies, CSCs share similar properties with normal stem cells, and it has been observed that hyaluronan (HA) plays a key factor in CSCs niches and that HA-mediated CD44 interaction promotes tumor progression. Therefore, HA-based multilayer films were used to fabricate sequential surface properties variation and to mimic CSC niches. A quartz crystal microbalance was used to investigate the layer-by-layer adsorption of PAH/HA multilayer films. Colony formation was observed on a series of poly(allylamine hydrochloride) PAH/HA multilayer films, and cytotoxicity and cell viability were evaluated by MTT, LDH and live/dead assay. It was observed that the cells isolated from (PAH/HA)3 displayed the best colony formation ability and that the expression of CD133/CD44 double positive cells was up-regulated to approximately 70% after 7 days of culture. Furthermore, the cells isolated from (PAH/HA)3 displayed higher chemo-resistance than the control group. The stem-cell-related genes expression of selected cells from (PAH/HA)3 after 7 days of culture was significantly different from that of the control group. In conclusion, this study provides a label-free selection and enrichment system that could serve as a new strategy for the future development of CSC selection and drug evaluation in cancer therapy.

Biomimetic niche for neural stem cell differentiation using poly-L-lysine/hyaluronic acid multilayer films

Polyelectrolyte multilayer films have been suggested as tunable substrates with flexible surface properties that can modulate cell behavior. However, these films’ biological effects on neural stem/progenitor cells have rarely been studied. Herein, biomimetic multilayer films composed of hyaluronic acid and poly-L-lysine were chosen to mimic the native extracellular matrix niche of brain tissue and were evaluated for their inductive effects, without the addition of chemical factors. Because neural stem/progenitor cells are sensitive to substrate properties, it is important that this system provides control over the surface charge, and slight stiffness variations are also possible. Both of these factors affect neural stem/progenitor cell differentiation. The results showed that neural stem/progenitor cells were induced to differentiate on the poly-L-lysine/hyaluronic acid multilayer films with 0.5–4 alternating layers. In addition, the neurite outgrowth length was regulated by the surface charge of the terminal layer but did not increase with the layer number. In contrast, the quantity of differentiated neurons was enhanced slightly as the number of layers increased but was not affected by the surface charge of the terminal layer. In sum, material pairs in the form of native poly-L-lysine/hyaluronic acid films achieved important targets for neural regenerative medicine, including enhancement of the neurite outgrowth length, regulation of neuron differentiation, and the formation of a network. These extracellular matrix–mimetic poly-L-lysine/hyaluronic acid multilayer films may provide a versatile platform that could be useful for surface modification for applications in neural engineering.

Promoting the selection and maintenance of fetal liver stem/progenitor cell colonies by layer-by-layer polypeptide tethered supported lipid bilayer

In this study, we designed and constructed a series of layer-by-layer polypeptide adsorbed supported lipid bilayer (SLB) films as a novel and label-free platform for the isolation and maintenance of rare populated stem cells. In particular, four alternative layers of anionic poly-l-glutamic acid and cationic poly-l-lysine were sequentially deposited on an anionic SLB. We found that the fetal liver stem/progenitor cells from the primary culture were selected and formed colonies on all layer-by-layer polypeptide adsorbed SLB surfaces, regardless of the number of alternative layers and the net charges on those layers. Interestingly, these isolated stem/progenitor cells formed colonies which were maintained for an 8 day observation period. Quartz crystal microbalance with dissipation measurements showed that all SLB-polypeptide films were protein resistant with serum levels significantly lower than those on the polypeptide multilayer films without an underlying SLB. We suggest the fluidic SLB promotes selective binding while minimizing the cell-surface interaction due to its nonfouling nature, thus limiting stem cell colonies from spreading.

Successful differentiation of neural stem/progenitor cells cultured on electrically adjustable indium tin oxide (ITO) surface

In order to control differentiation of neural cells and guide the developed neurites to targets, polyelectrolyte multilayer (PEM) films were used because of their capability of modulation of electrical charged characteristics, thickness, and stiffness. In this work, we suggested that indium tin oxide (ITO) is an alternative surface to achieve the above-mentioned objectives. A microfluidic system with four culture chambers was developed and each chamber consisted of parallel ITO surfaces for the application of adjustable electrical field. Neural stem/progenitor cells (NSPCs) were respectively cultured on the ITO surfaces with and without PEM film, constructed by alternate adsorption of poly(L-lysine) (PLL) and poly(L-glutamic acid) (PLGA). Analyses of cell morphology, cytotoxicity, process outgrowth, differentiated cell types, and neuron functionality were compared between both surfaces. In this study, NSPCs successfully differentiated on ITO surface with electrical stimulation. The optimal electrical potential was found to be 80 mV that could stimulate the longest process, i.e., >300 μm, after 3 days culture. Cell differentiation, process development, and functionality of differentiated neuron on ITO surface were shown to be strongly controlled by the electrical stimulation that can be simply adjusted by external equipment. The electrically adjustable cell differentiation reported here could potentially be applied to neurochip for the study of neural signal transmission in a well-constructed network.

Assembly of polyelectrolyte multilayer films on supported lipid bilayers to induce neural stem/progenitor cell differentiation into functional neurons

The key factors affecting the success of neural engineering using neural stem/progenitor cells (NSPCs) are the neuron quantity, the guidance of neurite outgrowth, and the induction of neurons to form functional synapses at synaptic junctions. Herein, a biomimetic material comprising a supported lipid bilayer (SLB) with adsorbed sequential polyelectrolyte multilayer (PEM) films was fabricated to induce NSPCs to form functional neurons without the need for serum and growth factors in a short-term culture. SLBs are suitable artificial substrates for neural engineering due to their structural similarity to synaptic membranes. In addition, PEM film adsorption provides protection for the SLB as well as the ability to vary the surface properties to evaluate the effects of physical and mechanical signals on NSPC differentiation. Our results revealed that NSPCs were inducible on SLB-PEM films consisting of up to eight alternating layers. In addition, the process outgrowth length, the percentage of differentiated neurons, and the synaptic function were regulated by the number of layers and the surface charge of the outermost layer. The average process outgrowth length was greater than 500 μm on SLB-PLL/PLGA (n = 7.5) after only 3 days of culture. Moreover, the quantity and quality of the differentiated neurons were obviously enhanced on the SLB-PEM system compared with those on the PEM-only substrates. These results suggest that the PEM films can induce NSPC adhesion and differentiation and that an SLB base may enhance neuron differentiation and trigger the formation of functional synapses.

Facilitating neural stem/progenitor cell niche calibration for neural lineage differentiation by polyelectrolyte multilayer films

Neural stem/progenitor cells (NSPCs) are a possible candidate for advancing development and lineage control in neural engineering. Differentiated protocols have been developed in this field to generate neural progeny and to establish neural networks. However, continued refinement is required to enhance differentiation specificity and prevent the generation of unwanted cell types. In this study, we fabricated a niche-modulated system to investigate surface effects on NSPC differentiation by the formation of polyelectrolyte multilayer (PEM) films governed by electrostatic interactions of poly-l-glutamine acid as a polyanion and poly-l-lysine as a polycation. The serum- and chemical agent-free system provided a clean and clear platform to observe in isolation the interaction between surface niche and stem cell differentiation. We found that NSPCs were inducible on PEM films of up to eight alternating layers. In addition, neurite outgrowth, neuron percentage, and synaptic function were regulated by layer number and the surface charge of the terminal layer. The average process outgrowth length was over 500μm on PLL/PLGA(n=7.5) only after 3 days of culture. Moreover, the quantity and quality of the differentiated neurons were enhanced as the number of layers increased, especially when the terminal layer was poly-l-lysine. Our results achieve important targets of neural engineering, including long processes, large neural network size, and large amounts of functional neurons. Our methodology for nanoscale control of material deposition can be successfully applied for surface modification, neural niche modulation, and neural engineering applications.

BMVC test, an improved fluorescence assay for detection of malignant pleural effusions

The diagnosis of malignant pleural effusions is an important issue in the management of malignancy patients. Generally, cytologic examination is a routine diagnostic technique. However, morphological interpretation of cytology is sometimes inconclusive. Here an ancillary method named BMVC test is developed for rapid detection of malignant pleural effusion to improve the diagnostic accuracy at low cost. A simple assay kit is designed to collect living cells from clinical pleural effusion and a fluorescence probe, 3,6-Bis(1-methyl-4-vinylpyridinium) carbazole diiodide (BMVC), is used to illuminate malignant cells. The fluorescence intensity is quantitatively analyzed by ImageJ program. This method yields digital numbers for the test results without any grey zone or ambiguities in the current cytology tests due to intra-observer and inter-observer variability. Comparing with results from double-blind cytologic examination, this simple test gives a good discrimination between malignant and benign specimens with sensitivity of 89.4% (42/47) and specificity of 93.3% (56/60) for diagnosis of malignant pleural effusion. BMVC test provides accurate results in a short time period, and the digital output could assist cytologic examination to become more objective and clear-cut. This is a convenient ancillary tool for detection of malignant pleural effusions.

Smart Layer-by-Layer Assemblies for Drug Delivery

Layer-by-layer (LbL) assembly is an effective tool for development of surface coatings and capsules for localized, controlled delivery of bioactive molecules. Because of the unprecedented versatility of the technique, a broad range of nanoobjects, including molecules, particles, micelles, vesicles and others with diverse chemistry and architecture can be used as building blocks for LbL assemblies, opening various routes for inclusion and delivery of functional molecules to/from LbL films. Moreover, the LbL technique continues to show its power in constructing three-dimensional (3D) delivery containers, in which LbL walls can additionally control delivery of functional molecules incorporated in the capsule interior. In this chapter, we discuss recent progress in the use of LbL assemblies to control release of therapeutic compounds via diffusion, hydrolytic degradation, pH, ionic strength or temperature variations, application of light, ultrasound, electric and magnetic field stimuli, redox activation or biological stimuli.

Use of surface properties to control the growth and differentiation of mouse fetal liver stem/progenitor cell colonies

Multilayers of poly-l-lysine/poly-l-glutamic acid (PLL/PLGA) were constructed by layer-by-layer deposition on an end-tethered cationic PLL brush film serving as an initial layer. Increasing the number of coupling layers increased the thickness and the hydration of the films, and decreased the films' shear modulus and serum adsorption. These films were used to culture primary mouse fetal liver cells. Fetal liver stem/progenitor cells (FLSPCs) were isolated and maintained on the PLGA-terminal PLL/PLGA surfaces, forming colonies with clear boundaries that were partially attached to the surface, with cross-sectional areas of ~500 to ~2500 μm(2) after 2 days culture. Long-term studies showed that the cluster size of colonies slowly expanded and was correlated with the surface properties. For example, on the thicker films with shear modulus, G, less than 5 kPa, FLSPCs cluster size was constrained within a small distribution with less than 4000 μm(2) of projected area, whereas on the thinner films with G > 30 kPa, clusters were expanded and widely distributed, with projected areas over 4000 um(2). Immunostaining studies suggested that clusters with a small size maintained the self-renewal characteristics of stem cells, while the expanded clusters were clearly the results of spontaneous differentiation, exhibiting hepatocyte-like properties. On PLL-terminal t-(PLL/PLGA) films, which are less favorable for stem cell cultures than PLGA-terminal t-(PLL/PLGA) films, the cluster size distribution was also correlated with the film thickness, with more clusters of small size preserved on the thicker films. We observed that a soft, hydrated, serum-free surface could restrict the FLSPC expansion, resulting in self-maintenance of FLSPC colonies.

Successful isolation of liver progenitor cells by aldehyde dehydrogenase activity in naïve mice

The role of progenitor cells in liver repair and fibrosis has been extensively described, but their purification remains a challenge, hampering their characterization and use in regenerative medicine. To address this issue, we developed an easy and reproducible liver progenitor cell (LPC) isolation strategy based on aldehyde dehydrogenase (ALDH) activity, a common feature shared by many progenitor cells. We demonstrate that a subset of nonparenchymal mouse liver cells displays high levels of ALDH activity, allowing the isolation of these cells by fluorescence-activated cell sorting. Immunocytochemistry and qPCR analyses on freshly isolated ALDH(+) cells reveal an enrichment in cells expressing liver stem cell markers such as EpCAM, CK19, CD133, and Sox9. In culture, the ALDH(+) population can give rise to functional hepatocyte-like cells as illustrated by albumin and urea secretion and cytochrome P450 activity. ALDH1A1 expression can be detected in canals of Hering and bile duct epithelial cells and is increased on liver injury. Finally, we showed that the isolation and differentiation toward hepatocyte-like cells of LPCs with high ALDH activity is also successfully applicable to human liver samples.

CONCLUSION

High ALDH activity is a feature of LPCs that can be taken advantage of to isolate these cells from untreated mouse as well as human liver tissues. This novel protocol is practically relevant, because it provides an easy and nontoxic method to isolate liver stem cells from normal tissue for potential therapeutic purposes.

Polyelectrolyte multilayers in tissue engineering

The layer-by-layer assembly of sequentially adsorbed, alternating polyelectrolytes has become increasingly important over the past two decades. The ease and versatility in assembling polyelectrolyte multilayers (PEMs) has resulted in numerous wide ranging applications of these materials. More recently, PEMs are being used in biological applications ranging from biomaterials, tissue engineering, regenerative medicine, and drug delivery. The ability to manipulate the chemical, physical, surface, and topographical properties of these multilayer architectures by simply changing the pH, ionic strength, thickness, and postassembly modifications render them highly suitable to probe the effects of external stimuli on cellular responsiveness. In the field of regenerative medicine, the ability to sequester growth factors and to tether peptides to PEMs has been exploited to direct the lineage of progenitor cells and to subsequently maintain a desired phenotype. Additional novel applications include the use of PEMs in the assembly of three-dimensional layered architectures and as coatings for individual cells to deliver tunable payloads of drugs or bioactive molecules. This review focuses on literature related to the modulation of chemical and physical properties of PEMs for tissue engineering applications and recent research efforts in maintaining and directing cellular phenotype in stem cell differentiation.