Impact of Nanotopography, Heparin Hydrogel Microstructures, and Encapsulated Fibroblasts on Phenotype of Primary Hepatocytes

Delivering Mechanical Stimulation to Cells: State of the Art in Materials and Devices Design

Biochemical signals, such as growth factors, cytokines, and transcription factors are known to play a crucial role in regulating a variety of cellular activities as well as maintaining the normal function of different tissues and organs. If the biochemical signals are assumed to be one side of the coin, the other side comprises biophysical cues. There is growing evidence showing that biophysical signals, and in particular mechanical cues, also play an important role in different stages of human life ranging from morphogenesis during embryonic development to maturation and maintenance of tissue and organ function throughout life. In order to investigate how mechanical signals influence cell and tissue function, tremendous efforts have been devoted to fabricating various materials and devices for delivering mechanical stimuli to cells and tissues. Here, an overview of the current state of the art in the design and development of such materials and devices is provided, with a focus on their design principles, and challenges and perspectives for future research directions are highlighted.

Primary Broiler Hepatocytes for Establishment of a Steatosis Model

Fatty liver hemorrhage syndrome (FLHS) in chickens is characterized by steatosis and bleeding in the liver, which has caused huge losses to the poultry industry. This study aimed to use primary cultured broiler hepatocytes to establish a steatosis model to explore the optimal conditions for inducing steatosis by incubating the cells with a fat emulsion. Primary hepatocytes were isolated from an AA broiler by a modified two-step in situ perfusion method. Hepatocytes were divided into an untreated control group and a fat emulsion group that was incubated with 2.5, 5, 10, or 20% fat emulsion for different times to determine the optimal conditions for inducing steatosis of primary hepatocytes. Incubation of the cells with 10% fat emulsion resulted in cell viability at 48 h of 67%, which was higher than the control group and met the requirements of the model. In the second experiment, steatosis was induced by incubating hepatocytes with 10% fat emulsion for 48 h. In consequence, the apoptosis rate decreased (p > 0.05) and the concentration of ALT (p < 0.001), AST (p < 0.01), and TG (p < 0.05) increased significantly; the expression level of SREBP-1c (p < 0.05) increased, and the expression levels of PPARα (p < 0.001), CPT1 (p < 0.001), and CPT2 (p < 0.05) were lower in the fat emulsion group than in the control group. In conclusion, the induction condition was selected as 10% fat emulsion incubation for 48 h, and we successfully established a fatty liver degeneration model for broilers.

Rational design of hydrogels for immunomodulation

The immune system protects organisms against endogenous and exogenous harm and plays a key role in tissue development, repair, and regeneration. Traditional immunomodulatory biologics exhibit limitations including degradation by enzymes, short half-life, and lack of targeting ability. Encapsulating or binding these biologics within biomaterials is an effective way to address these problems. Hydrogels are promising immunomodulatory materials because of their prominent biocompatibility, tuneability, and versatility. However, to take advantage of these opportunities and optimize material performance, it is important to more specifically elucidate, and leverage on, how hydrogels affect and control the immune response. Here, we summarize how key physical and chemical properties of hydrogels affect the immune response. We first provide an overview of underlying steps of the host immune response upon exposure to biomaterials. Then, we discuss recent advances in immunomodulatory strategies where hydrogels play a key role through a) physical properties including dimensionality, stiffness, porosity, and topography; b) chemical properties including wettability, electric property, and molecular presentation; and c) the delivery of bioactive molecules via chemical or physical cues. Thus, this review aims to build a conceptual and practical toolkit for the design of immune-instructive hydrogels capable of modulating the host immune response.

Influence of surface topography on PCL electrospun scaffolds for liver tissue engineering

Severe liver disease is one of the most common causes of death globally. Currently, whole organ transplantation is the only therapeutic method for end-stage liver disease treatment, however, the need for donor organs far outweighs demand. Recently liver tissue engineering is starting to show promise for alleviating part of this problem. Electrospinning is a well-known method to fabricate a nanofibre scaffold which mimics the natural extracellular matrix that can support cell growth. This study aims to investigate liver cell responses to topographical features on electrospun fibres. Scaffolds with large surface depression (2 μm) (LSD), small surface depression (0.37 μm) (SSD), and no surface depression (NSD) were fabricated by using a solvent-nonsolvent system. A liver cell line (HepG2) was seeded onto the scaffolds for up to 14 days. The SSD group exhibited higher levels of cell viability and DNA content compared to the other groups. Additionally, the scaffolds promoted gene expression of albumin, with all cases having similar levels, while the cell growth rate was altered. Furthermore, the scaffold with depressions showed 0.8 MPa higher ultimate tensile strength compared to the other groups. These results suggest that small depressions might be preferred by HepG2 cells over smooth and large depression fibres and highlight the potential for tailoring liver cell responses.

The effects of surface topography modification on hydrogel properties

Hydrogel has been an attractive biomaterial for tissue engineering, drug delivery, wound healing, and contact lens materials, due to its outstanding properties, including high water content, transparency, biocompatibility, tissue mechanical matching, and low toxicity. As hydrogel commonly possesses high surface hydrophilicity, chemical modifications have been applied to achieve the optimal surface properties to improve the performance of hydrogels for specific applications. Ideally, the effects of surface modifications would be stable, and the modification would not affect the inherent hydrogel properties. In recent years, a new type of surface modification has been discovered to be able to alter hydrogel properties by physically patterning the hydrogel surfaces with topographies. Such physical patterning methods can also affect hydrogel surface chemical properties, such as protein adsorption, microbial adhesion, and cell response. This review will first summarize the works on developing hydrogel surface patterning methods. The influence of surface topography on interfacial energy and the subsequent effects on protein adsorption, microbial, and cell interactions with patterned hydrogel, with specific examples in biomedical applications, will be discussed. Finally, current problems and future challenges on topographical modification of hydrogels will also be discussed.

Double-Network Heparin Dynamic Hydrogels: Dynagels as Anti-bacterial 3D Cell Culture Scaffolds

Double cross-linked dynamic hydrogels, dynagels, have been prepared through reversible imine bonds and supramolecular interactions, which showed good pH responsiveness, injectability, self-healing property and biocompatibility. With the further encapsulation of heparin, the obtained hydrogels exhibited good anti-bacterial activity and promotion effects for 3D cell culture.

Materials engineering, processing, and device application of hydrogel nanocomposites

Hydrogels are widely implemented as key materials in various biomedical applications owing to their soft, flexible, hydrophilic, and quasi-solid nature. Recently, however, new material properties over those of bare hydrogels have been sought for novel applications. Accordingly, hydrogel nanocomposites, i.e., hydrogels converged with nanomaterials, have been proposed for the functional transformation of conventional hydrogels. The incorporation of suitable nanomaterials into the hydrogel matrix allows the hydrogel nanocomposite to exhibit multi-functionality in addition to the biocompatible feature of the original hydrogel. Therefore, various hydrogel composites with nanomaterials, including nanoparticles, nanowires, and nanosheets, have been developed for diverse purposes, such as catalysis, environmental purification, bio-imaging, sensing, and controlled drug delivery. Furthermore, novel technologies for the patterning of such hydrogel nanocomposites into desired shapes have been developed. The combination of such material engineering and processing technologies has enabled the hydrogel nanocomposite to become a key soft component of electronic, electrochemical, and biomedical devices. We herein review the recent research trend in the field of hydrogel nanocomposites, particularly focusing on materials engineering, processing, and device applications. Furthermore, the conclusions are presented with the scope of future research outlook, which also includes the current technical limitations.

Advances of Stem Cell-Laden Hydrogels With Biomimetic Microenvironment for Osteochondral Repair

Osteochondral damage from trauma or osteoarthritis is a general joint disease that can lead to an increased social and economic burden in the modern society. The inefficiency of osteochondral defects is mainly due to the absence of suitable tissue-engineered substrates promoting tissue regeneration and replacing damaged areas. The hydrogels are becoming a promising kind of biomaterials for tissue regeneration. The biomimetic hydrogel microenvironment can be tightly controlled by modulating a number of biophysical and biochemical properties, including matrix mechanics, degradation, microstructure, cell adhesion, and intercellular interactions. In particular, advances in stem cell-laden hydrogels have offered new ideas for the cell therapy and osteochondral repair. Herein, the aim of this review is to underpin the importance of stem cell-laden hydrogels on promoting the development of osteochondral regeneration, especially in the field of manipulation of biomimetic microenvironment and utilization growth factors with various delivery methods.

Cardiac tissue engineering: state-of-the-art methods and outlook

The purpose of this review is to assess the state-of-the-art fabrication methods, advances in genome editing, and the use of machine learning to shape the prospective growth in cardiac tissue engineering. Those interdisciplinary emerging innovations would move forward basic research in this field and their clinical applications. The long-entrenched challenges in this field could be addressed by novel 3-dimensional (3D) scaffold substrates for cardiomyocyte (CM) growth and maturation. Stem cell-based therapy through genome editing techniques can repair gene mutation, control better maturation of CMs or even reveal its molecular clock. Finally, machine learning and precision control for improvements of the construct fabrication process and optimization in tissue-specific clonal selections with an outlook of cardiac tissue engineering are also presented.

Heparin-based and heparin-inspired hydrogels: size-effect, gelation and biomedical applications

The size-effect, fabrication methods and biomedical applications of heparin-based and heparin-inspired hydrogels are reviewed.

High-Performance Resistive Pressure Sensor Based on Elastic Composite Hydrogel of Silver Nanowires and Poly(ethylene glycol)

Improved pressure sensing is of great interest to enable the next-generation of bioelectronics systems. This paper describes the development of a transparent, flexible, highly sensitive pressure sensor, having a composite sandwich structure of elastic silver nanowires (AgNWs) and poly(ethylene glycol) (PEG). A simple PEG photolithography was employed to construct elastic AgNW-PEG composite patterns on flexible polyethylene terephthalate (PET) film. A porous PEG hydrogel structure enabled the use of conductive AgNW patterns while maintaining the elasticity of the composite material, features that are both essential for high-performance pressure sensing. The transparency and electrical properties of AgNW-PEG composite could be precisely controlled by varying the AgNW concentration. An elastic AgNW-PEG composite hydrogel with 0.6 wt % AgNW concentration exhibited high transmittance including T550nm of around 86%, low sheet resistance of 22.69 Ω·sq-1, and excellent bending durability (only 5.8% resistance increase under bending to 10 mm radius). A flexible resistive pressure sensor based on our highly transparent AgNW-PEG composite showed stable and reproducible response, high sensitivity (69.7 kPa-1), low sensing threshold (~2 kPa), and fast response time (20⁻40 ms), demonstrating the effectiveness of the AgNW-PEG composite material as an elastic conductor.

Multilineage Constructs for Scaffold-Based Tissue Engineering: A Review of Tissue-Specific Challenges

There is a growing interest in the regeneration of tissue in interfacial regions, where biological, physical, and chemical attributes vary across tissue type. The simultaneous use of distinct cell lineages can help in developing in vitro structures, analogous to native composite tissues. This literature review gathers the recent reports that have investigated multiple cell types of various sources and lineages in a coculture system for tissue-engineered constructs. Such studies aim at mimicking the native organization of tissues and their interfaces, and/or to improve the development of complex tissue substitutes. This paper thus distinguishes itself from those focusing on technical aspects of coculturing for a single specific tissue. The first part of this review is dedicated to variables of cocultured tissue engineering such as scaffold, cells, and in vitro culture environment. Next, tissue-specific coculture methods and approaches are covered for the most studied tissues. Finally, cross-analysis is performed to highlight emerging trends in coculture principles and to discuss how tissue-specific challenges can inspire new approaches for regeneration of different interfaces to improve the outcomes of various tissue engineering strategies.

Collagen Gels with Different Fibrillar Microarchitectures Elicit Different Cellular Responses

The extracellular matrix consists of a complex mixture of fibrillar proteins, in which the architecture and mechanical properties of the protein fibrils vary considerably in various tissues. Here, we systematically polymerized collagen gels at different temperatures, providing substrates with tunable mechanics and defined local microarchitecture. We studied the dependence of spreading dynamics, proliferation, migration, and differentiation of human mesenchymal stem cells (hMSCs) on the fibrillar properties as compared to the bulk properties of the matrix. We found that high fiber stiffness, together with shorter fiber lengths, limited the transfer of cellular traction forces to nearby fibers. As a result, cells were not able to build up sufficient tension, which suppressed cell spreading, proliferation, and migration. Cells on such fibers also showed limited focal adhesion formation and different lineage selection preferences. In contrast, cell spreading, proliferation, and migration was always associated with fiber recruitment, long-range deformations in the collagen gel networks and an increase in collagen density around cells. Typically, cells on such substrates had a preference for osteogenic differentiation and showed higher levels of focal adhesions formation. These results contribute to a further understanding of the mechanotransduction process and to the design criteria for future biomimetic materials for tissue-engineering applications.

One step fabrication of hydrogel microcapsules with hollow core for assembly and cultivation of hepatocyte spheroids

3D hepatic microtissues can serve as valuable liver analogues for cell-based therapies and for hepatotoxicity screening during preclinical drug development. However, hepatocytes rapidly dedifferentiate in vitro, and typically require 3D culture systems or co-cultures for phenotype rescue. In this work we present a novel microencapsulation strategy, utilizing coaxial flow-focusing droplet microfluidics to fabricate microcapsules with liquid core and poly(ethylene glycol) (PEG) gel shell. When entrapped inside these capsules, primary hepatocytes rapidly formed cell-cell contacts and assembled into compact spheroids. High levels of hepatic function were maintained inside the capsules for over ten days. The microencapsulation approach described here is compatible with difficult-to-culture primary epithelial cells, allows for tuning gel mechanical properties and diffusivity, and may be used in the future for high density suspension cell cultures.

STATEMENT OF SIGNIFICANCE

Our paper combines an interesting new way for making capsules with cultivation of difficult-to-maintain primary epithelial cells (hepatocytes). The microcapsules described here will enable high density suspension culture of hepatocytes or other cells and may be used as building blocks for engineering tissues.

Characterization of rat or human hepatocytes cultured in microphysiological systems (MPS) to identify hepatotoxicity

The liver is the main site for drug and xenobiotics metabolism, including inactivation or bioactivation. In order to improve the predictability of drug safety and efficacy in clinical development, and to facilitate the evaluation of the potential human health effects from exposure to environmental contaminants, there is a critical need to accurately model human organ systems such as the liver in vitro. We are developing a microphysiological system (MPS) based on a new commercial microfluidic platform (Nortis, Inc.) that can utilize primary liver cells from multiple species (e.g., rat and human). Compared to conventional monolayer cell culture, which typically survives for 5-7days or less, primary rat or human hepatocytes in an MPS exhibited higher viability and improved hepatic functions, such as albumin production, expression of hepatocyte marker HNF4α and canaliculi structure, for up to 14days. Additionally, induction of Cytochrome P450 (CYP) 1A and 3A4 in cryopreserved human hepatocytes was observed in the MPS. The acute cytotoxicity of the potent hepatotoxic and hepatocarcinogen, aflatoxin B₁, was evaluated in human hepatocytes cultured in an MPS, demonstrating the utility of this model for acute hepatotoxicity assessment. These results indicate that MPS-cultured hepatocytes provide a promising approach for evaluating chemical toxicity in vitro.

A Facile Approach for Constructing Conductive Polymer Patterns for Application in Electrochromic Devices and Flexible Microelectrodes

We developed a novel strategy for fabricating poly(3,4-ethylenedioxythiophene) (PEDOT) patterns on various substrates, including hydrogels, via sequential solution procedure without multistep chemical etching or lift-off processes. First, PEDOT nanothin films were prepared on a glass substrate by solution phase monomer casting and oxidative polymerization. As a second step, after UV-induced poly(ethylene glycol) (PEG) photolithography at the PEDOT/PEG interface through a photomask, the hydrogel was peeled away from the PEDOT-coated glass substrate to detach the UV-exposed PEDOT region, which left the UV nonexposed PEDOT region intact on the glass substrate, resulting in PEDOT patterns. In a final step, the PEDOT patterns were cleanly transferred from the glass to a flexible hydrogel substrate by a direct-transfer process based on a second round of gelation process. Using this strategy, PEDOT patterns on ITO glass or ITO film were used to successfully fabricate an electrochromic (EC) device that exhibited stable electrochromic switching as a function of applied potential. Furthermore, PEDOT patterns on hydrogel were used to fabricate all organic, flexible microelectrodes with good electrical properties and excellent mechanical flexibility. Importantly, the conductivity of PEDOT patterns on hydrogel (ca. 235 S cm^-1) described here is significantly higher than that previously reported (ca. 20-70 S cm^-1). This approach can be easily integrated into various technological fabrication steps for the development of next-generation bioelectronics systems.

Impact of Collagen/Heparin Multilayers for Regulating Bone Cellular Functions

Bone cell interaction with extracellular matrix (ECM) microenvironment is of critical importance when engineering surface interfaces for bone regeneration. In this work layer-by-layer films of type I collagen (coll), the major constituent of bone ECM, and heparin (hep), a glycosaminoglycan, were assembled on poly(l-lactic acid) (PLLA) substrates to evaluate the impact of the biomacromolecular coating on cell activity. The surface modification of PLLA demonstrated that the hep/coll multilayer is stable after 10 bilayers (confirmed by contact angle, infrared spectroscopy, and morphological analysis). This simple approach provided novel information on the effect of heparin on type I collagen hierarchical organization and subsequent cell response of osteoblast-like (MC3T3-E1) and human bone marrow-derived mesenchymal stem cells (hMSCs). Interestingly, the number of deposited heparin layers (1 or 10) appeared to play an important role in the self-assembly of collagen into fibrils, stabilizing the fibrous collagen layer, and potentially impacting hMSCs activity.

Cell biology is different in small volumes: endogenous signals shape phenotype of primary hepatocytes cultured in microfluidic channels

The approaches for maintaining hepatocytes in vitro are aimed at recapitulating aspects of the native liver microenvironment through the use of co-cultures, surface coatings and 3D spheroids. This study highlights the effects of spatial confinement-a less studied component of the in vivo microenvironment. We demonstrate that hepatocytes cultured in low-volume microfluidic channels (microchambers) retain differentiated hepatic phenotype for 21 days whereas cells cultured in regular culture plates under identical conditions de-differentiate after 7 days. Careful consideration of nutrient delivery and oxygen tension suggested that these factors could not solely account for enhanced cell function in microchambers. Through a series of experiments involving microfluidic chambers of various heights and inhibition of key molecular pathways, we confirmed that phenotype of hepatocytes in small volumes was shaped by endogenous signals, both hepato-inductive growth factors (GFs) such as hepatocyte growth factor (HGF) and hepato-disruptive GFs such as transforming growth factor (TGF)-β1. Hepatocytes are not generally thought of as significant producers of GFs–this role is typically assigned to nonparenchymal cells of the liver. Our study demonstrates that, in an appropriate microenvironment, hepatocytes produce hepato-inductive and pro-fibrogenic signals at the levels sufficient to shape their phenotype and function.

Direct photo-patterning on anthracene containing polymer for guiding stem cell adhesion

Background

Various micropatterned surfaces capable of guiding the selective adhesion of biomolecules such as proteins and cells are of great interests in biosensor, diagnostics, drug screening, and tissue engineering. In this study, we described a simple photo-patterning method to prepare micro-patterned films for stem cell patterning using anthracene containing polymers (PMAn). This micro patterned polymer film was prepared by the facile photo-reaction of anthracene units in polymer backbone structure.

Results

The UV irradiation of PMAn through a photomask resulted in the quenching of fluorescent intensity as well as the changes in surface wettability from hydrophobic to hydrophilic surface. As a result, UV exposed regions of PMAn film show lower fluorescent intensity as well as higher proliferation rate of mesenchymal stem cells (MSCs) than unexposed region of PMAn film. Furthermore, the selective MSC attachment was clearly observed in the UV exposed regions of PMAn film.

Conclusion

We developed a simple cell patterning method with a fluorescent, biocompatible, and patternable polymer film containing anthracene units. This method provides a facile stem cell patterning method and could be extended to various patterning of biomaterials without labor-intensive preparation and no pre-treatment for complex interactions of cell-microenvironment.

The effect and mechanism of bufalin on regulating hepatocellular carcinoma cell invasion and metastasis via Wnt/β-catenin signaling pathway

Hepatocellular carcinoma (HCC) is a highly malignant tumor with an extremely poor prognosis. Our preliminary study indicated that bufalin could restrain the proliferation of human hepatoma BEL-7402 cells in a time- and dose-dependent manner. In the present study, the colony formation assay, the Transwell invasion assay, the western blot analysis and the immunofluorescence method were respectively used to investigate the effect and mechanism of bufalin against HCC cell invasion and metastasis. We found that: i) bufalin had significant inhibitory effect on the cell proliferation of BEL-7402 cells; ii) bufalin markedly inhibited the migration and invasion of BEL-7402 cells; iii) bufalin could suppress the phosphorylation of GSK-3β Ser9 site in BEL-7402 cells, decrease the expression of β-catenin, cyclin D1, metalloproteinases-7 (MMP-7) and cyclooxygenase-2 (COX-2) in the cytoplasm, and increase the expression of E-cadherin and β-catenin on the cell membrane; and iv) the expression of α-fetoprotein significantly decreased and the expression of albumin increased in BEL-7402 cells after bufalin was used. Our results indicate that: i) bufalin can regulate the expression of associated factors in Wnt/β-catenin signaling pathway of BEL-7402 cells through suppressing the phosphorylation of GSK-3β Ser9 site; ii) bufalin can strengthen intercellular E-cadherin/β-catenin complex to control epithelial-mesenchymal transition; and iii) bufalin can reverse the malignant phenotype and promote the differentiation and maturation by regulating the AFP and ALB expression in BEL-7402 cells. These are very important mechanisms of bufalin on the inhibition of the invasion and metastasis of HCC cells.