Mechanochemical manipulation of hepatocyte aggregation can selectively induce or repress liver-specific function

The Pathophysiology of Portal Hypertension

This article reviews the pathophysiology of portal hypertension that includes multiple mechanisms internal and external to the liver. This article starts with a review of literature describing the cellular and molecular mechanisms of portal hypertension, microvascular thrombosis, sinusoidal venous congestion, portal angiogenesis, vascular hypocontractility, and hyperdynamic circulation. Mechanotransduction and the gut-liver axis, which are newer areas of research, are reviewed. Dysfunction of this axis contributes to chronic liver injury, inflammation, fibrosis, and portal hypertension. Sequelae of portal hypertension are discussed in subsequent studies.

Analysis of culture and RNA isolation methods for precision-cut liver slices from cirrhotic rats

Precision-cut liver slices (PCLS) are increasingly used as a model to investigate anti-fibrotic therapies. However, many studies use PCLS from healthy animals treated with pro-fibrotic stimuli in culture, which reflects only the early stages of fibrosis. The effects of different culture conditions on PCLS from cirrhotic animals has not been well characterized and there is no consensus on optimal methods. In this study, we report a method for the collection and culture of cirrhotic PCLS and compare the effect of common culture conditions on viability, function, and gene expression. Additionally, we compared three methods of RNA isolation and identified a protocol with high yield and purity. We observed significantly increased albumin production when cultured with insulin-transferrin-selenium and dexamethasone, and when incubated on a rocking platform. Culturing with insulin-transferrin-selenium and dexamethasone maintained gene expression closer to the levels in fresh slices. However, despite stable viability and function up to 4 days, we found significant changes in expression of key genes by day 2. Interestingly, we also observed that cirrhotic PCLS maintain viability in culture longer than slices from healthy animals. Due to the influence of matrix stiffness on fibrosis and hepatocellular function, it is important to evaluate prospective anti-fibrotic therapies in a platform that preserves tissue biomechanics. PCLS from cirrhotic animals represent a promising tool for the development of treatments for chronic liver disease.

Function of hepatocyte spheroids in bioactive microcapsules is enhanced by endogenous and exogenous hepatocyte growth factor

The ability to maintain functional hepatocytes has important implications for bioartificial liver development, cell-based therapies, drug screening, and tissue engineering. Several approaches can be used to restore hepatocyte function in vitro, including coating a culture substrate with extracellular matrix (ECM), encapsulating cells within biomimetic gels (Collagen- or Matrigel-based), or co-cultivation with other cells. This paper describes the use of bioactive heparin-based core-shell microcapsules to form and cultivate hepatocyte spheroids. These microcapsules are comprised of an aqueous core that facilitates hepatocyte aggregation into spheroids and a heparin hydrogel shell that binds and releases growth factors. We demonstrate that bioactive microcapsules retain and release endogenous signals thus enhancing the function of encapsulated hepatocytes. We also demonstrate that hepatic function may be further enhanced by loading exogenous hepatocyte growth factor (HGF) into microcapsules and inhibiting transforming growth factor (TGF)-β1 signaling. Overall, bioactive microcapsules described here represent a promising new strategy for the encapsulation and maintenance of primary hepatocytes and will be beneficial for liver tissue engineering, regenerative medicine, and drug testing applications.

The Impact of the Cellular Environment and Aging on Modeling Alzheimer's Disease in 3D Cell Culture Models

Creating a cellular model of Alzheimer's disease (AD) that accurately recapitulates disease pathology has been a longstanding challenge. Recent studies showed that human AD neural cells, integrated into three-dimensional (3D) hydrogel matrix, display key features of AD neuropathology. Like in the human brain, the extracellular matrix (ECM) plays a critical role in determining the rate of neuropathogenesis in hydrogel-based 3D cellular models. Aging, the greatest risk factor for AD, significantly alters brain ECM properties. Therefore, it is important to understand how age-associated changes in ECM affect accumulation of pathogenic molecules, neuroinflammation, and neurodegeneration in AD patients and in vitro models. In this review, mechanistic hypotheses is presented to address the impact of the ECM properties and their changes with aging on AD and AD-related dementias. Altered ECM characteristics in aged brains, including matrix stiffness, pore size, and composition, will contribute to disease pathogenesis by modulating the accumulation, propagation, and spreading of pathogenic molecules of AD. Emerging hydrogel-based disease models with differing ECM properties provide an exciting opportunity to study the impact of brain ECM aging on AD pathogenesis, providing novel mechanistic insights. Understanding the role of ECM aging in AD pathogenesis should also improve modeling AD in 3D hydrogel systems.

Rat liver ECM incorporated into electrospun polycaprolactone scaffolds as a platform for hepatocyte culture

Liver disease is expanding across the globe; however, health-care systems still lack approved pharmaceutical treatment strategies to mitigate potential liver failures. Organ transplantation is the only treatment for liver failure and with increasing cases of liver disease, transplant programs increasingly cannot provide timely transplant availability for all patients. The development of pharmaceutical mitigation strategies is clearly necessary and methods to improve drug development processes are considered vital for this purpose. Herein, we present a methodology for incorporating whole organ decellularised rat liver ECM (rLECM) into polycaprolactone (PCL) electrospun scaffolds with the aim of producing biologically relevant liver tissue models. rLECM PCL scaffolds have been produced with 5 w/w% and 10 w/w% rLECM:PCL and were analyzed by SEM imaging, tensile mechanical analyses and FTIR spectroscopy. The hepatocellular carcinoma cell line, HepG2, was cultured upon the scaffolds for 14 days and were analyzed through cell viability assay, DNA quantification, albumin quantification, immunohistochemistry, and RT-qPCR gene expression analysis. Results showed significant increases in proliferative activity of HepG2 on rLECM containing scaffolds alongside maintained key gene expression. This study confirms that rLECM can be utilized to modulate the bioactivity of electrospun PCL scaffolds and has the potential to produce electrospun scaffolds suitable for enhanced hepatocyte cultures and in-vitro liver tissue models.

In vitro long term differentiation and functionality of three-dimensional bioprinted primary human hepatocytes: application for in vivo engraftment

In recent decades, 3D in vitro cultures of primary human hepatocytes (PHH) have been increasingly developed to establish models capable of faithfully mimicking main liver functions. The use of 3D bioprinting, capable of recreating structures composed of cells embedded in matrix with controlled microarchitectures, is an emergent key feature for tissue engineering. In this work, we used an extrusion-based system to print PHH in a methacrylated gelatin matrix (GelMa). PHH bioprinted in GelMa rapidly organized into polarized hollow spheroids and were viable for at least 28 days of culture. These PHH were highly differentiated with maintenance of liver differentiation genes over time, as demonstrated by transcriptomic analysis and functional approaches. The cells were polarized with localization of apico/canalicular regions, and displayed activities of phase I and II biotransformation enzymes that could be regulated by inducers. Furthermore, the implantation of the bioprinted structures in mice demonstrated their capability to vascularize, and their ability to maintain human hepatic specific functions for at least 28 days was illustrated by albumin secretion and debrisoquine metabolism. This model could hold great promise for human liver tissue generation and its use in future biotechnological developments.

Biophysical properties of hydrogels for mimicking tumor extracellular matrix

The extracellular matrix (ECM) is an essential component of the tumor microenvironment. It plays a critical role in regulating cell-cell and cell-matrix interactions. However, there is lack of systematic and comparative studies on different widely-used ECM mimicking hydrogels and their properties, making the selection of suitable hydrogels for mimicking different in vivo conditions quite random. This study systematically evaluates the biophysical attributes of three widely used natural hydrogels (Matrigel, collagen gel and agarose gel) including complex modulus, loss tangent, diffusive permeability and pore size. A new and facile method was developed combining Critical Point Drying, Scanning Electron Microscopy imaging and a MATLAB image processing program (CSM method) for the characterization of hydrogel microstructures. This CSM method allows accurate measurement of the hydrogel pore size down to nanometer resolution. Furthermore, a microfluidic device was implemented to measure the hydrogel permeability (P_d) as a function of particle size and gel concentration. Among the three gels, collagen gel has the lowest complex modulus, medium pore size, and the highest loss tangent. Agarose gel exhibits the highest complex modulus, the lowest loss tangent and the smallest pore size. Collagen gel and Matrigel produced complex moduli close to that estimated for cancer ECM. The P_d of these hydrogels decreases significantly with the increase of particle size. By assessing different hydrogels' biophysical characteristics, this study provides valuable insights for tailoring their properties for various three-dimensional cancer models.

Cell-cell adhesion impacts epithelia response to substrate stiffness: Morphology and gene expression

Monolayer epithelial cells interact constantly with the substrate they reside on and their surrounding neighbors. As such, the properties of epithelial cells are profoundly governed by the mechanical and molecular cues that arise from both the substrate and contiguous cell neighbors. Although both cell-substrate and cell-cell interactions have been studied individually, these results are difficult to apply to native confluent epithelia, in which both jointly regulate the cell phenotype. Specifically, it remains poorly understood about the intertwined contributions from intercellular adhesion and substrate stiffness on cell morphology and gene expression, two essential microenvironment properties. Here, by adjusting the substrate modulus and altering the intercellular adhesion within confluent kidney epithelia, we found that cell-substrate and cell-cell interactions can mask each other's influence. For example, we found that epithelial cells exhibit an elongated morphological phenotype only when the substrate modulus and intercellular adhesions are both reduced, whereas their motility can be upregulated by either reduction. These results illustrate that combinatorial changes of the physical microenvironment are required to alter cell morphology and gene expression.

Autonomously Propelled Colloids for Penetration and Payload Delivery in Complex Extracellular Matrices

For effective treatment of diseases such as cancer or fibrosis, it is essential to deliver therapeutic agents such as drugs to the diseased tissue, but these diseased sites are surrounded by a dense network of fibers, cells, and proteins known as the extracellular matrix (ECM). The ECM forms a barrier between the diseased cells and blood circulation, the main route of administration of most drug delivery nanoparticles. Hence, a stiff ECM impedes drug delivery by limiting the transport of drugs to the diseased tissue. The use of self-propelled particles (SPPs) that can move in a directional manner with the application of physical or chemical forces can help in increasing the drug delivery efficiency. Here, we provide a comprehensive look at the current ECM models in use to mimic the in vivo diseased states, the different types of SPPs that have been experimentally tested in these models, and suggest directions for future research toward clinical translation of SPPs in diverse biomedical settings.

Biomaterials Regulate Mechanosensors YAP/TAZ in Stem Cell Growth and Differentiation

Tissue-resident stem cells are surrounded by a microenvironment known as 'stem cell niche' which is specific for each stem cell type. This niche comprises of cell-intrinsic and -extrinsic factors like biochemical and biophysical signals, which regulate stem cell characteristics and differentiation. Biochemical signals have been thoroughly studied however, the effect of biophysical signals on stem cell regulation is yet to be completely understood. Biomaterials have aided in addressing this issue since they can provide a defined and tuneable microenvironment resembling in vivo conditions. We review various biomaterials used in many studies which have shown a connection between biomaterial-generated mechanical signals and alteration in stem cell behaviour. Researchers probed to understand the mechanism of mechanotransduction and reported that the signals from the extracellular matrix regulate a transcription factor yes-associated protein (YAP)/transcriptional coactivator with PDZ-binding motif (TAZ), which is a downstream-regulator of the Hippo pathway and it transduces the mechanical signals inside the nucleus. We highlight the role of the YAP/TAZ as mechanotransducers in stem cell self-renewal and differentiation in response to substrate stiffness, also the possibility of mechanobiology as the emerging field of regenerative medicines and three-dimensional tissue printing.

Scaffold-based 3D cellular models mimicking the heterogeneity of osteosarcoma stem cell niche

The failure of the osteosarcoma conventional therapies leads to the growing need for novel therapeutic strategies. The lack of specificity for the Cancer Stem Cells (CSCs) population has been recently identified as the main limitation in the current therapies. Moreover, the traditional two-dimensional (2D) in vitro models, employed in the drug testing and screening as well as in the study of cell and molecular biology, are affected by a poor in vitro-in vivo translation ability. To overcome these limitations, this work provides two tumour engineering approaches as new tools to address osteosarcoma and improve therapy outcomes. In detail, two different hydroxyapatite-based bone-mimicking scaffolds were used to recapitulate aspects of the in vivo tumour microenvironment, focusing on CSCs niche. The biological performance of human osteosarcoma cell lines (MG63 and SAOS-2) and enriched-CSCs were deeply analysed in these complex cell culture models. The results highlight the fundamental role of the tumour microenvironment proving the mimicry of osteosarcoma stem cell niche by the use of CSCs together with the biomimetic scaffolds, compared to conventional 2D culture systems. These advanced 3D cell culture in vitro tumour models could improve the predictivity of preclinical studies and strongly enhance the clinical translation.

Synthetic alternatives to Matrigel

Matrigel, a basement-membrane matrix extracted from Engelbreth-Holm-Swarm mouse sarcomas, has been used for more than four decades for a myriad of cell culture applications. However, Matrigel is limited in its applicability to cellular biology, therapeutic cell manufacturing and drug discovery owing to its complex, ill-defined and variable composition. Variations in the mechanical and biochemical properties within a single batch of Matrigel - and between batches - have led to uncertainty in cell culture experiments and a lack of reproducibility. Moreover, Matrigel is not conducive to physical or biochemical manipulation, making it difficult to fine-tune the matrix to promote intended cell behaviours and achieve specific biological outcomes. Recent advances in synthetic scaffolds have led to the development of xenogenic-free, chemically defined, highly tunable and reproducible alternatives. In this Review, we assess the applications of Matrigel in cell culture, regenerative medicine and organoid assembly, detailing the limitations of Matrigel and highlighting synthetic scaffold alternatives that have shown equivalent or superior results. Additionally, we discuss the hurdles that are limiting a full transition from Matrigel to synthetic scaffolds and provide a brief perspective on the future directions of synthetic scaffolds for cell culture applications.

The development of a high throughput drug-responsive model of white adipose tissue comprising adipogenic 3T3-L1 cells in a 3D matrix

Adipose models have been applied to mechanistic studies of metabolic diseases (such as diabetes) and the subsequent discovery of new therapeutics. However, typical models are either insufficiently complex (2D cell cultures) or expensive and labor intensive (mice/in vivo). To bridge the gap between these models and in order to better inform pre-clinical studies we have developed a drug-responsive 3D model of white adipose tissue (WAT). Here, spheroids (680 ± 60 μm) comprising adipogenic 3T3-L1 cells encapsulated in 3D matrix were fabricated manually on a 96 well scale. Spheroids were highly characterised for lipid morphology, selected metabolite and adipokine secretion, and gene expression; displaying significant upregulation of certain adipogenic-specific genes compared with a 2D model. Furthermore, induction of lipolysis and promotion of lipogenesis in spheroids could be triggered by exposure to 8-br-cAMP and oleic-acid respectively. Metabolic and high content imaging data of spheroids exposed to an adipose-targeting drug, rosiglitazone, resulted in dose-responsive behavior. Thus, our 3D WAT model has potential as a powerful scalable tool for compound screening and for investigating adipose biology.

Injectable Silk Nanofiber Hydrogels for Sustained Release of Small-Molecule Drugs and Vascularization

Strategies to control neovascularization in damaged tissues remain a key issue in regenerative medicine. Unlike most reported desferrioxamine (DFO)-loaded systems where DFO demonstrates a burst release, here we attain zero-order release behavior above 40 days. This outcome was achieved by blending DFO with silk nanofibers with special hydrophilic-hydrophobic properties. The special silk nanofibers showed strong physical binding capacity with DFO, avoiding chemical cross-linking. Using these new biomaterials in vivo in a rat wound model suggested that the DFO-loaded silk nanofiber hydrogel systems stimulated angiogenesis by the sustained release of DFO, but also facilitated cell migration and tissue ingrowth. These features resulted in faster formation of a blood vessel network in the wounds, as well improved healing when compared to the free DFO system. The DFO-loaded systems are also suitable for the regeneration of other tissues, such as nerve and bone, suggesting universality in the biomedical field.

Liver-specific extracellular matrix hydrogel promotes liver-specific functions of hepatocytes in vitro and survival of transplanted hepatocytes in vivo

A solubilized liver-specific extracellular matrix (L-ECM) substratum was obtained by decellularization of porcine liver using Triton X-100 and pepsin treatments. The L-ECM was able to immobilize hepatocyte growth factor at a high efficiency of 87%. L-ECM gelled spontaneously in a physiologically neutral environment. Primary hepatocytes embedded in the L-ECM gel showed a high albumin synthesis activity and ethoxyresorufin-O-deethylase (EROD) activity even at 3 weeks in culture. In addition, the L-ECM gel-embedded hepatocytes implanted subcutaneously into partial hepatectomized rats showed a high survival rate (18%) and formed a large liver tissue-like structure. Their efficiencies of EROD activity and large liver tissue-like structure formation were about twice those of collagen gel-embedded hepatocytes. Based on these results, we clarified the effectiveness of L-ECM gel as a substrate for hepatocyte culture and transplantation.

Cell force-mediated matrix reorganization underlies multicellular network assembly

Vasculogenesis is the de novo formation of a vascular network from individual endothelial progenitor cells occurring during embryonic development, organogenesis, and adult neovascularization. Vasculogenesis can be mimicked and studied in vitro using network formation assays, in which endothelial cells (ECs) spontaneously form capillary-like structures when seeded in the appropriate microenvironment. While the biochemical regulators of network formation have been well studied using these assays, the role of mechanical and topographical properties of the extracellular matrix (ECM) is less understood. Here, we utilized both natural and synthetic fibrous materials to better understand how physical attributes of the ECM influence the assembly of EC networks. Our results reveal that active cell-mediated matrix recruitment through actomyosin force generation occurs concurrently with network formation on Matrigel, a reconstituted basement membrane matrix regularly used to promote EC networks, and on synthetic matrices composed of electrospun dextran methacrylate (DexMA) fibers. Furthermore, modulating physical attributes of DexMA matrices that impair matrix recruitment consequently inhibited the formation of cellular networks. These results suggest an iterative process in which dynamic cell-induced changes to the physical microenvironment reciprocally modulate cell behavior to guide the formation and stabilization of multicellular networks.

Bioinspired liver scaffold design criteria

Maintaining hepatic functional characteristics in-vitro is considered one of the main challenges in engineering liver tissue. As hepatocytes cultured ex-vivo are deprived of their native extracellular matrix (ECM) milieu, developing scaffolds that mimic the biomechanical and physicochemical properties of the native ECM is thought to be a promising approach for successful tissue engineering and regenerative medicine applications. On the basis that the decellularized liver matrix represents the ideal design template for engineering bioinspired hepatic scaffolds, to derive quantitative descriptors of liver ECM architecture, we characterised decellularised liver matrices in terms of their biochemical, viscoelastic and structural features along with porosity, permeability and wettability. Together, these data provide a unique set of quantitative design criteria which can be used to generate guidelines for fabricating biomaterial scaffolds for liver tissue engineering. As proof-of-concept, we investigated hepatic cell response to substrate viscoelasticity. On collagen hydrogels mimicking decellularised liver mechanics, cells showed superior morphology, higher viability and albumin secretion than on stiffer and less viscous substrates. Although scaffold properties are generally inspired by those of native tissues, our results indicate significant differences between the mechano-structural characteristics of untreated and decellularised hepatic tissue. Therefore, we suggest that design rules - such as mechanical properties and swelling behaviour - for engineering biomimetic scaffolds be re-examined through further studies on substrates matching the features of decellularized liver matrices.

A Genome-wide Analysis of Human Pluripotent Stem Cell-Derived Endothelial Cells in 2D or 3D Culture

A defined protocol for efficiently deriving endothelial cells from human pluripotent stem cells was established and vascular morphogenesis was used as a model system to understand how synthetic hydrogels influence global biological function compared with common 2D and 3D culture platforms. RNA sequencing demonstrated that gene expression profiles were similar for endothelial cells and pericytes cocultured in polyethylene glycol (PEG) hydrogels or Matrigel, while monoculture comparisons identified distinct vascular signatures for each cell type. Endothelial cells cultured on tissue-culture polystyrene adopted a proliferative phenotype compared with cells cultured on or encapsulated in PEG hydrogels. The proliferative phenotype correlated to increased FAK-ERK activity, and knockdown or inhibition of ERK signaling reduced proliferation and expression for cell-cycle genes while increasing expression for “3D-like” vasculature development genes. Our results provide insight into the influence of 2D and 3D culture formats on global biological processes that regulate cell function.

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Defined, high-efficiency differentiation of human PSCs to endothelial cell

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Comprehensive genome-wide comparisons of 2D and 3D cell-culture formats

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Gene expression profiles for endothelial cells and pericytes in 3D cell culture

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Highly proliferative phenotypes on tissue-culture polystyrene surfaces

ECM Composition and Rheology Regulate Growth, Motility, and Response to Photodynamic Therapy in 3D Models of Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma is characterized by prominent stromal involvement, which plays complex roles in regulating tumor growth and therapeutic response. The extracellular matrix (ECM)-rich stroma associated with this disease has been implicated as a barrier to drug penetration, although stromal depletion strategies have had mixed clinical success. It remains less clear how interactions with ECM, acting as a biophysical regulator of phenotype, not only a barrier to drug perfusion, regulate susceptibilities and resistance to specific therapies. In this context, an integrative approach is used to evaluate invasive behavior and motility in rheologically characterized ECM as determinants of chemotherapy and photodynamic therapy (PDT) responses. We show that in 3D cultures with ECM conditions that promote invasive progression, response to PDT is markedly enhanced in the most motile ECM-infiltrating populations, whereas the same cells exhibit chemoresistance. Conversely, drug-resistant sublines with enhanced invasive potential were generated to compare differential treatment response in identical ECM conditions, monitored by particle tracking microrheology measurements of matrix remodeling. In both scenarios, ECM-infiltrating cell populations exhibit increased sensitivity to PDT, whether invasion is consequent to selection of chemoresistance, or whether chemoresistance is correlated with acquisition of invasive behavior. However, while ECM-invading, chemoresistant cells exhibit mesenchymal phenotype, induction of EMT in monolayers without ECM was not sufficient to enhance PDT sensitivity, yet does impart chemoresistance as expected. In addition to containing platform development with broader applicability to inform microenvironment-dependent therapeutics, these results reveal the efficacy of PDT for targeting the most aggressive, chemoresistant, invasive pancreatic ductal adenocarcinoma associated with dismal outcomes for this disease.

IMPLICATIONS

ECM-infiltrating and chemoresistant pancreatic tumor populations exhibit increased sensitivity to PDT. Mol Cancer Res; 15(1); 15-25. ©2016 AACR.

Sample, testing and analysis variables affecting liver mechanical properties: A review

Given the critical role of liver mechanics in regulating cell response and directing the development of tissue fibrosis, accurately characterising its mechanical behaviour is of relevance for both diagnostic purposes as well as for tissue engineering and for the development of in-vitro models. Determining and quantifying the mechanical behaviour of soft biological tissues is, however, highly challenging due to their intrinsic labile nature. Indeed, a unique set of values of liver mechanical properties is still lacking to date; testing conditions can significantly affect sample status and hence the measured behaviour and reported results are strongly dependent on the adopted testing method and configuration as well as sample type and status. This review aims at summarising the bulk mechanical properties of liver described in the literature, discussing the possible sources of variation and their implications on the reported results. We distinguish between the intrinsic mechanical behaviour of hepatic tissue, which depends on sample variables, and the measured mechanical properties which also depend on the testing and analysis methods. Finally, the review provides guidelines on tissue preparation and testing conditions for generating reproducible data which can be meaningfully compared across laboratories.

STATEMENT OF SIGNIFICANCE

Soft tissue mechanics is widely investigated, but poorly understood. This review identifies and discusses sample and testing variables which can influence the mechanical behaviour of hepatic tissue and consequently the measured mechanical properties. To encourage the biomaterial community towards more standardized testing of soft tissues and enable comparisons between data from different laboratories, we have established new testing methods and experimental recommendations for sample preparation and testing. The review could be of wide interest to scientists involved in biomaterials research because it addresses and proposes guidelines for several issues related to the mechanical testing of soft tissues whose implications have not been considered together before.

Effect of amine content and chemistry on long-term, three-dimensional hepatocyte spheroid culture atop aminated elastin-like polypeptide coatings

Culture conditions that induce hepatic spheroidal aggregates sustain liver cells with metabolism that mimics in vivo hepatocytes. Here we present an array of elastin-like polypeptide conjugate coating materials (Aminated-ELPs) that are biocompatible, have spheroid-forming capacity, can be coated atop traditional culture surfaces, and maintain structural integrity while ensuring adherence of spheroids over long culture period. The Aminated-ELPs were synthesized either by direct conjugation of ELP and various polyelectrolytes or by conjugating both ELP and various small electrolytes to the reactive polymer poly(2-vinyl-4,4-dimethyl azlactone) (PVDMA). Spheroid morphology, cellular metabolic function, and liver-specific gene expression over the long-term, 20-day culture period were assessed through optical microscopy, measurement of total protein content and albumin and urea production, and quantitative real-time (qRT) PCR. We found that the amine content of the Aminated-ELP coatings dictated the initial hepatocyte attachment, but not the subsequent hepatocyte spheroid formation and their continued attachment. A lower amine content was generally found to sustain higher albumin production by the spheroids. Out of the 19 Aminated-ELP coatings tested, we found that the lysine-containing substrates comprising ELP-polylysine or ELP-PVDMA-butanediamine proved to consistently culture productive spheroidal hepatocytes. We suggest that the incorporation of lysine functional groups in Aminated-ELP rendered more biocompatible surfaces, increasing spheroid attachment and leading to increased liver-specific function. Taken together, the Aminated-ELP array presented here has the potential to create in vitro hepatocyte culture models that mimic in vivo liver functionality and thus, lead to better understanding of liver pathophysiology and superior screening methods for drug efficacy and toxicity. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 377-388, 2017.

Screening out irrelevant cell-based models of disease

The common and persistent failures to translate promising preclinical drug candidates into clinical success highlight the limited effectiveness of disease models currently used in drug discovery. An apparent reluctance to explore and adopt alternative cell- and tissue-based model systems, coupled with a detachment from clinical practice during assay validation, contributes to ineffective translational research. To help address these issues and stimulate debate, here we propose a set of principles to facilitate the definition and development of disease-relevant assays, and we discuss new opportunities for exploiting the latest advances in cell-based assay technologies in drug discovery, including induced pluripotent stem cells, three-dimensional (3D) co-culture and organ-on-a-chip systems, complemented by advances in single-cell imaging and gene editing technologies. Funding to support precompetitive, multidisciplinary collaborations to develop novel preclinical models and cell-based screening technologies could have a key role in improving their clinical relevance, and ultimately increase clinical success rates.

Physiological ranges of matrix rigidity modulate primary mouse hepatocyte function in part through hepatocyte nuclear factor 4 alpha

Matrix rigidity has important effects on cell behavior and is increased during liver fibrosis; however, its effect on primary hepatocyte function is unknown. We hypothesized that increased matrix rigidity in fibrotic livers would activate mechanotransduction in hepatocytes and lead to inhibition of liver-specific functions. To determine the physiologically relevant ranges of matrix stiffness at the cellular level, we performed detailed atomic force microscopy analysis across liver lobules from normal and fibrotic livers. We determined that normal liver matrix stiffness was around 150 Pa and increased to 1-6 kPa in areas near fibrillar collagen deposition in fibrotic livers. In vitro culture of primary hepatocytes on collagen matrix of tunable rigidity demonstrated that fibrotic levels of matrix stiffness had profound effects on cytoskeletal tension and significantly inhibited hepatocyte-specific functions. Normal liver stiffness maintained functional gene regulation by hepatocyte nuclear factor 4 alpha (HNF4α), whereas fibrotic matrix stiffness inhibited the HNF4α transcriptional network. Fibrotic levels of matrix stiffness activated mechanotransduction in primary hepatocytes through focal adhesion kinase. In addition, blockade of the Rho/Rho-associated protein kinase pathway rescued HNF4α expression from hepatocytes cultured on stiff matrix.

CONCLUSION

Fibrotic levels of matrix stiffness significantly inhibit hepatocyte-specific functions in part by inhibiting the HNF4α transcriptional network mediated through the Rho/Rho-associated protein kinase pathway. Increased appreciation of the role of matrix rigidity in modulating hepatocyte function will advance our understanding of the mechanisms of hepatocyte dysfunction in liver cirrhosis and spur development of novel treatments for chronic liver disease. (Hepatology 2016;64:261-275).

Characterization of a functional C3A liver spheroid model

More predictive in vitro liver models are a critical requirement for preclinical screening of compounds demonstrating hepatotoxic liability. 3D liver spheroids have been shown to have an enhanced functional lifespan compared to 2D monocultures; however a detailed characterisation of spatiotemporal function and structure of spheroids still needs further attention before widespread use in industry. We have developed and characterized the structure and function of a 3D liver spheroid model formed from C3A hepatoma cells. Spheroids were viable and maintained a compact in vivo-like structure with zonation features for up to 32 days. MRP2 and Pgp transporters had polarised expression on the canalicular membrane of cells in the spheroids and were able to functionally transport CMFDA substrate into these canalicular structures. Spheroids expressed CYP2E1 and were able to synthesise and secrete albumin and urea to a higher degree than monolayer C3A cultures. Penetration of doxorubicin throughout the spheroid core was demonstrated. Spheroids showed increased susceptibility to hepatotoxins when compared to 2D cultures, with acetaminophen having an IC50 of 7.2 mM in spheroids compared to 33.8 mM in monolayer culture. To conclude, we developed an alternative method for creating C3A liver spheroids and demonstrated cellular polarisation and zonation, as well as superior liver-specific functionality and more sensitive toxicological response compared to standard 2D liver models, confirming a more in vivo-like liver model.

Stem cells and injectable hydrogels: Synergistic therapeutics in myocardial repair

One of the major problems in the treatment of cardiovascular diseases is the inability of myocardium to self-regenerate. Current therapies are unable to restore the heart's function after myocardial infarction. Myocardial tissue engineering is potentially a key approach to regenerate damaged heart muscle. Myocardial patches are applied surgically, whereas injectable hydrogels provide effective minimally invasive approaches to recover functional myocardium. These hydrogels are easily administered and can be either cell free or loaded with bioactive agents and/or cardiac stem cells, which may apply paracrine effects. The aim of this review is to investigate the advantages and disadvantages of injectable stem cell-laden hydrogels and highlight their potential applications for myocardium repair.

A heparin-modified thermoresponsive surface with heparin-binding epidermal growth factor-like growth factor for maintaining hepatic functions in vitro and harvesting hepatocyte sheets

A heparin-modified thermoresponsive surface bound with heparin-binding epidermal growth factor-like growth factor (HB-EGF) was designed to allow creation of transferrable and functional hepatocyte sheets. A heparin-modified thermoresponsive surface was prepared by covalently tethering heparin onto poly(N-isopropylacrylamide-co-2-carboxyisopropylacrylamide)-grafted tissue culture polystyrene surfaces (Heparin-IC). HB-EGFs were able to stably bind to heparin-IC via affinity interaction. The survival of primary rat hepatocytes was maintained through HB-EGF-bound heparin-IC (HB-EGF/heparin-IC). Moreover, cultured rat primary hepatocytes on HB-EGF/heparin-IC exhibited higher albumin-secretion than hepatocytes cultured on PIPAAm-grafted and collagen-coated surfaces with soluble HB-EGF in the culture medium, regardless of whether soluble EGF was added. These results suggested that HB-EGF/heparin-IC is able to effectively maintain hepatic function via continuous signaling of HB-EGF. After a 4-day cultivation, the cultured hepatocytes on HB-EGF/heparin-IC detached as a cell sheet with fibronectin and HB-EGF only after the temperature was lowered to 20 °C. In addition, higher expression of hepatocyte-specific genes (albumin, hepatocyte nuclear factor 4 alpha, coagulation factor VII, and coagulation factor IX) in hepatocyte sheets was detected on HB-EGF/heparin-IC than on a PIPAAm surface with soluble HB-EGF, indicating that HB-EGF/heparin-IC suppressed the dedifferentiation of cultured hepatocytes. Hence, heparin-modified thermoresponsive surfaces bound with HB-EGF facilitate the fabrication of transferrable hepatocyte sheets with intact hepatic functions and have the potential to provide an in vitro culture system using functional hepatocyte sheet tissues, which may serve as an effective hepatocyte-based tissue engineering platform for liver disease treatments.

Selectivity of biopolymer membranes using HepG2 cells

Bioartificial liver (BAL) system has emerged as an alternative treatment to bridge acute liver failure to either liver transplantation or liver regeneration. One of the main reasons that the efficacy of the current BAL systems was not convincing in clinical trials is attributed to the lack of friendly interface between the membrane and the hepatocytes in liver bioreactor, the core unit of BAL system. Here, we systematically compared the biological responses of hepatosarcoma HepG2 cells seeded on eight, commercially available biocompatible membranes made of acetyl cellulose–nitrocellulose mixed cellulose (CA–NC), acetyl cellulose (CA), nylon (JN), polypropylene (PP), nitrocellulose (NC), polyvinylidene fluoride (PVDF), polycarbonate (PC) and polytetrafluoroethylene (PTFE). Physicochemical analysis and mechanical tests indicated that CA, JN and PP membranes yield high adhesivity and reasonable compressive and/or tensile features with friendly surface topography for cell seeding. Cells prefer to adhere on CA, JN, PP or PTFE membranes with high proliferation rate in spheriod-like shape. Actin, albumin and cytokeratin 18 expressions are favorable for cells on CA or PP membrane, whereas protein filtration is consistent among all the eight membranes. These results further the understandings of cell growth, morphology and spreading, as well as protein filtration on distinct membranes in designing a liver bioreactor.

Myocardial infarction: stem cell transplantation for cardiac regeneration

It is estimated that by 2030, almost 23.6 million people will perish from cardiovascular disease, according to the WHO. The review discusses advances in stem cell therapy for myocardial infarction, including cell sources, methods of differentiation, expansion selection and their route of delivery. Skeletal muscle cells, hematopoietic cells and mesenchymal stem cells (MSCs) and embryonic stem cells (ESCs)-derived cardiomyocytes have advanced to the clinical stage, while induced pluripotent cells (iPSCs) are yet to be considered clinically. Delivery of cells to the sites of injury and their subsequent retention is a major issue. The development of supportive scaffold matrices to facilitate stem cell retention and differentiation are analyzed. The review outlines clinical translation of conjugate stem cell-based cellular therapeutics post-myocardial infarction.

Stiffness of hyaluronic acid gels containing liver extracellular matrix supports human hepatocyte function and alters cell morphology

Tissue engineering and cell based liver therapies have utilized primary hepatocytes with limited success due to the failure of hepatocytes to maintain their phenotype in vitro. In order to overcome this challenge, hyaluronic acid (HA) cell culture substrates were formulated to closely mimic the composition and stiffness of the normal liver cellular microenvironment. The stiffness of the substrate was modulated by adjusting HA hydrogel crosslinking. Additionally, the repertoire of bioactive molecules within the HA substrate was bolstered by supplementation with normal liver extracellular matrix (ECM). Primary human hepatocyte viability and phenotype were determined over a narrow physiologically relevant range of substrate stiffnesses from 600 to 4600Pa in both the presence and absence of liver ECM. Cell attachment, viability, and organization of the actin cytoskeleton improved with increased stiffness up to 4600Pa. These differences were not evident in earlier time points or substrates containing only HA. However, gene expression for the hepatocyte markers hepatocyte nuclear factor 4 alpha (HNF4α) and albumin significantly decreased on the 4600Pa stiffness at day 7 indicating that cells may not have maintained their phenotype long-term at this stiffness. Function, as measured by albumin secretion, varied with both stiffness and time in culture and peaked at day 7 at the 1200Pa stiffness, slightly below the stiffness of normal liver ECM at 3000Pa. Overall, gel stiffness affected primary human hepatocyte cell adhesion, functional marker expression, and morphological characteristics dependent on both the presence of liver ECM in gel substrates and time in culture.

Matrigel coatings for Parylene sheath neural probes

The biologically derived hydrogel Matrigel (MG) was used to coat a Parylene-based sheath intracortical electrode to act as a mechanical and biological buffer as well as a matrix for delivering bioactive molecules to modulate the cellular response and improve recording quality. MG was loaded with dexamethasone to reduce the immune response together with nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) to maintain neuronal density and encourage neuronal ingrowth toward electrodes within the sheath. Coating the Parylene sheath electrode with the loaded MG significantly improved the signal-to-noise ratio for neural events recorded from the motor cortex in rat for more than 3 months. Electron microscopy showed even coverage of both the Parylene substrate and the platinum recording electrodes. Electrochemical impedance spectroscopy (EIS) of coated electrodes in 1× phosphate-buffered saline demonstrated low impedance required for recording neural signals. This result was confirmed by in vivo EIS data, showing significantly decreased impedance during the first week of recording. Dexamethasone, NGF, and BDNF loaded into MG were released within 1 day in 1× phosphate-buffered saline. Although previous studies showed that MG loaded with either the immunosuppressant or the neurotrophic factor cocktail provided modest improvement in recording quality in a 1-month in vivo study, the combination of these bioactive molecules did not improve the signal quality over coating probes with only MG in a 3-month in vivo study. The MG coating may further improve recording quality by optimizing the in vivo release profile for the bioactive molecules.

Photopatterning of hydrogel scaffolds coupled to filter materials using stereolithography for perfused 3D culture of hepatocytes

In vitro models that recapitulate the liver's structural and functional complexity could prolong hepatocellular viability and function to improve platforms for drug toxicity studies and understanding liver pathophysiology. Here, stereolithography (SLA) was employed to fabricate hydrogel scaffolds with open channels designed for post-seeding and perfused culture of primary hepatocytes that form 3D structures in a bioreactor. Photopolymerizable polyethylene glycol-based hydrogels were fabricated coupled to chemically activated, commercially available filters (polycarbonate and polyvinylidene fluoride) using a chemistry that permitted cell viability, and was robust enough to withstand perfused culture of up to 1 µL/s for at least 7 days. SLA energy dose, photoinitiator concentrations, and pretreatment conditions were screened to determine conditions that maximized cell viability and hydrogel bonding to the filter. Multiple open channel geometries were readily achieved, and included ellipses and rectangles. Rectangular open channels employed for subsequent studies had final dimensions on the order of 350 µm by 850 µm. Cell seeding densities and flow rates that promoted cell viability were determined. Perfused culture of primary hepatocytes in hydrogel scaffolds in the presence of soluble epidermal growth factor (EGF) prolonged the maintenance of albumin production throughout the 7-day culture relative to 2D controls. This technique of bonding hydrogel scaffolds can be employed to fabricate soft scaffolds for a number of bioreactor configurations and applications.

Efficient large-scale generation of functional hepatocytes from mouse embryonic stem cells grown in a rotating bioreactor with exogenous growth factors and hormones

Introduction

Embryonic stem (ES) cells are considered a potentially advantageous source of hepatocytes for both transplantation and the development of bioartificial livers. However, the efficient large-scale generation of functional hepatocytes from ES cells remains a major challenge, especially for those methods compatible with clinical applications.

Methods

In this study, we investigated whether a large number of functional hepatocytes can be differentiated from mouse ES (mES) cells using a simulated microgravity bioreactor. mES cells were cultured in a rotating bioreactor in the presence of exogenous growth factors and hormones to form embryoid bodies (EBs), which then differentiated into hepatocytes.

Results

During the rotating culture, most of the EB-derived cells gradually showed the histologic characteristics of normal hepatocytes. More specifically, the expression of hepatic genes and proteins was detected at a higher level in the differentiated cells from the bioreactor culture than in cells from a static culture. On further growing, the EBs on tissue-culture plates, most of the EB-derived cells were found to display the morphologic features of hepatocytes, as well as albumin synthesis. In addition, the EB-derived cells grown in the rotating bioreactor exhibited higher levels of liver-specific functions, such as glycogen storage, cytochrome P450 activity, low-density lipoprotein, and indocyanine green uptake, than did differentiated cells grown in static culture. When the EB-derived cells from day-14 EBs and the cells’ culture supernatant were injected into nude mice, the transplanted cells were engrafted into the recipient livers.

Conclusions

Large quantities of high-quality hepatocytes can be generated from mES cells in a rotating bioreactor via EB formation. This system may be useful in the large-scale generation of hepatocytes for both cell transplantation and the development of bioartificial livers.

Liver bioengineering: from the stage of liver decellularized matrix to the multiple cellular actors and bioreactor special effects

Liver bioengineering has been a field of intense research and popular excitement in the past decades. It experiences great interest since the introduction of whole liver acellular scaffolds generated by perfusion decellularization (1-3). Nevertheless, the different strategies developed so far have failed to generate hepatic tissue in vitro bioequivalent to native liver tissue. Even notable novel strategies that rely on iPSC-derived liver progenitor cells potential to self-organize in association with endothelial cells in hepatic organoids are lacking critical components of the native tissue (e.g., bile ducts, functional vascular network, hepatic microarchitecture, etc) (4). Hence, it is vital to understand the strengths and short comes of our current strategies in this quest to re-create liver organogenesis in vitro. To shed some light into these issues, this review describes the different actors that play crucial roles in liver organogenesis and highlights the steps still missing to successfully generate whole livers and hepatic organoids in vitro for multiple applications.

In vitro platforms for evaluating liver toxicity

The liver is a heterogeneous organ with many vital functions, including metabolism of pharmaceutical drugs and is highly susceptible to injury from these substances. The etiology of drug-induced liver disease is still debated although generally regarded as a continuum between an activated immune response and hepatocyte metabolic dysfunction, most often resulting from an intermediate reactive metabolite. This debate stems from the fact that current animal and in vitro models provide limited physiologically relevant information, and their shortcomings have resulted in "silent" hepatotoxic drugs being introduced into clinical trials, garnering huge financial losses for drug companies through withdrawals and late stage clinical failures. As we advance our understanding into the molecular processes leading to liver injury, it is increasingly clear that (a) the pathologic lesion is not only due to liver parenchyma but is also due to the interactions between the hepatocytes and the resident liver immune cells, stellate cells, and endothelial cells; and (b) animal models do not reflect the human cell interactions. Therefore, a predictive human, in vitro model must address the interactions between the major human liver cell types and measure key determinants of injury such as the dosage and metabolism of the drug, the stress response, cholestatic effect, and the immune and fibrotic response. In this mini-review, we first discuss the current state of macro-scale in vitro liver culture systems with examples that have been commercialized. We then introduce the paradigm of microfluidic culture systems that aim to mimic the liver with physiologically relevant dimensions, cellular structure, perfusion, and mass transport by taking advantage of micro and nanofabrication technologies. We review the most prominent liver-on-a-chip platforms in terms of their physiological relevance and drug response. We conclude with a commentary on other critical advances such as the deployment of fluorescence-based biosensors to identify relevant toxicity pathways, as well as computational models to create a predictive tool.

Epithelial-mesenchymal transition delayed by E-cad to promote tissue formation in hepatic differentiation of mouse embryonic stem cells in vitro

Hepatic differentiation of embryonic stem cells (ESCs) usually results in a single cell lineage, and the formation of liver tissues remains difficult. Here, we examine the role of epithelial-mesenchymal transition (EMT) that is regulated by epithelial cadherin (E-cad) expression in hepatic tissue formation from ESCs. E-cad was transfected into mouse ESCs to enable a stable expression of E-cad. Hepatic differentiation of ESCs was then induced by hepatic growth factors. Wnt/β-catenin signaling and EMT speed were examined to determine the differentiation process. Hepatic and angiogenesis markers, as well as differentiated cell-adhesive force were also examined to identify the hepatic tissue differentiation. In our results, E-cad expression gradually decreased in normal ESC (N-ESC) differentiation, but remained stable in the E-cad transfected ESC (EC-ESC) group. In EC-ESC differentiation, expressions of cytoplastic β-catenin and EMT were much lower and significantly prolonged. Angiogenesis markers vascular endothelial growth factor receptor-1 (VEGFR-1) and CD31/PECAM-1 were expressed only on day 5-13 in N-ESC differentiation, whereas VEGFR-1 and CD31/PECAM-1 were expressed prolonged on day 5-17 in the EC-ESC group and were coincident with the expression of hepatic markers. Finally, EC-ESC differentiation maintained multilayer-growth patterns, and abundant vascular network structures appeared and migrated in albumin-positive cell areas. The cellular adhesion forces between embryonic body cells in EC-ESC differentiation during day 13-17 were similar to those of mouse liver tissue. In conclusion, accelerated EMT due to the decreased E-cad expression may partially contribute to the failure of hepatic tissue formation in N-ESC differentiation. E-cad can act in synergy with hepatic growth factors and facilitate the early-stage formation of hepatic tissues through down-regulating Wnt/β-catenin signaling and delaying EMT. This work provides a new insight into hepatic tissue differentiation that is mediated by E-cad from ESC.

Recent advances in 2D and 3D in vitro systems using primary hepatocytes, alternative hepatocyte sources and non-parenchymal liver cells and their use in investigating mechanisms of hepatotoxicity, cell signaling and ADME

This review encompasses the most important advances in liver functions and hepatotoxicity and analyzes which mechanisms can be studied in vitro. In a complex architecture of nested, zonated lobules, the liver consists of approximately 80 % hepatocytes and 20 % non-parenchymal cells, the latter being involved in a secondary phase that may dramatically aggravate the initial damage. Hepatotoxicity, as well as hepatic metabolism, is controlled by a set of nuclear receptors (including PXR, CAR, HNF-4α, FXR, LXR, SHP, VDR and PPAR) and signaling pathways. When isolating liver cells, some pathways are activated, e.g., the RAS/MEK/ERK pathway, whereas others are silenced (e.g. HNF-4α), resulting in up- and downregulation of hundreds of genes. An understanding of these changes is crucial for a correct interpretation of in vitro data. The possibilities and limitations of the most useful liver in vitro systems are summarized, including three-dimensional culture techniques, co-cultures with non-parenchymal cells, hepatospheres, precision cut liver slices and the isolated perfused liver. Also discussed is how closely hepatoma, stem cell and iPS cell-derived hepatocyte-like-cells resemble real hepatocytes. Finally, a summary is given of the state of the art of liver in vitro and mathematical modeling systems that are currently used in the pharmaceutical industry with an emphasis on drug metabolism, prediction of clearance, drug interaction, transporter studies and hepatotoxicity. One key message is that despite our enthusiasm for in vitro systems, we must never lose sight of the in vivo situation. Although hepatocytes have been isolated for decades, the hunt for relevant alternative systems has only just begun.

Solubilized matrix derived from decellularized liver as a growth factor-immobilizable scaffold for hepatocyte culture

Tissue engineering requires growth factors, cells and a scaffold to permit effective tissue regeneration. This study focused on the development of a scaffold for liver tissue engineering, because the liver is a central organ for metabolism. We aimed to develop a scaffold to promote expression of liver-specific functions of hepatocytes, with a focus on immobilizing growth factors onto an organ-specific matrix for liver tissue regeneration. Solubilized extracellular matrix from decellularized liver (L-ECM) was obtained following Triton X-100 treatment and consisted of protein and polysaccharide. L-ECM was found to immobilize hepatocyte growth factor (HGF), even in the presence of albumin, with an efficiency of 75%. Additionally, the immobilized HGF on L-ECM film was stably remained in culture condition for 5 days. Immobilized HGF promoted hepatocyte migration, thus indicating that L-ECM-immobilized HGF maintained its native biological activity. Furthermore, L-ECM stimulated the expression of liver-specific functions, including albumin secretion, urea synthesis and ethoxyresorufin-O-deethylase activity, in primary rat hepatocytes cultured in growth factor-free medium. In summary, L-ECM has the potential to become an effective material in the field of regenerative medicine.

Development of a salmon-derived crosslinked atelocollagen sponge disc containing osteogenic protein-1 for articular cartilage regeneration: in vivo evaluations with rabbits

Background

We have developed crosslinked salmon-derived atelocollagen sponge, which has a denaturation temperature of 47 degrees Celsius. The purpose of this study is to evaluate the fundamental in vivo efficacy of the osteogenic protein (OP) -1 containing salmon-derived collagen sponge disc (SCS) on cartilage regeneration, using a rabbit model.

Methods

A total of 24 rabbits were used in this study. In each animal, a full-thickness osteochondral defect was created in each femoral trochlea. Then, each 12 rabbits were randomly divided into the two groups. In Group I, an OP1-SCS disc was implanted into the defect in the right knee. In Group II, a SCS disc without OP-1 was implanted into the defect in the right knee. A control group of 12 rabbits was assembled from randomly-selected left knees from among the first two groups. In Group-III, we applied no treatment for a defect in the left knee to obtain the untreated control. All rabbits were sacrificed at 12 weeks after surgery. In each group, 10 animals were used for histological and immunohistological evaluations, and the remaining 2 were used for real-time polymerase chain reaction (PCR) analyses.

Results

In Group I, a regenerated cartilage tissue rich in proteoglycan and type-2 collagen was found at 12 weeks, although the width was thicker than that of Group II. In Group II, the defect was filled with thick inhomogeneous tissues, including cartilage, fibrous, and bone tissues at 12 weeks. Concerning the gross observation and histological scores at 12 weeks, the ANOVA showed significant differences (p < 0.0001, and p < 0.0001, respectively). The post-hoc test indicated that the gross observation and histological scores of Group I was significantly greater than those of Groups II (p = 0.035, and p = 0.0104, respectively) and III (p < 0.0001, and p < 0.0001, respectively), while Group II was significantly greater than Group III (p = 0.0069, and p = 0.005, respectively). The real time PCR analysis showed that gene expression of type-2 collagen and aggrecan of Group I was greater than that of Group II.

Conclusions

The present study clearly demonstrated that the implantation of the OP1-SCS disc without any cultured cells may induce spontaneous hyaline-like cartilage regeneration to greater degrees than implantation of only the salmon-derived collagen sponge disc.

Heparin-conjugated gelatin as a growth factor immobilization scaffold

Tissue engineering requires growth factors, cells and a scaffold to permit effective tissue regeneration. This study aimed to develop a scaffold with a focus on immobilizing growth factors within gelatin. We focused on the extracellular matrix and developed a heparin-conjugated gelatin (Hep-gela). Conjugation was confirmed using the alcian blue assay and X-ray diffraction patterns. The mechanical strength and stability of the Hep-gela gel in protease solution were improved compared with collagen gel. Hep-gela was able to immobilize vascular endothelial growth factor (VEGF) even in the presence of albumin, with an efficiency of 54.2%. Immobilized VEGF promoted proliferation of human umbilical vein endothelial cells. Hep-gela-immobilized VEGF maintained its native biological activity. In summary, Hep-gela has the potential to become an effective material in the field of regenerative medicine.

Minimally invasive cell-seeded biomaterial systems for injectable/epicardial implantation in ischemic heart disease

Myocardial infarction (MI) is characterized by heart-wall thinning, myocyte slippage, and ventricular dilation. The injury to the heart-wall muscle after MI is permanent, as after an abundant cell loss the myocardial tissue lacks the intrinsic capability to regenerate. New therapeutics are required for functional improvement and regeneration of the infarcted myocardium, to overcome harmful diagnosis of patients with heart failure, and to overcome the shortage of heart donors. In the past few years, myocardial tissue engineering has emerged as a new and ambitious approach for treating MI. Several left ventricular assist devices and epicardial patches have been developed for MI. These devices and acellular/cellular cardiac patches are employed surgically and sutured to the epicardial surface of the heart, limiting the region of therapeutic benefit. An injectable system offers the potential benefit of minimally invasive release into the myocardium either to restore the injured extracellular matrix or to act as a scaffold for cell delivery. Furthermore, intramyocardial injection of biomaterials and cells has opened new opportunities to explore and also to augment the potentials of this technique to ease morbidity and mortality rates owing to heart failure. This review summarizes the growing body of literature in the field of myocardial tissue engineering, where biomaterial injection, with or without simultaneous cellular delivery, has been pursued to enhance functional and structural outcomes following MI. Additionally, this review also provides a complete outlook on the tissue-engineering therapies presently being used for myocardial regeneration, as well as some perceptivity into the possible issues that may hinder its progress in the future.

Cells and materials for liver tissue engineering

Liver transplantation is currently the most efficacious treatment for end-stage liver diseases. However, one main problem with liver transplantation is the limited number of donor organs that are available. Therefore, liver tissue engineering based on cell transplantation that combines materials to mimic the liver is under investigation with the goal of restoring normal liver functions. Tissue engineering aims to mimic the interactions among cells with a scaffold. Particular materials or a matrix serve as a scaffold and provide a three-dimensional environment for cell proliferation and interaction. Moreover, the scaffold plays a role in regulating cell maturation and function via these interactions. In cultures of hepatic lineage cells, regulation of cell proliferation and specific function using biocompatible synthetic, biodegradable bioderived matrices, protein-coated materials, surface-modified nanofibers, and decellularized biomatrix has been demonstrated. Furthermore, beneficial effects of addition of growth factor cocktails to a flow bioreactor or coculture system on cell viability and function have been observed. In addition, a system for growing stem cells, liver progenitor cells, and primary hepatocytes for transplantation into animal models was developed, which produces hepatic lineage cells that are functional and that show long-term proliferation following transplantation. The major limitation of cells proliferated with matrix-based transplantation systems is the high initial cell loss and dysfunction, which may be due to the absence of blood flow and the changes in nutrients. Thus, the development of vascular-like scaffold structures, the formation of functional bile ducts, and the maintenance of complex metabolic functions remain as major problems in hepatic tissue engineering and will need to be addressed to enable further advances toward clinical applications.

Extracellular matrix ligand and stiffness modulate immature nucleus pulposus cell-cell interactions

The nucleus pulposus (NP) of the intervertebral disc functions to provide compressive load support in the spine, and contains cells that play a critical role in the generation and maintenance of this tissue. The NP cell population undergoes significant morphological and phenotypic changes during maturation and aging, transitioning from large, vacuolated immature cells arranged in cell clusters to a sparse population of smaller, isolated chondrocyte-like cells. These morphological and organizational changes appear to correlate with the first signs of degenerative changes within the intervertebral disc. The extracellular matrix of the immature NP is a soft, gelatinous material containing multiple laminin isoforms, features that are unique to the NP relative to other regions of the disc and that change with aging and degeneration. Based on this knowledge, we hypothesized that a soft, laminin-rich extracellular matrix environment would promote NP cell-cell interactions and phenotypes similar to those found in immature NP tissues. NP cells were isolated from porcine intervertebral discs and cultured in matrix environments of varying mechanical stiffness that were functionalized with various matrix ligands; cellular responses to periods of culture were assessed using quantitative measures of cell organization and phenotype. Results show that soft (<720 Pa), laminin-containing extracellular matrix substrates promote NP cell morphologies, cell-cell interactions, and proteoglycan production in vitro, and that this behavior is dependent upon both extracellular matrix ligand and substrate mechanical properties. These findings indicate that NP cell organization and phenotype may be highly sensitive to their surrounding extracellular matrix environment.