Macromolecular crowding for tailoring tissue-derived fibrillated matrices

Hierarchical Design of Tissue-Mimetic Fibrillar Hydrogel Scaffolds

Most tissues of the human body present hierarchical fibrillar extracellular matrices (ECMs) that have a strong influence over their physicochemical properties and biological behavior. Of great interest is the introduction of this fibrillar structure to hydrogels, particularly due to the water-rich composition, cytocompatibility, and tunable properties of this class of biomaterials. Here, the main bottom-up fabrication strategies for the design and production of hierarchical biomimetic fibrillar hydrogels and their most representative applications in the fields of tissue engineering and regenerative medicine are reviewed. For example, the controlled assembly/arrangement of peptides, polymeric micelles, cellulose nanoparticles (NPs), and magnetically responsive nanostructures, among others, into fibrillar hydrogels is discussed, as well as their potential use as fibrillar-like hydrogels (e.g., those from cellulose NPs) with key biofunctionalities such as electrical conductivity or remote stimulation. Finally, the major remaining barriers to the clinical translation of fibrillar hydrogels and potential future directions of research in this field are discussed.

Renal tissue engineering for regenerative medicine using polymers and hydrogels

Chronic Kidney Disease (CKD) is a growing worldwide problem, leading to end-stage renal disease (ESRD). Current treatments for ESRD include haemodialysis and kidney transplantation, but both are deemed inadequate since haemodialysis does not address all other kidney functions, and there is a shortage of suitable donor organs for transplantation. Research in kidney tissue engineering has been initiated to take a regenerative medicine approach as a potential treatment alternative, either to develop effective cell therapy for reconstruction or engineer a functioning bioartificial kidney. Currently, renal tissue engineering encompasses various materials, mainly polymers and hydrogels, which have been chosen to recreate the sophisticated kidney architecture. It is essential to address the chemical and mechanical aspects of the materials to ensure they can support cell development to restore functionality and feasibility. This paper reviews the types of polymers and hydrogels that have been used in kidney tissue engineering applications, both natural and synthetic, focusing on the processing and formulation used in creating bioactive substrates and how these biomaterials affect the cell biology of the kidney cells used.

3D bioprinting and its innovative approach for biomedical applications

3D bioprinting or additive manufacturing is an emerging innovative technology revolutionizing the field of biomedical applications by combining engineering, manufacturing, art, education, and medicine. This process involved incorporating the cells with biocompatible materials to design the required tissue or organ model in situ for various in vivo applications. Conventional 3D printing is involved in constructing the model without incorporating any living components, thereby limiting its use in several recent biological applications. However, this uses additional biological complexities, including material choice, cell types, and their growth and differentiation factors. This state-of-the-art technology consciously summarizes different methods used in bioprinting and their importance and setbacks. It also elaborates on the concept of bioinks and their utility. Biomedical applications such as cancer therapy, tissue engineering, bone regeneration, and wound healing involving 3D printing have gained much attention in recent years. This article aims to provide a comprehensive review of all the aspects associated with 3D bioprinting, from material selection, technology, and fabrication to applications in the biomedical fields. Attempts have been made to highlight each element in detail, along with the associated available reports from recent literature. This review focuses on providing a single platform for cancer and tissue engineering applications associated with 3D bioprinting in the biomedical field.

Macromolecular crowding in the development of a three-dimensional organotypic human breast cancer model

Although cell-derived matrices are at the forefront of scientific research and technological innovation for the development of in vitro tumour models, their two-dimensional structure and low extracellular matrix composition restrict their capacity to accurately predict toxicity of candidate molecules. Herein, we assessed the potential of macromolecular crowding (a biophysical phenomenon that significantly enhances and accelerates extracellular matrix deposition, resulting in three-dimensional tissue surrogates) in improving cell-derived matrices in vitro tumour models. Among the various decellularisation protocols assessed (NH4OH, DOC, SDS/EDTA, NP40), the NP40 appeared to be the most effective in removing cellular matter and the least destructive to the deposited matrix. Among the various cell types (mammary, skin, lung fibroblasts) used to produce the cell-derived matrices, the mammary fibroblast derived matrices produced under macromolecular crowding conditions and decellularised with NP40 resulted in significant increase in focal adhesion molecules, matrix metalloproteinases and proinflammatory cytokines, when seeded with MDA-MB-231 cells. Further, macromolecular crowding derived matrices significantly increased doxorubicin resistance and reduced the impact of intracellular reactive oxygen species mediated cell death. Collectively our data clearly illustrate the potential of macromolecular crowding in the development of cell-derived matrices-based in vitro tumour models that more accurately resemble the tumour microenvironment.

Poly(2-alkyl-2-oxazoline)-Heparin Hydrogels-Expanding the Physicochemical Parameter Space of Biohybrid Materials

Poly(ethylene glycol) (PEG)-glycosaminoglycan (GAG) hydrogel networks are established as very versatile biomaterials. Herein, the synthetic gel component of the biohybrid materials is systematically varied by combining different poly(2-alkyl-2-oxazolines) (POx) with heparin applying a Michael-type addition crosslinking scheme: POx of gradated hydrophilicity and temperature-responsiveness provides polymer networks of distinctly different stiffness and swelling. Adjusting the mechanical properties and the GAG concentration of the gels to similar values allows for modulating the release of GAG-binding growth factors (VEGF165 and PDGF-BB) by the choice of the POx and its temperature-dependent conformation. Adsorption of fibronectin, growth of fibroblasts, and bacterial adhesion scale with the hydrophobicity of the gel-incorporated POx. In vitro hemocompatibility tests with freshly drawn human whole blood show advantages of POx-based gels compared to the PEG-based reference materials. Biohybrid POx hydrogels can therefore enable biomedical technologies requiring GAG-based materials with customized and switchable physicochemical characteristics.

Renal Regeneration: The Role of Extracellular Matrix and Current ECM-Based Tissue Engineered Strategies

Natural extracellular matrices (ECM) are currently being studied as an alternative source for organ transplantation or as new solutions to treat kidney injuries, which can evolve to end-stage renal disease, a life devastating condition. This paper provides an overview on the current knowledge in kidney ECM and its usefulness on future investigations. The composition and structure of kidney ECM is herein associated with its intrinsic capacity of remodeling and repair after insult. Moreover, it provides a deeper insight on altered ECM components during disease. The use of decellularized kidney matrices is discussed in the second part of the review, with emphasis on how these matrices contribute to tissue-specific differentiation of embryonic, pluripotent, and other stem cells. The evolution on the field toward different uses of xenogeneic ECM as a biological scaffold material is discussed, namely the major outcomes on whole kidney recellularization and its in vivo implantation. At last, the recent literature on the use of processed kidney decellularized ECM to produce diverse biomaterial substrates, such as hydrogels, membranes, and bioinks are reviewed, with emphasis on future perspectives of its translation into the clinic.

It is time to crowd your cell culture media - Physicochemical considerations with biological consequences

In vivo, the interior and exterior of cells is populated by various macromolecules that create an extremely crowded milieu. Yet again, in vitro eukaryotic cell culture is conducted in dilute culture media that hardly imitate the native tissue density. Herein, the concept of macromolecular crowding is discussed in both intracellular and extracellular context. Particular emphasis is given on how the physicochemical properties of the crowding molecules govern and determine kinetics, equilibria and mechanism of action of biochemical and biological reactions, processes and functions. It is evidenced that we are still at the beginning of appreciating, let alone effectively implementing, the potential of macromolecular crowding in permanently differentiated and stem cell culture systems.

Bioactive Decellularized Extracellular Matrix Derived from 3D Stem Cell Spheroids under Macromolecular Crowding Serves as a Scaffold for Tissue Engineering

Scaffolds for tissue engineering aim to mimic the native extracellular matrix (ECM) that provides physical support and biochemical signals to modulate multiple cell behaviors. However, the majority of currently used biomaterials are oversimplified and therefore fail to provide a niche required for the stimulation of tissue regeneration. In the present study, 3D decellularized ECM (dECM) scaffolds derived from mesenchymal stem cell (MSC) spheroids and with intricate matrix composition are developed. Specifically, application of macromolecular crowding (MMC) to MSC spheroid cultures facilitate ECM assembly in a 3D configuration, resulting in the accumulation of ECM and associated bioactive components. Decellularized 3D dECM constructs produced under MMC are able to adequately preserve the microarchitecture of structural ECM components and are characterized by higher retention of growth factors. This results in a stronger proangiogenic bioactivity as compared to constructs produced under uncrowded conditions. These dECM scaffolds can be homogenously populated by endothelial cells, which direct the macroassembly of the structures into larger cell-carrying constructs. Application of empty scaffolds enhances intrinsic revascularization in vivo, indicating that the 3D dECM scaffolds represent optimal proangiogenic bioactive blocks for the construction of larger engineered tissue constructs.

Scaffold-free cell-based tissue engineering therapies: advances, shortfalls and forecast

Cell-based scaffold-free therapies seek to develop in vitro organotypic three-dimensional (3D) tissue-like surrogates, capitalising upon the inherent capacity of cells to create tissues with efficiency and sophistication that is still unparalleled by human-made devices. Although automation systems have been realised and (some) success stories have been witnessed over the years in clinical and commercial arenas, in vitro organogenesis is far from becoming a standard way of care. This limited technology transfer is largely attributed to scalability-associated costs, considering that the development of a borderline 3D implantable device requires very high number of functional cells and prolonged ex vivo culture periods. Herein, we critically discuss advancements and shortfalls of scaffold-free cell-based tissue engineering strategies, along with pioneering concepts that have the potential to transform regenerative and reparative medicine.

Macromolecular Crowding as a Tool to Screen Anti-fibrotic Drugs: The Scar-in-a-Jar System Revisited

An unsolved therapeutic problem in fibrosis is the overproduction of collagen. In order to screen the effect of anti-fibrotic drugs on collagen deposition, the Scar-in-a-Jar approach has been introduced about a decade ago. With macromolecular crowding a rapid deposition of collagen is seen, resulting in a substantial decrease in culture time, but the system has never been tested in an adequate way. We therefore have compared six different macromolecular crowders [Ficoll PM 70 (Fc70), Ficoll PM 400 (Fc400), a mixture of Ficoll 70 and 400 (Fc70/400), polyvinylpyrrolidone 40 (PVP40), polyvinylpyrrolidone 360 (PVP360), neutral dextran 670 (ND670), dextran sulfate 500 (DxS500), and carrageenan (CR)] under profibrotic conditions (addition of TGFβ1) with primary human adult dermal fibroblasts in the presence of 0.5 and 10% FBS. We found that (1) collagen deposition and myofibroblast formation was superior with 0.5% FBS, (2) DxS500 and CR results in an aberrant collagen deposition pattern, (3) ND670 does not increase collagen deposition, and (4) CR, DxS500, and Fc40/700 affected important phenotypical properties of the cells when cultured under pro-fibrotic conditions, whereas PVP40 and PVP360 did less or not. Because of viscosity problems with PVP360, we conclude that PVP40 is the most optimal crowder for the screening of anti-fibrotic drugs. Finally, the effect of various concentrations of Imatinib, Galunisertib, Omipalisib or Nintedanib on collagen deposition and myofibroblast formation was tested with PVP40 as the crowder.

A biomimetic model of 3D fluid extracellular macromolecular crowding microenvironment fine-tunes ovarian cancer cells dissemination phenotype

An early fundamental step in ovarian cancer progression is the dissemination of cancer cells through liquid environments, one of them being cancer ascites accumulated in the peritoneal cavity. These biological fluids are highly crowded with a high total macromolecule concentration. This biophysical property of fluids is widely used in tissue engineering for a few decades now, yet is largely underrated in cancer biomimetic models. To unravel the role of fluids extracellular macromolecular crowding (MMC), we exposed ovarian cancer cells (OCC) to high molecular weight inert polymer solutions. High macromolecular composition of extracellular liquid presented a differential effect: i) it impeded non-adherent OCC aggregation in suspension and, decreased their adhesion; ii) it promoted adherent OCC migration by decreasing extracellular matrix deposition. Besides, there seemed to be a direct link between the extracellular MMC and intracellular processes, especially the actin cytoskeleton organization and the nucleus morphology. In conclusion, extracellular fluid MMC orients OCC dissemination phenotype. Integrating MMC seems crucial to produce more relevant mimetic 3D in vitro fluid models to study ovarian dissemination but also to screen drugs.

Cell derived extracellular matrix-rich biomimetic substrate supports podocyte proliferation, differentiation and maintenance of native phenotype

Current technologies and available scaffold materials do not support long-term cell viability, differentiation and maintenance of podocytes, the ultra-specialized kidney resident cells that are responsible for the filtration of the blood. We developed a new platform which imitates the native kidney microenvironment by decellularizing fibroblasts grown on surfaces with macromolecular crowding. Human immortalized podocytes cultured on this platform displayed superior viability and metabolic activity up to 28 days compared to podocytes cultured on tissue culture plastic surfaces. The new platform displayed a softer surface and an abundance of growth factors and associated molecules. More importantly it enabled podocytes to display molecules responsible for their structure and function and a superior development of intercellular connections/interdigitations, consistent with maturation. The new platform can be used to study podocyte biology, test drug toxicity and determine whether sera from patients with podocytopathies are involved in the expression of glomerular pathology.

Bioprinting of Collagen: Considerations, Potentials, and Applications

Collagen is the most abundant extracellular matrix protein that is widely used in tissue engineering (TE). There is little research done on printing pure collagen. To understand the bottlenecks in printing pure collagen, it is imperative to understand collagen from a bottom-up approach. Here it is aimed to provide a comprehensive overview of collagen printing, where collagen assembly in vivo and the various sources of collagen available for TE application are first understood. Next, the current printing technologies and strategy for printing collagen-based materials are highlighted. Considerations and key challenges faced in collagen printing are identified. Finally, the key research areas that would enhance the functionality of printed collagen are presented.

Emerging themes and unifying concepts underlying cell behavior regulation by the pericellular space

Cells reside in a complex three-dimensional (3D) microenvironment where physical, chemical, and architectural features of the pericellular space regulate important cellular functions like migration, differentiation, and morphogenesis. A major goal of tissue engineering is to identify which properties of the pericellular space orchestrate these emergent cell behaviors and how. In this review, we highlight recent studies at the interface of biomaterials and single cell biophysics that are lending deeper insight towards this goal. Advanced methods have enabled the decoupling of architectural and mechanical features of the microenvironment, revealing multiple mechanisms of adhesion and mechanosensing modulation by biomaterials. Such studies are revealing important roles for pericellular space degradability, hydration, and adhesion competition in cell shape, volume, and differentiation regulation. STATEMENT OF SIGNIFICANCE: Cell fate and function are closely regulated by the local extracellular microenvironment. Advanced methods at the interface of single cell biophysics and biomaterials have shed new light on regulators of cell-pericellular space interactions by decoupling more features of the complex pericellular milieu than ever before. These findings lend deeper mechanistic insight into how biomaterials can be designed to fine-tune outcomes like differentiation, migration, and collective morphogenesis.

Engineering Hydrogels beyond a Hydrated Network

In recent years, many mechanical, physical, chemical, and biochemical features of biomatrices have emerged as important properties to dictate the fates of cells. To construct chemically defined biomaterials to recapitulate various biological niches for both cell biology research and therapeutic utilities, it has become increasingly clear that a simple hydrated polymer network would not be able to provide the complex cues and signaling required for many types of cells. The researchers are facing a growing list of mechanophysical and biochemical properties, while each of them could be an important cellular trigger. To include all these design parameters in screening and synthesis is practically difficult, if not impossible. Developing novel high throughput screening technology by combining assay miniaturization, computer simulations, and modeling can help researchers to tackle the challenge to identify the most relevant parameters to tailor materials for specific applications.

A high content, phenotypic 'scar-in-a-jar' assay for rapid quantification of collagen fibrillogenesis using disease-derived pulmonary fibroblasts

BACKGROUND

Excessive extracellular matrix (ECM) deposition is a hallmark feature in fibrosis and tissue remodelling diseases. Typically, mesenchymal cells will produce collagens under standard 2D cell culture conditions, however these do not assemble into fibrils. Existing assays for measuring ECM production are often low throughput and not disease relevant. Here we describe a robust, high content, pseudo-3D phenotypic assay to quantify mature fibrillar collagen deposition which is both physiologically relevant and amenable to high throughput compound screening. Using pulmonary fibroblasts derived from patients with idiopathic pulmonary fibrosis (IPF), we developed the 'scar-in-a-jar' assay into a medium-throughput phenotypic assay to robustly quantify collagen type I deposition and other extracellular matrix (ECM) proteins over 72 h.

RESULTS

This assay utilises macromolecular crowding to induce an excluded volume effect and enhance enzyme activity, which in combination with TGF-β1 stimulation significantly accelerates ECM production. Collagen type I is upregulated approximately 5-fold with a negligible effect on cell number. We demonstrate the robustness of the assay achieving a Z prime of approximately 0.5, and % coefficient of variance (CV) of < 5 for the assay controls SB-525334 (ALK5 inhibitor) and CZ415 (mTOR inhibitor). This assay has been used to confirm the potency of a number of potential anti-fibrotic agents. Active compounds from the 'scar-in-a-jar' assay can be further validated for other markers of ECM deposition and fibroblast activation such as collagen type IV and α-smooth muscle actin exhibiting a 4-fold and 3-fold assay window respectively.

CONCLUSION

In conclusion, we have developed 'scar -in-a-jar is' into a robust disease-relevant medium-throughput in vitro assay to accurately quantify ECM deposition. This assay may enable iterative compound profiling for IPF and other fibroproliferative and tissue remodelling diseases.

The extracellular fluid macromolecular composition differentially affects cell-substrate adhesion and cell morphology

Soluble macromolecules present in the tumour microenvironment (TME) alter the physical characteristics of the extracellular fluid and can affect cancer cell behaviour. A fundamental step in cancer progression is the formation of a new vascular network which may originate from both pre-existing normal endothelium and cancer-derived cells. To study the role of extracellular macromolecules in the TME affecting endothelial cells we exposed normal and cancer-derived endothelial cells to inert polymer solutions with different physicochemical characteristics. The cancer cell line SK-HEP-1, but not normal human umbilical vein endothelial cells, responded to high-macromolecular-content solutions by elongating and aligning with other cells, an effect that was molecular weight-dependent. Moreover, we found that neither bulk viscosity, osmotic pressure, nor the fractional volume occupancy of polymers alone account for the induction of these effects. Furthermore, these morphological changes were accompanied by an increased extracellular matrix deposition. Conversely, cell-substrate adhesion was enhanced by polymers increasing the bulk viscosity of the culture medium independently of polymer molecular weight. These results show that the complex macromolecular composition of the extracellular fluid strongly influences cancer-derived endothelial cell behaviour, which may be crucial to understanding the role of the TME in cancer progression.

Macromolecular crowding tunes 3D collagen architecture and cell morphogenesis

Collagen I is the primary extracellular matrix component of most solid tumors and influences metastatic progression. Collagen matrix engineering techniques are useful for understanding how this complex biomaterial regulates cancer cell behavior and for improving in vitro cancer models. Here, we establish an approach to tune collagen fibril architecture using PEG as an inert molecular crowding agent during gelation and cell embedding. We find that crowding produces matrices with tighter fibril networks that are less susceptible to proteinase mediated degradation, but does not significantly alter matrix stiffness. The resulting matrices have the effect of preventing cell spreading, confining cells, and reducing cell contractility. Matrix degradability and fibril length are identified as strong predictors of cell confinement. Further, the degree of confinement predicts whether breast cancer cells will ultimately undergo individual or collective behaviors. Highly confined breast cancer cells undergo morphogenesis to form either invasive networks reminiscent of aggressive tumors or gland and lobule structures reminiscent of normal breast epithelia. This morphological transition is accompanied by expression of cell-cell adhesion genes, including PECAM1 and ICAM1. Our study suggests that cell confinement, mediated by matrix architecture, is a design feature that tunes the transcriptional and morphogenic state of breast cancer cells.

Interaction Between Skeletal Muscle Cells and Extracellular Matrix Proteins Using a Serum Free Culture System

The ability to grow C2C12 myoblasts in a completely defined, serum free medium enables researchers to investigate the role of specific factors in myoblast proliferation, migration, fusion, and differentiation without the confounding effects of serum. The use of defined, animal free in vitro culture systems will improve reproducibility between research groups and may also enhance translation of tissue engineering techniques into clinical applications. Here, we describe the use and characterization of a serum free culture system for C2C12 myoblasts using standard tissue culture medium and readily available, defined growth factors and supplements.

Chasing Chimeras - The elusive stable chondrogenic phenotype

The choice of the best-suited cell population for the regeneration of damaged or diseased cartilage depends on the effectiveness of culture conditions (e.g. media supplements, three-dimensional scaffolds, mechanical stimulation, oxygen tension, co-culture systems) to induce stable chondrogenic phenotype. Herein, advances and shortfalls in in vitro, preclinical and clinical setting of various in vitro microenvironment modulators on maintaining chondrocyte phenotype or directing stem cells towards chondrogenic lineage are critically discussed. Chondrocytes possess low isolation efficiency, limited proliferative potential and rapid phenotypic drift in culture. Mesenchymal stem cells are relatively readily available, possess high proliferation potential, exhibit great chondrogenic differentiation capacity, but they tend to acquire a hypertrophic phenotype when exposed to chondrogenic stimuli. Embryonic and induced pluripotent stem cells, despite their promising in vitro and preclinical data, are still under-investigated. Although a stable chondrogenic phenotype remains elusive, recent advances in in vitro microenvironment modulators are likely to develop clinically- and commercially-relevant therapies in the years to come.

Macromolecular crowding for materials-directed controlled self-assembly

Macromolecular crowding refers to intracellular environments where various macromolecules, including proteins and nucleic acids, are present at high total concentrations. Its influence on biological processes has been investigated using a highly concentrated in vitro solution of water-soluble polymers as a model. Studies have revealed significant effects of macromolecular crowding on the thermodynamic equilibria and dynamics of biomolecular self-assembly in vivo. Recently, macromolecular crowding has attracted materials scientists, especially those in bio-related areas, as a tool to control molecular/colloidal self-assembly. Macromolecular crowding has been exploited to control the structure of supramolecular materials, assemble nanomaterials, and improve the performance of polymeric materials. Furthermore, nanostructured materials have been shown to be an interesting alternative to water-soluble polymers for creating crowded environments for controlled self-assembly. In this review article, we summarize recent progress in research on macromolecular crowding for controlled self-assembly in bio-related materials chemistry.

Kidney decellularized extracellular matrix hydrogels: Rheological characterization and human glomerular endothelial cell response to encapsulation

Hydrogels, highly-hydrated crosslinked polymer networks, closely mimic the microenvironment of native extracellular matrix (ECM) and thus present as ideal platforms for three-dimensional cell culture. Hydrogels derived from tissue- and organ-specific decellularized ECM (dECM) may retain bioactive signaling cues from the native tissue or organ that could in turn modulate cell-material interactions and response. In this study, we demonstrate that porcine kidney dECM can be processed to form hydrogels suitable for cell culture and encapsulation studies. Scanning electron micrographs of hydrogels demonstrated a fibrous ultrastructure with interconnected pores, and rheological analysis revealed rapid gelation times with shear moduli dependent upon the protein concentration of the hydrogels. Conditionally-immortalized human glomerular endothelial cells (GEnCs) cultured on top of or encapsulated within hydrogels exhibited high cell viability and proliferation over a one-week culture period. However, gene expression analysis of GEnCs encapsulated within kidney dECM hydrogels revealed significantly lower expression of several relevant genes of interest compared to those encapsulated within hydrogels composed of only purified collagen I. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A:2448-2462, 2018.

Reshaping the Tumor Stroma for Treatment of Pancreatic Cancer

Pancreatic cancer is accompanied by a fibrotic reaction that alters interactions between tumor cells and the stroma to promote tumor progression. Consequently, strategies to target the tumor stroma might be used to treat patients with pancreatic cancer. We review recently developed approaches for reshaping the pancreatic tumor stroma and discuss how these might improve patient outcomes. We also describe relationships between the pancreatic tumor extracellular matrix, the vasculature, the immune system, and metabolism, and discuss the implications for the development of stromal compartment-specific therapies.

Applying macromolecular crowding to 3D bioprinting: fabrication of 3D hierarchical porous collagen-based hydrogel constructs

3D bioprinting of hierarchical porous structures for tissue engineering.