Fibril growth kinetics link buffer conditions and topology of 3D collagen I networks

Physical network regimes of 3D fibrillar collagen networks trigger invasive phenotypes of breast cancer cells

The mechanical characteristics of the extracellular environment are known to significantly influence cancer cell behavior in vivo and in vitro. The structural complexity and viscoelastic dynamics of the extracellular matrix (ECM) pose significant challenges in understanding its impact on cancer cells. Herein, we report distinct regulatory signatures in the invasion of different breast cancer cell lines into three-dimensional (3D) fibrillar collagen networks, caused by systematic modifications of the physical network properties. By reconstituting collagen networks of thin fibrils, we demonstrate that such networks can display network strand flexibility akin to that of synthetic polymer networks, known to exhibit entropic rubber elasticity. This finding contrasts with the predominant description of the mechanics of fibrillar collagen networks by an enthalpic bending elasticity of rod-like fibrils. Mean-squared displacement analysis of free-standing fibrils confirmed a flexible fiber regime in networks of thin fibrils. Furthermore, collagen fibrils in both networks were softened by the adsorption of highly negatively charged sulfonated polymers and colloidal probe force measurements of network elastic modulus again proofed the occurrence of the two different physical network regimes. Our cell assays revealed that the cellular behavior (morphology, clustering, invasiveness, matrix metalloproteinase (MMP) activity) of the 'weakly invasive' MCF-7 and 'highly invasive' MDA-MB-231 breast cancer cell lines is distinctively affected by the physical (enthalpic/entropic) network regime, and cannot be explained by changes of the network elastic modulus, alone. These results highlight an essential pathway, albeit frequently overlooked, how the physical characteristics of fibrillar ECMs affect cellular behavior. Considering the coexistence of diverse physical network regimes of the ECM in vivo, our findings underscore their critical role of ECM's physical network regimes in tumor progression and other cell functions, and moreover emphasize the significance of 3D in vitro collagen network models for quantifying cell responses in both healthy and pathological states.

The Influence of Sulfation Degree of Glycosaminoglycan-Functionalized 3D Collagen I Networks on Cytokine Profiles of In Vitro Macrophage-Fibroblast Cocultures

Cell-cell interactions between fibroblasts and immune cells, like macrophages, are influenced by interaction with the surrounding extracellular matrix during wound healing. In vitro hydrogel models that mimic and modulate these interactions, especially of soluble mediators like cytokines, may allow for a more detailed investigation of immunomodulatory processes. In the present study, a biomimetic extracellular matrix model based on fibrillar 3D collagen I networks with a functionalization with heparin or 6-ON-desulfated heparin, as mimics of naturally occurring heparan sulfate, was developed to modulate cytokine binding effects with the hydrogel matrix. The constitution and microstructure of the collagen I network were found to be stable throughout the 7-day culture period. A coculture study of primary human fibroblasts/myofibroblasts and M-CSF-stimulated macrophages was used to show its applicability to simulate processes of progressed wound healing. The quantification of secreted cytokines (IL-8, IL-10, IL-6, FGF-2) in the cell culture supernatant demonstrated the differential impact of glycosaminoglycan functionalization of the collagen I network. Most prominently, IL-6 and FGF-2 were shown to be regulated by the cell culture condition and network constitution, indicating changes in paracrine and autocrine cell-cell communication of the fibroblast-macrophage coculture. From this perspective, we consider our newly established in vitro hydrogel model suitable for mechanistic coculture analyses of primary human cells to unravel the role of extracellular matrix factors in key events of tissue regeneration and beyond.

A Systems Approach to Study Collagen Type I Self-Assembly: Kinetics and Morphology

Collagen type I, the main component of the extracellular matrix in vertebrates, is widely used in tissue engineering applications. This is on account that collagen molecules can self-assemble under certain conditions into 3D fibrillar hydrogels. Although there is an extensive body of literature studying collagen self-assembly, there is a lack of systematic understanding on how different experimental factors, such as pH and temperature, and their cumulative effects guide the self-assembly process. In this work, a comprehensive workflow to study the interactive effects of several assembly parameters on the collagen self-assembly process is implemented. This workflow consists of: 1) efficient statistical sampling based on Design of Experiments, 2) high-throughput and automated data collection and 3) automated data analysis. This approach enables to screen several parameters simultaneously and derive a set of mathematical equations that link parameters with the kinetics and morphological aspects of collagen self-assembly, and can be used to design collagen constructs with predefined characteristics.

Fibrillogenesis in collagen hydrogels accelerated by carboxylated microbeads

Collagen type I is a material widely used for 3D cell culture and tissue engineering. Different architectures, such as gels, sponges, membranes, and nanofibers, can be fabricated with it. In collagen hydrogels, the formation of fibrils and fibers depends on various parameters, such as the source of collagen, pH, temperature, concentration, age, etc. In this work, we study the fibrillogenesis process in collagen type I hydrogels with different types of microbeads embedded, using optical techniques such as turbidity assay and confocal reflectance microscopy. We observe that microbeads embedded in the collagen matrix hydrogels modify the fibrillogenesis. Our results show that carboxylated fluorescent microbeads accelerate 3.6 times the gelation, while silica microbeads slow down the formation of collagen fibrils by a factor of 1.9, both compared to pure collagen hydrogels. Our observations suggest that carboxylate microbeads act as nucleation sites and the early collagen fibrils bind to the microbeads.

Correlation between Fibrin Fibrillation Kinetics and the Resulting Fibrin Network Microstructure

Fibrin, the prominent extracellular matrix in early wound tissue, is discussed to influence immune cells and healing. The nature of fibrinogen/fibrin to form fibrillary networks is frequently exploited to engineer microenvironments for cellular analysis. This study focuses on revealing the correlation of fibril formation kinetic and the resulting network microstructure of engineered 3D fibrin networks. Different concentrations of fibrinogen (1-3 mg mL^-1 ), thrombin (0.01-0.15 U mL^-1 ), sodium chloride (40-120 mm), and calcium chloride (1-10 mm) are applied to assess the impact on the fibril growth kinetics by turbidity analysis and on the resulting fibril and pore diameter by laser scanning microscopy. The results highlight a direct influence of the sodium chloride concentration on fibrillation kinetics and reveal a strong correlation between fibrillation kinetics and network microstructure. With the assumption of a first-order growth kinetic, an increase of the growth constant k (0.015-0.04 min^-1 ) is found to correlate to a decrease in fibril diameter (1-0.65 µm) and pore diameter (11-5 µm). The new findings enable an easy prediction of 3D fibrin network microstructure by the fibril formation kinetic and contribute to an improved engineering of defined scaffolds for tissue engineering and cell culture applications.

Snake venom-defined fibrin architecture dictates fibroblast survival and differentiation

Fibrin is the provisional matrix formed after injury, setting the trajectory for the subsequent stages of wound healing. It is commonly used as a wound sealant and a natural hydrogel for three-dimensional (3D) biophysical studies. However, the traditional thrombin-driven fibrin systems are poorly controlled. Therefore, the precise roles of fibrin's biophysical properties on fibroblast functions, which underlie healing outcomes, are unknown. Here, we establish a snake venom-controlled fibrin system with precisely and independently tuned architectural and mechanical properties. Employing this defined system, we show that fibrin architecture influences fibroblast survival, spreading phenotype, and differentiation. A fine fibrin architecture is a key prerequisite for fibroblast differentiation, while a coarse architecture induces cell loss and disengages fibroblast's sensitivity towards TGF-β1. Our results demonstrate that snake venom-controlled fibrin can precisely control fibroblast differentiation. Applying these biophysical principles to fibrin sealants has translational significance in regenerative medicine and tissue engineering.

Self-assembly of mesoscale collagen architectures and applications in 3D cell migration

3D in vitro tumor models have recently been investigated as they can recapitulate key features in the tumor microenvironment. Reconstruction of a biomimetic scaffold is critical in these models. However, most current methods focus on modulating local properties, e.g. micro- and nano-scaled topographies, without capturing the global millimeter or intermediate mesoscale features. Here we introduced a method for modulating the collagen I-based extracellular matrix structure by disruption of fibrillogenesis and the gelation process through mechanical agitation. With this method, we generated collagen scaffolds that are thickened and wavy at a larger scale while featuring global softness. Thickened collagen patches were interconnected with loose collagen networks, highly resembling collagen architecture in the tumor stroma. This thickened collagen network promoted tumor cell dissemination. In addition, this novel modified scaffold triggered differences in morphology and migratory behaviors of tumor cells. Altogether, our method for altered collagen architecture paves new ways for studying in detail cell behavior in physiologically relevant biological processes. STATEMENT OF SIGNIFICANCE: Tumor progression usually involves chronic tissue damage and repair processes. Hallmarks of tumors are highly overlapped with those of wound healing. To mimic the tumor milieu, collagen-based scaffolds are widely used. These scaffolds focus on modulating microscale topographies and mechanics, lacking global architecture similarity compared with in vivo architecture. Here we introduced one type of thick collagen bundles that mimics ECM architecture in human skin scars. These thickened collagen bundles are long and wavy while featuring global softness. This collagen architecture imposes fewer steric restraints and promotes tumor cell dissemination. Our findings demonstrate a distinct picture of cell behaviors and intercellular interactions, highlighting the importance of collagen architecture and spatial heterogeneity of the tumor microenvironment.

Biomaterial Integration in the Joint: Pathological Considerations, Immunomodulation, and the Extracellular Matrix

Defects of articular joints are becoming an increasing societal burden due to a persistent increase in obesity and aging. For some patients suffering from cartilage erosion, joint replacement is the final option to regain proper motion and limit pain. Extensive research has been undertaken to identify novel strategies enabling earlier intervention to promote regeneration and cartilage healing. With the introduction of decellularized extracellular matrix (dECM), researchers have tapped into the potential for increased tissue regeneration by designing biomaterials with inherent biochemical and immunomodulatory signals. Compared to conventional and synthetic materials, dECM-based materials invoke a reduced foreign body response. It is therefore highly beneficial to understand the interplay of how these native tissue-based materials initiate a favorable remodeling process by the immune system. Yet, such an understanding also demands increasing considerations of the pathological environment and remodeling processes, especially for materials designed for early disease intervention. This knowledge would avoid rejection and help predict complications in conditions with inflammatory components such as arthritides. This review outlines general issues facing biomaterial integration and emphasizes the importance of tissue-derived macromolecular components in regulating essential homeostatic, immunological, and pathological processes to increase biomaterial integration for patients suffering from joint degenerative diseases. This article is protected by copyright. All rights reserved.

Extracellular Vesicles Mediate the Intercellular Exchange of Nanoparticles

To exert their therapeutic effects, nanoparticles (NPs) often need to travel into the tissues composed of multilayered cells. Accumulative evidence has revealed the crucial role of transcellular transport route (entry into one cell, exocytosis, and re-entry into another) in this process. While NP endocytosis and subcellular transport are intensively characterized, the exocytosis and re-entry steps are poorly understood, which becomes a barrier for NP delivery into complex tissues. Here, the authors term the exocytosis and re-entry steps together as intercellular exchange. A collagen-based three-dimension assay is developed to specifically quantify the intercellular exchange of NPs, and distinguish the contributions of several potential mechanisms. The authors show that NPs can be exocytosed freely or enclosed inside extracellular vesicles (EVs) for re-entry, while direct cell-cell contact is hardly involved. EVs account for a significant fraction of NP intercellular exchange, and its importance in NP transport is demonstrated in vitro and in vivo. While freely released NPs engage with the same receptors for re-entry, EV-enclosed ones bypass this dependence. These studies provide an easy and precise system to investigate the intercellular exchange stage of NP delivery, and shed the first light in the importance of EVs in NP transport between cells and into complex tissues.

Mesopore Controls the Responses of Blood Clot-Immune Complex via Modulating Fibrin Network

Formation of blood clots, particularly the fibrin network and fibrin network-mediated early inflammatory responses, plays a critical role in determining the eventual tissue repair or regeneration following an injury. Owing to the potential role of fibrin network in mediating clot-immune responses, it is of great importance to determine whether clot-immune responses can be regulated via modulating the parameters of fibrin network. Since the diameter of D-terminal of a fibrinogen molecule is 9 nm, four different pore sizes (2, 8, 14, and 20 nm) are rationally selected to design mesoporous silica to control the fibrinogen adsorption and modulate the subsequent fibrin formation process. The fiber becomes thinner and the contact area with macrophages decreases when the pore diameters of mesoporous silica are greater than 9 nm. Importantly, these thinner fibers grown in pores with diameters larger than 9 nm inhibit the M1-polorazation of macrophages and reduce the productions of pro-inflammatory cytokines and chemokines by macrophages. These thinner fibers reduce inflammation of macrophages through a potential signaling pathway of cell adhesion-cytoskeleton assembly-inflammatory responses. Thus, the successful regulation of the clot-immune responses via tuning of the mesoporous pore sizes indicates the feasibility of developing advanced clot-immune regulatory materials.

Stiffness Variation of 3D Collagen Networks by Surface Functionalization of Network Fibrils with Sulfonated Polymers

Fibrillar collagen is the most prominent protein in the mammalian extracellular matrix. Therefore, it is also widely used for cell culture research and clinical therapy as a biomimetic 3D scaffold. Charged biopolymers, such as sulfated glycosaminoglycans, occur in vivo in close contact with collagen fibrils, affecting many functional properties such as mechanics and binding of growth factors. For in vitro application, the functions of sulfated biopolymer decorations of fibrillar collagen materials are hardly understood. Herein, we report new results on the stiffness dependence of 3D collagen I networks by surface functionalization of the network fibrils with synthetic sulfonated polymers, namely, poly(styrene sulfonate) (PSS) and poly(vinyl sulfonate) (PVS). A non-monotonic stiffness dependence on the amount of adsorbed polymer was found for both polymers. The stiffness dependence correlated to a transition from mono- to multilayer adsorption of sulfonated polymers on the fibrils, which was most prominent for PVS. PVS mono- and multilayers caused a network stiffness change by a factor of 0.3 and 2, respectively. A charge-dependent weakening of intrafibrillar salt bridges by the adsorbed sulfonated polymers leading to fibrillar softening is discussed as the mechanism for the stiffness decrease in the monolayer regime. In contrast, multilayer adsorption can be assumed to induce interfibrillar bridging and an increase in network stiffness. Our in vitro results have a strong implication on in vivo characteristics of fibrillar collagen I, as sulfated glycosaminoglycans frequently attach to collagen fibrils in various tissues, calling for an up to now overlooked impact on matrix and tendon mechanics.

Impact of binding mode of low-sulfated hyaluronan to 3D collagen matrices on its osteoinductive effect for human bone marrow stromal cells

Synthetically sulfated hyaluronan derivatives were shown to facilitate osteogenic differentiation of human bone marrow stromal cells (hBMSC) by application in solution or incorporated in thin collagen-based coatings. In the presented study, using a biomimetic three-dimensional (3D) cell culture model based on fibrillary collagen I (3D Col matrix), we asked on the impact of binding mode of low sulfated hyaluronan (sHA) in terms of adsorptive and covalent binding on osteogenic differentiation of hBMSC. Both binding modes of sHA induced osteogenic differentiation. Although for adsorptive binding of sHA a strong intracellular uptake of sHA was observed, implicating an intracellular mode of action, covalent binding of sHA to the 3D matrix induced also intense osteoinductive effects pointing towards an extracellular mode of action of sHA in osteogenic differentiation. In summary, the results emphasize the relevance of fibrillary 3D Col matrices as a model to study hBMSC differentiation in vitro in a physiological-like environment and that sHA can display dose-dependent osteoinductive effects in dependence on presentation mode in cell culture scaffolds.

Investigation of the Structural Mechanism and Film Growth on Cytoprotective Type I Collagen-Based Nanocoating of Individual Cellular Surfaces

Cell surface coating using the layer-by-layer assembly (LbL) method has many advantages for biomedical applications. Because the cell surface is a dynamic and highly complex structure, it is hypothesized that LbL multilayer films on cells have characteristics different from those observed in traditional film characterization results. Here, to demonstrate the mechanism of LbL-film formation on cells, LbL films are prepared on HeLa cells using collagen (Col) and hyaluronic acid (HA). The growth behavior of the film and the main driving forces inducing the formation of an LbL film on the cells are investigated. Col self-assembles via electrostatic and hydrophobic interactions; therefore, the Col-based film on the cells grows laterally rather than volumetrically. For the film construction conditions, the ionic density and chain conformation of the polymers change, resulting in mainly hydrophobic interactions. Additional interactions, such as hydrophobic interactions and biological recognition between the substrate and building blocks, also exist and tightly stabilize the films on the cells. The Col/HA film shows an even distribution on the cell surface as the extracellular matrix, and it activates proliferation and the cytoprotective signaling pathway under harsh conditions, resulting in the focal adhesion kinase signaling pathway and low lactate dehydrogenase release. Therefore, information for film construction on cells is beneficial to understand the effectiveness of an LbL film for cells.

A tough act to follow: collagen hydrogel modifications to improve mechanical and growth factor loading capabilities

Collagen hydrogels are among ​the most well-studied platforms for drug delivery and in situ tissue engineering, thanks to their low cost, low immunogenicity, versatility, biocompatibility, and similarity to the natural extracellular matrix (ECM). Despite collagen being largely responsible for the tensile properties of native connective tissues, collagen hydrogels have relatively low mechanical properties in the absence of covalent cross-linking. This is particularly problematic when attempting to regenerate stiffer and stronger native tissues such as bone. Furthermore, in contrast to hydrogels based on ECM proteins such as fibronectin, collagen hydrogels do not have any growth factor (GF)-specific binding sites and often cannot sequester physiological (small) amounts of the protein. GF binding and in situ presentation are properties that can aid significantly in the tissue regeneration process by dictating cell fate without causing adverse effects such as malignant tumorigenic tissue growth. To alleviate these issues, researchers have developed several strategies to increase the mechanical properties of collagen hydrogels using physical or chemical modifications. This can expand the applicability of collagen hydrogels to tissues subject to a continuous load. GF delivery has also been explored, mathematically and experimentally, through the development of direct loading, chemical cross-linking, electrostatic interaction, and other carrier systems. This comprehensive article explores the ways in which these parameters, mechanical properties and GF delivery, have been optimized in collagen hydrogel systems ​and examines their in vitro or in vivo biological effect. This article can, therefore, be a useful tool to streamline future studies in the field, by pointing researchers into the appropriate direction according to their collagen hydrogel design requirements.

Fibronectin-functionalization of 3D collagen networks supports immune tolerance and inflammation suppression in human monocyte-derived macrophages

The extracellular matrix (ECM) is dynamically reorganized during wound healing. Concomitantly, recruited monocytes differentiate into macrophages. However, the role of the wound's ECM during this transition remain to be fully understood. Fibronectin is a multifunctional glycoprotein present in early wound ECM with a potential immunomodulatory role during monocyte-to-macrophage differentiation. Hence, to investigate the impact of fibronectin during this differentiation step, 3D fibrillar collagen type I networks with or without fibronectin-functionalization were engineered with defined topology (fibril and pore diameter: 0.8 μm; 7 μm) and amount of adsorbed fibronectin (0.15 μg per μg collagen). Primary, human monocytes were then differentiated into macrophages inside these networks. The immunological imprinting of the resulting macrophages was monitored by means of the expression of FABP4, CLEC4E, SLC2A6, and SOD2 which discriminate naïve and tolerized macrophages, as well pro-inflammatory (M1) and anti-inflammatory (M2) macrophage polarization. The analyses indicate that fibronectin-functionalization of collagen I networks induces macrophage tolerance rather than M1 or M2 macrophage phenotypes. This finding was confirmed by release profiles of pro- and anti-inflammatory cytokines such as IL6, IL8, CXCL10, and IL10. Nevertheless, upon LPS challenge, immune suppression by fibronectin was overridden since these macrophages could then deploy an efficient immune response. Our results therefore provide new perspectives in biomaterial science of wound healing scaffolds and the design of instructive materials for human monocyte-derived cells.

Construction of a 3D brain extracellular matrix model to study the interaction between microglia and T cells in co-culture

Neurodegenerative disorders are characterised by the activation of brain-resident microglia cells and by the infiltration of peripheral T cells. However, their interplay in disease has not been clarified yet. It is difficult to investigate complex cellular dynamics in living animals, and simple two-dimensional (2D) cell culture models do not resemble the soft 3D structure of brain tissue. Therefore, we developed a biomimetic 3D in vitro culture system for co-cultivation of microglia and T cells. As the activation and/or migration of immune cells in the brain might be affected by components of the extracellular matrix, defined 3D fibrillar collagen I-based matrices were constructed and modified with hyaluronan and/or chondroitin sulphate, resembling aspects of brain extracellular matrix. Murine microglia and spleen-derived T cells were cultured alone or in co-culture on the constructed matrices. Microglia exhibited in vivo-like morphology and T cells showed enhanced survival when co-cultured with microglia or to a minor degree in the presence of glia-conditioned medium. The open and porous fibrillar structure of the matrix allowed for cell invasion and direct cell-cell interaction, with stronger invasion of T cells. Both cell types showed no dependence on the matrix modifications. Microglia could be activated on the matrices by lipopolysaccharide resulting in interleukin-6 and tumour necrosis factor-α secretion. The findings herein indicate that biomimetic 3D matrices allow for co-cultivation and activation of primary microglia and T cells and provide useful tools to study their interaction in vitro.

Collagen microarchitecture mechanically controls myofibroblast differentiation

Altered microarchitecture of collagen type I is a hallmark of wound healing and cancer that is commonly attributed to myofibroblasts. However, it remains unknown which effect collagen microarchitecture has on myofibroblast differentiation. Here, we combined experimental and computational approaches to investigate the hypothesis that the microarchitecture of fibrillar collagen networks mechanically regulates myofibroblast differentiation of adipose stromal cells (ASCs) independent of bulk stiffness. Collagen gels with controlled fiber thickness and pore size were microfabricated by adjusting the gelation temperature while keeping their concentration constant. Rheological characterization and simulation data indicated that networks with thicker fibers and larger pores exhibited increased strain-stiffening relative to networks with thinner fibers and smaller pores. Accordingly, ASCs cultured in scaffolds with thicker fibers were more contractile, expressed myofibroblast markers, and deposited more extended fibronectin fibers. Consistent with elevated myofibroblast differentiation, ASCs in scaffolds with thicker fibers exhibited a more proangiogenic phenotype that promoted endothelial sprouting in a contractility-dependent manner. Our findings suggest that changes of collagen microarchitecture regulate myofibroblast differentiation and fibrosis independent of collagen quantity and bulk stiffness by locally modulating cellular mechanosignaling. These findings have implications for regenerative medicine and anticancer treatments.

Bundling of Collagen Fibrils Using Sodium Sulfate for Biomimetic Cell Culturing

Collagen is the most abundant extracellular matrix protein. The concentrations, structural arrangement, and directionality of collagen depend on the type of tissue. Thick fibril bundles of collagen are observed in most collagenous tissues, including connective tissues, bones, and tendons, indicating that they play a critical role in many cell functions. In this study, we developed a new method to regulate collagen bundling without altering the protein concentration, temperature, or pH by using sodium sulfate to replicate bundled collagen fibrils found in vivo. Microstructure analysis revealed that both the thickness of the fibril bundles and the pore size of the matrix increased with the amount of sodium sulfate. In contrast, there was no significant change in the bulk mechanical stiffness of the collagen matrix. The modified collagen bundle matrix was used to investigate the responses of human cervical cancer cells by mimicking the extracellular environments of a tumor. Compared to the normal collagen matrix, cells on the collagen bundle matrix exhibited significant changes in morphology, with a reduced cell perimeter and aspect ratio. The cell motility, which was analyzed in terms of the speed of migration and mean squared displacement, decreased for the collagen bundle matrix. Additionally, the critical time taken for the peak turning angle to converge to 90° decreased, indicating that the migration direction was regulated by geometric cues provided by collagen bundles rather than by the intrinsic cell persistence. The experimental results imply that collagen bundles play an important role in determining the magnitude and direction in cancer cell migration. The proposed method of extracellular matrix modification can be applied to investigate various cellular behaviors in both physiological and pathological environments.

A miniaturized hydrogel-based in vitro model for dynamic culturing of human cells overexpressing beta-amyloid precursor protein

Recent findings have highlighted an interconnection between intestinal microbiota and the brain, referred to as microbiota-gut-brain axis, and suggested that alterations in microbiota composition might affect brain functioning, also in Alzheimer's disease. To investigate microbiota-gut-brain axis biochemical pathways, in this work we developed an innovative device to be used as modular unit in an engineered multi-organ-on-a-chip platform recapitulating in vitro the main players of the microbiota-gut-brain axis, and an innovative three-dimensional model of brain cells based on collagen/hyaluronic acid or collagen/poly(ethylene glycol) semi-interpenetrating polymer networks and β-amyloid precursor protein-Swedish mutant-expressing H4 cells, to simulate the pathological scenario of Alzheimer's disease. We set up the culturing conditions, assessed cell response, scaled down the three-dimensional models to be hosted in the organ-on-a-chip device, and cultured them both in static and in dynamic conditions. The results suggest that the device and three-dimensional models are exploitable for advanced engineered models representing brain features also in Alzheimer's disease scenario.

3D Scaffold-Based Macrophage Fibroblast Coculture Model Reveals IL-10 Dependence of Wound Resolution Phase

Persistent inflammation and impaired repair in dermal wound healing are frequently associated with cell-cell and cell-matrix miscommunication. A direct coculture model of primary human myofibroblasts (MyoFB) and M-CSF-differentiated macrophages (M-Mɸ) in fibrillar three-dimensional Collagen I (Coll I) matrices is developed to study intercellular interactions. The coculture experiments reveal the number of M-Mɸ regulated MyoFB dedifferentiation in a dose-dependent manner. The amount of MyoFB decreases in dependence of the number of cocultured M-Mɸ, even in the presence of MyoFB-inducing transforming growth factor β₁ (TGF-β₁ ). Gene expression analysis of matrix proteins (collagen I, collagen III, ED-A-fibronectin) confirms the results of an altered MyoFB phenotype. Additionally, M-Mɸ is shown to be the main source of secreted cytokine interleukin-10 (IL-10), which is suggested to affect MyoFB dedifferentiation. These findings indicate a paracrine impact of IL-10 secretion by M-Mɸ on the MyoFB differentiation status counteracting the TGF-β₁ -driven MyoFB activation. Hence, the in vitro coculture model simulates physiological situations during wound resolution and underlines the importance of paracrine IL-10 signals by M-Mɸ. In sum, the 3D Coll I-based matrices with a MyoFB-M-Mɸ coculture form a highly relevant biomimetic model of late stages of wound healing.

Self-association of type I collagen directed by thymoquinone through alteration of molecular forces

Type I collagen is a vital structural component of the extracellular matrix providing the connective tissues with biomechanical support. One of the interesting properties of collagen is to self-associate into fibrils. The present work aims to direct the self-assembly of collagen through different molecular forces, which are tuned on the addition of thymoquinone a well-known phytochemical. A change in relative viscosity and stress of collagen-thymoquinone blends influenced the interfibrillar aggregates around its hydration shell. Further, secondary structural integrity was studied via cotton curve effect, and vibrational frequency shifts showed a characteristic interaction of thymoquinone at the N-terminal residues of the triple helix. Finally, the spontaneous self-association of fibrils was tracked by calculating the rate of fibril growth kinetics, which potentially decreased with increase in thymoquinone concentration. The fibrils were eventually visualized under the high resolution-scanning microscope showing morphological variations. Therefore, such a protein-phytochemical interaction may tend to play with the hydration network of collagen and covalently interact with its imino acid residues. It may be speculated that such an inhibitory process portrayed by thymoquinone may have a fortune in the targeted and sustainable delivery to the site of action for certain diseases, which includes collagen accumulation. Moreover, its directed assembly could be utilized for designing templates as in manipulating the collagen as a nanoporous membrane to make nanofibers and further tuned by small molecules for nanoparticle synthesis application.

Governing the Inhibition of Reconstituted Collagen Type I Assemblies Mediated Through Noncovalent Forces of (±)-α Lipoic Acid

Type I collagen is a fibrous protein, which is highly biocompatible and biodegradable and exhibits low immunogenicity with its unique feature of undergoing a spontaneous self-assembly process. However, the excessive accumulation of collagen may lead to a condition known as fibrosis in vertebrates. Recently, saturated fatty acids have gained much attention as biomedical and therapeutic agents. Therefore, drawing inspiration from the biological and structural tunability of these fatty acids, this work aims to inhibit the self-assembly of type I collagen using (±)-α-lipoic acid (ALA). Reconstituted collagen and its blends with (±)-ALA under physiological conditions were subjected to fibril growth kinetics measurements, which exhibited the decrease in the rate of fibrillogenesis ( t_1/2) with an increase in the concentration of ALA. Variations in the viscoelasticity of collagen and ALA blend with respect to rate and frequency showed significant changes. Further, the frequency shifts of different functional groups via FT-IR (ATR) and the morphological changes associated with fibril inhibition were visualized using a cryoscanning electron microscope. Molecular dynamics simulation of the collagen-like peptide with the (±)-ALA molecule at different molar ratios proved that (±)-ALA had a strong potential to bind at various sites of collagen mediated by conventional secondary or noncovalent forces. Thus, the protein-small molecule interaction dominates the forces prevailing between protein-protein binding, leading to the inhibition of the self-assembly process. Such inhibitory effects by a fatty acid may unfold newer avenues for development of targeted and sustainable drug delivery systems for fibrotic diseases.

Imaging of Ag NP transport through collagen-rich microstructures in fibroblast multicellular spheroids by high-resolution laser ablation inductively coupled plasma time-of-flight mass spectrometry

We investigated the penetration of silver nanoparticles (Ag NPs) into a three-dimensional in vitro tissue analog using NPs with various sizes and surface coatings, and with different incubation times. A high-resolution laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) time-of-flight (TOF) instrument was applied for imaging the distributions of elements in thin sample sections (20 μm thick). A fibroblast multicellular spheroid (MCS) was selected as the model system and cultured for more than 8 days to produce a natural barrier formed by the extracellular matrix containing collagen. The MCS was then exposed for up to 48 h to one of four types of Ag NPs (∅ 5 nm citrate coated, ∅ 20 nm citrate coated, ∅ 20 nm polyvinylpyrrolidone coated, and ∅ 50 nm citrate coated). Imaging showed that the penetration pathway was strongly related to steric networks formed by collagen fibrils, and Ag NPs with a hydrodynamic diameter of more than 41 nm were completely trapped in an outer rim of the MCSs even after incubation for 48 h. In addition, we examined the impact of these NPs on essential elements (P, Fe, Cu, and Zn) in areas of Ag NP accumulation. We observed a linear increase at the sub-femtogram level in the total concentration of Cu (fg per pixel) in samples treated with small or large Ag NPs (∅ 5 nm or ∅ 50 nm) for 48 h.

Fibril bending stiffness of 3D collagen matrices instructs spreading and clustering of invasive and non-invasive breast cancer cells

Extracellular matrix stiffening of breast tissues has been clinically correlated with malignant transformation and poor prognosis. An increase of collagen fibril diameter and lysyl-oxidase mediated crosslinking has been observed in advanced tumor stages. Many current reports suggest that the local mechanical properties of single fibrillar components dominantly regulate cancer cell behavior. Here, we demonstrate by an independent control of fibril diameter and intrafibrillar crosslinking of three-dimensional (3D) collagen matrices that fibril bending stiffness instructs cell behavior of invasive and non-invasive breast cancer cells. Two types of collagen matrices with fibril diameter of either 650 nm or 800 nm at a similar pore size of 10 μm were reconstituted and further modified with the zero-length crosslinker 1-ethyl-3-(3-dimethyl aminopropyl)-carbodiimide (EDC) at concentrations of 0, 20, 100 and 500 mM. This approach yields two sets of collagen matrices with overlapping variation of matrix elasticity. With these matrices we could prove the common assumption that matrix elasticity of collagen networks is bending dominated with a linear dependence on fibril bending stiffness. We derive that the measured variation of matrix elasticity is directly correlated to the variation of fibril bending stiffness, being independently controlled either by fibril diameter or by intrafibrillar crosslinking. We use these defined matrices to demonstrate that the adjustment of fibril bending stiffness allows to instruct the behavior of two different breast cancer cell lines, invasive MDA-MB-231 (human breast carcinoma) and non-invasive MCF-7 cells (human breast adenocarcinoma). Invasiveness and spreading of invasive MDA-MB-231 cells as well as clustering of non-invasive MCF-7 cells is thereby investigated over a broad parameter range. Our results demonstrate and quantify the direct dependence of cancer cell phenotypes on the matrix mechanical properties on the scale of single fibrils.

Systems for localized release to mimic paracrine cell communication in vitro

Paracrine cell communication plays a pivotal role for signal exchange between proximal cells in vivo. However, this localized, gradient type release of mediators at very low concentrations (pg/ml), relevant during physiological and pathological processes, is rarely reflected within in vitro approaches. This review gives an overview on state-of-the-art approaches, which transfer the paracrine cell-to-cell communication into in vitro cell culture model setups. The traditional methods like trans-well assays and more advanced microfluidic approaches are included. The review focusses on systems for localized release, mostly based on microparticles, which tightly mimic the paracrine interaction between single cells in 3D microenvironments. Approaches based on single microparticles, with the main focus on affinity-controlled storage and release of cytokines, are reviewed and their importance for understanding paracrine communication is highlighted. Various methods to study the cytokine release and their advantages and disadvantages are discussed. Basic principles of the release characteristics, like diffusion mechanisms, are quantitatively described, including the formation of resulting gradients around the local sources. In vitro cell experiments using such localized microparticle release systems in approaches to increase understanding of stem cell behavior within their niches and regulation of wound healing are highlighted as examples of successful localized release systems for mimicking paracrine cell communication.

Biomimetic tumor microenvironments based on collagen matrices

This review provides an overview of the current approaches to engineer defined 3D matrices for the investigation of tumor cell behaviorin vitro, with a focus on collagen-based fibrillar systems.