The differential regulation of cell motile activity through matrix stiffness and porosity in three dimensional collagen matrices

Elastocapillary effects determine early matrix deformation by glioblastoma cell spheroids

During cancer pathogenesis, cell-generated mechanical stresses lead to dramatic alterations in the mechanical and organizational properties of the extracellular matrix (ECM). To date, contraction of the ECM is largely attributed to local mechanical stresses generated during cell invasion, but the impact of "elastocapillary" effects from surface tension on the tumor periphery has not been examined. Here, we embed glioblastoma cell spheroids within collagen gels, as a model of tumors within the ECM. We then modulate the surface tension of the spheroids, such that the spheroid contracts or expands. Surprisingly, in both cases, at the far-field, the ECM is contracted toward the spheroids prior to cellular migration from the spheroid into the ECM. Through computational simulation, we demonstrate that contraction of the ECM arises from a balance of spheroid surface tension, cell-ECM interactions, and time-dependent, poroelastic effects of the gel. This leads to the accumulation of ECM near the periphery of the spheroid and the contraction of the ECM without regard to the expansion or contraction of the spheroid. These results highlight the role of tissue-level surface stresses and fluid flow within the ECM in the regulation of cell-ECM interactions.

Characterization of lamina propria remodeling in pediatric eosinophilic esophagitis using second harmonic generation microscopy

Eosinophilic esophagitis (EoE) is a chronic inflammatory condition characterized by an intense infiltration of eosinophils into the esophageal epithelium. When not adequately controlled, eosinophilic inflammation can lead to changes in components of the extracellular matrix (ECM) of the lamina propria. Particularly, alterations to the collagen fiber matrix can lead to lamina propria fibrosis (LPF), which plays an important role in the fibrostenotic complications of EoE. Current approaches to assess LPF in EoE are prone to inter-observer inconsistencies and provide limited insight into the structural remodeling of the ECM. An objective approach to quantify LPF can eliminate inter-observer inconsistencies and provide novel insights into the fibrotic transformation of the lamina propria in EoE. Second harmonic generation (SHG) microscopy is a powerful modality for objectively quantifying disease associated alterations in ECM collagen structure that is finding increasing use for clinical research. We used SHG with morphometric analysis (SHG-MA) to characterize lamina propria collagen fibers and ECM porosity in esophageal biopsies collected from children with active EoE (n = 11), inactive EoE (n = 11), and non-EoE (n = 11). The collagen fiber width quantified by SHG-MA correlated positively with peak eosinophil count (r = 0.65, p < 0.005) and histopathologist scoring of LPF (r = 0.52, p < 0.005) in the esophageal biopsies. Patients with active EoE had a significant enlargement of ECM pores compared to inactive EoE and non-EoE (p < 0.005), with the mean pore area correlating positively with EoE activity (r = 0.76, p < 0.005) and LPF severity (r = 0.65, p < 0.005). These results indicate that SHG-MA can be utilized to objectively characterize and provide novel insights into lamina propria ECM structural remodeling in children with EoE, which could aid in monitoring disease progression.

Development of biomimetic co-culture and tri-culture models to mimic the complex structure of the alveolar-capillary barrier

Alveoli are the functional area of respiratory system where the gaseous exchanges take place at level of the alveolar-capillary barrier. The development of safe and effective therapeutic approaches for treating lung disease is currently limited due to the lack of realistic preclinical models for their testing and validation. In this work, tissue engineering approaches were exploited to develop a biomimetic platform that provide an appropriate mimicking of the extracellular environment and the multicellular architecture of human alveoli. Here, we propose the implementation of two biomimetic in vitro models to reproduce the features of the main anatomic portions of the physiological alveolar-capillary barrier. First, a co-culture barrier model was obtained by integrating an electrospun polycaprolactone-gelatin (PCL-Gel) membrane in a modified transwell insert (PCL-Gel TW) to mimic the alveolar basement membrane (coded as thin model). Alveolar epithelial (A549) and lung microvascular endothelial (HULEC-5a) cells were cultured on the apical and basolateral side of the PCL-Gel membrane, respectively, under physiologic air-liquid interface (ALI) conditions for 7 days. The ALI condition promoted the expression of type I and type II alveolar epithelial cell markers and the secretion of mucus in A549 cells. Increased cell viability and barrier properties in co-cultures of A549 and HULEC-5a compared to mono-cultures revealed the effectiveness of the model to reproduce in vitro physiological-relevant features of the alveolar-capillary barrier. The second portion of the alveolar-capillary barrier was developed implementing a tri-culture model (coded as thick model) including a type I collagen (COLL) hydrogel formulated to host lung fibroblasts (MRC-5). The thick barrier model was implemented by seeding HULEC-5a on the basolateral side of PCL-Gel TW and then pouring sequentially MRC-5-laden COLL hydrogel and A549 cells on the apical side of the electrospun membrane. The thick model was maintained up to 7 days at ALI and immunofluorescence staining of tight and adherent junctions demonstrated the formation of a tight barrier. Lastly, the ability of models to emulate pathological inflammatory conditions was validated by exposing the apical compartment of the PCL-Gel TW to lipopolysaccharide (LPS). The damage of A549 tight junctions, the increase of barrier permeability and IL-6 pro-inflammatory cytokine release was observed after 48 h exposure to LPS.

Echo intensity and gray-level co-occurrence matrix analysis of soft tissue grafting biomaterials and dental implants: an in vitro ultrasonographic pilot study

OBJECTIVE

To characterize different allogeneic and xenogeneic soft tissue graft substitutes and to assess their echo intensity and grayscale texture-related outcomes by using high-frequency ultrasonography (HFUS).

METHODS

Ten samples from each of the following biomaterials were scanned using HFUS: bilayered collagen matrix (CM), cross-linked collagen matrix (CCM), multilayered cross-linked collagen matrix (MCCM), human-derived acellular dermal matrix (HADM), porcine-derived acellular dermal matrix (PADM), collagen tape dressing (C) and dental implants (IMPs). The obtained images were then imported in a commercially available software for grayscale analysis. First-order grayscale outcomes included mean echo intensity (EI), standard deviation, skewness, and kurtosis, while second-order grayscale outcomes comprised entropy, contrast, correlation, energy and homogeneity derive from the gray-level co-occurrence matrix analysis. Descriptive statistics were performed for visualization of results, and one-way analysis of variance with Bonferroni post-hoc tests were performed to relative assessments of the biomaterials.

RESULTS

The statistical analysis revealed a statistically significant difference among the groups for EI (p < .001), with the group C showing the lowest EI, and the IMP group presenting with the greatest EI values. All groups showed significantly higher EI when compared with C (p < .001). No significant differences were observed for energy, and correlation, while a statistically significant difference among the groups was found in terms of entropy (p < 0.01), contrast (p < .001) and homogeneity (p < .001). IMP exhibited the highest contrast, that was significantly higher than C, HADM, PADM, CCM and CM.

CONCLUSIONS

HFUS grayscale analysis can be applied to characterize the structure of different biomaterials and holds potential for translation to in-vivo assessment following soft tissue grafting-related procedures.

In-Depth Analysis of the Pancreatic Extracellular Matrix during Development for Next-Generation Tissue Engineering

The pancreas is a complex organ consisting of differentiated cells and extracellular matrix (ECM) organized adequately to enable its endocrine and exocrine functions. Although much is known about the intrinsic factors that control pancreas development, very few studies have focused on the microenvironment surrounding pancreatic cells. This environment is composed of various cells and ECM components, which play a critical role in maintaining tissue organization and homeostasis. In this study, we applied mass spectrometry to identify and quantify the ECM composition of the developing pancreas at the embryonic (E) day 14.5 and postnatal (P) day 1 stages. Our proteomic analysis identified 160 ECM proteins that displayed a dynamic expression profile with a shift in collagens and proteoglycans. Furthermore, we used atomic force microscopy to measure the biomechanical properties and found that the pancreatic ECM was soft (≤400 Pa) with no significant change during pancreas maturation. Lastly, we optimized a decellularization protocol for P1 pancreatic tissues, incorporating a preliminary crosslinking step, which effectively preserved the 3D organization of the ECM. The resulting ECM scaffold proved suitable for recellularization studies. Our findings provide insights into the composition and biomechanics of the pancreatic embryonic and perinatal ECM, offering a foundation for future studies investigating the dynamic interactions between the ECM and pancreatic cells.

Release systems based on self-assembling RADA16-I hydrogels with a signal sequence which improves wound healing processes

Self-assembling peptides can be used for the regeneration of severely damaged skin. They can act as scaffolds for skin cells and as a reservoir of active compounds, to accelerate scarless wound healing. To overcome repeated administration of peptides which accelerate healing, we report development of three new peptide biomaterials based on the RADA16-I hydrogel functionalized with a sequence (AAPV) cleaved by human neutrophil elastase and short biologically active peptide motifs, namely GHK, KGHK and RDKVYR. The peptide hybrids were investigated for their structural aspects using circular dichroism, thioflavin T assay, transmission electron microscopy, and atomic force microscopy, as well as their rheological properties and stability in different fluids such as water or plasma, and their susceptibility to digestion by enzymes present in the wound environment. In addition, the morphology of the RADA-peptide hydrogels was examined with a unique technique called scanning electron cryomicroscopy. These experiments enabled us to verify if the designed peptides increased the bioactivity of the gel without disturbing its gelling processes. We demonstrate that the physicochemical properties of the designed hybrids were similar to those of the original RADA16-I. The materials behaved as expected, leaving the active motif free when treated with elastase. XTT and LDH tests on fibroblasts and keratinocytes were performed to assess the cytotoxicity of the RADA16-I hybrids, while the viability of cells treated with RADA16-I hybrids was evaluated in a model of human dermal fibroblasts. The hybrid peptides revealed no cytotoxicity; the cells grew and proliferated better than after treatment with RADA16-I alone. Improved wound healing following topical delivery of RADA-GHK and RADA-KGHK was demonstrated using a model of dorsal skin injury in mice and histological analyses. The presented results indicate further research is warranted into the engineered peptides as scaffolds for wound healing and tissue engineering.

Reduced Fibroblast Activation on Electrospun Polycaprolactone Scaffolds

In vivo, quiescent fibroblasts reside in three-dimensional connective tissues and are activated in response to tissue injury before proliferating rapidly and becoming migratory and contractile myofibroblasts. When deregulated, chronic activation drives fibrotic disease. Fibroblasts cultured on stiff 2D surfaces display a partially activated phenotype, whilst many 3D environments limit fibroblast activation. Cell mechanotransduction, spreading, polarity, and integrin expression are controlled by material mechanical properties and micro-architecture. Between 3D culture systems, these features are highly variable, and the challenge of controlling individual properties without altering others has led to an inconsistent picture of fibroblast behaviour. Electrospinning offers greater control of mechanical properties and microarchitecture making it a valuable model to study fibroblast activation behaviour in vitro. Here, we present a comprehensive characterisation of the activation traits of human oral fibroblasts grown on a microfibrous scaffold composed of electrospun polycaprolactone. After over 7 days in the culture, we observed a reduction in proliferation rates compared to cells cultured in 2D, with low KI67 expression and no evidence of cellular senescence. A-SMA mRNA levels fell, and the expression of ECM protein-coding genes also decreased. Electrospun fibrous scaffolds, therefore, represent a tuneable platform to investigate the mechanisms of fibroblast activation and their roles in fibrotic disease.

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.

Culturing and Imaging Glioma Stem Cells in 3D Collagen Matrices

Methods to maintain human glioma stem cells as neurosphere cultures and image their dynamic behavior in 3D collagen matrices are described. Additional approaches to monitor glioma stem cell differentiation into mesenchymal-type cells, along with example data are included. Together, these approaches enable glioma stem cell differentiation to be controlled while maintaining the cells in culture, as well as allowing cell dynamics to be captured and analyzed. These methods should be helpful for those seeking to understand the molecular mechanisms driving the invasion of glioma cells through three-dimensional environments. © 2023 Wiley Periodicals LLC. Basic Protocol 1: Culturing human glioma stem cells as neurospheres Basic Protocol 2: Inducing GSC adherence and monitoring their differentiation into mesenchymal cells Support Protocol 1: Preparing fibronectin-coated dishes for cell microscopy Basic Protocol 3: Embedding GSCs in a 3D collagen matrix to study their invasive behavior Support Protocol 2: Phase-contrast imaging with a tiled matrix to study cell migration in a 3D gel.

Deduction of signaling mechanisms from cellular responses to multiple cues

Cell signaling networks are complex and often incompletely characterized, making it difficult to obtain a comprehensive picture of the mechanisms they encode. Mathematical modeling of these networks provides important clues, but the models themselves are often complex, and it is not always clear how to extract falsifiable predictions. Here we take an inverse approach, using experimental data at the cell level to deduce the minimal signaling network. We focus on cells' response to multiple cues, specifically on the surprising case in which the response is antagonistic: the response to multiple cues is weaker than the response to the individual cues. We systematically build candidate signaling networks one node at a time, using the ubiquitous ingredients of (i) up- or down-regulation, (ii) molecular conversion, or (iii) reversible binding. In each case, our method reveals a minimal, interpretable signaling mechanism that explains the antagonistic response. Our work provides a systematic way to deduce molecular mechanisms from cell-level data.

Extracellular Matrix Stiffness in Lung Health and Disease

The extracellular matrix (ECM) provides structural support and imparts a wide variety of environmental cues to cells. In the past decade, a growing body of work revealed that the mechanical properties of the ECM, commonly known as matrix stiffness, regulate the fundamental cellular processes of the lung. There is growing appreciation that mechanical interplays between cells and associated ECM are essential to maintain lung homeostasis. Dysregulation of ECM-derived mechanical signaling via altered mechanosensing and mechanotransduction pathways is associated with many common lung diseases. Matrix stiffening is a hallmark of lung fibrosis. The stiffened ECM is not merely a sequelae of lung fibrosis but can actively drive the progression of fibrotic lung disease. In this article, we provide a comprehensive view on the role of matrix stiffness in lung health and disease. We begin by summarizing the effects of matrix stiffness on the function and behavior of various lung cell types and on regulation of biomolecule activity and key physiological processes, including host immune response and cellular metabolism. We discuss the potential mechanisms by which cells probe matrix stiffness and convert mechanical signals to regulate gene expression. We highlight the factors that govern matrix stiffness and outline the role of matrix stiffness in lung development and the pathogenesis of pulmonary fibrosis, pulmonary hypertension, asthma, chronic obstructive pulmonary disease (COPD), and lung cancer. We envision targeting of deleterious matrix mechanical cues for treatment of fibrotic lung disease. Advances in technologies for matrix stiffness measurements and design of stiffness-tunable matrix substrates are also explored. © 2022 American Physiological Society. Compr Physiol 12:3523-3558, 2022.

Variation in Hydrogel Formation and Network Structure for Telo-, Atelo- and Methacrylated Collagens

As the most abundant protein in the extracellular matrix, collagen has become widely studied in the fields of tissue engineering and regenerative medicine. Of the various collagen types, collagen type I is the most commonly utilised in laboratory studies. In tissues, collagen type I forms into fibrils that provide an extended fibrillar network. In tissue engineering and regenerative medicine, little emphasis has been placed on the nature of the network that is formed. Various factors could affect the network structure, including the method used to extract collagen from native tissue, since this may remove the telopeptides, and the nature and extent of any chemical modifications and crosslinking moieties. The structure of any fibril network affects cellular proliferation and differentiation, as well as the overall modulus of hydrogels. In this study, the network-forming properties of two distinct forms of collagen (telo- and atelo-collagen) and their methacrylated derivatives were compared. The presence of the telopeptides facilitated fibril formation in the unmodified samples, but this benefit was substantially reduced by subsequent methacrylation, leading to a loss in the native self-assembly potential. Furthermore, the impact of the methacrylation of the collagen, which enables rapid crosslinking and makes it suitable for use in 3D printing, was investigated. The crosslinking of the methacrylated samples (both telo- and atelo-) was seen to improve the fibril-like network compared to the non-crosslinked samples. This contrasted with the samples of methacrylated gelatin, which showed little, if any, fibrillar or ordered network structure, regardless of whether they were crosslinked.

Construction of in vitro 3-D model for lung cancer-cell metastasis study

Background

Cancer metastasis is the main cause of mortality in cancer patients. However, the drugs targeting metastasis processes are still lacking, which is partially due to the short of effective in vitro model for cell invasion studies. The traditional 2-D culture method cannot reveal the interaction between cells and the surrounding extracellular matrix during invasion process, while the animal models usually are too complex to explain mechanisms in detail. Therefore, a precise and efficient 3-D in vitro model is highly desirable for cell invasion studies and drug screening tests.

Methods

Precise micro-fabrication techniques are developed and integrated with soft hydrogels for constructing of 3-D lung-cancer micro-environment, mimicking the pulmonary gland or alveoli as in vivo.

Results

A 3-D in vitro model for cancer cell culture and metastasis studies is developed with advanced micro-fabrication technique, combining microfluidic system with soft hydrogel. The constructed microfluidic platform can provide nutrition and bio-chemical factors in a continuous transportation mode and has the potential to form stable chemical gradient for cancer invasion research. Hundreds of micro-chamber arrays are constructed within the collagen gel, ensuring that all surrounding substrates for tumor cells are composed of natural collagen hydrogel, like the in vivo micro-environment. The 3-D in vitro model can also provide a fully transparent platform for the visual observation of the cell morphology, proliferation, invasion, cell-assembly, and even the protein expression by immune-fluorescent tests if needed.

The lung-cancer cells A549 and normal lung epithelial cells (HPAEpiCs) have been seeded into the 3-D system. It is found out that cells can normally proliferate in the microwells for a long period. Moreover, although the cancer cells A549 and alveolar epithelial cells HPAEpiCs have the similar morphology on 2-D solid substrate, in the 3-D system the cancer cells A549 distributed sparsely as single round cells on the extracellular matrix (ECM) when they attached to the substrate, while the normal lung epithelial cells can form cell aggregates, like the structure of normal tissue. Importantly, cancer cells cultured in the 3-D in vitro model can exhibit the interaction between cells and extracellular matrix. As shown in the confocal microscope images, the A549 cells present round and isolated morphology without much invasion into ECM, while starting from around Day 5, cells changed their shape to be spindle-like, as in mesenchymal morphology, and then started to destroy the surrounding ECM and invade out of the micro-chambers.

Conclusions

A 3-D in vitro model is constructed for cancer cell invasion studies, combining the microfluidic system and micro-chamber structures within hydrogel. To show the invasion process of lung cancer cells, the cell morphology, proliferation, and invasion process are all analyzed. The results confirmed that the micro-environment in the 3-D model is vital for revealing the lung cancer cell invasion as in vivo.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-022-09546-9.

Synergistic performance of collagen-g-chitosan-glucan fiber biohybrid scaffold with tunable properties

Hybrid biocomposite scaffolds (HBS) that serve as a carrier for cell proliferation and differentiation are increasingly used for tissue regeneration. 3D hybrid scaffold based on collagen-grafted-chitosan-glucan fiber (CO-g-CGF-HBS) was prepared by freeze-drying technique. The swelling percentage, hydrolytic stability, and modulus of elasticity of HBS were enhanced after the chemical modification of CO with CGF. Pore size and porosity of HBS were decreased with an increased CGF ratio. HBS exhibits a higher reduction rate against different types of bacteria compared with a control sample. Thus, chemical modification of CO with different ratios of CGF significantly improved the physicochemical, antibacterial properties of HBS.

The biophysics of cancer: emerging insights from micro- and nanoscale tools

Cancer is a complex and dynamic disease that is aberrant both biologically and physically. There is growing appreciation that physical abnormalities with both cancer cells and their microenvironment that span multiple length scales are important drivers for cancer growth and metastasis. The scope of this review is to highlight the key advancements in micro- and nano-scale tools for delineating the cause and consequences of the aberrant physical properties of tumors. We focus our review on three important physical aspects of cancer: 1) solid mechanical properties, 2) fluid mechanical properties, and 3) mechanical alterations to cancer cells. Beyond posing physical barriers to the delivery of cancer therapeutics, these properties are also known to influence numerous biological processes, including cancer cell invasion and migration leading to metastasis, and response and resistance to therapy. We comment on how micro- and nanoscale tools have transformed our fundamental understanding of the physical dynamics of cancer progression and their potential for bridging towards future applications at the interface of oncology and physical sciences.

From local to global matrix organization by fibroblasts: a 4D laser-assisted bioprinting approach

Fibroblasts and myofibroblasts play a central role in skin homeostasis through dermal organization and maintenance. Nonetheless, the dynamic interactions between (myo)fibroblasts and the extracellular matrix (ECM) remain poorly exploited in skin repair strategies. Indeed, there is still an unmet need for soft tissue models allowing to study the spatial-temporal remodeling properties of (myo)fibroblasts. In vivo, wound healing studies in animals are limited by species specificity. In vitro, most models rely on collagen gels reorganized by randomly distributed fibroblasts. But biofabrication technologies have significantly evolved over the past ten years. High-resolution bioprinting now allows to investigate various cellular micropatterns and the emergent tissue organizations over time. In order to harness the full dynamic properties of cells and active biomaterials, it is essential to consider "time" as the 4th dimension in soft tissue design. Following this 4D bioprinting approach, we aimed to develop a novel model that could replicate fibroblast dynamic remodeling in vitro. For this purpose, (myo)fibroblasts were patterned on collagen gels with laser-assisted bioprinting (LAB) to study the generated matrix deformations and reorganizations. First, distinct populations, mainly composed of fibroblasts or myofibroblasts, were established in vitro to account for the variety of fibroblastic remodeling properties. Then, LAB was used to organize both populations on collagen gels in even isotropic patterns with high resolution, high density and high viability. With maturation, bioprinted patterns of fibroblasts and myofibroblasts reorganized into dispersed or aggregated cells, respectively. Stress-release contraction assays revealed that these phenotype-specific pattern maturations were associated with distinct lattice tension states. The two populations were then patterned in anisotropic rows in order to direct the cell-generated deformations and to orient global matrix remodeling. Only maturation of anisotropic fibroblast patterns, but not myofibroblasts, resulted in collagen anisotropic reorganizations both at tissue-scale, with lattice contraction, and at microscale, with embedded microbead displacements. Following a 4D bioprinting approach, LAB patterning enabled to elicit and orient the dynamic matrix remodeling mechanisms of distinct fibroblastic populations and organizations on collagen. For future studies, this method provides a new versatile tool to investigate in vitro dermal organizations and properties, processes of remodeling in healing, and new treatment opportunities.

Collagen- and hyaluronic acid-based hydrogels and their biomedical applications

Hydrogels have been widely investigated in biomedical fields due to their similar physical and biochemical properties to the extracellular matrix (ECM). Collagen and hyaluronic acid (HA) are the main components of the ECM in many tissues. As a result, hydrogels prepared from collagen and HA hold inherent advantages in mimicking the structure and function of the native ECM. Numerous studies have focused on the development of collagen and HA hydrogels and their biomedical applications. In this extensive review, we provide a summary and analysis of the sources, features, and modifications of collagen and HA. Specifically, we highlight the fabrication, properties, and potential biomedical applications as well as promising commercialization of hydrogels based on these two natural polymers.

A Synthetic Hydrogel, VitroGel® ORGANOID-3, Improves Immune Cell-Epithelial Interactions in a Tissue Chip Co-Culture Model of Human Gastric Organoids and Dendritic Cells

Immunosurveillance of the gastrointestinal epithelium by mononuclear phagocytes (MNPs) is essential for maintaining gut health. However, studying the complex interplay between the human gastrointestinal epithelium and MNPs such as dendritic cells (DCs) is difficult, since traditional cell culture systems lack complexity, and animal models may not adequately represent human tissues. Microphysiological systems, or tissue chips, are an attractive alternative for these investigations, because they model functional features of specific tissues or organs using microscale culture platforms that recreate physiological tissue microenvironments. However, successful integration of multiple of tissue types on a tissue chip platform to reproduce physiological cell-cell interactions remains a challenge. We previously developed a tissue chip system, the gut organoid flow chip (GOFlowChip), for long term culture of 3-D pluripotent stem cell-derived human intestinal organoids. Here, we optimized the GOFlowChip platform to build a complex microphysiological immune-cell-epithelial cell co-culture model in order to study DC-epithelial interactions in human stomach. We first tested different tubing materials and chip configurations to optimize DC loading onto the GOFlowChip and demonstrated that DC culture on the GOFlowChip for up to 20 h did not impact DC activation status or viability. However, Transwell chemotaxis assays and live confocal imaging revealed that Matrigel, the extracellular matrix (ECM) material commonly used for organoid culture, prevented DC migration towards the organoids and the establishment of direct MNP-epithelial contacts. Therefore, we next evaluated DC chemotaxis through alternative ECM materials including Matrigel-collagen mixtures and synthetic hydrogels. A polysaccharide-based synthetic hydrogel, VitroGel®-ORGANOID-3 (V-ORG-3), enabled significantly increased DC chemotaxis through the matrix, supported organoid survival and growth, and did not significantly alter DC activation or viability. On the GOFlowChip, DCs that were flowed into the chip migrated rapidly through the V-ORG matrix and reached organoids embedded deep within the chip, with increased interactions between DCs and gastric organoids. The successful integration of DCs and V-ORG-3 embedded gastric organoids into the GOFlowChip platform now permits real-time imaging of MNP-epithelial interactions and other investigations of the complex interplay between gastrointestinal MNPs and epithelial cells in their response to pathogens, candidate drugs and mucosal vaccines.

The vascular niche in next generation microphysiological systems

In recent years, microphysiological system (MPS, also known as, organ-on-a-chip or tissue chip) platforms have emerged with great promise to improve the predictive capacity of preclinical modeling thereby reducing the high attrition rates when drugs move into trials. While their designs can vary quite significantly, in general MPS are bioengineered in vitro microenvironments that recapitulate key functional units of human organs, and that have broad applications in human physiology, pathophysiology, and clinical pharmacology. A critical next step in the evolution of MPS devices is the widespread incorporation of functional vasculature within tissues. The vasculature itself is a major organ that carries nutrients, immune cells, signaling molecules and therapeutics to all other organs. It also plays critical roles in inducing and maintaining tissue identity through expression of angiocrine factors, and in providing tissue-specific milieus (i.e., the vascular niche) that can support the survival and function of stem cells. Thus, organs are patterned, maintained and supported by the vasculature, which in turn receives signals that drive tissue specific gene expression. In this review, we will discuss published vascularized MPS platforms and present considerations for next-generation devices looking to incorporate this critical constituent. Finally, we will highlight the organ-patterning processes governed by the vasculature, and how the incorporation of a vascular niche within MPS platforms will establish a unique opportunity to study stem cell development.

Collagen Bioinks for Bioprinting: A Systematic Review of Hydrogel Properties, Bioprinting Parameters, Protocols, and Bioprinted Structure Characteristics

Bioprinting is a modern tool suitable for creating cell scaffolds and tissue or organ carriers from polymers that mimic tissue properties and create a natural environment for cell development. A wide range of polymers, both natural and synthetic, are used, including extracellular matrix and collagen-based polymers. Bioprinting technologies, based on syringe deposition or laser technologies, are optimal tools for creating precise constructs precisely from the combination of collagen hydrogel and cells. This review describes the different stages of bioprinting, from the extraction of collagen hydrogels and bioink preparation, over the parameters of the printing itself, to the final testing of the constructs. This study mainly focuses on the use of physically crosslinked high-concentrated collagen hydrogels, which represents the optimal way to create a biocompatible 3D construct with sufficient stiffness. The cell viability in these gels is mainly influenced by the composition of the bioink and the parameters of the bioprinting process itself (temperature, pressure, cell density, etc.). In addition, a detailed table is included that lists the bioprinting parameters and composition of custom bioinks from current studies focusing on printing collagen gels without the addition of other polymers. Last but not least, our work also tries to refute the often-mentioned fact that highly concentrated collagen hydrogel is not suitable for 3D bioprinting and cell growth and development.

Understanding Fibroblast Behavior in 3D Biomaterials

Traditional monolayer culture fails to fully recapitulate the in vivo environment of connective tissue cells such as the fibroblast. When cultured on stiff two-dimensional (2D) plastic, fibroblasts become highly proliferative forming broad lamellipodia and stress fibers. Conversely, in different three-dimensional (3D) culture systems, fibroblasts have displayed a diverse array of features; from an "activated" phenotype like that observed in 2D cultures and by myofibroblasts, to a quiescent state that likely better represents in vivo fibroblasts at rest. Today, a plethora of microfabrication techniques have made 3D culture commonplace, for both tissue engineering purposes and in the study of basic biological interactions. However, establishing the in vivo mimetic credentials of different biomimetic materials is not always straightforward, particularly in the context of fibroblast responses. Fibroblast behavior is governed by the complex interplay of biological features such as integrin binding sites, material mechanical properties that influence cellular mechanotransduction, and microarchitectural features like pore and fiber size, as well as chemical cues. Furthermore, fibroblasts are a heterogeneous group of cells with specific phenotypic traits dependent on their tissue of origin. These features have made understanding the influence of biomaterials on fibroblast behavior a challenging task. In this study, we present a review of the strategies used to investigate fibroblast behavior with a focus on the material properties that influence fibroblast activation, a process that becomes pathological in fibrotic diseases and certain cancers.

3D stem cell-laden artificial endometrium: successful endometrial regeneration and pregnancy

Thin endometrium lining or severe endometrial injury which may occur during artificial abortion can cause defective endometrial receptivity and subsequent infertility. Therefore, much effort has been devoted toward regenerating thin or damaged endometrial lining by applying multiple types of stem cells. Even though there are some positive preliminary outcomes, repairing the injured endometrium with stem cells is considerably challenging, due to the lack of an adequate microenvironment for the administrated stem cells within the tissues and subsequent poor therapeutic efficiency. In this context, as an alternative, we fabricated a 3D stem cell-laden artificial endometrium by incorporating several biodegradable biomaterials (collagen and hyaluronic acid) and multiple cellular components of endometrium (endometrial stem cells, stromal cells, and vessel cells) to properly recapitulate the multicellular microenvironment and multilayered structure. Agarose was used as an inert filler substrate to enhance the mechanical integrity of the three-layered artificial endometrium. Various mechanical characteristics, such as morphology, compression properties, swelling, and viscosity, have been evaluated. Various biological features, such as steroid hormone responsiveness, specific endometrial cell-surface marker expressions, and the secretion of multiple growth factors and steroid hormones, as well as the viability of encapsulated endometrial cells are relatively well maintained within the artificial endometrium. More importantly, severe tissue injuries were significantly relieved by transplanting our 3D artificial endometrium into endometrial ablation mice. Remarkably, artificial endometrium transplantation resulted in a successful pregnancy with subsequent live birth without any morphological or chromosomal abnormalities.

Shear dynamics of confined membranes

We model the nonlinear response of a lubricated contact composed of a two-dimensional lipid membrane immersed in a simple fluid between two parallel flat and porous walls under shear. The nonlinear dynamics of the membrane gives rise to a rich dynamical behavior depending on the shear velocity. In quiescent conditions (i.e., absence of shear), the membrane freezes into a disordered labyrinthine wrinkle pattern. We determine the wavelength of this pattern as a function of the excess area of the membrane for a fairly general form of the confinement potential using a sine-profile ansatz for the wrinkles. In the presence of shear, we find four different regimes depending on the shear rate. Regime I. For small shear, the labyrinthine pattern is still frozen, but exhibits a small drift which is mainly along the shear direction. In this regime, the tangential forces on the walls due to the presence of the membrane increase linearly with the shear rate. Regime II. When the shear rate is increased above a critical value, the membrane rearranges, and wrinkles start to align along the shear direction. This regime is accompanied by a sharp drop of the tangential forces on the wall. The membrane usually reaches a steady-state configuration drifting with a small constant velocity at long times. However, we also rarely observe oscillatory dynamics in this regime. Regime III. For larger shear rates, the wrinkles align strongly along the shear direction, with a set of dislocation defects which assemble in pairs. The tangential forces are then controlled by the number of dislocations, and by the number of wrinkles between the two dislocations within each dislocation pairs. In this dislocation-dominated regime, the tangential forces in the transverse direction most often exceed those in the shear direction. Regime IV. For even larger shear, the membrane organizes into a perfect array of parallel stripes with no defects. The wavelength of the wrinkles is still identical to the wavelength in the absence of shear. In this final regime, the tangential forces due to the membrane vanish. These behaviors give rise to a non-linear rheological behavior of lubricated contacts containing membranes.

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.

A new 3D finite element-based approach for computing cell surface tractions assuming nonlinear conditions

Advances in methods for determining the forces exerted by cells while they migrate are essential for attempting to understand important pathological processes, such as cancer or angiogenesis, among others. Precise data from three-dimensional conditions are both difficult to obtain and manipulate. For this purpose, it is critical to develop workflows in which the experiments are closely linked to the subsequent computational postprocessing. The work presented here starts from a traction force microscopy (TFM) experiment carried out on microfluidic chips, and this experiment is automatically joined to an inverse problem solver that allows us to extract the traction forces exerted by the cell from the displacements of fluorescent beads embedded in the extracellular matrix (ECM). Therefore, both the reconstruction of the cell geometry and the recovery of the ECM displacements are used to generate the inputs for the resolution of the inverse problem. The inverse problem is solved iteratively by using the finite element method under the hypothesis of finite deformations and nonlinear material formulation. Finally, after mathematical postprocessing is performed, the traction forces on the surface of the cell in the undeformed configuration are obtained. Therefore, in this work, we demonstrate the robustness of our computational-based methodology by testing it under different conditions in an extreme theoretical load problem and then by applying it to a real case based on experimental results. In summary, we have developed a new procedure that adds value to existing methodologies for solving inverse problems in 3D, mainly by allowing for large deformations and not being restricted to any particular material formulation. In addition, it automatically bridges the gap between experimental images and mechanical computations.

Design and construction of a novel measurement device for mechanical characterization of hydrogels: A case study

Natural biopolymer-based hydrogels especially agarose and collagen gels, considering their biocompatibility with cells and their capacity to mimic biological tissues, have widely been used for in-vitro experiments and tissue engineering applications in recent years; nevertheless their mechanical properties are not always optimal for these purposes. Regarding the importance of the mechanical properties of hydrogels, many mechanical characterization studies have been carried out for such biopolymers. In this work, we have focused on understanding the mechanical role of agarose and collagen concentration on the hydrogel strength and elastic behavior. In this direction, Amirkabir Magnetic Bead Rheometry (AMBR) characterization device equipped with an optimized electromagnet, was designed and constructed for the measurement of hydrogel mechanical properties. The operation of AMBR set-up is based on applying a magnetic field to actuate magnetic beads in contact with the gel surface in order to actuate the gel itself. In simple terms the magnetic beads leads give rise to mechanical shear stress on the gel surface when under magnetic influence and together with the associated bead-gel displacement it is possible to calculate the hydrogel shear modulus. Agarose and Collagen gels with respectively 0.2-0.6 wt % and 0.2-0.5 wt % percent concentrations were prepared for mechanical characterization in terms of their shear modulus. The shear modulus values for the different percent concentrations of the agarose gel were obtained in the range 250-650 Pa, indicating the shear modulus increases by increasing in the agar gel concentration. In addition to this, the values of shear modulus for the collagen gel increase as function of concentration in the range 240-520 Pa in accordance with an approximately linear relationship between collagen concentration and gel strength.

Collagen/kerateine multi-protein hydrogels as a thermally stable extracellular matrix for 3D in vitro models

Objective: To determine whether the addition of kerateine (reduced keratin) in rat tail collagen type I hydrogels increases thermal stability and changes material properties and supports cell growth for use in cellular hyperthermia studies for tumor treatment.Methods: Collagen type I extracted from rat tail tendon was combined with kerateine extracted from human hair fibers. Thermal, mechanical, and biocompatibility properties and cell behavior was assessed and compared to 100% collagen type I hydrogels to demonstrate their utility as a tissue model for 3D in vitro testing.Results: A combination (i.e., containing both collagen 'C/KNT') hydrogel was more thermally stable than pure collagen hydrogels and resisted thermal degradation when incubated at a hyperthermic temperature of 47°C for heating durations up to 60 min with a higher melting temperature measured by DSC. An increase in the storage modulus was only observed with an increased collagen concentration rather than an increased KTN concentration; however, a change in ECM structure was observed with greater fiber alignment and width with an increase in KTN concentration. The C/KTN hydrogels, specifically 50/50 C/KTN hydrogels, also supported the growth and of fibroblasts and MDA-MB-231 breast cancer cells similar to those seeded in 100% collagen hydrogels.Conclusion: This multi-protein C/KTN hydrogel shows promise for future studies involving thermal stress studies without compromising the 3D ECM environment or cell growth.

Surface Engineering of Cardiovascular Devices for Improved Hemocompatibility and Rapid Endothelialization

Cardiovascular devices have been widely applied in the clinical treatment of cardiovascular diseases. However, poor hemocompatibility and slow endothelialization on their surface still exist. Numerous surface engineering strategies have mainly sought to modify the device surface through physical, chemical, and biological approaches to improve surface hemocompatibility and endothelialization. The alteration of physical characteristics and pattern topographies brings some hopeful outcomes and plays a notable role in this respect. The chemical and biological approaches can provide potential signs of success in the endothelialization of vascular device surfaces. They usually involve therapeutic drugs, specific peptides, adhesive proteins, antibodies, growth factors and nitric oxide (NO) donors. The gene engineering can enhance the proliferation, growth, and migration of vascular cells, thus boosting the endothelialization. In this review, the surface engineering strategies are highlighted and summarized to improve hemocompatibility and rapid endothelialization on the cardiovascular devices. The potential outlook is also briefly discussed to help guide endothelialization strategies and inspire further innovations. It is hoped that this review can assist with the surface engineering of cardiovascular devices and promote future advancements in this emerging research field.

Migration of endothelial cells and mesenchymal stem cells into hyaluronic acid hydrogels with different moduli under induction of pro-inflammatory macrophages

The design of hyaluronic acid (HA)-based and stimuli-responsive hydrogels to elicit highly controlled and tunable cell response and behaviors is a major field of interest in tissue engineering and regenerative medicine. The pH-responsive hydrogel can respond to pH variation during wound healing, which may in turn regulate the tissue regeneration process. In this study, a double-network hydrogel cross-linked with vinyl double bonds and Schiff base was prepared, whose properties were further adjusted by incubation in pH 7.4 and pH 5 buffers. The endothelial cells (ECs) migrated much deeper into the softer HA hydrogel pre-treated with pH 5 buffer than the stiffer hydrogel. By contrast, the mesenchymal stem cells (MSCs) migrated easily into the stiffer hydrogel. The ECs highly expressed RhoA and non-muscle myosin (NM) II genes in the softer hydrogel, which may facilitate amoeboid migration. Meanwhile, the MSCs were stiffer than the ECs, and highly expressed Rac1, RhoA, vinculin, NM II, hyaluronidase (HYAL) 2 and CD44 genes in the stiffer hydrogel, which facilitate mesenchymal migration. These results provide important clues for revealing the different migration strategies of the ECs and MSCs in HA hydrogels with different stiffness, and suggest that the mechanical properties and the network structure of hydrogels play an important role in regulating the three-dimensional migration process of these cells.

Characterization of Hen's Egg White To Use It as a Novel Platform To Culture Three-Dimensional Multicellular Tumor Spheroids

We are standardizing protocols to develop egg white (EW) as a cost-effective platform for culture of three-dimensional (3-D) multicellular tumor spheroids for application in understanding tumor microenvironments and drug screening. In this article, we describe several physical and physiological characteristics of EW to use it as 3-D cell culture platform. Field emission scanning electron microscopy revealed the presence of different microstructures. Hydrodynamic size distribution data indicated nano- and micron-sized particles. Rheological measurements revealed the viscosity and viscoelastic behavior appropriate for maintaining cell viability and supporting 3-D cell growth under high-sheer conditions. It was found that thereis no autofluorescence, a requirement for imparting transparency and for microscopic observations of the spheroids. The EW facilitated the development of 3-D tumor spheroids, with an emphasis of difference in cell proliferation and intercellular cytoskeletal organization between two-dimensional and 3-D spheroid cultures. Put together, EW proves to be a cost-affordable and simple platform for 3-D culture of tumor spheroids.

Environmentally controlled magnetic nano-tweezer for living cells and extracellular matrices

The magnetic tweezer technique has become a versatile tool for unfolding or folding of individual molecules, mainly DNA. In addition to single molecule analysis, the magnetic tweezer can be used to analyze the mechanical properties of cells and extracellular matrices. We have established a magnetic tweezer that is capable of measuring the linear and non-linear viscoelastic behavior of a wide range of soft matter in precisely controlled environmental conditions, such as temperature, CO₂ and humidity. The magnetic tweezer presented in this study is suitable to detect specific differences in the mechanical properties of different cell lines, such as human breast cancer cells and mouse embryonic fibroblasts, as well as collagen matrices of distinct concentrations in the presence and absence of fibronectin crosslinks. The precise calibration and control mechanism employed in the presented magnetic tweezer setup provides the ability to apply physiological force up to 5 nN on 4.5 µm superparamagnetic beads coated with fibronectin and coupled to the cells or collagen matrices. These measurements reveal specific local linear and non-linear viscoelastic behavior of the investigated samples. The viscoelastic response of cells and collagen matrices to the force application is best described by a weak power law behavior. Our results demonstrate that the stress stiffening response and the fluidization of cells is cell type specific and varies largely between differently invasive and aggressive cancer cells. Finally, we showed that the viscoelastic behavior of collagen matrices with and without fibronectin crosslinks measured by the magnetic tweezer can be related to the microstructure of these matrices.

Collagen, stiffness, and adhesion: the evolutionary basis of vertebrate mechanobiology

The emergence of collagen I in vertebrates resulted in a dramatic increase in the stiffness of the extracellular environment, supporting long-range force propagation and the development of low-compliant tissues necessary for the development of vertebrate traits including pressurized circulation and renal filtration. Vertebrates have also evolved integrins that can bind to collagens, resulting in the generation of higher tension and more efficient force transmission in the extracellular matrix. The stiffer environment provides an opportunity for the vertebrates to create new structures such as the stress fibers, new cell types such as endothelial cells, new developmental processes such as neural crest delamination, and new tissue organizations such as the blood-brain barrier. Molecular players found only in vertebrates allow the modification of conserved mechanisms as well as the design of novel strategies that can better serve the physiological needs of the vertebrates. These innovations collectively contribute to novel morphogenetic behaviors and unprecedented increases in the complexities of tissue mechanics and functions.

Using Acoustic Fields to Fabricate ECM-Based Biomaterials for Regenerative Medicine Applications

Ultrasound is emerging as a promising tool for both characterizing and fabricating engineered biomaterials. Ultrasound-based technologies offer a diverse toolbox with outstanding capacity for optimization and customization within a variety of therapeutic contexts, including improved extracellular matrix-based materials for regenerative medicine applications. Non-invasive ultrasound fabrication tools include the use of thermal and mechanical effects of acoustic waves to modify the structure and function of extracellular matrix scaffolds both directly, and indirectly via biochemical and cellular mediators. Materials derived from components of native extracellular matrix are an essential component of engineered biomaterials designed to stimulate cell and tissue functions and repair or replace injured tissues. Thus, continued investigations into biological and acoustic mechanisms by which ultrasound can be used to manipulate extracellular matrix components within three-dimensional hydrogels hold much potential to enable the production of improved biomaterials for clinical and research applications.

Actomyosin-dependent invasion of endothelial sprouts in collagen

During sprouting angiogenesis-the growth of blood vessels from the existing vasculature-endothelial cells (ECs) adopt an elongated invasive form and exert forces at cell-cell and cell-matrix interaction sites. These cell shape changes and cellular tractions require extensive reorganizations of the actomyosin network. However, the respective roles of actin and myosin for endothelial sprouting are not fully elucidated. In this study, we further investigate these roles by treating 2D-migrating and 3D-sprouting ECs with chemical compounds targeting either myosin or actin. These treatments affected the endothelial cytoskeleton drastically and reduced the invasive response in a compound-specific manner; pointing toward a tight control of the actin and myosin activity during sprouting. Clusters in the data further illustrate that endothelial sprout morphology is sensitive to the in vitro model mechanical microenvironment and directs future research toward mechanical substrate guidance as a strategy for promoting engineered tissue vascularization. In summary, our results add to a growing corpus of research highlighting a key role of the cytoskeleton for sprouting angiogenesis.

An engineered three-dimensional stem cell niche in the inner ear by applying a nanofibrillar cellulose hydrogel with a sustained-release neurotrophic factor delivery system

Although the application of human embryonic stem cells (hESCs) in stem cell-replacement therapy remains promising, its potential is hindered by a low cell survival rate in post-transplantation within the inner ear. Here, we aim to enhance the in vitro and in vivo survival rate and neuronal differentiation of otic neuronal progenitors (ONPs) by generating an artificial stem cell niche consisting of three-dimensional (3D) hESC-derived ONP spheroids with a nanofibrillar cellulose hydrogel and a sustained-release brain-derivative neurotrophic factor delivery system. Our results demonstrated that the transplanted hESC-derived ONP spheroids survived and neuronally differentiated into otic neuronal lineages in vitro and in vivo and also extended neurites toward the bony wall of the cochlea 90 days after the transplantation without the use of immunosuppressant medication. Our data in vitro and in vivo presented here provide sufficient evidence that we have established a robust, reproducible protocol for in vivo transplantation of hESC-derived ONPs to the inner ear. Using our protocol to create an artificial stem cell niche in the inner ear, it is now possible to work on integrating transplanted hESC-derived ONPs further and also to work toward achieving functional auditory neurons generated from hESCs. Our findings suggest that the provision of an artificial stem cell niche can be a future approach to stem cell-replacement therapy for inner-ear regeneration. STATEMENT OF SIGNIFICANCE: Inner ear regeneration utilizing human embryonic stem cell-derived otic neuronal progenitors (hESC-derived ONPs) has remarkable potential for treating sensorineural hearing loss. However, the local environment of the inner ear requires a suitable stem cell niche to allow hESC-derived ONP engraftment as well as neuronal differentiation. To overcome this obstacle, we utilized three-dimensional spheroid formation (direct contact), nanofibrillar cellulose hydrogel (extracellular matrix), and a neurotrophic factor delivery system to artificially create a stem cell niche in vitro and in vivo. Our in vitro and in vivo data presented here provide sufficient evidence that we have established a robust, reproducible protocol for in vivo transplantation of hESC-derived ONPs to the inner ear.

Environmental Restrictions: A New Concept Governing HIV-1 Spread Emerging from Integrated Experimental-Computational Analysis of Tissue-Like 3D Cultures

HIV-1 can use cell-free and cell-associated transmission modes to infect new target cells, but how the virus spreads in the infected host remains to be determined. We recently established 3D collagen cultures to study HIV-1 spread in tissue-like environments and applied iterative cycles of experimentation and computation to develop a first in silico model to describe the dynamics of HIV-1 spread in complex tissue. These analyses (i) revealed that 3D collagen environments restrict cell-free HIV-1 infection but promote cell-associated virus transmission and (ii) defined that cell densities in tissue dictate the efficacy of these transmission modes for virus spread. In this review, we discuss, in the context of the current literature, the implications of this study for our understanding of HIV-1 spread in vivo, which aspects of in vivo physiology this integrated experimental-computational analysis takes into account, and how it can be further improved experimentally and in silico.

Collagen Fibril Density Modulates Macrophage Activation and Cellular Functions during Tissue Repair

Monocytes circulate in the bloodstream, extravasate into the tissue and differentiate into specific macrophage phenotypes to fulfill the immunological needs of tissues. During the tissue repair process, tissue density transits from loose to dense tissue. However, little is known on how changes in tissue density affects macrophage activation and their cellular functions. In this work, monocytic cell line THP-1 cells were embedded in three-dimensional (3D) collagen matrices with different fibril density and were then differentiated into uncommitted macrophages (MPMA) using phorbol-12-myristate-13-acetate (PMA). MPMA macrophages were subsequently activated into pro-inflammatory macrophages (MLPS/IFNγ) and anti-inflammatory macrophages (MIL-4/IL-13) using lipopolysaccharide and interferon-gamma (IFNγ), and interleukin 4 (IL-4) and IL-13, respectively. Although analysis of cell surface markers, on both gene and protein levels, was inconclusive, cytokine secretion profiles, however, demonstrated differences in macrophage phenotype. In the presence of differentiation activators, MLPS/IFNγ secreted high amounts of IL-1β and tumor necrosis factor alpha (TNFα), while M0PMA secreted similar cytokines to MIL-4/IL-13, but low IL-8. After removing the activators and further culture for 3 days in fresh cell culture media, the secretion of IL-6 was found in high concentrations by MIL-4/IL-13, followed by MLPS/IFNγ and MPMA. Interestingly, the secretion of cytokines is enhanced with an increase of fibril density. Through the investigation of macrophage-associated functions during tissue repair, we demonstrated that M1LPS/IFNγ has the potential to enhance monocyte infiltration into tissue, while MIL-4/IL-13 supported fibroblast differentiation into myofibroblasts via transforming growth factor beta 1 (TGF-β1) in dependence of fibril density, suggesting a M2a-like phenotype. Overall, our results suggest that collagen fibril density can modulate macrophage response to favor tissue functions. Understanding of immune response in such complex 3D microenvironments will contribute to the novel therapeutic strategies for improving tissue repair, as well as guidance of the design of immune-modulated materials.

Self-Organization of Fibroblast-Laden 3D Collagen Microstructures from Inkjet-Printed Cell Patterns

One of the major challenges encountered in engineering complex tissues in vitro is to increase levels of complexity at the micron scale in 3D structures. Here, a strategy to create self-organized 3D collagen microstructures by 2D micropatterning of fibroblasts is developed. Drop-on-demand inkjet printing is used to pattern fibroblast cells on a collagen substrate in pre-designed patterns and with controlled density. It is found that cell-to-ECM interaction promotes cellular self-organization of 3D microstructures on collagen hydrogel, whereas the formation of 3D microstructure is inhibited by disruption of actin polymerization. Using this phenomena, the controlled sizes and morphologies of the 3D collagen microstructures is demonstrated by manipulating the designs of cell patterns and the density of cells. Finally, this technique is applied to build a human skin model with papillary microstructures at the dermo-epidermal junction. This approach to create 3D cell-laden collagen microstructures by cell patterning provides a simple and powerful way to mimic the structures and functions of complex tissues and organs, and can make a contribution to reduce the gap between the human body and in vitro tissue models.

Fast quantitative time lapse displacement imaging of endothelial cell invasion

In order to unravel rapid mechano-chemical feedback mechanisms in sprouting angiogenesis, we combine selective plane illumination microscopy (SPIM) and tailored image registration algorithms - further referred to as SPIM-based displacement microscopy - with an in vitro model of angiogenesis. SPIM successfully tackles the problem of imaging large volumes while upholding the spatial resolution required for the analysis of matrix displacements at a subcellular level. Applied to in vitro angiogenic sprouts, this unique methodological combination relates subcellular activity - minute to second time scale growing and retracting of protrusions - of a multicellular systems to the surrounding matrix deformations with an exceptional temporal resolution of 1 minute for a stack with multiple sprouts simultaneously or every 4 seconds for a single sprout, which is 20 times faster than with a conventional confocal setup. Our study reveals collective but non-synchronised, non-continuous activity of adjacent sprouting cells along with correlations between matrix deformations and protrusion dynamics.

Colloidal crystals of compliant microgel beads to study cell migration and mechanosensitivity in 3D

Tissues are defined not only by their biochemical composition, but also by their distinct mechanical properties. It is now widely accepted that cells sense their mechanical environment and respond to it. However, studying the effects of mechanics in in vitro 3D environments is challenging since current 3D hydrogel assays convolve mechanics with gel porosity and adhesion. Here, we present novel colloidal crystals as modular 3D scaffolds where these parameters are principally decoupled by using monodisperse, protein-coated PAAm microgel beads as building blocks, so that variable stiffness regions can be achieved within one 3D colloidal crystal. Characterization of the colloidal crystal and oxygen diffusion simulations suggested the suitability of the scaffold to support cell survival and growth. This was confirmed by live-cell imaging and fibroblast culture over a period of four days. Moreover, we demonstrate unambiguous durotactic fibroblast migration and mechanosensitive neurite outgrowth of dorsal root ganglion neurons in 3D. This modular approach of assembling 3D scaffolds from mechanically and biochemically well-defined building blocks allows the spatial patterning of stiffness decoupled from porosity and adhesion sites in principle and provides a platform to investigate mechanosensitivity in 3D environments approximating tissues in vitro.

iPreP is a three-dimensional nanofibrillar cellulose hydrogel platform for long-term ex vivo preservation of human islets

Islet transplantation is an effective therapy for achieving and maintaining normoglycemia in patients with type 1 diabetes mellitus. However, the supply of transplantable human islets is limited. Upon removal from the pancreas, islets rapidly disintegrate and lose function, resulting in a short interval for studies of islet biology and pretransplantation assessment. Here, we developed a biomimetic platform that can sustain human islet physiology for a prolonged period ex vivo. Our approach involved the creation of a multichannel perifusion system to monitor dynamic insulin secretion and intracellular calcium flux simultaneously, enabling the systematic evaluation of glucose-stimulated insulin secretion under multiple conditions. Using this tool, we developed a nanofibrillar cellulose hydrogel-based islet-preserving platform (iPreP) that can preserve islet viability, morphology, and function for nearly 12 weeks ex vivo, and with the ability to ameliorate glucose levels upon transplantation into diabetic hosts. Our platform has potential applications in the prolonged maintenance of human islets, providing an expanded time window for pretransplantation assessment and islet studies.

Molecular analysis of muscle progenitor cells on extracellular matrix coatings and hydrogels

Development of an ex vivo culture system to expand satellite cells, the resident muscle stem cell population, will be necessary for the development of their use as therapeutics. The loss of the niche environment is often cited as the reason that culture results in both the loss of myogenic potential and low re-engraftment rates of these cells. Studies have shown that culture of satellite cells on more elastic substrates maintained their quiescence and potential and increased re-engraftment, but there was limited proliferation. We examined whether substrates composed of extracellular matrix proteins, as either coatings or hydrogels, could support expansion of this population whilst maintaining the potency of these cells. The collagen based hydrogels were very pliant and our studies demonstrate that stiffer substrates are necessary for in vitro proliferation and differentiation of satellite cells, and the ECM composition was not significantly important. Our data further indicates that culture on highly elastic substrates allowed satellite cells to down-regulate myogenic specific transcription factors, resulting in an expression profile similar to a G_alert state. These satellite cells could be subsequently cultured on Matrigel and induced to differentiate. Proliferation and gene expression data further indicated that C2C12 cells are not a good proxy for studies of satellite cell proliferation and differentiation on alternative substrates. STATEMENT OF SIGNIFICANCE: Although biomaterials and muscle stem cell-based therapeutics for muscle loss due to trauma and disease have been studied intensely for the last decade, significant challenges remain; satellite cells lose their myogenic potential after in vitro culture, and do not re-engraft efficiently when delivered to skeletal muscle. We cultured adult mouse derived satellite cells and C2C12 cells on biomimetic, extracellular matrix based, hydrogels and coated plates and carried out a detailed analysis of proliferation, differentiation, and gene expression. These studies were designed to allow for the examination of the roles of both matrix composition and elasticity. The data demonstrated that satellite cells were most affected by elasticity. Examining the expression of lineage and cell cycle specific genes provided important insight into the behavior of both cell types, and point to fundamental differences that affect the interpretation of studies aimed at understanding the in vitro requirements of muscle progenitor cells. Understanding how satellite cells respond to various biochemical and biophysical cues at the molecular level will inform future efforts to design therapeutics for muscle regeneration.

Roadmap to Local Tumour Growth: Insights from Cervical Cancer

Wide tumour excision is currently the standard approach to surgical treatment of solid cancers including carcinomas of the lower genital tract. This strategy is based on the premise that tumours exhibit isotropic growth potential. We reviewed and analysed local tumour spreading patterns in 518 patients with cancer of the uterine cervix who underwent surgical tumour resection. Based on data obtained from pathological examination of the surgical specimen, we applied computational modelling techniques to simulate local tumour spread in order to identify parameters influencing preferred infiltration patterns and used area-proportional Euler diagrams to detect and confirm ordered patterns of tumour spread. Some anatomical structures, e.g. tissues of the urinary bladder, were significantly more likely to be infiltrated than other structures, e.g. the ureter and the rectum. Computational models assuming isotropic growth could not explain these infiltration patterns. Introducing ontogenetic distance of a tissue relative to the uterine cervix as a parameter led to accurate predictions of the clinically observed infiltration likelihoods. The clinical data indicates that successive infiltration likelihoods of ontogenetically distant tissues are nearly perfect subsets of ontogenetically closer tissues. The prevailing assumption of isotropic tumour extension has significant shortcomings in the case of cervical cancer. Rather, cervical cancer spread seems to follow ontogenetically defined trajectories.

Investigation of Conjunctival Fibrosis Response Using a 3D Glaucoma Tenon's Capsule + Conjunctival Model

Purpose

Surgical techniques such as trabeculectomy aim to treat glaucoma by making an incision into the scleral tissue, to create an alternative drainage pathway for aqueous to flow into the sub-Tenon's/subconjunctival space. However, tissue fibrosis and wound healing occurring after the procedures can reduce the success rate. This study aims to investigate the synergistic effects of aqueous humor in combination with shear stress on the fibrosis response occurring in Tenon's capsule and conjunctival tissue (TCCT) after glaucoma surgery.

Methods

Two-dimensional (2D) and 3D in vitro TCCT models were constructed by seeding porcine Tenon's capsule + conjunctival fibroblasts in collagen gel. These were used to investigate key growth factors (singular and natural form) with shear stress, which are believed to influence tissue fibrosis after glaucoma surgery. In addition to cell proliferation assessments, a nondestructive assay to quantify neocollagen synthesis in TCCT models, in response to these factors, has been applied up to 14 days.

Results

TCCT fibroblast proliferation increased significantly with doses of TGF-β, TNF-α, and VEGF, in comparison with the control. Furthermore, fibroblasts exposed to 50% aqueous humor had significantly increased proliferation and actin expression. Shear stress-induced mechanotransduction was also found to promote metabolic activity across experimental conditions. Neocollagen labeling cross validated the fibrosis process.

Conclusions

Shear stress appeared to enhance the influence of key growth factors and further promoted fibrotic response within the model. These findings offer a useful insight for further study into the wound-healing response triggered by aqueous fluid outflow after glaucoma surgery.

Predictable fibroblast tension generation by measuring compaction of anchored collagen matrices using microscopy and optical coherence tomography

The anchored fibroblast-populated collagen matrix (aFPCM) is an appropriate model to study fibrocontractive disease mechanisms. Our goal was to determine if aFPCM height reduction (compaction) during development is sufficient to predict tension generation. Compaction was quantified daily by both traditional light microscopy and an optical coherence tomography (OCT) system. Contraction in aFPCM was revealed by releasing them from anchorage. We found that aFPCM contraction increase was correlated to the compaction increase. Cytochalasin D treatment reversibly inhibited compaction. Therefore, we demonstrated that aFPCM height reduction efficiently measures compaction, contraction, and relative maturity of the collagen matrix during development or treatment. In addition, we showed that OCT is suitable for effectively imaging the cross-sectional morphology of the aFPCM in culture. This study will pave the way for more efficient studies on the mechanisms of (and treatments that target) migration and contraction in wound healing and Dupuytren’s contracture in a tissue environment.

The matrix environmental and cell mechanical properties regulate cell migration and contribute to the invasive phenotype of cancer cells

The minimal structural unit of a solid tumor is a single cell or a cellular compartment such as the nucleus. A closer look inside the cells reveals that there are functional compartments or even structural domains determining the overall properties of a cell such as the mechanical phenotype. The mechanical interaction of these living cells leads to the complex organization such as compartments, tissues and organs of organisms including mammals. In contrast to passive non-living materials, living cells actively respond to the mechanical perturbations occurring in their microenvironment during diseases such as fibrosis and cancer. The transformation of single cancer cells in highly aggressive and hence malignant cancer cells during malignant cancer progression encompasses the basement membrane crossing, the invasion of connective tissue, the stroma microenvironments and transbarrier migration, which all require the immediate interaction of the aggressive and invasive cancer cells with the surrounding extracellular matrix environment including normal embedded neighboring cells. All these steps of the metastatic pathway seem to involve mechanical interactions between cancer cells and their microenvironment. The pathology of cancer due to a broad heterogeneity of cancer types is still not fully understood. Hence it is necessary to reveal the signaling pathways such as mechanotransduction pathways that seem to be commonly involved in the development and establishment of the metastatic and mechanical phenotype in several carcinoma cells. We still do not know whether there exist distinct metastatic genes regulating the progression of tumors. These metastatic genes may then be activated either during the progression of cancer by themselves on their migration path or in earlier stages of oncogenesis through activated oncogenes or inactivated tumor suppressor genes, both of which promote the metastatic phenotype. In more detail, the adhesion of cancer cells to their surrounding stroma induces the generation of intracellular contraction forces that deform their microenvironments by alignment of fibers. The amplitude of these forces can adapt to the mechanical properties of the microenvironment. Moreover, the adhesion strength of cancer cells seems to determine whether a cancer cell is able to migrate through connective tissue or across barriers such as the basement membrane or endothelial cell linings of blood or lymph vessels in order to metastasize. In turn, exposure of adherent cancer cells to physical forces, such as shear flow in vessels or compression forces around tumors, reinforces cell adhesion, regulates cell contractility and restructures the ordering of the local stroma matrix that leads subsequently to secretion of crosslinking proteins or matrix degrading enzymes. Hence invasive cancer cells alter the mechanical properties of their microenvironment. From a mechanobiological point-of-view, the recognized physical signals are transduced into biochemical signaling events that guide cellular responses such as cancer progression after the malignant transition of cancer cells from an epithelial and non-motile phenotype to a mesenchymal and motile (invasive) phenotype providing cellular motility. This transition can also be described as the physical attempt to relate this cancer cell transitional behavior to a T1 phase transition such as the jamming to unjamming transition. During the invasion of cancer cells, cell adaptation occurs to mechanical alterations of the local stroma, such as enhanced stroma upon fibrosis, and therefore we need to uncover underlying mechano-coupling and mechano-regulating functional processes that reinforce the invasion of cancer cells. Moreover, these mechanisms may also be responsible for the awakening of dormant residual cancer cells within the microenvironment. Physicists were initially tempted to consider the steps of the cancer metastasis cascade as single events caused by a single mechanical alteration of the overall properties of the cancer cell. However, this general and simple view has been challenged by the finding that several mechanical properties of cancer cells and their microenvironment influence each other and continuously contribute to tumor growth and cancer progression. In addition, basement membrane crossing, cell invasion and transbarrier migration during cancer progression is explained in physical terms by applying physical principles on living cells regardless of their complexity and individual differences of cancer types. As a novel approach, the impact of the individual microenvironment surrounding cancer cells is also included. Moreover, new theories and models are still needed to understand why certain cancers are malignant and aggressive, while others stay still benign. However, due to the broad variety of cancer types, there may be various pathways solely suitable for specific cancer types and distinct steps in the process of cancer progression. In this review, physical concepts and hypotheses of cancer initiation and progression including cancer cell basement membrane crossing, invasion and transbarrier migration are presented and discussed from a biophysical point-of-view. In addition, the crosstalk between cancer cells and a chronically altered microenvironment, such as fibrosis, is discussed including the basic physical concepts of fibrosis and the cellular responses to mechanical stress caused by the mechanically altered microenvironment. Here, is highlighted how biophysical approaches, both experimentally and theoretically, have an impact on classical hallmarks of cancer and fibrosis and how they contribute to the understanding of the regulation of cancer and its progression by sensing and responding to the physical environmental properties through mechanotransduction processes. Finally, this review discusses various physical models of cell migration such as blebbing, nuclear piston, protrusive force and unjamming transition migration modes and how they contribute to cancer progression. Moreover, these cellular migration modes are influenced by microenvironmental perturbances such as fibrosis that can induce mechanical alterations in cancer cells, which in turn may impact the environment. Hence, the classical hallmarks of cancer need to be refined by including biomechanical properties of cells, cell clusters and tissues and their microenvironment to understand mechano-regulatory processes within cancer cells and the entire organism.