Biomechanical regulation of cell orientation and fate

Reorganizing chromatin by cellular deformation

Biologists have the capability to edit a genome at the nanometer scale and then observe whether or not the edit affects the structure of a developing organ or organism at the centimeter scale. Our understanding of the underlying mechanisms driving this emergent phenomenon from a multiscale perspective remains incomplete. This review focuses predominantly on recent experimental developments in uncovering the mechanical interplay between the chromatin and cell scale since mechanics plays a major role in determining nuclear, cellular, and tissue structure. Here, we discuss the generation and transmission of forces through the cytoskeleton, affecting chromatin diffusivity and organization. Decoding such pieces of these multiscale connections lays the groundwork for solving the genotype-to-phenotype puzzle in biology.

Inhibition of Renin Expression Is Regulated by an Epigenetic Switch From an Active to a Poised State

BACKGROUND

Renin-expressing cells are myoendocrine cells crucial for the maintenance of homeostasis. Renin is regulated by cAMP, p300 (histone acetyltransferase p300)/CBP (CREB-binding protein), and Brd4 (bromodomain-containing protein 4) proteins and associated pathways. However, the specific regulatory changes that occur following inhibition of these pathways are not clear.

METHODS

We treated As4.1 cells (tumoral cells derived from mouse juxtaglomerular cells that constitutively express renin) with 3 inhibitors that target different factors required for renin transcription: H-89-dihydrochloride, PKA (protein kinase A) inhibitor; JQ1, Brd4 bromodomain inhibitor; and A-485, p300/CBP inhibitor. We performed assay for transposase-accessible chromatin with sequencing (ATAC-seq), single-cell RNA sequencing, cleavage under targets and tagmentation (CUT&Tag), and chromatin immunoprecipitation sequencing for H3K27ac (acetylation of lysine 27 of the histone H3 protein) and p300 binding on biological replicates of treated and control As4.1 cells.

RESULTS

In response to each inhibitor, Ren1 expression was significantly reduced and reversible upon washout. Chromatin accessibility at the Ren1 locus did not markedly change but was globally reduced at distal elements. Inhibition of PKA led to significant reductions in H3K27ac and p300 binding specifically within the Ren1 super-enhancer region. Further, we identified enriched TF (transcription factor) motifs shared across each inhibitory treatment. Finally, we identified a set of 9 genes with putative roles across each of the 3 renin regulatory pathways and observed that each displayed differentially accessible chromatin, gene expression, H3K27ac, and p300 binding at their respective loci.

CONCLUSIONS

Inhibition of renin expression in cells that constitutively synthesize and release renin is regulated by an epigenetic switch from an active to poised state associated with decreased cell-cell communication and an epithelial-mesenchymal transition. This work highlights and helps define the factors necessary for renin cells to alternate between myoendocrine and contractile phenotypes.

Unravelling anisotropic nonlinear shear elasticity in muscles: Towards a non-invasive assessment of stress in living organisms

Acoustoelasticity theory describes propagation of shear waves in uniaxially stressed medium and allows the retrieval of nonlinear elastic coefficients of tissues. In transverse isotropic medium such as muscles the theory leads to 9 different configurations of propagating shear waves (stress axis vs. fibers axis vs. shear wave polarization axis vs. shear wave propagation axis). In this work we propose to use 4 configurations to quantify these nonlinear parameters ex vivo and in vivo. Ex vivo experiments combining ultrasound shear wave elastography and mechanical testing were conducted on iliopsoas pig muscles to quantify three third-order nonlinear coefficients A, H and K that are possibly linked to the architectural structure of muscles. In vivo experiments were performed with human volunteers on biceps brachii during a stretching exercise on an ergometer. A combination of the third order nonlinear elastic parameters was assessed. The knowledge of this nonlinear elastic parameters paves the way to quantify in vivo the local forces produced by muscle during exercise, contraction or movements.

Mechanosensitive hormone signaling promotes mammary progenitor expansion and breast cancer risk

Tissue stem-progenitor cell frequency has been implicated in tumor risk and progression, but tissue-specific factors linking these associations remain ill-defined. We observed that stiff breast tissue from women with high mammographic density, who exhibit increased lifetime risk for breast cancer, associates with abundant stem-progenitor epithelial cells. Using genetically engineered mouse models of elevated integrin mechanosignaling and collagen density, syngeneic manipulations, and spheroid models, we determined that a stiff matrix and high mechanosignaling increase mammary epithelial stem-progenitor cell frequency and enhance tumor initiation in vivo. Augmented tissue mechanics expand stemness by potentiating extracellular signal-related kinase (ERK) activity to foster progesterone receptor-dependent RANK signaling. Consistently, we detected elevated phosphorylated ERK and progesterone receptors and increased levels of RANK signaling in stiff breast tissue from women with high mammographic density. The findings link fibrosis and mechanosignaling to stem-progenitor cell frequency and breast cancer risk and causally implicate epidermal growth factor receptor-ERK-dependent hormone signaling in this phenotype.

Cancer metastasis: Molecular mechanisms and clinical perspectives

Metastatic progression combined with non-responsiveness towards systemic therapy often shapes the course of disease for cancer patients and commonly determines its lethal outcome. The complex molecular events that promote metastasis are a combination of both, the acquired pro-metastatic properties of cancer cells and a metastasis-permissive or -supportive tumor micro-environment (TME). Yet, dissemination is a challenging process for cancer cells that requires a series of events to enable cancer cell survival and growth. Metastatic cancer cells have to initially detach themselves from primary tumors, overcome the challenges of their intravasal journey and colonize distant sites that are suited for their metastases. The implicated obstacles including anoikis and immune surveillance, can be overcome by intricate intra- and extracellular signaling pathways, which we will summarize and discuss in this review. Further, emerging modulators of metastasis, like the immune-microenvironment, microbiome, sublethal cell death engagement, or the nervous system will be integrated into the existing working model of metastasis.

Invasion and Secondary Site Colonization as a Function of In Vitro Primary Tumor Matrix Stiffness: Breast to Bone Metastasis

Increased breast tissue stiffness is correlated with breast cancer risk and invasive cancer progression. However, its role in promoting bone metastasis, a major cause of mortality, is not yet understood. It is previously identified that the composition and stiffness of alginate-based hydrogels mimicking normal (1-2 kPa) and cancerous (6-10 kPa) breast tissue govern phenotype of breast cancer cells (including MDA-MB-231) in vitro. Here, to understand the causal effect of primary tumor stiffness on metastatic potential, a new breast-to-bone in vitro model is described. Together with alginate-gelatin hydrogels to mimic breast tissue, 3D printed biohybrid poly-caprolactone (PCL)-composite scaffolds, decellularized following bone-ECM deposition through Saos-2 engraftment, are used to mimic the bone tissue. It is reported that higher hydrogel stiffness results in the increased migration and invasion capacity of MDA-MB 231 cells. Interestingly, increased expression of osteolytic factors PTHrP and IL-6 is observed when MDA-MB-231 cells pre-conditioned in stiffer hydrogels (10 kPa, 3% w/v gelatin) colonize the bone/PCL scaffolds. The new breast-to-bone in vitro models herein described are designed with relevant tissue microenvironmental factors and could emerge as future non-animal technological platforms for monitoring metastatic processes and therapeutic efficacy.

Correlation analysis between shear-wave elastography and pathological profiles in breast cancer

PURPOSE

To explore the correlation between shear-wave elastography (SWE) parameters and pathological profiles of invasive breast cancer.

METHODS

A total of 197 invasive breast cancers undergoing preoperative SWE and primary surgical treatment were included. Maximum elastic modulus (Emax), mean elastic modulus (Emean), and elastic modulus standard deviation (Esd) were calculated by SWE. Pathological profile was gold standard according to postoperative pathology. The relationship between SWE parameters and pathological factors were analyzed using univariate and multivariate analysis.

RESULTS

In univariate analysis, large cancers showed significantly higher Emax, Emean and Esd (all P < 0.001). Emax and Esd in the group of histological grade III were higher than those in the group of grade I (both P < 0.05). Invasive lobular carcinomas (ILC) showed higher Emean than invasive ductal carcinoma (IDC) (P < 0.001). Lymphovascular invasion (LVI) group showed higher Emax values than negative group (P < 0.05). Emax, Emean and Esd of the Ki-67 positive group presented higher values than negative group (all P < 0.05). Androgen receptor (AR) positive lesions had lower Esd than AR negative lesions (P < 0.05). In multivariate analysis, invasive size independently influenced Emax (P < 0.001). Invasive size and pathological type both independently influenced Emean (both P < 0.001). Invasive size and AR status were both independently influenced Esd (both P < 0.05).

CONCLUSION

SWE parameters correlated with pathological profiles of invasive breast cancer.In particular, AR positive group showed significantly low Esd than negative group.

Gold Nano-Bio-Interaction to Modulate Mechanobiological Responses for Cancer Therapy Applications

In the present study, we investigate the mechanobiological responses of human lung cancer that may occur through their interactions with two different types of gold nanoparticles: nanostars and nanospheres. Hyperspectral images of nanoparticle-treated cells revealed different spatial distributions of nanoparticles in cells depending on their morphology, with nanospheres being more uniformly distributed in cells than nanostars. Gold nanospheres were also found to be more effective in mechanobiological modulations. They significantly suppressed the migratory ability of cells under different incubation times while lowering the bulk stiffness and adhesion of cells. This in vitro study suggests the potential applications of gold nanoparticles to manage cell migration. Nano-bio-interactions appeared to impact the cytoskeletal organization of cells and consequently alter the mechanical properties of cells, which could influence the cellular functions of cells. According to the results and migratory index model, it is thought that nanoparticle-treated cells experience mechanical changes in their body, which largely reduces their migratory potentials. These findings provide a better understanding of nano-bio-interaction in terms of cell mechanics and highlight the importance of mechanobiological responses in designing gold nanoparticles for cancer therapy.

Aligned forces: Origins and mechanisms of cancer dissemination guided by extracellular matrix architecture

Organized extracellular matrix (ECM), in the form of aligned architectures, is a critical mediator of directed cancer cell migration by contact guidance, leading to metastasis in solid tumors. Current models suggest anisotropic force generation through the engagement of key adhesion and cytoskeletal complexes drives contact-guided migration. Likewise, disrupting the balance between cell-cell and cell-ECM forces, driven by ECM engagement for cells at the tumor-stromal interface, initiates and drives local invasion. Furthermore, processes such as traction forces exerted by cancer and stromal cells, spontaneous reorientation of matrix-producing fibroblasts, and direct binding of ECM modifying proteins lead to the emergence of collagen alignment in tumors. Thus, as we obtain a deeper understanding of the origins of ECM alignment and the mechanisms by which it is maintained to direct invasion, we are poised to use the new paradigm of stroma-targeted therapies to disrupt this vital axis of disease progression in solid tumors.

The Role of miRNAs in Extracellular Matrix Repair and Chronic Fibrotic Lung Diseases

The lung extracellular matrix (ECM) plays a key role in the normal architecture of the lung, from embryonic lung development to mechanical stability and elastic recoil of the breathing adult lung. The lung ECM can modulate the biophysical environment of cells through ECM stiffness, porosity, topography and insolubility. In a reciprocal interaction, lung ECM dynamics result from the synthesis, degradation and organization of ECM components by the surrounding structural and immune cells. Repeated lung injury and repair can trigger a vicious cycle of aberrant ECM protein deposition, accompanied by elevated ECM stiffness, which has a lasting effect on cell and tissue function. The processes governing the resolution of injury repair are regulated by several pathways; however, in chronic lung diseases such as asthma, chronic obstructive pulmonary disease (COPD) and idiopathic pulmonary disease (IPF) these processes are compromised, resulting in impaired cell function and ECM remodeling. Current estimates show that more than 60% of the human coding transcripts are regulated by miRNAs. miRNAs are small non-coding RNAs that regulate gene expressions and modulate cellular functions. This review is focused on the current knowledge of miRNAs in regulating ECM synthesis, degradation and topography by cells and their dysregulation in asthma, COPD and IPF.

A Signaling View into the Inflammatory Tumor Microenvironment

The development of tumors requires an initiator event, usually exposure to DNA damaging agents that cause genetic alterations such as gene mutations or chromosomal abnormalities, leading to deregulated cell proliferation. Although the mere stochastic accumulation of further mutations may cause tumor progression, it is now clear that an inflammatory microenvironment has a major tumor-promoting influence on initiated cells, in particular when a chronic inflammatory reaction already existed before the initiated tumor cell was formed. Moreover, inflammatory cells become mobilized in response to signals emanating from tumor cells. In both cases, the microenvironment provides signals that initiated tumor cells perceive by membrane receptors and transduce via downstream kinase cascades to modulate multiple cellular processes and respond with changes in cell gene expression, metabolism, and morphology. Cytokines, chemokines, and growth factors are examples of major signals secreted by immune cells, fibroblast, and endothelial cells and mediate an intricate cell-cell crosstalk in an inflammatory microenvironment, which contributes to increased cancer cell survival, phenotypic plasticity and adaptation to surrounding tissue conditions. Eventually, consequent changes in extracellular matrix stiffness and architecture, coupled with additional genetic alterations, further fortify the malignant progression of tumor cells, priming them for invasion and metastasis. Here, we provide an overview of the current knowledge on the composition of the inflammatory tumor microenvironment, with an emphasis on the major signals and signal-transducing events mediating different aspects of stromal cell-tumor cell communication that ultimately lead to malignant progression.

Regulation and mechanism of YAP/TAZ in the mechanical microenvironment of stem cells (Review)

Stem cells receive cues from their physical and mechanical microenvironment via mechanosensing and mechanotransduction. These cues affect proliferation, self‑renewal and differentiation into specific cell fates. A growing body of evidence suggests that yes‑associated protein (YAP) and transcriptional coactivator with PDZ‑binding motif (TAZ) mechanotransduction is key for driving stem cell behavior and regeneration via the Hippo and other signaling pathways. YAP/TAZ receive a range of physical cues, including extracellular matrix stiffness, cell geometry, flow shear stress and mechanical forces in the cytoskeleton, and translate them into cell‑specific transcriptional programs. However, the mechanism by which mechanical signals regulate YAP/TAZ activity in stem cells is not fully understand. The present review summarizes the current knowledge of the mechanisms involved in YAP/TAZ regulation on the physical and mechanical microenvironment, as well as its potential effects on stem cell differentiation.

Chemokines and the extracellular matrix: Set of targets for tumor development and treatment

The extracellular matrix (ECM) consists of various molecules that support tissue cells, including proteins, fibronectin, laminin, collagen IV, and glycosaminoglycans. In addition to interactions between the ECM and cells, the ECM also interacts with chemokines, and growth factors, and these interactions ensure cell survival, development, differentiation, and migration of both immune system cells and tumor cells. This review provides an overview of the mechanisms of interaction between the ECM and chemokines, focusing on the tumor microenvironment and the modulation of these elements as a target for therapies in several types of cancer.

Electrospun nanofiber scaffolds for the propagation and analysis of breast cancer stem cells in vitro

Despite advances in cancer treatment, breast cancer remains the second foremost cause of cancer mortality among women, with a high rate of relapse after initial treatment success. A subpopulation of highly malignant cancer cells, known as cancer stem cells (CSCs), is suspected to be linked to metastasis and relapse. Targeting of CSCs may therefore provide a means of addressing cancer-related mortality. However, due to their low population in vivo and a lack of proper culture platform for their propagation, much of the CSC biology remains unknown. Since maintenance of CSCs is heavily influenced by the tumor microenvironment, this study developed a 3D culture platform that mimics the metastatic tumor extracellular matrix (ECM) to effectively increase CSC population in vitro and allow CSC analysis. Through electrospinning, nanofibers that were aligned, porous, and collagen-coated were fabricated from polycaprolactone to recreate the metastatic tumor ECM assemblage. Breast cancer cells seeded onto the nanofiber scaffolds exhibited gross morphology and cytoskeletal phenotype similar to invasive cancer cells. Moreover, the population of breast cancer stem cells increased in nanofiber scaffolds. Analysis of breast cancer cells grown on the nanofiber scaffolds demonstrated an upregulation of mesenchymal markers and an increase in cell invasiveness suggesting the cells have undergone epithelial-mesenchymal transition. These results indicate that the fabricated nanofiber scaffolds effectively mimicked the tumor microenvironment that maintains the cancer stem cell population, offering a platform to enrich and analyze CSCs in vitro.

Adipose tissue-derived mesenchymal stem cells for breast tissue regeneration

With an escalating incidence of breast cancer cases all over the world and the deleterious psychological impact that mastectomy has on patients along with several limitations of the currently applied modalities, it's plausible to seek unconventional approaches to encounter such a burgeoning issue. Breast tissue engineering may allow that chance via providing more personalized solutions which are able to regenerate, mimicking natural tissues also facing the witnessed limitations. This review is dedicated to explore the utilization of adipose tissue-derived mesenchymal stem cells for breast tissue regeneration among postmastectomy cases focusing on biomaterials and cellular aspects in terms of harvesting, isolation, differentiation and new tissue formation as well as scaffolds types, properties, material-host interaction and an in vitro breast tissue modeling.

Effect of alginate matrix engineered to mimic the pancreatic microenvironment on encapsulated islet function

Islet transplantation is emerging as a therapeutic option for type 1 diabetes, albeit, only a small number of patients meeting very stringent criteria are eligible for the treatment because of the side effects of the necessary immunosuppressive therapy and the relatively short time frame of normoglycemia that most patients achieve. The challenge of the immune-suppressive regimen can be overcome through microencapsulation of the islets in a perm-selective coating of alginate microbeads with poly-l-lysine or poly- l-ornithine. In addition to other issues including the nutrient supply challenge of encapsulated islets a critical requirement for these cells has emerged as the need to engineer the microenvironment of the encapsulation matrix to mimic that of the native pancreatic scaffold that houses islet cells. That microenvironment includes biological and mechanical cues that support the viability and function of the cells. In this study, the alginate hydrogel was modified to mimic the pancreatic microenvironment by incorporation of extracellular matrix (ECM). Mechanical and biological changes in the encapsulating alginate matrix were made through stiffness modulation and incorporation of decellularized ECM, respectively. Islets were then encapsulated in this new biomimetic hydrogel and their insulin production was measured after 7 days in vitro. We found that manipulation of the alginate hydrogel matrix to simulate both physical and biological cues for the encapsulated islets enhances the mechanical strength of the encapsulated islet constructs as well as their function. Our data suggest that these modifications have the potential to improve the success rate of encapsulated islet transplantation.

Strain-induced Differentiation of Mesenchymal Stem Cells

Directing the fate of human mesenchymal stem/stromal cells (hMSCs) toward bone formation using mechanical strain is a promising approach in regenerative medicine related to bone diseases. Numerous studies have evaluated the effects of vibration or cyclic tensile strain on MSCs towards developing a mechanically-based method for stimulating differentiation. Here, we study the differentiation of hMSCs cultured on elastic polydimethylsiloxane (PDMS) membrane, which is magnetically actuated to induce periodically varying strain. The strain distribution across the membrane was calculated by finite-element modeling and demonstrates three main areas of different strain amplitudes. The strain effect on the hMSCs was evaluated by measuring the mineralization of differentiated hMSCs using Alizarin S red stain. The results indicate a strain-dependent differentiation of hMSCs, where the highest region of strain on the membrane resulted in the most accelerated differentiation. Osteogenic differentiation was achieved as early as two weeks, which is significantly sooner than control hMSCs treated with osteogenic media alone.

Nanoscale Architecture of the Cortical Actin Cytoskeleton in Embryonic Stem Cells

Mechanical cues influence pluripotent stem cell differentiation, but the underlying mechanisms are not well understood. Mouse embryonic stem cells (mESCs) exhibit unusual cytomechanical properties, including low cell stiffness and attenuated responses to substrate rigidity, but the underlying structural basis remains obscure. Using super-resolution microscopy to investigate the actin cytoskeleton in mESCs, we observed that the actin cortex consists of a distinctively sparse and isotropic network. Surprisingly, the architecture and mechanics of the mESC actin cortex appear to be largely myosin II-independent. The network density can be modulated by perturbing Arp2/3 and formin, whereas capping protein (CP) negatively regulates cell stiffness. Transient Arp2/3-containing aster-like structures are implicated in the organization and mechanical homeostasis of the cortical network. By generating a low-density network that physically excludes myosin II, the interplay between Arp2/3, formin, and CP governs the nanoscale architecture of the actin cortex and prescribes the cytomechanical properties of mESCs.

The protective effect of betacellulin against acute pancreatitis is ERBB4 dependent

BACKGROUND

The EGFR ligand betacellulin (BTC) has been previously shown to protect mice against experimentally induced acute pancreatitis (AP). BTC binds both autonomous ERBB receptors EGFR and ERBB4. In this study, we evaluated the mechanism underlying the protection from AP-associated inflammation in detail.

METHODS

AP was induced with cerulein or L-arginine and investigated in a pancreas-specific ERBB4 knockout and in an EGFR knockdown mouse model (Egfr^Wa5/+). Pancreatitis was evaluated by scoring inflammation, necrosis, and edema, while microarrays were performed to analyze alterations in the transcriptome between mice with AP and animals which were protected against AP. The intracellular domain (ICD) of ERBB4 was analyzed in different cell compartments.

RESULTS

While the pancreas of BTC transgenic mice in the background of Egfr^Wa5/+ is still protected against AP, the BTC-mediated protection is no longer present in the absence of ERBB4. We further demonstrate that BTC activates the ICD of ERBB4, and increases the expression of the extracellular matrix (ECM) proteins periostin and matrix gla protein as well as the ECM modulators matrix metalloproteinases 2 and 3, but only in the presence of ERBB4. Notably, the increased expression of these proteins is not accompanied by an increased ECM amount.

CONCLUSIONS

These findings suggest that BTC derivates, as a drug, or the ERBB4 receptor, as a druggable target protein, could play an important role in modulating the course of AP and even prevent AP in humans.

Low-intensity pulsed ultrasound affects growth, differentiation, migration, and epithelial-to-mesenchymal transition of colorectal cancer cells

Ultrasound (US) offers potentially important opportunities from a therapeutic point of view. Thus, the study of the biological effects of US on cancer cells is important to understand the consequences of these changes on the malignant phenotype. This study aimed to investigate the effects of low-intensity ultrasound (LIPUS) on the phenotype of colorectal cancer cell lines. Cell proliferation was evaluated by viability test and by evaluation of pERK expression, while cell motility using the scratch test. Cell differentiation was evaluated assessing alkaline phosphatase activity. Epithelial mesenchymal transition was assessed by analyzing the expression of Vimentin and E-Cadherin. Release and uptake of extracellular vesicles (EVs) were evaluated by flow cytometry. LIPUS effects on the organization of cytoskeleton were analyzed by confocal microscopy and by evaluation of Rho GTPase expression. No alterations in vitality and clonogenicity were observed when the intermediate (0.4 MPa) and the lowest (0.035 MPa) acoustic intensities were administered while the treatment with high intensity (1 MPa) induced a reduction of both cell viability and clonogenicity in both cell lines in a frequency-dependent manner. LIPUS promoted the differentiation of colon cancer cells, affected epithelial-to-mesenchymal transition, promoted the closure of a wound as well as increased the release of EVs compared with untreated cells. LIPUS-induced increase in cell motility was likely due to a Rho GTPase-dependent mechanism. Overall, the results obtained warrant further studies on the potential combined effect of LIPUS with differentiating agents and on their potential use in a clinical setting.

Tumour Initiation: a Discussion on Evidence for a "Load-Trigger" Mechanism

Appropriate mechanical forces on cells are vital for normal cell behaviour and this review discusses the possibility that tumour initiation depends partly on the disruption of the normal physical architecture of the extracellular matrix (ECM) around a cell. The alterations that occur thence promote oncogene expression. Some questions, that are not answered with certainty by current consensus mechanisms of tumourigenesis, are elegantly explained by the triggering of tumours being a property of the physical characteristics of the ECM, which is operative following loading of the tumour initiation process with a relevant gene variant. Clinical observations are consistent with this alternative hypothesis which is derived from studies that have, together, accumulated an extensive variety of data incorporating biochemical, genetic and clinical findings. Thus, this review provides support for the view that the ECM may have an executive function in induction of a tumour. Overall, reported observations suggest that either restoring an ECM associated with homeostasis or targeting the related signal transduction mechanisms may possibly be utilised to modify or control the early progression of cancers. The review provides a coherent template for discussing the notion, in the context of contemporary knowledge, that tumourigenesis is an alliance of biochemistry, genetics and biophysics, in which the physical architecture of the ECM may be a fundamental component. For more definitive clarification of the concept there needs to be a phalanx of experiments conceived around direct questions that are raised by this paper.

Efficient Spatial Sampling for AFM-Based Cancer Diagnostics: A Comparison between Neural Networks and Conventional Data Analysis

Atomic force microscopy (AFM) in spectroscopy mode receives a lot of attention because of its potential in distinguishing between healthy and cancer tissues. However, the AFM translational process in clinical practice is hindered by the fact that it is a time-consuming technique in terms of measurement and analysis time. In this paper, we attempt to address both issues. We propose the use of neural networks for pattern recognition to automatically classify AFM force–distance (FD) curves, with the aim of avoiding curve-fitting with the Sneddon model or more complicated ones. We investigated the applicability of this method to the classification of brain cancer tissues. The performance of the classifier was evaluated with receiving operating characteristic (ROC) curves for the approach and retract curves separately and in combination with each other. Although more complex and comprehensive models are required to demonstrate the general applicability of the proposed approach, preliminary evidence is given for the accuracy of the results, and arguments are presented to support the possible applicability of neural networks to the classification of brain cancer tissues. Moreover, we propose a possible strategy to shorten measurement times based on the estimation of the minimum number of FD curves needed to classify a tissue with a confidence level of 0.005. Taken together, these results have the potential to stimulate the design of more effective protocols to reduce AFM measurement times and to get rid of curve-fitting, which is a complex and time-consuming issue that requires experienced staff with a strong data-analysis background.

Advances and Current Challenges in Intestinal in vitro Model Engineering: A Digest

The physiological environment of the intestine is characterized by its variegated composition, numerous functions and unique dynamic conditions, making it challenging to recreate the organ in vitro. This review outlines the requirements for engineering physiologically relevant intestinal in vitro models, mainly focusing on the importance of the mechano-structural cues that are often neglected in classic cell culture systems. More precisely: the topography, motility and flow present in the intestinal epithelium. After defining quantitative descriptors for these features, we describe the current state of the art, citing relevant approaches used to address one (or more) of the elements in question, pursuing a progressive conceptual construction of an "ideal" biomimetic intestinal model. The review concludes with a critical assessment of the currently available methods to summarize the important features of the intestinal tissue in the light of their different applications.

The Effect of Mammary Extracellular Matrix in Controlling Oral and Mammary Cancer Cells

Extracellular matrix (ECM) plays an important role in the normal physiology of tissues and progression to disease. Earlier studies and our external microarray data analysis indicated that mammary matrix from involuting tissue showed upregulation of genes involved in ECM remodeling. The present study examines the fate of mammary and oral cancer cells grown in the ECM from lactating mammary gland. Our findings show that non-tumorigenic cells, MCF10A and DOK cells did not proliferate but the tumorigenic and metastatic cells, SCC25 and MDA-MB-231, underwent apoptosis when grown on mammary ECM isolated from lactating mice. In addition, the cytokinesis marker, CEP55, was repressed in the oral and breast cancer cells. In contrast, these cells proliferated normally on mammary ECM isolated from mice undergoing involution. External microarray data analysis of mammary tissue further revealed over expression (~16 fold) of QSOX1 gene, which promotes cellular quiescence, in lactating mammary gland. A recent study has indicated that QSOX1 overexpression in breast cancer cells led to reduced proliferation and tumorigenic properties. This extracellular protein in mammary ECM may be responsible for reduced cellular proliferation. The present study has shown that ECM from lactating mammary gland can regulate signals to oral and breast cancer cells to halt cell division. This preliminary observation provided insights into the potential role of ECM factors present in lactating mammary gland as therapeutic targets to control cancer cell division. This preliminary study is an attempt to understand not only the requirement of ECM remodeling factors essential for the growth and survival of cancer cells but also the factors present in the lactation matrix that simultaneously halts cell division and selectively inhibits the growth of cancer cells.

Traction Force Microscopy for Noninvasive Imaging of Cell Forces

The forces exerted by cells on their surroundings play an integral role in both physiological processes and disease progression. Traction force microscopy is a noninvasive technique that enables the in vitro imaging and quantification of cell forces. Utilizing expertise from a variety of disciplines, recent developments in traction force microscopy are enhancing the study of cell forces in physiologically relevant model systems, and hold promise for further advancing knowledge in mechanobiology. In this chapter, we discuss the methods, capabilities, and limitations of modern approaches for traction force microscopy, and highlight ongoing efforts and challenges underlying future innovations.

Real-Time Bioimpedance Sensing of Antifibrotic Drug Action in Primary Human Cells

Fibrotic diseases are among the most serious health issues with severe burdens due to their chronic nature and a large number of patients suffering from the debilitating effects and long-term sequelae. Collagenase treatment is a nonsurgical option but has limited results. To date, there is no potent noninvasive solution for fibrosis. Part of the reason for this is the lack of appropriate in vitro live cell screening tools to assess the efficacy of new therapeutical agents. Here, we demonstrate the utility of a cell-based electrochemical impedance biosensor platform to screen the efficacy of potential antifibrotic compounds. The platform employs a label-free and noninvasive strategy to detect the progression of fibrosis and the potency of the antifibrotic molecules in real-time. The fundamental principle that governs this novel system is that dynamic changes in cell shape and adhesion during fibrosis can be measured accurately by monitoring the changes in the impedance. This is achieved by growing the cells on a transparent interdigitated indium tin oxide (ITO) electrodes. It was demonstrated by monitoring the efficacy of a model antifibrotic compound, PXS64, on cells collected from patients with Dupuytren's contracture. We confirmed the validity of the developed biochemical impedance biosensor as an tool for in vitro screening of antifibrotic compounds and provided quantitative information on subcellular influences of the examined chemical molecules using correlative microscopy analyses that monitor the average cell area, cell morphology, and the amount and directionality of the deposited extracellular matrix protein collagen and measurement of cytosolic Ca²⁺ changes.

Model of vascular desmoplastic multispecies tumor growth

We present a three-dimensional nonlinear tumor growth model composed of heterogeneous cell types in a multicomponent-multispecies system, including viable, dead, healthy host, and extra-cellular matrix (ECM) tissue species. The model includes the capability for abnormal ECM dynamics noted in tumor development, as exemplified by pancreatic ductal adenocarcinoma, including dense desmoplasia typically characterized by a significant increase of interstitial connective tissue. An elastic energy is implemented to provide elasticity to the connective tissue. Cancer-associated fibroblasts (myofibroblasts) are modeled as key contributors to this ECM remodeling. The tumor growth is driven by growth factors released by these stromal cells as well as by oxygen and glucose provided by blood vasculature which along with lymphatics are stimulated to proliferate in and around the tumor based on pro-angiogenic factors released by hypoxic tissue regions. Cellular metabolic processes are simulated, including respiration and glycolysis with lactate fermentation. The bicarbonate buffering system is included for cellular pH regulation. This model system may be of use to simulate the complex interactions between tumor and stromal cells as well as the associated ECM and vascular remodeling that typically characterize malignant cancers notorious for poor therapeutic response.

The peritoneum: healing, immunity, and diseases

The peritoneum defines a confined microenvironment, which is stable under normal conditions, but is exposed to the damaging effect of infections, surgical injuries, and other neoplastic and non-neoplastic events. Its response to damage includes the recruitment, proliferation, and activation of a variety of haematopoietic and stromal cells. In physiological conditions, effective responses to injuries are organized; inflammatory triggers are eliminated; inflammation quickly abates; and the normal tissue architecture is restored. However, if inflammatory triggers are not cleared, fibrosis or scarring occurs and impaired tissue function ultimately leads to organ failure. Autoimmune serositis is characterized by the persistence of self-antigens and a relapsing clinical pattern. Peritoneal carcinomatosis and endometriosis are characterized by the persistence of cancer cells or ectopic endometrial cells in the peritoneal cavity. Some of the molecular signals orchestrating the recruitment of inflammatory cells in the peritoneum have been identified in the last few years. Alternative activation of peritoneal macrophages was shown to guide angiogenesis and fibrosis, and could represent a novel target for molecular intervention. This review summarizes current knowledge of the alterations to the immune response in the peritoneal environment, highlighting the ambiguous role played by persistently activated reparative macrophages in the pathogenesis of common human diseases. Copyright © 2017 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

The role of the microenvironment in the biophysics of cancer

During the last decades, cell mechanics has been recognized as a quantitative measure to discriminate between many physiological and pathological states of single cells. In the field of biophysics of cancer, a large body of research has been focused on the comparison between normal and cancer mechanics and slowly the hypothesis that cancer cells are softer than their normal counterparts has been accepted, even though in situ tumor tissue is usually stiffer than the surrounding normal tissue. This corroborates the idea that the extra-cellular matrix (ECM) has a critical role in regulating tumor cell properties and behavior. Rearrangements in ECM can lead to changes in cancer cell mechanics and in specific conditions the general assumption about cancer cell softening could be confuted. Here, we highlight the contribution of ECM in cancer cell mechanics and argue that the statement that cancer cells are softer than normal cells should be firmly related to the properties of cell environment and the specific stage of cancer cell progression. In particular, we will discuss that when employing cell mechanics in cancer diagnosis and discrimination, the chemical, the topographical and - last but not least - the mechanical properties of the microenvironment are very important.

The role of shear stress and altered tissue properties on endothelial to mesenchymal transformation and tumor-endothelial cell interaction

Tumor development is influenced by stromal cells in aspects including invasion, growth, angiogenesis, and metastasis. Activated fibroblasts are one group of stromal cells involved in cancer metastasis, and one source of activated fibroblasts is endothelial to mesenchymal transformation (EndMT). EndMT begins when the endothelial cells delaminate from the cell monolayer, lose cell-cell contacts, lose endothelial markers such as vascular endothelial-cadherin (VE-cadherin), gain mesenchymal markers like alpha-smooth muscle actin (α-SMA), and acquire mesenchymal cell-like properties. A three-dimensional (3D) culture microfluidic device was developed for investigating the role of steady low shear stress (1 dyne/cm2) and altered extracellular matrix (ECM) composition and stiffness on EndMT. Shear stresses resulting from fluid flow within tumor tissue are relevant to both cancer metastasis and treatment effectiveness. Low and oscillatory shear stress rates have been shown to enhance the invasion of metastatic cancer cells through specific changes in actin and tubulin remodeling. The 3D ECM within the device was composed of type I collagen and glycosaminoglycans (GAGs), hyaluronic acid and chondroitin sulfate. An increase in collagen and GAGs has been observed in the solid tumor microenvironment and has been correlated with poor prognosis in many different cancer types. In this study, it was found that ECM composition and low shear stress upregulated EndMT, including upregulation of mesenchymal-like markers (α-SMA and Snail) and downregulated endothelial marker protein and gene expression (VE-cadherin). Furthermore, this novel model was utilized to investigate the role of EndMT in breast cancer cell proliferation and migration. Cancer cell spheroids were embedded within the 3D ECM of the microfluidic device. The results using this device show for the first time that the breast cancer spheroid size is dependent on shear stress and that the cancer cell migration rate, distance, and proliferation are induced by EndMT-derived activated fibroblasts. This model can be used to explore new therapeutics in a tumor microenvironment.

Bioinspired 3D Multilayered Shape Memory Scaffold with a Hierarchically Changeable Micropatterned Surface for Efficient Vascularization

How to achieve three-dimensional (3D) cell alignment and subsequent prompt tissue regeneration remains a great challenge. Here, inspired by the interior 3D architecture of native arteries, we develop a new 3D multilayered shape memory vascular scaffold with a hierarchically changeable micropatterned surface for vascularization. The shape memory function renders the implantation of the scaffold safe and convenient via minimally invasive surgery. By co-culturing endothelial cells (ECs) and vascular smooth muscle cells (VSMCs) on the 3D multilayered structure, the inner monolayer, which has a square micropatterned surface, can promote EC adhesion and migration, resulting in a rapid endothelialization, and the outer multilayers, which have rectangular micropatterned surfaces, can induce a circumferential alignment of VSMCs. After implantation in the cervical artery of a New Zealand rabbit for 120 days, the graft developed a high capacity for modulating cellular 3D alignment, to generate a neonatal functional blood vessel with an endothelium layer in the inner layer and multilevel VSMC circumferential alignments in the outer layers.

Role of LOXL2 in the epithelial-mesenchymal transition and colorectal cancer metastasis

Colorectal cancer (CRC) is one of the most dangerous types of malignant tumors, and cancer metastasis is a major factor in the failure of CRC therapy. Recently, LOXL2 (lysyl oxidase-like 2) has been shown to represent a regulator of epithelial-mesenchymal transition (EMT) in different cancer types. However, LOXL2 has not been reported to be involved in CRC metastasis. In this study, we demonstrated that LOXL2 expression is strongly correlated with the rate of CRC metastasis, it participates in the regulation of EMT-related molecule expression in CRC cells in vitro, and it is involved in migratory potential alterations. Additionally, tissue microarray analysis of CRC patients showed an increase in the probability of developing CRC distant metastasis and a decrease in the survival rate of patients with high LOXL2 expression. The results obtained in this study indicate that LOXL2 is involved in the development and progression of CRC metastasis, and therefore, its expression levels may represent a useful prognostic marker.

Predicting cell viability within tissue scaffolds under equiaxial strain: multi-scale finite element model of collagen-cardiomyocytes constructs

Successful tissue engineering and regenerative therapy necessitate having extensive knowledge about mechanical milieu in engineered tissues and the resident cells. In this study, we have merged two powerful analysis tools, namely finite element analysis and stochastic analysis, to understand the mechanical strain within the tissue scaffold and residing cells and to predict the cell viability upon applying mechanical strains. A continuum-based multi-length scale finite element model (FEM) was created to simulate the physiologically relevant equiaxial strain exposure on cell-embedded tissue scaffold and to calculate strain transferred to the tissue scaffold (macro-scale) and residing cells (micro-scale) upon various equiaxial strains. The data from FEM were used to predict cell viability under various equiaxial strain magnitudes using stochastic damage criterion analysis. The model validation was conducted through mechanically straining the cardiomyocyte-encapsulated collagen constructs using a custom-built mechanical loading platform (EQUicycler). FEM quantified the strain gradients over the radial and longitudinal direction of the scaffolds and the cells residing in different areas of interest. With the use of the experimental viability data, stochastic damage criterion, and the average cellular strains obtained from multi-length scale models, cellular viability was predicted and successfully validated. This methodology can provide a great tool to characterize the mechanical stimulation of bioreactors used in tissue engineering applications in providing quantification of mechanical strain and predicting cellular viability variations due to applied mechanical strain.

Myofibroblast repair mechanisms post-inflammatory response: a fibrotic perspective

INTRODUCTION

Fibrosis is a complex chronic disease characterized by a persistent repair response. Its pathogenesis is poorly understood but it is typically the result of chronic inflammation and maintained with the required activity of transforming growth factor-β (TGFβ) and extracellular matrix (ECM) tension, both of which drive fibroblasts to transition into a myofibroblast phenotype.

FINDINGS

As the effector cells of repair, myofibroblasts migrate to the site of injury to deposit excessive amounts of matrix proteins and stimulate high levels of contraction. Myofibroblast activity is a decisive factor in whether a tissue is properly repaired by controlled wound healing or rendered fibrotic by deregulated repair. Extensive studies have documented the various contributing factors to an abrogated repair response. Though these fibrotic factors are known, very little is understood about the opposing antifibrotic molecules that assist in a successful repair, such as prostaglandin E2 (PGE₂) and ECM retraction. The following review will discuss the general development of fibrosis through the transformation of myofibroblasts, focusing primarily on the prominent profibrotic pathways of TGFβ and ECM tension and antifibrotic pathways of PGE₂ and ECM retraction.

CONCLUSIONS

The idea is to understand the ways in which the cell, after an injury and inflammatory response, normally controls its repair mechanisms through its homeostatic regulators so as to mimic them therapeutically to control abnormal pathways.

αvβ3 integrins negatively regulate cellular forces by phosphorylation of its distal NPXY site

BACKGROUND INFORMATION

Integrins are key receptors that allow cells to sense and respond to their mechanical environment. Although they bind the same ligand, β1 and β3 integrins have distinct and cooperative roles in mechanotransduction.

RESULTS

Using traction force microscopy on unconstrained cells, we show that deleting β3 causes traction forces to increase, whereas the deletion of β1 integrin results in a strong decrease of contractile forces. Consistently, loss of β3 integrin also induces an increase in β1 integrin activation. Using a genetic approach, we identified the phosphorylation of the distal NPXY domain as an essential process for β3 integrin to be able to modulate traction forces. Loss of β3 integrins also impacted cell shape and the spatial distribution of traction forces, by causing forces to be generated closer to the cell edge, and the cell shape.

CONCLUSIONS

Our results emphasize the role of β3 integrin in spatial distribution of cellular forces. We speculate that, by modulating its affinity with kindlin, β3 integrins may be able to locate near the cell edge where it can control β1 integrin activation and clustering.

SIGNIFICANCE

Tensional homeostasis at the single cell level is performed by the ability of β3 adhesions to negatively regulate the activation degree and spatial localization of β1 integrins. By combining genetic approaches and new tools to analyze traction distribution and cell morphology on a population of cells we were able to identify the molecular partners involved in cellular forces regulation.

Keloid progression: a stiffness gap hypothesis

Keloids are fibroproliferative skin disorders characterised clinically by continuous horizontal progression and post-surgical recurrence and histologically by the accumulation of collagen and fibroblast ingredients. Till now, their aetiology remains clear, which may cover genetic, environmental and metabolic factors. Evidence in the involvement of local mechanics (e.g. predilection site and typical shape) and the progress in mechanobiology have incubated our stiffness gap hypotheses in illustrating the chronic but constant development in keloid. We put forward that the enlarged gap between extracellular matrix (ECM) stiffness and cellular stiffness potentiates keloid progression. Matrix stiffness itself provides organisational guidance cues to regulate the mechanosensitive resident cells (e.g. proliferation, migration and apoptosis). During this dynamic process, the ECM stiffness and cell stiffness are not well balanced, and the continuously enlarged stiffness gap between them potentiates keloid progression. The cushion factors, such as prestress for cell stiffness and topology for ECM stiffness, serve as compensations, the decompensation of which aggravates keloid development. It can well explain the typical shape of keloids, their progression in a horizontal but not vertical direction and the post-surgical recurrence, which were evidenced by our clinical cases. Such a stiffness gap hypothesis might be bridged to mechanotherapeutic approaches for keloid progression.

Dynamic Microenvironment Induces Phenotypic Plasticity of Esophageal Cancer Cells Under Flow

Cancer microenvironment is a remarkably heterogeneous composition of cellular and non-cellular components, regulated by both external and intrinsic physical and chemical stimuli. Physical alterations driven by increased proliferation of neoplastic cells and angiogenesis in the cancer microenvironment result in the exposure of the cancer cells to elevated levels of flow-based shear stress. We developed a dynamic microfluidic cell culture platform utilizing eshopagael cancer cells as model cells to investigate the phenotypic changes of cancer cells upon exposure to fluid shear stress. We report the epithelial to hybrid epithelial/mesenchymal transition as a result of decreasing E-Cadherin and increasing N-Cadherin and vimentin expressions, higher clonogenicity and ALDH positive expression of cancer cells cultured in a dynamic microfluidic chip under laminar flow compared to the static culture condition. We also sought regulation of chemotherapeutics in cancer microenvironment towards phenotypic control of cancer cells. Such in vitro microfluidic system could potentially be used to monitor how the interstitial fluid dynamics affect cancer microenvironment and plasticity on a simple, highly controllable and inexpensive bioengineered platform.

Regenerative Medicine: Charting a New Course in Wound Healing

Significance: Chronic wounds are a prevalent and costly problem in the United States. Improved treatments are needed to heal these wounds and prevent serious complications such as infection and amputation. Recent Advances: In wound healing, as in other areas of medicine, technologies that have the potential to regenerate as opposed to repair tissue are gaining ground. These include customizable nanofiber matrices incorporating novel materials; a variety of autologous and allogeneic cell types at various stages of differentiation (e.g., pluripotent, terminally differentiated); peptides; proteins; small molecules; RNA inhibitors; and gene therapies. Critical Issues: Wound healing is a logical target for regenerative medicine due to the accessibility and structure of skin, the regenerative nature of healing, the lack of good limb salvage treatments, and the current use of cell therapies. However, more extensive knowledge of pathophysiologic targets is needed to inform regenerative strategies, and new technologies must demonstrate value in terms of outcomes and related health economic measures to achieve successful market access and penetration. Future Directions: Due to similarities in cell pathways and developmental mechanisms, regenerative technologies developed in one therapeutic area may be applicable to others. Approaches that proceed from human genomic or other big data sources to models are becoming increasingly common and will likely suggest novel therapeutic avenues. To fully capitalize on the advances in regenerative medicine, studies must demonstrate the value of new therapies in identified patient populations, and sponsors must work with regulatory agencies to develop appropriate dossiers supporting timely approval.

Guiding cell migration with microscale stiffness patterns and undulated surfaces

By placing stiff structures under soft materials, prior studies have demonstrated that cells sense and prefer to position themselves over the stiff structures. However, an understanding of how cells migrate on such surfaces has not been established. Many studies have also shown that cells readily align to surface topography. Here we investigate the influence of these two aspects in directing cell migration on surfaces with 5 and 10μm line stiffness patterns (a cellular to subcellular length scale). A simple approach to create flat, stiffness-patterned surfaces by suspending a thin, low modulus polydimethylsiloxane (PDMS) film over a high modulus PDMS structure is presented, as well as a route to add undulations. We confirm that cells are able to sense through the thin film by observation of focal adhesions being positioned on stiff regions. We examine migration by introducing migration efficiency, a quantitative parameter to determine how strongly cells migrate in a certain direction. We found that cells have a preference to align and migrate along stiffness patterns while the addition of undulations boosts this effect, significantly increasing migration efficiency in either case. Interestingly, we found speed to play little role in the migration efficiency and to be mainly influenced by the top layer modulus. Our results demonstrate that both stiffness patterns and surface undulations are important considerations when investigating the interactions of cells with biomaterial surfaces.

STATEMENT OF SIGNIFICANCE

Two common physical considerations for cell-surface interactions include patterned stiffness and patterned topography. However, their relative influences on cell migration behavior have not been established, particularly on cellular to subcellular scale patterns. For stiffness patterning, it has been recently shown that cells tend to position themselves over a stiff structure that is placed under a thin soft layer. By quantifying the directional migration efficiency on such surfaces with and without undulations, we show that migration can be manipulated by flat stiffness patterns, although surface undulations also play a strong role. Our results offer insight on the effect of cellular scale stiffness and topographical patterns on cell migration, which is critical for the development of fundamental cell studies and engineered implants.

Static magnetic field enhances the viability and proliferation rate of adipose tissue-derived mesenchymal stem cells potentially through activation of the phosphoinositide 3-kinase/Akt (PI3K/Akt) pathway

The aim of this work was to investigate the effects of 0.5T static magnetic field (sMF) on the viability and proliferation rate of human adipose-derived mesenchymal stromal stem cells (hASCs) via activation of the phosphoinositide 3-kinase/Akt (PI3K/Akt) signaling pathway. In a 7-d culture we examined cell growth kinetic and population doubling time (PDT). We also examined cell morphology and the cellular senescence markers level. Exposure to sMF enhanced the viability of these cells. However, the effect was blocked by treating the cells with LY294002, a P13K inhibitor. We compared this effect by Western Blot analysis of Akt protein expression. We also examined whether the cell response on sMF stimulation is dependent on integrin engagement and we measured integrin gene expression. Our results suggest that stimulation using sMF is a viable method to improve hASC viability. sMF is involved in mechanisms associated with controlling cell proliferative potential signaling events.

Mechano-reciprocity is maintained between physiological boundaries by tuning signal flux through the Rho-associated protein kinase

The mechanical properties of the ECM strongly influence the behavior of all cell types within a given tissue. Increased matrix tension promotes epithelial cell proliferation by engaging mitogenic mechanotransduction signaling including the Salvador/Warts/Hippo, PI 3-kinase, Rho, Wnt and MAP kinase pathways. The Rho signaling pathways in particular are capable of increasing intra-cellular tension by elevating the production and contractility of the actomyosin cytoskeleton, which counteracts tension changes within the matrix in a process termed mechano-reciprocity. We have discovered that Rho-ROCK signaling increases the production of ECM through paracrine signaling between the epithelium and fibroblasts and also the remodeling of the ECM by regulating focal adhesion dynamics in fibroblasts. These two phenomena together cause increased ECM tension. Enhanced mechano-reciprocity results in ever-increasing intra- and extra-cellular tension in a vicious cycle that promotes cell proliferation and tumor progression. These insights reveal that inhibiting mechano-reciprocity, reducing ECM tension and targeting cancer-associated fibroblasts in a coordinated fashion has potential as cancer therapy.

A photo-polymerized poly(Nε-acryloyl l-lysine) hydrogel for 3D culture of MCF-7 breast cancer cells

The most common in vitro cell culture platform, standard two-dimensional (2D) monolayer cell culture, often fails to mimic the tumor microenvironment, while animal models complicate research on the effect of individual factors on cell behaviors. Both are unsatisfactory in the research of molecular mechanisms of tumor development and progression and the discovery and development of anticancer drugs. In vitro three-dimensional (3D) cell culture can partially simulate in vivo conditions and 3D-cultured cancer cells can recapture many essential features of native tumor tissues. In this study, to mimic the in vivo breast tumor microenvironment, novel reduction-responsive poly(N_ε-acryloyl l-lysine) (pLysAAm) hydrogels were synthesized by rapid photo-polymerization of N_ε-acryloyl l-lysine and using N,N'-bis(acryloyl)-(l)-cystine as a crosslinker, and their physicochemical properties were characterized systemically. The results showed that the pLysAAm hydrogels were formed within 93 s under UV irradiation and exhibited almost total elastic recovery from compressions as high as 75%. The lyophilized hydrogel samples displayed a highly porous structure with interconnected pores, had an equilibrium swelling ratio of about 20, and were degraded faster in a glutathione-containing solution than in PBS solution. The biological versatility of the pLysAAm hydrogels was demonstrated by both in vitro MCF-7 cell culture and in vivo tumor formation. Compared to cells cultured as 2D monolayers, the 3D-cultured cells presented 3D cell morphology, exhibited better cell viability, expressed higher levels of pro-angiogenic factors, and showed significantly greater migration and invasion abilities. The results from assay of tumorigenicity in nude mice and histologic analysis demonstrated the enhanced tumorigenic and angiogenic capabilities of the MCF-7 cells pre-cultured in pLysAAm hydrogels. These findings suggest that pLysAAm hydrogels may be used to bridge the gap between standard in vitro cell cultures and living tissues, aid breast cancer research, and help researchers to develop novel anticancer therapeutics.

Structure-induced nonlinear viscoelasticity of non-woven fibrous matrices

Fibrous materials are widely utilized as tissue engineering scaffolds for tissue regeneration and other bioengineering applications. The structural as well as mechanical characteristics of the fibrous matrices under static and dynamic mechanical loading conditions influence the response of the cells. In this paper, we study the mechanical response of the non-woven fibrous matrices under oscillatory loading conditions and its dependence on the structural properties of fibrous matrix. We demonstrate that under oscillatory shear and elongation, the fibrous matrices demonstrate nonlinear viscoelasticity at all strain amplitudes. This is contrary to the behavior of other soft polymeric materials for which nonlinearity in the viscoelastic response vanishes for small strains. These observations suggest that despite their prevalence, the measures of linear viscoelasticity (e.g., storage and loss moduli) are inadequate for the general description of the viscoelastic nature of the fibrous materials. It was, however, found that linear viscoelastic nature of fibrous matrices for small amplitudes is restored when a pre-stretch is applied to the fibrous matrix along with oscillatory strains. Further, we also explored the influence of the structural properties of the fibrous matrices (fiber orientation, alignment and curvature) on their viscoelastic nature.