Interstitial flow and its effects in soft tissues

Evaporation-Induced Diffusion Acceleration in Liquid-Filled Porous Materials

Liquid-filled porous materials exist widely in nature and engineering fields, with the diffusion of substances in them playing an important role in system functions. Although surface evaporation is often inevitable in practical scenarios, the evaporation effects on diffusion behavior in liquid-filled porous materials have not been well explored yet. In this work, we performed noninvasive diffusion imaging experiments to observe the diffusion process of erioglaucine disodium salt dye in a liquid-filled nitrocellulose membrane under a wide range of relative humidities (RHs). We found that evaporation can significantly accelerate the diffusion rate and alter concentration distribution compared with the case without evaporation. We explained the accelerated diffusion phenomenon by the mechanism that evaporation would induce a weak flow in liquid-filled porous materials, which leads to convective diffusion, i.e., evaporation-induced flow and diffusion (EIFD). Based on the EIFD mechanism, we proposed a convective diffusion model to quantitatively predict the diffusion process in liquid-filled porous materials under evaporation and experimentally validated the model. Introducing the dimensionless Peclet (P _e) number to measure the relative contribution of the evaporation effect to pure molecular diffusion, we demonstrated that even at a high RH of 95%, where the evaporation effect is usually assumed negligible in common sense, the evaporation-induced diffusion still overwhelms the molecular diffusion. The flow velocity induced by evaporation in liquid-filled porous materials was found to be 0.4-5 μm/s, comparable to flow in many biological and biomedical systems. The present analysis may help to explain the driving mechanism of tissue perfusion and provide quantitative analysis or inspire new control methods of flow and material exchange in numerous cutting-edge technologies, such as paper-based diagnostics, hydrogel-based flexible electronics, evaporation-induced electricity generation, and seawater purification.

Macrophage-stroma interactions in fibrosis: biochemical, biophysical, and cellular perspectives

Fibrosis results from aberrant wound healing and is characterized by an accumulation of extracellular matrix, impairing the function of an affected organ. Increased deposition of extracellular matrix proteins, disruption of matrix degradation, but also abnormal post-translational modifications alter the biochemical composition and biophysical properties of the tissue microenvironment - the stroma. Macrophages are known to play an important role in wound healing and tissue repair, but the direct influence of fibrotic stroma on macrophage behaviour is still an under-investigated element in the pathogenesis of fibrosis. In this review, the current knowledge on interactions between macrophages and (fibrotic) stroma will be discussed from biochemical, biophysical, and cellular perspectives. Furthermore, we provide future perspectives with regard to how macrophage-stroma interactions can be examined further to ultimately facilitate more specific targeting of these interactions in the treatment of fibrosis. © 2021 The Authors. The Journal of Pathology published by John Wiley & Sons, Ltd. on behalf of The Pathological Society of Great Britain and Ireland.

Osmotic pressure modulates single cell cycle dynamics inducing reversible growth arrest and reactivation of human metastatic cells

Biophysical cues such as osmotic pressure modulate proliferation and growth arrest of bacteria, yeast cells and seeds. In tissues, osmotic regulation takes place through blood and lymphatic capillaries and, at a single cell level, water and osmoregulation play a critical role. However, the effect of osmotic pressure on single cell cycle dynamics remains poorly understood. Here, we investigate the effect of osmotic pressure on single cell cycle dynamics, nuclear growth, proliferation, migration and protein expression, by quantitative time-lapse imaging of single cells genetically modified with fluorescent ubiquitination-based cell cycle indicator 2 (FUCCI2). Single cell data reveals that under hyperosmotic stress, distinct cell subpopulations emerge with impaired nuclear growth, delayed or growth arrested cell cycle and reduced migration. This state is reversible for mild hyperosmotic stress, where cells return to regular cell cycle dynamics, proliferation and migration. Thus, osmotic pressure can modulate the reversible growth arrest and reactivation of human metastatic cells.

Recent Advances in Tumor Targeting via EPR Effect for Cancer Treatment

Cancer causes the second-highest rate of death world-wide. A major shortcoming inherent in most of anticancer drugs is their lack of tumor selectivity. Nanodrugs for cancer therapy administered intravenously escape renal clearance, are unable to penetrate through tight endothelial junctions of normal blood vessels and remain at a high level in plasma. Over time, the concentration of nanodrugs builds up in tumors due to the EPR effect, reaching several times higher than that of plasma due to the lack of lymphatic drainage. This review will address in detail the progress and prospects of tumor-targeting via EPR effect for cancer therapy.

In-vivoviscoelastic properties estimation in subcutaneous adipose tissue by integration of poroviscoelastic-mass transport model (pve-MTM) into wearable electrical impedance tomography (w-EIT)

In-vivoviscoelastic properties have been estimated in human subcutaneous adipose tissue (SAT) by integration of poroviscoelastic-mass transport model (pve-MTM) into wearable electrical impedance tomography (w-EIT) under the influence of external compressive pressure-P.Thepve-MTM predicts the ion concentration distributioncmod(t)by coupling the poroviscoelastic and mass transport model to describe the hydrodynamics, rheology, and transport phenomena inside SAT. Thew-EIT measures the time-difference conductivity distribution∆γ(t)in SAT resulted from the ion transport. Based on the integration, the two viscoelastic properties which are viscoelastic shear modulus of SATGvand relaxation time of SATτvare estimated by applying an iterative curve-fitting between the normalized average ion concentration distributioncˆmod(t)predicted frompve-MTM and the experimental normalized average ion concentration distributioncˆexp(t)derived fromw-EIT. Thein-vivoexperiments were conducted by applying external compressive pressure-Pon human calf boundary to induce interstitial fluid flow and ion movement in SAT. As a result, the value ofGvwas range from 4.9-6.3 kPa and the value ofτvwas range from 27.50-38.5 s with the value of average goodness-of-fit curve fittingR² > 0.76. These values ofGvandτvwere compared to the human and animal tissue from the literature in order to verify this method. The results frompve-MTM provide evidence thatGvandτvplay a role in the predicted value ofcˆmod.

Electrokinetic Perfusion Through Three-Dimensional Culture Reduces Cell Mortality

Cell proliferation and survival are dependent on mass transfer. In vivo, fluid flow promotes mass transfer through the vasculature and interstitial space, providing a continuous supply of nutrients and removal of cellular waste products. In the absence of sufficient flow, mass transfer is limited by diffusion and poses significant challenges to cell survival during tissue engineering, tissue transplantation, and treatment of degenerative diseases. Artificial perfusion may overcome these challenges. In this work, we compare the efficacy of pressure driven perfusion (PDP) with electrokinetic perfusion (EKP) toward reducing cell mortality in three-dimensional cultures of Matrigel extracellular matrix. We characterize electro-osmotic flow through Matrigel to identify conditions that generate similar interstitial flow rates to those induced by pressure. We also compare changes in cell mortality induced by continuous or pulsed EKP. We report that continuous EKP significantly reduced mortality throughout the perfusion channels more consistently than PDP at similar flow rates, and pulsed EKP decreased mortality just as effectively as continuous EKP. We conclude that EKP has significant advantages over PDP for promoting tissue survival before neovascularization and angiogenesis. Impact statement Interstitial flow helps promote mass transfer and cell survival in tissues and organs. This study generated interstitial flow using pressure driven perfusion (PDP) or electrokinetic perfusion (EKP) to promote cell viability in three-dimensional cultures. EKP through charged extracellular matrices possesses significant advantages over PDP and may promote cell survival during tissue engineering, transplantations, and treatment of degenerative diseases.

Go with the flow: modeling unique biological flows in engineered in vitro platforms

Interest in recapitulating in vivo phenomena in vitro using organ-on-a-chip technology has grown rapidly and with it, attention to the types of fluid flow experienced in the body has followed suit. These platforms offer distinct advantages over in vivo models with regards to human relevance, cost, and control of inputs (e.g., controlled manipulation of biomechanical cues from fluid perfusion). Given the critical role biophysical forces play in several tissues and organs, it is therefore imperative that engineered in vitro platforms capture the complex, unique flow profiles experienced in the body that are intimately tied with organ function. In this review, we outline the complex and unique flow regimes experienced by three different organ systems: blood vasculature, lymphatic vasculature, and the intestinal system. We highlight current state-of-the-art platforms that strive to replicate physiological flows within engineered tissues while introducing potential limitations in current approaches.

Evidence for continuity of interstitial spaces across tissue and organ boundaries in humans

Bodies have continuous reticular networks, comprising collagens, elastin, glycosaminoglycans, and other extracellular matrix components, through all tissues and organs. Fibrous coverings of nerves and blood vessels create structural continuity beyond organ boundaries. We recently validated fluid flow through human fibrous tissues, though whether these interstitial spaces are continuous through the body or discontinuous, confined within individual organs, remains unclear. Here we show evidence for continuity of interstitial spaces using two approaches. Non-biological particles (tattoo pigment, colloidal silver) were tracked within colon and skin interstitial spaces and into adjacent fascia. Hyaluronic acid, a macromolecular component of interstitial spaces, was also visualized. Both techniques demonstrate interstitial continuity within and between organs including within perineurium and vascular adventitia traversing organs and the spaces between them. We suggest that there is a body-wide network of fluid-filled interstitial spaces that has significant implications for molecular signaling, cell trafficking, and the spread of malignant and infectious disease.

Engineering Vascularized Organoid-on-a-Chip Models

Recreating human organ-level function in vitro is a rapidly evolving field that integrates tissue engineering, stem cell biology, and microfluidic technology to produce 3D organoids. A critical component of all organs is the vasculature. Herein, we discuss general strategies to create vascularized organoids, including common source materials, and survey previous work using vascularized organoids to recreate specific organ functions and simulate tumor progression. Vascularization is not only an essential component of individual organ function but also responsible for coupling the fate of all organs and their functions. While some success in coupling two or more organs together on a single platform has been demonstrated, we argue that the future of vascularized organoid technology lies in creating organoid systems complete with tissue-specific microvasculature and in coupling multiple organs through a dynamic vascular network to create systems that can respond to changing physiological conditions.

Effect of Acoustic Radiation Force on the Distribution of Nanoparticles in Solid Tumors

Acoustic radiation force (ARF) might improve the distribution of nanoparticles (NPs) in tumors. To study this, tumors growing subcutaneously in mice were exposed to focused ultrasound (FUS) either 15 min or 4 h after the injection of NPs, to investigate the effect of ARF on the transport of NPs across the vessel wall and through the extracellular matrix. Quantitative analysis of confocal microscopy images from frozen tumor sections was performed to estimate the displacement of NPs from blood vessels. Using the same experimental exposure parameters, ARF was simulated and compared with the experimental data. Enhanced interstitial transport of NPs in tumor tissues was observed when FUS (10 MHz, acoustic power 234 W/cm², 3.3% duty cycle) was given either 15 min or 4 h after NP administration. According to acoustic simulations, the FUS generated an ARF per unit volume of 2.0×10⁶ N/m³. The displacement of NPs was larger when FUS was applied 4 h after NP injection compared with after 15 min. This study shows that ARF might contribute to a modest improved distribution of NPs into the tumor interstitium.

Effect of Acoustic Radiation Force on Displacement of Nanoparticles in Collagen Gels

Penetration of nanoscale therapeutic agents into the extracellular matrix (ECM) of a tumor is a limiting factor for the sufficient delivery of drugs in tumors. Ultrasound (US) in combination with microbubbles causing cavitation is reported to improve delivery of nanoparticles (NPs) and drugs to tumors. Acoustic radiation force (ARF) could also enhance the penetration of NPs in tumor ECM. In this work, a collagen gel was used as a model for tumor ECM to study the effects of ARF on the penetration of NPs as well as the deformation of collagen gels applying different US parameters (varying pressure and duty cycle). The collagen gel was characterized, and the diffusion of water and NPs was measured. The penetration of NPs into the gel was measured by confocal laser scanning microscopy and numerical simulations were performed to determine the ARF and to estimate the penetration distance and extent of deformation. ARF had no effect on the penetration of NPs into the collagen gels for the US parameters and gel used, whereas a substantial deformation was observed. The width of the deformation on the collagen gel surface corresponded to the US beam. Comparing ARF caused by attenuation within the gel and Langevin pressure caused by reflection at the gel-water surface, ARF was the prevalent mechanism for the gel deformation. The experimental and theoretical results were consistent both with respect to the NP penetration and the gel deformation.

A 3D human adipose tissue model within a microfluidic device

An accurate in vitro model of human adipose tissue could assist in the study of adipocyte function and allow for better tools for screening new therapeutic compounds. Cell culture models on two-dimensional surfaces fall short of mimicking the three-dimensional in vivo adipose environment, while three-dimensional culture models are often unable to support long-term cell culture due, in part, to insufficient mass transport. Microfluidic systems have been explored for adipose tissue models. However, current systems have primarily focused on 2D cultured adipocytes. In this work, a 3D human adipose microtissue was engineered within a microfluidic system. Human adipose-derived stem cells (ADSCs) were used as the cell source for generating differentiated adipocytes. The ADSCs differentiated within the microfluidic system formed a dense lipid-loaded mass with the expression of adipose tissue genetic markers. Engineered adipose tissue showed a decreased adiponectin secretion and increased free fatty acid secretion with increasing shear stress. Adipogenesis markers were downregulated with increasing shear stress. Overall, this microfluidic system enables the on-chip differentiation and development of a functional 3D human adipose microtissue supported by the interstitial flow. This system could potentially serve as a platform for in vitro drug testing for adipose tissue-related diseases.

Mammographic density as an image-based biomarker of therapy response in neoadjuvant-treated breast cancer patients

Purpose

Personalized cancer treatment requires predictive biomarkers, including image-based biomarkers. Breast cancer (BC) patients receiving neoadjuvant chemotherapy (NACT) are in a clinically vulnerable situation with the tumor present. This study investigated whether mammographic density (MD), assessed pre-NACT, is predictive of pathological complete response (pCR).

Methods

A total of 495 BC patients receiving NACT in Sweden 2005–2019 were included, merged from two different cohorts. Cohort 1 was retrospectively collected (n = 295) and cohort 2 was prospectively collected (n = 200). Mammograms were scored for MD pre-NACT according to the Breast Imaging-Reporting and Data System (BI-RADS), 5th Edition. The association between MD and accomplishing pCR post-NACT was analyzed using logistic regression models—for the whole cohort, stratified by menopausal status, and in different St. Gallen surrogate subtypes.

Results

In comparison to patients with low MD (BI-RADS a), the multivariable-adjusted odds ratio (OR) of accomplishing pCR following NACT was on a descending scale: 0.62 (95% confidence interval (CI) 0.24–1.57), 0.38 (95% CI 0.14–1.02), and 0.32 (95% CI 0.09–1.08) for BI-RADS b, c, and d, respectively. For premenopausal patients selectively, the corresponding point estimates were lower, although wider CIs: 0.31 (95% CI 0.06–1.62), 0.24 (95% CI 0.04–1.27), and 0.13 (95% CI 0.02–0.88). Subgroup analyses based on BC subtypes resulted in imprecise estimates, i.e., wide CIs.

Conclusions

It seemed as though patients with higher MD at baseline were less likely to reach pCR after NACT—a finding more pronounced in premenopausal women. Larger multicenter studies are needed to enable analyses and interpretation for different BC subtypes.

Supplementary Information

The online version of this article (10.1007/s10552-020-01379-w) contains supplementary material, which is available to authorized users.

Patterning Biological Gels for 3D Cell Culture inside Microfluidic Devices by Local Surface Modification through Laminar Flow Patterning

Microfluidic devices are used extensively in the development of new in vitro cell culture models like organs-on-chips. A typical feature of such devices is the patterning of biological hydrogels to offer cultured cells and tissues a controlled three-dimensional microenvironment. A key challenge of hydrogel patterning is ensuring geometrical confinement of the gel, which is generally solved by inclusion of micropillars or phaseguides in the channels. Both of these methods often require costly cleanroom fabrication, which needs to be repeated even when only small changes need be made to the gel geometry, and inadvertently expose cultured cells to non-physiological and mechanically stiff structures. Here, we present a technique for facile patterning of hydrogel geometries in microfluidic chips, but without the need for any confining geometry built into the channel. Core to the technique is the use of laminar flow patterning to create a hydrophilic path through an otherwise hydrophobic microfluidic channel. When a liquid hydrogel is injected into the hydrophilic region, it is confined to this path by the surrounding hydrophobic regions. The various surface patterns that are enabled by laminar flow patterning can thereby be rendered into three-dimensional hydrogel structures. We demonstrate that the technique can be used in many different channel geometries while still giving the user control of key geometric parameters of the final hydrogel. Moreover, we show that human umbilical vein endothelial cells can be cultured for multiple days inside the devices with the patterned hydrogels and that they can be stimulated to migrate into the gel under the influence of trans-gel flows. Finally, we demonstrate that the patterned gels can withstand trans-gel flow velocities in excess of physiological interstitial flow velocities without rupturing or detaching. This novel hydrogel-patterning technique addresses fundamental challenges of existing methods for hydrogel patterning inside microfluidic chips, and can therefore be applied to improve design time and the physiological realism of microfluidic cell culture assays and organs-on-chips.

Tissue Failure Propagation as Mediated by Circulatory Flow

Aging is driven by subcellular processes that are relatively well understood. However, the qualitative mechanisms and quantitative dynamics of how these micro-level failures cascade to a macro-level catastrophe in a tissue or organs remain largely unexplored. Here, we experimentally and theoretically study how cell failure propagates in an engineered tissue in the presence of advective flow. We argue that cells secrete cooperative factors, thereby forming a network of interdependence governed by diffusion and flow, which fails with a propagating front parallel to advective circulation.

The effects of luminal and trans-endothelial fluid flows on the extravasation and tissue invasion of tumor cells in a 3D in vitro microvascular platform

Throughout the process of metastatic dissemination, tumor cells are continuously subjected to mechanical forces resulting from complex fluid flows due to changes in pressures in their local microenvironments. While these forces have been associated with invasive phenotypes in 3D matrices, their role in key steps of the metastatic cascade, namely extravasation and subsequent interstitial migration, remains poorly understood. In this study, an in vitro model of the human microvasculature was employed to subject tumor cells to physiological luminal, trans-endothelial, and interstitial flows to evaluate their effects on those key steps of metastasis. Luminal flow promoted the extravasation potential of tumor cells, possibly as a result of their increased intravascular migration speed. Trans-endothelial flow increased the speed with which tumor cells transmigrated across the endothelium as well as their migration speed in the matrix following extravasation. In addition, tumor cells possessed a greater propensity to migrate in close proximity to the endothelium when subjected to physiological flows, which may promote the successful formation of metastatic foci. These results show important roles of fluid flow during extravasation and invasion, which could determine the local metastatic potential of tumor cells.

Probability of Immobilization on Host Cell Surface Regulates Viral Infectivity

The efficiency of a virus to establish its infection in host cells varies broadly among viruses. It remains unclear if there is a key step in this process that controls viral infectivity. To address this question, we use single-particle tracking and Brownian dynamics simulation to examine human immunodeficiency virus type 1 (HIV-1) infection in cell culture. We find that the frequency of viral-cell encounters is consistent with diffusion-limited interactions. However, even under the most favorable conditions, only 1% of the viruses can become immobilized on cell surface and subsequently enter the cell. This is a result of weak interaction between viral surface gp120 and CD4 receptor, which is insufficient to form a stable complex the majority of the time. We provide the first direct quantitation for efficiencies of these events relevant to measured HIV-1 infectivity and demonstrate that immobilization on host cell surface post-virion-diffusion is the key step in viral infection. Variation of its probability controls the efficiency of a virus to infect its host cells. These results explain the low infectivity of cell-free HIV-1 in vitro and offer a potential rationale for the pervasive high efficiency of cell-to-cell transmission of animal viruses.

Patient-Specific Characterization of Breast Cancer Hemodynamics Using Image-Guided Computational Fluid Dynamics

The overall goal of this study is to employ quantitative magnetic resonance imaging (MRI) data to constrain a patient-specific, computational fluid dynamics (CFD) model of blood flow and interstitial transport in breast cancer. We develop image processing methodologies to generate tumor-related vasculature-interstitium geometry and realistic material properties, using dynamic contrast enhanced MRI (DCE-MRI) and diffusion weighted MRI (DW-MRI) data. These data are used to constrain CFD simulations for determining the tumor-associated blood supply and interstitial transport characteristics unique to each patient. We then perform a proof-of-principle statistical comparison between these hemodynamic characteristics in 11 malignant and 5 benign lesions from 12 patients. Significant differences between groups (i.e., malignant versus benign) were observed for the median of tumor-associated interstitial flow velocity ( P = 0.028 ), and the ranges of tumor-associated blood pressure (P = 0.016) and vascular extraction rate (P = 0.040). The implication is that malignant lesions tend to have larger magnitude of interstitial flow velocity, and higher heterogeneity in blood pressure and vascular extraction rate. Multivariable logistic models based on combinations of these hemodynamic data achieved excellent differentiation between malignant and benign lesions with an area under the receiver operator characteristic curve of 1.0, sensitivity of 1.0, and specificity of 1.0. This image-based model system is a fundamentally new way to map flow and pressure fields related to breast tumors using only non-invasive, clinically available imaging data and established laws of fluid mechanics. Furthermore, the results provide preliminary evidence for this methodology's utility for the quantitative characterization of breast cancer.

Angiographic biomarkers of filtering bleb function after XEN gel implantation for glaucoma: an optical coherence tomography-angiography study

PURPOSE

To evaluate, using optical coherence tomography-angiography (OCT-A), the vascular features of good bleb function after XEN gel implantation (XGI) for uncontrolled glaucoma.

METHODS

Forty-three patients (43 eyes), who underwent XGI, were enrolled. According to the intraocular pressure (IOP) reduction, patients were classified into Group 1 (21 eyes; success) and Group 2 (22 eyes; failure). Optical coherence tomography-angiography (OCT-A) was performed to image the vascularization of the conjunctival bleb-wall. The main outcomes were as follows: vessel displacement areas (VDAs), major vessel displacement area (MVDA; mm2 ), non-flow whole area (NFWA; mm2 ) and bleb-wall vessel density (BVD; %). Co-registered B-scans were also considered to evaluate the bleb-wall cyst-like structure density and area (BCSD, cysts/mm2 ; BCSA, mm2 ), and the bleb-wall thickness (BT, µm).

RESULTS

Mean postoperative follow-up was 7.5 ± 0.14 months; Group 1 and 2 IOP were 14.0 ± 2.5 and 25.3 ± 2.1 mmHg, respectively (p < 0.001). Greater VDA (p < 0.001), MVDA (p = 0.046) and NFWA (p = 0.001) values, and lower BVD (p < 0.001) was found in Group 1 compared to Group 2. Group 1 showed higher BSCD, BSCA and BT values compared to Group 2 (p < 0.001). Postoperative IOP positively correlated with BVD (r = 0.567; p = 0.003), but negatively with VDAs, MVDA (r = -0.581, p = 0.002; r = -0.619, p = 0.001, respectively), BCSD, BCSA (r = -0.580; p = 0.002; r = -0.664; p < 0.001) and BT (r = -0.627, p = 0.001).

CONCLUSION

Successful filtration blebs after XGI present numerous and large areas of vessel displacement within the bleb-wall, along with a rarefied vascular network. These OCT-A features can be considered angiographic biomarkers of a good aqueous humour percolation through the bleb-wall layers.

Controlled anti-cancer drug release through advanced nano-drug delivery systems: Static and dynamic targeting strategies

Advances in nanomedicine, including early cancer detection, targeted drug delivery, and personalized approaches to cancer treatment are on the rise. For example, targeted drug delivery systems can improve intracellular delivery because of their multifunctionality. Novel endogenous-based and exogenous-based stimulus-responsive drug delivery systems have been proposed to prevent the cancer progression with proper drug delivery. To control effective dose loading and sustained release, targeted permeability and individual variability can now be described in more-complex ways, such as by combining internal and external stimuli. Despite these advances in release control, certain challenges remain and are identified in this research, which emphasizes the control of drug release and applications of nanoparticle-based drug delivery systems. Using a multiscale and multidisciplinary approach, this study investigates and analyzes drug delivery and release strategies in the nanoparticle-based treatment of cancer, both mathematically and clinically.

ECM-based microfluidic gradient generator for tunable surface environment by interstitial flow

We present an extracellular matrix (ECM)-based gradient generator that provides a culture surface with continuous chemical concentration gradients created by interstitial flow. The gelatin-based microchannels harboring gradient generators and in-channel micromixers were rapidly fabricated by sacrificial molding of a 3D-printed water-soluble sacrificial mold. When fluorescent dye solutions were introduced into the channel, the micromixers enhanced mixing of two solutions joined at the junction. Moreover, the concentration gradients generated in the channel diffused to the culture surface of the device through the interstitial space facilitated by the porous nature of the ECM. To check the functionality of the gradient generator for investigating cellular responses to chemical factors, we demonstrated that human umbilical vein endothelial cells cultured on the surface shrunk in response to the concentration gradient of histamine generated by interstitial flow from the microchannel. We believe that our device could be useful for the basic biological study of the cellular response to chemical stimuli and for the in vitro platform in drug testing.

The Importance of Mechanical Forces for in vitro Endothelial Cell Biology

Blood and lymphatic vessels are lined by endothelial cells which constantly interact with their luminal and abluminal extracellular environments. These interactions confer physical forces on the endothelium, such as shear stress, stretch and stiffness, to mediate biological responses. These physical forces are often altered during disease, driving abnormal endothelial cell behavior and pathology. Therefore, it is critical that we understand the mechanisms by which endothelial cells respond to physical forces. Traditionally, endothelial cells in culture are grown in the absence of flow on stiff substrates such as plastic or glass. These cells are not subjected to the physical forces that endothelial cells endure in vivo, thus the results of these experiments often do not mimic those observed in the body. The field of vascular biology now realize that an intricate analysis of endothelial signaling mechanisms requires complex in vitro systems to mimic in vivo conditions. Here, we will review what is known about the mechanical forces that guide endothelial cell behavior and then discuss the advancements in endothelial cell culture models designed to better mimic the in vivo vascular microenvironment. A wider application of these technologies will provide more biologically relevant information from cultured cells which will be reproducible to conditions found in the body.

Tumor spheroids under perfusion within a 3D microfluidic platform reveal critical roles of cell-cell adhesion in tumor invasion

Tumor invasion within the interstitial space is critically regulated by the force balance between cell-extracellular matrix (ECM) and cell-cell interactions. Interstitial flows (IFs) are present in both healthy and diseased tissues. However, the roles of IFs in modulating cell force balance and subsequently tumor invasion are understudied. In this article, we develop a microfluidic model in which tumor spheroids are embedded within 3D collagen matrices with well-defined IFs. Using co-cultured tumor spheroids (1:1 mixture of metastatic and non-tumorigenic epithelial cells), we show that IFs downregulate the cell-cell adhesion molecule E-cadherin on non-tumorigenic cells and promote tumor invasion. Our microfluidic model advances current tumor invasion assays towards a more physiologically realistic model using tumor spheroids instead of single cells under perfusion. We identify a novel mechanism by which IFs can promote tumor invasion through an influence on cell-cell adhesion within the tumor and highlight the importance of biophysical parameters in regulating tumor invasion.

Microfluidics for the study of mechanotransduction

Mechanical forces regulate a diverse set of biological processes at cellular, tissue, and organismal length scales. Investigating the cellular and molecular mechanisms that underlie the conversion of mechanical forces to biological responses is challenged by limitations of traditional animal models and in vitro cell culture, including poor control over applied force and highly artificial cell culture environments. Recent advances in fabrication methods and material processing have enabled the development of microfluidic platforms that provide precise control over the mechanical microenvironment of cultured cells. These devices and systems have proven to be powerful for uncovering and defining mechanisms of mechanotransduction. In this review, we first give an overview of the main mechanotransduction pathways that function at sites of cell adhesion, many of which have been investigated with microfluidics. We then discuss how distinct microfluidic fabrication methods can be harnessed to gain biological insight, with description of both monolithic and replica molding approaches. Finally, we present examples of how microfluidics can be used to apply both solid forces (substrate mechanics, strain, and compression) and fluid forces (luminal, interstitial) to cells. Throughout the review, we emphasize the advantages and disadvantages of different fabrication methods and applications of force in order to provide perspective to investigators looking to apply forces to cells in their own research.

Targeted antibody and cytokine cancer immunotherapies through collagen affinity

Cancer immunotherapy with immune checkpoint inhibitors (CPIs) and interleukin-2 (IL-2) has demonstrated clinical efficacy but is frequently accompanied with severe adverse events caused by excessive and systemic immune system activation. Here, we addressed this need by targeting both the CPI antibodies anti-cytotoxic T lymphocyte antigen 4 antibody (αCTLA4) + anti-programmed death ligand 1 antibody (αPD-L1) and the cytokine IL-2 to tumors via conjugation (for the antibodies) or recombinant fusion (for the cytokine) to a collagen-binding domain (CBD) derived from the blood protein von Willebrand factor (VWF) A3 domain, harnessing the exposure of tumor stroma collagen to blood components due to the leakiness of the tumor vasculature. We show that intravenously administered CBD protein accumulated mainly in tumors. CBD conjugation or fusion decreases the systemic toxicity of both αCTLA4 + αPD-L1 combination therapy and IL-2, for example, eliminating hepatotoxicity with the CPI molecules and ameliorating pulmonary edema with IL-2. Both CBD-CPI and CBD-IL-2 suppressed tumor growth compared to their unmodified forms in multiple murine cancer models, and both CBD-CPI and CBD-IL-2 increased tumor-infiltrating CD8⁺ T cells. In an orthotopic breast cancer model, combination treatment with CPI and IL-2 eradicated tumors in 9 of 13 animals with the CBD-modified drugs, whereas it did so in only 1 of 13 animals with the unmodified drugs. Thus, the A3 domain of VWF can be used to improve safety and efficacy of systemically administered tumor drugs with high translational promise.

Lymphology and translational medicine

Lymphology is evolving in search of a better management of lymphedema patients, both as to the diagnostic pathway and as to the therapeutic options. Similarly, lymphatic system is involved in a wide spectrum of pathophysiologic processes of most chronic degenerative diseases. Translational medicine integrates the interdisciplinary scientific knowledge to improve diagnostic and therapeutic options in the biomedical field. Inflammation and lymphatic function are regarded as the connecting biochemical factors in most diseases. This review focuses on the scientific publications regarding lymphatic system in connection to psycho-neuroendocrine immunology, hormesis, epigenetics and more generally nutrition and lifestyle. The interaction between lymphology and translational medicine may play a relevant role to improve management of lymphedema on the one hand, and of chronic degenerative diseases on the other.

Interpreting In Vitro Release Performance from Long-Acting Parenteral Nanosuspensions Using USP-4 Dissolution and Spectroscopic Techniques

Injectable sustained release dosage forms have emerged as desirable therapeutic routes for patients that require life-long treatments. The prevalence of drug molecules with low aqueous solubility and bioavailability has added momentum toward the development of suspension-based long-acting parenteral (LAP) formulations; the previously undesirable physicochemical properties of Biopharmaceutics Classification System (BCS) Class II/IV compounds are best suited for extended release applications. Effective in vitro release (IVR) testing of crystalline suspensions affirms product quality during early-stage development and provides connections with in vivo performance. However, before in vitro-in vivo correlations (IVIVCs) can be established, it is necessary to evaluate formulation attributes that directly affect IVR properties. In this work, a series of crystalline LAP nanosuspensions were formulated with different stabilizing polymers and applied to a continuous flow-through (USP-4) dissolution method. This technique confirmed the role of salt effects on the stability of polymer-coated nanoparticles through the detection of disparate active pharmaceutical ingredient (API) release profiles. The polymer stabilizers with extended hydrophilic chains exhibited elevated intrapolymer activity from the loss of hydrogen-bond cushioning in dissolution media with heightened ionic strength, confirmed through one-dimensional (1D) ¹H NMR and two-dimensional nuclear Overhauser effect spectroscopy (2D NOESY) experiments. Thus, steric repulsion within the affected nanosuspensions was limited and release rates decreased. Additionally, the strength of interaction between hydrophobic polymer components and the API crystalline surface contributed to suspension dissolution properties, confirmed through solution- and solid-state spectroscopic analyses. This study provides a unique perspective on the dynamic interface between the crystalline drug and aqueous microenvironment during dissolution.

Numerical optimization of plasmid DNA delivery combined with hyaluronidase injection for electroporation protocol

BACKGROUND AND OBJECTIVE

The paper focuses on the numerical strategies to optimize a plasmid DNA delivery protocol, which combines hyaluronidase and electroporation.

METHODS

A well-defined continuum mechanics model of muscle porosity and advanced numerical optimization strategies have been used, to propose a substantial improvement of a pre-existing experimental protocol of DNA transfer in mice. Our work suggests that a computational model might help in the definition of innovative therapeutic procedures, thanks to the fine tuning of all the involved experimental steps. This approach is particularly interesting in optimizing complex and costly protocols, to make in vivo DNA therapeutic protocols more effective.

RESULTS

Our preliminary work suggests that computational model might help in the definition of innovative therapeutic protocol, thanks to the fine tuning of all the involved operations.

CONCLUSIONS

This approach is particularly interesting in optimizing complex and costly protocols for which the number of degrees of freedom prevents a experimental test of the possible configuration.

Recellularized Colorectal Cancer Patient-derived Scaffolds as in vitro Pre-clinical 3D Model for Drug Screening

Colorectal cancer (CRC) shows highly ineffective therapeutic management. An urgent unmet need is the random assignment to adjuvant chemotherapy of high-risk stage II and stage III CRC patients without any predictive factor of efficacy. In the field of drug discovery, a critical step is the preclinical evaluation of drug cytotoxicity, efficacy, and efficiency. We proposed a patient-derived 3D preclinical model for drug evaluation that could mimic in vitro the patient's disease. Surgically resected CRC tissue and adjacent healthy colon mucosa were decellularized by a detergent-enzymatic treatment. Scaffolds were recellularized with HT29 and HCT116 cells. Qualitative and quantitative characterization of matched recellularized samples were evaluated through histology, immunofluorescences, scanning electron microscopy, and DNA amount quantification. A chemosensitivity test was performed using an increasing concentration of 5-fluorouracil (5FU). In vivo studies were carried out using zebrafish (Danio rerio) animal model. Permeability test and drug absorption were also determined. The decellularization protocol allowed the preservation of the original structure and ultrastructure. Five days after recellularization with HT29 and HCT116 cell lines, the 3D CRC model exhibited reduced sensitivity to 5FU treatments compared with conventional 2D cultures. Calculated the half maximal inhibitory concentration (IC50) for HT29 treated with 5FU resulted in 11.5 µM in 3D and 1.3 µM in 2D, and for HCT116, 9.87 µM in 3D and 1.7 µM in 2D. In xenograft experiments, HT29 extravasation was detected after 4 days post-injection, and we obtained a 5FU IC50 fully comparable to that observed in the 3D CRC model. Using confocal microscopy, we demonstrated that the drug diffused through the repopulated 3D CRC scaffolds and co-localized with the cell nuclei. The bioengineered CRC 3D model could be a reliable preclinical patient-specific platform to bridge the gap between in vitro and in vivo drug testing assays and provide effective cancer treatment.

Photodynamic Therapy and the Biophysics of the Tumor Microenvironment

Targeting the tumor microenvironment (TME) provides opportunities to modulate tumor physiology, enhance the delivery of therapeutic agents, impact immune response and overcome resistance. Photodynamic therapy (PDT) is a photochemistry-based, nonthermal modality that produces reactive molecular species at the site of light activation and is in the clinic for nononcologic and oncologic applications. The unique mechanisms and exquisite spatiotemporal control inherent to PDT enable selective modulation or destruction of the TME and cancer cells. Mechanical stress plays an important role in tumor growth and survival, with increasing implications for therapy design and drug delivery, but remains understudied in the context of PDT and PDT-based combinations. This review describes pharmacoengineering and bioengineering approaches in PDT to target cellular and noncellular components of the TME, as well as molecular targets on tumor and tumor-associated cells. Particular emphasis is placed on the role of mechanical stress in the context of targeted PDT regimens, and combinations, for primary and metastatic tumors.

Liver Bioreactor Design Issues of Fluid Flow and Zonation, Fibrosis, and Mechanics: A Computational Perspective

Tissue engineering, with the goal of repairing or replacing damaged tissue and organs, has continued to make dramatic science-based advances since its origins in the late 1980’s and early 1990’s. Such advances are always multi-disciplinary in nature, from basic biology and chemistry through physics and mathematics to various engineering and computer fields. This review will focus its attention on two topics critical for tissue engineering liver development: (a) fluid flow, zonation, and drug screening, and (b) biomechanics, tissue stiffness, and fibrosis, all within the context of 3D structures. First, a general overview of various bioreactor designs developed to investigate fluid transport and tissue biomechanics is given. This includes a mention of computational fluid dynamic methods used to optimize and validate these designs. Thereafter, the perspective provided by computer simulations of flow, reactive transport, and biomechanics responses at the scale of the liver lobule and liver tissue is outlined, in addition to how bioreactor-measured properties can be utilized in these models. Here, the fundamental issues of tortuosity and upscaling are highlighted, as well as the role of disease and fibrosis in these issues. Some idealized simulations of the effects of fibrosis on lobule drug transport and mechanics responses are provided to further illustrate these concepts. This review concludes with an outline of some practical applications of tissue engineering advances and how efficient computational upscaling techniques, such as dual continuum modeling, might be used to quantify the transition of bioreactor results to the full liver scale.

The immediate effects of kinesiology taping on cutaneous blood flow in healthy humans under resting conditions: A randomised controlled repeated-measures laboratory study

BACKGROUND

Kinesiology taping (KT) is used in musculoskeletal practice for preventive and rehabilitative purposes. It is claimed that KT improves blood flow in the microcirculation by creating skin convolutions and that this reduces swelling and facilitates healing of musculoskeletal injuries. There is a paucity of physiological studies evaluating the effect of KT on cutaneous blood microcirculation.

OBJECTIVES

The purpose of this parallel-group controlled laboratory repeated measures design study was to evaluate the effects of KT on cutaneous blood microcirculation in healthy human adults using a dual wavelength (infrared and visible-red) laser Doppler Imaging (LDI) system. KT was compared with rigid taping and no taping controls to isolate the effects associated with the elasticity of KT.

METHODS

Forty-five healthy male and female human adults were allocated to one of the three interventions using constrained randomisation following the pre-intervention measurement: (i) KT (ii) ST (standard taping) (iii) NT (no taping). Cutaneous blood perfusion was measured using LDI in the ventral surface of forearm at pre-intervention, during-intervention and post-intervention in a normothermic environment at resting conditions.

RESULTS

Mixed ANOVA of both infrared and visible-red datasets revealed no statistically significant interaction between Intervention and Time. There was statistically significant main effect for Time but not Intervention.

CONCLUSION

KT does not increase cutaneous blood microcirculation in healthy human adults under resting physiological conditions in a normothermic environment. On the contrary, evidence suggests that taping, regardless of the elasticity in the tape, is associated with immediate reductions in cutaneous blood flow.

Poroelasticity of (bio)polymer networks during compression: theory and experiment

Soft living tissues like cartilage can be considered as biphasic materials comprising a fibrous complex biopolymer network and a viscous background liquid. Here, we show by a combination of experiment and theoretical analysis that both the hydraulic permeability and the elastic properties of (bio)polymer networks can be determined with simple ramp compression experiments in a commercial rheometer. In our approximate closed-form solution of the poroelastic equations of motion, we find the normal force response during compression as a combination of network stress and fluid pressure. Choosing fibrin as a biopolymer model system with controllable pore size, measurements of the full time-dependent normal force during compression are found to be in excellent agreement with the theoretical calculations. The inferred elastic response of large-pore (μm) fibrin networks depends on the strain rate, suggesting a strong interplay between network elasticity and fluid flow. Phenomenologically extending the calculated normal force into the regime of nonlinear elasticity, we find strain-stiffening of small-pore (sub-μm) fibrin networks to occur at an onset average tangential stress at the gel-plate interface that depends on the polymer concentration in a power-law fashion. The inferred permeability of small-pore fibrin networks scales approximately inverse squared with the fibrin concentration, implying with a microscopic cubic lattice model that the number of protofibrils per fibrin fiber cross-section decreases with protein concentration. Our theoretical model provides a new method to obtain the hydraulic permeability and the elastic properties of biopolymer networks and hydrogels with simple compression experiments, and paves the way to study the relation between fluid flow and elasticity in biopolymer networks during dynamical compression.

Integrated Biophysical Characterization of Fibrillar Collagen-Based Hydrogels

This paper describes an experimental characterization scheme of the biophysical properties of reconstituted hydrogel matrices based on indentation testing, quantification of transport via microfluidics, and confocal reflectance microscopy analysis. While methods for characterizing hydrogels exist and are widely used, they often do not measure diffusive and convective transport concurrently, determine the relationship between microstructure and transport properties, and decouple matrix mechanics and transport properties. Our integrated approach enabled independent and quantitative measurements of the structural, mechanical, and transport properties of hydrogels in a single study. We used fibrillar type I collagen as the base matrix and investigated the effects of two different matrix modifications: (1) cross-linking with human recombinant tissue transglutaminase II (hrTGII) and (2) supplementation with the nonfibrillar matrix constituent hyaluronic acid (HA). hrTGII modified the matrix structure and transport but not mechanical parameters. Furthermore, changes in the matrix structure due to hrTGII were seen to be dependent on the concentration of collagen. In contrast, supplementation of HA at different collagen concentrations altered the matrix microstructure and mechanical indentation behavior but not transport parameters. These experimental observations reveal the important relationship between extracellular matrix (ECM) composition and biophysical properties. The integrated techniques are versatile, robust, and accessible; and as matrix-cell interactions are instrumental for many biological processes, the methods and findings described here should be broadly applicable for characterizing hydrogel materials used for three-dimensional (3-D) tissue-engineered culture models.

A mechanobiological model to study upstream cell migration guided by tensotaxis

Cell migration is a process of crucial importance for the human body. It is responsible for important processes such as wound healing and tumor metastasis. Migration may occur in response to stimuli of chemical, physical and mechanical nature occurring in the cellular microenvironment. The interstitial flow (IF) can generate mechanical stimuli in cells that influence the cell behavior and interactions of the cells with the extracellular matrix (ECM). One of the phenomena is upstream migration, which is observed in some tumors. In this work, we present a new approach to study the adherent cell migration in a porous medium using a mechanobiological model, attempting to understand if upstream migration can be generated exclusively by mechanical factors. The influence of IF on the behavior of cells and the extracellular matrix was considered. The model is based on a system of coupled nonlinear differential equations solved by the finite element method. Several simulations were performed to study the upstream cell migration and evaluate the effects of pressure, permeability, ECM stiffness and cellular concentration variations on the cell velocity. The results indicated that upstream migration can occur in the presence of mechanical stimuli generated by IF and that the tested parameters have a direct influence on the cellular velocity, especially the pressure and the permeability.

Fluids and their mechanics in tumour transit: shaping metastasis

Metastasis is a dynamic succession of events involving the dissemination of tumour cells to distant sites within the body, ultimately reducing the survival of patients with cancer. To colonize distant organs and, therefore, systemically disseminate within the organism, cancer cells and associated factors exploit several bodily fluid systems, which provide a natural transportation route. Indeed, the flow mechanics of the blood and lymphatic circulatory systems can be co-opted to improve the efficiency of cancer cell transit from the primary tumour, extravasation and metastatic seeding. Flow rates, vessel size and shear stress can all influence the survival of cancer cells in the circulation and control organotropic seeding patterns. Thus, in addition to using these fluids as a means to travel throughout the body, cancer cells exploit the underlying physical forces within these fluids to successfully seed distant metastases. In this Review, we describe how circulating tumour cells and tumour-associated factors leverage bodily fluids, their underlying forces and imposed stresses during metastasis. As the contribution of bodily fluids and their mechanics raises interesting questions about the biology of the metastatic cascade, an improved understanding of this process might provide a new avenue for targeting cancer cells in transit.

A microfluidic platform culturing two cell lines paralleled under in-vivo like fluidic microenvironment for testing the tumor targeting of nanoparticles

Nanoparticles are attractive in medicine because their surfaces can be chemically modified for targeting specific disease cells, especially for cancer. Providing an in-vivo like platform is crucial to evaluate the biological behaviours of nanoparticles. This paper presents a microfluidic device that could culture two cell lines in parallel in in-vivo like fluidic microenvironments and be used for testing the tumor targeting of folic acid - cholesterol - chitosan (FACC) nanoparticles. The uniformity and uniformity of flow fields inside the cell culture units are investigated using the finite element method and particle tracking technology. HeLa and A549 cells are cultured in the microfluidic chip under continuous media supplementation, mimicking the fluid microenvironment in vivo. Cell introducing processes are presented by the flow behaviours of inks with different colours. The two cell lines are identified by detecting folate receptors on the cellular membranes. The growth curves of the two cell lines are measured. The two cell lines cultured paralleled inside the microfluidic device are treated with FITC-FACC to investigate the targeting of FACC. The tumor targeting of FACC are also detected by in vivo imaging of HeLa cells growth in nude mice models. The results indicate that the microfluidic device could provide a dynamic, uniform and stable fluidic microenvironment to test the tumor targeting of FACC nanoparticles.

Mammographic density is a potential predictive marker of pathological response after neoadjuvant chemotherapy in breast cancer

Background

Our aim is to study if mammographic density (MD) prior to neoadjuvant chemotherapy is a predictive factor in accomplishing a pathological complete response (pCR) in neoadjuvant-treated breast cancer patients.

Methods

Data on all neoadjuvant treated breast cancer patients in Southern Sweden (2005–2016) were retrospectively identified, with patient and tumor characteristics retrieved from their medical charts. Diagnostic mammograms were used to evaluate and score MD as categorized by breast composition with the Breast Imaging-Reporting and Data System (BI-RADS) 5th edition. Logistic regression was used in complete cases to assess the odds ratios (OR) for pCR compared to BI-RADS categories (a vs b-d), adjusting for patient and pre-treatment tumor characteristics.

Results

A total of 302 patients were included in the study population, of which 57 (18.9%) patients accomplished pCR following neoadjuvant chemotherapy. The number of patients in the BI-RADS category a, b, c, and d were separately 16, 120, 140, and 26, respectively. In comparison to patients with BI-RADS breast composition a, patients with denser breasts had a lower OR of accomplishing pCR: BI-RADS b 0.32 (95%CI 0.07–0.1.5), BI-RADS c 0.30 (95%CI 0.06–1.45), and BI-RADS d 0.06 (95%CI 0.01–0.56). These associations were measured with lower point estimates, but wider confidence interval, in premenopausal patients; OR of accomplishing pCR for BI-RADS d in comparison to BI-RADS a: 0.03 (95%CI 0.00–0.76).

Conclusions

The likelihood of accomplishing pCR is indicated to be lower in breast cancer patients with higher MD, which need to be analysed in future studies for improved clinical decision-making regarding neoadjuvant treatment.

Spatiotemporal pattern of glucose in a microfluidic device depend on the porosity and permeability of the medium: A finite element study

BACKGROUND

Glucose plays an important role as a source of nutrients and influence cellular processes such as differentiation, proliferation and migration. In vitro models based on microfluidic devices represent an alternative to study several biological processes in a more reproducible and controllable method compared to in vivo models. Glucose concentration across a microfluidic chip and its behavior in experimental conditions is not completely understood.

OBJECTIVE

This paper investigated the spatiotemporal distribution of glucose across the hydrogel inside a microfluidic chip. The influence of different parameters, boundary and initial conditions of experiments on glucose concentration was studied.

METHODS

A finite element model using a two dimensional geometry was developed. With this model, patterns of glucose concentration were investigated for different combinations of flow rate of culture medium, permeability and porosity of the medium. Patterns were also studied for two hydrogels made of collagen type I and fibrin with different initial and boundary conditions for pressure and glucose concentration.

RESULTS

Porosity influenced significantly on the chemical gradients generated when interstitial fluid flow was null or neglectable. A difference in concentration lower than 15% was obtained at the input of microchamber and after 90 min, when porosity changed from 0.5 to 0.99. In addition, no significant effects of modifications in permeability were observed. Regarding the collagen and fibrin matrices, in the presence of a pressure gradient of 40 Pa, the permeability significantly influenced on the concentration gradients generated.

CONCLUSIONS

Porosity influences importantly on patterns when diffusion is the main transport mechanism. Permeability is the most influencing parameter when a fluid flow is present. Common insertion rates of culture medium does not significantly modify the patterns of glucose inside the chips. Thus, new experiments must consider the impact of such parameters on the distribution and the time span that nutrients occupy the medium. To better contribute with experimental trials, other studies involving cell-cell and cell-extracellular matrix interactions, and different chip geometries should be developed. The results of the present work could assist to develop specific systems for experimentation, to design new experiments and to improve the analysis of the obtained results.

Fluid Flow and Mass Transport in Brain Tissue

Despite its small size, the brain consumes 25% of the body’s energy, generating its own weight in potentially toxic proteins and biological debris each year. The brain is also the only organ lacking lymph vessels to assist in removal of interstitial waste. Over the past 50 years, a picture has been developing of the brain’s unique waste removal system. Experimental observations show cerebrospinal fluid, which surrounds the brain, enters the brain along discrete pathways, crosses a barrier into the spaces between brain cells, and flushes the tissue, carrying wastes to routes exiting the brain. Dysfunction of this cerebral waste clearance system has been demonstrated in Alzheimer’s disease, traumatic brain injury, diabetes, and stroke. The activity of the system is observed to increase during sleep. In addition to waste clearance, this circuit of flow may also deliver nutrients and neurotransmitters. Here, we review the relevant literature with a focus on transport processes, especially the potential role of diffusion and advective flows.

Fabrication Techniques for Vascular and Vascularized Tissue Engineering

Impaired or damaged blood vessels can occur at all levels in the hierarchy of vascular systems from large vasculatures such as arteries and veins to meso- and microvasculatures such as arterioles, venules, and capillary networks. Vascular tissue engineering has become a promising approach for fabricating small-diameter vascular grafts for occlusive arteries. Vascularized tissue engineering aims to fabricate meso- and microvasculatures for the prevascularization of engineered tissues and organs. The ideal small-diameter vascular graft is biocompatible, bridgeable, and mechanically robust to maintain patency while promoting tissue remodeling. The desirable fabricated meso- and microvasculatures should rapidly integrate with the host blood vessels and allow nutrient and waste exchange throughout the construct after implantation. A number of techniques used, including engineering-based and cell-based approaches, to fabricate these synthetic vasculatures are herein explored, as well as the techniques developed to fabricate hierarchical structures that comprise multiple levels of vasculature.

Dissecting and rebuilding the glioblastoma microenvironment with engineered materials

Glioblastoma (GBM) is the most aggressive and common form of primary brain cancer. Several decades of research have provided great insight into GBM progression; however, the prognosis remains poor with a median patient survival time of ~ 15 months. The tumour microenvironment (TME) of GBM plays a crucial role in mediating tumour progression and thus is being explored as a therapeutic target. Progress in the development of treatments targeting the TME is currently limited by a lack of model systems that can accurately recreate the distinct extracellular matrix composition and anatomic features of the brain, such as the blood-brain barrier and axonal tracts. Biomaterials can be applied to develop synthetic models of the GBM TME to mimic physiological and pathophysiological features of the brain, including cellular and ECM composition, mechanical properties, and topography. In this Review, we summarize key features of the GBM microenvironment and discuss different strategies for the engineering of GBM TME models, including 2D and 3D models featuring chemical and mechanical gradients, interfaces and fluid flow. Finally, we highlight the potential of engineered TME models as platforms for mechanistic discovery and drug screening as well as preclinical testing and precision medicine.

Quantitative characterization of viscoelastic fracture induced by time-dependent intratumoral pressure in a 3D model tumor

In the tumor environment, interstitial pressure drives interstitial flow drainage from the tumor core to the lymphatic vessels. Recent studies have highlighted the key role of interstitial pressure in tumor development and cell migration. High intratumoral pressures, up to 60 mm Hg , have been reported in cancer patients. In a previous study, we showed that such pressure levels induce fracture in an experimental tumor model consisting of a microfluidic system holding a cellular aggregate. Here, we investigate and quantify the characteristics of tumor model fracture under a range of flow conditions. Our findings suggest a strong dependence of viscoelastic fracture behavior on the loading rate exerted by flow. The aggregate exhibits fragile fracture at high loading rates and ductile fracture at lower rates. The loading rate also modifies the permeability of the cellular aggregate, as well as the persistence time of the load required to induce fracture. The quantification parameters we propose here, evaluated for an in vitro model tumor without the extracellular matrix, could be applied to characterize tumor fracture under more realistic interstitial flow conditions.

Estimation of Vascular Permeability in Irregularly Shaped Cancers Using Ultrasound Poroelastography

OBJECTIVE

Vascular permeability (VP) is a mechanical parameter which plays an important role in cancer initiation, metastasis, and progression. To date, there are only a few non-invasive methods that can be used to image VP in solid tumors. Most of these methods require the use of contrast agents and are expensive, limiting widespread use.

METHODS

In this paper, we propose a new method to image VP in tumors, which is based on the use of ultrasound poroelastography. Estimation of VP by poroelastography requires knowledge of the Young's modulus (YM), Poisson's ratio (PR), and strain time constant (TC) in the tumors. In our method, we find the ellipse which best fits the tumor (regardless of its shape) using an eigen-system-based fitting technique and estimate the YM and PR using Eshelby's elliptic inclusion formulation. A Fourier method is used to estimate the axial strain TC, which does not require any initial guess and is highly robust to noise.

RESULTS

It is demonstrated that the proposed method can estimate VP in irregularly shaped tumors with an accuracy of above [Formula: see text] using ultrasound simulation data with signal-to-noise ratio of 20 dB or higher. In vivo feasibility of the proposed technique is demonstrated in an orthotopic mouse model of breast cancer.

CONCLUSION

The proposed imaging method can provide accurate and localized estimation of VP in cancers non-invasively and cost-effectively.

SIGNIFICANCE

Accurate and non-invasive assessment of VP can have a significant impact on diagnosis, prognosis, and treatment of cancers.

Development of an in vitro media perfusion model of Leishmania major macrophage infection

Background

In vitro assays are widely used in studies on pathogen infectivity, immune responses, drug and vaccine discovery. However, most in vitro assays display significant differences to the in vivo situation and limited predictive properties. We applied medium perfusion methods to mimic interstitial fluid flow to establish a novel infection model of Leishmania parasites.

Methods

Leishmania major infection of mouse peritoneal macrophages was studied within the Quasi Vivo QV900 macro-perfusion system. Under a constant flow of culture media at a rate of 360μl/min, L. major infected macrophages were cultured either at the base of a perfusion chamber or raised on 9mm high inserts. Mathematical and computational modelling was conducted to estimate medium flow speed, shear stress and oxygen concentration. The effects of medium flow on infection rate, intracellular amastigote division, macrophage phagocytosis and macropinocytosis were measured.

Results

Mean fluid speeds at the macrophage cell surface were estimated to be 1.45 x 10⁻⁹ m/s and 1.23 x 10⁻⁷ m/s for cells at the base of the chamber and cells on an insert, respectively. L. major macrophage infection was significantly reduced under both media perfusion conditions compared to cells maintained under static conditions; a 85±3% infection rate of macrophages at 72 hours in static cultures compared to 62±5% for cultures under slow medium flow and 55±3% under fast medium flow. Media perfusion also decreased amastigote replication and both macrophage phagocytosis (by 44±4% under slow flow and 57±5% under fast flow compared with the static condition) and macropinocytosis (by 40±4% under slow flow and 62±5% under fast flow compared with the static condition) as measured by uptake of latex beads and pHrodo Red dextran.

Conclusions

Perfusion of culture medium in an in vitro L. major macrophage infection model (simulating in vivo lymphatic flow) reduced the infection rate of macrophages, the replication of the intracellular parasite, macrophage phagocytosis and macropinocytosis with greater reductions achieved under faster flow speeds.