Interstitial flow and its effects in soft tissues

Towards a comprehensive definition of the human fascial system

The absence of a clear consensus on the definition and significance of fascia and the indiscriminate use of the term throughout the clinical and scientific literature has led to skepticism regarding its importance in the human body. To address this challenge, we propose that: (1) fasciae, and the fascial interstitia within them, constitute an anatomical system, defined as a layered body-wide multiscale network of connective tissue that allows tensional loading and shearing mobility along its interfaces; (2) the fascial system comprises four anatomical organs: the superficial fascia, musculoskeletal (deep) fascia, visceral fascia, and neural fascia; (3) these organs are further composed of anatomical structures, some of which are eponymous; (4) all these fascial organs and their structural components contain variable combinations and arrangements of the four classically defined tissues: epithelial, connective, muscle, and neural; (5) the overarching functions of the fascial system arise from the contrasting biomechanical properties of the two basic types of layers distributed throughout the system: one predominantly collagenous and relatively stiff, the other rich in hyaluronic acid and viscous, allowing for the free flow of fluid; (6) the topographical organization of these layers in different locations is related to local variations in function (e.g. unidirectional arrangements favor tensional loading, interwoven structures favor shear mobility) thereby accounting for both the system's universal functional aspects and the site-specific variations between them. A universal language related to fascia will break down linguistic barriers and facilitate cross-disciplinary cooperation, enabling scientists and practitioners from diverse backgrounds to contribute their expertise seamlessly.

Compartmentalized perfusion for temporal control of the chemical microenvironment of iPSC-derived cardiac cells

Organ-on-chip structures are predicted to have a significant influence in drug research. In these structures, perfusion can provide cells a more controllable environment to receive signaling molecules. In many current organ-on-chip applications, perfusion is used for shear stress stimulus for the cells, but it can also provide a more precise way of controlling the chemical microenvironment around the cells. In this paper, we propose an open-top organ-on-chip structure with compartment-specific perfusion to introduce stimulating molecules to cells with only minimal extra unspecific stimulus. Using numerical simulations, we show that shear stress sensed by the cells within the structure is low. We further validated the flow profile experimentally. We showed that the hiPSC-CMs accommodate to the flow environment where the shear stress is kept below 0.035 mPa. We also show that the beating rate of hiPSC-CMs increases due to the stimulation provided by chemical stimulant molecules introduced through the flow.

Understanding the Lymphatic System: Tissue-on-Chip Modeling

The lymphatic vasculature plays critical roles in maintaining fluid homeostasis, transporting lipid, and facilitating immune surveillance. A growing body of work has identified lymphatic dysfunction as contributing to the severity of myriad diseases and to systemic inflammation, as well as modulating drug responses. Here, we review efforts to reconstruct lymphatic vessels in vitro toward establishing humanized, functional models to advance understanding of lymphatic biology and pathophysiology. We first review lymphatic endothelial cell biology and the biophysical lymphatic microenvironment, with a focus on features that are unique to the lymphatics and that have been used as design parameters for lymphatic-on-chip devices. We then discuss the state of the art for recapitulating lymphatic function in vitro, and we acknowledge limitations and challenges to current approaches. Finally, we discuss opportunities and the need for further development of microphysiological lymphatic systems to bridge the gap in model systems between lymphatic cell culture and animal physiology.

Mechanisms and Therapeutic Strategies for Minority Cell-Induced Paclitaxel Resistance and Tumor Progression Mediated by Mechanical Forces

Chemotherapy remains a prevalent strategy in cancer therapy; however, the emergence of drug resistance poses a considerable challenge to its efficacy. Most drug resistance arises from the accumulation of genetic mutations in a minority of resistant cells. The mechanisms underlying the emergence and progression of cancer resistance from these minority-resistant cells (MRCs) remain poorly understood. This study employs force-induced remnant magnetization spectroscopy (FIRMS) alongside various biological investigations to reveal the mechanical pathways for MRCs fostering drug resistance and tumor progression. The findings show that minority Paclitaxel-resistant cancer cells have enhanced mechanical properties. These cells can transmit high-intensity forces to surrounding sensitive cells (SCs) through the force transducer, Merlin. This force transmission facilitates the assimilation of surrounding SCs, subsequently strengthening the contraction and adhesion of tumor cells. This process is termed "mechano-assimilation," which accelerates the development of drug resistance and tumor progression. Interestingly, disturbances and reductions of mechano-assimilation within tumors can restore sensitivity to Paclitaxel both in vitro and in vivo. This study provides preliminary evidence highlighting the contribution of MRCs to the development of drug resistance and malignancy, mediated through mechanical interactions. It also establishes a foundation for future research focused on integrating mechanical factors into innovative cancer therapies.

Caveolin-1: an ambiguous entity in breast cancer

Breast cancer (BC) is the most frequently diagnosed cancer in women and the second leading cause of death from cancer among women. Metastasis is the major cause of BC-associated mortality. Accumulating evidence implicates Caveolin-1 (Cav-1), a structural protein of plasma membrane caveolae, in BC metastasis. Cav-1 exhibits a dual role, as both a tumor suppressor and promoter depending on the cellular context and BC subtype. This review highlights the role of Cav-1 in modulating glycolytic metabolism, tumor-stromal interactions, apoptosis, and senescence. Additionally, stromal Cav-1's expression is identified as a potential prognostic marker, offering insights into its contrasting roles in tumor suppression and progression. Furthermore, Cav-1's context-dependent effects are explored in BC subtypes including hormone receptor-positive, HER2-positive, and triple-negative BC (TNBC). The review further delves into the role of Cav-1 in regulating the metastatic cascade including extracellular matrix interactions, cell migration and invasion, and premetastatic niche formation. The later sections discuss the therapeutic targeting of Cav-1 by metabolic inhibitors such as betulinic acid and Cav-1 modulating compounds. While Cav-1 may be a potential biomarker and therapeutic target, its heterogeneous expression and context-specific activity necessitates further research to develop precise interventions. Future studies investigating the mechanistic role of Cav-1 in metastasis may pave the way for effective treatment of metastatic BC.

Poroelasticity and permeability of fibrous polymer networks under compression

Soft biopolymer networks play pivotal roles in governing cellular mechanics, tissue structure, and physiological processes such as blood coagulation. Understanding their permeability and mechanical responses under compression is crucial for elucidating mass transport phenomena and their impact on extra- and intra-cellular behavior as well as processes affecting functionality of blood clots, cartilage and other fibrous tissues. The nonlinear responses of these networks to mechanical stresses prevent application of established linear poro-elasticity models. Despite extensive studies of fibrous network viscoelastic properties under shear deformations, their dynamic responses to compressive deformations remain poorly understood, particularly in physiological contexts of growth and collective migration of solid bodies. Conventional experimental techniques face challenges in accurately evaluating the permeability of these networks, hindering comprehensive understanding of their poromechanical behavior. In this study, we employ a novel poroelastic hybrid approach combining rheometer-based compression rheology with camera-facilitated sample shape detection to directly measure fluid flux and network permeability under controlled compressive strains. Accompanying experimental investigations, a continuum model implemented in finite elements, and an analytical model are developed to interpret the findings. The experimental data align well with the analytical model, revealing the emergence and disappearance of distinct densification regimes within the gel under mechanical stress. This study advances our understanding of the intricate interplay between mechanical forces, fluid flow, and structural properties in soft biopolymer networks, with a specific focus on fibrin- and collagen-based gels which represent the most abundant protein networks in the extracellular environment.

Comparative assessment of macrophage responses and antileishmanial efficacy in dynamic vs. Static culture systems utilizing chitosan-based formulations

The discovery of novel anti-leishmanial compounds is essential due to the limitations of current treatments and the lack of new drugs in development. In this study, we employed the Quasi Vivo 900 medium perfusion system (QV900, Kirkstall Ltd, UK) to simulate physiological fluid flow, allowing us to compare macrophage responses and therapeutic outcomes under dynamic versus static conditions. After 24 hours, phagocytosis and macropinocytosis decreased in all cell types under flow conditions compared to static cultures. Under slow (1.45 x 10-9 m/s) and faster (1.23 x 10-7 m/s) flow conditions ((simulating in vivo lymphatic flow), phagocytosis decreased by around 42.55% and 56.98% in peritoneal macrophages (PEMs), 42.21% and 56.11% in bone marrow-derived macrophages (BMMs), and 49.75% and 63.32% in THP-1 cells, respectively. Similarly, macropinocytosis decreased by approximately 40.7% and 62.2% in PEMs, 34.8% and 60.9% in BMMs, and 33.3% and 59.3% in THP-1 cell line under this same conditions. In this study, we further assessed the impact of medium perfusion on drug efficacy and macrophage functions using a Leishmania major amastigote-macrophage assay. We evaluated the performance of both standard and nanoparticle-based drug formulations within dynamic and static culture systems. After 72 hours of medium perfusion, chitosan solution, blank chitosan-sodium tripolyphosphate (TPP) nanoparticles, and amphotericin B (AmB)-loaded chitosan-TPP nanoparticles exhibited a statistically significant reduction in antileishmanial activity by approximately 30-50% under slow flow conditions and 60-80% under faster flow conditions. In comparison, pure AmB showed a 40% decrease in efficacy at slow flow and a 67% decrease at faster flow, both statistically significant. These results highlighted the importance of considering fluid flow dynamics in in vitro studies for a more accurate simulation of in vivo conditions, potentially leading to better therapeutic strategies for cutaneous leishmaniasis (CL).

Mechanical interaction between a hydrogel and an embedded cell in biomicrofluidic applications

Thanks to their softness, biocompatibility, porosity, and ready availability, hydrogels are commonly used in microfluidic assays and organ-on-chip devices as a matrix for cells. They not only provide a supporting scaffold for the differentiating cells and the developing organoids, but also serve as the medium for transmitting oxygen, nutrients, various chemical factors, and mechanical stimuli to the cells. From a bioengineering viewpoint, the transmission of forces from fluid perfusion to the cells through the hydrogel is critical to the proper function and development of the cell colony. In this paper, we develop a poroelastic model to represent the fluid flow through a hydrogel containing a biological cell modeled as a hyperelastic inclusion. In geometries representing shear and normal flows that occur frequently in microfluidic experiments, we use finite-element simulations to examine how the perfusion engenders interstitial flow in the gel and displaces and deforms the embedded cell. The results show that pressure is the most important stress component in moving and deforming the cell, and the model predicts the velocity in the gel and stress transmitted to the cell that is comparable to in vitro and in vivo data. This work provides a computational tool to design the geometry and flow conditions to achieve optimal flow and stress fields inside the hydrogels and around the cell.

Differential impact of lymphatic outflow pathways on cerebrospinal fluid homeostasis

Dysfunctional lymphatic drainage from the central nervous system (CNS) has been linked to neuroinflammatory and neurodegenerative disorders, but our understanding of the lymphatic contribution to CNS fluid autoregulation remains limited. Here, we studied forces that drive the outflow of the cerebrospinal fluid (CSF) into the deep and superficial cervical lymph nodes (dcLN and scLN) and tested how the blockade of lymphatic networks affects CNS fluid homeostasis. Outflow to the dcLN occurred spontaneously in the absence of lymphatic pumping and was coupled to intracranial pressure (ICP), whereas scLN drainage was driven by pumping. Impaired dcLN drainage led to elevated CSF outflow resistance and delayed CSF-to-blood efflux despite the recruitment of the nasal-to-scLN pathway. Fluid regulation was better compensated after scLN obstruction. The dcLN pathway exhibited steady, consistent drainage across conditions, while the nasal-to-scLN pathway was dynamically activated to mitigate perturbances. These findings highlight the complex physiology of CSF homeostasis and lay the groundwork for future studies aimed at assessing and modulating CNS lymphatic function.

Decoding complex transport patterns in flow-induced autologous chemotaxis of multicellular systems

Cell migration via autologous chemotaxis in the presence of interstitial fluid flow is important in cancer metastasis and embryonic development. Despite significant recent progress, our understanding of flow-induced autologous chemotaxis of multicellular systems remains poor. The literature presents inconsistent findings regarding the effectiveness of collective autologous chemotaxis of densely packed cells under interstitial fluid flow. Here, we present a high-fidelity computational model to analyze the migration of multicellular systems performing autologous chemotaxis in the presence of interstitial fluid flow. Our simulations show that the details of the complex transport dynamics of the chemoattractant and fluid flow patterns that occur in the extracellular space, previously overlooked, are essential to understand this cell migration mechanism. We find that, although flow-induced autologous chemotaxis is a robust migration mechanism for individual cells, the cell-cell interactions that occur in multicellular systems render autologous chemotaxis an inefficient mechanism of collective cell migration. Our results offer new perspectives on the potential role of autologous chemotaxis in the tumor microenvironment, where fluid flow is an important modulator of transport.

Probing the physical hallmarks of cancer

The physical microenvironment plays a crucial role in tumor development, progression, metastasis and treatment. Recently, we proposed four physical hallmarks of cancer, with distinct origins and consequences, to characterize abnormalities in the physical tumor microenvironment: (1) elevated compressive-tensile solid stresses, (2) elevated interstitial fluid pressure and the resulting interstitial fluid flow, (3) altered material properties (for example, increased tissue stiffness) and (4) altered physical micro-architecture. As this emerging field of physical oncology is being advanced by tumor biologists, cell and developmental biologists, engineers, physicists and oncologists, there is a critical need for model systems and measurement tools to mechanistically probe these physical hallmarks. Here, after briefly defining these physical hallmarks, we discuss the tools and model systems available for probing each hallmark in vitro, ex vivo, in vivo and in clinical settings. We finally review the unmet needs for mechanistic probing of the physical hallmarks of tumors and discuss the challenges and unanswered questions associated with each hallmark.

A 3D-printed multi-compartment organ-on-chip platform with a tubing-free pump models communication with the lymph node

Multi-organ-on-chip systems (MOOCs) have the potential to mimic communication between organ systems and reveal mechanisms of health and disease. However, many existing MOOCs are challenging for non-experts to implement due to complex tubing, electronics, or pump mechanisms. In addition, few MOOCs have incorporated immune organs such as the lymph node (LN), limiting their applicability to model critical events such as vaccination. Here we developed a 3D-printed, user-friendly device and companion tubing-free impeller pump with the capacity to co-culture two or more tissue samples, including a LN, under a recirculating common media. Native tissue structure and immune function were incorporated by maintaining slices of murine LN tissue ex vivo in 3D-printed mesh supports for at least 24 h. In a two-compartment model of a LN and an upstream injection site in mock tissue, vaccination of the multi-compartment chip was similar to in vivo vaccination in terms of locations of antigen accumulation and acute changes in activation markers and gene expression in the LN. We anticipate that in the future, this flexible platform will enable models of multi-organ immune responses throughout the body.

Developing a Flow-Resistance Module for Elucidating Cell Mechanotransduction on Multiple Shear Stresses

Fluid shear stress plays a pivotal role in regulating cellular behaviors, maintaining tissue homeostasis, and driving disease progression. Cells in various tissues are specifically adapted to physiological levels of shear stress and exhibit sensitivity to variations in its magnitude, highlighting the requirement for a comprehensive understanding of cellular responses to both physiologically and pathologically relevant levels of shear stress. In this study, we developed an independent upstream flow-resistance module with high fluidic resistances comprising three microchannels. The validity of the flow-resistance module was confirmed via computational fluid dynamics (CFD) simulations and flow calibration experiments, resulting in the generation of steady wall shear stresses ranging from 0.06 to 11.57 dyn/cm2 within the interconnected cell culture chips. Gene expression profiles, cytoskeletal remodeling, and morphological changes, as well as Yes-associated protein (YAP) nuclear translocation, were investigated in response to various shear stresses to authenticate the reliability of our experimental platform, indicating an increasing trend as the shear stress increases, reaching its maximum at various shear stresses. Our findings suggest that this flow-resistance module can be readily employed for precise characterization of cellular responses under various shear stresses.

Unraveling the Role of the Tumor Extracellular Matrix to Inform Nanoparticle Design for Nanomedicine

The extracellular matrix (ECM)-and its mechanobiology-regulates key cellular functions that drive tumor growth and development. Accordingly, mechanotherapy is emerging as an effective approach to treat fibrotic diseases such as cancer. Through restoring the ECM to healthy-like conditions, this treatment aims to improve tissue perfusion, facilitating the delivery of chemotherapies. In particular, the manipulation of ECM is gaining interest as a valuable strategy for developing innovative treatments based on nanoparticles (NPs). However, further progress is required; for instance, it is known that the presence of a dense ECM, which hampers the penetration of NPs, primarily impacts the efficacy of nanomedicines. Furthermore, most 2D in vitro studies fail to recapitulate the physiological deposition of matrix components. To address these issues, a comprehensive understanding of the interactions between the ECM and NPs is needed. This review focuses on the main features of the ECM and its complex interplay with NPs. Recent advances in mechanotherapy are discussed and insights are offered into how its combination with nanomedicine can help improve nanomaterials design and advance their clinical translation.

Measurement of Covalent Bond Formation in Light-Curing Hydrogels Predicts Physical Stability under Flow

Photo-crosslinking hydrogels are promising for tissue engineering and regenerative medicine, but challenges in reaction monitoring often leave their optimization subject to trial and error. The stability of crosslinked gels under fluid flow, as in the case of a microfluidic device, is particularly challenging to predict, both because of obstacles inherent to solid-state macromolecular analysis that prevent accurate chemical monitoring and because stability is dependent on size of the patterned features. To solve both problems, we obtained 1H NMR spectra of cured hydrogels which were enzymatically degraded. This allowed us to take advantage of the high-resolution that solution NMR provides. This unique approach enabled the measurement of degree of cross-linking (DoC) and prediction of material stability under physiological fluid flow. We showed that NMR spectra of enzyme-digested gels successfully reported on DoC as a function of light exposure and wavelength within two classes of photo-cross-linkable hydrogels: methacryloyl-modified gelatin and a composite of thiol-modified gelatin and norbornene-terminated polyethylene glycol. This approach revealed that a threshold DoC was required for patterned features in each material to become stable and that smaller features required a higher DoC for stability. Finally, we demonstrated that DoC was predictive of the stability of architecturally complex features when photopatterning, underscoring the value of monitoring DoC when using light-reactive gels. We anticipate that the ability to quantify chemical cross-links will accelerate the design of advanced hydrogel materials for structurally demanding applications such as photopatterning and bioprinting.

Evaluation of Drug Effectiveness and Controlled Release Profiles of Clay Minerals Loaded with Anti-Carcinogenic Agent as a Drug Delivery System on Leukemia

Objective

Myeloid leukemia is a stem cell disease with high mortality due to the challenges of high-dose treatments and side effects. Innovative nanoparticle drug delivery systems are being explored to enhance efficacy and tissue-targeted therapy. This study investigates the potential of Bentonite (BNT)-based nanoparticles (NPs) as drug carriers for azacitidine (AZA) in treating THP-1 and K562 myeloid leukemia (AML) cell lines, aiming to improve drug stability, bioavailability, and therapeutic efficacy while ensuring controlled release.

Material and Method

Bentonite clay morphology was analyzed using Scanning Electron Microscopes. The BNT-AZA combination was tested in THP-1 and K562 cell cultures via in vitro proliferation tests, CCK-8 assays, and drug release tests with dialysis membranes. Apoptosis and internalization were evaluated using Annexin V-FITC and fluorescence methods, respectively.

Results

The BNT-AZA exhibited controlled release over 8 hours, with 50% released within 2 hours, 90% by the 4th hour, and prolonged release beyond 8 hours. This profile reduces side effects while increasing efficacy in target cells. Bentonite demonstrated significant drug-loading capacity, controlled release, and tumor-targeting capabilities. At concentrations of 10, 25, 50, and 100 µg/mL, BNT showed dose-dependent antiproliferative effects, maintaining low cytotoxicity at lower concentrations. The combination of azacytidine and bentonite exhibited a synergistic effect in inhibiting cell proliferation, with significant decreases in cell viability in the 1 µM azacytidine + 10 µg/mL bentonite, 5 µM azacytidine + 10 µg/mL bentonite, and 10 µM azacytidine + 10 µg/mL bentonite groups compared to the controls. The combination of 1 µM AZA with 10 µg/mL BNT achieved similar efficacy to 10 µM AZA alone, suggesting a potential for dose reduction and improved safety.

Conclusion

BNT nanoparticles are promising carriers for AZA, enhancing targeted delivery, reducing side effects, and potentially lowering the required dose for leukemia treatment. These findings support further investigation into the clinical application of BNT-AZA in hematologic cancers.

Exploring tissue permeability of brain tumours in different grades: Insights from pore-scale fluid dynamics analysis

Interstitial fluid (ISF) flow is identified as an essential physiological process that plays an important role in the development and progression of brain tumours. However, the relationship between the permeability of the tumour tissue, a complex porous medium, and the interstitial fluid flow around the tumour cells at the microscale is not well understood. To shed light on this issue, and in the absence of experimental techniques that can provide direct measurements, we develop a computational model to predict the tissue permeability of brain tumours in different grades by analysing the ISF flow at the pore scale. The 3-D geometrical models of tissue extracellular spaces are digitally reconstructed for each grade tumour based on their morphological properties measured from microscopic images. The predictive accuracy of the framework is validated by experimental results reported in the literature. Our results indicate that high-grade brain tumours are less permeable despite their higher porosity, whereas necrotic areas of glioblastoma are more permeable than the viable tumour areas. This implies that tissue permeability is primarily governed by both tissue porosity and the deposition of hyaluronic acid (HA), a key component of the extracellular matrix, while the HA deposition can have a greater effect than macro-level porosity. Parametric studies show that tissue permeability falls exponentially with increasing HA concentration in all grades of brain tumours, and this can be captured using an empirically derived relationship in a quantitative manner. These findings provide an improved understanding of the hydraulic properties of brain tumours and their intrinsic links to tumour microstructure. This work can be used to reveal the intratumoural physiochemical processes that rely on fluid flow and offer a powerful tool to tune textured and porous biomaterials for desired transport properties. STATEMENT OF SIGNIFICANCE: Interstitial fluid flow in the extracellular space of brain tumours plays a crucial role in their progression, development, and response to drug treatments. However, the mechanisms of interstitial fluid transport around tumour cells and the characterization of these microscale transports at the tissue scale to meet clinical requirements are largely unknown. In the absence of advanced experimental techniques to capture these pore-scale transport phenomena, we have developed and validated a computational framework to successfully reveal these phenomena across all grades of brain tumours. For the first time, we have quantitatively determined the tissue permeability of all grades of brain tumours as a function of the concentration of hyaluronic acid, a key component of the extracellular matrix. This framework will enhance our ability to capture the intratumoural physicochemical processes in brain tumours and correlate them with tumour tissue-scale behaviours.

Current poisson's ratio values of finite element models are too low to consider soft tissues nearly-incompressible: illustration on the human heel region

Tissues' nearly incompressibility was well reported in the literature but little effort has been made to compare volume variations computed by simulations with in vivo measurements. In this study, volume changes of the fat pad during controlled indentations of the human heel region were estimated from segmented medical images using digital volume correlation. The experiment was reproduced using finite element modelling with several values of Poisson's ratio for the fat pad, from 0.4500 to 0.4999. A single value of Poisson's ratio could not fit all the indentation cases. Estimated volume changes were between 0.9% - 11.7%.

Towards a 3D-Printed Millifluidic Device for Investigating Cellular Processes

Microfluidic devices (µFDs) have been explored extensively in drug screening and studying cellular processes such as migration and metastasis. However, the fabrication and implementation of microfluidic devices pose cost and logistical challenges that limit wider-spread adoption. Despite these challenges, light-based 3D printing offers a potential alternative to device fabrication. This study reports on the development of millifluidic devices (MiFDs) for disease modeling and elucidates the methods and implications of the design, production, and testing of 3D-printed MiFDs. It further details how such millifluidic devices can be cost-efficiently and effortlessly produced. The MiFD was developed through an iterative process with analytical tests (flow tests, leak tests, cytotoxicity assays, and microscopic analyses), driving design evolution and determination of the suitability of the devices for disease modeling and cancer research. The design evolution also considered flow within tissues and replicates interstitial flow between the main flow path and the modules designed to house and support organ-mimicking cancer cell spheroids. Although the primary stereolithographic (SLA) resin used in this study showed cytotoxic potential despite its biocompatibility certifications, the MiFDs possessed essential attributes for cell culturing. In summary, SLA 3D printing enables the production of MiFDs as a cost-effective, rapid prototyping alternative to standard µFD fabrication for investigating disease-related processes.

Is Kinesio taping acutely effective for peripheral tissue perfusion in women with mild to moderate chronic venous insufficiency? A randomized controlled trial

Objective To evaluate the acute effect of Kinesio Taping® (KT) on peripheral tissue perfusion in women with chronic venous insufficiency (CVI).

METHODS

This randomized, double-blind controlled trial included 59 women with mild to moderate CVI. They were randomized to a control group (n = 23; 54.08 ± 9.04 years) and KT group (n = 36; 55.87 ± 9.97 years). Near-infrared spectroscopy was positioned in the medial gastrocnemius muscle for assessment of resting tissue perfusion 48 h after the first day of evaluation and after placement of the Kinesio Taping® tape. The evaluation also consisted of performing movements of the plethysmography examination. To verify the comparisons of pre- and post-Kinesio Taping® data, the variation delta was used for analysis. Mann-Whitney U test was performed an an alpha of 5% was considered statistically significant.

RESULTS

There wasn't a significant difference between groups regarding the peripheral tissue perfusion evaluation variables Peripheral Oxygen Saturation Difference - DELTA_SPO2: (KT Group 3.21 (0.84-3.62); Control 2.21 (1.59-4.83), p = 0.219) and Difference in deoxygenate hemoglobin values - DELTA_HHB (units) KT Group -0.62 (-2.14-0.67); Control Group -0.07 (-2.15-2.62) p = 0.238). Despite the lack of statistical significance, the KT group had a 785.7% greater drop in HHB values than the control group.

CONCLUSIONS

Acute use of Kinesio Taping® in women with CVI did not significantly alter tissue perfusion of calf muscles. However, it was possible to observe percentage differences in venous retention to be considered from a clinical point of view.

Evaluating the breadth of nucleic acid-based payloads delivered in lipid nanoparticles to establish fundamental differences in development

INTRODUCTION

Nucleic acid (NA)-based therapeutics have shown great potential for downregulating or augmenting gene expression, and for promising applications, e.g., protein-replacement therapy and vaccination, a comprehensive understanding of the requirements for their targeted delivery to specific tissues or cells is needed.

AREAS COVERED

In this review, we discuss clinical applications of four representative types of NA-based therapeutics, i.e. antisense oligonucleotides, small interfering RNA, messenger RNA, and circular RNA, with a focus on the lipid nanoparticle (LNP) technology used for intracellular delivery. The in vivo fate of LNPs is discussed to improve the understanding of trafficking of nanomedicines at the systemic and cellular levels. In addition, NA-based vaccines are discussed, focusing on targeting antigen-presenting cells and immune activation.

EXPERT OPINION

Optimization of delivery systems for NA-based therapeutics is mainly focused on the standard requirements of prolonged systemic circulation and enhancing endosomal escape. Depending on the final destination in specific target tissues or cells, strategies should be adjusted to achieve the desired biodistribution of NA-based payloads. More studies relating to the pharmacokinetics of both cargo and carrier are encouraged, because their in vivo fates may differ, considering the possibility of premature cargo release before reaching the target.

Microfluidic Applications in Prostate Cancer Research

Prostate cancer is a disease in which cells in the prostate, a gland in the male reproductive system below the bladder, grow out of control and, among men, it is the second-most frequently diagnosed cancer (other than skin cancer). In recent years, prostate cancer death rate has stabilized and, currently, it is the second-most frequent cause of cancer death in men (after lung cancer). Most deaths occur due to metastasis, as cancer cells from the original tumor establish secondary tumors in distant organs. For a long time, classical cell cultures and animal models have been utilized in basic and applied scientific research, including clinical applications for many diseases, such as prostate cancer, since no better alternatives were available. Although helpful in dissecting cellular mechanisms, these models are poor predictors of physiological behavior mainly because of the lack of appropriate microenvironments. Microfluidics has emerged in the last two decades as a technology that could lead to a paradigm shift in life sciences and, in particular, controlling cancer. Microfluidic systems, such as organ-on-chips, have been assembled to mimic the critical functions of human organs. These microphysiological systems enable the long-term maintenance of cellular co-cultures in vitro to reconstitute in vivo tissue-level microenvironments, bridging the gap between traditional cell cultures and animal models. Several reviews on microfluidics for prostate cancer studies have been published focusing on technology advancement and disease progression. As metastatic castration-resistant prostate cancer remains a clinically challenging late-stage cancer, with no curative treatments, we expanded this review to cover recent microfluidic applications related to prostate cancer research. The review includes discussions of the roles of microfluidics in modeling the human prostate, prostate cancer initiation and development, as well as prostate cancer detection and therapy, highlighting potentially major contributions of microfluidics in the continuous march toward eradicating prostate cancer.

Construction of multilayered small intestine-like tissue by reproducing interstitial flow

Recent advances have made modeling human small intestines in vitro possible, but it remains a challenge to recapitulate fully their structural and functional characteristics. We suspected interstitial flow within the intestine, powered by circulating blood plasma during embryonic organogenesis, to be a vital factor. We aimed to construct an in vivo-like multilayered small intestinal tissue by incorporating interstitial flow into the system and, in turn, developed the micro-small intestine system by differentiating definitive endoderm and mesoderm cells from human pluripotent stem cells simultaneously on a microfluidic device capable of replicating interstitial flow. This approach enhanced cell maturation and led to the development of a three-dimensional small intestine-like tissue with villi-like epithelium and an aligned mesenchymal layer. Our micro-small intestine system not only overcomes the limitations of conventional intestine models but also offers a unique opportunity to gain insights into the detailed mechanisms underlying intestinal tissue development.

A multi-scale numerical study of monoclonal antibodies uptake by initial lymphatics after subcutaneous injection

This paper studies the transport of monoclonal antibodies through skin tissue and initial lymphatics, which impacts the pharmacokinetics of monoclonal antibodies. Our model integrates a macroscale representation of the entire skin tissue with a mesoscale model that focuses on the papillary dermis layer. Our results indicate that it takes hours for the drugs to disperse from the injection site to the papillary dermis before entering the initial lymphatics. Additionally, we observe an inhomogeneous drug distribution in the interstitial space of the papillary dermis, with higher drug concentrations near initial lymphatics and lower concentrations near blood capillaries. To validate our model, we compare our numerical simulation results with experimental data, finding a good alignment. Our parametric studies on the drug molecule properties and injection parameters suggest that a higher diffusion coefficient increases the transport and uptake rate while binding slows down these processes. Furthermore, shallower injection depths lead to faster lymphatic uptake, whereas the size of the injection plume has a minor effect on the uptake rate. These findings advance our understanding of drug transport and lymphatic absorption after subcutaneous injection, offering valuable insights for optimizing drug delivery strategies and the design of biotherapeutics.

Assessment of subcutaneously administered insulins using in vitro release cartridge: Medium composition and albumin binding

Biotherapeutics is the fastest growing class of drugs administered by subcutaneous injection. In vitro release testing mimicking physiological conditions at the injection site may guide formulation development and improve biopredictive capabilities. Here, anin vitrorelease cartridge (IVR cartridge) comprising a porous agarose matrix emulating subcutaneous tissue was explored. The objective was to assess effects of medium composition and incorporation of human serum albumin into the matrix. Drug disappearance was assessed for solution, suspension and in situ precipitating insulin products (Actrapid, Levemir, Tresiba, Mixtard 30, Insulatard, Lantus) using the flow-based cartridge. UV-Vis imaging and light microscopy visualized dissolution, precipitation and albumin binding phenomena at the injection site. Divalent cations present in the release medium resulted in slower insulin disappearance for suspension-based and in situ precipitating insulins. Albumin-binding acylated insulin analogs exhibited rapid disappearance from the cartridge; however, sustained retention was achieved by coupling albumin to the matrix. An in vitro-in vivorelation was established for the non-albumin-binding insulins.The IVR cartridge is flexible with potential in formulation development as shown by the ability to accommodate solutions, suspensions, and in situ forming formulations while tailoring of the system to probe in vivo relevant medium effects and tissue constituent interactions.

Using Microfluidics to Align Matrix Architecture and Generate Chemokine Gradients Promotes Directional Branching in a Model of Epithelial Morphogenesis

The mechanical cue of fiber alignment plays a key role in the development of various tissues in the body. The ability to study the effect of these stimuli in vitro has been limited previously. Here, we present a microfluidic device capable of intrinsically generating aligned fibers using the microchannel geometry. The device also features tunable interstitial fluid flow and the ability to form a morphogen gradient. These aspects allow for the modeling of complex tissues and to differentiate cell response to different stimuli. To demonstrate the abilities of our device, we incorporated luminal epithelial cysts into our device and induced growth factor stimulation. We found the mechanical cue of fiber alignment to play a dominant role in cell elongation and the ability to form protrusions was dependent on cadherin-3. Together, this work serves as a springboard for future potential with these devices to answer questions in developmental biology and complex diseases such as cancers.

A quadriphasic mechanical model of the human dermis

The present study investigates the multiphasic nature of the mechanical behavior of human dermis. Motivated by experimental observations and by consideration of its composition, a quadriphasic model of the dermis is proposed, distinguishing solid matrix components, interstitial fluid and charged constituents moving within the fluid, i.e., anions and cations. Compression and tensile experiments with and without change of osmolarity of the bath are performed to characterize the chemo-mechanical coupling in the dermis. Model parameters are determined through inverse analysis. The computations predict a dominant role of the permeability in the determination of the temporal evolution of the mechanical response of the tissue. In line with the previous studies on other tissues, the analysis shows that an ideal model based on Donnan's equilibrium overestimates the osmotic pressure in skin for the case of very dilute solutions. The quadriphasic model is applied to predict changes in dermal cell environment and therefore alterations in what is called the "mechanome," associated with skin stretch. The simulations indicate that skin deformation causes a variation in several local variables, including in particular the electric field associated with a deformation-induced non-homogeneous distribution of fixed charges.

Measurement of covalent bond formation in light-curing hydrogels predicts physical stability under flow

Photocrosslinking hydrogels are promising for tissue engineering and regenerative medicine, but challenges in reaction monitoring often leave their optimization subject to trial and error. The stability of crosslinked gels under fluid flow, as in the case of a microfluidic device, is particularly challenging to predict, both because of obstacles inherent to solid-state macromolecular analysis that prevent accurate chemical monitoring, and because stability is dependent on size of the patterned features. To solve both problems, we obtained 1H NMR spectra of cured hydrogels which were enzymatically degraded. This allowed us to take advantage of the high-resolution that solution NMR provides. This unique approach enabled the measurement of degree of crosslinking (DoC) and prediction of material stability under physiological fluid flow. We showed that NMR spectra of enzyme-digested gels successfully reported on DoC as a function of light exposure and wavelength within two classes of photocrosslinkable hydrogels: methacryloyl-modified gelatin and a composite of thiol-modified gelatin and norbornene-terminated polyethylene glycol. This approach revealed that a threshold DoC was required for patterned features in each material to become stable, and that smaller features required a higher DoC for stability. Finally, we demonstrated that DoC was predictive of the stability of architecturally complex features when photopatterning, underscoring the value of monitoring DoC when using light-reactive gels. We anticipate that the ability to quantify chemical crosslinks will accelerate the design of advanced hydrogel materials for structurally demanding applications such as photopatterning and bioprinting.

Construction of multileveled and oriented micro/nano channels in Mg doped hydroxyapitite bioceramics and their effect on mimicking mechanical property of cortical bone and biological performance of cancellous bone

Drawing on the structure and components of natural bone, this study developed Mg-doped hydroxyapatite (Mg-HA) bioceramics, characterized by multileveled and oriented micro/nano channels. These channels play a critical role in ensuring both mechanical and biological properties, making bioceramics suitable for various bone defects, particularly those bearing loads. Bioceramics feature uniformly distributed nanogrooves along the microchannels. The compressive strength or fracture toughness of the Mg-HA bioceramics with micro/nano channels formed by single carbon nanotube/carbon fiber (CNT/CF) (Mg-HA(05-CNT/CF)) are comparable to those of cortical bone, attributed to a combination of strengthened compact walls and microchannels, along with a toughening mechanism involving crack pinning and deflection at nanogroove intersections. The introduction of uniform nanogrooves also enhanced the porosity by 35.4 %, while maintaining high permeability owing to the capillary action in the oriented channels. This leads to superior degradation properties, protein adsorption, and in vivo osteogenesis compared with bioceramics with only microchannels. Mg-HA(05-CNT/CF) exhibited not only high strength and toughness comparable to cortical bone, but also permeability similar to cancellous bone, enhanced cell activity, and excellent osteogenic properties. This study presents a novel approach to address the global challenge of applying HA-based bioceramics to load-bearing bone defects, potentially revolutionizing their application in tissue engineering.

Modeling hypoxia-induced radiation resistance and the impact of radiation sources

Hypoxia contributes significantly to resistance in radiotherapy. Our research rigorously examines the influence of microvascular morphology on radiotherapy outcome, specifically focusing on how microvasculature shapes hypoxia within the microenvironment and affects resistance to a standard treatment regimen (30×2GyRBE). Our computational modeling extends to the effects of different radiation sources. For photons and protons, our analysis establishes a clear correlation between hypoxic volume distribution and treatment effectiveness, with vascular density and regularity playing a crucial role in treatment success. On the contrary, carbon ions exhibit distinct effectiveness, even in areas of intense hypoxia and poor vascularization. This finding points to the potential of carbon-based hadron therapy in overcoming hypoxia-induced resistance to RT. Considering that the spatial scale analyzed in this study is closely aligned with that of imaging data voxels, we also address the implications of these findings in a clinical context envisioning the possibility of detecting subvoxel hypoxia.

Using a probabilistic approach to derive a two-phase model of flow-induced cell migration

Interstitial fluid flow is a feature of many solid tumors. In vitro experiments have shown that such fluid flow can direct tumor cell movement upstream or downstream depending on the balance between the competing mechanisms of tensotaxis (cell migration up stress gradients) and autologous chemotaxis (downstream cell movement in response to flow-induced gradients of self-secreted chemoattractants). In this work we develop a probabilistic-continuum, two-phase model for cell migration in response to interstitial flow. We use a kinetic description for the cell velocity probability density function, and model the flow-dependent mechanical and chemical stimuli as forcing terms that bias cell migration upstream and downstream. Using velocity-space averaging, we reformulate the model as a system of continuum equations for the spatiotemporal evolution of the cell volume fraction and flux in response to forcing terms that depend on the local direction and magnitude of the mechanochemical cues. We specialize our model to describe a one-dimensional cell layer subject to fluid flow. Using a combination of numerical simulations and asymptotic analysis, we delineate the parameter regime where transitions from downstream to upstream cell migration occur. As has been observed experimentally, the model predicts downstream-oriented chemotactic migration at low cell volume fractions, and upstream-oriented tensotactic migration at larger volume fractions. We show that the locus of the critical volume fraction, at which the system transitions from downstream to upstream migration, is dominated by the ratio of the rate of chemokine secretion and advection. Our model also predicts that, because the tensotactic stimulus depends strongly on the cell volume fraction, upstream, tensotaxis-dominated migration occurs only transiently when the cells are initially seeded, and transitions to downstream, chemotaxis-dominated migration occur at later times due to the dispersive effect of cell diffusion.

Cardiovascular human organ-on-a-chip platform for disease modeling, drug development, and personalized therapy

Cardiovascular organ-on-a-chip (OoC) devices are composed of engineered or native functional tissues that are cultured under controlled microenvironments inside microchips. These systems employ microfabrication and tissue engineering techniques to recapitulate human physiology. This review focuses on human OoC systems to model cardiovascular diseases, to perform drug screening, and to advance personalized medicine. We also address the challenges in the generation of organ chips that can revolutionize the large-scale application of these systems for drug development and personalized therapy.

A new lymphedema treatment using pyro-drive jet injection

Lymphedema, resulting from impaired lymphatic drainage, causes inflammation, fibrosis and tissue damage leading to symptoms such as limb swelling and restricted mobility. Despite various treatments under exploration, no standard effective therapy exists. Here a novel technique using the pyro-drive jet injection (PJI) was used to create artificial clefts between collagen fibers, which facilitated the removal of excess interstitial fluid. The PJI was used to deliver a mixture of lactated Ringer's solution and air into the tail of animals with secondary skin edema. Edema levels were assessed using micro-CT scanning. Histopathological changes and neovascularization were evaluated on the injury-induced regenerative tissue. Regarding tissue remodeling, we focused on connective tissue growth factor (CTGF) and vascular endothelial growth factor (VEGF)-C. PJI markedly diminished soft tissue volume in the experimental lymphedema animals compared to the non-injected counterparts. The PJI groups exhibited a significantly reduced proportion of inflammatory granulation tissue and an enhanced density of lymphatic vessels and α-smooth muscle actin (αSMA)-positive small vessels in the fibrous granulation tissue compared to the controls. In addition, PJI curtailed the prevalence of CTGF- and VEGF-C-positive cells in regenerative tissue. In a lymphedema animal model, PJI notably ameliorated interstitial edema, promoted lymphatic vessel growth, and bolstered αSMA-positive capillaries in fibrous granulation tissue. PJI's minimal tissue impact post-lymph node dissection indicates significant potential as an early, standard preventative measure. Easily applied in general clinics without requiring specialized training, it offers a cost-effective and highly versatile solution to the management of lymphedema.

Mathematical model of oxygen, nutrient, and drug transport in tuberculosis granulomas

Physiological abnormalities in pulmonary granulomas-pathological hallmarks of tuberculosis (TB)-compromise the transport of oxygen, nutrients, and drugs. In prior studies, we demonstrated mathematically and experimentally that hypoxia and necrosis emerge in the granuloma microenvironment (GME) as a direct result of limited oxygen availability. Building on our initial model of avascular oxygen diffusion, here we explore additional aspects of oxygen transport, including the roles of granuloma vasculature, transcapillary transport, plasma dilution, and interstitial convection, followed by cellular metabolism. Approximate analytical solutions are provided for oxygen and glucose concentration, interstitial fluid velocity, interstitial fluid pressure, and the thickness of the convective zone. These predictions are in agreement with prior experimental results from rabbit TB granulomas and from rat carcinoma models, which share similar transport limitations. Additional drug delivery predictions for anti-TB-agents (rifampicin and clofazimine) strikingly match recent spatially-resolved experimental results from a mouse model of TB. Finally, an approach to improve molecular transport in granulomas by modulating interstitial hydraulic conductivity is tested in silico.

Microfluidic-Based Reconstitution of Functional Lymphatic Microvasculature: Elucidating the Role of Lymphatics in Health and Disease

The knowledge of the blood microvasculature and its functional role in health and disease has grown significantly attributable to decades of research and numerous advances in cell biology and tissue engineering; however, the lymphatics (the secondary vascular system) has not garnered similar attention, in part due to a lack of relevant in vitro models that mimic its pathophysiological functions. Here, a microfluidic-based approach is adopted to achieve precise control over the biological transport of growth factors and interstitial flow that drive the in vivo growth of lymphatic capillaries (lymphangiogenesis). The engineered on-chip lymphatics with in vivo-like morphology exhibit tissue-scale functionality with drainage rates of interstitial proteins and molecules comparable to in vivo standards. Computational and scaling analyses of the underlying transport phenomena elucidate the critical role of the three-dimensional geometry and lymphatic endothelium in recapitulating physiological drainage. Finally, the engineered on-chip lymphatics enabled studies of lymphatic-immune interactions that revealed inflammation-driven responses by the lymphatics to recruit immune cells via chemotactic signals similar to in vivo, pathological events. This on-chip lymphatics platform permits the interrogation of various lymphatic biological functions, as well as screening of lymphatic-based therapies such as interstitial absorption of protein therapeutics and lymphatic immunomodulation for cancer therapy.

Interstitial flow potentiates TGF-β/Smad-signaling activity in lung cancer spheroids in a 3D-microfluidic chip

Within the tumor microenvironment (TME), cancer cells use mechanotransduction pathways to convert biophysical forces to biochemical signals. However, the underlying mechanisms and functional significance of these pathways remain largely unclear. The upregulation of mechanosensitive pathways from biophysical forces such as interstitial flow (IF), leads to the activation of various cytokines, including transforming growth factor-β (TGF-β). TGF-β promotes in part via a Smad-dependent signaling pathway the epithelial-mesenchymal transition (EMT) in cancer cells. The latter process is linked to increased cancer cell motility and invasion. Current research models have limited ability to investigate the combined effects of biophysical forces (such as IF) and cytokines (TGF-β) in a 3D microenvironment. We used a 3D-matrix based microfluidic platform to demonstrate the potentiating effect of IF on exogenous TGF-β induced upregulation of the Smad-signaling activity and the expression of mesenchymal marker vimentin in A549 lung cancer spheroids. To monitor this, we used stably integrated fluorescent based reporters into the A549 cancer cell genome. Our results demonstrate that IF enhances exogenous TGF-β induced Smad-signaling activity in lung cancer spheroids embedded in a matrix microenvironment. In addition, we observed an increased cell motility for A549 spheroids when exposed to IF and TGF-β. Our 3D-microfluidic model integrated with real-time imaging provides a powerful tool for investigating cancer cell signaling and motility associated with invasion characteristics in a physiologically relevant TME.

A compartment model for subcutaneous injection of monoclonal antibodies

Despite the growing popularity of subcutaneous (SC) administration for monoclonal antibodies (mAbs), there remains a limited understanding of the significance of mAb transport rate constants within the interstitial space and the lymphatic system on their pharmacokinetics. To bridge this knowledge gap, we introduce a compartmental model for subcutaneously administered mAbs. Our model differentiates FcRn-expressing cells across various sites, and the model predictions agree with experimental data from both human and rat studies. Our findings indicate that the time to reach the maximum mAb concentration in the plasma, denoted by Tmax, displays a weak positive correlation with mAb half-life and a negligible correlation with bioavailability. In contrast, the half-life of mAbs exhibits a strong positive correlation with bioavailability. Moreover, the rate of mAb transport from lymph to plasma significantly affects the mAb half-life. Increasing the transport rates of mAbs from the injection site to the lymph or from lymph to plasma enhances bioavailability. These insights, combined with our compartmental model, contribute to a deeper understanding of the pharmacokinetics of subcutaneously administered mAbs.

Chondroitin sulfate, dermatan sulfate, and hyaluronic acid differentially modify the biophysical properties of collagen-based hydrogels

Fibrillar collagens and glycosaminoglycans (GAGs) are structural biomolecules that are natively abundant to the extracellular matrix (ECM). Prior studies have quantified the effects of GAGs on the bulk mechanical properties of the ECM. However, there remains a lack of experimental studies on how GAGs alter other biophysical properties of the ECM, including ones that operate at the length scales of individual cells such as mass transport efficiency and matrix microstructure. This study focuses on the GAG molecules chondroitin sulfate (CS), dermatan sulfate (DS), and hyaluronic acid (HA). CS and DS are stereoisomers while HA is the only non-sulfated GAG. We characterized and decoupled the effects of these GAG molecules on the stiffness, transport, and matrix microarchitecture properties of type I collagen hydrogels using mechanical indentation testing, microfluidics, and confocal reflectance imaging, respectively. We complement these biophysical measurements with turbidity assays to profile collagen aggregate formation. Surprisingly, only HA enhanced the ECM indentation modulus, while all three GAGs had no effect on hydraulic permeability. Strikingly, we show that CS, DS, and HA differentially regulate the matrix microarchitecture of hydrogels due to their alterations to the kinetics of collagen self-assembly. In addition to providing information on how GAGs define key physical properties of the ECM, this work shows new ways in which stiffness measurements, microfluidics, microscopy, and turbidity kinetics can be used complementarily to reveal details of collagen self-assembly and structure. STATEMENT OF SIGNIFICANCE: Collagen and glycosaminoglycans (GAGs) are integral to the structure, function, and bioactivity of the extracellular matrix (ECM). Despite widespread interest in collagen-GAG composite hydrogels, there is a lack of quantitative understanding of how different GAGs alter the biophysical properties of the ECM across tissue, cellular, and subcellular length scales. Here we show using mechanical, microfluidic, microscopy, and analytical methods and measurements that the GAG molecules chondroitin sulfate, dermatan sulfate, and hyaluronic acid differentially regulate the mechanical, transport, and microstructural properties of hydrogels due to their alterations to the kinetics of collagen self-assembly. As such, these results will inform improved design and utilization of collagen-based scaffolds of tailored composition, mechanical properties, molecular availability due to mass transport, and microarchitecture.

Exploring chronic and transient tumor hypoxia for predicting the efficacy of hypoxia-activated pro-drugs

Hypoxia, a low level of oxygen in the tissue, arises due to an imbalance between the vascular oxygen supply and oxygen demand by the surrounding cells. Typically, hypoxia is viewed as a negative marker of patients' survival, because of its implication in the development of aggressive tumors and tumor resistance. Several drugs that specifically target the hypoxic cells have been developed, providing an opportunity for exploiting hypoxia to improve cancer treatment. Here, we consider combinations of hypoxia-activated pro-drugs (HAPs) and two compounds that transiently increase intratumoral hypoxia: a vasodilator and a metabolic sensitizer. To effectively design treatment protocols with multiple compounds we used mathematical micro-pharmacology modeling and determined treatment schedules that take advantage of heterogeneous and dynamically changing oxygenation in tumor tissue. Our model was based on data from murine pancreatic cancers treated with evofosfamide (as a HAP) and either hydralazine (as a vasodilator), or pyruvate (as a metabolic sensitizer). Subsequently, this model was used to identify optimal schedules for different treatment combinations. Our simulations showed that schedules of HAPs with the vasodilator had a bimodal distribution, while HAPs with the sensitizer showed an elongated plateau. All schedules were more successful than HAP monotherapy. The three-compound combination had three local optima, depending on the HAPs clearance from the tissue interstitium, each two-fold more effective than baseline HAP treatment. Our study indicates that the three-compound therapy administered in the defined order will improve cancer response and that designing complex schedules could benefit from the use of mathematical modeling.

Directional Cell Migration Guided by a Strain Gradient

Strain gradients widely exist in development and physiological activities. The directional movement of cells is essential for proper cell localization, and directional cell migration in responses to gradients of chemicals, rigidity, density, and topography of extracellular matrices have been well-established. However; it is unclear whether strain gradients imposed on cells are sufficient to drive directional cell migration. In this work, a programmable uniaxial cell stretch device is developed that creates controllable strain gradients without changing substrate stiffness or ligand distributions. It is demonstrated that over 60% of the single rat embryonic fibroblasts migrate toward the lower strain side in static and the 0.1 Hz cyclic stretch conditions at ≈4% per mm strain gradients. It is confirmed that such responses are distinct from durotaxis or haptotaxis. Focal adhesion analysis confirms higher rates of contact area and protrusion formation on the lower strain side of the cell. A 2D extended motor-clutch model is developed to demonstrate that the strain-introduced traction force determines integrin fibronectin pairs' catch-release dynamics, which drives such directional migration. Together, these results establish strain gradient as a novel cue to regulate directional cell migration and may provide new insights in development and tissue repairs.

Comparing the effectiveness of novel high-end compression garment with common compression garment and kinesio tape in preventing edema and improving tissue perfusion in lower extremities

CONTEXT

Global sales of compression garments have risen sharply in recent years. Due to the availability of a wide range of compression garments, this study aims to evaluate the effect of two types of compression garments and kinesio tape on edema formation and tissue perfusion in the lower extremities. Over-the-counter compression knee stockings and kinesio tape were compared with a prototype of high-end compression stockings that combine kinesio tape and a common knee bandage. The high-end compression stockings were designed by Cube with the aim of combining the positive effects of kinesio tape and compression garments on edema formation and tissue perfusion.

DESIGN

Clinical cross-over study.

METHODS

Before and after a 6-hour compression period, the knee regions on both, the treated and non-treated leg, of participants were examined using a 3-D scan to detect changes in volume. Also measured were local temperature (°C), oxygen saturation (SpO2), perfusion index (Pi), blood pressure (mmHg), compression pressure (mmHg), range of motion, body-mass-index (BMI) and limb-circumference (cm). Two different types of compression garments were examined: a novel high-end compression stocking (A) and a common compression stocking (B). In addition, kinesio tape was compared to compression garments (C). After each experimental day, a one-day break was taken to prevent an unwanted overlay effect. Male and female participants between the ages of 18 and 60 were randomly selected.

RESULTS

The high-end compression garment (A) showed a statistically significant (P = 0.009) reduction of edema intraindividually. Comparing the three treatment groups, compression (A) lead to a reduction of edema. However, the reduction was not statistically significant (P = 0.585). The compression garment B and kinesio tape showed an increase in edema in the lower limb. There was a positive correlation between the highest compression pressure (A: 9.8 mmHg) and volume decrease over the period of 6 hours. Lighter compression (B: 8.2 mmHg) led to an increase in leg volume after compression application over 6 hours. There was no significant difference in tissue oxygen saturation with the two types of compression and kinesio tape. The tissue temperature below the compression garment was highest in the compression group A. Nevertheless, we could not demonstrate a statistically significant correlation between tissue temperature and volume difference.The range in motion of the lower limb decreased after 6 hours with both compression A and B and with kinesio tape.

CONCLUSION

The novel bandage showed a statistically significant reduction in edema when compared intraindividually, but no statistically significant advantage was found when compared with the other compression garment B and kinesio tape.Despite the widespread use of kinesio tape, we did not find any improvement in the range of motion, edema prevention and circulation in the lower limb after application of kinesio tape.

Photoacoustic imaging of the dynamics of a dye-labeled IgG4 monoclonal antibody in subcutaneous tissue reveals a transient decrease in murine blood oxygenation under anesthesia

Significance

Over 100 monoclonal antibodies have been approved by the U.S. Food and Drug Administration (FDA) for clinical use; however, a paucity of knowledge exists regarding the injection site behavior of these formulated therapeutics, particularly the effect of antibody, formulation, and tissue at the injection site. A deeper understanding of antibody behavior at the injection site, especially on blood oxygenation through imaging, will help design improved versions of the therapeutics for a wide range of diseases.

Aim

The aim of this research is to understand the dynamics of monoclonal antibodies at the injection site as well as how the antibody itself affects the functional characteristics of the injection site [e.g., blood oxygen saturation (sO 2 )].

Approach

We employed triple-wavelength equipped functional photoacoustic imaging to study the dynamics of dye-labeled and unlabeled monoclonal antibodies at the site of injection in a mouse ear. We injected a near-infrared dye-labeled (and unlabeled) human IgG4 isotype control antibody into the subcutaneous space in mouse ears to analyze the injection site dynamics and quantify molecular movement, as well as its effect on local hemodynamics.

Results

We performed pharmacokinetic studies of the antibody in different regions of the mouse body to show that dye labeling does not alter the pharmacokinetic characteristics of the antibody and that mouse ear is a viable model for these initial studies. We explored the movement of the antibody in the interstitial space to show that the bolus area grows by ∼ 300 % over 24 h. We discovered that injection of the antibody transiently reduces the local sO 2 levels in mice after prolonged anesthesia without affecting the total hemoglobin content and oxygen extraction fraction.

Conclusions

This finding on local oxygen saturation opens a new avenue of study on the functional effects of monoclonal antibody injections. We also show the suitability of the mouse ear model to study antibody dynamics through high-resolution imaging techniques. We quantified the movement of antibodies at the injection site caused by the interstitial fluid, which could be helpful for designing antibodies with tailored absorption speeds in the future.

Sensitivity analysis of a multi-physics model for the vascular microenvironment

The vascular microenvironment is the scale at which microvascular transport, interstitial tissue properties and cell metabolism interact. The vascular microenvironment has been widely studied by means of quantitative approaches, including multi-physics mathematical models as it is a central system for the pathophysiology of many diseases, such as cancer. The microvascular architecture is a key factor for fluid balance and mass transfer in the vascular microenvironment, together with the physical parameters characterizing the vascular wall and the interstitial tissue. The scientific literature of this field has witnessed a long debate about which factor of this multifaceted system is the most relevant. The purpose of this work is to combine the interpretative power of an advanced multi-physics model of the vascular microenvironment with state of the art and robust sensitivity analysis methods, in order to determine the factors that most significantly impact quantities of interest, related in particular to cancer treatment. We are particularly interested in comparing the factors related to the microvascular architecture with the ones affecting the physics of microvascular transport. Ultimately, this work will provide further insight into how the vascular microenvironment affects cancer therapies, such as chemotherapy, radiotherapy or immunotherapy.

In vitro microvascular engineering approaches and strategies for interstitial tissue integration

The increasing gap between clinical demand for tissue or organ transplants and the availability of donated tissue highlights the emerging opportunities for lab-grown or synthetically engineered tissue. While the field of tissue engineering has existed for nearly half a century, its clinical translation remains unrealised, in part, due to a limited ability to engineer sufficient vascular supply into fabricated tissue, which is necessary to enable nutrient and waste exchange, prevent cellular necrosis, and support tissue proliferation. Techniques to develop anatomically relevant, functional vascular networks in vitro have made significant progress in the last decade, however, the challenge now remains as to how best incorporate these throughout dense parenchymal tissue-like structures to address diffusion-limited development and allow for the fabrication of large-scale vascularised tissue. This review explores advances made in the laboratory engineering of vasculature structures and summarises recent attempts to integrate vascular networks together with sophisticated in vitro avascular tissue and organ-like structures. STATEMENT OF SIGNIFICANCE: The ability to grow full scale, functional tissue and organs in vitro is primarily limited by an inability to adequately diffuse oxygen and nutrients throughout developing cellularised structures, which generally results from the absence of perfusable vessel networks. Techniques to engineering both perfusable vascular networks and avascular miniaturised organ-like structures have recently increased in complexity, sophistication, and physiological relevance. However, integrating these two essential elements into a single functioning vascularised tissue structure represents a significant spatial and temporal engineering challenge which is yet to be surmounted. Here, we explore a range of vessel morphogenic phenomena essential for tissue-vascular co-development, as well as evaluate a range of recent noteworthy approaches for generating vascularised tissue products in vitro.

Travelling under pressure - hypoxia and shear stress in the metastatic journey

Cancer cell invasion, intravasation and survival in the bloodstream are early steps of the metastatic process, pivotal to enabling the spread of cancer to distant tissues. Circulating tumor cells (CTCs) represent a highly selected subpopulation of cancer cells that tamed these critical steps, and a better understanding of their biology and driving molecular principles may facilitate the development of novel tools to prevent metastasis. Here, we describe key research advances in this field, aiming at describing early metastasis-related processes such as collective invasion, shedding, and survival of CTCs in the bloodstream, paying particular attention to microenvironmental factors like hypoxia and mechanical stress, considered as important influencers of the metastatic journey.

A facile fluid pressure system reveals differential cellular response to interstitial pressure gradients and flow

Interstitial fluid pressure gradients and interstitial flow have been shown to drive morphogenic processes that shape tissues and influence progression of diseases including cancer. The advent of porous media microfluidic approaches has enabled investigation of the cellular response to interstitial flow, but questions remain as to the critical biophysical and biochemical signals imparted by interstitial fluid pressure gradients and resulting flow on resident cells and extracellular matrix (ECM). Here, we introduce a low-cost method to maintain physiological interstitial fluid pressures that is built from commonly accessible laboratory equipment, including a laser pointer, camera, Arduino board, and a commercially available linear actuator. We demonstrate that when the system is connected to a microfluidic device containing a 3D porous hydrogel, physiologic pressure is maintained with sub-Pascal resolution and when basic feedback control is directed using an Arduino, constant pressure and pressure gradient can be maintained even as cells remodel and degrade the ECM hydrogel over time. Using this model, we characterized breast cancer cell growth and ECM changes to ECM fibril structure and porosity in response to constant interstitial fluid pressure or constant interstitial flow. We observe increased collagen fibril bundling and the formation of porous structures in the vicinity of cancer cells in response to constant interstitial fluid pressure as compared to constant interstitial flow. Collectively, these results further define interstitial fluid pressure as a driver of key pathogenic responses in cells, and the systems and methods developed here will allow for future mechanistic work investigating mechanotransduction of interstitial fluid pressures and flows.

Biomechanical control of lymphatic vessel physiology and functions

The ever-growing research on lymphatic biology has clearly identified lymphatic vessels as key players that maintain human health through their functional roles in tissue fluid homeostasis, immunosurveillance, lipid metabolism and inflammation. It is therefore not surprising that the list of human diseases associated with lymphatic malfunctions has grown larger, including issues beyond lymphedema, a pathology traditionally associated with lymphatic drainage insufficiency. Thus, the discovery of factors and pathways that can promote optimal lymphatic functions may offer new therapeutic options. Accumulating evidence indicates that aside from biochemical factors, biomechanical signals also regulate lymphatic vessel expansion and functions postnatally. Here, we review how mechanical forces induced by fluid shear stress affect the behavior and functions of lymphatic vessels and the mechanisms lymphatic vessels employ to sense and transduce these mechanical cues into biological signals.

Fluid flow to mimic organ function in 3D in vitro models

Many different strategies can be found in the literature to model organ physiology, tissue functionality, and disease in vitro; however, most of these models lack the physiological fluid dynamics present in vivo. Here, we highlight the importance of fluid flow for tissue homeostasis, specifically in vessels, other lumen structures, and interstitium, to point out the need of perfusion in current 3D in vitro models. Importantly, the advantages and limitations of the different current experimental fluid-flow setups are discussed. Finally, we shed light on current challenges and future focus of fluid flow models applied to the newest bioengineering state-of-the-art platforms, such as organoids and organ-on-a-chip, as the most sophisticated and physiological preclinical platforms.

Computational pulmonary edema: A microvascular model of alveolar capillary and interstitial flow

We present a microvascular model of fluid transport in the alveolar septa related to pulmonary edema. It consists of a two-dimensional capillary sheet coursing by several alveoli. The alveolar epithelial membrane runs parallel to the capillary endothelial membrane with an interstitial layer in between, making one long septal tract. A coupled system of equations uses lubrication theory for the capillary blood, Darcy flow for the porous media of the interstitium, a passive alveolus, and the Starling equation at both membranes. Case examples include normal physiology, cardiogenic pulmonary edema, acute respiratory distress syndrome (ARDS), hypoalbuminemia, and effects of PEEP. COVID-19 has dramatically increased ARDS in the world population, raising the urgency for such a model to create an analytical framework. Under normal conditions fluid exits the alveolus, crosses the interstitium, and enters the capillary. For edema, this crossflow is reversed with fluid leaving the capillary and entering the alveolus. Because both the interstitial and capillary pressures decrease downstream, the reversal can occur within a single septal tract, with edema upstream and clearance downstream. Clinically useful solution forms are provided allowing calculation of interstitial fluid pressure, crossflows, and critical capillary pressures. Overall, the interstitial pressures are found to be significantly more positive than values used in the traditional physiological literature. That creates steep gradients near the upstream and downstream end outlets, driving significant flows toward the distant lymphatics. This new physiological flow provides an explanation to the puzzle, noted since 1896, of how pulmonary lymphatics can function so far from the alveoli: the interstitium is self-clearing.

SubQ-Sim: A Subcutaneous Physiologically Based Biopharmaceutics Model. Part 1: The Injection and System Parameters

PURPOSE

To construct a detailed mechanistic and physiologically based biopharmaceutics model capable of predicting 1) device-formulation-tissue interaction during the injection process and 2) binding, degradation, local distribution, diffusion, and drug absorption, following subcutaneous injection. This paper is part of a series and focusses on the first aspect.

METHODS

A mathematical model, SubQ-Sim, was developed incorporating the details of the various substructures within the subcutaneous environment together with the calculation of dynamic drug disposition towards the lymph ducts and venous capillaries. Literature was searched to derive key model parameters in healthy and diseased subjects. External factors such as body temperature, exercise, body position, food or stress provide a means to calculate the impact of "life events" on the pharmacokinetics of subcutaneously administered drugs.

RESULTS

The model predicts the tissue backpressure time profile during the injection as a function of injection rate, volume injected, solution viscosity, and interstitial fluid viscosity. The shape of the depot and the concentrations of the formulation and proteins in the depot are described. The model enables prediction of formulation backflow following premature needle removal and the resulting formulation losses. Finally, the effect of disease (type 2 diabetes) or the presence of recombinant human hyaluronidase in the formulation on the injection pressure, are explored.

CONCLUSIONS

This novel model can successfully predict tissue back pressure, depot dimensions, drug and protein concentration and formulation losses due to incorrect injection, which are all important starting conditions for predicting drug absorption from a subcutaneous dose. The next article will describe the absorption model and validation against clinical data.