Cross-scale mechanobiological regulation of cylindrical compressible liquid inclusion via coating.

The double-bag theory in modern anatomy suggests that structures with coatings are commonly found in human body at various length scales, such as osteocyte processes covered by pericellular matrix and bones covered by muscle tissue. To understand the mechanical behaviors and physiological responses of such biological structures, we develop an analytical model to quantify surface effects on the deformation of a coated cylindrical compressible liquid inclusion in an elastic matrix subjected to remote loading. Our analytical solution reveals that coating can either amplify or attenuate the volumetric strain of the inclusion, depending on the relative elastic moduli of inclusion, coating, and matrix. For illustration, we utilize this solution to explore amplification/attenuation of volumetric strain in musculoskeletal systems, nerve cells, and vascular tissues. We demonstrate that coating often plays a crucial role in mechanical regulation of the development and repair of human tissues and cells. Our model provides qualitative analysis of cross-scale mechanical response of coated liquid inclusions, helpful for constructing mechanical microenvironment of cells.

Three-Dimensional Printing of Ultrasoft Silicone with a Functional Stiffness Gradient.

A methodology for three-dimensionally printing ultrasoft silicone with a functional stiffness gradient is presented. Ultraviolet-cure silicone was deposited via two independently controlled extruders into a thixotropic, gel-like, silicone oil-based support matrix. Each extruder contained a different liquid silicone formulation. The extrusion rates were independently varied during printing such that the combined selectively deposited material contained different ratios of the two silicones, resulting in localized control of material stiffness. Tests to validate the process are reported, including tensile testing of homogeneous cubic specimens to quantify the range of material stiffness that could be printed, indentation testing of cuboid specimens to characterize printed stiffness gradients, and vibratory testing of synthetic multilayer vocal fold (VF) models to demonstrate that the method may be applied to the fabrication of biomechanical models for voice production research. The cubic specimens exhibited linear stress-strain data with tensile elasticity modulus values between 1.11 and 27.1 kPa, more than a factor of 20 in stiffness variation. The cuboid specimens exhibited material variations that were visually recognizable and quantifiable via indentation testing. The VF models withstood rigorous phonatory flow-induced vibration and exhibited vibratory characteristics comparable to those of previous models. Overall, while process refinements are needed, the results of these tests demonstrate the ability to print ultrasoft silicone with stiffness gradients.

Uncoupling of the center-to-periphery arterial stiffness gradient and pulse pressure amplification in viral pneumonia infection.

OBJECTIVES: Arterial stiffness is a common manifestation of viral pneumonia infections, including COVID-19. Nevertheless, the relationship between the center-to-periphery arterial stiffness gradient and pulse pressure amplification (PPA) in infectious diseases remains unclear. This study aimed to investigate this relationship utilizing arterial pressure volume index (API) and arterial velocity pulse index (AVI) ratio. METHODS: API/AVI and PPA were measured in 219 participants with COVID-19 and 374 normal participants. Multiple linear regression was used to assess the association of API/AVI and PPA, and restricted cubic spline was used to investigate the non-linear relationship between API/AVI and PPA. Receiver operating characteristic curve (ROC) analysis was used to evaluate the effects of API/AVI in identifying COVID-19 infection and severe stage. RESULTS: There was a significant J-shaped relationship between API/AVI and PPA in COVID-19 group, while a M-shaped relationship was observed in normal group. API/AVI decreased rapidly as PPA decreased until API/AVI decreased slowly at PPA of 1.07, and then API/AVI decreased slowly again at PPA of 0.78. ROC results showed that API/AVI demonstrated excellent accuracy in identifying COVID-19 infection (AUC = 0.781) and a high specificity (84.88%) in identifying severe stage. CONCLUSIONS: There was a J-shaped association between the API/AVI and PPA in viral infected patients, while a M-shaped relationship in the normal participants. API/AVI is better for identifying infected and uninfected patients, with a high specificity in identifying those in severe stages of the disease. The attenuation or reversal of API/AVI may be associated with the loss of PPA coupling.

Design and performance analysis of 3D-printed stiffness gradient femoral scaffold.

Studies on 3D-printed porous bone scaffolds mostly focus on materials or structural parameters, while the repair of large femoral defects needs to select appropriate structural parameters according to the needs of different parts. In this paper, a kind of stiffness gradient scaffold design idea is proposed. Different structures are selected according to the different functions of different parts of the scaffold. At the same time, an integrated fixation device is designed to fix the scaffold. Finite element method was used to analyze the stress and strain of homogeneous scaffolds and the stiffness gradient scaffolds, and the relative displacement and stress between stiffness gradient scaffolds and bone in the case of integrated fixation and steel plate fixation. The results showed that the stress distribution of the stiffness gradient scaffolds was more uniform, and the strain of host bone tissue was changed greatly, which was beneficial to the growth of bone tissue. The integrated fixation method is more stable, less stress and evenly distributed. Therefore, the integrated fixation device combined with the design of stiffness gradient can repair the large femoral bone defect well.

Purse-string contraction guides mechanical gradient-dictated heterogeneous migration of epithelial monolayer.

Mechanical heterogeneity has been recognized as an important role in mediating collective cell migration, yet the related mechanism has not been elucidated. Herein, we fabricate heterogeneous stiffness gradients by leveraging microelastically-patterned hydrogels with varying periodic distance. We observe that a decrease in the periodic distance of the mechanical heterogeneity is accompanied by an overall increase in the velocity and directionality of the migrating monolayer. Moreover, inhibition of ROCK- and myosin ⅡA- but not Rac1-mediated contraction reduces monolayer migration on the mechanically heterogeneous substrates. Furthermore, we find that F-actin and myosin ⅡA form purse-string at the leading edge on the mechanically heterogeneous substrates. Together, these findings not only show that the orientational cell-cell contraction promotes collective cell migration under the mechanical heterogeneity, but also demonstrate that the mechanosensation arising from large-scale cell-cell interactions through purse-string formation mediated cell-cell orientational contraction can feed back to regulate the reorganization of epithelial tissues. STATEMENT OF SIGNIFICANCE: By detecting the links between heterogenous rigidity and collective cell migration behavior at the molecular level, we reveal that collective cell migration in the mechanical heterogeneity is driven by ROCK- and myosin-ⅡA-dependent cytoskeletal tension. We confirm that cytoskeletal tension across the epithelial tissue is holistically linked through F-actin and myosin-ⅡA, which cooperate to form purse-string structures for modulating collective tissue behavior on the exogenous matrix with mechanical heterogeneity. Mechanical heterogeneity initiates tissue growth, remodelling, and morphogenesis by orientating cell contractility. Therefore, tensional homeostasis across large-scale cell interactions appears to be necessary and sufficient to trigger collective tissue behavior. Overall, these findings shed light on the role of mechanical heterogeneity in tissue microenvironment for reorganization and morphogenesis.

Triphasic 3D In Vitro Model of Bone-Tendon-Muscle Interfaces to Study Their Regeneration.

The transition areas between different tissues, known as tissue interfaces, have limited ability to regenerate after damage, which can lead to incomplete healing. Previous studies focussed on single interfaces, most commonly bone-tendon and bone-cartilage interfaces. Herein, we develop a 3D in vitro model to study the regeneration of the bone-tendon-muscle interface. The 3D model was prepared from collagen and agarose, with different concentrations of hydroxyapatite to graduate the tissues from bones to muscles, resulting in a stiffness gradient. This graduated structure was fabricated using indirect 3D printing to provide biologically relevant surface topographies. MG-63, human dermal fibroblasts, and Sket.4U cells were found suitable cell models for bones, tendons, and muscles, respectively. The biphasic and triphasic hydrogels composing the 3D model were shown to be suitable for cell growth. Cells were co-cultured on the 3D model for over 21 days before assessing cell proliferation, metabolic activity, viability, cytotoxicity, tissue-specific markers, and matrix deposition to determine interface formations. The studies were conducted in a newly developed growth chamber that allowed cell communication while the cell culture media was compartmentalised. The 3D model promoted cell viability, tissue-specific marker expression, and new matrix deposition over 21 days, thereby showing promise for the development of new interfaces.

Biomaterials with stiffness gradient for interface tissue engineering.

Interface tissue engineering is a rapidly growing field that aims to develop engineered tissue alternates with the goal of promoting integration between multiple tissue types. Engineering interface tissues is a challenging process, which requires biomaterials with specific composition, stiffness, cell types, and biochemical molecules. Among these, stiffness-controllable substrates have been developed to investigate the effect of stiffness on cell behavior. Especially these substrates with graded stiffness are advantageous since they allow multiple cell types differentiation and the following tissue development. In this review, we highlight various types of manufacturing techniques that can be applied to fabricate scaffolds with stiffness gradient, discuss methods to characterize them, and gradient biomaterials for regulating cellular behavior including attachment, migration, proliferation, and differentiation. We also address fundamentals of interface tissue organization, and stiffness gradient biomaterials for interface tissue regeneration. Potential challenges and future prospects of this emerging field are also included.

Central and brachial pulse pressure predicts cardiovascular and renal events in treated hypertensive patients.

PURPOSES: Central blood pressure is a stronger predictor of cardiovascular prognosis rather than brachial blood pressure. The reflection wave reaches the abdominal aorta sooner than ascending aorta. Thus, the contribution of central pulse pressure (cPP) to renal events may differ from that of cardiovascular events. METHODS: The subanalysis of the ABC-J II study was performed. Subjects were 3434 treated hypertensive patients with a mean follow-up of 4.7 years. Left ventricular hypertrophy, an index of cardiovascular risk, correlated with cPP better than central systolic blood pressure in this cohort. The contribution of brachial pulse pressure (bPP) and cPP to cardiovascular and renal events was analysed. RESULTS: Cox proportional-hazard analysis revealed that sex (p < 0.001), height (p < 0.05), history of cardiovascular diseases (p < 0.001), number of antihypertensive drugs (p < 0.05), and cPP (p < 0.05) contributed to cardiovascular events. However, Cox proportional-hazard analysis disclosed that baseline serum creatinine (p < 0.001) and bPP (p < 0.05) predicted renal events. After adjusting for the history of cardiovascular diseases, Cox regression demonstrated only sex as a significant predictor of cardiovascular events. After adjusting for baseline serum creatinine, no parameters were shown to predict renal events. CONCLUSIONS: The present findings support our previous data that the absence of cardiovascular or renal diseases is an important determinant for event-free survival, and suggest that cPP and bPP contribute to cardiovascular and renal events in treated hypertensive patients.

Octopus-inspired sucker to absorb soft tissues: stiffness gradient and acetabular protuberance improve the adsorption effect.

Rigid suckers commonly used in surgical procedures often cause absorption damage, while their soft counterparts are difficult to handle due to their weak anchoring. Alternatively, the octopus sucker is both soft and has strong suction power. Further observation revealed that its structure is self-sealing and that the tissues are layered in hardness. Inspired by said structure and the characteristics of associated materials, a bionic soft sucker with stiffness gradient and acetabular roof structure was proposed, made of silicone with varying hardness including structures such as acetabular roof and circle muscles. The automatic tensile force measurement system was used to experimentally analyze the adsorption performance of the suckers to the soft curved contact surface. Both dry and wet conditions were tested, along with practical tests on organisms. The bionic sucker adsorption force was increased by 25.1% and 34.6% on the cylindrical surface, and 45.2% and 7.3% on the spherical surface for dry and wet conditions, respectively. During the experiment, the bionic suckers did not cause notable suction damage to the contact surfaces. Thus, this type of bionic sucker shows good application prospects in the field of surgery.

Predicting neurite extension for varying extracellular matrix stiffness and topography.

Neurite extension is a dynamic process and is dependent on the microenvironment. The mechanical properties of the extracellular matrix (ECM), such as stiffness and topography influence the microenvironment and affects neurite extension; however, the mechanistic basis for this dynamic response of neurite extension remains elusive. In this study, we develop a computational model that predicts neurite extension dynamics process as the stiffness and patterned topography of ECM changes. The model includes the contribution of receptors integrin and neural cellular adhesion molecule toward the growth of neurite tip. We use non-linear finite element analysis (FEA) to model the neuronal cell, neurite, and the ECM, which is then coupled to the force-deformation receptor properties obtained from molecular dynamics simulations. Using an empirical relation, we develop a neurite extension algorithm that simulates the dynamic process of growth cone induced by growth cone extension, receptor density, and rupture. We investigate the dependence of neurite extension on ECM stiffness using three distinct materials, the effect of width and spacing of continuous (cylindrical) and discontinuous (pillar) patterned topography, as well as the topography steepness and stiffness gradient. We find that an increasing stiffness and width of patterned topography results in increased neurite extension, but the magnitude of the increase differs depending on the growth cone extension and receptor density between them. These findings will aid in vitro studies in determining an ECM with appropriate mechanical properties, such as stiffness and topography that will improve neurite extension, thus resulting in the formation of functional neurons.

Hydrogel Models with Stiffness Gradients for Interrogating Pancreatic Cancer Cell Fate.

Pancreatic ductal adenocarcinoma (PDAC) is the most common type of pancreatic cancer and has seen only modest improvements in patient survival rate over the past few decades. PDAC is highly aggressive and resistant to chemotherapy, owing to the presence of a dense and hypovascularized fibrotic tissue, which is composed of stromal cells and extracellular matrices. Increase deposition and crosslinking of matrices by stromal cells lead to a heterogeneous microenvironment that aids in PDAC development. In the past decade, various hydrogel-based, in vitro tumor models have been developed to mimic and recapitulate aspects of the tumor microenvironment in PDAC. Advances in hydrogel chemistry and engineering should provide a venue for discovering new insights regarding how matrix properties govern PDAC cell growth, migration, invasion, and drug resistance. These engineered hydrogels are ideal for understanding how variation in matrix properties contributes to the progressiveness of cancer cells, including durotaxis, the directional migration of cells in response to a stiffness gradient. This review surveys the various hydrogel-based, in vitro tumor models and the methods to generate gradient stiffness for studying migration and other cancer cell fate processes in PDAC.

Modulation of Arterial Stiffness Gradient by Acute Administration of Nitroglycerin.

Background: Physiologically, the aorta is less stiff than peripheral conductive arteries, creating an arterial stiffness gradient, protecting microcirculation from high pulsatile pressure. However, the pharmacological manipulation of arterial stiffness gradient has not been thoroughly investigated. We hypothesized that acute administration of nitroglycerin (NTG) may alter the arterial stiffness gradient through a more significant effect on the regional stiffness of medium-sized muscular arteries, as measured by pulse wave velocity (PWV). The aim of this study was to examine the differential impact of NTG on regional stiffness, and arterial stiffness gradient as measured by the aortic-brachial PWV ratio (AB-PWV ratio) and aortic-femoral PWV ratio (AF-PWV ratio). Methods: In 93 subjects (age: 61 years, men: 67%, chronic kidney disease [CKD]: 41%), aortic, brachial, and femoral stiffnesses were determined by cf-PWV, carotid-radial (cr-PWV), and femoral-dorsalis pedis artery (fp-PWV) PWVs, respectively. The measurements were repeated 5 min after the sublingual administration of NTG (0.4 mg). The AB-PWV and AF-PWV ratios were obtained by dividing cf-PWV by cr-PWV or fp-PWV, respectively. The central pulse wave profile was determined by radial artery tonometry through the generalized transfer function. Results: At baseline, cf-PWV, cr-PWV, and fp-PWV were 12.12 ± 3.36, 9.51 ± 1.81, and 9.71 ± 1.89 m/s, respectively. After the administration of NTG, there was a significant reduction in cr-PWV of 0.86 ± 1.27 m/s (p < 0.001) and fp-PWV of 1.12 ± 1.74 m/s (p < 0.001), without any significant changes in cf-PWV (p = 0.928), leading to a significant increase in the AB-PWV ratio (1.30 ± 0.39 vs. 1.42 ± 0.46; p = 0.001) and AF-PWV ratio (1.38 ± 0.47 vs. 1.56 ± 0.53; p = 0.001). There was a significant correlation between changes in the AF-PWV ratio and changes in the timing of wave reflection (r = 0.289; p = 0.042) and the amplitude of the heart rate-adjusted augmented pressure (r = - 0.467; p < 0.001). Conclusion: This study shows that acute administration of NTG reduces PWV of muscular arteries (brachial and femoral) without modifying aortic PWV. This results in an unfavorable profile of AB-PWV and AF-PWV ratios, which could lead to higher pulse pressure transmission into the microcirculation.

Macrophage Phenotypic Changes on FN-Coated Physical Gradient Hydrogels.

The chemical and physical properties are two crucial cues when designing tissue engineering scaffold to mimic living tissue. Macrophages, the major players in the immune response, react rapidly to microenvironmental signals, including gradients of physical or chemical cues. Spatiotemporal gradients can modulate cell behavior, such as polarization, proliferation, and adhesion. Here, we studied macrophage phenotypic changes on untreated and fibronectin (FN)-coated methacrylated gellan gum with varying stiffnesses. The compressive moduli of hydrogel with different stiffnesses ranged from ∼5 to 30 kPa. Fibronectin was chemically attached to the substrate to facilitate macrophage proliferation, adhesion, and polarization. Classically (M1) and alternatively (M2) activated macrophages were cultured on both untreated and FN-coated gels. FN-coated substrates elevated cell numbers and enhanced macrophage spreading. The urea/nitrite ratio indicated that untreated rigid substrates shifted both polarizations toward a more proinflammatory phenotype. FN-coated substrates had no impact on M1 polarization. In contrast, FN-coated stiffer gels polarized M2 cells toward an anti-proinflammatory state based on arginine activity and CD206 expression. In addition, macrophage polarization on the softer gel was not influenced by the neighboring cells cultured on the stiffer side of the gel. Using mechanical gradients to control macrophage polarization can be a useful tool in ensuring a proper healing response and for tissue engineering.

Curved Foldable Tailored Fiber Reinforcements for Moldless Customized Bio-Composite Structures. Proof of Concept: Biomimetic NFRP Stools.

Fiber Reinforced Polymers (FRPs) are increasingly popular building materials, mainly because of their high strength to weight ratio. Despite these beneficial properties, these composites are often fabricated in standardized mass production. This research aims to eliminate costly molds in order to simplify the fabrication and allow for a higher degree of customization. Complex three-dimensional shapes were instead achieved by a flat reinforcement, which was resin infused and curved folded into a spatial object before hardening. Structural stability was gained through geometries with closed cross-sections. To enable this, the resource-saving additive fabrication technique of tailored fiber placement (TFP) was chosen. This method allowed for precise fibers' deposition, making a programmed anisotropic behavior of the material possible. Principles regarding the fiber placement were transferred from a biological role-model. Five functional stools were produced as demonstrators to prove the functionality and advantages of the explained system. Partially bio-based materials were applied to fabricate the stool models of natural fiber-reinforced polymer composites (NFRP). A parametric design tool for the global design and fiber layout generation was developed. As a result, varieties of customized components can be produced without increasing the design and manufacturing effort.

Mechano-responsiveness of fibrillar adhesions on stiffness-gradient gels.

Fibrillar adhesions are important structural and adhesive components in fibroblasts, and are required for fibronectin fibrillogenesis. While nascent and focal adhesions are known to respond to mechanical cues, the mechanoresponsive nature of fibrillar adhesions remains unclear. Here, we used ratiometric analysis of paired adhesion components to determine an appropriate fibrillar adhesion marker. We found that active α5ß1-integrin exhibits the most definitive fibrillar adhesion localization compared to other proteins, such as tensin-1, reported to be in fibrillar adhesions. To elucidate the mechanoresponsiveness of fibrillar adhesions, we designed a cost-effective and reproducible technique to fabricate physiologically relevant stiffness gradients on thin polyacrylamide (PA) hydrogels, embedded with fluorescently labelled beads. We generated a correlation curve between bead density and hydrogel stiffness, thus enabling a readout of stiffness without the need for specialized knowhow, such as atomic force microscopy (AFM). We find that stiffness promotes growth of fibrillar adhesions in a tensin-1-dependent manner. Thus, the formation of these extracellular matrix-depositing structures is coupled to the mechanical parameters of the cell environment and may enable cells to fine-tune their matrix environment in response to changing physical conditions.

Anisotropic stiffness gradient-regulated mechanical guidance drives directional migration of cancer cells.

Interfacial interactions between cancer cells and surrounding microenvironment involve complex mechanotransduction mechanisms that are directly associated with tumor invasion and metastasis. Matrix remodeling triggers heterogeneity of stiffness in tumor microenvironment and thus generates anisotropic stiffness gradient (ASG). The migration of cancer cells mediated by ASG, however, still remains elusive. Based on a multi-layer polymerization method of microstructured hydrogels with surface topology, we develop an in vitro experimental platform for mechanical interactions of cancer cells with ASG matrix microenvironment. We show that mechanical guidance of mesenchymal cells is essentially modulated by ASG, leading to a spontaneous directional migration along the orientation parallel to the maximum stiffness although there is no stiffness gradient in the direction. The ASG-regulated mechanical guidance presents an alternative way of cancer cell directional migration. Further, our findings indicate that the mechanical guidance occurs only in mesenchymal cancer cells, but not in epithelial cancer cells, implying that cell contractility may contribute to ASG-regulated migration of cells. This work is not only helpful for elucidating the role of matrix remodeling in mediating tumor cell invasion and metastasis, but has potential implications for developing specific cancer treatments. STATEMENT OF SIGNIFICANCE: Local extracellular matrix (ECM) stiffening triggers mechanical heterogeneity in tumor microenvironment, which can exert a crucial impact on interfacial interactions between tumor cells and surrounding ECM. The underlying mechanobiological mechanism that tumor cells are modulated by mechanically heterogeneous ECM, however, still remains mysterious to a great extent. Through our established in vitro platform and analysis, we have demonstrated that anisotropic stiffness gradient (ASG) has the ability to elicit directional migration of cells, essentially depending on local stiffness gradients and the corresponding absolute stiffness values. This study is not only crucial for revealing the role of matrix remodeling in regulating tumor invasion and metastasis, but also offers a valuable guidance for developing anti-tumor therapies from the biomechanical perspective.

Grayscale mask-assisted photochemical crosslinking for a dense collagen construct with stiffness gradient.

Despite the potential of a collagen construct with a stiffness gradient for investigating cell-extracellular matrix (ECM) stiffness interaction or recapitulating an in vivo tissue interface, it has been developed in a limited way due to the low and poorly controllable mechanical properties of the collagen. This study proposes a novel fabrication process to achieve a compressed collagen construct with a stiffness gradient, named COSDIENT, at a level of ~ 1 MPa while maintaining in vivo ECM-like dense collagen fibrillar structures. The COSDIENT was fabricated by collagen compression followed by grayscale mask-assisted UV-riboflavin crosslinking. The collagen compression process enabled the remarkable increase in the stiffness of the collagen gel from ~ 1-10 kPa to ~ 1 MPa by physical compaction. The subsequent UV-riboflavin crosslinking with a continuous-tone grayscale mask could simply generate a gradual change of UV irradiation followed by modulating riboflavin-mediated crosslinking, thereby resulting in a continuous stiffness gradient with a range of 1.16-4.38 MPa in the single compressed collagen construct. The suggested grayscale mask-assisted photochemical crosslinking had no effect on the physical and optical properties of the original compressed collagen construct, while inducing gradual changes of chemical bonds among collagen fibrils. A skin wound healing assay with epidermal keratinocytes was finally applied as an application example of the COSDIENT to examine the effect of stiffness on the skin keratinocyte behavior.

Volume Adaptation Controls Stem Cell Mechanotransduction.

Recent studies have found discordant mechanosensitive outcomes when comparing 2D and 3D, highlighting the need for tools to study mechanotransduction in 3D across a wide spectrum of stiffness. A gelatin methacryloyl (GelMA) hydrogel with a continuous stiffness gradient ranging from 5 to 38 kPa was developed to recapitulate physiological stiffness conditions. Adipose-derived stem cells (ASCs) were encapsulated in this hydrogel, and their morphological characteristics and expression of both mechanosensitive proteins (Lamin A, YAP, and MRTFa) and differentiation markers (PPARγ and RUNX2) were analyzed. Low-stiffness regions (∼8 kPa) permitted increased cellular and nuclear volume and enhanced mechanosensitive protein localization in the nucleus. This trend was reversed in high stiffness regions (∼30 kPa), where decreased cellular and nuclear volumes and reduced mechanosensitive protein nuclear localization were observed. Interestingly, cells in soft regions exhibited enhanced osteogenic RUNX2 expression, while those in stiff regions upregulated the adipogenic regulator PPARγ, suggesting that volume, not substrate stiffness, is sufficient to drive 3D stem cell differentiation. Inhibition of myosin II (Blebbistatin) and ROCK (Y-27632), both key drivers of actomyosin contractility, resulted in reduced cell volume, especially in low-stiffness regions, causing a decorrelation between volume expansion and mechanosensitive protein localization. Constitutively active and inactive forms of the canonical downstream mechanotransduction effector TAZ were stably transfected into ASCs. Activated TAZ resulted in higher cellular volume despite increasing stiffness and a consistent, stiffness-independent translocation of YAP and MRTFa into the nucleus. Thus, volume adaptation as a function of 3D matrix stiffness can control stem cell mechanotransduction and differentiation.

Studying Cell Mechanobiology in 3D: The Two-Photon Lithography Approach.

Two-photon lithography is a laser writing technique that can produce 3D microstructures with resolutions below the diffraction limit. This review focuses on its applications to study mechanical properties of cells, an emerging field known as mechanobiology. We review 3D structural designs and materials in the context of new experimental designs, including estimating forces exerted by single cells, studying selective adhesion on substrates, and creating 3D networks of cells. We then focus on emerging applications, including structures for assessing cancer cell invasiveness, whose migration properties depend on the cell mechanical response to the environment, and 3D architectures and materials to study stem cell differentiation, as 3D structure shape and patterning play a key role in defining cell fates.

Numerical Test for Cell Durotaxis Migration on Substrate with Moderate Gradient Stiffness / 医用生物力学

Objective Based on fibroblast cell model and photopolymerized hydrogel substrate with moderate gradient stiffness, to analyze the effect of process and performance parameters on cell migration and provide theoretical guidance for artificial scaffold design and fabrication. Methods A mathematical model of the test system was built and the corresponding numerical program was compiled, including viscoelastic dynamic finite element of the cell model, reaction kinetic equation of focal adhesions, and the strategy to deal with dynamic boundary and multi-scale time. Results The relationship between process parameters and performance parameters was formulated based on experimental data; cell migration speed and traction increased with the substrate stiffness increasing and were accompanied by rapid fluctuation when stiffness gradient was constant, then cell movement gradually stabilized with the extension of observation time. Increasing stiffness gradient moderately obviously promoted cell migration, and cells could maintain a limited speed on substrate with a large stiffness gradient. Smaller photomask opacity gradient resulted in larger substrate stiffness gradient and less time spent for cell to reach the target. These results agreed with the experimental results reported in the literature. Conclusions The experimental result provided an effective digital simulation platform to test the influence of process and performance parameter of photopolymerized hydrogel substrate with moderate gradient stiffness on cell migration.