3D microniches reveal the importance of cell size and shape

Spectrin mediates 3D-specific matrix stress-relaxation response in neural stem cell lineage commitment

While extracellular matrix (ECM) stress relaxation is increasingly appreciated to regulate stem cell fate commitment and other behaviors, much remains unknown about how cells process stress-relaxation cues in tissue-like three-dimensional (3D) geometries versus traditional 2D cell culture. Here, we develop an oligonucleotide-crosslinked hyaluronic acid-based ECM platform with tunable stress relaxation properties capable of use in either 2D or 3D. Strikingly, stress relaxation favors neural stem cell (NSC) neurogenesis in 3D but suppresses it in 2D. RNA sequencing and functional studies implicate the membrane-associated protein spectrin as a key 3D-specific transducer of stress-relaxation cues. Confining stress drives spectrin's recruitment to the F-actin cytoskeleton, where it mechanically reinforces the cortex and potentiates mechanotransductive signaling. Increased spectrin expression is also accompanied by increased expression of the transcription factor EGR1, which we previously showed mediates NSC stiffness-dependent lineage commitment in 3D. Our work highlights spectrin as an important molecular sensor and transducer of 3D stress-relaxation cues.

Hydrogels: a promising therapeutic platform for inflammatory skin diseases treatment

Inflammatory skin diseases, such as psoriasis and atopic dermatitis, pose significant health challenges due to their long-lasting nature, potential for serious complications, and significant health risks, which requires treatments that are both effective and exhibit minimal side effects. Hydrogels offer an innovative solution due to their biocompatibility, tunability, controlled drug delivery capabilities, enhanced treatment adherence and minimized side effects risk. This review explores the mechanisms that guide the design of hydrogel therapeutic platforms from multiple perspectives, focusing on the components of hydrogels, their adjustable physical and chemical properties, and their interactions with cells and drugs to underscore their clinical potential. We also examine various therapeutic agents for psoriasis and atopic dermatitis that can be integrated into hydrogels, including traditional drugs, novel compounds targeting oxidative stress, small molecule drugs, biologics, and emerging therapies, offering insights into their mechanisms and advantages. Additionally, we review clinical trial data to evaluate the effectiveness and safety of hydrogel-based treatments in managing psoriasis and atopic dermatitis under complex disease conditions. Lastly, we discuss the current challenges and future opportunities for hydrogel therapeutics in treating psoriasis and atopic dermatitis, such as improving skin barrier penetration and developing multifunctional hydrogels, and highlight emerging opportunities to enhance long-term safety and stability.

Cofunctionalization of Macroporous Dextran Hydrogels with Adhesive Peptides and Growth Factors Enables Vascular Spheroid Sprouting

Ensuring good definition of scaffolds used for 3D cell culture is a prominent challenge that hampers the development of tissue engineering platforms. Since dextran repels cell adhesion, using dextran-based materials biofunctionalized through a bottom-up approach allows for precise control over material definition. Here, we report the design of dextran hydrogels displaying a fully interconnected macropore network for the culture of vascular spheroids in vitro. We biofunctionalized the hydrogels with the RGD peptide sequence to promote cell adhesion. We used an affinity peptide pair, the E/K coiled coil, to load the gels with epidermal growth factor (EGF) and vascular endothelial growth factor (VEGF). Dual functionalization with adhesive and proliferative cues allows vascular spheroids to colonize naturally cell-repellant dextran. In supplement-depleted medium, we report improved colonization of the macropores compared to that of unmodified dextran. Altogether, we propose a well-defined and highly versatile platform for tissue engineering and tissue vascularization applications.

Unveiling the Intricate Connection: Cell Volume as a Key Regulator of Mechanotransduction

The volumes of living cells undergo dynamic changes to maintain the cells' structural and functional integrity in many physiological processes. Minor fluctuations in cell volume can serve as intrinsic signals that play a crucial role in cell fate determination during mechanotransduction. In this review, we discuss the variability of cell volume and its role in vivo, along with an overview of the mechanisms governing cell volume regulation. Additionally, we provide insights into the current approaches used to control cell volume in vitro. Furthermore, we summarize the biological implications of cell volume regulation and discuss recent advances in understanding the fundamental relationship between cell volume and mechanotransduction. Finally, we delve into the potential underlying mechanisms, including intracellular macromolecular crowding and cellular mechanics, that govern the global regulation of cell fate in response to changes in cell volume. By exploring the intricate interplay between cell volume and mechanotransduction, we underscore the importance of considering cell volume as a fundamental signaling cue to unravel the basic principles of mechanotransduction. Additionally, we propose future research directions that can extend our current understanding of cell volume in mechanotransduction. Overall, this review highlights the significance of considering cell volume as a fundamental signal in understanding the basic principles in mechanotransduction and points out the possibility of controlling cell volume to control cell fate, mitigate disease-related damage, and facilitate the healing of damaged tissues.

The Role of Biophysical Factors in Organ Development: Insights from Current Organoid Models

Biophysical factors play a fundamental role in human embryonic development. Traditional in vitro models of organogenesis focused on the biochemical environment and did not consider the effects of mechanical forces on developing tissue. While most human tissue has a Young's modulus in the low kilopascal range, the standard cell culture substrate, plasma-treated polystyrene, has a Young's modulus of 3 gigapascals, making it 10,000-100,000 times stiffer than native tissues. Modern in vitro approaches attempt to recapitulate the biophysical niche of native organs and have yielded more clinically relevant models of human tissues. Since Clevers' conception of intestinal organoids in 2009, the field has expanded rapidly, generating stem-cell derived structures, which are transcriptionally similar to fetal tissues, for nearly every organ system in the human body. For this reason, we conjecture that organoids will make their first clinical impact in fetal regenerative medicine as the structures generated ex vivo will better match native fetal tissues. Moreover, autologously sourced transplanted tissues would be able to grow with the developing embryo in a dynamic, fetal environment. As organoid technologies evolve, the resultant tissues will approach the structure and function of adult human organs and may help bridge the gap between preclinical drug candidates and clinically approved therapeutics. In this review, we discuss roles of tissue stiffness, viscoelasticity, and shear forces in organ formation and disease development, suggesting that these physical parameters should be further integrated into organoid models to improve their physiological relevance and therapeutic applicability. It also points to the mechanotransductive Hippo-YAP/TAZ signaling pathway as a key player in the interplay between extracellular matrix stiffness, cellular mechanics, and biochemical pathways. We conclude by highlighting how frontiers in physics can be applied to biology, for example, how quantum entanglement may be applied to better predict spontaneous DNA mutations. In the future, contemporary physical theories may be leveraged to better understand seemingly stochastic events during organogenesis.

The impact of tumor microenvironment: unraveling the role of physical cues in breast cancer progression

Metastasis accounts for the vast majority of breast cancer-related fatalities. Although the contribution of genetic and epigenetic modifications to breast cancer progression has been widely acknowledged, emerging evidence underscores the pivotal role of physical stimuli in driving breast cancer metastasis. In this review, we summarize the changes in the mechanics of the breast cancer microenvironment and describe the various forces that impact migrating and circulating tumor cells throughout the metastatic process. We also discuss the mechanosensing and mechanotransducing molecules responsible for promoting the malignant phenotype in breast cancer cells. Gaining a comprehensive understanding of the mechanobiology of breast cancer carries substantial potential to propel progress in prognosis, diagnosis, and patient treatment.

Functional meniscus reconstruction with biological and biomechanical heterogeneities through topological self-induction of stem cells

Meniscus injury is one of the most common sports injuries within the knee joint, which is also a crucial pathogenic factor for osteoarthritis (OA). The current meniscus substitution products are far from able to restore meniscal biofunctions due to the inability to reconstruct the gradient heterogeneity of natural meniscus from biological and biomechanical perspectives. Here, inspired by the topology self-induced effect and native meniscus microstructure, we present an innovative tissue-engineered meniscus (TEM) with a unique gradient-sized diamond-pored microstructure (GSDP-TEM) through dual-stage temperature control 3D-printing system based on the mechanical/biocompatibility compatible high Mw poly(ε-caprolactone) (PCL). Biologically, the unique gradient microtopology allows the seeded mesenchymal stem cells with spatially heterogeneous differentiation, triggering gradient transition of the extracellular matrix (ECM) from the inside out. Biomechanically, GSDP-TEM presents excellent circumferential tensile modulus and load transmission ability similar to the natural meniscus. After implantation in rabbit knee, GSDP-TEM induces the regeneration of biomimetic heterogeneous neomeniscus and efficiently alleviates joint degeneration. This study provides an innovative strategy for functional meniscus reconstruction. Topological self-induced cell differentiation and biomechanical property also provides a simple and effective solution for other complex heterogeneous structure reconstructions in the human body and possesses high clinical translational potential.

ARTseq-FISH reveals position-dependent differences in gene expression of micropatterned mESCs

Differences in gene-expression profiles between individual cells can give rise to distinct cell fate decisions. Yet how localisation on a micropattern impacts initial changes in mRNA, protein, and phosphoprotein abundance remains unclear. To identify the effect of cellular position on gene expression, we developed a scalable antibody and mRNA targeting sequential fluorescence in situ hybridisation (ARTseq-FISH) method capable of simultaneously profiling mRNAs, proteins, and phosphoproteins in single cells. We studied 67 (phospho-)protein and mRNA targets in individual mouse embryonic stem cells (mESCs) cultured on circular micropatterns. ARTseq-FISH reveals relative changes in both abundance and localisation of mRNAs and (phospho-)proteins during the first 48 hours of exit from pluripotency. We confirm these changes by conventional immunofluorescence and time-lapse microscopy. Chemical labelling, immunofluorescence, and single-cell time-lapse microscopy further show that cells closer to the edge of the micropattern exhibit increased proliferation compared to cells at the centre. Together these data suggest that while gene expression is still highly heterogeneous position-dependent differences in mRNA and protein levels emerge as early as 12 hours after LIF withdrawal.

Effect of Functionalization of Texturized Polypropylene Surface by Silanization and HBII-RGD Attachment on Response of Primary Abdominal and Vaginal Fibroblasts

Soft tissue defects, such as incisional hernia or pelvic organ prolapse, are prevalent pathologies characterized by a tissue microenvironment rich in fragile and dysfunctional fibroblasts. Precision medicine could improve their surgical repair, currently based on polymeric materials. Nonetheless, biomaterial-triggered interventions need first a better understanding of the cell-material interfaces that truly consider the patients' biology. Few tools are available to study the interactions between polymers and dysfunctional soft tissue cells in vitro. Here, we propose polypropylene (PP) as a matrix to create microscale surfaces w/wo functionalization with an HBII-RGD molecule, a fibronectin fragment modified to include an RGD sequence for promoting cell attachment and differentiation. Metal mold surfaces were roughened by shot blasting with aluminum oxide, and polypropylene plates were obtained by injection molding. HBII-RGD was covalently attached by silanization. As a proof of concept, primary abdominal and vaginal wall fasciae fibroblasts from control patients were grown on the new surfaces. Tissue-specific significant differences in cell morphology, early adhesion and cytoskeletal structure were observed. Roughness and biofunctionalization parameters exerted unique and combinatorial effects that need further investigation. We conclude that the proposed model is effective and provides a new framework to inform the design of smart materials for the treatment of clinically compromised tissues.

Nectin-4 regulates cellular senescence-associated enlargement of cell size

Cellular senescence is defined as irreversible growth arrest induced by various stress, such as DNA damage and oxidative stress. Senescent cells exhibit various characteristic morphological changes including enlarged morphology. In our recent study, we identified Nectin-4 to be upregulated in cellular senescence by comparative transcriptomic analysis. However, there are few reports on the relationship between Nectin-4 and senescence. Therefore, we analyzed the function of Nectin-4 in senescence and its biological significance. When overexpressed with Nectin-4, the cells exhibited the enlarged cell morphology closely resembling senescent cells. In addition, the cell size enlargement during DNA damage-induced senescence was suppressed by knockdown of Nectin-4, while there were no significant changes in senescence induction. These results suggest that Nectin-4 is not involved in the regulation of senescence itself but contributes to the senescence-associated cell size increase. Furthermore, the Nectin-4-dependent cell size increase was found to be mediated by Src family kinase (SFK)/PI3 kinase (PI3K)/Rac1 pathway. To explore the functional consequences of cell size enlargement, we analyzed cell survival in Nectin-4-depleted senescent cells. Single-cell tracking experiments revealed that Nectin-4 knockdown induced apoptosis in senescent cells, and there is a strong positive correlation between cell size and survival rate. These results collectively indicate that Nectin-4 plays a causative role in the senescence-associated cell size enlargement via SFK/PI3K/Rac1, which can contribute to survival of senescent cells.

Tumor-Derived Membrane Vesicles Restrain Migration in Gliomas By Altering Collective Polarization

Mechanobiology is a cornerstone in physiology. However, its role in biomedical applications remains considerably undermined. In this study, we employed cell membrane vesicles (CMVs), which are currently being used as nanodrug carriers, as tactile cues for mechano-regulation of collective cell behaviors. Gliomas, which are among the most resilient brain tumors and have a low patient survival rate, were used as the cell model. We observed that mechanical responses due to the application of glioma- or microglia-derived CMVs resulted in the doubling of the traction stress of glioma cell collectives with a 10-fold increase in the CMV concentration. Glioma-CMVs constrained cell protrusions and hindered their collective migration, with the migration speed of such cells declining by almost 40% compared to the untreated cells. We speculated that the alteration of collective polarization leads to migration speed changes, and this phenomenon was elucidated using the cellular Potts model. In addition to intracellular force modulation and cytoskeletal reorganization, glioma-CMVs altered drug diffusion within glioma spheroids by downregulating the mechano-signaling protein YAP-1 while also marginally enhancing the associated apoptotic events. Our results suggest that glioma-CMVs can be applied as an adjuvant to current treatment approaches to restrict tumor invasion and enhance the penetration of reagents within tumors. Considering the broad impact of mechano-transduction on cell functions, the regulation of cell mechanics through CMVs can provide a foundation for alternative therapeutic strategies.

Implications of Cellular Mechanical Memory in Bioengineering

The ability to maintain and differentiate cells in vitro is critical to many advances in the field of bioengineering. However, on traditional, stiff (E ≈ GPa) culture substrates, cells are subjected to sustained mechanical stress that can lead to phenotypic changes. Such changes may remain even after transferring the cells to another scaffold or engrafting them in vivo and bias the outcomes of the biological investigation or clinical treatment. This persistence─or mechanical memory─was initially observed for sustained myofibroblast activation of pulmonary fibroblasts after culturing them on stiff (E ≈ 100 kPa) substrates. Aspects of mechanical memory have now been described in many in vitro contexts. In this Review, we discuss the stiffness-induced effectors of mechanical memory: structural changes in the cytoskeleton and activity of transcription factors and epigenetic modifiers. We then focus on how mechanical memory impacts cell expansion and tissue regeneration outcomes in bioengineering applications relying on prolonged 2D plastic culture, such as stem cell therapies and disease models. We propose that alternatives to traditional cell culture substrates can be used to mitigate or erase mechanical memory and improve the efficiency of downstream cell-based bioengineering applications.

Dynamic Stiffening Hydrogel with Instructive Stiffening Timing Modulates Stem Cell Fate In Vitro and Enhances Bone Remodeling In Vivo

Biomechanical stimuli derived from the extracellular matrix (ECM) extremely tune stem cell fate through 3D and spatiotemporal changes in vivo. The matrix stiffness is a crucial factor during bone tissue development. However, most in vitro models to study the osteogenesis of mesenchymal stem cells (MSCs) are static or stiffening in a 2D environment. Here, a dynamic and controllable stiffening 3D biomimetic model is created to regulate the osteogenic differentiation of MSCs with a dual-functional gelatin macromer that can generate a double-network hydrogel by sequential enzymatic and light-triggered crosslinking reactions. The findings show that these dynamic hydrogels allowed cells to spread and expand prior to the secondary crosslinking and to sense high stiffness after stiffening. The MSCs in the dynamic hydrogels, especially the hydrogel stiffened at the late period, present significantly elevated osteogenic ECM secretion, gene expression, and nuclear localization of Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ). In vivo evaluation of animal experiments further indicates that the enhancement of dynamic stiffening on osteogenesis of MSCs substantially promotes bone remodeling. Consequently, this work reveals that the 3D dynamic stiffening microenvironment as a critical biophysical cue not only mediates the stem cell fate in vitro, but also augments bone restoration in vivo.

Acoustic quasi-periodic bioassembly based diverse stem cell arrangements for differentiation guidance

Arrangement patterns and geometric cues have been demonstrated to influence cell function and fate, which calls for efficient and versatile cell patterning techniques. Despite constant achievements that mainly focus on individual cells and uniform cell patterns, simultaneously constructing cellular arrangements with diverse patterns and positional relationships in a flexible and contact-free manner remains a challenge. Here, stem cell arrangements possessing multiple geometries and structures are proposed based on powerful and diverse pattern-building capabilities of quasi-periodic acoustic fields, with advantages of rich patterns and structures and flexibility in structure modulation. Eight-fold waves' interference produces regular potentials that result in higher rotational symmetry and more complex arrangement of geometric units. Moreover, through flexible modulation of the phase relations among these wave vectors, a wide variety of cellular pattern units are arranged in this potential, such as circular-, triangular- and square-shape, simultaneously. It is proved that these diverse cellular patterns conveniently build human mesenchymal stem cell (hMSC) models, for research on the effect of cellular arrangement on stem cell differentiation. This work fills the gap of acoustic cell patterning in quasi-periodic patterns and shows promising potential in tissue engineering and regenerative medicine.

Towards single cell encapsulation for precision biology and medicine

The primary impetus of therapeutic cell encapsulation in the past several decades has been to broaden the options for donor cell sources by countering against immune-mediated rejection. However, another significant advantage of encapsulation is to provide donor cells with physiologically relevant cues that become compromised in disease. The advances in biomaterial design have led to the fundamental insight that cells sense and respond to various signals encoded in materials, ranging from biochemical to mechanical cues. The biomaterial design for cell encapsulation is becoming more sophisticated in controlling specific aspects of cellular phenotypes and more precise down to the single cell level. This recent progress offers a paradigm shift by designing single cell-encapsulating materials with predefined cues to precisely control donor cells after transplantation.

Effects of ionic liquids on biomembranes: A review on recent biophysical studies

Ionic liquids (ILs) have been emerged as a versatile class of compounds that can be easily tuned to achieve desirable properties for various applications. The ability of ILs to interact with biomembranes has attracted significant interest, as they have been shown to modulate membrane properties in ways that may have implications for various biological processes. This review provides an overview of recent studies that have investigated the interaction between ILs and biomembranes. We discuss the effects of ILs on the physical and chemical properties of biomembranes, including changes in membrane fluidity, permeability, and stability. We also explore the mechanisms underlying the interaction of ILs with biomembranes, such as electrostatic interactions, hydrogen bonding, and van der Waals forces. Additionally, we discuss the future prospects of this field.

Metabolic regulation of endothelial senescence

Endothelial cell (EC) senescence is increasingly recognized as a significant contributor to the development of vascular dysfunction and age-related disorders and diseases, including cancer and cardiovascular diseases (CVD). The regulation of cellular senescence is known to be influenced by cellular metabolism. While extensive research has been conducted on the metabolic regulation of senescence in other cells such as cancer cells and fibroblasts, our understanding of the metabolic regulation of EC senescence remains limited. The specific metabolic changes that drive EC senescence are yet to be fully elucidated. The objective of this review is to provide an overview of the intricate interplay between cellular metabolism and senescence, with a particular emphasis on recent advancements in understanding the metabolic changes preceding cellular senescence. I will summarize the current knowledge on the metabolic regulation of EC senescence, aiming to offer insights into the underlying mechanisms and future research directions.

3D micropattern force triggers YAP nuclear entry by transport across nuclear pores and modulates stem cells paracrine

Biophysical cues of the cellular microenvironment tremendously influence cell behavior by mechanotransduction. However, it is still unclear how cells sense and transduce the mechanical signals from 3D geometry to regulate cell function. Here, the mechanotransduction of human mesenchymal stem cells (MSCs) triggered by 3D micropatterns and its effect on the paracrine of MSCs are systematically investigated. Our findings show that 3D micropattern force could influence the spatial reorganization of the cytoskeleton, leading to different local forces which mediate nucleus alteration such as orientation, morphology, expression of Lamin A/C and chromatin condensation. Specifically, in the triangular prism and cuboid micropatterns, the ordered F-actin fibers are distributed over and fully transmit compressive forces to the nucleus, which results in nuclear flattening and stretching of nuclear pores, thus enhancing the nuclear import of YES-associated protein (YAP). Furthermore, the activation of YAP significantly enhances the paracrine of MSCs and upregulates the secretion of angiogenic growth factors. In contrast, the fewer compressive forces on the nucleus in cylinder and cube micropatterns cause less YAP entering the nucleus. The skin repair experiment provides the first in vivo evidence that enhanced MSCs paracrine by 3D geometry significantly promotes tissue regeneration. The current study contributes to understanding the in-depth mechanisms of mechanical signals affecting cell function and provides inspiration for innovative design of biomaterials.

Downregulation of YAP Activity Restricts P53 Hyperactivation to Promote Cell Survival in Confinement

Cell migration through confining three dimensional (3D) topographies can lead to loss of nuclear envelope integrity, DNA damage, and genomic instability. Despite these detrimental phenomena, cells transiently exposed to confinement do not usually die. Whether this is also true for cells subjected to long-term confinement remains unclear at present. To investigate this, photopatterning and microfluidics are employed to fabricate a high-throughput device that circumvents limitations of previous cell confinement models and enables prolonged culture of single cells in microchannels with physiologically relevant length scales. The results of this study show that continuous exposure to tight confinement can trigger frequent nuclear envelope rupture events, which in turn promote P53 activation and cell apoptosis. Migrating cells eventually adapt to confinement and evade cell death by downregulating YAP activity. Reduced YAP activity, which is the consequence of confinement-induced YAP1/2 translocation to the cytoplasm, suppresses the incidence of nuclear envelope rupture and abolishes P53-mediated cell death. Cumulatively, this work establishes advanced, high-throughput biomimetic models for better understanding cell behavior in health and disease, and underscores the critical role of topographical cues and mechanotransduction pathways in the regulation of cell life and death.

Geometric Confinement-Mediated Mechanical Tension Directs Patterned Differentiation of Mouse ESCs into Organized Germ Layers

The self-organization of embryonic stem cells (ESCs) into organized tissues with three distinct germ layers is critical to morphogenesis and early development. While the regulation of this self-organization by soluble signals is well established, the involvement of mechanical force gradients in this process remains unclear due to the lack of a suitable platform to study this process. In this study, we developed a 3D microenvironment to examine the influence of mechanical tension gradients on ESC-patterned differentiation during morphogenesis by controlling the geometrical signals (shape and size) of ESC colonies. We found that changes in colony geometry impacted the germ layer pattern, with Cdx2-positive cells being more abundant at edges and in areas with high curvatures. The differentiation patterns were determined by geometry-mediated cell tension gradients, with an extraembryonic mesoderm-like layer forming in high-tension regions and ectodermal-like lineages at low-tension regions in the center. Suppression of cytoskeletal tension hindered ESC self-organization. These results indicate that geometric confinement-mediated mechanical tension plays a crucial role in linking multicellular organization to cell differentiation and impacting tissue patterning.

Cell-extracellular matrix mechanotransduction in 3D

Mechanical properties of extracellular matrices (ECMs) regulate essential cell behaviours, including differentiation, migration and proliferation, through mechanotransduction. Studies of cell-ECM mechanotransduction have largely focused on cells cultured in 2D, on top of elastic substrates with a range of stiffnesses. However, cells often interact with ECMs in vivo in a 3D context, and cell-ECM interactions and mechanisms of mechanotransduction in 3D can differ from those in 2D. The ECM exhibits various structural features as well as complex mechanical properties. In 3D, mechanical confinement by the surrounding ECM restricts changes in cell volume and cell shape but allows cells to generate force on the matrix by extending protrusions and regulating cell volume as well as through actomyosin-based contractility. Furthermore, cell-matrix interactions are dynamic owing to matrix remodelling. Accordingly, ECM stiffness, viscoelasticity and degradability often play a critical role in regulating cell behaviours in 3D. Mechanisms of 3D mechanotransduction include traditional integrin-mediated pathways that sense mechanical properties and more recently described mechanosensitive ion channel-mediated pathways that sense 3D confinement, with both converging on the nucleus for downstream control of transcription and phenotype. Mechanotransduction is involved in tissues from development to cancer and is being increasingly harnessed towards mechanotherapy. Here we discuss recent progress in our understanding of cell-ECM mechanotransduction in 3D.

In vitro strategies for mimicking dynamic cell-ECM reciprocity in 3D culture models

The extracellular microenvironment regulates cell decisions through the accurate presentation at the cell surface of a complex array of biochemical and biophysical signals that are mediated by the structure and composition of the extracellular matrix (ECM). On the one hand, the cells actively remodel the ECM, which on the other hand affects cell functions. This cell-ECM dynamic reciprocity is central in regulating and controlling morphogenetic and histogenetic processes. Misregulation within the extracellular space can cause aberrant bidirectional interactions between cells and ECM, resulting in dysfunctional tissues and pathological states. Therefore, tissue engineering approaches, aiming at reproducing organs and tissues in vitro, should realistically recapitulate the native cell-microenvironment crosstalk that is central for the correct functionality of tissue-engineered constructs. In this review, we will describe the most updated bioengineering approaches to recapitulate the native cell microenvironment and reproduce functional tissues and organs in vitro. We have highlighted the limitations of the use of exogenous scaffolds in recapitulating the regulatory/instructive and signal repository role of the native cell microenvironment. By contrast, strategies to reproduce human tissues and organs by inducing cells to synthetize their own ECM acting as a provisional scaffold to control and guide further tissue development and maturation hold the potential to allow the engineering of fully functional histologically competent three-dimensional (3D) tissues.

Chromatin remodeling and nucleoskeleton synergistically control osteogenic differentiation in different matrix stiffnesses

Matrix stiffness plays an important role in determining cell differentiation. The expression of cell differentiation-associated genes can be regulated by chromatin remodeling-mediated DNA accessibility. However, the effect of matrix stiffness on DNA accessibility and its significance for cell differentiation have not been investigated. In this study, gelatin methacryloyl (GelMA) hydrogels with different degrees of substitution were used to simulate soft, medium, and stiff matrices, and it was found that a stiff matrix promoted osteogenic differentiation of MC3T3-E1 cells by activating the Wnt pathway. In the soft matrix, the acetylation level of histones in cells was decreased, and chromatin condensed into a closed conformation, affecting the activation of β-catenin target genes (Axin2, c-Myc). Histone deacetylase inhibitor (TSA) was used to decondense chromatin. However, there was no significant increase in the expression of β-catenin target genes and the osteogenic protein Runx2. Further studies revealed that β-catenin was restricted to the cytoplasm due to the downregulation of lamin A/C in the soft matrix. Overexpression of lamin A/C and concomitant treatment of cells with TSA successfully activated β-catenin/Wnt signaling in cells in the soft matrix. The results of this innovative study revealed that matrix stiffness regulates cell osteogenic differentiation through multiple pathways, which involve complex interactions between transcription factors, epigenetic modifications of histones, and the nucleoskeleton. This trio is critical for the future design of bionic extracellular matrix biomaterials.

Function follows form: How cell size is harnessed for developmental decisions

Cell size has profound effects on biological function, influencing a wide range of processes, including biosynthetic capacity, metabolism, and nutrient uptake. As a result, size is typically maintained within a narrow, population-specific range through size control mechanisms, which are an active area of study. While the physiological consequences of cell size are relatively well-characterized, less is known about its developmental consequences, and specifically its effects on developmental transitions. In this review, we compare systems where cell size is linked to developmental transitions, paying particular attention to examples from plants. We conclude by proposing that size can offer a simple readout of complex inputs, enabling flexible decisions during plant development.

Protease-degradable hydrogels with multifunctional biomimetic peptides for bone tissue engineering

Mimicking bone extracellular matrix (ECM) is paramount to develop novel biomaterials for bone tissue engineering. In this regard, the combination of integrin-binding ligands together with osteogenic peptides represents a powerful approach to recapitulate the healing microenvironment of bone. In the present work, we designed polyethylene glycol (PEG)-based hydrogels functionalized with cell instructive multifunctional biomimetic peptides (either with cyclic RGD-DWIVA or cyclic RGD-cyclic DWIVA) and cross-linked with matrix metalloproteinases (MMPs)-degradable sequences to enable dynamic enzymatic biodegradation and cell spreading and differentiation. The analysis of the intrinsic properties of the hydrogel revealed relevant mechanical properties, porosity, swelling and degradability to engineer hydrogels for bone tissue engineering. Moreover, the engineered hydrogels were able to promote human mesenchymal stem cells (MSCs) spreading and significantly improve their osteogenic differentiation. Thus, these novel hydrogels could be a promising candidate for applications in bone tissue engineering, such as acellular systems to be implanted and regenerate bone or in stem cells therapy.

Mechanobiology of cancer cell responsiveness to chemotherapy and immunotherapy: Mechanistic insights and biomaterial platforms

Mechanical forces are central to how cancer treatments such as chemotherapeutics and immunotherapies interact with cells and tissues. At the simplest level, electrostatic forces underlie the binding events that are critical to therapeutic function. However, a growing body of literature points to mechanical factors that also affect whether a drug or an immune cell can reach a target, and to interactions between a cell and its environment affecting therapeutic efficacy. These factors affect cell processes ranging from cytoskeletal and extracellular matrix remodeling to transduction of signals by the nucleus to metastasis of cells. This review presents and critiques the state of the art of our understanding of how mechanobiology impacts drug and immunotherapy resistance and responsiveness, and of the in vitro systems that have been of value in the discovery of these effects.

Elastomeric Pillar Cages Modulate Actomyosin Contractility of Epithelial Microtissues by Substrate Stiffness and Topography

Cell contractility regulates epithelial tissue geometry development and homeostasis. The underlying mechanobiological regulation circuits are poorly understood and experimentally challenging. We developed an elastomeric pillar cage (EPC) array to quantify cell contractility as a mechanoresponse of epithelial microtissues to substrate stiffness and topography. The spatially confined EPC geometry consisted of 24 circularly arranged slender pillars (1.2 MPa, height: 50 µm; diameter: 10 µm, distance: 5 µm). These high-aspect-ratio pillars were confined at both ends by planar substrates with different stiffness (0.15-1.2 MPa). Analytical modeling and finite elements simulation retrieved cell forces from pillar displacements. For evaluation, highly contractile myofibroblasts and cardiomyocytes were assessed to demonstrate that the EPC device can resolve static and dynamic cellular force modes. Human breast (MCF10A) and skin (HaCaT) cells grew as adherence junction-stabilized 3D microtissues within the EPC geometry. Planar substrate areas triggered the spread of monolayered clusters with substrate stiffness-dependent actin stress fiber (SF)-formation and substantial single-cell actomyosin contractility (150-200 nN). Within the same continuous microtissues, the pillar-ring topography induced the growth of bilayered cell tubes. The low effective pillar stiffness overwrote cellular sensing of the high substrate stiffness and induced SF-lacking roundish cell shapes with extremely low cortical actin tension (11-15 nN). This work introduced a versatile biophysical tool to explore mechanobiological regulation circuits driving low- and high-tensional states during microtissue development and homeostasis. EPC arrays facilitate simultaneously analyzing the impact of planar substrate stiffness and topography on microtissue contractility, hence microtissue geometry and function.

3D bioprinting of a gradient stiffened gelatin-alginate hydrogel with adipose-derived stem cells for full-thickness skin regeneration

Current hydrogel-based scaffolds offer a promising approach to accelerate tissue regeneration, but great challenges remain in developing platforms that mimic the physical microenvironment of tissues combined with therapeutic biological cues. Here, a 3D bioprinting gelatin-alginate hydrogel for the construction of gradient composite scaffolds that mimic the dermal stiffness microenvironment was developed for architecture construction by extruding the bioink on calcium-containing substrates to achieve gradient secondary cross-linking, meanwhile, adipose-derived stem cells were encapsulated in the present hydrogels for therapeutic purposes. The gradient-stiffness scaffold exhibited good stability and biocompatibility as well as enhanced proliferation and migration of the adipose-derived stem cells. In addition, the promoted angiogenesis and healing efficiency was demonstrated via the animal wound model and was mainly attributed to the enhanced paracrine secretion of adipose-derived stem cells by the physical microenvironment provided within the gradient stiffness scaffold. The current 3D printed gradient scaffolds provide adipose-derived stem cells with a distinct yet successive architecture rather than the typical uniform microenvironment to accelerate skin regeneration, which may have broader applications in other chronic wounds or tissue defects.

Static and Dynamic: Evolving Biomaterial Mechanical Properties to Control Cellular Mechanotransduction

The extracellular matrix (ECM) is a highly dynamic system that constantly offers physical, biological, and chemical signals to embraced cells. Increasing evidence suggests that mechanical signals derived from the dynamic cellular microenvironment are essential controllers of cell behaviors. Conventional cell culture biomaterials, with static mechanical properties such as chemistry, topography, and stiffness, have offered a fundamental understanding of various vital biochemical and biophysical processes, such as cell adhesion, spreading, migration, growth, and differentiation. At present, novel biomaterials that can spatiotemporally impart biophysical cues to manipulate cell fate are emerging. The dynamic properties and adaptive traits of new materials endow them with the ability to adapt to cell requirements and enhance cell functions. In this review, an introductory overview of the key players essential to mechanobiology is provided. A biophysical perspective on the state-of-the-art manipulation techniques and novel materials in designing static and dynamic ECM-mimicking biomaterials is taken. In particular, different static and dynamic mechanical cues in regulating cellular mechanosensing and functions are compared. This review to benefit the development of engineering biomechanical systems regulating cell functions is expected.

Deterministic Single Cell Encapsulation in Asymmetric Microenvironments to Direct Cell Polarity

Various signals in tissue microenvironments are often unevenly distributed around cells. Cellular responses to asymmetric cell-matrix adhesion in a 3D space remain generally unclear and are to be studied at the single-cell resolution. Here, the authors developed a droplet-based microfluidic approach to manufacture a pure population of single cells in a microscale layer of compartmentalized 3D hydrogel matrices with a tunable spatial presentation of ligands at the subcellular level. Cells elongate with an asymmetric presentation of the integrin adhesion ligand Arg-Gly-Asp (RGD), while cells expand isotropically with a symmetric presentation of RGD. Membrane tension is higher on the side of single cells interacting with RGD than on the side without RGD. Finite element analysis shows that a non-uniform isotropic cell volume expansion model is sufficient to recapitulate the experimental results. At a longer timescale, asymmetric ligand presentation commits mesenchymal stem cells to the osteogenic lineage. Cdc42 is an essential mediator of cell polarization and lineage specification in response to asymmetric cell-matrix adhesion. This study highlights the utility of precisely controlling 3D ligand presentation around single cells to direct cell polarity for regenerative engineering and medicine.

Cell-Laden Gradient Microgel Suspensions for Spatial Control of Differentiation During Biofabrication

During tissue development, stem and progenitor cells form functional tissue with high cellular diversity and intricate micro- and macro-architecture. Current approaches have attempted to replicate this process with materials cues or through spontaneous cell self-organization. However, cell-directed and materials-directed organization are required simultaneously to achieve biomimetic structure and function. Here, it is shown how integrating live adipose derived stem cells with gradient microgel suspensions steers divergent differentiation outcomes. Microgel matrices composed of small particles are found to promote adipogenic differentiation, while larger particles fostered increased cell spreading and osteogenic differentiation. Tuning the matrix formulation demonstrates that early cell adhesion and spreading dictate differentiation outcome. Combining small and large microgels into gradients spatially directs proliferation and differentiation over time. After 21 days of culture, osteogenic conditions foster significant mineralization within the individual microgels, thereby providing cell-directed changes in composition and mechanics within the gradient porous scaffold. Freeform printing of high-density cell suspensions is performed across these gradients to demonstrate the potential for hierarchical tissue biofabrication. Interstitial porosity influences cell expansion from the print and microgel size guides spatial differentiation, thereby providing scope to fabricate tissue gradients at multiple scales through integrated and printed cell populations.

Adding a new dimension: Multi-level structure and organization of mixed-species Pseudomonas aeruginosa and Staphylococcus aureus biofilms in a 4-D wound microenvironment

Biofilms in wounds typically consist of aggregates of bacteria, most often Pseudomonas aeruginosa and Staphylococcus aureus, in close association with each other and the host microenvironment. Given this, the interplay across host and microbial elements, including the biochemical and nutrient profile of the microenvironment, likely influences the structure and organization of wound biofilms. While clinical studies, in vivo and ex vivo model systems have provided insights into the distribution of P. aeruginosa and S. aureus in wounds, they are limited in their ability to provide a detailed characterization of biofilm structure and organization across the host-microbial interface. On the other hand, biomimetic in vitro systems, such as host cell surfaces and simulant media conditions, albeit reductionist, have been shown to support the co-existence of P. aeruginosa and S. aureus biofilms, with species-dependent localization patterns and interspecies interactions. Therefore, composite in vitro models that bring together key features of the wound microenvironment could provide unprecedented insights into the structure and organization of mixed-species biofilms. We have built a four-dimensional (4-D) wound microenvironment consisting of a 3-D host cell scaffold of co-cultured human epidermal keratinocytes and dermal fibroblasts, and an in vitro wound milieu (IVWM); the IVWM provides the fourth dimension that represents the biochemical and nutrient profile of the wound infection state. We leveraged this 4-D wound microenvironment, in comparison with biofilms in IVWM alone and standard laboratory media, to probe the structure of mixed-species P. aeruginosa and S. aureus biofilms across multiple levels of organization such as aggregate dimensions and biomass thickness, species co-localization and spatial organization within the biomass, overall biomass composition and interspecies interactions. In doing so, the 4-D wound microenvironment platform provides multi-level insights into the structure of mixed-species biofilms, which we incorporate into the current understanding of P. aeruginosa and S. aureus organization in the wound bed.

Cellular shape reinforces niche to stem cell signaling in the small intestine

Niche-derived factors regulate tissue stem cells, but apart from the mechanosensory pathways, the effect of niche geometry is not well understood. We used organoids and bioengineered tissue culture platforms to demonstrate that the conical shape of Lgr5+ small intestinal stem cells (ISCs) facilitate their self-renewal and function. Inhibition of non-muscle myosin II (NM II)-driven apical constriction altered ISC shape and reduced niche curvature and stem cell capacity. Niche curvature is decreased in aged mice, suggesting that suboptimal interactions between old ISCs and their niche develop with age. We show that activation of NM IIC or physical restriction to young topology improves in vitro regeneration by old epithelium. We propose that the increase in lateral surface area of ISCs induced by apical constriction promotes interactions between neighboring cells, and the curved topology of the intestinal niche has evolved to maximize signaling between ISCs and neighboring cells.

Mechanotransduction in high aspect ratio nanostructured meta-biomaterials: The role of cell adhesion, contractility, and transcriptional factors

Black Ti (bTi) surfaces comprising high aspect ratio nanopillars exhibit a rare combination of bactericidal and osteogenic properties, framing them as cell-instructive meta-biomaterials. Despite the existing data indicating that bTi surfaces induce osteogenic differentiation in cells, the mechanisms by which this response is regulated are not fully understood. Here, we hypothesized that high aspect ratio bTi nanopillars regulate cell adhesion, contractility, and nuclear translocation of transcriptional factors, thereby inducing an osteogenic response in the cells. Upon the observation of significant changes in the morphological characteristics, nuclear localization of Yes-associated protein (YAP), and Runt-related transcription factor 2 (Runx2) expression in the human bone marrow-derived mesenchymal stem cells (hMSCs), we inhibited focal adhesion kinase (FAK), Rho-associated protein kinase (ROCK), and YAP in separate experiments to elucidate their effects on the subsequent expression of Runx2. Our findings indicated that the increased expression of Runx2 in the cells residing on the bTi nanopillars compared to the flat Ti is highly dependent on the activity of FAK and ROCK. A mechanotransduction pathway is then postulated in which the FAK-dependent adhesion of cells to the extreme topography of the surface is in close relation with ROCK to increase the endogenous forces within the cells, eventually determining the cell shape and area. The nuclear translocation of YAP may also enhance in response to the changes in cell shape and area, resulting in the translation of mechanical stimuli to biochemical factors such as Runx2.

Stem-cell-based human and mouse embryo models

Synthetic embryology aims to develop embryo-like structures from stem cells to provide new insight into early stages of mammalian development. Recent advances in synthetic embryology have highlighted the remarkable capacity of stem cells to self-organize under certain biochemical or biophysical stimulations, generating structures that recapitulate the fate and form of early mouse/human embryos, in which symmetry breaking, pattern formation, or proper morphogenesis can be observed spontaneously. Here we review recent progress on the design principles for different types of embryoids and discuss the impact of different biochemical and biophysical factors on the process of stem-cell self-organization. We also offer our thoughts about the principal future challenges.

Targeting the Hippo/YAP/TAZ signalling pathway: Novel opportunities for therapeutic interventions into skin cancers

Skin cancers are by far the most frequently diagnosed human cancers. The closely related transcriptional co-regulator proteins YAP and TAZ (WWTR1) have emerged as important drivers of tumour initiation, progression and metastasis in melanoma and non-melanoma skin cancers. YAP/TAZ serve as an essential signalling hub by integrating signals from multiple upstream pathways. In this review, we summarize the roles of YAP/TAZ in skin physiology and tumorigenesis and discuss recent efforts of therapeutic interventions that target YAP/TAZ in in both preclinical and clinical settings, as well as their prospects for use as skin cancer treatments.

Recent Advances in Macroporous Hydrogels for Cell Behavior and Tissue Engineering

Hydrogels have been extensively used as scaffolds in tissue engineering for cell adhesion, proliferation, migration, and differentiation because of their high-water content and biocompatibility similarity to the extracellular matrix. However, submicron or nanosized pore networks within hydrogels severely limit cell survival and tissue regeneration. In recent years, the application of macroporous hydrogels in tissue engineering has received considerable attention. The macroporous structure not only facilitates nutrient transportation and metabolite discharge but also provides more space for cell behavior and tissue formation. Several strategies for creating and functionalizing macroporous hydrogels have been reported. This review began with an overview of the advantages and challenges of macroporous hydrogels in the regulation of cellular behavior. In addition, advanced methods for the preparation of macroporous hydrogels to modulate cellular behavior were discussed. Finally, future research in related fields was discussed.

3D Interfacial and Spatiotemporal Regulation of Human Neuroepithelial Organoids

Neuroepithelial (NE) organoids with dorsal-ventral patterning provide a useful three-dimensional (3D) in vitro model to interrogate neural tube formation during early development of the central nervous system. Understanding the fundamental processes behind the cellular self-organization in NE organoids holds the key to the engineering of organoids with higher, more in vivo-like complexity. However, little is known about the cellular regulation driving the NE development, especially in the presence of interfacial cues from the microenvironment. Here a simple 3D culture system that allows generation and manipulation of NE organoids from human-induced pluripotent stem cells (hiPSCs), displaying developmental phases of hiPSC differentiation and self-aggregation, first into NE cysts with lumen structure and then toward NE organoids with floor-plate patterning, is established. Longitudinal inhibition reveals distinct and dynamic roles of actomyosin contractility and yes-associated protein (YAP) signaling in governing these phases. By growing NE organoids on culture chips containing anisotropic surfaces or confining microniches, it is further demonstrated that interfacial cues can sensitively exert dimension-dependent influence on luminal cyst and organoid morphology, successful floor-plate patterning, as well as cytoskeletal regulation and YAP activity. This study therefore sheds new light on how organoid and tissue architecture can be steered through intracellular and extracellular means.

An Appearance Data-Driven Model Visualizes Cell State and Predicts Mesenchymal Stem Cell Regenerative Capacity

Mesenchymal stem cells (MSCs) are widely used in treating various diseases. However, lack of a reliable evaluation approach to characterize the potency of MSCs has dampened their clinical applications. Here, a function-oriented mathematical model is established to evaluate and predict the regenerative capacity (RC) of MSCs. Processed by exhaustive testing, the model excavates four optimal fitted indices, including nucleus roundness, nucleus/cytoplasm ratio, side-scatter height, and ERK1/2 from the given index combinations. Notably, three of them except ERK1/2 are cell appearance-associated features. The predictive power of the model is validated via screening experiments of these indices by predicting the RC of newly enrolled and chemical inhibitor-treated MSCs. Further RNA-sequencing analysis reveals that cell appearance-based indices may serve as major indicators to visualize the results of integration-weighted signals in and out of cells and reflect MSC stemness. In general, this study proposes an appearance data-driven predictive model for the RC and stemness of MSCs.

[Hypoxia promotes differentiation of human induced pluripotent stem cells into embryoid bodies in vitro]

OBJECTIVE

To investigate effects of physiological hypoxic conditions on suspension and adherence of embryoid bodies (EBs) during differentiation of human induced pluripotent stem cells (hiPSCs) and explore the underlying mechanisms.

METHODS

EBs in suspension culture were divided into normoxic (21% O₂) and hypoxic (5% O₂) groups, and those in adherent culture were divided into normoxic, hypoxic and hypoxia + HIF-1α inhibitor (echinomycin) groups. After characterization of the pluripotency with immunofluorescence assay, the hiPSCs were digested and suspended under normoxic and hypoxic conditions for 5 days, and the formation and morphological changes of the EBs were observed microscopically; the expressions of the markers genes of the 3 germ layers in the EBs were detected. The EBs were then inoculated into petri dishes for further culture in normoxic and hypoxic conditions for another 2 days, after which the adhesion and peripheral expansion rate of the adherent EBs were observed; the changes in the expressions of HIF-1α, β-catenin and VEGFA were detected in response to hypoxic culture and echinomycin treatment.

RESULTS

The EBs cultured in normoxic and hypoxic conditions were all capable of differentiation into the 3 germ layers. The EBs cultured in hypoxic conditions showed reduced apoptotic debris around them with earlier appearance of cystic EBs and more uniform sizes as compared with those in normoxic culture. Hypoxic culture induced more adherent EBs than normoxic culture (P < 0.05) with also a greater outgrowth rate of the adherent EBs (P < 0.05). The EBs in hypoxic culture showed significantly up-regulated mRNA expressions of β-catenin and VEGFA (P < 0.05) and protein expressions of HIF-1 α, β-catenin and VEGFA (P < 0.05), and their protein expresisons levels were significantly lowered after treatment with echinomycin (P < 0.05).

CONCLUSION

Hypoxia can promote the formation and maturation of suspended EBs and enhance their adherence and post-adherent proliferation without affecting their pluripotency for differentiation into all the 3 germ layers. Our results provide preliminary evidence that activation of HIF-1α/β-catenin/VEGFA signaling pathway can enhance the differentiation potential of hiPSCs.

Versatile polyphenolic platforms in regulating cell biology

Polyphenolic materials are a class of fascinating and versatile bioinspired materials for biointerfacial engineering. In particular, due to the presence of active chemical groups, a series of unique physicochemical properties become accessible and tunable of the as-prepared polyphenolic platforms, which could delicately regulate the cell activities via cell-material contact-dependent interactions. More interestingly, polyphenols could also affect the cell behaviors via cell-material contact-independent manner, which arise due to their intrinsically functional characteristics (e.g., antioxidant and photothermal behaviors). As such, a comprehensive understanding on the relationship between material properties and desired biomedical applications, as well as the underlying mechanism at the cellular and molecular level would provide material design principles and accelerate the lab-to-clinic translation of polyphenolic platforms. In this review, we firstly give a brief overview of cell hallmarks governed by surrounding cues, followed by the introduction of polyphenolic material engineering strategies. Subsequently, a detailed discussion on cell-polyphenols contact-dependent interfacial interaction and contact-independent interaction was also carefully provided. Lastly, their biomedical applications were elaborated. We believe that this review could provide guidances for the rational material design of multifunctional polyphenols and extend their application window.

Heterogeneous spheroids with tunable interior morphologies by droplet-based microfluidics

Heterogeneous spheroids that mimic the complex three-dimensional environment of natural tissues are needed in various biomedical applications. Geometric cues from cellular matrix play invaluable roles in governing cell behavior and phenotype. However, the structural complexity of interior morphologies of spheroids is currently limited due to poor spatial resolution of positioning/orientation of cellular constructs. Here, a coaxial capillary microfluidic device is developed to generate gelatin methacrylate (GelMA) microspheres with tunable dimensions and interior morphologies, such as core-shell, or microspheres with interior undulated wavy, or spiral canals, by manipulating the two-phase flow of hydrogel precursor solution and methylcellulose solution. The formation of diverse and exquisite interior morphologies is caused by the interacting viscous instabilities of the two-phase flow in the microfluidic system, followed by water-in-oil emulsion and photo-initiated polymerization. Polyethylene glycol diacrylate (PEGDA) is incorporated into the GelMA solution to tune the mechanical properties of the fabricated microspheres, and an optimized concentration of PEGDA is confirmed by evaluating the in vitro proliferation and vascularization of human umbilical endothelial cells. Further, a heterogeneous spheroid with spiral blood vessel lumen is constructed to demonstrate the versatility and potential of the proposed droplet-based microfluidic approach for building functional tissue constructs.

Nanoimprinting for high-throughput replication of geometrically precise pillars in fused silica to regulate cell behavior

Developing high-throughput nanopatterning techniques that also allow for precise control over the dimensions of the fabricated features is essential for the study of cell-nanopattern interactions. Here, we developed a process that fulfills both of these criteria. Firstly, we used electron-beam lithography (EBL) to fabricate precisely controlled arrays of submicron pillars with varying values of interspacing on a large area of fused silica. Two types of etching procedures with two different systems were developed to etch the fused silica and create the final desired height. We then studied the interactions of preosteoblasts (MC3T3-E1) with these pillars. Varying interspacing was observed to significantly affect the morphological characteristics of the cell, the organization of actin fibers, and the formation of focal adhesions. The expression of osteopontin (OPN) significantly increased on the patterns, indicating the potential of the pillars for inducing osteogenic differentiation. The EBL pillars were thereafter used as master molds in two subsequent processing steps, namely soft lithography and thermal nanoimprint lithography for high-fidelity replication of the pillars on the substrates of interest. The molding parameters were optimized to maximize the fidelity of the generated patterns and minimize the wear and tear of the master mold. Comparing the replicated feature with those present on the original mold confirmed that the geometry and dimensions of the replicated pillars closely resemble those of the original ones. The method proposed in this study, therefore, enables the precise fabrication of submicron- and nanopatterns on a wide variety of materials that are relevant for systematic cell studies. STATEMENT OF SIGNIFICANCE: Submicron pillars with specific dimensions on the bone implants have been proven to be effective in controlling cell behaviors. Nowadays, numerous methods have been proposed to produce bio-instructive submicron-topographies. However, most of these techniques are suffering from being low-throughput, low-precision, and expensive. Here, we developed a high-throughput nanopatterning technique that allows for control over the dimensions of the features for the study of cell-nanotopography interactions. Assessing the adaptation of preosteoblast cells showed the potential of the pillars for inducing osteogenic differentiation. Afterward, the pillars were used for high-fidelity replication of the bio-instructive features on the substrates of interest. The results show the advantages of nanoimprint lithography as a unique technique for the patterning of large areas of bio-instructive surfaces.

Programmable Electrodeposition of Janus Alginate/Poly-L-Lysine/Alginate (APA) Microcapsules for High-Resolution Cell Patterning and Compartmentalization

Encapsulation of live cells in protective, semipermeable microcapsules is one of the kernel techniques for in vitro tissue regeneration, cell therapies, and pharmaceutical screening. Advanced fabrication techniques for cell encapsulation have been developed to meet different requirements. Existing cell encapsulation techniques place substantial constraints on the spatial patterning of live cells as well as on the compartmentalization of heterotypic cells. Alginate-Poly-L-lysine-alginate (APA) microcapsules that use sodium alginate as the polyanion and poly-L-lysine (PLL) as the polycation have been extensively employed for cell microencapsulation due to their excellent biocompatibility and biodegradability. This study proposes a novel method for developing programmable Janus APA microcapsules with variable shapes and sizes by using electrodeposition. By the versatile design of the microelectrode device, sequential electrodeposition is triggered to electro-address the cells at specific locations immobilized within a Janus APA microcapsule. The osteogenesis is evaluated by resembling cell compartmentalized and vascularized osteoblast-laden constructs. This technique allows precise spatial patterning of heterotypic cells inside the APA microcapsule, enabling the observation of cellular growth, interactions, and differentiation in a well-controlled chemical and mechanical microenvironment.

The Effect of Geometry and TGF-β Signaling on Tumor Cell Migration from Free-Standing Microtissues

Recapitulation of 3D multicellular tissues in vitro is of great interest to the field of tumor biology to study the integrated effect of local biochemical and biophysical signals on tumor cell migration and invasion. However, most microengineered tissues and spheroids are unable to recapitulate in vitro the complexities of 3D geometries found in vivo. Here, lithographically defined degradable alginate microniches are presented to produce free-standing tumor microtissues, with precisely controlled geometry, high viability, and allowing for high cell proliferation. The role of microtissue geometry and TGF-β signaling in tumor cell migration is further investigated. TGF-β is found to induce the expression of p-myosin II, vimentin, and YAP/TAZ nuclear localization at the periphery of the microtissue, where enhanced nuclear stiffness and orientation are also observed. Upon embedding in a collagen matrix, microtissues treated with TGF-β maintain their geometric integrity, possibly due to the higher cell tension observed around the periphery. In contrast, cells in microtissues not treated with TGF-β are highly mobile and invade the surrounding matrix rapidly, with the initial migration strongly dependent on the local geometry. The microtissues presented here are promising model systems for studying the influence of biophysical properties and soluble factors on tumor cell migration.

Luciferin-Bioinspired Click Ligation Enables Hydrogel Platforms with Fine-Tunable Properties for 3D Cell Culture

There is an increasing interest in coupling reactions for cross-linking of cell-encapsulating hydrogels under biocompatible, chemoselective, and tunable conditions. Inspired by the biosynthesis of luciferins in fireflies, here we exploit the cyanobenzothiazole-cysteine (CBT-Cys) click ligation to develop polyethylene glycol hydrogels as tunable scaffolds for cell encapsulation. Taking advantage of the chemoselectivity and versatility of CBT-Cys ligation, a highly flexible gel platform is reported here. We demonstrate luciferin-inspired hydrogels with important advantages for cell encapsulation applications: (i) gel precursors derived from inexpensive reagents and with good stability in aqueous solution (>4 weeks), (ii) adjustable gel mechanics within physiological ranges (E = 180-6240 Pa), (iii) easy tunability of the gelation rate (seconds to minutes) by external means, (iv) high microscale homogeneity, (v) good cytocompatibility, and (iv) regulable biological properties. These flexible and robust CBT-Cys hydrogels are proved as supportive matrices for 3D culture of different cell types, namely, fibroblasts and human mesenchymal stem cells. Our findings expand the toolkit of click chemistries for the fabrication of tunable biomaterials.

Scaffold geometry modulation of mechanotransduction and its influence on epigenetics

The dynamics of cell mechanics and epigenetic signatures direct cell behaviour and fate, thus influencing regenerative outcomes. In recent years, the utilisation of 2D geometric (i.e. square, circle, hexagon, triangle or round-shaped) substrates for investigating cell mechanics in response to the extracellular microenvironment have gained increasing interest in regenerative medicine due to their tunable physicochemical properties. In contrast, there is relatively limited knowledge of cell mechanobiology and epigenetics in the context of 3D biomaterial matrices, i.e., hydrogels and scaffolds. Scaffold geometry provides biophysical signals that trigger a nucleus response (regulation of gene expression) and modulates cell behaviour and function. In this review, we explore the potential of additive manufacturing to incorporate multi length-scale geometry features on a scaffold. Then, we discuss how scaffold geometry direct cell and nuclear mechanosensing. We further discuss how cell epigenetics, particularly DNA/histone methylation and histone acetylation, are modulated by scaffold features that lead to specific gene expression and ultimately influence the outcome of tissue regeneration. Overall, we highlight that geometry of different magnitude scales can facilitate the assembly of cells and multicellular tissues into desired functional architectures through the mechanotransduction pathway. Moving forward, the challenge confronting biomedical engineers is the distillation of the vast knowledge to incorporate multiscaled geometrical features that would collectively elicit a favourable tissue regeneration response by harnessing the design flexibility of additive manufacturing. STATEMENT OF SIGNIFICANCE: It is well-established that cells sense and respond to their 2D geometric microenvironment by transmitting extracellular physiochemical forces through the cytoskeleton and biochemical signalling to the nucleus, facilitating epigenetic changes such as DNA methylation, histone acetylation, and microRNA expression. In this context, the current review presents a unique perspective and highlights the importance of 3D architectures (dimensionality and geometries) on cell and nuclear mechanics and epigenetics. Insight into current challenges around the study of mechanobiology and epigenetics utilising additively manufactured 3D scaffold geometries will progress biomaterials research in this space.

Adipogenesis or osteogenesis: destiny decision made by mechanical properties of biomaterials

Regenerative medicine affords an effective approach for restoring defect-associated diseases, and biomaterials play a pivotal role as cell niches to support the cell behavior and decide the destiny of cell differentiation. Except for chemical inducers, mechanical properties such as stiffness, pore size and topography of biomaterials play a crucial role in the regulation of cell behaviors and functions. Stiffness may determine the adipogenesis or osteogenesis of mesenchymal stem cells (MSCs) via the translocation of yes-associated protein (YAP) and the transcriptional coactivator with a PDZ-binding motif (TAZ). External forces transmit through cytoskeleton reorientation to assist nuclear deformation and molecule transport, meanwhile, signal pathways including the Hippo, FAK/RhoA/ROCK, and Wnt/β-catenin have been evidenced to participate in the mechanotransduction. Different pore sizes not only tailor the scaffold stiffness but also conform to the requirements of cell migration and vessels in-growth. Topography guides cell geometry along with mobility and determines the cell fate ascribed to micro/nano-scale contact. Herein, we highlight the recent progress in exploring the regulation mechanism by the physical properties of biomaterials, which might lead to more innovative regenerative strategies for adipose or bone tissue repair.

Regenerative medicine affords an effective approach for restoring defect-associated diseases, and biomaterials play a pivotal role as cell niches to support the cell behavior and decide the destiny of cell differentiation.