Topographic Cues Guiding Cell Polarization via Distinct Cellular Mechanosensing Pathways

Exploring the mechanical and biological interplay in the periodontal ligament

The periodontal ligament (PDL) plays a crucial role in transmitting and dispersing occlusal force, acting as mechanoreceptor for muscle activity during chewing, as well as mediating orthodontic tooth movement. It transforms mechanical stimuli into biological signals, influencing alveolar bone remodeling. Recent research has delved deeper into the biological and mechanical aspects of PDL, emphasizing the importance of understanding its structure and mechanical properties comprehensively. This review focuses on the latest findings concerning both macro- and micro- structural aspects of the PDL, highlighting its mechanical characteristics and factors that influence them. Moreover, it explores the mechanotransduction mechanisms of PDL cells under mechanical forces. Structure-mechanics-mechanotransduction interplay in PDL has been integrated ultimately. By providing an up-to-date overview of our understanding on PDL at various scales, this study lays the foundation for further exploration into PDL-related biomechanics and mechanobiology.

Cellular Spatial Sensing Determines Cell Mechanotransduction Activity on the Aligned Nanofibers

The geometric properties of extracellular matrix (ECM) fibers play a crucial role in regulating cellular behaviors and functions. Although extensive research has examined the effects of fiber alignment, conflicting results have often arisen, leaving the precise mechanisms by which electrospun fiber alignment affects cellular behavior still unclear. This study investigates how the arrangement of polycaprolactone (PCL) electrospun fiber substrates affects cellular mechanosensing by modulating cell positioning. Larger cells, whose width on a coverslip exceeds 5 times the width of the aligned fiber gaps (≈8 µm in this study) and that span multiple aligned fibers, demonstrate enhanced spreading and mechanotransduction. Conversely, smaller cells, whose width is less than or equal to 2.5 times the width of the aligned fiber gaps and are confined within fiber interstices, exhibit limited mechanotransductive signaling. These findings are further supported by manipulating cell size and, more importantly, have led to the fabrication of semi-aligned fiber networks that enhance both cell spreading and mechanotransduction. This research emphasizes the importance of optimizing fiber architecture to improve cellular interactions, offering valuable insights for the design of biomimetic scaffolds in tissue regeneration.

In situ magnetic-field-assisted bioprinting process using magnetorheological bioink to obtain engineered muscle constructs

Tissue-engineered anisotropic cell constructs are promising candidates for treating volumetric muscle loss (VML). However, achieving successful cell alignment within macroscale 3D cell constructs for skeletal muscle tissue regeneration remains challenging, owing to difficulties in controlling cell arrangement within a low-viscosity hydrogel. Herein, we propose the concept of a magnetorheological bioink to manipulate the cellular arrangement within a low-viscosity hydrogel. This bioink consisted of gelatin methacrylate (GelMA), iron oxide nanoparticles, and human adipose stem cells (hASCs). The cell arrangement is regulated by the responsiveness of iron oxide nanoparticles to external magnetic fields. A bioprinting process using ring magnets was developed for in situ bioprinting, resulting in well-aligned 3D cell structures and enhanced mechanotransduction effects on hASCs. In vitro analyses revealed upregulation of cellular activities, including myogenic-related gene expression, in hASCs. When implanted into a VML mouse model, the bioconstructs improved muscle functionality and regeneration, validating the effectiveness of the proposed approach.

Aflatoxin B1 Exposure Suppresses the Migration of Dendritic Cells by Reshaping the Cytoskeleton

Exposure to Aflatoxin B1 (AFB1) is considered a significant risk factor for human diseases, including the immune function impairment of immune cells. Dendritic cells (DCs), as essential antigen-presenting cells, play a pivotal role in bridging innate and adaptive immunity. However, the impact of AFB1 exposure on DCs has not been fully elucidated. In this study, we investigated the effects of AFB1 exposure on the migration ability of DCs and its underlying action model. Initially, we observed that AFB1 exposure inhibited the survival of DCs and altered their cellular morphology. Further investigation revealed that AFB1 promotes cell adhesion and inhibits DC migration by modulating the expression of cell adhesion molecules. Additionally, our findings indicated that cytoskeletal remodeling plays a crucial role in these processes. Experimental techniques such as immunofluorescence and RNA sequencing confirmed that AFB1 exposure regulates the expression of cytoskeleton-related genes. Moreover, we found that the perturbation of the gene expression profile through AFB1 exposure is associated with cell communication. Collectively, our study findings demonstrate that AFB1 can disrupt the expression of cytoskeleton- and adhesion-related molecules in DCs, thereby altering cell morphology and migration. These insights could provide new perspectives for further understanding the immunosuppressive effects of AFB1 and developing therapeutic strategies for diseases associated with AFB1 exposure.

The role of RAP2 in regulation of cell volume on bone marrow mesenchymal stem cell fate determination

The extracellular matrix guides cell behavior through mechanical properties, which plays a role in determining cell function and can even influence stem cell fate. Compared with adherent culture, the three-dimensional culture environment is closer to the growth conditions in vivo, but is limited by standardization of material properties and observation and measurement methods. Therefore, it is necessary to study the relationship among the three-dimensional morphological characteristics of cells, cytoskeleton, and stem cell differentiation under adherent culture conditions. Here, we control the cell volume by adjusting the cell density, microfilament cytoskeleton tension, and osmotic pressure of the culture environment, and analyze the cell morphological features and differentiation to the osteoblastic and adipogenic lineages. Based on the in vitro and in vivo results, we identify cell volume as the true reflection of the cytoskeleton tension under stress stimuli compared with cell spreading area. By adjusting cell volume, cytoskeletal tension and cell differentiation can be regulated without affecting cell spreading area. Further study shows that the Ras-related small GTPase RAP2 inhibits the activity of mechanical transducers Lamin A/C and YAP1, playing an important role in cell volume regulation of cell differentiation. In summary, our results support the close relationship between cell volume and cytoskeleton tension. The regulatory role of cell volume on cell differentiation is modulated, at least in part, by RAP2-related mechanosensitive pathways. Our insights into how cell volume regulates cell differentiation may build a bridge between two-dimensional and three-dimensional mechanical studies in cell biology.

Heterogeneous focal adhesion cytoskeleton nanoarchitectures from microengineered interfacial curvature to oversee nuclear remodeling and mechanotransduction of mesenchymal stem cells

BACKGROUND

Interfacial heterogeneity is widely explored to reveal molecular mechanisms of force-mediated pathways due to biased tension. However, the influence of cell density,, curvature, and interfacial heterogeneity on underlying pathways of mechanotransduction is obscure.

METHODS

Polydimethylsiloxane (PDMS)-based stencils were micropatterned to prepare the micropores for cell culture. The colonies of human mesenchymal stem cells (hMSCs) were formed by controlling cell seeding density to investigate the influences of cell density, curvature and heterogeneity on mechanotransduction. Immunofluorescent staining of integrin, vinculin, and talin-1 was conducted to evaluate adhesion-related expression levels. Then, immunofluorescent staining of actin, actinin, and myosin was performed to detect cytoskeleton distribution, especially at the periphery. Nuclear force-sensing mechanotransduction was explained by yes-associated protein (YAP) and laminA/C analysis.

RESULTS

The micropatterned colony of hMSCs demonstrated the coincident characters with engineered micropores of microstencils. The cell colony obviously developed the heterogeneous morphogenesis. Heterogeneous focal adhesion guided the development of actin, actinin, and myosin together to regulate cellular contractility and movement by integrin, vinculin, and talin-1. Cytoskeletal staining showed that actin, actinin, and myosin fibers were reorganized at the periphery of microstencils. YAP nuclear translocation and laminA/C nuclear remodeling were enhanced at the periphery by the regulation of heterogeneous focal adhesion (FA) and cytoskeleton arrangement.

CONCLUSIONS

The characters of the engineered clustering colony showed similar results with prepared microstencils, and colony curvature was also well adjusted to establish heterogeneous balance at the periphery of cell colony. The mechanism of curvature, spreading, and elongation was also investigated to disclose the compliance of FA and cytoskeleton along with curvature microarrays for increased nuclear force-sensing mechanotransduction. The results may provide helpful information for understanding interfacial heterogeneity and nuclear mechanotransduction of stem cells.

Engineering Surface-Adaptive Metal-Organic Framework Armor to Promote Infected Wound Healing

Metal-organic frameworks (MOFs) hold enormous promise for treating bacterial infections to circumvent the threat of antibiotic resistance. However, positioning MOFs on wound dressings is hindered and remains a significant challenge. Herein, a facile heterointerfacial engineering strategy was developed to tailor the "MOF armor" that adaptively weaponized the poly(ε-caprolactone) electrospun dressing with excellent bacteria-killing efficacy. Hydrophilic epitaxial crystallization to enhance the interfacial wettability is the key to induce the uniform seeding of Cu2+ and thus to generate a compact MOF layer on the electrospun dressing. The universality of the proposed strategy was demonstrated by the construction of different kinds of MOFs (HKUST-1, ZIF-8, and ZIF-67) on variously shaped substrates (nanofibers, pellets, plates, and 3D-printed porous scaffolds). By optimizing the Cu2+ loading, the Cu-MOF armor exhibited sustained ion release behavior, strong antibacterial activity, and good biocompatibility. In vivo rat model revealed that the Cu-MOF armor significantly promoted infected wound healing by inhibiting inflammatory factors, promoting collagen deposition, and angiogenesis. This unique MOF armor provides an appealing and effective solution for designing and fabricating advanced wound dressings.

Stiffness and surface topology of silicone implants competitively mediate inflammatory responses of macrophages and foreign body response

Adverse inflammatory responses, dominated by macrophages, that are induced by physical cues of silicone implants can heavily damage the life quality of patients via causing fibrosis and device failure. As stiffness and surface topology affect macrophages at the same time, the competition or partnership among physical cues against the regulation of macrophages is still ambiguous. Herein, a series of PDMS implants with different stiffness at ∼ MPa and surface topology at tens of micrometers were fabricated to investigate the relationship, the regulation rule, and the underlying mechanism of the two physical cues against the inflammatory responses of M1 macrophages. There is a competitive rule: surface topology could suppress the inflammatory responses of M1 macrophages in the soft group but did not have the same effect in the stiff group. Without surface topology, lower stiffness unexpectedly evoked stronger inflammatory responses of M1 macrophages. Implanting experiments also proved that the competitive state against mediating in vivo immune responses and the unexpected inflammatory responses. The reason is that stiffness could strongly up-regulate focal adhesion and activate the MAPK/NF-κB signaling axis to evoke inflammatory responses, which could shield the effect of surface topology. Therefore, for patient healthcare, it is crucial to prioritize stiffness while not surface topology at MPa levels to minimize adverse reactions.

Advances in the Development of Gradient Scaffolds Made of Nano-Micromaterials for Musculoskeletal Tissue Regeneration

The intricate hierarchical structure of musculoskeletal tissues, including bone and interface tissues, necessitates the use of complex scaffold designs and material structures to serve as tissue-engineered substitutes. This has led to growing interest in the development of gradient bone scaffolds with hierarchical structures mimicking the extracellular matrix of native tissues to achieve improved therapeutic outcomes. Building on the anatomical characteristics of bone and interfacial tissues, this review provides a summary of current strategies used to design and fabricate biomimetic gradient scaffolds for repairing musculoskeletal tissues, specifically focusing on methods used to construct compositional and structural gradients within the scaffolds. The latest applications of gradient scaffolds for the regeneration of bone, osteochondral, and tendon-to-bone interfaces are presented. Furthermore, the current progress of testing gradient scaffolds in physiologically relevant animal models of skeletal repair is discussed, as well as the challenges and prospects of moving these scaffolds into clinical application for treating musculoskeletal injuries.

An immunomodulatory and osteogenic bacterial cellulose scaffold for bone regeneration via regulating the immune microenvironment

Creating a bone homeostasis microenvironment that balances osteogenesis and immunity is a substantial challenge for bone regeneration. Here, we prepared an immunomodulatory and osteogenic bacterial cellulose scaffold (FOBS) via a facile one-pot approach. The aldehyde groups were generated via selective oxidation of the hydroxyl groups of bacterial cellulose, offering the bonding sites for dopamine through a Schiff base reaction. At the same time, the deposition of Ca2+ and PO43- was promoted on the aldehyde cellulose scaffold because of the high affinity of the catechol moiety for Ca2+. Compared with that of the unmodified scaffold, the hydroxyapatite content of FOBS increased by 47.1 % according to the ICP results. Interestingly, FOBS regulated the immune microenvironment to accelerate the conversion of M1 to M2 macrophages. The expressions of ARG-1 and Dectin-1 (M2) in the FOBS group increased by >100 %. The expression of osteogenic differentiation of BMSCs was also upregulated. In a rat cranial defect model, the BV/TV of FOBS was significantly increased. Further immunohistochemical analysis revealed that an improved immune microenvironment promoted the osteogenic differentiation of stem cells in vivo. This work provides an effective and easy-to-operate strategy for the development of the bone tissue engineering scaffolds.

Creating a bionic scaffold via light-curing liquid crystal ink to reveal the role of osteoid-like microenvironment in osteogenesis

Osteoid plays a crucial role in directing cell behavior and osteogenesis through its unique characteristics, including viscoelasticity and liquid crystal (LC) state. Thus, integrating osteoid-like features into 3D printing scaffolds proves to be a promising approach for personalized bone repair. Despite extensive research on viscoelasticity, the role of LC state in bone repair has been largely overlooked due to the scarcity of suitable LC materials. Moreover, the intricate interplay between LC state and viscoelasticity in osteogenesis remains poorly understood. Here, we developed innovative hydrogel scaffolds with osteoid-like LC state and viscoelasticity using digital light processing with a custom LC ink. By utilizing these LC scaffolds as 3D research models, we discovered that LC state mediates high protein clustering to expose accessible RGD motifs to trigger cell-protein interactions and osteogenic differentiation, while viscoelasticity operates via mechanotransduction pathways. Additionally, our investigation revealed a synergistic effect between LC state and viscoelasticity, amplifying cell-protein interactions and osteogenic mechanotransduction processes. Furthermore, the interesting mechanochromic response observed in the LC hydrogel scaffolds suggests their potential application in mechanosensing. Our findings shed light on the mechanisms and synergistic effects of LC state and viscoelasticity in osteoid on osteogenesis, offering valuable insights for the biomimetic design of bone repair scaffolds.

Biomimetic concentric microgrooved titanium surfaces influence bone marrow-derived mesenchymal stem cell osteogenic differentiation via H3K4 trimethylation epigenetic regulation

Material surface micromorphology can modulate cellular behavior and promote osteogenic differentiation through cytoskeletal rearrangement. Bone reconstruction requires precise regulation of gene expression in cells, a process governed by epigenetic mechanisms such as histone modifications, DNA methylation, and chromatin remodeling. We constructed osteon-mimetic concentric microgrooved titanium surfaces with different groove sizes and cultured bone marrow-derived mesenchymal stem cells (BMSCs) on the material surfaces to study how they regulate cell biological behavior and osteogenic differentiation through epigenetics. We found that the cells arranged in concentric circles along the concentric structure in the experimental group, and the concentric microgrooved surface did not inhibit cell proliferation. The results of a series of osteogenic differentiation experiments showed that the concentric microgrooves facilitated calcium deposition and promoted osteogenic differentiation of the BMSCs. Concentric microgrooved titanium surfaces that were 30 μm wide and 10 μm deep promoted osteogenic differentiation of BMSC by increasing WDR5 expression via H3K4 trimethylation upregulation.

Shp2 contributes to the regulation of nuclear shape and cellular viscoelasticity in response to substrate spatial cues

Cell polarization can be guided by substrate topology through space constraints and adhesion induction, which are part of cellular mechanosensing pathways. Here, we demonstrated that protein tyrosine phosphatase Shp2 plays a crucial role in mediating the response of cells to substrate spatial cues. When compared to cells spreading on surfaces coated uniformly with fibronectin (FN), cells attached to 10 μm-width FN-strip micropattern (MP), which provides spatial cues for uniaxial spreading, exhibited elongated focal adhesions (FAs) and aligned stress fibers in the direction of the MP. As a result of uniaxial cell spreading, nuclei became elongated, dependent on ROCK-mediated actomyosin contractility. Additionally, intracellular viscoelasticity also increased. Shp2-deficient cells did not display elongated FAs mediated by MP, well-aligned stress fibers, or changes in nuclear shape and intracellular viscoelasticity. Overall, our data suggest that Shp2 is involved in regulating FAs and the actin cytoskeleton to modulate nuclear shape and intracellular physical properties in response to substrate spatial cues.

Hierarchically Biomimetic Scaffolds with Anisotropic Micropores and Nanotopological Patterns to Promote Bone Regeneration via Geometric Modulation

Structural engineering is an appealing means to modulate osteogenesis without the intervention of exogenous cells or therapeutic agents. In this work, a novel 3D scaffold with anisotropic micropores and nanotopographical patterns is developed. Scaffolds with oriented pores are fabricated via the selective extraction of water-soluble polyethylene oxide from its poly(ε-caprolactone) co-continuous mixture and uniaxial stretching. The plate apatite-like lamellae are subsequently hatched on the pore walls through surface-induced epitaxial crystallization. Such a unique geometric architecture yields a synergistic effect on the osteogenic capability. The prepared scaffold leads to a 19.2% and 128.0% increase in the alkaline phosphatase activity of rat bone mesenchymal stem cells compared to that of the scaffolds with only oriented pores and only nanotopographical patterns, respectively. It also induces the greatest upregulation of osteogenic-related gene expression in vitro. The cranial defect repair results demonstrate that the prepared scaffold effectively promotes new bone regeneration, as indicated by a 350% increase in collagen I expression in vivo compared to the isotropic porous scaffold without surface nanotopology after implantation for 14 weeks. Overall, this work provides geometric motifs for the transduction of biophysical cues in 3D porous scaffolds, which is a promising option for tissue engineering applications.

A Biomimetic Fibrous Composite Scaffold with Nanotopography-Regulated Mineralization for Bone Defect Repair

The effective regeneration of large bone defects via bone tissue engineering is challenging due to the difficulty in creating an osteogenic microenvironment. Inspired by the fibrillar architecture of the natural extracellular matrix, we developed a nanoscale bioengineering strategy to produce bone fibril-like composite scaffolds with enhanced osteogenic capability. To activate the surface for biofunctionalization, self-adaptive ridge-like nanolamellae were constructed on poly(ε-caprolactone) (PCL) electrospinning scaffolds via surface-directed epitaxial crystallization. This unique nanotopography with a markedly increased specific surface area offered abundant nucleation sites for Ca2+ recruitment, leading to a 5-fold greater deposition weight of hydroxyapatite than that of the pristine PCL scaffold under stimulated physiological conditions. Bone marrow mesenchymal stem cells (BMSCs) cultured on bone fibril-like scaffolds exhibited enhanced adhesion, proliferation, and osteogenic differentiation in vitro. In a rat calvarial defect model, the bone fibril-like scaffold significantly accelerated bone regeneration, as evidenced by micro-CT, histological histological and immunofluorescence staining. This work provides the way for recapitulating the osteogenic microenvironment in tissue-engineered scaffolds for bone repair.

Electrowriting patterns and electric field harness directional cell migration for skin wound healing

Directional cell migration is a crucial step in wound healing, influenced by electrical and topographic stimulations. However, the underlying mechanism and the combined effects of these two factors on cell migration remain unclear. This study explores cell migration under various combinations of guided straight line (SL) spacing, conductivity, and the relative direction of electric field (EF) and SL. Electrowriting is employed to fabricate conductive (multiwalled carbon nanotube/polycaprolactone (PCL)) and nonconductive (PCL) SL, with narrow (50 μm) and wide (400 μm) spacing that controls the topographic stimulation strength. Results show that various combinations of electrical and topographic stimulation yield significantly distinct effects on cell migration direction and speed; cells migrate fastest with the most directivity in the case of conductive, narrow-spacing SL parallel to EF. A physical model based on intercellular interactions is developed to capture the underlying mechanism of cell migration under SL and EF stimulations, in agreement with experimental observations. In vivo skin wound healing assay further confirmed that the combination of EF (1 V cm-1) and parallelly aligned conductive fibers accelerated the wound healing process. This study presents a promising approach to direct cell migration and enhance wound healing by optimizing synergistic electrical and topographic stimulations.

Chitin whisker/chitosan liquid crystal hydrogel assisted scaffolds with bone-like ECM microenvironment for bone regeneration

Natural bone exhibits a complex anisotropic and micro-nano hierarchical structure, more importantly, bone extracellular matrix (ECM) presents liquid crystal (LC) phase and viscoelastic characteristics, providing a unique microenvironment for guiding cell behavior and regulating osteogenesis. However, in bone tissue engineering scaffolds, the construction of bone-like ECM microenvironment with exquisite microstructure is still a great challenge. Here, we developed a novel polysaccharide LC hydrogel supported 3D printed poly(l-lactide) (PLLA) scaffold with bone-like ECM microenvironment and micro-nano aligned structure. First, we prepared a chitin whisker/chitosan polysaccharide LC precursor, and then infuse it into the pores of 3D printed PLLA scaffold, which was previously surface modified with a polydopamine layer. Next, the LC precursor was chemical cross-linked by genipin to form a hydrogel network with bone-like ECM viscoelasticity and LC phase in the scaffold. Subsequently, we performed directional freeze-casting on the composite scaffold to create oriented channels in the LC hydrogel. Finally, we soaked the composite scaffold in phytic acid to further physical cross-link the LC hydrogel through electrostatic interactions and impart antibacterial effects to the scaffold. The resultant biomimetic scaffold displays osteogenic activity, vascularization ability and antibacterial effect, and is expected to be a promising candidate for bone repair.

Biomimetic Mineralized 3D-Printed Polycaprolactone Scaffold Induced by Self-Adaptive Nanotopology to Accelerate Bone Regeneration

Three-dimensional (3D)-printed biodegradable polymer scaffolds are at the forefront of personalized constructs for bone tissue engineering. However, it remains challenging to create a biological microenvironment for bone growth. Herein, we developed a novel yet feasible approach to facilitate biomimetic mineralization via self-adaptive nanotopography, which overcomes difficulties in the surface biofunctionalization of 3D-printed polycaprolactone (PCL) scaffolds. The building blocks of self-adaptive nanotopography were PCL lamellae that formed on the 3D-printed PCL scaffold via surface-directed epitaxial crystallization and acted as a linker to nucleate and generate hydroxyapatite crystals. Accordingly, a uniform and robust mineralized layer was immobilized throughout the scaffolds, which strongly bound to the strands and had no effect on the mechanical properties of the scaffolds. In vitro cell culture experiments revealed that the resulting scaffold was biocompatible and enhanced the proliferation and osteogenic differentiation of mouse embryolous osteoblast cells. Furthermore, we demonstrated that the resulting scaffold showed a strong capability to accelerate in vivo bone regeneration using a rabbit bone defect model. This study provides valuable opportunities to enhance the application of 3D-printed scaffolds in bone repair, paving the way for translation to other orthopedic implants.

[Integrin and N-cadherin Co-Regulate the Polarity of Mesenchymal Stem Cells via Mechanobiological Mechanisms]

Objective

To investigate the synergistic regulation of the polarization of mesenchymal stem cells by integrin and N-cadherin-mediated mechanical adhesion and the underlying mechanobiological mechanisms.

Methods

Bilayer polyethylene glyeol (PEG) hydrogels were formulated and modified with RGD and HAVDI peptides, respectively, to achieve mechanical adhesion to integrin and N-cadherin and to replicate the integrin-mediated mechanical interaction between cells and the extracellular matrix and the N-cadherin-mediated cell-cell mechanical interaction. The polar proteins, phosphatidylinositol 3-kinase (PI3K) and phosphorylated myosin light chain (pMLC), were characterized through immunofluorescence staining in individual cells with or without contact with HAVDI peptides under integrin-mediated adhesion, N-cadherin-mediated adhesion, and different intracellular forces. Their expression levels and polar distribution were analyzed using Image J.

Results

Integrin-mediated adhesion induced significantly higher polar strengths of PI3K and pMLC in the contact group than in those in the no contact group, resulting in the concentration of the polar angle of PI3K to β-catenin in the range of 135° to 180° and the concentration of the polar angle of pMLC to β-catenin in the range of 0° to 45° in the contact group. Inhibition of integrin function led to inhibition of the polarity distribution of PI3K in the contact group, but did not change the polarity distribution of pMLC protein. The effect of N-cadherin on the polarity distributions of PI3K and pMLC was similar to that of integrin. However, inhibition of the mechanical adhesion of N-cadherin led to inhibition of the polarity intensity and polarity angle distribution of PI3K and pMLC proteins in the contact group. Furthermore, inhibition of the mechanical adhesion of N-cadherin caused weakened polarity intensity of integrin β1, reducing the proportion of cells with polarity angles between integrin β1 and β-catenin concentrating in the range of 135° to 180°. Additionally, intracellular forces influenced the polar distribution of PI3K and pMLC proteins. Reducing intracellular forces weakened the polarity intensity of PI3K and pMLC proteins and their polarity distribution, while increasing intracellular forces enhanced the polarity intensity of PI3K and pMLC proteins and their polarity distribution.

Conclusion

Integrin and N-cadherin co-regulate the polarity distribution of cell proteins and N-cadherin can play an important role in the polarity regulation of stem cells through local inhibition of integrin.

Aligned Nanofibers Promote Myoblast Polarization and Myogenesis through Activating Rac-Related Signaling Pathways

The extracellular matrix (ECM) plays a crucial role in regulating cellular behaviors and functions. However, the impact of ECM topography on muscle cell adhesion and differentiation remains poorly understood from a mechanosensing perspective. In this study, we fabricated aligned and random electrospun polycaprolactone (PCL) nanofibers to mimic the structural characteristics of ECM. Mechanism investigations revealed that the orientation of nanofibers promoted C2C12 polarization and myogenesis through Rac-related signaling pathways. Conversely, cells cultured on random fibers exhibited spreading behavior mediated by RhoA/ROCK pathways, resulting in enhanced stress fiber formation but reduced capacity for myogenic differentiation. Our findings highlight the critical role of an ECM structure in muscle regeneration and damage repair, providing novel insights into mechanosensing mechanisms underlying muscle injury diseases.

Matrix Nonlinear Viscoelasticity Regulates Skeletal Myogenesis through MRTF Nuclear Localization and Nuclear Mechanotransduction

Mechanically sensitive tissues (e.g., skeletal muscles) greatly need mechanical stimuli during the development and maturation. The extracellular matrix (ECM) mediates these signals through nonlinear viscoelasticity of collagen networks that are predominant components of the ECM. However, the interactions between cells and ECM form a feedback loop, and it has not yet been possible to determine the degree to which, if any, of the features of matrix nonlinear viscoelasticity affect skeletal muscle development and regeneration. In this study, a nonlinear viscoelastic feature (i.e., strain-enhanced stress relaxation (SESR)) in normal skeletal muscles is observed, which however is almost absent in diseased muscles from Duchenne muscular dystrophy mice. It is recapitulated such SESR feature in vitro and separated the effects of mechanical strain and ECM viscoelasticity on myoblast response by developing a collagen-based hydrogel platform. Both strain and stress relaxation induce myogenic differentiation and myotube formation by C2C12 myoblasts, and myogenesis is more promoted by applying SESR. This promotion can be explained by the effects of SESR on actin polymerization-mediated myocardin related transcription factor (MRTF) nuclear localization and nuclear mechanotransduction. This study represents the first attempt to investigate the SESR phenomenon in skeletal muscles and reveal underlying mechanobiology, which will provide new opportunities for the tissue injury treatments.

Spider-Silk-like Fiber Mat-Covered Polypropylene Warp-Knitted Hernia Mesh for Inhibition of Fibrosis under Dynamic Environment

Hernia surgery is a widely performed procedure, and the use of a polypropylene mesh is considered the standard approach. However, the mesh often leads to complications, including the development of scar tissue that wraps around the mesh and causes it to shrink. Consequently, there is a need to investigate the relationship between the mesh and scar formation as well as to develop a hernia mesh that can prevent fibrosis. In this study, three different commercial polypropylene hernia meshes were examined to explore the connection between the fabric structure and mechanical properties. In vitro dynamic culture was used to investigate the mechanism by which the mechanical properties of the mesh in a dynamic environment affect cell differentiation. Additionally, electrospinning was employed to create polycaprolactone spider-silk-like fiber mats to achieve mechanical energy dissipation in dynamic conditions. These fiber mats were then combined with the preferred hernia mesh. The results demonstrated that the composite mesh could reduce the activation of fibroblast mechanical signaling pathways and inhibit its differentiation into myofibroblasts in dynamic environments.

Anisotropic microtopography surface of chitosan scaffold regulating skin precursor-derived Schwann cells towards repair phenotype promotes neural regeneration

For repairing peripheral nerve and spinal cord defects, biomaterial scaffold-based cell-therapy was emerged as an effective strategy, requiring the positive response of seed cells to biomaterial substrate and environment signals. Previous work highlighted that the imposed surface properties of scaffold could provide important guidance cues to adhered cells for polarization. However, the insufficiency of native Schwann cells and unclear cellular response mechanisms remained to be addressed. Given that, this study aimed to illuminate the micropatterned chitosan-film action on the rat skin precursor-derived Schwann cells (SKP-SCs). Chitosan-film with different ridge/groove size was fabricated and applied for the SKP-SCs induction. Results indicated that SKP-SCs cultured on 30 μm size microgroove surface showed better oriented alignment phenotype. Induced SKP-SCs presented similar genic phenotype as repair Schwann cells, increasing expression of c-Jun, neural cell adhesion molecule, and neurotrophic receptor p75. Moreover, SKP-SC-secretome was subjected to cytokine array GS67 assay, data indicated the regulation of paracrine phenotype, a panel of cytokines was verified up-regulated at secreted level and gene expression level in induced SKP-SCs. These up-regulated cytokines exhibit a series of promotive neural regeneration functions, including cell survival, cell migration, cell proliferation, angiogenesis, axon growth, and cellular organization etc. through bioinformatics analysis. Furthermore, the effectively polarized SKP-SCs-sourced secretome, promoted the proliferation and migration capacity of the primarily cultured native rat Schwann cells, and augmented neurites growth of the cultured motoneurons, as well as boosted axonal regrowth of the axotomy-injured motoneurons. Taken together, SKP-SCs obtained pro-neuroregeneration phenotype in adaptive response to the anisotropic topography surface of chitosan-film, displayed the oriented parallel growth, the transition towards repair Schwann cell genic phenotype, and the enhanced paracrine effect on neural regeneration. This study provided novel insights into the potency of anisotropic microtopography surface to Schwann-like cells phenotype regulation, that facilitating to provide promising engineered cell-scaffold in neural injury therapies.

[Spatial Constraints of Rectangular Hydrogel Microgrooves Regulate the Morphology and Arrangement of Human Umbilical Vein Endothelial Cells]

Objective

To construct microscale rectangular hydrogel grooves and to investigate the morphology and alignment of human umbilical vein endothelial cells (HUVECs) under spatial constraints. Vascular endothelial cell morphology and alignment are important factors in vascular development and the maintenance of homeostasis.

Methods

A 4-arm polyethylene glycol-acrylate (PEG-acrylate) hydrogel was used to fabricate rectangular microgrooves of the widths of 60 μm, 100 μm, and 140 μm. The sizes and the fibronectin (FN) adhesion of these hydrogel microgrooves were measured. HUVECs were seeded onto the FN-coated microgrooves, while the flat surface without micropatterns was used as the control. After 48 hours of incubation, the morphology and orientation of the cells were examined. The cytoskeleton was labelled with phalloidine and the orientation of the cytoskeleton in the hydrogel microgrooves was observed by laser confocal microscopy.

Results

The hydrogel microgrooves constructed exhibited uniform and well-defined morphology, a complete structure, and clear edges, with the width deviation being less than 3.5%. The depth differences between the hydrogel microgrooves of different widths were small and the FN adhesion is uniform, providing a micro-patterned growth interface for cells. In the control group, the cells were arranged haphazardly in random orientations and the cell orientation angle was (46.9±1.8)°. In contrast, the cell orientation angle in the hydrogel microgrooves was significantly reduced (P<0.001). However, the cell orientation angles increased with the increase in hydrogel microgroove width. For the 60 μm, 100 μm, and 140 μm hydrogel microgrooves, the cell orientation angles were (16.4±2.8)°, (24.5±3.2)°, and (30.3±3.5)°, respectively. Compared to that of the control group (35.7%), the number of cells with orientation angles <30° increased significantly in the hydrogel microgrooves of different widths (P<0.001). However, as the width of the hydrogel microgrooves increased, the number of cells with orientation angles <30° gradually decreased (79.9%, 62.3%, 54.7%, respectively), while the number of cells with orientation angles between 60°-90° increased (P<0.001). The cell bodies in the microgrooves were smaller and more rounded in shape. The cells were aligned along the direction of the microgrooves and corresponding changes occurred in the arrangement of the cell cytoskeleton. In the control group, cytoskeletal filaments were aligned in random directions, presenting an orientation angle of (45.5±3.7)°. Cytoskeletal filaments were distributed evenly within various orientation angles. However, in the 60 μm, 100 μm, and 140 μm hydrogel microgrooves, the orientation angles of the cytoskeletal filaments were significantly decreased, measuring (14.4±3.1)°, (24.7±3.5)°, and (31.9±3.3)°, respectively. The number of cytoskeletal filaments with orientation angles <30° significantly increased in hydrogel microgrooves of different widths (P<0.001). However, as the width of the hydrogel microgrooves increased, the number of cytoskeletal filaments with orientation angles <30° gradually decreased, while the number of cytoskeletal filaments with orientation angles between 60°-90° gradually increased (P<0.001).

Conclusion

Hydrogel microgrooves can regulate the morphology and orientation of HUVECs and mimic to a certain extent the in vivo microenvironment of vascular endothelial cells, providing an experimental model that bears better resemblance to human physiology for the study of the unique physiological functions of vascular endothelial cells. Nonetheless, the molecular mechanism of spatial constraints on the morphology and the assembly of vascular endothelial cell needs to be further investigated.

Highly anisotropic and elastic cellulosic scaffold guiding cell orientation and osteogenic differentiation via topological and mechanical cues

Inspired by the similarity of anisotropic channels in wood to the canals of bone, the elastic wood-derived (EW) scaffolds with anisotropic channels were prepared via simple delignification treatment of natural wood (NW). We hypothesize that the degree of delignification will lead to differences in mechanical properties of scaffolds, which in turn directly affect the behaviors and fate of stem cells. The delignification process did not destroy the anisotropic channel structure of the scaffolds, but endowed the scaffolds with good elasticity and rapid stress relaxation. Interestingly, the micron-scale anisotropic channels of the scaffolds can highly promote the polarization of cells along the direction of channels. We also found that the alkaline phosphatase of EW scaffold can reach to about 13.1 U/gprot, which was about double that of NW scaffold. Moreover, the longer the delignification time, the better the osteogenic activity of the EW scaffolds. We further hypothesize that the osteogenic activity of scaffolds is related to the stress relaxation properties. The immunofluorescence staining showed that when the stress relaxation time of scaffold was shortened to about 10 s, the nuclear ratio of YAP of scaffold increased to 0.22, which well supports our hypothesis.

Fiber Microarchitecture in Interpenetrating Collagen-Alginate Hydrogel with Tunable Mechanical Plasticity Regulates Tumor Cell Migration

The fiber structures of tumor microenvironment (TME) are well-known in regulating tumor cell behaviors, and the plastic remolding of TME has recently been suggested to enhance tumor metastasis as well. However, the interrelationship between the fiber microarchitecture and matrix plasticity is inextricable by existing in vitro models. The individual roles of fiber microarchitecture and matrix plasticity in tuning tumor cell behaviors remain elusive. This study develops an interpenetrating collagen-alginate hydrogel platform with independently tunable matrix plasticity and fiber microarchitecture through an interpenetrating strategy of alginate networks and collagen I networks. With this hydrogel platform, it is demonstrated that tumor cells in high plasticity hydrogels are more extensive and aggressive than in low plasticity hydrogels and fiber structures only have influence in high plasticity hydrogels. The study further elucidates the underlying mechanisms through analyzing the distribution of forces within the matrix and tracking the focal adhesions (FAs) and finds that highly plastic hydrogels can activate the FAs formation, whereas the maturation and stability of FAs are dominated by fiber dispersion. This study not only establishes new ideas on how cells interact with TME cues but also would help to further finely tailor engineered hydrogel platforms for studying tumor behaviors in vitro.

Mechanically enhanced and osteobioactive synthetic periosteum via development of poly(ε-caprolactone)/microtantalum composite

Periosteum, the thin layer covering adjacent to bone containing specific architecture, is important for functional bone regeneration and remodeling. Synthetic periosteum investigated presently lacks the resemblance of natural periosteum, suffering from poor mechanical strength and cell attachment. Here, we report a newly-developed biomimetic film to function as synthetic periosteum. Based on poly(ε-caprolactone) (PCL), where surface wettability of the synthetic periosteum is enhanced by microtantalum (mTa) particle blending and after a cold drawing process, further obtains topographical anisotropy without any involvement of solvent. This new blend shows mechanical enhancement over pure PCL, with yield stress and elastic strain approaching the natural periosteum. A distinct degradation mechanism is proposed for the blend, and by seeding with mouse calvarial preosteoblasts, cell proliferation is promoted on surface of the drawn PCL but delayed on the mTa-blended PCL. However, cell mineralization is accelerated on the mTa-blended surface. This is less on the drawn PCL. The synergistical integration of cellular proliferation, alignment and osteogenic enhancement suggest that the cold drawn PCL/Ta blend has unique potential for developing into a synthetic periosteum and other tissue-engineering products.

Promoting Stem Cell Mechanosensing and Osteogenesis by Hybrid Soft Fibers

Bone regenerative biomaterials are essential in treating bone defects as they serve as extracellular matrix (ECM) mimics, creating a favorable environment for cell attachment, proliferation, and differentiation. However, the currently used bone regenerative biomaterials mostly exhibit high stiffness, which may lead to difficulties in degradation and thus increase the risk of foreign body ingestion. In this study, we prepared soft fibrous scaffolds modified with Zn-MOF-74 nanoparticles via electrostatic spinning. The soft fibers (only 1 kPa) permit remodeling under cellular adhesive force, optimizing the mechanical cues in the microenvironment to support cell adhesion and mechanosensing. In addition, the incorporation of Zn-MOF-74 nanoparticles enables the stable and sustained release of zinc ions, promoting stem cell mechanotransduction and osteogenic differentiation. Therefore, the hybrid soft fibers facilitate the regeneration of new bone in the rat femoral defect model, which provides a promising approach for regenerative medicine.

Nanomanipulation of Ligand Nanogeometry Modulates Integrin/Clathrin-Mediated Adhesion and Endocytosis of Stem Cells

Nanosubstrate engineering can be a biomechanical approach for modulating stem cell differentiation in tissue engineering. However, the study of the effect of clathrin-mediated processes on manipulating this behavior is unexplored. Herein, we develop integrin-binding nanosubstrates with confined nanogeometries that regulate clathrin-mediated adhesion- or endocytosis-active signaling pathways for modulating stem fates. Isotropically presenting ligands on the nanoscale enhances the expression of clathrin in cells, thereby facilitating uptake of dexamethasone-loaded nanoparticles (NPs) to boost osteogenesis of stem cells. In contrast, anisotropic ligand nanogeometry suppresses this clathrin-mediated NP entry by strengthening the association between clathrin and adhesion spots to reinforce mechanotransduced signaling, which can be abrogated by the pharmacological inhibition of clathrin. Meanwhile, inhibiting focal adhesion formation hinders cell spreading and enables a higher endocytosis efficiency. Our findings reveal the crucial roles of clathrin in both endocytosis and mechanotransduction of stem cells and provide the parameter of ligand nanogeometry for the rational design of biomaterials for tissue engineering.

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.

Scalable Fabrication of Polymeric Composite Microspheres to Inhibit Oral Pathogens and Promote Osteogenic Differentiation of Periodontal Membrane Stem Cells

Periodontitis is a worldwide bacterial infectious disease, resulting in the resorption of tooth-supporting structures. Biodegradable polymeric microspheres are emerging as an appealing local therapy candidate for periodontal defect regeneration but suffer from tedious procedures and low yields. Herein, we developed a facile yet scalable approach to prepare polylactide composite microspheres with outstanding drug-loading capability. It was realized by blending equimolar polylactide enantiomers at the temperature between the melting point of homocrystallites and stereocomplex (sc) crystallites, enabling the precipitation of sc crystallites in the form of microspheres. Meanwhile, epigallocatechin gallate (EGCG) and nano-hydroxyapatite were encapsulated in the microspheres in the designated amount. Such an assembly allowed the fast and sustained release of EGCG and Ca2+ ions. The resultant hybrid composite microspheres not only exhibited strong antimicrobial activity against typical oral pathogens (Porphyromonas gingivalis and Enterococcus faecalis), but also directly promoted osteogenic differentiation of periodontal ligament stem cells with good cytocompatibility. These dual-functional composite microspheres offer a desired drug delivery platform to address the practical needs for periodontitis treatment.

Exploiting the Biophysical Cues toward Dual Differentiation of hMSC's within Geometrical Patterns

A wide variety of cues from the extracellular matrix (ECM) have been known to affect the differentiation of stem cells in vivo. In particular, the biophysical cues and cell shape have been known to affect the stem cell function, yet very little is known about the interplay between how these cues control differentiation. For the first time, by using photolithography to pattern poly(ethylene glycol) (PEG), patterns of square and triangular geometries were created, and the effect of these structures and the biophysical cues arising were utilized to differentiate cells into multiple lineages inside a same pattern without the use of any adhered protein or growth factors. The data from these studies showed that the cells present at the edges were well elongated, exhibit high aspect ratios, and differentiated into osteogenic lineage, whereas the cells present at the center exhibit lower aspect ratio and were primarily adipogenic lineage regardless of the geometry. This was correlated to the higher expression of focal adhesion proteins at the edges, the expression of which have been known to affect the osteogenic differentiation. By showing MSC lineage commitment relationships due to physical signals, this study highlights the importance of these cues and cell shape in further understanding stem cell behavior for tissue engineering applications.

Regulation of Macrophage Polarization on Chiral Potential Distribution of CFO/P(VDF-TrFE) Films

Surface potentials of biomaterials have been shown to regulate cell fate commitment. However, the effects of chirality-patterned potential distribution on macrophage polarization are still only beginning to be explored. In this work, we demonstrated that the chirality-patterned potential distribution of CoFe₂O₄/poly(vinylidene fluoride-trifluoroethylene) (CFO/P(VDF-TrFE)) films could significantly down-regulate the M1 polarization of bone marrow-derived macrophages (BMDMs). Specifically, the dextral-patterned surface potential distribution simultaneously up-regulated the expression of M2-related markers of BMDMs. The results were attributed to the sensitive difference of integrin subunits (α₅β₁ and α_vβ₃) to the dextral- and sinistral-patterned surface potential distribution, respectively. The interaction difference between the integrin subunits and surface potential distribution altered the cell adhesion and cytoskeletal structure and thereby the polarization behavior of BMDMs. This work, therefore, emphasizes the importance of chirality of potential distribution on cell behavior and provides a new strategy to regulate the immune response of biomaterials.

Microgroove Cues Guiding Fibrogenesis of Stem Cells via Intracellular Force

Groove patterns are widely used in material surface modifications. However, the independent role of ditches/ridges in regulating fibrosis of soft tissues is not well-understood, especially the lack of linkage evidence in vitro and in vivo. Herein, two kinds of combinational microgroove chips with the gradient ditch/ridge width were fabricated by photolithography technology, termed R and G groups, respectively. In group R, the ridge width was 1, 5, 10, and 30 μm, with a ditch width of 30 μm; in group G, the groove width was 5, 10, 20, and 30 μm, and the ridge width was 5 μm. The effect of microgrooves on the morphology, proliferation, and expression of fibrous markers of stem cells was systematically investigated in vitro. Moreover, thicknesses of fibrous capsules were evaluated after chips were implanted into the muscular pouches of rats for 5 months. The results show that microgrooves have almost no effect on cell proliferation but significantly modulate the morphology of cells and focal adhesions (FAs) in vitro, as well as fibrosis differentiation. In particular, the differentiation of stem cells is attenuated after the intracellular force caused by stress fibers and FAs is interfered by drugs, such as rotenone and blebbistatin. Histological analysis shows that patterns of high intracellular force can apparently stimulate soft tissue fibrosis in vivo. This study not only reveals the specific rules and mechanisms of ditch/ridge regulating stem cell behaviors but also offers insight into tailoring implant surface patterns to induce controlled soft tissue fibrosis.

Biomimetic natural biomaterials for tissue engineering and regenerative medicine: new biosynthesis methods, recent advances, and emerging applications

Biomimetic materials have emerged as attractive and competitive alternatives for tissue engineering (TE) and regenerative medicine. In contrast to conventional biomaterials or synthetic materials, biomimetic scaffolds based on natural biomaterial can offer cells a broad spectrum of biochemical and biophysical cues that mimic the in vivo extracellular matrix (ECM). Additionally, such materials have mechanical adaptability, microstructure interconnectivity, and inherent bioactivity, making them ideal for the design of living implants for specific applications in TE and regenerative medicine. This paper provides an overview for recent progress of biomimetic natural biomaterials (BNBMs), including advances in their preparation, functionality, potential applications and future challenges. We highlight recent advances in the fabrication of BNBMs and outline general strategies for functionalizing and tailoring the BNBMs with various biological and physicochemical characteristics of native ECM. Moreover, we offer an overview of recent key advances in the functionalization and applications of versatile BNBMs for TE applications. Finally, we conclude by offering our perspective on open challenges and future developments in this rapidly-evolving field.

Topographical cues of PLGA membranes modulate the behavior of hMSCs, myoblasts and neuronal cells

Biomaterial surface modification through the introduction of defined and repeated patterns of topography helps study cell behavior in response to defined geometrical cues. The lithographic molding technique is widely used for conferring biomaterial surface microscale cues and enhancing the performance of biomedical devices. In this work, different master molds made by UV mask lithography were used to prepare poly (D,L-lactide-co-glycolide) - PLGA micropatterned membranes to present different features of topography at the cellular interface: channels, circular pillars, rectangular pillars, and pits. The effects of geometrical cues were investigated on different cell sources, such as neuronal cells, myoblasts, and stem cells. Morphological evaluation revealed a peculiar cell arrangement in response to a specific topographical stimulus sensed over the membrane surface. Cells seeded on linear-grooved membranes showed that this cue promoted elongated cell morphology. Rectangular and circular pillars act instead as discontinuous cues at the cell-membrane interface, inducing cell growth in multiple directions. The array of pits over the surface also highlighted the precise spatiotemporal organization of the cell; they grew between the interconnected membrane space within the pits, avoiding the microscale hole. The overall approach allowed the evaluation of the responses of different cell types adhered to various surface patterns, build-up on the same polymeric membrane, and disclosing the effect of specific topographical features. We explored how various microtopographic signals play distinct roles in different cells, thus affecting cell adhesion, migration, differentiation, cell-cell interactions, and other metabolic activities.

Biomimetic Mineralized Fiber Bundle-Inspired Scaffolding Surface on Polyetheretherketone Implants Promotes Osseointegration

The stress shielding effect caused by traditional metal implants is circumvented by using polyetheretherketone (PEEK), due to its excellent mechanical properties; however, the biologically inert nature of PEEK limits its application. Endowing PEEK with biological activity to promote osseointegration would increase its applicability for bone replacement implants. A biomimetic study is performed, inspired by mineralized collagen fiber bundles that contact bone marrow mesenchymal stem cells (BMMSCs) on the native trabecular bone surface. The PEEK surface (P) is first sulfonated with sulfuric acid to form a porous network structure (sP). The surface is then encapsulated with amorphous hydroxyapatite (HA) by magnetron sputtering to form a biomimetic scaffold that resembles mineralized collagen fiber bundles (sPHA). Amorphous HA simulates the composition of osteogenic regions in vivo and exhibits strong biological activity. In vitro results show that more favorable cell adhesion and osteogenic differentiation can be attained with the novelsurface of sPHA than with SP. The results of in vivo experiments show that sPHA exhibits osteoinductive and osteoconductive activity and facilitates bone formation and osseointegration. Therefore, the surface modification strategy can significantly improve the biological activity of PEEK, facilitate effective osseointegration, and inspire further bionic modification of other inert polymers similar to PEEK.

Curved Nanofiber Network Induces Cellular Bridge Formation to Promote Stem Cell Mechanotransduction

Remarkable exertions are directed to reveal and understand topographic cues that induce cell mechanical sensitive responses including lineage determination. Extracellular matrix (ECM) is the sophisticated ensemble of diverse factors offering the complicated cellular microenvironment to regulate cell behaviors. However, the functions of only a few of these factors are revealed; most of them are still poorly understood. Herein, the focus is on understanding the curved structure in ECM network for regulating stem cell mechanotransduction. A curved nanofiber network mimicking the curved structure in ECM is fabricated by an improved electrospinning technology. Compared with the straight fibers, the curved fibers promote cell bridge formation because of the cytoskeleton tension. The actomyosin filaments are condensed near the curved edge of the non-adhesive bridge in the bridging cells, which generates higher myosin-II-based intracellular force. This force drives cell lineage commitment toward osteogenic differentiation. This study enriches and perfects the knowledge of the effects of topographic cues on cell behaviors and guides the development of novel biomaterials.

Rational Design of Soft-Hard Interfaces through Bioinspired Engineering

Soft-hard tissue interfaces in nature present a diversity of hierarchical transitions in composition and structure to address the challenge of stress concentrations that would otherwise arise at their interface. The translation of these into engineered materials holds promise for improved function of biomedical interfaces. Here, soft-hard tissue interfaces found in the body in health and disease, and the application of the diverse, functionally graded, and hierarchical structures that they present to bioinspired engineering materials are reviewed. A range of such bioinspired engineering materials and associated manufacturing technologies that are on the horizon in interfacial tissue engineering, hydrogel bioadhesion at the interfaces, and healthcare and medical devices are described.

Evaluation of 'surgery-friendly' bone scaffold characteristics: 3D printed ductile BG/PCL scaffold with high inorganic content to repair critical bone defects

The repair of irregular and complex critical bone defects remains a challenge in clinical practice. The application of 3D-printed bioceramics particle/polymer composite scaffolds in bone tissue engineering has been widely studied. At present, the inorganic particle content of the composite scaffolds is generally low, resulting in poor osteogenic activity. However, scaffold with high inorganic content are highly brittle, difficult to operate during surgery, and cannot be in close contact with surrounding bones. Therefore, it is of great significance to design a 'surgery-friendly' scaffold with high bioceramic content and good ductility. In this study, we used the solvent method to add high concentration (wt% 70%) bioglass (BG) into polycaprolactone (PCL), and polyethylene glycol was used as plasticizer to prepare 70% BG/PCL composite scaffolds with high ductility using 3D printing technology.In vitroexperiments showed that the scaffold had good mechanical properties: easy extension, easy folding and strong compressive resistance. It also showed good performance in biocompatibility and osteogenic activity. It was further observed that compared with pure BG or PCL implantation, the scaffold with higher BG content could have more new bone tissue appeared after 12 weeks. All these results indicate that 3D-printed 70% BG/PCL scaffolds have great potential for personalized repair of bone defects.

Recent advances in regenerative biomaterials

Nowadays, biomaterials have evolved from the inert supports or functional substitutes to the bioactive materials able to trigger or promote the regenerative potential of tissues. The interdisciplinary progress has broadened the definition of 'biomaterials', and a typical new insight is the concept of tissue induction biomaterials. The term 'regenerative biomaterials' and thus the contents of this article are relevant to yet beyond tissue induction biomaterials. This review summarizes the recent progress of medical materials including metals, ceramics, hydrogels, other polymers and bio-derived materials. As the application aspects are concerned, this article introduces regenerative biomaterials for bone and cartilage regeneration, cardiovascular repair, 3D bioprinting, wound healing and medical cosmetology. Cell-biomaterial interactions are highlighted. Since the global pandemic of coronavirus disease 2019, the review particularly mentions biomaterials for public health emergency. In the last section, perspectives are suggested: (i) creation of new materials is the source of innovation; (ii) modification of existing materials is an effective strategy for performance improvement; (iii) biomaterial degradation and tissue regeneration are required to be harmonious with each other; (iv) host responses can significantly influence the clinical outcomes; (v) the long-term outcomes should be paid more attention to; (vi) the noninvasive approaches for monitoring in vivo dynamic evolution are required to be developed; (vii) public health emergencies call for more research and development of biomaterials; and (viii) clinical translation needs to be pushed forward in a full-chain way. In the future, more new insights are expected to be shed into the brilliant field-regenerative biomaterials.

Topographical biointerface regulating cellular functions for bone tissue engineering

The physiochemical properties of the implant interface significantly influence cell growth, differentiation, cellular matrix deposition, and mineralisation, and eventually, determine the bone regeneration efficiency. Cells directly sense and respond to the physical, chemical, and mechanical cues of the implant surface, and it is increasingly recognized that surface topography can evoke specific cellular responses, conferring biological functions on substrate materials and regulating tissue regeneration. Current progress towards the fundamental understanding of the interplay between the cell and topographical surface has been made by combined advance in fabrication technologies and cell biology. Particularly, the precise fabrication and control of nano/microscale topographies can provide the fundamental knowledge of the mechanotransduction process that governs the cellular response as well as the knowledge of how the specific features drive cells towards a defined differentiation outcome. In this review, we first introduce common techniques and substrate materials for designing and fabricating micro/nano‐topographical surfaces for bone regeneration. We then illustrate the intrinsic relationship of topological cues, cellular signal transduction, and cell functions and fates in osteogenic differentiation. Finally, we discuss the challenges and the future of using topological cues as a cell therapy to direct bone tissue regeneration.

Biophysical Regulations of Epigenetic State and Notch Signaling in Neural Development Using Microgroove Substrates

A number of studies have recently shown how surface topography can alter the behavior and differentiation patterns of different types of stem cells. Although the exact mechanisms and molecular pathways involved remain unclear, a consistent portion of the literature points to epigenetic changes induced by nuclear remodeling. In this study, we investigate the behavior of clinically relevant neural populations derived from human pluripotent stem cells when cultured on polydimethylsiloxane microgrooves (3 and 10 μm depth grooves) to investigate what mechanisms are responsible for their differentiation capacity and functional behavior. Our results show that microgrooves enhance cell alignment, modify nuclear geometry, and significantly increase cellular stiffness, which we were able to measure at high resolution with a combination of light and electron microscopy, scanning ion conductance microscopy (SICM), and atomic force microscopy (AFM) coupled with quantitative image analysis. The microgrooves promoted significant changes in the epigenetic landscape, as revealed by the expression of key histone modification markers. The main behavioral change of neural stem cells on microgrooves was an increase of neuronal differentiation under basal conditions on the microgrooves. Through measurements of cleaved Notch1 levels, we found that microgrooves downregulate Notch signaling. We in fact propose that microgroove topography affects the differentiation potential of neural stem cells by indirectly altering Notch signaling through geometric segregation and that this mechanism in parallel with topography-dependent epigenetic modulations acts in concert to enhance stem cell neuronal differentiation.

Bubble-Patterned Films by Inkjet Printing and Gas Foaming

The micropatterning of thin films represents a challenging task, even for additive manufacturing techniques. In this work, we introduce the use of inkjet-printing technology coupled with a gas-foaming process, to produce patterned porosities on polymeric thin films, to develop a bubble-writing method. Inkjet printing of an aqueous solution of poly (vinyl alcohol) (PVA), a well-known gas-barrier polymer, allows the selective coating of a thin poly (lactic acid) (PLA) film, which is, successively, exposed to a gas-foaming process. The foaming of the thin PLA film is effective, only when PVA is printed on top, since the PVA barrier hinders the premature loss of the gas, thus allowing the formation of cavities (bubbles) in the covered areas; then, removing the PVA coating by water washing forms a bubble pattern. As a proof of concept, the surface-morphology features of the patterned porous PLA films have been proven effective at driving endothelial cell growth. A new technological platform is, hence, introduced in the field of tissue engineering and, in general, in fields involving thin films, where a patterned porous structure may add value.

Mechanotransduction Regulates the Interplays Between Alveolar Epithelial and Vascular Endothelial Cells in Lung

Mechanical stress plays a critical role among development, functional maturation, and pathogenesis of pulmonary tissues, especially for the alveolar epithelial cells and vascular endothelial cells located in the microenvironment established with vascular network and bronchial-alveolar network. Alveolar epithelial cells are mainly loaded by cyclic strain and air pressure tension. While vascular endothelial cells are exposed to shear stress and cyclic strain. Currently, the emerging evidences demonstrated that non-physiological mechanical forces would lead to several pulmonary diseases, including pulmonary hypertension, fibrosis, and ventilation induced lung injury. Furthermore, a series of intracellular signaling had been identified to be involved in mechanotransduction and participated in regulating the physiological homeostasis and pathophysiological process. Besides, the communications between alveolar epithelium and vascular endothelium under non-physiological stress contribute to the remodeling of the pulmonary micro-environment in collaboration, including hypoxia induced injuries, endothelial permeability impairment, extracellular matrix stiffness elevation, metabolic alternation, and inflammation activation. In this review, we aim to summarize the current understandings of mechanotransduction on the relation between mechanical forces acting on the lung and biological response in mechanical overloading related diseases. We also would like to emphasize the interplays between alveolar epithelium and vascular endothelium, providing new insights into pulmonary diseases pathogenesis, and potential targets for therapy.

Electrospun Nanofibers for Bone Regeneration: From Biomimetic Composition, Structure to Function

In recent years, a variety of novel materials and processing technologies have been developed to prepare tissue engineering scaffolds for bone defect repair. Among them, nanofibers fabricated via electrospinning technology...