Surface Topography Guides Morphology and Spatial Patterning of Induced Pluripotent Stem Cell Colonies

Nanofiber-microwell cell culture system for spatially patterned differentiation of pluripotent stem cells in 3D

The intricate interplay between biochemical and physical cues dictates pluripotent stem cell (PSC) differentiation to form various tissues. While biochemical modulation has been extensively studied, the role of biophysical microenvironments in early lineage commitment remains elusive. Here, we introduce a novel 3D cell culture system combining electrospun nanofibers with microfabricated polydimethylsiloxane (PDMS) patterns. This system enables the controlled formation of semispherical human induced pluripotent stem cell (hiPSC) colonies, facilitating the investigation of local mechanical stem cell niches on mechano-responsive signaling and lineage specification. Our system unveiled spatially organized RhoA activity coupled with actin-myosin cable formation, suggesting mechano-dependent hiPSC behaviors. Nodal network analysis of RNA-seq data revealed RhoA downstream regulation of YAP signaling, DNA histone modifications, and patterned germ layer specification. Notably, altering colony morphology through controlled PDMS microwell shaping effectively modulated the spatial distribution of mechano-sensitive mediators and subsequent differentiation. This study provides a cell culture platform to decipher the role of biophysical cues in early embryogenesis, offering valuable insights for material design in tissue engineering and regenerative medicine applications.

Bioactive 3D Electrohydrodynamic Printed Lattice Architectures Augment Tenogenesis of Tendon Stem/Progenitor Cells

Tendon defect repair remains a tough clinical procedure that hinders functional motion in patients. Electrohydrodynamic (EHD) three-dimensional (3D) printing, as a novel strategy, can controllably fabricate biomimetic micro/nanoscale architecture, but the hydrophobic and bioinert nature of polymers might be adverse to cell-material interplay. In this work, 3D EHD printed polycaprolactone (PCL) was immobilized on basic fibroblast growth factor (bFGF) using polydopamine (PDA), and the proliferation and tenogenic differentiation of tendon stem/progenitor cells (TSPCs) in vitro was researched. A subcutaneous model was established to evaluate the effects of tenogenesis and immunomodulation. We then investigated the in situ implantation and immunomodulation effects in an Achilles tendon defect model. After immobilization of bFGF, the scaffolds profoundly facilitated proliferation and tenogenic differentiation; however, PDA had only a proliferative effect. Intriguingly, the bFGF immobilized on EHD printed PCL indicated a synergistic effect on the highest expression of tenogenic gene and protein markers at 14 days, and the tenogenesis may be induced by activating the transforming growth factor-β (TGF-β) signal pathway in vitro. The subcutaneous engraftment study confirmed a tendon-like structure, similar to that of the native tendon, as well as an M2 macrophage polarization effect. Additionally, the bioactive scaffold exhibited superior efficacy in new collagen formation and repair of Achilles tendon defects. Our study revealed that the topographic cues alone were insufficient to trigger tenogenic differentiation, requiring appropriate chemical signals, and that appropriate immunomodulation was conducive to tenogenesis. The tenogenesis of TSPCs on the bioactive scaffold may be correlated with the TGF-β signal pathway and M2 macrophage polarization.

Multiplex miRNA reporting platform for real-time profiling of living cells

Accurately characterizing cell types within complex cell structures provides invaluable information for comprehending the cellular status during biological processes. In this study, we have developed an miRNA-switch cocktail platform capable of reporting and tracking the activities of multiple miRNAs (microRNAs) at the single-cell level, while minimizing disruption to the cell culture. Drawing on the principles of traditional miRNA-sensing mRNA switches, our platform incorporates subcellular tags and employs intelligent engineering to segment three subcellular regions using two fluorescent proteins. These designs enable the quantification of multiple miRNAs within the same cell. Through our experiments, we have demonstrated the platform's ability to track marker miRNA levels during cell differentiation and provide spatial information of heterogeneity on outlier cells exhibiting extreme miRNA levels. Importantly, this platform offers real-time and in situ miRNA reporting, allowing for multidimensional evaluation of cell profile and paving the way for a comprehensive understanding of cellular events during biological processes.

Electrical Stimulation of Human Mesenchymal Stem Cells on Conductive Substrates Promotes Neural Priming

Electrical stimulation (ES) within a conductive scaffold is potentially beneficial in encouraging the differentiation of stem cells toward a neuronal phenotype. To improve stem cell-based regenerative therapies, it is essential to use electroconductive scaffolds with appropriate stiffnesses to regulate the amount and location of ES delivery. Herein, biodegradable electroconductive substrates with different stiffnesses are fabricated from chitosan-grafted-polyaniline (CS-g-PANI) copolymers. Human mesenchymal stem cells (hMSCs) cultured on soft conductive scaffolds show a morphological change with significant filopodial elongation after electrically stimulated culture along with upregulation of neuronal markers and downregulation of glial markers. Compared to stiff conductive scaffolds and non-conductive CS scaffolds, soft conductive CS-g-PANI scaffolds promote increased expression of microtubule-associated protein 2 (MAP2) and neurofilament heavy chain (NF-H) after application of ES. At the same time, there is a decrease in the expression of the glial markers glial fibrillary acidic protein (GFAP) and vimentin after ES. Furthermore, the elevation of intracellular calcium [Ca2+ ] during spontaneous, cell-generated Ca2+ transients further suggests that electric field stimulation of hMSCs cultured on conductive substrates can promote a neural-like phenotype. The findings suggest that the combination of the soft conductive CS-g-PANI substrate and ES is a promising new tool for enhancing neuronal tissue engineering outcomes.

Direct deep UV lithography to micropattern PMMA for stem cell culture

Microengineering is increasingly being used for controlling the microenvironment of stem cells. Here, a novel method for fabricating structures with subcellular dimensions in commonly available thermoplastic poly(methyl methacrylate) (PMMA) is shown. Microstructures are produced in PMMA substrates using Deep Ultraviolet lithography, and the effect of different developers is described. Microgrooves fabricated in PMMA are used for the neuronal differentiation of mouse embryonic stem cells (mESCs) directly on the polymer. The fabrication of 3D, curvilinear patterned surfaces is also highlighted. A 3D multilayered microfluidic chip is fabricated using this method, which includes a porous polycarbonate (PC) membrane as cell culture substrate. Besides directly manufacturing PMMA-based microfluidic devices, an application of the novel approach is shown where a reusable PMMA master is created for replicating microstructures with polydimethylsiloxane (PDMS). As an application example, microchannels fabricated in PDMS are used to selectively expose mESCs to soluble factors in a localized manner. The described microfabrication process offers a remarkably simple method to fabricate for example multifunctional topographical or microfluidic culture substrates outside cleanrooms, thereby using inexpensive and widely accessible equipment. The versatility of the underlying process could find various applications also in optical systems and surface modification of biomedical implants.

Transformative Materials to Create 3D Functional Human Tissue Models In Vitro in a Reproducible Manner

Recreating human tissues and organs in the petri dish to establish models as tools in biomedical sciences has gained momentum. These models can provide insight into mechanisms of human physiology, disease onset, and progression, and improve drug target validation, as well as the development of new medical therapeutics. Transformative materials play an important role in this evolution, as they can be programmed to direct cell behavior and fate by controlling the activity of bioactive molecules and material properties. Using nature as an inspiration, scientists are creating materials that incorporate specific biological processes observed during human organogenesis and tissue regeneration. This article presents the reader with state-of-the-art developments in the field of in vitro tissue engineering and the challenges related to the design, production, and translation of these transformative materials. Advances regarding (stem) cell sources, expansion, and differentiation, and how novel responsive materials, automated and large-scale fabrication processes, culture conditions, in situ monitoring systems, and computer simulations are required to create functional human tissue models that are relevant and efficient for drug discovery, are described. This paper illustrates how these different technologies need to converge to generate in vitro life-like human tissue models that provide a platform to answer health-based scientific questions.

Stiffness-Tunable Hydrogel-Sandwich Culture Modulates the YAP-Mediated Mechanoresponse in Induced-Pluripotent Stem Cell Embryoid Bodies and Augments Cardiomyocyte Differentiation

Microenvironmental factors, including substrate stiffness, regulate stem cell behavior and differentiation. However, the effects of substrate stiffness on the behavior of induced pluripotent stem cell (iPSC)- derived embryoid bodies (EB) remain unclear. To investigate the effects of mechanical cues on iPSC-EB differentiation, a 3D hydrogel-sandwich culture (HGSC) system is developed that controls the microenvironment surrounding iPSC-EBs using a stiffness-tunable polyacrylamide hydrogel assembly. Mouse iPSC-EBs are seeded between upper and lower polyacrylamide hydrogels of differing stiffness (Young's modulus [E'] = 54.3 ± 7.1 kPa [hard], 28.1 ± 2.3 kPa [moderate], and 5.1 ± 0.1 kPa [soft]) and cultured for 2 days. HGSC induces stiffness-dependent activation of the yes-associated protein (YAP) mechanotransducer and actin cytoskeleton rearrangement in the iPSC-EBs. Moreover, moderate-stiffness HGSC specifically upregulates the mRNA and protein expression of ectoderm and mesoderm lineage differentiation markers in iPSC-EBs via YAP-mediated mechanotransduction. Pretreatment of mouse iPSC-EBs with moderate-stiffness HGSC promotes cardiomyocyte (CM) differentiation and structural maturation of myofibrils. The proposed HGSC system provides a viable platform for investigating the role of mechanical cues on the pluripotency and differentiation of iPSCs that can be beneficial for research into tissue regeneration and engineering.

YAP1 is essential for self-organized differentiation of pluripotent stem cells

Induced pluripotent stem cells (iPSCs) form aggregates that recapitulate aspects of the self-organization in early embryogenesis. Within few days, cells undergo a transition from epithelial-like structures to organized three-dimensional embryoid bodies (EBs) with upregulation of germ layer-specific genes. However, it is largely unclear, which signaling cascades regulate self-organized differentiation. The Yes-associated protein 1 (YAP1) is a downstream effector of the Hippo pathway and essential mechanotransducer. YAP1 has been suggested to play a crucial role for early embryo development, but the relevance for early germ layer commitment of human iPSCs remains to be elucidated. To gain insights into the function of YAP1 in early cell-fate decisions, we generated YAP1 knockout (YAP^-/-) iPSC lines with CRISPR/Cas9 technology and analyzed transcriptomic and epigenetic modifications. YAP^-/- iPSCs showed increased expression of several YAP1 targets and of NODAL, an important regulator of cell differentiation. Furthermore, YAP1 deficiency evoked global DNA methylation changes. Directed differentiation of adherent iPSC colonies towards endoderm, mesoderm, and ectoderm could be induced, albeit endodermal and ectodermal differentiation showed transcriptomic and epigenetic changes in YAP^-/- lines. Notably, in undirected self-organized YAP^-/- EBs germ layer specification was clearly impaired. This phenotype was rescued via lentiviral overexpression of YAP1 and also by NODAL inhibitors. Our results demonstrate that YAP1 plays an important role during early germ layer specification of iPSCs, particularly for the undirected self-organization of EBs, and this is at least partly attributed to activation of the NODAL signaling.

Engineered substrates incapable of induction of chondrogenic differentiation compared to the chondrocyte imprinted substrates

It is well established that surface topography can affect cell functions. However, finding a reproducible and reliable method for regulating stem cell behavior is still under investigation. It has been shown that cell imprinted substrates contain micro- and nanoscale structures of the cell membrane that serve as hierarchical substrates, can successfully alter stem cell fate. This study investigated the effect of the overall cell shape by fabricating silicon wafers containing pit structure in the average size of spherical-like chondrocytes using photolithography technique. We also used chondrocyte cell line (C28/I2) with spindle-like shape to produce cell imprinted substrates. The effect of all substrates on the differentiation of adipose-derived mesenchymal stem cells (ADSCs) has been studied. The AFM and scanning electron microscopy images of the prepared substrates demonstrated that the desired shapes were successfully transferred to the substrates. Differentiation of ADSCs was investigated by immunostaining for mature chondrocyte marker, collagen II, and gene expression of collagen II, Sox9, and aggrecan markers. C28/I2 imprinted substrate could effectively enhanced chondrogenic differentiation compared to regular pit patterns on the wafer. It can be concluded that cell imprinted substrates can induce differentiation signals better than engineered lithographic substrates. The nanostructures on the cell-imprinted patterns play a crucial role in harnessing cell fate. Therefore, the patterns must include the nano-topographies to have reliable and reproducible engineered substrates.

Regulation of Mesenchymal Stem Cell Morphology Using Hydrogel Substrates with Tunable Topography and Photoswitchable Stiffness

Cell function can be directly influenced by the mechanical and structural properties of the extracellular environment. In particular, cell morphology and phenotype can be regulated via the modulation of both the stiffness and surface topography of cell culture substrates. Previous studies have highlighted the ability to design cell culture substrates to optimise cell function. Many such examples, however, employ photo-crosslinkable polymers with a terminal stiffness or surface profile. This study presents a system of polyacrylamide hydrogels, where the surface topography can be tailored and the matrix stiffness can be altered in situ with photoirradiation. The process allows for the temporal regulation of the extracellular environment. Specifically, the surface topography can be tailored via reticulation parameters to include creased features with control over the periodicity, length and branching. The matrix stiffness can also be dynamically tuned via exposure to an appropriate dosage and wavelength of light, thus, allowing for the temporal regulation of the extracellular environment. When cultured on the surface of the hydrogels, the morphology and alignment of immortalised human mesenchymal stem cells can be directly influenced through the tailoring of surface creases, while cell size can be altered via changes in matrix stiffness. This system offers a new platform to study cellular mechanosensing and the influence of extracellular cues on cell phenotype and function.

Role of YAP as a Mechanosensing Molecule in Stem Cells and Stem Cell-Derived Hematopoietic Cells

Yes-associated protein (YAP) and WW domain-containing transcription regulator protein 1 (WWTR1, also known as TAZ) are transcriptional coactivators in the Hippo signaling pathway. Both are well-known regulators of cell proliferation and organ size control, and they have significant roles in promoting cell proliferation and differentiation. The roles of YAP and TAZ in stem cell pluripotency and differentiation have been extensively studied. However, the upstream mediators of YAP and TAZ are not well understood. Recently, a novel role of YAP in mechanosensing and mechanotransduction has been reported. The present review updates information on the regulation of YAP by mechanical cues such as extracellular matrix stiffness, fluid shear stress, and actin cytoskeleton tension in stem cell behaviors and differentiation. The review explores mesenchymal stem cell fate decisions, pluripotent stem cells (PSCs), self-renewal, pluripotency, and differentiation to blood products. Understanding how cells sense their microenvironment or niche and mimic those microenvironments in vitro could improve the efficiency of producing stem cell products and the efficacy of the products.

Multifunctional-high resolution imaging plate based on hydrophilic graphene for digital pathology

In the present study, we showed that hydrophilic graphene can serve as an ideal imaging plate for biological specimens. Graphene being a single-atom-thick semi-metal with low secondary electron emission, array tomography analysis of serial sections of biological specimens on a graphene substrate showed excellent image quality with improvedz-axis resolution, without including any conductive surface coatings. However, the hydrophobic nature of graphene makes the placement of biological specimens difficult; graphene functionalized with polydimethylsiloxane oligomer was fabricated using a simple soft lithography technique and then processed with oxygen plasma to provide hydrophilic graphene with minimal damage to graphene. High-quality scanning electron microscopy images of biological specimens free from charging effects or distortion were obtained, and the optical transparency of graphene enabled fluorescence imaging of the specimen; high-resolution correlated electron and light microscopy analysis of the specimen became possible with the hydrophilic graphene plate.

Chondrogenic differentiation of mesenchymal stem cells through cartilage matrix-inspired surface coatings

The stem cell niche comprises soluble molecules and extracellular matrix components which provide chemical and mechanical cues that determine the differentiation of stem cells. Here, the effect of polyelectrolyte multilayer (PEM) composition and terminal layer fabricated with layer-by-layer technique (LBL) pairing either hyaluronan [in its native (nHA) and oxidized form (oHA)] or chondroitin sulfate (CS) with type I collagen (Col I) is investigated on chondrogenic differentiation of human umbilical mesenchymal stem cells (hUC-MSCs). Physical studies performed to investigate the establishment and structure of the surface coatings show that PEM composed of HA and Col I show a dominance of nHA or oHA with considerably lesser organization of Col I fibrils. In contrast, distinguished fibrilized Col I is found in nCS-containing PEM. Generally, Col I-terminated PEM promote the adhesion, migration, and growth of hUC-MSCs more than GAG-terminated surfaces due to the presence of fibrillar Col I but show a lower degree of differentiation towards the chondrogenic lineage. Notably, the Col I/nHA PEM not only supports adhesion and growth of hUC-MSCs but also significantly promotes cartilage-associated gene and protein expression as found by histochemical and molecular biology studies, which is not seen on the Col I/oHA PEM. This is related to ligation of HA to the cell receptor CD44 followed by activation of ERK/Sox9 and noncanonical TGF-β signaling-p38 pathways that depends on the molecular weight of HA as found by immune histochemical and western blotting. Hence, surface coatings on scaffolds and other implants by PEM composed of nHA and Col I may be useful for programming MSC towards cartilage regeneration.

Semi-three-dimensional cultures using laminin 221 as a coating material for human induced pluripotent stem cells

It was previously believed that human induced pluripotent stem cells (hiPSCs) did not show adhesion to the coating material Laminin 221, which is known to have specific affinity for cardiomyocytes. In this study, we report that human mononuclear cell-derived hiPSCs, established with Sendai virus vector, form peninsular-like colonies rather than embryonic stem cell-like colonies; these peninsular-like colonies can be passaged more than 10 times after establishment. Additionally, initialization-deficient cells with residual Sendai virus vector adhered to the coating material Laminin 511 but not to Laminin 221. Therefore, the expression of undifferentiated markers tended to be higher in hiPSCs established on Laminin 221 than on Laminin 511. On Laminin 221, hiPSCs15M66 showed a semi-floating colony morphology. The expression of various markers of cell polarity was significantly lower in hiPSCs cultured on Laminin 221 than in hiPSCs cultured on Laminin 511. Furthermore, 201B7 and 15M66 hiPSCs showed 3D cardiomyocyte differentiation on Laminin 221. Thus, the coating material Laminin 221 provides semi-floating culture conditions for the establishment, culture and induced differentiation of hiPSCs.

Macroporous Aligned Hydrogel Microstrands for 3D Cell Guidance

Tissue engineering strongly relies on the use of hydrogels as highly hydrated 3D matrices to support the maturation of laden cells. However, because of the lack of microarchitecture and sufficient porosity, common hydrogel systems do not provide physical cell-instructive guidance cues and efficient transport of nutrients and oxygen to the inner part of the construct. A controlled, organized cellular alignment and resulting alignment of secreted ECM are hallmarks of muscle, tendons, and nerves and play an important role in determining their functional properties. Although several strategies to induce cellular alignment have been investigated in 2D systems, the generation of cell-instructive 3D hydrogels remains a challenge. Here, we report on the development of a simple and scalable method to efficiently generate highly macroporous constructs featuring aligned guidance cues. A precross-linked bulk hydrogel is pressed through a grid with variable opening sizes, thus deconstructing it into an array of aligned, high aspect ratio microgels (microstrands) with tunable diameter that are eventually stabilized by a second photoclick cross-linking step. This method has been investigated and optimized both in silico and in vitro, thereby leading to conditions with excellent viability and organized cellular alignment. Finally, as proof of concept, the method has been shown to direct aligned muscle tissue maturation. These findings demonstrate the 3D physical guidance potential of our system, which can be used for a variety of anisotropic tissues and applications.

Delivering Mechanical Stimulation to Cells: State of the Art in Materials and Devices Design

Biochemical signals, such as growth factors, cytokines, and transcription factors are known to play a crucial role in regulating a variety of cellular activities as well as maintaining the normal function of different tissues and organs. If the biochemical signals are assumed to be one side of the coin, the other side comprises biophysical cues. There is growing evidence showing that biophysical signals, and in particular mechanical cues, also play an important role in different stages of human life ranging from morphogenesis during embryonic development to maturation and maintenance of tissue and organ function throughout life. In order to investigate how mechanical signals influence cell and tissue function, tremendous efforts have been devoted to fabricating various materials and devices for delivering mechanical stimuli to cells and tissues. Here, an overview of the current state of the art in the design and development of such materials and devices is provided, with a focus on their design principles, and challenges and perspectives for future research directions are highlighted.

Cells Dynamically Adapt to Surface Geometry by Remodeling Their Focal Adhesions and Actin Cytoskeleton

Cells probe their environment and adapt their shape accordingly via the organization of focal adhesions and the actin cytoskeleton. In an earlier publication, we described the relationship between cell shape and physiology, for example, shape-induced differentiation, metabolism, and proliferation in mesenchymal stem cells and tenocytes. In this study, we investigated how these cells organize their adhesive machinery over time when exposed to microfabricated surfaces of different topographies and adhesive island geometries. We further examined the reciprocal interaction between stress fiber and focal adhesion formation by pharmacological perturbations. Our results confirm the current literature that spatial organization of adhesive sites determines the ability to form focal adhesions and stress fibers. Therefore, cells on roughened surfaces have smaller focal adhesion and fewer stress fibers. Our results further highlight the importance of integrin-mediated adhesion in the adaptive properties of cells and provide clear links to the development of bioactive materials.

An update of nanotopographical surfaces in modulating stem cell fate: a narrative review

Stem cells have been one of the ideal sources for tissue regeneration owing to their capability of self-renewal and differentiation. In vivo, the extracellular microenvironment plays a vital role in modulating stem cell fate. When developing biomaterials for regenerative medicine, incorporating biochemical and biophysical cues to mimic extracellular matrix can enhance stem cell lineage differentiation. More specifically, modulating the stem cell fate can be achieved by controlling the nanotopographic features on synthetic surfaces. Optimization of nanotopographical features leads to desirable stem cell functions, which can maximize the effectiveness of regenerative treatment. In this review, nanotopographical surfaces, including static patterned surface, dynamic patterned surface, and roughness are summarized, and their fabrication, as well as the impact on stem cell behaviour, are discussed. Later, the recent progress of applying nanotopographical featured biomaterials for altering different types of stem cells is presented, which directs the design and fabrication of functional biomaterial. Last, the perspective in fundamental research and for clinical application in this field is discussed.

Design of chemically defined synthetic substrate surfaces for the in vitro maintenance of human pluripotent stem cells: A review

Human pluripotent stem cells (hPSCs) have the potential of long-term self-renewal and differentiation into nearly all cell types in vitro. Prior to the downstream applications, the design of chemically defined synthetic substrates for the large-scale proliferation of quality-controlled hPSCs is critical. Although great achievements have been made, Matrigel and recombinant proteins are still widely used in the fundamental research and clinical applications. Therefore, much effort is still needed to improve the performance of synthetic substrates in the culture of hPSCs, realizing their commercial applications. In this review, we summarized the design of reported synthetic substrates and especially their limitations in terms of cell culture. Moreover, much attention was paid to the development of promising peptide displaying surfaces. Besides, the biophysical regulation of synthetic substrate surfaces as well as the three-dimensional culture systems were described.

The Bumpy Road to Stem Cell Therapies: Rational Design of Surface Topographies to Dictate Stem Cell Mechanotransduction and Fate

Cells sense and respond to a variety of physical cues from their surrounding microenvironment, and these are interpreted through mechanotransductive processes to inform their behavior. These mechanisms have particular relevance to stem cells, where control of stem cell proliferation, potency, and differentiation is key to their successful application in regenerative medicine. It is increasingly recognized that surface micro- and nanotopographies influence stem cell behavior and may represent a powerful tool with which to direct the morphology and fate of stem cells. Current progress toward this goal has been driven by combined advances in fabrication technologies and cell biology. Here, the capacity to generate precisely defined micro- and nanoscale topographies has facilitated the studies that provide knowledge of the mechanotransducive processes that govern the cellular response as well as knowledge of the specific features that can drive cells toward a defined differentiation outcome. However, the path forward is not fully defined, and the "bumpy road" that lays ahead must be crossed before the full potential of these approaches can be fully exploited. This review focuses on the challenges and opportunities in applying micro- and nanotopographies to dictate stem cell fate for regenerative medicine. Here, key techniques used to produce topographic features are reviewed, such as photolithography, block copolymer lithography, electron beam lithography, nanoimprint lithography, soft lithography, scanning probe lithography, colloidal lithography, electrospinning, and surface roughening, alongside their advantages and disadvantages. The biological impacts of surface topographies are then discussed, including the current understanding of the mechanotransductive mechanisms by which these cues are interpreted by the cells, as well as the specific effects of surface topographies on cell differentiation and fate. Finally, considerations in translating these technologies and their future prospects are evaluated.

The spatial self-organization within pluripotent stem cell colonies is continued in detaching aggregates

Colonies of induced pluripotent stem cells (iPSCs) reveal aspects of self-organization even under culture conditions that maintain pluripotency. To investigate the dynamics of this process under spatial confinement, we used either polydimethylsiloxane (PDMS) pillars or micro-contact printing of vitronectin. There was a progressive upregulation of OCT4, E-cadherin, and NANOG within 70 μm from the outer rim of iPSC colonies. Single-cell RNA-sequencing and spatial reconstruction of gene expression demonstrated that OCT4^high subsets, residing at the edge of the colony, have pronounced up-regulation of the TGF-β pathway, particularly of NODAL and its inhibitor LEFTY. Interestingly, after 5-7 days, iPSC colonies detached spontaneously from micro-contact printed substrates to form 3D aggregates. This new method allowed generation of embryoid bodies (EBs) of controlled size without enzymatic or mechanical treatment. Within the early 3D aggregates, radial organization and differential gene expression continued in analogy to the changes observed during self-organization of iPSC colonies. Early self-detached aggregates revealed up-regulated germline-specific gene expression patterns as compared to conventional EBs. However, there were no marked differences after further directed differentiation toward hematopoietic, mesenchymal, and neuronal lineages. Our results provide further insight into the gradual self-organization within iPSC colonies and at their transition into EBs.

Pillar-Based Mechanical Induction of an Aggressive Tumorigenic Lung Cancer Cell Model

Tissue microarchitecture imposes physical constraints to the migration of individual cells. Especially in cancer metastasis, three-dimensional structural barriers within the extracellular matrix are known to affect the migratory behavior of cells, regulating the pathological state of the cells. Here, we employed a culture platform with micropillar arrays of 2 μm diameter and 16 μm pitch (2.16 micropillar) as a mechanical stimulant. Using this platform, we investigated how a long-term culture of A549 human lung carcinoma cells on the (2.16) micropillar-embossed dishes would influence the pathological state of the cell. A549 cells grown on the (2.16) micropillar array with 10 μm height exhibited a significantly elongated morphology and enhanced migration even after the detachment and reattachment, as evidenced in the conventional wound-healing assay, single-cell tracking analysis, and in vivo tumor colonization assays. Moreover, the pillar-induced morphological deformation in nuclei was accompanied by cell-cycle arrest in the S phase, leading to suppressed proliferation. While these marked traits of morphology-migration-proliferation support more aggressive characteristics of metastatic cancer cells, typical indices of epithelial-mesenchymal transition were not found, but instead, remarkable traces of amoeboidal transition were confirmed. Our study also emphasizes the importance of mechanical stimuli from the microenvironment during pathogenesis and how gained traits can be passed onto subsequent generations, ultimately affecting their pathophysiological behavior. Furthermore, this study highlights the potential use of pillar-based mechanical stimuli as an in vitro cell culture strategy to induce more aggressive tumorigenic cancer cell models.

Endothelialization strategy of implant materials surface: The newest research in recent 5 years

In recent years, more and more metal or non-metal materials have been used in the treatment of cardiovascular diseases, but the vascular complications after transplantation are still the main factors restricting the clinical application of most grafts, such as acute thrombosis and graft restenosis. Implant materials have been extensively designed and surface optimized by researchers, but it is still too difficult to avoid complications. Natural vascular endodermis has excellent function, anti-coagulant and anti-intimal hyperplasia, and it is also the key to maintaining the homeostasis of normal vascular microenvironment. Therefore, how to promote the adhesion of endothelial cells (ECs) on the surface of cardiovascular materials to achieve endothelialization of the surface is the key to overcoming the complications after implant materialization. At present, the surface endothelialization design of materials based on materials surface science, bioactive molecules, and biological function intervention and feedback has attracted much attention. In this review, we summarize the related research on the surface modification of materials by endothelialization in recent years, and analyze the advantages and challenges of current endothelialization design ideas, explain the relationship between materials, cells, and vascular remodeling in order to find a more ideal endothelialization surface modification strategy for future researchers to meet the requirements of clinical biocompatibility of cardiovascular materials.

Molecular imprinting as a simple way for the long-term maintenance of the stemness and proliferation potential of adipose-derived stem cells: an in vitro study

Culturing adipose-derived stem cells (ADSCs) on the biomimetic ADSC-imprinted substrate is a simple way for long-term maintenance of their stemness and proliferation potential.

Culturing Human Pluripotent Stem Cells on Micropatterned Silicon Surfaces

Human pluripotent stem cell culture conditions are constantly being optimized, thus providing insight to the environmental cues that affect cell choices. A wide variety of media, coating materials, and substrates is now available for use, serving different scientific needs. Factors such as material stiffness, roughness, and topography are being recognized to contribute or even direct the acquisition of specific phenotypes. Here, we describe the use of patterned silicon substrates coated with Matrigel for the propagation and differentiation of human pluripotent stem cells.

Intrinsic Mechanical Cues and Their Impact on Stem Cells and Embryogenesis

Although understanding how soluble cues direct cellular processes revolutionised the study of cell biology in the second half of the 20th century, over the last two decades, new insights into how mechanical cues similarly impact cell fate decisions has gained momentum. During development, extrinsic cues such as fluid flow, shear stress and compressive forces are essential for normal embryogenesis to proceed. Indeed, both adult and embryonic stem cells can respond to applied forces, but they can also detect intrinsic mechanical cues from their surrounding environment, such as the stiffness of the extracellular matrix, which impacts differentiation and morphogenesis. Cells can detect changes in their mechanical environment using cell surface receptors such as integrins and focal adhesions. Moreover, dynamic rearrangements of the cytoskeleton have been identified as a key means by which forces are transmitted from the extracellular matrix to the cell and vice versa. Although we have some understanding of the downstream mechanisms whereby mechanical cues are translated into changes in cell behaviour, many of the signalling pathways remain to be defined. This review discusses the importance of intrinsic mechanical cues on adult cell fate decisions, the emerging roles of cell surface mechano-sensors and the cytoskeleton in enabling cells to sense its microenvironment, and the role of intracellular signalling in translating mechanical cues into transcriptional outputs. In addition, the contribution of mechanical cues to fundamental processes during embryogenesis such as apical constriction and convergent extension is discussed. The continued development of tools to measure the biomechanical properties of soft tissues in vivo is likely to uncover currently underestimated contributions of these cues to adult stem cell fate decisions and embryogenesis, and may inform on regenerative strategies for tissue repair.

Endothelial Cell Migration Regulated by Surface Topography of Poly(ε-caprolactone) Nanofibers

The study of cell migration on biomaterials is of great significance in tissue engineering and regenerative medicine. In recent years, there has been increasing evidence that the physical properties of the extracellular matrix (ECM), such as surface topography, affect various cellular behaviors such as proliferation, adhesion, and migration. However, the biological mechanism of surface topography influencing cellular behavior is still unclear. In this study, we prepared polycaprolactone (PCL) fibrous materials with different surface microstructures by solvent casting, electrospinning, and self-induced crystallization. The corresponding topographical structure obtained is a two-dimensional (2D) flat surface, 2.5-dimensional (2.5D) fibers, and three-dimensional (3D) fibers with a multilevel microstructure. We then investigated the effects of the complex topographical structure on endothelial cell migration. Our study demonstrates that cells can sense the changes of micro- and nanomorphology on the surface of materials, adapt to the physical environment through biochemical reactions, and regulate actin polymerization and directional migration through Rac1 and Cdc42. The cells on the nanofibers are elongated spindles, and the positive feedback of cell adhesion and actin polymerization along the fiber direction makes the plasma membrane continue to protrude, promoting cell polarization and directional migration. This study might provide new insights into the biomaterial design, especially those used for artificial vascular grafts.

Guiding cell adhesion and motility by modulating cross-linking and topographic properties of microgel arrays

Biomaterial-driven modulation of cell adhesion and migration is a challenging aspect of tissue engineering. Here, we investigated the impact of surface-bound microgel arrays with variable geometry and adjustable cross-linking properties on cell adhesion and migration. We show that cell migration is inversely correlated with microgel array spacing, whereas directionality increases as array spacing increases. Focal adhesion dynamics is also modulated by microgel topography resulting in less dynamic focal adhesions on surface-bound microgels. Microgels also modulate the motility and adhesion of Sertoli cells used as a model for cell migration and adhesion. Both focal adhesion dynamics and speed are reduced on microgels. Interestingly, Gas2L1, a component of the cytoskeleton that mediates the interaction between microtubules and microfilaments, is dispensable for the regulation of cell adhesion and migration on microgels. Finally, increasing microgel cross-linking causes a clear reduction of focal adhesion turnover in Sertoli cells. These findings not only show that spacing and rigidity of surface-grafted microgels arrays can be effectively used to modulate cell adhesion and motility of diverse cellular systems, but they also form the basis for future developments in the fields of medicine and tissue engineering.

A blueprint of the topology and mechanics of the human ovary for next-generation bioengineering and diagnosis

Although the first dissection of the human ovary dates back to the 17^th century, the biophysical characteristics of the ovarian cell microenvironment are still poorly understood. However, this information is vital to deciphering cellular processes such as proliferation, morphology and differentiation, as well as pathologies like tumor progression, as demonstrated in other biological tissues. Here, we provide the first readout of human ovarian fiber morphology, interstitial and perifollicular fiber orientation, pore geometry, topography and surface roughness, and elastic and viscoelastic properties. By determining differences between healthy prepubertal, reproductive-age, and menopausal ovarian tissue, we unravel and elucidate a unique biophysical phenotype of reproductive-age tissue, bridging biophysics and female fertility. While these data enable to design of more biomimetic scaffolds for the tissue-engineered ovary, our analysis pipeline is applicable for the characterization of other organs in physiological or pathological states to reveal their biophysical markers or design their bioinspired analogs.

Although the first dissection of the human ovary dates back to the 17th century, its characterization is still limited. Here, the authors have unraveled a unique biophysical and topological phenotype of reproductive-age tissue, bridging biophysics and female fertility and providing a blueprint for the artificial ovary.

Engineering hydrogels for personalized disease modeling and regenerative medicine

Technological innovations and advances in scientific understanding have created an environment where data can be collected, analyzed, and interpreted at scale, ushering in the era of personalized medicine. The ability to isolate cells from individual patients offers tremendous promise if those cells can be used to generate functional tissue replacements or used in disease modeling to determine optimal treatment strategies. Here, we review recent progress in the use of hydrogels to create artificial cellular microenvironments for personalized tissue engineering and regenerative medicine applications, as well as to develop personalized disease models. We highlight engineering strategies to control stem cell fate through hydrogel design, and the use of hydrogels in combination with organoids, advanced imaging methods, and novel bioprinting techniques to generate functional tissues. We also discuss the use of hydrogels to study molecular mechanisms underlying diseases and to create personalized in vitro disease models to complement existing pre-clinical models. Continued progress in the development of engineered hydrogels, in combination with other emerging technologies, will be essential to realize the immense potential of personalized medicine. STATEMENT OF SIGNIFICANCE: In this review, we cover recent advances in hydrogel engineering strategies with applications in personalized medicine. Specifically, we focus on material systems to expand or control differentiation of patient-derived stem cells, and hydrogels to reprogram somatic cells to pluripotent states. We then review applications of hydrogels in developing personalized engineered tissues. We also highlight the use of hydrogel systems as personalized disease models, focusing on specific examples in fibrosis and cancer, and more broadly on drug screening strategies using patient-derived cells and hydrogels. We believe this review will be a valuable contribution to the Special Issue and the readership of Acta Biomaterialia will appreciate the comprehensive overview of the utility of hydrogels in the developing field of personalized medicine.

Bioengineering platforms for cell therapeutics derived from pluripotent and direct reprogramming

Pluripotent and direct reprogramming technologies hold great potential for tissue repair and restoration of tissue and organ function. The implementation of induced pluripotent stem cells and directly reprogrammed cells in biomedical research has resulted in a significant leap forward in the highly promising area of regenerative medicine. While these therapeutic strategies are promising, there are several obstacles to overcome prior to the introduction of these therapies into clinical settings. Bioengineering technologies, such as biomaterials, bioprinting, microfluidic devices, and biostimulatory systems, can enhance cell viability, differentiation, and function, in turn the efficacy of cell therapeutics generated via pluripotent and direct reprogramming. Therefore, cellular reprogramming technologies, in combination with tissue-engineering platforms, are poised to overcome current bottlenecks associated with cell-based therapies and create new ways of producing engineered tissue substitutes.

2D biointerfaces to study stem cell-ligand interactions

Stem cells have great potential in the field of tissue engineering and regenerative medicine due to their inherent regenerative capabilities. However, an ongoing challenge within their clinical translation is to elicit or predict the desired stem cell behavior once transplanted. Stem cell behavior and function are regulated by their interaction with biophysical and biochemical signals present in their natural environment (i.e., stem cell niches). To increase our understanding about the interplay between stem cells and their resident microenvironments, biointerfaces have been developed as tools to study how these substrates can affect stem cell behaviors. This article aims to review recent developments on fabricating cell-instructive interfaces to control cell adhesion processes towards directing stem cell behavior. After an introduction on stem cells and their natural environment, static surfaces exhibiting predefined biochemical signals to probe the effect of chemical features on stem cell behaviors are discussed. In the third section, we discuss more complex dynamic platforms able to display biochemical cues with spatiotemporal control using on-off ligand display, reversible ligand display, and ligand mobility. In the last part of the review, we provide the reader with an outlook on future designs of biointerfaces. STATEMENT OF SIGNIFICANCE: Stem cells have great potential as treatments for many degenerative disorders prevalent in our aging societies. However, an ongoing challenge within their clinical translation is to promote stem cell mediated regeneration once they are transplanted in the body. Stem cells reside within our bodies where their behavior and function are regulated by interactions with their natural environment called the stem cell niche. To increase our understanding about the interplay between stem cells and their niche, 2D materials have been developed as tools to study how specific signals can affect stem cell behaviors. This article aims to review recent developments on fabricating cell-instructive interfaces to control cell adhesion processes towards directing stem cell behavior.

Nano-Second Laser Interference Photoembossed Microstructures for Enhanced Cell Alignment

Photoembossing is a powerful photolithographic technique to prepare surface relief structures relying on polymerization-induced diffusion in a solventless development step. Conveniently, surface patterns are formed by two or more interfering laser beams without the need for a lithographic mask. The use of nanosecond pulsed light-based interference lithography strengthens the pattern resolution through the absence of vibrational line pattern distortions. Typically, a conventional photoembossing protocol consists of an exposure step at room temperature that is followed by a thermal development step at high temperature. In this work, we explore the possibility to perform the pulsed holographic exposure directly at the development temperature. The surface relief structures generated using this modified photoembossing protocol are compared with those generated using the conventional one. Importantly, the enhancement of surface relief height has been observed by exposing the samples directly at the development temperature, reaching approximately double relief heights when compared to samples obtained using the conventional protocol. Advantageously, the light dose needed to reach the optimum height and the amount of photoinitiator can be substantially reduced in this modified protocol, demonstrating it to be a more efficient process for surface relief generation in photopolymers. Kidney epithelial cell alignment studies on substrates with relief-height optimized structures generated using the two described protocols demonstrate improved cell alignment in samples generated with exposure directly at the development temperature, highlighting the relevance of the height enhancement reached by this method. Although cell alignment is well-known to be enhanced by increasing the relief height of the polymeric grating, our work demonstrates nano-second laser interference photoembossing as a powerful tool to easily prepare polymeric gratings with tunable topography in the range of interest for fundamental cell alignment studies.

Tunable, conductive, self-healing, adhesive and injectable hydrogels for bioelectronics and tissue regeneration applications

Conductive hydrogels are attracting considerable interest in view of their potential in a wide range of applications that include healthcare and electronics. Such hydrogels are generally incorporated with conductive materials/polymers. Herein, we present a series of conductive hydrogels (Ch-CMC-PDA), prepared with no additional conductive material. The hydrogels were synthesized using a combination of chitosan, cellulose (CMC) and dopamine (DA). The conductivity (0.01-3.4 × 10^-3 S cm^-1) in these gels is attributed to ionic conductivity. Very few conductive hydrogels are endowed with additional properties like injectability, adhesiveness and self-healing, which would help to widen their scope for applications. While the dynamic Schiff base coupling in our hydrogels facilitated self-healing and injectable properties, polydopamine imparted tissue adhesiveness. The porosity, rheological, mechanical and conductive properties of the hydrogels are regulated by the CMC-dialdehyde-polydopamine (CMC-D-PDA) content. The hydrogel was evaluated in various bioelectronics applications like ECG monitoring and triboelectric nanogenerators (TENG). The ability of the hydrogel to support cell growth and serve as a template for tissue regeneration was confirmed using in vitro and in vivo studies. In summary, the integration of such remarkable features in the ionic-conductive hydrogel would enable its usage in bioelectronics and biomedical applications.

Expanding Biomaterial Surface Topographical Design Space through Natural Surface Reproduction

Surface topography is a tool to endow biomaterials with bioactive properties. However, the large number of possible designs makes it challenging to find the optimal surface structure to induce a specific cell response. The TopoChip platform is currently the largest collection of topographies with 2176 in silico designed microtopographies. Still, it is exploring only a small part of the design space due to design algorithm limitations and the surface engineering strategy. Inspired by the diversity of natural surfaces, it is assessed as to what extent the topographical design space and consequently the resulting cellular responses can be expanded using natural surfaces. To this end, 26 plant and insect surfaces are replicated in polystyrene and their surface properties are quantified using white light interferometry. Through machine-learning algorithms, it is demonstrated that natural surfaces extend the design space of the TopoChip, which coincides with distinct morphological and focal adhesion profiles in mesenchymal stem cells (MSCs) and Pseudomonas aeruginosa colonization. Furthermore, differentiation experiments reveal the strong potential of the holy lotus to improve osteogenesis in MSCs. In the future, the design algorithms will be trained with the results obtained by natural surface imprint experiments to explore the bioactive properties of novel surface topographies.

High-Throughput Routes to Biomaterials Discovery

Many existing clinical treatments are limited in their ability to completely restore decreased or lost tissue and organ function, an unenviable situation only further exacerbated by a globally aging population. As a result, the demand for new medical interventions has increased substantially over the past 20 years, with the burgeoning fields of gene therapy, tissue engineering, and regenerative medicine showing promise to offer solutions for full repair or replacement of damaged or aging tissues. Success in these fields, however, inherently relies on biomaterials that are engendered with the ability to provide the necessary biological cues mimicking native extracellular matrixes that support cell fate. Accelerating the development of such "directive" biomaterials requires a shift in current design practices toward those that enable rapid synthesis and characterization of polymeric materials and the coupling of these processes with techniques that enable similarly rapid quantification and optimization of the interactions between these new material systems and target cells and tissues. This manuscript reviews recent advances in combinatorial and high-throughput (HT) technologies applied to polymeric biomaterial synthesis, fabrication, and chemical, physical, and biological screening with targeted end-point applications in the fields of gene therapy, tissue engineering, and regenerative medicine. Limitations of, and future opportunities for, the further application of these research tools and methodologies are also discussed.

Modulating the foreign body response of implants for diabetes treatment

Diabetes Mellitus is a group of diseases characterized by high blood glucose levels due to patients' inability to produce sufficient insulin. Current interventions often require implants that can detect and correct high blood glucose levels with minimal patient intervention. However, these implantable technologies have not reached their full potential in vivo due to the foreign body response and subsequent development of fibrosis. Therefore, for long-term function of implants, modulating the initial immune response is crucial in preventing the activation and progression of the immune cascade. This review discusses the different molecular mechanisms and cellular interactions involved in the activation and progression of foreign body response (FBR) and fibrosis, specifically for implants used in diabetes. We also highlight the various strategies and techniques that have been used for immunomodulation and prevention of fibrosis. We investigate how these general strategies have been applied to implants used for the treatment of diabetes, offering insights on how these devices can be further modified to circumvent FBR and fibrosis.

Compounded topographical and physicochemical cueing by micro-engineered chitosan substrates on rat dorsal root ganglion neurons and human mesenchymal stem cells

Given the intertwined physicochemical effects exerted in vivo by both natural and synthetic (e.g., biomaterial) interfaces on adhering cells, the evaluation of structure-function relationships governing cellular response to micro-engineered surfaces for applications in neuronal tissue engineering requires the use of in vitro testing platforms which consist of a clinically translatable material with tunable physiochemical properties. In this work, we micro-engineered chitosan substrates with arrays of parallel channels with variable width (20 and 60 μm). A citric acid (CA)-based crosslinking approach was used to provide an additional level of synergistic cueing on adhering cells by regulating the chitosan substrate's stiffness. Morphological and physicochemical characterization was conducted to unveil the structure-function relationships which govern the activity of rat dorsal root ganglion neurons (DRGs) and human mesenchymal stem cells (hMSCs), ultimately singling out the key role of microtopography, roughness and substrate's stiffness. While substrate's stiffness predominantly affected hMSC spreading, the modulation of the channels' design affected the neuronal architecture's complexity and guided the morphological transition of hMSCs. Finally, the combined analysis of tubulin expression and cell morphology allowed us to cast new light on the predominant role of the microtopography over substrate's stiffness in the process of hMSCs neurogenic differentiation.

Combinatorial effect of plasma treatment, fiber alignment and fiber scale of poly (ε-caprolactone)/collagen multiscale fibers in inducing tenogenesis in non-tenogenic media

Tendon being a hypocellular, low vascularized tissue often requires assistance for restoration after complete tear. Tendon tissue engineering aims in the development of suitable scaffold that could support the regeneration of tendon after damage. The success of such scaffolds is dependent on its integration with the native tissue which in turn is influenced by the cell-material interaction. In this work aligned poly(ε-caprolactone)/collagen (PCL/collagen) multiscale fibers were developed and plasma treatment using argon, nitrogen and its combination was accessed for inducing tenogenic differentiation in mesenchymal stem cells. The developed fibers mimicked tendon extracellular matrix (ECM) which upon plasma treatment maintained moderate hydrophilicity. Oxygen and nitrogen containing groups were observed to be incorporated after argon and nitrogen treatment respectively. Statistically significant (p < 0.001) enhancement was observed in average and root mean square (RMS) roughness after plasma treatment with the maximum in argon treated fibers. Vitronectin was competitively (statistically significant, p < 0.05) adsorbed after argon and combination treatment whereas nitrogen treatment led to the competitive adsorption of fibronectin (statistically significant, p < 0.05). Human mesenchymal stem cells (hMSCs) showed enhanced proliferation and attachment on plasma treated fibers. Increased porosity due to the presence of sacrificial collagen nanofibers improved cell infiltration which was further enhanced upon plasma treatment. RhoA activation was observed (statistically significant, p < 0.05) on aligned PCL/collagen multiscale fibers and PCL microfibers, which proved its impact on tenogenic differentiation. Further enhancement in rhoA expression was observed on argon (p < 0.01) and combination plasma (p < 0.05) treated fibers. Tenogenic differentiation of hMSCs was enhanced (statistically significant) on argon plasma treated aligned fibers which was confirmed by the expression of scleraxis, mohawk (early markers) and tenomodulin (late marker) at protein level and mohawk, collagen I, collagen III (early markers), thrombospondin 4 and tenascin C (late markers) at gene level. Thus argon plasma treatment on aligned fibers is an effective method to induce tenogenesis even in non-tenogenic media.

High-Throughput Methods in the Discovery and Study of Biomaterials and Materiobiology

The complex interaction of cells with biomaterials (i.e., materiobiology) plays an increasingly pivotal role in the development of novel implants, biomedical devices, and tissue engineering scaffolds to treat diseases, aid in the restoration of bodily functions, construct healthy tissues, or regenerate diseased ones. However, the conventional approaches are incapable of screening the huge amount of potential material parameter combinations to identify the optimal cell responses and involve a combination of serendipity and many series of trial-and-error experiments. For advanced tissue engineering and regenerative medicine, highly efficient and complex bioanalysis platforms are expected to explore the complex interaction of cells with biomaterials using combinatorial approaches that offer desired complex microenvironments during healing, development, and homeostasis. In this review, we first introduce materiobiology and its high-throughput screening (HTS). Then we present an in-depth of the recent progress of 2D/3D HTS platforms (i.e., gradient and microarray) in the principle, preparation, screening for materiobiology, and combination with other advanced technologies. The Compendium for Biomaterial Transcriptomics and high content imaging, computational simulations, and their translation toward commercial and clinical uses are highlighted. In the final section, current challenges and future perspectives are discussed. High-throughput experimentation within the field of materiobiology enables the elucidation of the relationships between biomaterial properties and biological behavior and thereby serves as a potential tool for accelerating the development of high-performance biomaterials.

Conductive chitosan/polyaniline hydrogel with cell-imprinted topography as a potential substrate for neural priming of adipose derived stem cells

Biophysical characteristics of engineered scaffolds such as topography and electroconductivity have shown potentially beneficial effects on stem cell morphology, proliferation, and differentiation toward neural cells. In this study, we fabricated a conductive hydrogel made from chitosan (CS) and polyaniline (PANI) with induced PC12 cell surface topography using a cell imprinting technique to provide both topographical properties and conductivity in a platform. The engineered hydrogel's potential for neural priming of rat adipose-derived stem cells (rADSCs) was determined in vitro. The biomechanical analysis revealed that the electrical conductivity, stiffness, and hydrophobicity of flat (F) and cell-imprinted (CI) substrates increased with increased PANI content in the CS/PANI scaffold. The conductive substrates exhibited a lower degradation rate compared to non-conductive substrates. According to data obtained from F-actin staining and AFM micrographs, both CI(CS) and CI(CS-PANI) substrates induced the morphology of rADSCs from their irregular shape (on flat substrates) into the elongated and bipolar shape of the neuronal-like PC12 cells. Immunostaining analysis revealed that both CI(CS) and CI (CS-PANI) significantly upregulated the expression of GFAP and MAP2, two neural precursor-specific genes, in rADSCs compared with flat substrates. Although the results reveal that both cell-imprinted topography and electrical conductivity affect the neural lineage differentiation, some data demonstrate that the topography effects of the cell-imprinted surface have a more critical role than electrical conductivity on neural priming of ADSCs. The current study provides new insight into the engineering of scaffolds for nerve tissue engineering.

MiR-181d-5p regulates implant surface roughness-induced osteogenic differentiation of bone marrow stem cells

Constructing moderate surface roughness is a widely used, non-toxic, cost-effective, and outcome-predictable approach to accelerate implant osteointegration in clinical settings. MicroRNAs (miRNAs) play vital regulatory roles in the osteogenic differentiation of bone marrow stem cells (BMSCs). However, their specific contribution to the influence of surface roughness on osteoblastic behavior remains unknown. Therefore, applying the smooth titanium surface as a control, a typical titanium surface with moderate roughness was prepared here to reveal the mechanism through which surface roughness regulates cell osteogenic behavior by altering miRNA expression. First, the morphology and roughness of two surfaces were characterized, and the enhanced osteogenic differentiation of BMSCs on rough surfaces was verified. Then, twenty-nine differentially expressed miRNAs in BMSCs cultured on different surfaces were selected via miRNA chip and corresponding functional prediction. After verifying the expression of these miRNAs using quantitative real-time polymerase chain reaction, four were considered eligible candidates. Among these, only miR-181d-5p significantly affected RUNX2 gene expression based on overexpression and knockdown experiments. From the osteogenesis-related gene and protein expression, as well as alkaline phosphatase and alizarin red experiments, we further confirmed that the downregulation of miR-181d-5p promoted osteogenic differentiation of BMSCs, and vice versa. In addition, rescue assays showed that the knockdown of miR-181d-5p improved the inferior osteogenesis observed on smooth surfaces, whereas the overexpression of miR-181d-5p suppressed the superior osteogenesis observed on rough surfaces. These results indicate that the moderate surface roughness of the implant stimulates the osteogenic differentiation of BMSCs by remarkably downregulating miR-181d-5p. These findings provide helpful information and a theoretical basis for the development of advanced implant materials for fast osteointegration.

The Effect of Physical Cues of Biomaterial Scaffolds on Stem Cell Behavior

Stem cells have been sought as a promising cell source in the tissue engineering field due to their proliferative capacity as well as differentiation potential. Biomaterials have been utilized to facilitate the delivery of stem cells in order to improve their engraftment and long-term viability upon implantation. Biomaterials also have been developed as scaffolds to promote stem cell induced tissue regeneration. This review focuses on the latter where the biomaterial scaffold is designed to provide physical cues to stem cells in order to promote their behavior for tissue formation. Recent work that explores the effect of scaffold physical properties, topography, mechanical properties and electrical properties, is discussed. Although still being elucidated, the biological mechanisms, including cell shape, focal adhesion distribution, and nuclear shape, are presented. This review also discusses emerging areas and challenges in clinical translation.

On/off switchable physical stimuli regulate the future direction of adherent cellular fate

The utilization of cell-manipulating techniques reveals information about biological behaviors suited to address a wide range of questions in the field of life sciences. Here, we introduced an on/off switchable physical stimuli technique that offers precise stimuli for reversible cell patterning to allow regulation of the future direction of adherent cellular behavior by leveraging enzymatically degradable alginate hydrogels with defined chemistry and topography. As a proof of concept, targeted muscle cells adherent to TCP exhibited a reshaped structure when the hydrogel-based physical stimuli were applied. This simple tool offers easy manipulation of adherent cells to reshape their morphology and to influence future direction depending on the characteristics of the hydrogel without limitations of time and space. The findings from this study are broadly applicable to investigations into the relationships between cells and physiological extracellular matrix environments as well as has potential to open new horizons for regenerative medicine with manipulated cells.

The Research Advance of Cell Bridges in vitro

The microenvironment in which cells reside in vivo dictates their biological and mechanical functioning is associated with morphogenetic and regenerative processes and may find implications in regenerative medicine and tissue engineering. The development of nano- and micro-fabricated technologies, three-dimensional (3D) printing technique, and biomimetic medical materials have enabled researchers to prepare novel advanced substrates mimicking the in vivo microenvironment. Most of the novel morphologies and behaviors of cells, including contact guidance and cell bridges which are observed in vivo but are not perceived in the traditional two-dimensional (2D) culture system, emerged on those novel substrates. Using cell bridges, cell can span over the surface of substrates to maintain mechanical stability and integrity of tissue, as observed in physiological processes, such as wound healing, regeneration and development. Compared to contact guidance, which has received increased attention and is investigated extensively, studies on cell bridges remain scarce. Therefore, in this mini-review, we have comprehensively summarized and classified different kinds of cell bridges formed on various substrates and highlighted possible biophysical mechanisms underlying cell bridge formation for their possible implication in the fields of tissue engineering and regenerative medicine.

Artificial Intelligence Aided Design of Microtextured Surfaces: Application to Controlling Wettability

Artificial intelligence (AI) has emerged as a powerful set of tools for engineering innovative materials. However, the AI-aided design of materials textures has not yet been researched in depth. In order to explore the potentials of AI for discovering innovative biointerfaces and engineering materials surfaces, especially for biomedical applications, this study focuses on the control of wettability through design-controlled hierarchical surfaces, whose design is supported and its performance predicted thanks to adequately structured and trained artificial neural networks (ANN). The authors explain the creation of a comprehensive library of microtextured surfaces with well-known wettability properties. Such a library is processed and employed for the generation and training of artificial neural networks, which can predict the actual wetting performance of new design biointerfaces. The present research demonstrates that AI can importantly support the engineering of innovative hierarchical or multiscale surfaces when complex-to-model properties and phenomena, such as wettability and wetting, are involved.