Biomimetic substrate control of cellular mechanotransduction

Cyclic stretch induced epigenetic activation of periodontal ligament cells

Periodontal ligament (PDL) cells play a crucial role in maintaining periodontal integrity and function by providing cell sources for ligament regeneration. While biophysical stimulation is known to regulate cell behaviors and functions, its impact on epigenetics of PDL cells has not yet been elucidated. Here, we aimed to investigate the cytoskeletal changes, epigenetic modifications, and lineage commitment of PDL cells following the application of stretch stimuli to PDL. PDL cells were subjected to stretching (0.1 Hz, 10 %). Subsequently, changes in focal adhesion, tubulin, and histone modification were observed. The survival ability in inflammatory conditions was also evaluated. Furthermore, using a rat hypo-occlusion model, we verified whether these phenomena are observed in vivo. Stretched PDL cells showed maximal histone 3 acetylation (H3Ace) at 2 h, aligning perpendicularly to the stretch direction. RNA sequencing revealed stretching altered gene sets related to mechanotransduction, histone modification, reactive oxygen species (ROS) metabolism, and differentiation. We further found that anchorage, cell elongation, and actin/microtubule acetylation were highly upregulated with mechanosensitive chromatin remodelers such as H3Ace and histone H3 trimethyl lysine 9 (H3K9me3) adopting euchromatin status. Inhibitor studies showed mechanotransduction-mediated chromatin modification alters PDL cells behaviors. Stretched PDL cells displayed enhanced survival against bacterial toxin (C12-HSL) or ROS (H2O2) attack. Furthermore, cyclic stretch priming enhanced the osteoclast and osteoblast differentiation potential of PDL cells, as evidenced by upregulation of lineage-specific genes. In vivo, PDL cells from normally loaded teeth displayed an elongated morphology and higher levels of H3Ace compared to PDL cells with hypo-occlusion, where mechanical stimulus is removed. Overall, these data strongly link external physical forces to subsequent mechanotransduction and epigenetic changes, impacting gene expression and multiple cellular behaviors, providing important implications in cell biology and tissue regeneration.

Stretching of porous poly (l-lactide-co-ε-caprolactone) membranes regulates the differentiation of mesenchymal stem cells

Background: Among a variety of biomaterials supporting cell growth for therapeutic applications, poly (l-lactide-co-ε-caprolactone) (PLCL) has been considered as one of the most attractive scaffolds for tissue engineering owing to its superior mechanical strength, biocompatibility, and processibility. Although extensive studies have been conducted on the relationship between the microstructure of polymeric materials and their mechanical properties, the use of the fine-tuned morphology and mechanical strength of PLCL membranes in stem cell differentiation has not yet been studied. Methods: PLCL membranes were crystallized in a combination of diverse solvent-nonsolvent mixtures, including methanol (MeOH), isopropanol (IPA), chloroform (CF), and distilled water (DW), with different solvent polarities. A PLCL membrane with high mechanical strength induced by limited pore formation was placed in a custom bioreactor mimicking the reproducible physiological microenvironment of the vascular system to promote the differentiation of mesenchymal stem cells (MSCs) into smooth muscle cells (SMCs). Results: We developed a simple, cost-effective method for fabricating porosity-controlled PLCL membranes based on the crystallization of copolymer chains in a combination of solvents and non-solvents. We confirmed that an increase in the ratio of the non-solvent increased the chain aggregation of PLCL by slow evaporation, leading to improved mechanical properties of the PLCL membrane. Furthermore, we demonstrated that the cyclic stretching of PLCL membranes induced MSC differentiation into SMCs within 10 days of culture. Conclusion: The combination of solvent and non-solvent casting for PLCL solidification can be used to fabricate mechanically durable polymer membranes for use as mechanosensitive scaffolds for stem cell differentiation.

Molecular Mobility of Polyrotaxane Surfaces Alleviates Oxidative Stress-Induced Senescence in Mesenchymal Stem Cells

Polyrotaxane is a supramolecular assembly consisting of multiple cyclic molecules threaded by a linear polymer. One of the unique properties of polyrotaxane is molecular mobility, cyclic molecules moving along the linear polymer. Molecular mobility of polyrotaxane surfaces affects cell spreading, differentiation, and other cell-related aspects through changing subcellular localization of yes-associated proteins (YAPs). Subcellular YAP localization is also related to cell senescence derived from oxidative stress, which is known to cause cancer, diabetes, and heart disease. Herein, the effects of polyrotaxane surface molecular mobility on subcellular YAP localization and cell senescence following H2 O2 -induced oxidative stress are evaluated in human mesenchymal stem cells (HMSCs) cultured on polyrotaxane surfaces with different molecular mobilities. Oxidative stress promotes cytoplasmic YAP localization in HMSCs on high-mobility polyrotaxane surfaces; however, low-mobility polyrotaxane surfaces more effectively maintain nuclear YAP localization, exhibiting lower senescence-associated β-galactosidase activity and senescence-related gene expression and DNA damage than that seen with the high-mobility surfaces. These results suggest that the molecular mobility of polyrotaxane surfaces regulates subcellular YAP localization, thereby protecting HMSCs from oxidative stress-induced cell senescence. Applying the molecular mobility of polyrotaxane surfaces to implantable scaffolds can provide insights into the prevention and treatment of diseases caused by oxidative stress.

Modulation of myoblast differentiation by electroactive scaffold morphology and biochemical stimuli

The physico-chemical properties of the scaffold materials used for tissue regeneration strategies have a direct impact on cell shape, adhesion, proliferation, phenotypic and differentiation. Herewith, biophysical and biochemical cues have been widely used to design and develop biomaterial systems for specific tissue engineering strategies. In this context, the patterning of piezoelectric polymers that can provide electroactive stimuli represents a suitable strategy for skeletal muscle tissue engineering applications once it has been demonstrated that mechanoelectrical stimuli promote C2C12 myoblast differentiation. In this sense, this works reports on how C2C12 myoblast cells detect and react to physical and biochemical stimuli based on micropatterned poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) electroactive scaffolds produced by soft lithography in the form of arrays of lines and hexagons (anisotropic and isotropic morphology, respectively) combined with differentiation medium. The scaffolds were evaluated for the proliferation and differentiation of C2C12 myoblast cell line and it is demonstrated that anisotropic microstructures promote muscle differentiation which is further reinforced with the introduction of biochemical stimulus. However, when the physical stimulus is not adequate to the tissue, e.g. isotropic microstructure, the biochemical stimulus has the opposite effect, hindering the differentiation process. Therefore, the proper morphological design of the scaffold combined with biochemical stimulus allows to enhance skeletal muscle differentiation and allows the development of advanced strategies for effective muscle tissue engineering.

PIP4K2B is mechanoresponsive and controls heterochromatin-driven nuclear softening through UHRF1

Phosphatidylinositol-5-phosphate (PtdIns5P)-4-kinases (PIP4Ks) are stress-regulated phosphoinositide kinases able to phosphorylate PtdIns5P to PtdIns(4,5)P2. In cancer patients their expression is typically associated with bad prognosis. Among the three PIP4K isoforms expressed in mammalian cells, PIP4K2B is the one with more prominent nuclear localisation. Here, we unveil the role of PIP4K2B as a mechanoresponsive enzyme. PIP4K2B protein level strongly decreases in cells growing on soft substrates. Its direct silencing or pharmacological inhibition, mimicking cell response to softness, triggers a concomitant reduction of the epigenetic regulator UHRF1 and induces changes in nuclear polarity, nuclear envelope tension and chromatin compaction. This substantial rewiring of the nucleus mechanical state drives YAP cytoplasmic retention and impairment of its activity as transcriptional regulator, finally leading to defects in cell spreading and motility. Since YAP signalling is essential for initiation and growth of human malignancies, our data suggest that potential therapeutic approaches targeting PIP4K2B could be beneficial in the control of the altered mechanical properties of cancer cells.

Control of hydrostatic pressure and osmotic stress in 3D cell culture for mechanobiological studies

Hydrostatic pressure (HP) and osmotic stress (OS) play an important role in various biological processes, such as cell proliferation and differentiation. In contrast to canonical mechanical signals transmitted through the anchoring points of the cells with the extracellular matrix, the physical and molecular mechanisms that transduce HP and OS into cellular functions remain elusive. Three-dimensional cell cultures show great promise to replicate physiologically relevant signals in well-defined host bioreactors with the goal of shedding light on hidden aspects of the mechanobiology of HP and OS. This review starts by introducing prevalent mechanisms for the generation of HP and OS signals in biological tissues that are subject to pathophysiological mechanical loading. We then revisit various mechanisms in the mechanotransduction of HP and OS, and describe the current state of the art in bioreactors and biomaterials for the control of the corresponding physical signals.

[Physiotherapeutic Scar Therapy for Large Scars]

Physiotherapeutic Scar Therapy for Large Scars Abstract. Deep dermal defects can result from burns, necrotizing fasciitis, and severe soft tissue trauma. Physiological scar restriction during wound healing becomes increasingly relevant in proportion to the area affected. It is massively restrictive for the general mobility of patients. External mechanical influences (activity or immobilization in everyday life) can cause pronounced scar strands and adhesions to form. Overloading ends in a renewed inflammatory reaction and thus in further restriction. Adequate mechanical stimuli can positively influence the scar tissue. The current state of research does not allow a direct transfer to the clinical treatment of large-area scars. However, the continuous clinical implementation of study results regarding the mechanosensitivity of isolated fibroblasts and the constant adaptation of manual techniques have resulted in an evidence-based foundation for manual scar therapy. Early manual treatment in combination with appropriate compression therapy is important.

The role of cellular traction forces in deciphering nuclear mechanics

Cellular forces exerted on the extracellular matrix (ECM) during adhesion and migration under physiological and pathological conditions regulate not only the overall cell morphology but also nuclear deformation. Nuclear deformation can alter gene expression, integrity of the nuclear envelope, nucleus-cytoskeletal connection, chromatin architecture, and, in some cases, DNA damage responses. Although nuclear deformation is caused by the transfer of forces from the ECM to the nucleus, the role of intracellular organelles in force transfer remains unclear and a challenging area of study. To elucidate nuclear mechanics, various factors such as appropriate biomaterial properties, processing route, cellular force measurement technique, and micromanipulation of nuclear forces must be understood. In the initial phase of this review, we focused on various engineered biomaterials (natural and synthetic extracellular matrices) and their manufacturing routes along with the properties required to mimic the tumor microenvironment. Furthermore, we discussed the principle of tools used to measure the cellular traction force generated during cell adhesion and migration, followed by recently developed techniques to gauge nuclear mechanics. In the last phase of this review, we outlined the principle of traction force microscopy (TFM), challenges in the remodeling of traction forces, microbead displacement tracking algorithm, data transformation from bead movement, and extension of 2-dimensional TFM to multiscale TFM.

Versatile polyphenolic platforms in regulating cell biology

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

Rac1-GTPase regulates compression-induced actin protrusions (CAPs) of mesenchymal stem cells in 3D collagen micro-tissues

Cells can sense mechanical signals through cytoskeleton reorganization. We previously discovered the formation of omni-directional actin protrusions upon compression loading, namely compression-induced actin protrusions (CAPs), in human mesenchymal stem cells (MSCs) in 3D micro-tissues. Here, the regulatory roles of three RhoGTPases (CDC42, Rac1 and RhoA) in the formation of CAPs were investigated. Upon compression loading, extensive formation of CAPs was found, significantly associated with an upregulated mRNA expression of Rac1 only, but not CDC42, nor RhoA. Upon chemical inhibition of these RhoGTPase activity during compression, only Rac1 activity was significantly suppressed, associating with the reduced CAP formation. Silencing the upstream regulators of these RhoGTPase pathways including Rac1 by specific siRNA dramatically disrupted actin cytoskeleton, distorted cell morphology and aborted CAP formation. Silencing cortactin (CTTN), a downstream effector of the Rac1 pathway, induced a compensatory upregulation of Rac1, enabling the MSCs to respond to the compression loading stimulus in terms of CAP formation, although at a reduced number. The importance of Rac1 signalling in CAP formation and the corresponding upregulation of lamellipodial markers also suggest that these CAPs are lamellipodia in nature. This study delineates the mechanism of compression-induced cytoskeleton reorganization, contributing to rationalizing mechanical loading regimes for functional tissue engineering.

Topographic Guidance in Melt-Electrowritten Tubular Scaffolds Enhances Engineered Kidney Tubule Performance

Introduction: To date, tubular tissue engineering relies on large, non-porous tubular scaffolds (Ø > 2 mm) for mechanical self-support, or smaller (Ø 150-500 μm) tubes within bulk hydrogels for studying renal transport phenomena. To advance the engineering of kidney tubules for future implantation, constructs should be both self-supportive and yet small-sized and highly porous. Here, we hypothesize that the fabrication of small-sized porous tubular scaffolds with a highly organized fibrous microstructure by means of melt-electrowriting (MEW) allows the development of self-supported kidney proximal tubules with enhanced properties. Materials and Methods: A custom-built melt-electrowriting (MEW) device was used to fabricate tubular fibrous scaffolds with small diameter sizes (Ø = 0.5, 1, 3 mm) and well-defined, porous microarchitectures (rhombus, square, and random). Human umbilical vein endothelial cells (HUVEC) and human conditionally immortalized proximal tubular epithelial cells (ciPTEC) were seeded into the tubular scaffolds and tested for monolayer formation, integrity, and organization, as well as for extracellular matrix (ECM) production and renal transport functionality. Results: Tubular fibrous scaffolds were successfully manufactured by fine control of MEW instrument parameters. A minimum inner diameter of 1 mm and pore sizes of 0.2 mm were achieved and used for subsequent cell experiments. While HUVEC were unable to bridge the pores, ciPTEC formed tight monolayers in all scaffold microarchitectures tested. Well-defined rhombus-shaped pores outperformed and facilitated unidirectional cell orientation, increased collagen type IV deposition, and expression of the renal transporters and differentiation markers organic cation transporter 2 (OCT2) and P-glycoprotein (P-gp). Discussion and Conclusion: Here, we present smaller diameter engineered kidney tubules with microgeometry-directed cell functionality. Due to the well-organized tubular fiber scaffold microstructure, the tubes are mechanically self-supported, and the self-produced ECM constitutes the only barrier between the inner and outer compartment, facilitating rapid and active solute transport.

Convergence of 3D printed biomimetic wound dressings and adult stem cell therapy

Biomimetically designed medical-grade polycaprolactone (mPCL) dressings are 3D-printed with pore architecture and anisotropic mechanical characteristics that favor skin wound healing with reduced scarring. Melt electrowritten mPCL dressings are seeded with human gingival tissue multipotent mesenchymal stem/stromal cells and cryopreserved using a clinically approved method. The regenerative potential of fresh or frozen cell-seeded mPCL dressing is compared in a splinted full-thickness excisional wound in a rat model over six weeks. The application of 3D-printed mPCL dressings decreased wound contracture and significantly improved skin regeneration through granulation and re-epithelialization compared to control groups. Combining 3D-printed biomimetic wound dressings and precursor cell delivery enhances physiological wound closure with reduced scar tissue formation.

The Role of Fluid Shear and Metastatic Potential in Breast Cancer Cell Migration

During the migration of cancer cells for metastasis, cancer cells can be exposed to fluid shear conditions. We examined two breast cancer cell lines, MDA-MB-468 (less metastatic) and MDA-MB-231 (more metastatic), and a benign MCF-10A epithelial cell line for their responsiveness in migration to fluid shear. We tested fluid shear at 15 dyne/cm2 that can be encountered during breast cancer cells traveling through blood vessels or metastasizing to mechanically active tissues such as bone. MCF-10A exhibited the least migration with a trend of migrating in the flow direction. Intriguingly, fluid shear played a potent role as a trigger for MDA-MB-231 cell migration, inducing directional migration along the flow with significantly increased displacement length and migration speed and decreased arrest coefficient relative to unflowed MDA-MB-231. In contrast, MDA-MB-468 cells were markedly less migratory than MDA-MB-231 cells, and responded very poorly to fluid shear. As a result, MDA-MB-468 cells did not exhibit noticeable difference in migration between static and flow conditions, as was distinct in root-mean-square (RMS) displacement-an ensemble average of all participating cells. These may suggest that the difference between more metastatic MDA-MB-231 and less metastatic MDA-MB-468 breast cancer cells could be at least partly involved with their differential responsiveness to fluid shear stimulatory cues. Our study provides new data in regard to potential crosstalk between fluid shear and metastatic potential in mediating breast cancer cell migration.

Strategies for Using Polydopamine to Induce Biomineralization of Hydroxyapatite on Implant Materials for Bone Tissue Engineering

In the field of tissue engineering, there are several issues to consider when designing biomaterials for implants, including cellular interaction, good biocompatibility, and biochemical activity. Biomimetic mineralization has gained considerable attention as an emerging approach for the synthesis of biocompatible materials with complex shapes, categorized organization, controlled shape, and size in aqueous environments. Understanding biomineralization strategies could enhance opportunities for novel biomimetic mineralization approaches. In this regard, mussel-inspired biomaterials have recently attracted many researchers due to appealing features, such as strong adhesive properties on moist surfaces, improved cell adhesion, and immobilization of bioactive molecules via catechol chemistry. This molecular designed approach has been a key point in combining new functionalities into accessible biomaterials for biomedical applications. Polydopamine (PDA) has emerged as a promising material for biomaterial functionalization, considering its simple molecular structure, independence of target materials, cell interactions for adhesion, and robust reactivity for resulting functionalization. In this review, we highlight the strategies for using PDA to induce the biomineralization of hydroxyapatite (HA) on the surface of various implant materials with good mechanical strength and corrosion resistance. We also discuss the interactions between the PDA-HA coating, and several cell types that are intricate in many biomedical applications, involving bone defect repair, bone regeneration, cell attachment, and antibacterial activity.

Plant-Based Scaffolds Modify Cellular Response to Drug and Radiation Exposure Compared to Standard Cell Culture Models

Plant-based scaffolds present many advantages over a variety of biomaterials. Recent studies explored their potential to be repopulated with human cells and thus highlight a growing interest for their use in tissue engineering or for biomedical applications. However, it is still unclear if these in vitro plant-based scaffolds can modify cell phenotype or affect cellular response to external stimuli. Here, we report the characterization of the mechano-regulation of melanoma SK-MEL-28 and prostate PC3 cells seeded on decellularized spinach leaves scaffolds, compared to cells deposited on standard rigid cell culture substrate, as well as their response to drug and radiation treatment. The results showed that YAP/TAZ signaling was downregulated, cellular morphology altered and proliferation rate decreased when cells were cultured on leaf scaffold. Interestingly, cell culture on vegetal scaffold also affected cellular response to external stress. Thus, SK-MEL-28 cells phenotype is modified leading to a decrease in MITF activity and drug resistance, while PC3 cells showed altered gene expression and radiation response. These findings shed lights on the decellularization of vegetal materials to provide substrates that can be repopulated with human cells to better reproduce a soft tissue microenvironment. However, these complex scaffolds mediate changes in cell behavior and in order to exploit the capability of matching physical properties of the various plant scaffolds to diverse physiological functionalities of cells and human tissue constructs, additional studies are required to better characterize physical and biochemical cell-substrate interactions.

Mechanosensitive Aspects of Cell Biology in Manual Scar Therapy for Deep Dermal Defects

Deep dermal defects can result from burns, necrotizing fasciitis and severe soft tissue trauma. Physiological scar restriction during wound healing becomes increasingly relevant in proportion to the affected area. This massively restricts the general mobility of patients. External mechanical influences (activity or immobilization in everyday life) can lead to the formation of marked scar strands and adhesions. Overloading results in a renewed inflammatory reaction and thus in further restriction. Appropriate mechanical stimuli can have a positive influence on the scar tissue. “Use determines function,” and even minimal external forces are sufficient to cause functional alignment (mechanotransduction). The first and second remarkable increases in connective tissue resistance (R1 and R2) seem to be relevant clinical indications of adequate dosage in the proliferation and remodulation phase, making it possible to counteract potential overdosage in deep dermal defects. The current state of research does not allow a direct transfer to the clinical treatment of large scars. However, the continuous clinical implementation of study results with regard to the mechanosensitivity of isolated fibroblasts, and the constant adaptation of manual techniques, has nevertheless created an evidence-base for manual scar therapy. The manual dosages are adapted to tissue physiology and to respective wound healing phases. Clinical observations show improved mobility of the affected regions and fewer relapses into the inflammatory phase due to mechanical overload.

Stretching of fibroblast cells on micropatterned gelatin on silicone elastomer

Micropatterned gelatin was formed on the silicone elastomer surface. The micropattern enabled cell alignment, regulation of the cell shape, and endowed the cells with resistance against mechanical stress.

Chitosan films for regenerative medicine: fabrication methods and mechanical characterization of nanostructured chitosan films

Regenerative medicine is continuously facing new challenges and it is searching for new biocompatible, green/natural polymer materials, possibly biodegradable and non-immunogenic. Moreover, the critical importance of the nano/microstructuring of surfaces is overall accepted for their full biocompatibility and in vitro/in vivo performances. Chitosan is emerging as a promising biopolymer for tissue engineering and its application can be further improved by exploiting its nano/microstructuration. Here, we report the state of the art of chitosan films and scaffolds nano/micro-structuration. We show that it is possible to obtain, by solvent casting, chitosan thin films with good mechanical properties and to structure them at the microscale and even nanoscale level, with resolutions down to 100 nm.

Driving Cells with Light-Controlled Topographies

Cell-substrate interactions can modulate cellular behaviors in a variety of biological contexts, including development and disease. Light-responsive materials have been recently proposed to engineer active substrates with programmable topographies directing cell adhesion, migration, and differentiation. However, current approaches are affected by either fabrication complexity, limitations in the extent of mechanical stimuli, lack of full spatio-temporal control, or ease of use. Here, a platform exploiting light to plastically deform micropatterned polymeric substrates is presented. Topographic changes with remarkable relief depths in the micron range are induced in parallel, by illuminating the sample at once, without using raster scanners. In few tens of seconds, complex topographies are instructed on demand, with arbitrary spatial distributions over a wide range of spatial and temporal scales. Proof-of-concept data on breast cancer cells and normal kidney epithelial cells are presented. Both cell types adhere and proliferate on substrates without appreciable cell damage upon light-induced substrate deformations. User-provided mechanical stimulation aligns and guides cancer cells along the local deformation direction and constrains epithelial colony growth by biasing cell division orientation. This approach is easy to implement on general-purpose optical microscopy systems and suitable for use in cell biology in a wide variety of applications.

Low intensity pulsed ultrasound (LIPUS) maintains osteogenic potency by the increased expression and stability of Nanog through spleen tyrosine kinase (Syk) activation

Mesenchymal stem cells (MSCs) are a powerful tool for cell-based, clinical therapies like bone regeneration. Therapeutic use of cell transplantation requires many cells, however, the expansion process needed to produce large quantities of cells reduces the differentiation potential of MSCs. Here, we examined the protective effects of low intensity pulsed ultrasound (LIPUS) on the maintenance of osteogenic potency. Primary osteoblastic cells were serially passaged between 2 and 12 times with daily LIPUS treatment. We found that LIPUS stimulation maintains osteogenic differentiation capacity in serially passaged cells, as characterized by improved matrix mineralization and Osteocalcin mRNA expression. Decreased expression of Nanog, Sox2, and Msx2, and increased expression of Pparg2 from serial passaging was recovered in LIPUS-stimulated cells. We found that LIPUS stimulation not only increased but also sustained expression of Nanog in primary osteoblasts and ST2 cells, a mouse mesenchymal stromal cell line. Nanog overexpression in serially passaged cells mimicked the recuperative effects of LIPUS on osteogenic potency, highlighting the important role of Nanog in LIPUS stimulation. Additionally, we found that spleen tyrosine kinase (Syk) is an important signaling molecule to induce Nanog expression in LIPUS-stimulated cells. Syk activation was regulated by both Rho-associated kinase 1 (ROCK1) and extracellular ATP in a paracrine manner. Interestingly, the LIPUS-induced increase in Nanog mRNA expression was regulated by ATP-P2X4-Syk Y323 activation, while the improvement of Nanog protein stability was controlled by the ROCK1-Syk Y525/526 pathway. Taken together, these results indicate that LIPUS stimulation recovers and maintains the osteogenic potency of serially passaged cells through a Syk-Nanog axis.

Peptide nanostructures on nanofibers for peripheral nerve regeneration

Self-assembled peptide nanofibrous scaffolds with designer sequences, similar to neurite growth promoting molecules enhance the differentiation of neural stem cells. However, self-assembled peptide nanofibrous scaffolds lack the required mechanical strength to suffice to bridge long critical-sized peripheral nerve defects. Hence, there is a demand for a potential neural substrate, which could be biomimetic coupled with bioactive nanostructures to regrow the denuded axons towards the distal end. In the present study, we developed designer self-assembling peptide-based aligned poly(lactic-co-glycolic acid) (PLGA) nanofibrous scaffolds by simple surface coating of peptides or coelectrospinning. Retention of secondary structures of peptides in peptide-coated and cospun fibers was confirmed by circular dichroism spectroscopy. The rod-like peptide nanostructures enhance the typical bipolar morphology of Schwann cells. Although the peptide-coated PLGA scaffolds exhibited significant increase in Schwann cell proliferation than pristine PLGA and PLGA-peptide cospun scaffolds (p < .05), peptide cospun scaffolds demonstrated better cellular infiltration and significantly higher gene expression of neural cell adhesion molecule, glial fibrillary acidic protein, and peripheral myelin protein22 compared to the pristine PLGA and PLGA-peptide-coated scaffolds. Our results demonstrate the positive effects of aligned peptide coelectrospun scaffolds with biomimetic cell recognition motifs towards functional proliferation of Schwann cells. These scaffolds could subsequently repair peripheral nerve defects by augmenting axonal regeneration and functional nerve recovery.

Emerging Development of Microfluidics-Based Approaches to Improve Studies of Muscle Cell Migration

IMPACT STATEMENT

The essential interactions between and among cells in the three types of muscle tissue in development, wound healing, and regeneration of tissues, are underpinned by the ability of cardiac, smooth, and skeletal muscle cells to migrate in maintaining functional capacity after pathologies such as myocardial infarction, tissue grafting, and traumatic and postsurgical injury. Microfluidics-based devices now offer significant enhancement over conventional approaches to studying cell chemotaxis and haptotaxis that are inherent in migration. Advances in experimental approaches to muscle cell movement and tissue formation will contribute to innovations in tissue engineering for patching wound repair and muscle tissue replacement.

Genetically Engineered Phage Induced Selective H9c2 Cardiomyocytes Patterning in PDMS Microgrooves

A micro-patterned cell adhesive surface was prepared for future design of medical devices. One-dimensional polydimethylsiloxane (PDMS) micro-patterns were prepared by a photolithography process. Afterwards, recombinant filamentous phages that displayed a short binding motif with a cell adhesive peptide (-RGD-) on p8 proteins were immobilized on PDMS microgrooves through simple contact printing to study the cellular response of rat H9c2 cardiomyocyte. While the cell density decreased on PDMS micro-patterns, we observed enhanced cell proliferation and cell to surface interaction on the RGD-phage coated PDMS microgrooves. The RGD-phage coating also supported a better alignment of cell spreading rather than isotropic cell growths as we observed on non-pattered PDMS surface.

Study of myoblast differentiation using multi-dimensional scaffolds consisting of nano and micropatterns

BACKGROUND

The topographical cue is major influence on skeletal muscle cell culture because the structure is highly organized and consists of long parallel bundles of multinucleated myotubes that are formed by differentiation and fusion of myoblast satellite cells. In this technical report, we fabricated a multiscale scaffold using electrospinning and poly (ethylene glycol) (PEG) hydrogel micropatterns to monitor the cell behaviors on nano- and micro-alignment combined scaffolds with different combinations of angles.

RESULTS

We fabricated multiscale scaffolds that provide biocompatible and extracellular matrix (ECM)-mimetic environments via electrospun nanofiber and PEG hydrogel micro patterning. MTT assays demonstrated an almost four-fold increase in the proliferation rate during the 7 days of cell culture for all of the experimental groups. Cell orientation and elongation were measured to confirm the myogenic potential. On the aligned fibrous scaffolds, more than 90% of the cells were dispersed ± 20° of the fiber orientation. To determine cell elongation, we monitored nuclei aspect ratios. On a random nanofiber, the cells demonstrated an aspect ratio of 1.33, but on perpendicular and parallel nanofibers, the aspect ratio was greater than 2. Myosin heavy chain (MHC) expression was significantly higher i) on parallel compared to random fibers, ii) the 100 μm compared to the 200 μm line pattern. We confirmed the disparate trends of myotube formation that can be provoked through multi-dimensional scaffolds.

CONCLUSION

We studied more favorable environments that induce cell alignment and elongation for myogenesis by combining nano- and micro-scale patterns. The fabricated system can serve as a novel multi-dimensional platform to study in vitro cell behaviors.

The cell-stretcher: A novel device for the mechanical stimulation of cell populations

Mechanical stimulation appears to be a critical modulator for many aspects of biology, both of living tissue and cells. The cell-stretcher, a novel device for the mechanical uniaxial stimulation of populations of cells, is described. The system is based on a variable stroke cam-lever-tappet mechanism which allows the delivery of cyclic stimuli with frequencies of up to 10 Hz and deformation between 1% and 20%. The kinematics is presented and a simulation of the dynamics of the system is shown, in order to compute the contact forces in the mechanism. The cells, following cultivation and preparation, are plated on an ad hoc polydimethylsiloxane membrane which is then loaded on the clamps of the cell-stretcher via force-adjustable magnetic couplings. In order to show the viability of the experimentation and biocompatibility of the cell-stretcher, a set of two in vitro tests were performed. Human epithelial carcinoma cell line A431 and Adult Mouse Ventricular Fibroblasts (AMVFs) from a dual reporter mouse were subject to 0.5 Hz, 24 h cyclic stretching at 15% strain, and to 48 h stimulation at 0.5 Hz and 15% strain, respectively. Visual analysis was performed on A431, showing definite morphological changes in the form of cellular extroflections in the direction of stimulation compared to an unstimulated control. A cytometric analysis was performed on the AMVF population. Results show a post-stimulation live-dead ratio deviance of less than 6% compared to control, which proves that the environment created by the cell-stretcher is suitable for in vitro experimentation.

Silver nanoparticles functionalized with a fluorescent cyclic RGD peptide: a versatile integrin targeting platform for cells and bacteria

A green fluorescent RGD peptide–silver nanoparticle platform to target integrin receptors in cells and bacterial studies.