Mechanobiology of adult and stem cells

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.

Potential of Nano-Engineered Stem Cells in the Treatment of Multiple Sclerosis: A Comprehensive Review

Multiple sclerosis (MS) is a chronic and degrading autoimmune disorder mainly targeting the central nervous system, leading to progressive neurodegeneration, demyelination, and axonal damage. Current treatment options for MS are limited in efficacy, generally linked to adverse side effects, and do not offer a cure. Stem cell therapies have emerged as a promising therapeutic strategy for MS, potentially promoting remyelination, exerting immunomodulatory effects and protecting against neurodegeneration. Therefore, this review article focussed on the potential of nano-engineering in stem cells as a therapeutic approach for MS, focusing on the synergistic effects of combining stem cell biology with nanotechnology to stimulate the proliferation of oligodendrocytes (OLs) from neural stem cells and OL precursor cells, by manipulating neural signalling pathways-PDGF, BMP, Wnt, Notch and their essential genes such as Sox, bHLH, Nkx. Here we discuss the pathophysiology of MS, the use of various types of stem cells in MS treatment and their mechanisms of action. In the context of nanotechnology, we present an overview of its applications in the medical and research field and discuss different methods and materials used to nano-engineer stem cells, including surface modification, biomaterials and scaffolds, and nanoparticle-based delivery systems. We further elaborate on nano-engineered stem cell techniques, such as nano script, nano-exosome hybrid, nano-topography and their potentials in MS. The article also highlights enhanced homing, engraftment, and survival of nano-engineered stem cells, targeted and controlled release of therapeutic agents, and immunomodulatory and tissue repair effects with their challenges and limitations. This visual illustration depicts the process of utilizing nano-engineering in stem cells and exosomes for the purpose of delivering more accurate and improved treatments for Multiple Sclerosis (MS). This approach targets specifically the creation of oligodendrocytes, the breakdown of which is the primary pathological factor in MS.

Biomimetic Scaffolds for Tendon Tissue Regeneration

Tendon tissue connects muscle to bone and plays crucial roles in stress transfer. Tendon injury remains a significant clinical challenge due to its complicated biological structure and poor self-healing capacity. The treatments for tendon injury have advanced significantly with the development of technology, including the use of sophisticated biomaterials, bioactive growth factors, and numerous stem cells. Among these, biomaterials that the mimic extracellular matrix (ECM) of tendon tissue would provide a resembling microenvironment to improve efficacy in tendon repair and regeneration. In this review, we will begin with a description of the constituents and structural features of tendon tissue, followed by a focus on the available biomimetic scaffolds of natural or synthetic origin for tendon tissue engineering. Finally, we will discuss novel strategies and present challenges in tendon regeneration and repair.

A systematic review on the effects of ROCK inhibitors on proliferation and/or differentiation in human somatic stem cells: A hypothesis that ROCK inhibitors support corneal endothelial healing via acting on the limbal stem cell niche

Rho kinase inhibitors (ROCKi) have attracted growing multidisciplinary interest, particularly in Ophthalmology where the question as to how they promote corneal endothelial healing remains unresolved. Concurrently, stem cell biology has rapidly progressed in unravelling drivers of stem cell (SC) proliferation and differentiation, where mechanical niche factors and the actin cytoskeleton are increasingly recognized as key players. There is mounting evidence from the study of the peripheral corneal endothelium that supports the likelihood of an internal limbal stem cell niche. The possibility that ROCKi stimulate the endothelial SC niche has not been addressed. Furthermore, there is currently a paucity of data that directly evaluates whether ROCKi promotes corneal endothelial healing by acting on this limbal SC niche located near the transition zone. Therefore, we performed a systematic review examining the effects ROCKi on the proliferation and differentiation of human somatic SC, to provide insight into its effects on various human SC populations. An appraisal of electronic searches of four databases identified 1 in vivo and 58 in vitro studies (36 evaluated proliferation while 53 examined differentiation). Types of SC studied included mesenchymal (n = 32), epithelial (n = 11), epidermal (n = 8), hematopoietic and other (n = 8). The ROCK 1/2 selective inhibitor Y-27632 was used in almost all studies (n = 58), while several studies evaluated ≥2 ROCKi (n = 4) including fasudil, H-1152, and KD025. ROCKi significantly influenced human somatic SC proliferation in 81% of studies (29/36) and SC differentiation in 94% of studies (50/53). The present systemic review highlights that ROCKi are influential in regulating human SC proliferation and differentiation, and provides evidence to support the hypothesis that ROCKi promotes corneal endothelial division and maintenance via acting on the inner limbal SC niche.

Advances in non-invasive biosensing measures to monitor wound healing progression

Impaired wound healing is a significant financial and medical burden. The synthesis and deposition of extracellular matrix (ECM) in a new wound is a dynamic process that is constantly changing and adapting to the biochemical and biomechanical signaling from the extracellular microenvironments of the wound. This drives either a regenerative or fibrotic and scar-forming healing outcome. Disruptions in ECM deposition, structure, and composition lead to impaired healing in diseased states, such as in diabetes. Valid measures of the principal determinants of successful ECM deposition and wound healing include lack of bacterial contamination, good tissue perfusion, and reduced mechanical injury and strain. These measures are used by wound-care providers to intervene upon the healing wound to steer healing toward a more functional phenotype with improved structural integrity and healing outcomes and to prevent adverse wound developments. In this review, we discuss bioengineering advances in 1) non-invasive detection of biologic and physiologic factors of the healing wound, 2) visualizing and modeling the ECM, and 3) computational tools that efficiently evaluate the complex data acquired from the wounds based on basic science, preclinical, translational and clinical studies, that would allow us to prognosticate healing outcomes and intervene effectively. We focus on bioelectronics and biologic interfaces of the sensors and actuators for real time biosensing and actuation of the tissues. We also discuss high-resolution, advanced imaging techniques, which go beyond traditional confocal and fluorescence microscopy to visualize microscopic details of the composition of the wound matrix, linearity of collagen, and live tracking of components within the wound microenvironment. Computational modeling of the wound matrix, including partial differential equation datasets as well as machine learning models that can serve as powerful tools for physicians to guide their decision-making process are discussed.

A Role for Exchange of Extracellular Vesicles in Porcine Spermatogonial Co-Culture

Spermatogonial stem cells (SSCs) provide the basis for lifelong male fertility through self-renewal and differentiation. Prepubertal male cancer patients may be rendered infertile by gonadotoxic chemotherapy and, unlike sexually mature men, cannot store sperm. Alternatively, testicular biopsies taken prior to treatment may be used to restore fertility in adulthood. Testicular SSC populations are limited, and in vitro culture systems are required to increase numbers of SSCs for treatment, demanding culture systems for SSC propagation. Using the pig as a non-rodent model, we developed culture systems to expand spermatogonia from immature testis tissue, comparing different feeders (Sertoli cells, peritubular myoid cells (PMCs) and pig fetal fibroblasts (PFFs)). Spermatogonia co-cultured with Sertoli cells, PMCs and PFFs had comparable rates of proliferation and apoptosis. To elucidate the mechanism behind the beneficial nature of feeder layers, we investigated the role of extracellular vesicles in crosstalk between spermatogonia and feeder cells. Sertoli cell-released exosomes are incorporated by spermatogonia, and inhibition of exosomal release reduces spermatogonial proliferation. Together, these results show that PMCs, PFFs and Sertoli cells promote spermatogonial proliferation in co-culture, with exosomal exchange representing one possible mechanism. Further characterization of exosomal cargo may ultimately allow the development of feeder-free culture systems for clinical use.

Biocompatible and Enzymatically Degradable Gels for 3D Cellular Encapsulation under Extreme Compressive Strain

Cell encapsulating scaffolds are necessary for the study of cellular mechanosensing of cultured cells. However, conventional scaffolds used for loading cells in bulk generally fail at low compressive strain, while hydrogels designed for high toughness and strain resistance are generally unsuitable for cell encapsulation. Here we describe an alginate/gelatin methacryloyl interpenetrating network with multiple crosslinking modes that is robust to compressive strains greater than 70%, highly biocompatible, enzymatically degradable and able to effectively transfer strain to encapsulated cells. In future studies, this gel formula may allow researchers to probe cellular mechanosensing in bulk at levels of compressive strain previously difficult to investigate.

Steering cell behavior through mechanobiology in 3D: A regenerative medicine perspective

Mechanobiology, translating mechanical signals into biological ones, greatly affects cellular behavior. Steering cellular behavior for cell-based regenerative medicine approaches requires a thorough understanding of the orchestrating molecular mechanisms, among which mechanotransducive ones are being more and more elucidated. Because of their wide use and highly mechanotransduction dependent differentiation, this review focuses on mesenchymal stromal cells (MSCs), while also briefly relating the discussed results to other cell types. While the mechanotransduction pathways are relatively well-studied in 2D, much remains unknown of the role and regulation of these pathways in 3D. Ultimately, cells need to be cultured in a 3D environment to create functional de novo tissue. In this review, we explore the literature on the roles of different material properties on cellular behavior and mechanobiology in 2D and 3D. For example, while stiffness plays a dominant role in 2D MSCs differentiation, it seems to be of subordinate importance in 3D MSCs differentiation, where matrix remodeling seems to be key. Also, the role and regulation of some of the main mechanotransduction players are discussed, focusing on MSCs. We have only just begun to fundamentally understand MSCs and other stem cells behavior in 3D and more fundamental research is required to advance biomaterials able to replicate the stem cell niche and control cell activity. This better understanding will contribute to smarter tissue engineering scaffold design and the advancement of regenerative medicine.

Strain-induced Differentiation of Mesenchymal Stem Cells

Directing the fate of human mesenchymal stem/stromal cells (hMSCs) toward bone formation using mechanical strain is a promising approach in regenerative medicine related to bone diseases. Numerous studies have evaluated the effects of vibration or cyclic tensile strain on MSCs towards developing a mechanically-based method for stimulating differentiation. Here, we study the differentiation of hMSCs cultured on elastic polydimethylsiloxane (PDMS) membrane, which is magnetically actuated to induce periodically varying strain. The strain distribution across the membrane was calculated by finite-element modeling and demonstrates three main areas of different strain amplitudes. The strain effect on the hMSCs was evaluated by measuring the mineralization of differentiated hMSCs using Alizarin S red stain. The results indicate a strain-dependent differentiation of hMSCs, where the highest region of strain on the membrane resulted in the most accelerated differentiation. Osteogenic differentiation was achieved as early as two weeks, which is significantly sooner than control hMSCs treated with osteogenic media alone.

Evaluation of Dental Pulp Stem Cell Heterogeneity and Behaviour in 3D Type I Collagen Gels

Dental pulp stem cells (DPSCs) are increasingly being advocated for regenerative medicine-based therapies. However, significant heterogeneity in the genotypic/phenotypic properties of DPSC subpopulations exist, influencing their therapeutic potentials. As most studies have established DPSC heterogeneity using 2D culture approaches, we investigated whether heterogeneous DPSC proliferative and contraction/remodelling capabilities were further evident within 3D type I collagen gels in vitro. DPSC subpopulations were isolated from human third molars and identified as high/low proliferative and multipotent/unipotent, following in vitro culture expansion and population doubling (PD) analysis. High proliferative/multipotent DPSCs, such as A3 (30 PDs and 80 PDs), and low proliferative/unipotent DPSCs, such as A1 (17 PDs), were cultured in collagen gels for 12 days, either attached or detached from the surrounding culture plastic. Collagen architecture and high proliferative/multipotent DPSC morphologies were visualised by Scanning Electron Microscopy and FITC-phalloidin/Fluorescence Microscopy. DPSC proliferation (cell counts), contraction (% diameter reductions), and remodelling (MMP-2/MMP-9 gelatin zymography) of collagen gels were also evaluated. Unexpectedly, no proliferation differences existed between DPSCs, A3 (30 PDs) and A1 (17 PDs), although A3 (80 PDs) responses were significantly reduced. Despite rapid detached collagen gel contraction with A3 (30 PDs), similar contraction rates were determined with A1 (17 PDs), although A3 (80 PDs) contraction was significantly impaired. Gel contraction correlated to distinct gelatinase profiles. A3 (30 PDs) possessed superior MMP-9 and comparable MMP-2 activities to A1 (17 PDs), whereas A3 (80 PDs) had significantly reduced MMP-2/MMP-9. High proliferative/multipotent DPSCs, A3 (30 PDs), further exhibited fibroblast-like morphologies becoming polygonal within attached gels, whilst losing cytoskeletal organization and fibroblastic morphologies in detached gels. This study demonstrates that heterogeneity exists in the gel contraction and MMP expression/activity capabilities of DPSCs, potentially reflecting differences in their abilities to degrade biomaterial scaffolds and regulate cellular functions in 3D environments and their regenerative properties overall. Thus, such findings enhance our understanding of the molecular and phenotypic characteristics associated with high proliferative/multipotent DPSCs.

Extracellular matrix stiffness and Wnt/β-catenin signaling in physiology and disease

The Wnt/β-catenin signaling pathway plays fundamental roles during development, stem cell differentiation, and homeostasis, and its abnormal activation can lead to diseases. In recent years, it has become clear that this pathway integrates signals not only from Wnt ligands but also from other proteins and signaling routes. For instance, Wnt/β-catenin signaling involves YAP and TAZ, which are transcription factors with crucial roles in mechanotransduction. On the other hand, Wnt/β-catenin signaling is also modulated by integrins. Therefore, mechanical signals might similarly modulate the Wnt/β-catenin pathway. However, and despite the relevance that mechanosensitive Wnt/β-catenin signaling might have during physiology and diseases such as cancer, the role of mechanical cues on Wnt/β-catenin signaling has received less attention. This review aims to summarize recent evidence regarding the modulation of the Wnt/β-catenin signaling by a specific type of mechanical signal, the stiffness of the extracellular matrix. The review shows that mechanical stiffness can indeed modulate this pathway in several cell types, through differential expression of Wnt ligands, receptors and inhibitors, as well as by modulating β-catenin levels. However, the specific mechanisms are yet to be fully elucidated.

[Fabrication of poly (lactic-co-glycolic acid)/decellularized articular cartilage extracellular matrix scaffold by three-dimensional printing technology and investigating its physicochemical properties]

OBJECTIVE

To manufacture a poly (lactic-co-glycolic acid) (PLGA) scaffold by low temperature deposition three-dimensional (3D) printing technology, prepare a PLGA/decellularized articular cartilage extracellular matrix (DACECM) cartilage tissue engineered scaffold by combining DACECM, and further investigate its physicochemical properties.

METHODS

PLGA scaffolds were prepared by low temperature deposition 3D printing technology, and DACECM suspensions was prepared by modified physical and chemical decellularization methods. DACECM oriented scaffolds were prepared by using freeze-drying and physicochemical cross-linking techniques. PLGA/DACECM oriented scaffolds were prepared by combining DACECM slurry with PLGA scaffolds. The macroscopic and microscopic structures of the three kinds of scaffolds were observed by general observation and scanning electron microscope. The chemical composition of DACECM oriented scaffold was analyzed by histological and immunohistochemical stainings. The compression modulus of the three kinds of scaffolds were measured by biomechanical test. Three kinds of scaffolds were embedded subcutaneously in Sprague Dawley rats, and HE staining was used to observe immune response. The chondrocytes of New Zealand white rabbits were isolated and cultured, and the three kinds of cell-scaffold complexes were prepared. The growth adhesion of the cells on the scaffolds was observed by scanning electron microscope. Three kinds of scaffold extracts were cultured with L-929 cells, the cells were cultured in DMEM culture medium as control group, and cell counting kit 8 (CCK-8) was used to detect cell proliferation.

RESULTS

General observation and scanning electron microscope showed that the PLGA scaffold had a smooth surface and large pores; the surface of the DACECM oriented scaffold was rough, which was a 3D structure with loose pores and interconnected; and the PLGA/DACECM oriented scaffold had a rough surface, and the large hole and the small hole were connected to each other to construct a vertical 3D structure. Histological and immunohistochemical qualitative analysis demonstrated that DACECM was completely decellularized, retaining the glycosaminoglycans and collagen typeⅡ. Biomechanical examination showed that the compression modulus of DACECM oriented scaffold was significantly lower than those of the other two scaffolds ( P<0.05). There was no significant difference between PLGA scaffold and PLGA/DACECM oriented scaffold ( P>0.05). Subcutaneously embedded HE staining of the three scaffolds showed that the immunological rejections of DACECM and PLGA/DACECM oriented scaffolds were significantly weaker than that of the PLGA scaffold. Scanning electron microscope observation of the cell-scaffold complex showed that chondrocytes did not obviously adhere to PLGA scaffold, and a large number of chondrocytes adhered and grew on PLGA/DACECM oriented scaffold and DACECM oriented scaffold. CCK-8 assay showed that with the extension of culture time, the number of cells cultured in the three kinds of scaffold extracts and the control group increased. There was no significant difference in the absorbance ( A) value between the groups at each time point ( P>0.05).

CONCLUSION

The PLGA/DACECM oriented scaffolds have no cytotoxicity, have excellent physicochemical properties, and may become a promising scaffold material of tissue engineered cartilage.

Effect of mechanical vibration stress in cell culture on human induced pluripotent stem cells

The development of induced pluripotent stem cell (iPSC) techniques has solved various limitations in cell culture including cellular proliferation and potency. Hence, the expectations on wider applications and the quality of manufactured iPSCs are rapidly increasing. To answer such growing expectations, enhancement of technologies to improve cell-manufacturing efficiency is now a challenge for the bioengineering field. Mechanization of conventional manual operations, aimed at automation of cell manufacturing, is quickly advancing. However, as more processes are being automated in cell manufacturing, it is need to be more critical about influential parameters that may not be as important in manual operations. As a model of such parameters, we focused on the effect of mechanical vibration, which transmits through the vessel to the cultured iPSCs. We designed 7 types of vertical vibration conditions in cell culture vessels using a vibration calibrator. These conditions cover a wide range of potential situations in cell culture, such as tapping or closing an incubator door, and examined their effects by continuous passaging (P3 to P5). Detailed evaluation of cells by time-course image analysis revealed that vibrations can enhance cell growth as an early effect but can negatively affect cell adhesion and growth profile after several passages as a delayed effect. Such unexpected reductions in cell quality are potentially critical issues in maintaining consistency in cell manufacturing. Therefore, this work reveals the importance of continuous examination across several passages with detailed, temporal, quantitative measurements obtained by non-invasive image analysis to examine when and how the unknown parameters will affect the cell culture processes.

Cholesterol-dependent Modulation of Stem Cell Biomechanics: Application to Adipogenesis

Cell mechanics has been shown to regulate stem cell differentiation. We have previously reported that altered cell stiffness of mesenchymal stem cells can delay or facilitate biochemically directed differentiation. One of the factors that can affect the cell stiffness is cholesterol. However, the effect of cholesterol on differentiation of human mesenchymal stem cells (hMSCs) remains elusive. In this paper, we demonstrate that cholesterol is involved in the modulation of the cell stiffness and subsequent adipogenic differentiation. Rapid cytoskeletal actin reorganization was evident and correlated with the cell's Young's modulus measured using atomic force microscopy (AFM). In addition, the level of membrane-bound cholesterol was found to increase during adipogenic differentiation and inversely varied with the cell stiffness. Furthermore, cholesterol played a key role in the regulation of the cell morphology and biomechanics, suggesting its crucial involvement in mechanotransduction. To better understand the underlying mechanisms, we investigated the effect of cholesterol on the membrane-cytoskeleton linker proteins (ezrin and moesin). Cholesterol depletion was found to up-regulate the ezrin expression which promoted cell spreading, increased Young's modulus, and hindered adipogenesis. In contrast, cholesterol enrichment increased the moesin expression, decreased Young's modulus, and induced cell rounding and facilitated adipogenesis. Taken together, cholesterol appears to regulate the stem cell mechanics and adipogenesis through the membrane-associated linker proteins.

Astrocyte Mechano-Activation by High-Rate Overpressure Involves Alterations in Structural and Junctional Proteins

Primary blast neurotrauma represents a unique injury paradigm characterized by high-rate overpressure effects on brain tissue. One major hallmark of blast neurotrauma is glial reactivity, notably prolonged astrocyte activation. This cellular response has been mainly defined in primary blast neurotrauma by increased intermediate filament expression. Because the intermediate filament networks physically interface with transmembrane proteins for junctional support, it was hypothesized that cell junction regulation is altered in the reactive phenotype as well. This would have implications for downstream transcriptional regulation via signal transduction pathways like nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB). Therefore, a custom high-rate overpressure simulator was built for in vitro testing using mechanical conditions based on intracranial pressure measurements in a rat model of blast neurotrauma. Primary rat astrocytes were exposed to isolated high-rate mechanical stimulation to study cell junction dynamics in relation to their mechano-activation. First, a time course for "classical" features of reactivity was devised by evaluation of glial fibrillary acidic protein (GFAP) and proliferating cell nuclear antigen (PCNA) expression. This was followed by gene and protein expression for both gap junction (connexins) and anchoring junction proteins (integrins and cadherins). Signal transduction analysis was carried out by nuclear localization of two molecules, NF-κB p65 and mitogen-activated protein kinase (MAPK) p38. Results indicated significant increases in connexin-43 expression and PCNA first at 24 h post-overpressure (p < 0.05), followed by structural reactivity (via increased GFAP, p < 0.05) corresponding to increased anchoring junction dynamics at 48 h post-overpressure (p < 0.05). Moreover, increased phosphorylation of focal adhesion kinase (FAK) was observed in addition to increased nuclear localization of both p65 and p38 (p < 0.05) during the period of structural reactivity. To evaluate the transcriptional activity of p65 in the nucleus, electrophoretic mobility shift assay was conducted for a binding site on the promoter region for intracellular adhesion molecule-1 (ICAM-1), an antagonist of tight junctions. A significant increase in the interaction of nuclear proteins with the NF-κB site on the ICAM-1 corresponded to increased gene and protein expression of ICAM-1 (p < 0.05). Altogether, these results indicate multiple targets and corresponding signaling pathways which involve cell junction dynamics in the mechano-activation of astrocytes following high-rate overpressure.

Biomechanical Stimulus Based Strategies for Meniscus Tissue Engineering and Regeneration

Meniscus injuries are very common in the knee joint. Treating a damaged meniscus continues to be a scientific challenge in sport medicine because of its poor self-healing potential and few clinical therapeutic options. Tissue engineering strategies are very promising solutions for repairing and regenerating a damaged meniscus. Meniscus is exposed to a complex biomechanical microenvironment, and it plays a crucial role in meniscal development, growth, and repairing. Over the past decades, increasing attention has been focused on the use of biomechanical stimulus to enhance biomechanical properties of the engineered meniscus. Further understanding the influence of mechanical stimulation on cell proliferation and differentiation, metabolism, relevant gene expression, and pro/anti-inflammatory responses may be beneficial to enhance meniscal repair and regeneration. On the one hand, this review describes some basic information about meniscus; on the other hand, we sum up the various biomechanical stimulus based strategies applied in meniscus tissue engineering and how these factors affect meniscal regeneration. We hope this review will provide researchers with inspiration on tissue engineering strategies for meniscus regeneration in the future.

Regenerative Medicine Approaches for the Treatment of Pediatric Physeal Injuries

The physis, or growth plate, is a cartilaginous region at the end of children's long bones that serves as the primary center for longitudinal growth and characterizes the immature skeleton. Musculoskeletal injury, including fracture, infection, malignancy, or iatrogenic damage, has risk of physeal damage. Physeal injuries account for 30% of pediatric fractures and may result in impaired bone growth. Once damaged, cartilage tissue within the physis is often replaced by unwanted bony tissue, forming a "bony bar" that can lead to complications such as complete growth arrest, angular or rotational deformities, and altered joint mechanics. Children with a bony bar occupying <50% of the physis usually undergo bony bar resection and insertion of an interpositional material, such as a fat graft, to prevent recurrence and allow the surrounding uninjured physeal tissue to restore longitudinal bone growth. Clinical success for this procedure is <35% and often the bony bar and associated growth impairments return. Children who are not candidates for bony bar resection due to a physeal bar occupying >50% of their physis undergo corrective osteotomy or bone lengthening procedures. These approaches are complex and have variable success rates. As such, there is a critical need for regenerative approaches to not only prevent initial bony bar formation but also regenerate healthy physeal cartilage following injury. This review describes physeal anatomy, mechanisms of physeal injury, and current treatment options with associated limitations. Furthermore, we provide an overview of the current research using cell-based therapies, growth factors, and biomaterials in the different animal models of injury along with strategic directions for modulating intrinsic injury pathways to inhibit bony bar formation and/or promote physeal tissue formation. Pediatric physeal injuries constitute a unique niche within regenerative medicine for which there is a critical need for research to decrease child morbidity related to this injurious process.

Cellular mechanosensitivity to substrate stiffness decreases with increasing dissimilarity to cell stiffness

Computational modelling has received increasing attention to investigate multi-scale coupled problems in micro-heterogeneous biological structures such as cells. In the current study, we investigated for a single cell the effects of (1) different cell-substrate attachment (2) and different substrate modulus [Formula: see text] on intracellular deformations. A fibroblast was geometrically reconstructed from confocal micrographs. Finite element models of the cell on a planar substrate were developed. Intracellular deformations due to substrate stretch of [Formula: see text], were assessed for: (1) cell-substrate attachment implemented as full basal contact (FC) and 124 focal adhesions (FA), respectively, and [Formula: see text]140 KPa and (2) [Formula: see text], 140, 1000, and 10,000 KPa, respectively, and FA attachment. The largest strains in cytosol, nucleus and cell membrane were higher for FC (1.35[Formula: see text], 0.235[Formula: see text] and 0.6[Formula: see text]) than for FA attachment (0.0952[Formula: see text], 0.0472[Formula: see text] and 0.05[Formula: see text]). For increasing [Formula: see text], the largest maximum principal strain was 4.4[Formula: see text], 5[Formula: see text], 5.3[Formula: see text] and 5.3[Formula: see text] in the membrane, 9.5[Formula: see text], 1.1[Formula: see text], 1.2[Formula: see text] and 1.2[Formula: see text] in the cytosol, and 4.5[Formula: see text], 5.3[Formula: see text], 5.7[Formula: see text] and 5.7[Formula: see text] in the nucleus. The results show (1) the importance of representing FA in cell models and (2) higher cellular mechanical sensitivity for substrate stiffness changes in the range of cell stiffness. The latter indicates that matching substrate stiffness to cell stiffness, and moderate variation of the former is very effective for controlled variation of cell deformation. The developed methodology is useful for parametric studies on cellular mechanics to obtain quantitative data of subcellular strains and stresses that cannot easily be measured experimentally.

Fluid Dynamics Appearing during Simulated Microgravity Using Random Positioning Machines

Random Positioning Machines (RPMs) are widely used as tools to simulate microgravity on ground. They consist of two gimbal mounted frames, which constantly rotate biological samples around two perpendicular axes and thus distribute the Earth's gravity vector in all directions over time. In recent years, the RPM is increasingly becoming appreciated as a laboratory instrument also in non-space-related research. For instance, it can be applied for the formation of scaffold-free spheroid cell clusters. The kinematic rotation of the RPM, however, does not only distribute the gravity vector in such a way that it averages to zero, but it also introduces local forces to the cell culture. These forces can be described by rigid body analysis. Although RPMs are commonly used in laboratories, the fluid motion in the cell culture flasks on the RPM and the possible effects of such on cells have not been examined until today; thus, such aspects have been widely neglected. In this study, we used a numerical approach to describe the fluid dynamic characteristic occurring inside a cell culture flask turning on an operating RPM. The simulations showed that the fluid motion within the cell culture flask never reached a steady state or neared a steady state condition. The fluid velocity depends on the rotational velocity of the RPM and is in the order of a few centimeters per second. The highest shear stresses are found along the flask walls; depending of the rotational velocity, they can reach up to a few 100 mPa. The shear stresses in the "bulk volume," however, are always smaller, and their magnitude is in the order of 10 mPa. In conclusion, RPMs are highly appreciated as reliable tools in microgravity research. They have even started to become useful instruments in new research fields of mechanobiology. Depending on the experiment, the fluid dynamic on the RPM cannot be neglected and needs to be taken into consideration. The results presented in this study elucidate the fluid motion and provide insight into the convection and shear stresses that occur inside a cell culture flask during RPM experiments.

Modeling Stem Cell Myogenic Differentiation

The process of stem cell myogenesis (transformation into skeletal muscle cells) includes several stages characterized by the expression of certain combinations of myogenic factors. The first part of this process is accompanied by cell division, while the second part is mainly associated with direct differentiation. The mechanical cues are known to enhance stem cell myogenesis, and the paper focuses on the stem cell differentiation under the condition of externally applied strain. The process of stem cell myogenic differentiation is interpreted as the interplay among transcription factors, targeted proteins and strain-generated signaling molecule, and it is described by a kinetic multi-stage model. The model parameters are optimally adjusted by using the available data from the experiment with adipose-derived stem cells subjected to the application of cyclic uniaxial strains of the magnitude of 10%. The modeling results predict the kinetics of the process of myogenic differentiation, including the number of cells in each stage of differentiation and the rates of differentiation from one stage to another for different strains from 4% to 16%. The developed model can help better understand the process of myogenic differentiation and the effects of mechanical cues on stem cell use in muscle therapies.

Physical confinement signals regulate the organization of stem cells in three dimensions

During embryogenesis, the spherical inner cell mass (ICM) proliferates in the confined environment of a blastocyst. Embryonic stem cells (ESCs) are derived from the ICM, and mimicking embryogenesis in vitro, mouse ESCs (mESCs) are often cultured in hanging droplets. This promotes the formation of a spheroid as the cells sediment and aggregate owing to increased physical confinement and cell-cell interactions. In contrast, mESCs form two-dimensional monolayers on flat substrates and it remains unclear if the difference in organization is owing to a lack of physical confinement or increased cell-substrate versus cell-cell interactions. Employing microfabricated substrates, we demonstrate that a single geometric degree of physical confinement on a surface can also initiate spherogenesis. Experiment and computation reveal that a balance between cell-cell and cell-substrate interactions finely controls the morphology and organization of mESC aggregates. Physical confinement is thus an important regulatory cue in the three-dimensional organization and morphogenesis of developing cells.

The Study of Cell Motility by Cell Traction Force Microscopy (CTFM)

Migration is a vital characteristic of various cell types and enables various cellular functions during development and wound healing. Cell movement can be measured by monitoring cell traction forces, which are generated by individual cells and transmitted to the substrate below the migrant cells. This method, termed cell traction force microscopy (CTFM), has the advantage of directly measuring the "cause" (i.e., cell traction forces, CTFs) of cell movement rather than the "effect" (i.e., cell movement itself). This chapter details the methods involved in measuring cell traction forces. Several examples are also given to illustrate various applications of CTFM in cell biology research.

Mechanoregulation of Wound Healing and Skin Homeostasis

Basic and clinical studies on mechanobiology of cells and tissues point to the importance of mechanical forces in the process of skin regeneration and wound healing. These studies result in the development of new therapies that use mechanical force which supports effective healing. A better understanding of mechanobiology will make it possible to develop biomaterials with appropriate physical and chemical properties used to treat poorly healing wounds. In addition, it will make it possible to design devices precisely controlling wound mechanics and to individualize a therapy depending on the type, size, and anatomical location of the wound in specific patients, which will increase the clinical efficiency of the therapy. Linking mechanobiology with the science of biomaterials and nanotechnology will enable in the near future precise interference in abnormal cell signaling responsible for the proliferation, differentiation, cell death, and restoration of the biological balance. The objective of this study is to point to the importance of mechanobiology in regeneration of skin damage and wound healing. The study describes the influence of rigidity of extracellular matrix and special restrictions on cell physiology. The study also defines how and what mechanical changes influence tissue regeneration and wound healing. The influence of mechanical signals in the process of proliferation, differentiation, and skin regeneration is tagged in the study.

Capturing extracellular matrix properties in vitro: Microengineering materials to decipher cell and tissue level processes

Rapid advances in biology have led to the establishment of new fields with tremendous translational potential including regenerative medicine and immunoengineering. One commonality to these fields is the need to extract cells for manipulation in vitro; however, results obtained in laboratory cell culture will often differ widely from observations made in vivo. To more closely emulate native cell biology in the laboratory, designer engineered environments have proved a successful methodology to decipher the properties of the extracellular matrix that govern cellular decision making. Here, we present an overview of matrix properties that affect cell behavior, strategies for recapitulating important parameters in vitro, and examples of how these properties can affect cell and tissue level processes, with emphasis on leveraging these tools for immunoengineering.

A strain-dependent diffusivity model to study the nuclear import of mechanobiological transcription factors

Nuclear spreading plays a crucial role in stem cell fate determination. In previous works, we reported evidence of multipotency maintenance of mesenchymal stromal cells cultured on three-dimensional engineered niche substrates fabricated via two-photon laser polymerization (2PP). We correlated multipotency maintenance to a more roundish nuclear morphology of cells cultured in the 2PP-fabricated niches, with respect to those on flat substrates. To interpret these findings, here we present a multiphysics model coupling nuclear strains induced by cell adhesion to diffusive transport across the cell nucleus. We reconstructed the cell nuclear geometry from confocal Z-stack images of 2PP-cultured cells, and we estimated the volume, surface and shape factors. The levels of nuclear spreading significantly varied depending on the cell localization within the niche architecture. We assumed the cell diffusivity as a function of the local volumetric strain. The computational model also indicate that the larger the nuclear deformation (e.g. in spread nuclei), the higher the nuclear flux of small solutes such as transcription factors through the nuclear membrane. Our results point towards nuclear deformation as a primary mechanism by which the stem cell translates its shape into a fate decision, i.e. through a strain-dependent amplification of the diffusive flow of signaling molecules into the nucleus.

Stem cells: a promising source for vascular regenerative medicine

The rising and diversity of many human vascular diseases pose urgent needs for the development of novel therapeutics. Stem cell therapy represents a challenge in the medicine of the twenty-first century, an area where tissue engineering and regenerative medicine gather to provide promising treatments for a wide variety of diseases. Indeed, with their extensive regeneration potential and functional multilineage differentiation capacity, stem cells are now highlighted as promising cell sources for regenerative medicine. Their multilineage differentiation involves environmental factors such as biochemical, extracellular matrix coating, oxygen tension, and mechanical forces. In this review, we will focus on human stem cell sources and their applications in vascular regeneration. We will also discuss the different strategies used for their differentiation into both mature and functional smooth muscle and endothelial cells.

Computational prediction of strain-dependent diffusion of transcription factors through the cell nucleus

Nuclear spreading plays a crucial role in stem cell fate determination. In previous works, we reported evidence of multipotency maintenance for mesenchymal stromal cells cultured on three-dimensional engineered niche substrates, fabricated via two-photon laser polymerization. We correlated maintenance of multipotency to a more roundish morphology of these cells with respect to those cultured on conventional flat substrates. To interpret these findings, here we present a multiphysics model coupling nuclear strains induced by cell adhesion to passive diffusion across the cell nucleus. Fully three-dimensional reconstructions of cultured cells were developed on the basis of confocal images: in particular, the level of nuclear spreading resulted significantly dependent on the cell localization within the niche architecture. We assumed that the cell diffusivity varies as a function of the local volumetric strain. The model predictions indicate that the higher the level of spreading of the cell, the higher the flux across the nucleus of small solutes such as transcription factors. Our results point toward nuclear spreading as a primary mechanism by which the stem cell translates its shape into a fate decision, i.e., by amplifying the diffusive flow of transcriptional activators into the nucleus.

Coating flexible probes with an ultra fast degrading polymer to aid in tissue insertion

We report a fabrication process for coating neural probes with an ultrafast degrading polymer to create consistent and reproducible devices for neural tissue insertion. The rigid polymer coating acts as a probe insertion aid, but resorbs within hours post-implantation. Despite the feasibility for short term neural recordings from currently available neural prosthetic devices, most of these devices suffer from long term gliosis, which isolates the probes from adjacent neurons, increasing the recording impedance and stimulation threshold. The size and stiffness of implanted probes have been identified as critical factors that lead to this long term gliosis. Smaller, more flexible probes that match the mechanical properties of brain tissue could allow better long term integration by limiting the mechanical disruption of the surrounding tissue during and after probe insertion, while being flexible enough to deform with the tissue during brain movement. However, these small flexible probes inherently lack the mechanical strength to penetrate the brain on their own. In this work, we have developed a micromolding method for coating a non-functional miniaturized SU-8 probe with an ultrafast degrading tyrosine-derived polycarbonate (E5005(2K)). Coated, non-functionalized probes of varying dimensions were reproducibly fabricated with high yields. The polymer erosion/degradation profiles of the probes were characterized in vitro. The probes were also mechanically characterized in ex vivo brain tissue models by measuring buckling and insertion forces during probe insertion. The results demonstrate the ability to produce polymer coated probes of consistent quality for future in vivo use, for example to study the effects of different design parameters that may affect tissue response during long term chronic intra-cortical microelectrode neural recordings.

TGFβ3 secretion by three-dimensional cultures of human dental apical papilla mesenchymal stem cells

Mesenchymal stem cells (MSCs) can be isolated from dental tissues, such as pulp and periodontal ligament; the dental apical papilla (DAP) is a less-studied MSC source. These dental-derived MSCs are of great interest because of their potential as an accessible source for cell-based therapies and tissue-engineering (TE) approaches. Much of the interest regarding MSCs relies on the trophic-mediated repair and regenerative effects observed when they are implanted. TGFβ3 is a key growth factor involved in tissue regeneration and scarless tissue repair. We hypothesized that human DAP-derived MSCs (hSCAPs) can produce and secrete TGFβ3 in response to micro-environmental cues. For this, we encapsulated hSCAPs in different types of matrix and evaluated TGFβ3 secretion. We found that dynamic changes of cell-matrix interactions and mechanical stress that cells sense during the transition from a monolayer culture (two-dimensional, 2D) towards a three-dimensional (3D) culture condition, rather than the different chemical composition of the scaffolds, may trigger the TGFβ3 secretion, while monolayer cultures showed almost 10-fold less secretion of TGFβ3. The study of these interactions is provided as a cornerstone in designing future strategies in TE and cell therapy that are more efficient and effective for repair/regeneration of damaged tissues. Copyright © 2015 John Wiley & Sons, Ltd.

The proliferation and tenogenic differentiation potential of bone marrow-derived mesenchymal stromal cell are influenced by specific uniaxial cyclic tensile loading conditions

It has been previously demonstrated that mechanical stimuli are important for multipotent human bone marrow-derived mesenchymal stromal cells (hMSCs) to maintain good tissue homeostasis and even to enhance tissue repair processes. In tendons, this is achieved by promoting the cellular proliferation and tenogenic expression/differentiation. The present study was conducted to determine the optimal loading conditions needed to achieve the best proliferation rates and tenogenic differentiation potential. The effects of mechanical uniaxial stretching using different rates and strains were performed on hMSCs cultured in vitro. hMSCs were subjected to cyclical uniaxial stretching of 4, 8 or 12 % strain at 0.5 or 1 Hz for 6, 24, 48 or 72 h. Cell proliferation was analyzed using alamarBlue[Formula: see text] assay, while hMSCs differentiation was analyzed using total collagen assay and specific tenogenic gene expression markers (type I collagen, type III collagen, decorin, tenascin-C, scleraxis and tenomodulin). Our results demonstrate that the highest cell proliferation is observed when 4 % strain [Formula: see text] 1 Hz was applied. However, at 8 % strain [Formula: see text] 1 Hz loading, collagen production and the tenogenic gene expression were highest. Increasing strain or rates thereafter did not demonstrate any significant increase in both cell proliferation and tenogenic differentiation. In conclusion, our results suggest that 4 % [Formula: see text] 1 Hz cyclic uniaxial loading increases cell proliferation, but higher strains are required for superior tenogenic expressions. This study suggests that selected loading regimes will stimulate tenogenesis of hMSCs.

Modulus-dependent characteristics of Wharton's jelly mesenchymal stem cells (WJMSC) encapsulated in hydrogel microspheres

Recent studies revealing stem cell behavior dependence on mechanical properties of a substrate has initiated the need to probe matrix mechanics and its influence on stem cell fate in a physiologically relevant three-dimensional (3D) microenvironment. We investigated the proliferative and osteogenic potentials of Wharton's jelly mesenchymal stem cells (WJMSCs) immobilized in alginate microspheres with respect to the mechanical properties of alginate hydrogels (1, 1.5 and 2% (w/v)) post incubation in a simulated in vivo environment. Compressive moduli, degradation profile, and swelling kinetics of the hydrogels varied proportionally with alginate concentration and with exposure to simulated conditions. Degradation profile and morphological analysis showed that hydrogels exhibiting high modulus (2% w/v) remained the most intact at the end of day 21. High cell viability in all conditions was observed throughout the culture period. Low-modulus hydrogels (1% w/v) facilitated proliferation of WJMSCs whereas high-modulus hydrogels demonstrated better osteogenic differentiation inferred by an up regulation of osteo-specific genes, expressions of osteocalcin, and quantification of calcium deposition. These findings present a step forward in the development of application-specific hydrogel matrices for stem cell-based tissue engineering.

Biological responses of three-dimensional cultured fibroblasts by sustained compressive loading include apoptosis and survival activity

Pressure ulcers are characterized by chronicity, which results in delayed wound healing due to pressure. Early intervention for preventing delayed healing due to pressure requires a prediction method. However, no study has reported the prediction of delayed healing due to pressure. Therefore, this study focused on biological response-based molecular markers for the establishment of an assessment technology to predict delayed healing due to pressure. We tested the hypothesis that sustained compressive loading applied to three dimensional cultured fibroblasts leads to upregulation of heat shock proteins (HSPs), CD44, hyaluronan synthase 2 (HAS2), and cyclooxygenase 2 (COX2) along with apoptosis via disruption of adhesion. First, sustained compressive loading was applied to fibroblast-seeded collagen sponges. Following this, collagen sponge samples and culture supernatants were collected for apoptosis and proliferation assays, gene expression analysis, immunocytochemistry, and quantification of secreted substances induced by upregulation of mRNA and protein level. Compared to the control, the compressed samples demonstrated that apoptosis was induced in a time- and load- dependent manner; vinculin and stress fiber were scarce; HSP90α, CD44, HAS2, and COX2 expression was upregulated; and the concentrations of HSP90α, hyaluronan (HA), and prostaglandin E₂ (PGE₂) were increased. In addition, the gene expression of antiapoptotic Bcl2 was significantly increased in the compressed samples compared to the control. These results suggest that compressive loading induces not only apoptosis but also survival activity. These observations support that HSP90α, HA, and, PGE₂ could be potential molecular markers for prediction of delayed wound healing due to pressure.

Nanoengineered Platforms to Guide Pluripotent Stem Cell Fate

Tissue engineering utilizes cells, signaling molecules, and scaffolds towards creating functional tissue to repair damaged organs. Pluripotent stem cells (PSCs) are a promising cell source due to their ability to self-renewal indefinitely and their potential to differentiate into almost any cell type. Great strides have been taken to parse the physiological mechanisms by which PSCs respond to their microenvironment and commit to a specific lineage. The combination of physical cues and chemical factors is thought to have the most profound influence on stem cell behavior, therefore a major focus of tissue engineering strategies is scaffold design to incorporate these signals. One overlooked component of the in vivo microenvironment researchers attempt to recapitulate with three dimensional (3D) substrates is the nanoarchitecture formed by the fibrillar network of extracellular matrix (ECM) proteins. These nanoscale features have the ability to impact cell adhesion, migration, proliferation, and lineage commitment. Significant advances have been made in deciphering how these nanoscale cues interact with stem cells to determine phenotype, but much is still unknown as to how the interplay between physical and chemical signals regulate in vitro and in vivo cellular fate. This review dives deeper to investigate nanoscale platforms for engineering tissue, as well use the use of these nanotechnologies to drive pluripotent stem cell lineage determination.

Construction and characterization of a novel vocal fold bioreactor

In vitro engineering of mechanically active tissues requires the presentation of physiologically relevant mechanical conditions to cultured cells. To emulate the dynamic environment of vocal folds, a novel vocal fold bioreactor capable of producing vibratory stimulations at fundamental phonation frequencies is constructed and characterized. The device is composed of a function generator, a power amplifier, a speaker selector and parallel vibration chambers. Individual vibration chambers are created by sandwiching a custom-made silicone membrane between a pair of acrylic blocks. The silicone membrane not only serves as the bottom of the chamber but also provides a mechanism for securing the cell-laden scaffold. Vibration signals, generated by a speaker mounted underneath the bottom acrylic block, are transmitted to the membrane aerodynamically by the oscillating air. Eight identical vibration modules, fixed on two stationary metal bars, are housed in an anti-humidity chamber for long-term operation in a cell culture incubator. The vibration characteristics of the vocal fold bioreactor are analyzed non-destructively using a Laser Doppler Vibrometer (LDV). The utility of the dynamic culture device is demonstrated by culturing cellular constructs in the presence of 200-Hz sinusoidal vibrations with a mid-membrane displacement of 40 µm. Mesenchymal stem cells cultured in the bioreactor respond to the vibratory signals by altering the synthesis and degradation of vocal fold-relevant, extracellular matrix components. The novel bioreactor system presented herein offers an excellent in vitro platform for studying vibration-induced mechanotransduction and for the engineering of functional vocal fold tissues.

Tenascin-C and mechanotransduction in the development and diseases of cardiovascular system

Living tissue is composed of cells and extracellular matrix (ECM). In the heart and blood vessels, which are constantly subjected to mechanical stress, ECM molecules form well-developed fibrous frameworks to maintain tissue structure. ECM is also important for biological signaling, which influences various cellular functions in embryonic development, and physiological/pathological responses to extrinsic stimuli. Among ECM molecules, increased attention has been focused on matricellular proteins. Matricellular proteins are a growing group of non-structural ECM proteins highly up-regulated at active tissue remodeling, serving as biological mediators. Tenascin-C (TNC) is a typical matricellular protein, which is highly expressed during embryonic development, wound healing, inflammation, and cancer invasion. The expression is tightly regulated, dependent on the microenvironment, including various growth factors, cytokines, and mechanical stress. In the heart, TNC appears in a spatiotemporal-restricted manner during early stages of development, sparsely detected in normal adults, but transiently re-expressed at restricted sites associated with tissue injury and inflammation. Similarly, in the vascular system, TNC is strongly up-regulated during embryonic development and under pathological conditions with an increase in hemodynamic stress. Despite its intriguing expression pattern, cardiovascular system develops normally in TNC knockout mice. However, deletion of TNC causes acute aortic dissection (AAD) under strong mechanical and humoral stress. Accumulating reports suggest that TNC may modulate the inflammatory response and contribute to elasticity of the tissue, so that it may protect cardiovascular tissue from destructive stress responses. TNC may be a key molecule to control cellular activity during development, adaptation, or pathological tissue remodeling.

Dynamic vibration cooperates with connective tissue growth factor to modulate stem cell behaviors

Vocal fold disorders affect 3-9% of the U.S. population. Tissue engineering offers an alternative strategy for vocal fold repair. Successful engineering of vocal fold tissues requires a strategic combination of therapeutic cells, biomimetic scaffolds, and physiologically relevant mechanical and biochemical factors. Specifically, we aim to create a vocal fold-like microenvironment to coax stem cells to adopt the phenotype of vocal fold fibroblasts (VFFs). Herein, high frequency vibratory stimulations and soluble connective tissue growth factor (CTGF) were sequentially introduced to mesenchymal stem cells (MSCs) cultured on a poly(ɛ-caprolactone) (PCL)-derived microfibrous scaffold for a total of 6 days. The initial 3-day vibratory culture resulted in an increased production of hyaluronic acids (HA), tenascin-C (TNC), decorin (DCN), and matrix metalloproteinase-1 (MMP1). The subsequent 3-day CTGF treatment further enhanced the cellular production of TNC and DCN, whereas CTGF treatment alone without the vibratory preconditioning significantly promoted the synthesis of collagen I (Col 1) and sulfated glycosaminoglycans (sGAGs). The highest level of MMP1, TNC, Col III, and DCN production was found for cells being exposed to the combined vibration and CTGF treatment. Noteworthy, the vibration and CTGF elicited a differential stimulatory effect on elastin (ELN), HA synthase 1 (HAS1), and fibroblast-specific protein-1 (FSP-1). The mitogenic activity of CTGF was only elicited in naïve cells without the vibratory preconditioning. The combined treatment had profound, but opposite effects on mitogen-activated protein kinase (MAPK) pathways, Erk1/2 and p38, and the Erk1/2 pathway was critical for the observed mechano-biochemical responses. Collectively, vibratory stresses and CTGF signals cooperatively coaxed MSCs toward a VFF-like phenotype and accelerated the synthesis and remodeling of vocal fold matrices.

From mechanical stimulation to biological pathways in the regulation of stem cell fate

Mechanical stimuli are important in directing the fate of stem cells; the effects of mechanical stimuli reported in recent research are reviewed here. Stem cells normally undergo two fundamental processes: proliferation, in which their numbers multiply, and differentiation, in which they transform into the specialized cells needed by the adult organism. Mechanical stimuli are well known to affect both processes of proliferation and differentiation, although the complete pathways relating specific mechanical stimuli to stem cell fate remain to be elucidated. We identified two broad classes of research findings and organized them according to the type of mechanical stress (compressive, tensile or shear) of the stimulus. Firstly, mechanical stress of any type activates stretch-activated channels (SACs) on the cell membrane. Activation of SACs leads to cytoskeletal remodelling and to the expression of genes that regulate the basic growth, survival or apoptosis of the cells and thus regulates proliferation. Secondly, mechanical stress on cells that are physically attached to an extracellular matrix (ECM) initiates remodelling of cell membrane structures called integrins. This second process is highly dependent on the type of mechanical stress applied and result into various biological responses. A further process, the Wnt pathway, is also implicated: crosstalk between the integrin and Wnt pathways regulates the switch from proliferation to differentiation and finally regulates the type of differentiation. Therefore, the stem cell differentiation process involves different signalling molecules and their pathways and most likely depends upon the applied mechanical stimulation.

Comparing the effect of equiaxial cyclic mechanical stimulation on GATA4 expression in adipose-derived and bone marrow-derived mesenchymal stem cells

Myocardium is prone to mechanical stimuli among which pulsatile blood flow exerts both radial and longitudinal strains on the heart. Recent studies have shown that mechanical stimulation can notably influence regeneration of cardiac muscle cells. GATA4 is a cardiac-specific transcription factor that plays an important role in late embryonic heart development. Our study aimed at investigating the effect of equiaxial cyclic strain on GATA4 expression in adipose-derived (ASCs) and bone marrow-derived (BMSCs) mesenchymal stem cells. For this reason, both ASCs and BMSCs were studied in four distinct groups of chemical, mechanical, mechano-chemical and negative control. According to this categorisation, the cells were exposed to cyclic mechanical loading and/or 5-azacytidine as the chemical factor. The level of GATA4 expression was then quantified using real-time PCR method on the first, fourth and seventh days. The results show that: (1) equiaxial cyclic stimulation of mesenchymal stem cells could promote GATA4 expression from the early days of induction and as it went on, its combination with chemical factor elevated expression; (2) cyclic strain could accelerate GATA4 expression compared to the chemical factor; (3) in this regard, these results indicate a higher capacity of ASCs than BMSCs to express GATA4.

Adaptation capacity of microcirculatory bed of the skin under conditions of high-frequency rate fractionated automated tibial elongation

The status of the microcirculatory bed in the skin in the bone regenerate projection was studied under conditions of fractionated automated tibial elongation by transosteal distraction osteosynthesis at a rate of 3 mm/day in adult mongrel dogs. Histological and physiological data indicated that the distraction period was associated with changes in the functional components of the skin microcirculatory bed. Active neovasculogenesis and formation of additional arteriovenular anastomoses provided sufficient oxygenation of tissues and maintained venous outflow. This led to rapid recovery of the functional potentialities of skin microvessels as early as 1 month after the end of forced fixation.

Wound healing: a paradigm for regeneration

Human skin is a remarkably plastic organ that sustains insult and injury throughout life. Its ability to expeditiously repair wounds is paramount to survival and is thought to be regulated by wound components such as differentiated cells, stem cells, cytokine networks, extracellular matrix, and mechanical forces. These intrinsic regenerative pathways are integrated across different skin compartments and are being elucidated on the cellular and molecular levels. Recent advances in bioengineering and nanotechnology have allowed researchers to manipulate these microenvironments in increasingly precise spatial and temporal scales, recapitulating key homeostatic cues that may drive regeneration. The ultimate goal is to translate these bench achievements into viable bedside therapies that address the growing global burden of acute and chronic wounds. In this review, we highlight current concepts in cutaneous wound repair and propose that many of these evolving paradigms may underlie regenerative processes across diverse organ systems.

The role of focal adhesion complexes in fibroblast mechanotransduction during scar formation

Historically, great efforts have been made to elucidate the biochemical pathways that direct the complex process of wound healing; however only recently has there been recognition of the importance that mechanical signals play in the process of tissue repair and scar formation. The body's physiologic response to injury involves a dynamic interplay between mechanical forces and biochemical cues which directs a cascade of signals leading ultimately to the formation of fibrotic scar. Fibroblasts are a highly mechanosensitive cell type and are also largely responsible for the generation of the fibrotic matrix during scar formation and are thus a critical player in the process of mechanotransduction during tissue repair. Mechanotransduction is initiated at the interface between the cell membrane and the extracellular matrix where mechanical signals are first translated into a biochemical response. Focal adhesions are dynamic multi-protein complexes through which the extracellular matrix links to the intracellular cytoskeleton. These focal adhesion complexes play an integral role in the propagation of this initial mechanical cue into an extensive network of biochemical signals leading to widespread downstream effects including the influx of inflammatory cells, stimulation of angiogenesis, keratinocyte migration, fibroblast proliferation and collagen synthesis. Increasing evidence has demonstrated the importance of the biomechanical milieu in healing wounds and suggests that an integrated approach to the discovery of targets to decrease scar formation may prove more clinically efficacious than previous purely biochemical strategies.

Modulating the behaviors of mesenchymal stem cells via the combination of high-frequency vibratory stimulations and fibrous scaffolds

We are interested in the in vitro engineering of artificial vocal fold tissues via the strategic combination of multipotent mesenchymal stem cells (MSCs), physiologically relevant mechanical stimulations, and biomimetic artificial matrices. We have constructed a vocal fold bioreactor that is capable of imposing vibratory stimulations on the cultured cells at human phonation frequencies. Separately, fibrous poly (ɛ-caprolactone) (PCL) scaffolds emulating the ligamentous structure of the vocal fold were prepared by electrospinning, were incorporated in the vocal fold bioreactor, and were driven into a wave-like motion in an axisymmetrical fashion by the oscillating air. MSC-laden PCL scaffolds were subjected to vibrations at 200 Hz with a normal center displacement of ∼40 μm for a total of 7 days. A continuous (CT) or a 1 h-on-1 h-off (OF) regime with a total dynamic culture time of 12 h per day was applied. The dynamic loading did not cause any physiological trauma to the cells. Immunohistotochemical staining revealed the reinforcement of the actin filament and the enhancement of α5β1 integrin expression under selected dynamic culture conditions. Cellular expression of essential vocal fold extracellular matrix components, such as elastin, hyaluronic acid, and matrix metalloproteinase-1, was significantly elevated as compared with the static controls, and the OF regime is more conducive to matrix production than the CT vibration mode. Analyses of genes of typical fibroblast hallmarks (tenascin-C, collagen III, and procollagen I) as well as markers for MSC differentiation into nonfibroblastic lineages confirmed MSCs' adaptation of fibroblastic behaviors. Overall, the high-frequency vibratory stimulation, when combined with a synthetic fibrous scaffold, serves as a potent modulator of MSC functions. The novel bioreactor system presented here, as a versatile, yet well-controlled model, offers an in vitro platform for understanding vibration-induced mechanotransduction and for engineering of functional vocal fold tissues.

Autologous platelet-rich clot releasate stimulates proliferation and inhibits differentiation of adult rat tendon stem cells towards nontenocyte lineages

OBJECTIVE

To explore the effects of autologous platelet-rich clot releasate (PRCR) on proliferation and differentiation of adult rat tendon stem cells (TSCs) in vitro, following intense mechanical stretching.

METHODS

TSCs were subjected to 8% mechanical stretching and subsequently incubated in control medium or medium supplemented with 2% or 10% PRCR. Collagen types I and III, peroxisome proliferator-activated receptor-γ (PPARγ), sex determining region Y-box 9 (SOX-9) and runt-related transcription factor 2 (RUNX2) concentrations were assessed via Western blotting and flow cytometry. Transforming growth factor (TGF)-β1 and vascular endothelial growth factor concentrations were measured using enzyme-linked immunosorbent assay. Treated TSCs were also cultured in adipogenic, chondrogenic or osteogenic culture media.

RESULTS

PRCR increased the number of TSCs, and the concentrations of collagen types I and III and TGF-β1. In contrast, PRCR significantly reduced PPARγ, SOX-9 and RUNX2-positive cell numbers, and significantly reduced the numbers of TSC-derived adipocytes, chondrocytes and osteocytes.

CONCLUSION

PRCR induced tenocyte differentiation while suppressing the adipocyte, chondrocyte and osteocyte lineages believed to impede tendon healing.