Precise tissue bioengineering and niches of mesenchymal stem cells: Their size and hierarchy matter

Stem cell microterritories (niches), as a specialized part of the extracellular matrix (ECM), are considered an important target and tool for the development of new materials, medical implants, and devices. However, tissue bioengineering products that have stem cell niches of known size on the surface or in the bulk structure of artificial materials are practically unknown. This brief review attempts to draw attention to the problematic aspects of niches as specific parts of the ECM, such as their hierarchy and size for mesenchymal stromal/stem cells (MSCs). These parameters arise directly from numerous definitions of stem cell niches as specialized morphological microterritories found in various tissues. The authors of this review analyze the known information on the hierarchy of MSC microterritories by analogy with that of hematopoietic stem cells. Occasional reports on the size of artificial MSC niches compared to natural niche candidates are summarized. A consensus on a hierarchy and optimal range of niche sizes for MSCs and other stem cells is needed to accelerate the development of prototyping technologies and additive manufacturing in applications to precise tissue bioengineering and regenerative medicine.     

Tuning mesenchymal stem cell secretome therapeutic potential through mechanotransduction

Mesenchymal stem cells (MSCs) and their byproducts have been widely validated as potential therapeutic products for regenerative medicine. The therapeutic effects result mainly from the paracrine activity of MSCs, which consists of the secretion of bioactive molecules, whether dispersed in medium conditioned by cell culture or encapsulated in extracellular vesicles. The composition of the MSC secretome, which represents the set of these secreted cellular products, is crucial for the performance of the desired therapeutic functions. Different cell culture strategies have been employed to adjust the secretome composition of MSCs to obtain the best therapeutic responses for different clinical contexts. However, the manipulation of culture conditions has focused mainly on the use of different biochemical elements for the preconditioning of MSCs and less on the physical conditions of the cell culture environment. Herein, we offer our point of view regarding the importance of the physical properties of cell culture substrates and their mechanotransduction responses in preconditioning the MSCs secretome. We highlight the relevance of studying mechanotransduction events associating cell morphology and the modulation of gene expression to customize and expand the use of MSCs secretomes.     

Ultrastructural evaluation of mesenchymal stem cells from inflamed periodontium in different in vitro conditions

This research aimed to observe the behavior of mesenchymal stem cells (MSCs) isolated from periodontal granulation tissue (gt) when manipulated ex vivo to induce three‐dimensional (3D) spheroid (aggregates) formation as well as when seeded on two bone scaffolds of animal origin. Periodontal gt was chosen as a MSC source because of its availability, considering that it is eliminated as a waste material during conventional surgical therapies. 3D aggregates of cells were generated; they were grown for 3 and 7 days, respectively, and then prepared for transmission electron microscopic analysis. The two biomaterials were seeded for 72 h with gtMSCs and prepared for scanning electronic microscopic observation. The ultrastructural analysis of 3D spheroids remarked some differences between the inner and the outer cell layers, with a certain commitment observed at the inner cells. Both scaffolds showed a relatively smooth surface at low magnification. Macro‐ and micropores having a scarce distribution were observed on both bone substitutes. gtMSCs grew with relative difficulty on the biomaterials. After 72 h of proliferation, gtMSCs scarcely covered the surface of bovine bone scaffolds, demonstrating fibroblast‐like or star‐like shapes with elongated filiform extensions. Our results add other data on the possible usefulness of gtMSC and could question the current paradigm regarding the complete removal of chronically inflamed gts from the defects during periodontal surgeries. Until optimal protocols for ex vivo manipulation of MSCs are available for clinical settings, it is advisable to use biocompatible bone substitutes that allow the development of progenitor cells. Microsc. Res. Tech. 78:792–800, 2015. © 2015 Wiley Periodicals, Inc.     

Mesenchymal stem cells derived secretome as an innovative cell-free therapeutic approach

The paracrine and immunomodulatory cytokines secreted by mesenchymal stem cells (MSCs), generally referred to as the MSCs derived secretome, has substantial potential for the treatment of many chronic and degenerative diseases. MSCs secretome contains both common and disease specific cytokines and modulators that can be beneficial against a wide range of chronic diseases. Herein, we discuss the MSCs secretome composition profile and its translational applicability and the challenges surrounding its use in clinical settings.     

Mesenchymal stem cell secretome and nanotechnology: Combining therapeutic strategies

Mesenchymal stem cells (MSC) have pushed the field of stem cell-based therapies by inducing tissue regeneration, immunosuppression, and angiogenesis mainly through vesicles and soluble factors release (paracrine signaling). MSC-extracellular vesicles (MSC-EV) adaptable secretome and homing to injured sites allowed researchers to unlock a new era of cell-free based therapy. In parallel, nanoparticles (NP) have been explored in contributing to transport and drug delivery systems, giving drugs desired physical-chemical properties to exploit cell behavior. However, NPs can be quickly recognized by immune cells and cleared from circulation. In this viewpoint, we explore how combining both therapeutic strategies can improve efficacy and circumvent limitations of both therapies. MSCEV benefit from the potent MSC membrane composition, guiding chemotaxis to tumor sites, a very restricted microenvironment. MSC-EV has low immunogenicity, high stability, long half-life and can explore tissue targeting ligands as a precise drug carry, even across biological barriers. Those properties promote enhanced targeted drug delivery that can be combined with NP, exploring biological membrane production through: 1. direct cell therapy with NP-infused MSC; 2. NP-containing MSC-EV generated by NP-infused MSC; 3. by coating NP in MSC membrane (“MSC NanoGhosts”), allowing precise cargo definition without losing targeting. Therefore, nanotechnology combined with cell-based therapeutic resources can greatly improve targeted drug delivery, improving efficacy and opening a new venue of therapeutic possibilities.     

Dexmedetomidine alleviates oxygen and glucose deprivation-induced apoptosis in mesenchymal stem cell via downregulation of MKP-1

Bone marrow mesenchymal stem cell (MSC)-based therapy is a novel candidate for heart repair. But ischemia-reperfusion injury leads to low viability of MSC. Dexmedetomidine (Dex) has been found to protect neurons against ischemia-reperfusion injury. It remains unknown if Dex could increase the viability of MSCs under ischemia. The present study is to observe the potential protective effect of Dex on MSCs under ischemia and its underlying mechanisms. Specific mRNAs related to myocardial ischemia in the GEO database were selected from the mRNA profiles assessed in a previous study using microarray. The most dysregulated mRNAs of the specific ones from the above study were subject to bioinformatics analysis at our laboratory. These dysregulated mRNAs possibly regulated apoptosis of cardiomyocytes and were validated in vitro for their protective effect on MSCs under ischemia. MSCs were pre-treated with Dex at 10 μM concentration for 24 h under oxygen-glucose deprivation (OGD). Flow cytometry and TUNEL assay were carried out to detect apoptosis in Dex-pretreated MSCs under OGD. The relative expressions of mitogen-activated protein kinase phosphatase 1 (MKP-1) and related genes were detected by quantitative polymerase chain reaction and western blotting. Microarray data analysis revealed that Dex regulates MAPK phosphatase activity. Dex significantly reduced in vitro apoptosis of MSCs under OGD, which suppressed the synthesis level of Beclin1 and light chain 3 proteins. Dex down-regulated MKP-1 expression and attenuated an OGD-induced change in the mitogen activated protein kinase 3 (MAPK3) signaling pathway. Dex increases the viability of MSC and improves its tolerance to OGD in association with the MKP-1 signaling pathway, thus suggesting the potential of Dex as a novel strategy for promoting MSCs efficacy under ischemia.     

OPTIMIZATION OF ELECTRO-CHEMICAL MACHINING PROCESS PARAMETERS USING GENETIC ALGORITHMS

ECM and ECM-based processes (derived and hybrid processes) are one of the most widely used advanced machining processes (AMPs) to make complicated shapes of varying sizes in the products made of electrically conducting but difficult-to-machine materials such as superalloys, Ti-alloys, alloy steel, tool steel, stainless steel, etc. These materials are extensively used in aerospace, automobile, space, nuclear, defense, cutting tools, dies and mold making applications. ECM offers some unique advantages over other conventional and advanced machining processes but its use incurs relatively higher initial investment cost, operating cost, tooling cost, and maintenance cost. Use of optimum ECM process parameters can significantly reduce the ECM operating, tooling, and maintenance cost and will produce components of higher accuracy which is very important in some critical areas such as aerospace, space, defense, nuclear applications. Therefore, choice of optimum process parameters is essential to ensure the most cost-effective, efficient, and economic utilization of ECM process potentials. This paper describes optimization of three most important ECM process parameters namely tool feed rate, electrolyte flow velocity, and applied voltage with an objective to minimize geometrical inaccuracy subjected to temperature, choking, and passivity constraints using real-coded genetic algorithms. Comparison of the obtained optimization results with the results of past work in this direction shows an improvement in terms of geometrical accuracy.     

The antioxidant trolox inhibits aging and enhances prostaglandin E-2 secretion in mesenchymal stem cells

Mesenchymal stem cells (MSCs) have been widely used in regenerative medicine and clinical therapy due to their capabilities of proliferation, differentiation, and immune regulation. However, during in vitro expansion, MSCs are prone to aging, which largely limits their application. Prostaglandin E-2 (PGE-2) is a key effector secreted by MSCs to exert immunomodulatory effects. By screening the compound library for PGE-2 secretion, the antioxidant trolox was verified as a stimulator of MSCs to secrete PGE-2. The effect of antioxidant trolox on biological characteristics of MSCS, including aging, proliferation, and gene expression, was examined. The results demonstrated that trolox can resist aging, promote proliferation, and enhance PGE-2 secretion of MSCs without affecting their surface marker expression. Furthermore, trolox treatment up-regulates miR-17-92 clusters in MSCs and may contribute to its anti-aging effects. Thus, trolox addition might be beneficial for MSCs expansion and their application.     

Temperature-driven processing techniques for manufacturing fully interconnected porous scaffolds in bone tissue engineering

The development of structures with a predefined multiscale pore network is a major challenge in designing tissue engineering (TE) scaffolds. To address this, several strategies have been investigated to provide biocompatible, biodegradable porous materials that would be suitable for use as scaffolds, and able to guide and facilitate the cell activity involved in the generation of new tissue regeneration. This study seeks to provide an overview of different temperature-driven process technologies for developing scaffolds with tailored porosity, in which pore size distribution is strictly defined and pores are fully interconnected. Here, three-dimensional (3D) porous composite scaffolds based on poly(epsilon-caprolactone) (PCL) were fabricated by thermally induced phase separation (TIPS) and by melt co-continuous polymer blending (MCPB). The combination of these processes with a salt leaching technique enables the establishment of bimodal porosity within the polymer network. This feature may be exploited in the development of substrates with fully interconnected pores, which can be used effectively for tissue regeneration. Various combinations of the proposed techniques provide a range of procedures for the preparation of porous scaffolds with an appropriate combination of morphological and mechanical properties to reproduce the requisite features of the extracellular matrix (ECM) of hard tissues such as bone.     

Application of adaptive neuro-fuzzy inference system and cuckoo optimization algorithm for analyzing electro chemical machining process

Electrochemical machining process (ECM) is increasing its importance due to some of the specific advantages which can be exploited during machining operation. The process offers several special privileges such as higher machining rate, better accuracy and control, and wider range of materials that can be machined. Contribution of too many predominate parameters in the process, makes its prediction and selection of optimal values really complex, especially while the process is programmized for machining of hard materials. In the present work in order to investigate effects of electrolyte concentration, electrolyte flow rate, applied voltage and feed rate on material removal rate (MRR) and surface roughness (SR) the adaptive neuro-fuzzy inference systems (ANFIS) have been used for creation predictive models based on experimental observations. Then the ANFIS 3D surfaces have been plotted for analyzing effects of process parameters on MRR and SR. Finally, the cuckoo optimization algorithm (COA) was used for selection solutions in which the process reaches maximum material removal rate and minimum surface roughness simultaneously. Results indicated that the ANFIS technique has superiority in modeling of MRR and SR with high prediction accuracy. Also, results obtained while applying of COA have been compared with those derived from confirmatory experiments which validate the applicability and suitability of the proposed techniques in enhancing the performance of ECM process.     

振动筛下横梁结构的有限元分析

用Patran、Nastran软件建立并计算了振动筛下横梁的有限元模型,讨论了网格划分的数量不同对计算结果的影响,不同形状的网格在不同位置对计算结果的影响;还计算了不同位置、不同深度的裂纹对下横梁模态参数的影响.结果表明裂纹对固有频率有明显影响,但对模态振型影响不大.     

MSCs derived extracellular vesicles as a therapeutic paragon for neurodegenerative disorders: A viewpoint

Neurodegenerative disorders are a vicious woe to the public health and wellness. Uncertainty in their underlying causes, lack of effective biomarkers for their early detection, existence of only supportive therapy, and their ever rising incidence creates an unmatched need for targeted therapies. Mesenchymal Stem Cells (MSCs) have found to be promising candidates for regenerative and remedial therapy in neurodegenerative disorders, however several biological risks and practical issues impede in their translational utility. Deriving from MSCs are certain Extracellular Vesicles (EVs), which aid in the paracrine action of MSCs and have lately gained the scientific interest for their implacability in diverse set ups. Their cargo is of utmost importance and is being explored in various different diseases like heart diseases, neuronal diseases, respiratory diseases and hepatic diseases. They thereby hold the position of a likely prospective remedial candidate for therapy against neurodegenerative disorders.     

<Emphasis Type="Italic">Development of a Tissue Engineering Scaffold Structure Library for Rapid Prototyping. Part 1: Investigation and Classification</Emphasis>

In tissue engineering (TE), a porous scaffold structure may be required as a template to guide the proliferation, growth and development of cells appropriately in three dimensions. Although TE scaffolds can be created using one of many conventional techniques available, most will suffer from a lack of mechanical strength and/or uniformity in pore distribution and sizes. This study is focused on creating scaffolds using rapid prototyping (RP) techniques. Utilising these novel techniques, a computer-aided design (CAD) of the scaffold structure must first be modelled. The scaffold structure is then fabricated directly from CAD data using a RP system. The objective of this research is to (1) investigate and select various polyhedral shapes suitable for scaffold modelling, (2) classify the selected unit cells, (3) create a parametric library of scaffold structures and (4) verify by building the CAD models using the selective laser sintering process. The first two objectives are covered in Part 1 of this two-part paper. The remaining objectives will be described and discussed in Part 2. ID="A1"Correspondance and offprint requests to: Dr C. K. Chua, School of Mechanical and Production Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798. E-mail: mckchua@ntu.edu.sg     

Understanding cell-extracellular matrix interactions for topology-guided tissue regeneration

Tissues are made up of cells and the extracellular matrix (ECM) which surrounds them. These cells and tissues are actively adaptable to enduring significant stress that occurs in daily life. This astonishing mechanical stress develops due to the interaction between the live cells and the non-living ECM. Cells in the matrix microenvironment can sense the signals and forces produced and initiate a signaling cascade that plays a crucial role in the body’s normal functioning and influences various properties of the native cells, including growth, proliferation, and differentiation. However, the matrix’s characteristic features also impact the repair and regeneration of the damaged tissues. The current study reviewed how the cell-ECM interaction regulates cellular behavior and physicochemical properties. Herein, we have described the response of cells to mechanical stresses, the importance of substrate stiffness and geometry in tissue regeneration, and the development of scaffolds to mimic the nature of native ECM in 3D for tissue engineering applications has also been discussed. Finally, the study summarizes the conclusions and promising prospects based on the cell-ECM interplay.     

SEM sample preparation for cells on 3D scaffolds by freeze-drying and HMDS

Common dehydration methods of cells on biomaterials for scanning electron microscopy (SEM) include air drying, hexamethyldisilazane (HMDS) or tetramethysilane (TMS) treatment and critical point drying (CPD). On the other side, freeze-drying has been widely employed in dehydrating biological samples and also in preparing porous biomaterial scaffolds but not in preparing cells on three-dimensional (3D) biomaterials for SEM examination. In this study, we compare cells on porous hydroxyapatite (HA) prepared by air drying, HMDS and freeze-drying. The effects of fixation and using phosphate buffered saline (PBS) in the fixation were also assessed on three porous calcium phosphate (CaP) materials, namely, HA, α-tricalcium phosphate (α-TCP) and β-tricalcium phosphate (β-TCP) samples. There is no significant difference in samples prepared by HMDS treatment and freeze-drying viewed at low magnification. Besides, it is better not to use phosphate buffer in the fixation step for CaP materials to avoid undesirable spontaneous precipitation of CaPs. On the other hand, fewer exchanges of liquids are required for freeze-drying and hence chemical fixation may not be absolutely required for samples prepared by freeze-drying. Other technical details of the preparation were also investigated and discussed. This study suggests both HMDS and freeze-drying can be employed to dehydrate cells on 3D scaffolds for SEM examination.     

Mesenchymal stem cells,secretome and biomaterials in <i>in-vivo</i> animal models: Regenerative medicine application in cutaneous wound healing

The treatment of nonhealing and chronic cutaneous wounds still needs a clinical advancement to be effective. Both mesenchymal stem cells (MSCs), obtained from different sources, and their secretome derived thereof (especially exosomes) can activate signaling pathways related to promotion of cell migration, vascularization, collagen deposition, and inflammatory response demonstrating prohealing, angiogenetic and anti-scarring capacities. On the other hand, biodegradable biomimetic scaffolds can facilitate endogenous cell attachment and proliferation as well as extracellular matrix production. In this Review, we revise the complex composites made by biomimetic scaffolds, mainly hydrogels, and MSC-derived exosomes constructed for cutaneous wound healing. Studies demonstrate that there exists a synergistic action of scaffolds with encapsulated exosomes, displaying a sustained release profiles to facilitate longlasting healing effects. It can be envisioned that dressings made by biomimetic hydrogels and MSC-derived exosomes will be clinically applied in the near future for the effective treatment of nonhealing and chronic wounds.     

特种车辆发动机支架模态分析

利用有限元理论以及大型通用有限元分析软件MSC.Nastran(前、后置处理软件采用MSC.Patran)对发动机支架进行了自由模态的有限元分析,得出该发动机支架的前十阶模态参数(固有频率和模态振型),计算结果对特种车辆采取减振降噪措施具有一定的参考价值。     

Mechanical and histological properties of an electrospun scaffold with a modified surface by plasma polymerization implanted in an <i>in vivo</i> model

This article presents the construction of scaffolds composed of polylactic acid (PLA) with different concentrations of hydroxyapatite (HA) by electrospinning, which were superficially modified with polypyrrole (PPy/I) by plasma polymerization. A preliminary study was conducted of the biological and mechanical behavior of the scaffolds when they were implanted in the back of rabbits for 30 days; bone cells differentiated from mesenchymal stem cells (MSCs) were used. The bone cell and scaffold structures were characterized by histological, immunohistochemical, and mechanical stress tests. Hematoxylin–eosin staining showed good tissue conformation. The immunohistochemical tests highlighted the presence of the main bone tissue proteins, such as collagen, osteocalcin, and osteopontin. The PLA/HA scaffolds were observed to exhibit cell adhesion and proliferation properties; however, the response was much better in the scaffolds that had a higher concentration of HA and that were coated with PPy/I. The results of the mechanical tests of the scaffolds indicated that the plasma treatment improved the adhesion and cell proliferation properties and contributed to the mechanical support, allowing the formation of neotissues with good viability of cell growth.     

Therapeutic mechanisms and routes of delivery of mesenchymal stem cells in veterinary medicine: A point of view

Mesenchymal stem cells (MSCs) represent an important tool in veterinary regenerative medicine due to their ability to home to injury sites and secrete molecules that regulate niches into regenerative microenvironments. Successful cell therapy depends on many factors, including choice of administration route and application of understanding of cell potency and their therapeutic mechanisms. In this point of view, the authors leverage the tumultuous history of the field to demonstrate the need for clinicians to continually update themselves as new discoveries are made in order to avoid misalignments in the future, especially regarding administration routes and dose frequency, as well as to explore recent insights into MSC plasticity, therapeutic mechanisms, and cell delivery systems.