Application of low-frequency alternating current electric fields via interdigitated electrodes: effects on cellular viability, cytoplasmic calcium, and osteogenic differentiation of human adipose-derived stem cells

3D-Printed conductive polymeric scaffolds with direct current electrical stimulation for enhanced bone regeneration

Various methods have been used to treat bone defects caused by genetic disorders, injury, or disease. Yet, there is still great need to develop alternative approaches to repair damaged bone tissue. Bones naturally exhibit piezoelectric potential, or the ability to convert mechanical stresses into electrical impulses. This phenomenon has been utilized clinically to enhance bone regeneration in conjunction with electrical stimulation (ES) therapies; however, oftentimes with critical-sized bone defects, the bioelectric potential at the site of injury is compromised, resulting in less desirable outcomes. In the present study, the potential of a 3D-printed conductive polymer blend to enhance bone formation through restoration of the bioelectrical microenvironment was evaluated. A commercially available 3D printer was used to create circular, thin-film scaffolds consisting of either polylactide (PLA) or a conductive PLA (CPLA) composite. Preosteoblast cells were seeded onto the scaffolds and subjected to direct current ES via a purpose-built cell culture chamber. It was found that CPLA scaffolds had no adverse effects on cell viability, proliferation or differentiation when compared with control scaffolds. The addition of ES, however, resulted in a significant increase in the expression of osteocalcin, a protein indicative of osteoblast maturation, after 14 days of culture. Furthermore, xylenol orange staining also showed the presence of increased mineralized calcium nodules in cultures undergoing stimulation. This study demonstrates the potential for low-cost, conductive scaffolding materials to support cell viability and enhance in vitro mineralization in conjunction with ES.

Effects of Electrical Stimulation on Articular Cartilage Regeneration with a Focus on Piezoelectric Biomaterials for Articular Cartilage Tissue Repair and Engineering

There is increasing evidence that chondrocytes within articular cartilage are affected by endogenous force-related electrical potentials. Furthermore, electrical stimulation (ES) promotes the proliferation of chondrocytes and the synthesis of extracellular matrix (ECM) molecules, which accelerate the healing of cartilage defects. These findings suggest the potential application of ES in cartilage repair. In this review, we summarize the pathogenesis of articular cartilage injuries and the current clinical strategies for the treatment of articular cartilage injuries. We then focus on the application of ES in the repair of articular cartilage in vivo. The ES-induced chondrogenic differentiation of mesenchymal stem cells (MSCs) and its potential regulatory mechanism are discussed in detail. In addition, we discuss the potential of applying piezoelectric materials in the process of constructing engineering articular cartilage, highlighting the important advances in the unique field of tissue engineering.

Ultrasound-Driven On-Demand Transient Triboelectric Nanogenerator for Subcutaneous Antibacterial Activity

To prevent surgical site infection (SSI), which significantly increases the rate morbidity and mortality, eliminating microorganisms is prominent. Antimicrobial resistance is identified as a global health challenge. This work proposes a new strategy to eliminate microorganisms of deep tissue through electrical stimulation with an ultrasound (US)-driven implantable, biodegradable, and vibrant triboelectric nanogenerator (IBV-TENG). After a programmed lifetime, the IBV-TENG can be eliminated by provoking the on-demand device dissolution by controlling US intensity with no surgical removal of the device from the body. A voltage of ≈4 V and current of ≈22 µA generated from IBV-TENG under ultrasound in vitro, confirming inactivating ≈100% of Staphylococcus aureus and ≈99% of Escherichia coli. Furthermore, ex vivo results show that IBV-TENG implanted under porcine tissue successfully inactivates bacteria. This antibacterial technology is expected to be a countermeasure strategy against SSIs, increasing life expectancy and healthcare quality by preventing microorganisms of deep tissue.

Long-term stimulation with alternating electric fields modulates the differentiation and mineralization of human pre-osteoblasts

Biophysical stimulation by electric fields can promote bone formation in bone defects of critical size. Even though, long-term effects of alternating electric fields on the differentiation of osteoblasts are not fully understood. Human pre-osteoblasts were stimulated over 31 days to gain more information about these cellular processes. An alternating electric field with 0.7 V_rms and 20 Hz at two distances was applied and viability, mineralization, gene expression, and protein release of differentiation factors were analyzed. The viability was enhanced during the first days of stimulation. A higher electric field resulted in upregulation of typical osteogenic markers like osteoprotegerin, osteopontin, and interleukin-6, but no significant changes in mineralization. Upregulation of the osteogenic markers could be detected with a lower electric field after the first days of stimulation. As a significant increase in the mineralized matrix was identified, an enhanced osteogenesis due to low alternating electric fields can be assumed.

Electromagnetic Fields Generated by the IteraCoil Device Differentiate Mesenchymal Stem Progenitor Cells Into the Osteogenic Lineage

Rapid advances in mesenchymal stem progenitor cells (MSPCs) have rendered impetus into the area of cell therapy and regenerative medicine. The main promise of future stem cell therapies is their reliance on autologous stem cells derived from adipose tissue, which also includes treatments of bone fractures and degeneration. The effectiveness of different electric devices utilized to reprogram MSPCs toward osteogenic differentiation has provided varying degrees of effectiveness for clinical use. Adipose tissue-derived MSPCs were flow-cytometrically characterized and further differentiated into osteoblasts by culturing either in growth medium with pro-osteogenic supplements or without supplements with alternating electromagnetic field (EMF) generated by IteraCoil. IteraCoil is a multi-solenoid coil with a specific complex geometry that creates a 3D-EMF with desired parameters without directly applying electrodes to the cells and tissues. The flow-cytometric analysis of highly enriched (≥95%) adipose-derived MSPCs (CD34^- , CD73⁺ , CD90⁺ , and CD105⁺ ) was utilized for the study. Osteoblasts and chondrocyte differentiations were then assessed by specific staining and quantified using ImageJ (National Institutes of Health). The osteoblastic differentiation of MSPCs cultured in regular medium and exposed to EMF at 0.05 and 1 kHz frequencies was compared with MSPCs cultured in a pro-osteogenic supplemented medium. In this study, we demonstrated that EMF from IteraCoil might have affected the signaling pathways that induce the osteogenic differentiation of human adipose-derived MSPCs in the absence of exogenous osteogenic factors. Therefore, EMF-generated osteogenic differentiation of reprogrammed adipose-derived autologous MSPCs may treat the loss of osteoblasts and osteoporosis and open new avenues for the development of regenerative cellular therapy. © 2022 Bioelectromagnetics Society.

[Methods of improving the mechanical properties of hydrogels and their research progress in bone tissue engineering]

OBJECTIVE

To review the methods of improving the mechanical properties of hydrogels and the research progress in bone tissue engineering.

METHODS

The recent domestic and foreign literature on hydrogels in bone tissue engineering was reviewed, and the methods of improving the mechanical properties of hydrogels and the effect of bone repair in vivo and in vitro were summarized.

RESULTS

Hydrogels are widely used in bone tissue engineering, but their mechanical properties are poor. Improving the mechanical properties of hydrogels can enhance bone repair. The methods of improving the mechanical properties of hydrogels include the construction of dual network structures, inorganic nanoparticle composites, introduction of conductive materials, and fiber network reinforcement. These methods can improve the mechanical properties of hydrogels to various degrees while also demonstrating a significant bone repair impact.

CONCLUSION

The mechanical properties of hydrogels can be effectively improved by modifying the system, components, and fiber structure, and bone repair can be effectively promoted.

Primary cilia in hard tissue development and diseases

Bone and teeth are hard tissues. Hard tissue diseases have a serious effect on human survival and quality of life. Primary cilia are protrusions on the surfaces of cells. As antennas, they are distributed on the membrane surfaces of almost all mammalian cell types and participate in the development of organs and the maintenance of homeostasis. Mutations in cilium-related genes result in a variety of developmental and even lethal diseases. Patients with multiple ciliary gene mutations present overt changes in the skeletal system, suggesting that primary cilia are involved in hard tissue development and reconstruction. Furthermore, primary cilia act as sensors of external stimuli and regulate bone homeostasis. Specifically, substances are trafficked through primary cilia by intraflagellar transport, which affects key signaling pathways during hard tissue development. In this review, we summarize the roles of primary cilia in long bone development and remodeling from two perspectives: primary cilia signaling and sensory mechanisms. In addition, the cilium-related diseases of hard tissue and the manifestations of mutant cilia in the skeleton and teeth are described. We believe that all the findings will help with the intervention and treatment of related hard tissue genetic diseases.

Hormesis and adult adipose-derived stem cells

This paper provides a detailed assessment of the occurrence of hormetic dose responses in adipose-derived stem cells (ADSCs) of animal models and humans. While a broad range of endpoints has been considered, the predominant research focus in the literature has involved cell proliferation and differentiation. Hormetic dose responses have been commonly reported for ADSCs, encompassing a broad range of chemicals, including pharmaceuticals, dietary supplements and endogenous agents as well as a broad range of physical stressors such as low frequency vibrations, electromagnetic frequency (EMF), heat and sound waves. Numerous agents upregulate key functions such as cell proliferation and differentiation in ADSCs, following the quantitative features of the hormesis dose response model. The paper also assesses the capacity of agents to selectively and dose-dependently activate cell proliferation and/or differentiation, their underlying mechanistic foundations and potential clinical implications. These findings indicate that hormetic dose responses are a prominent feature of ADSC biology and may have a determinant role in their potential clinical applications.

Enhanced osteogenic differentiation of mesenchymal stem cells on P(VDF-TrFE) layer coated microelectrodes

Electrical stimulation has been proved to be critical to regulate cell behavior. But, cell behavior is also susceptible to multiple parameters of the adverse interferences such as surface current, electrochemical reaction products, and non-uniform compositions, which often occur during direct electric stimulation. To effectively prevent the adverse interferences, a novel piezoelectric poly(vinylidene fluoride-trfluoroethylene)(P(VDF-TrFE)) layer was designed to coat onto the indium tin oxide (ITO) planar microelectrode. We found the electrical stimulation was able to regulate the osteogenic differentiation of mesenchymal stem cells (MSCs) through calcium-mediated PKC signaling pathway. Meanwhile, the surface charge of the designed P(VDF-TrFE) coating layer could be easily controlled by the pre-polarization process, which was demonstrated to trigger integrin-mediated FAK signaling pathway, finally up-regulating the osteogenic differentiation of MSCs. Strikingly, the crosstalk in the downstream of the two signaling cascades further strengthened the ERK pathway activation for osteogenic differentiation of MSCs. This P(VDF-TrFE) layer coated electrical stimulation microelectrodes therefore provide a distinct strategy to manipulate multiple-elements of biomaterial surface to regulate stem cell fate commitment.

Recent Developed Strategies for Enhancing Chondrogenic Differentiation of MSC: Impact on MSC-Based Therapy for Cartilage Regeneration

Articular cartilage is susceptible to damage, but its self-repair is hindered by its avascular nature. Traditional treatment methods are not able to achieve satisfactory repair effects, and the development of tissue engineering techniques has shed new light on cartilage regeneration. Mesenchymal stem cells (MSCs) are one of the most commonly used seed cells in cartilage tissue engineering. However, MSCs tend to lose their multipotency, and the composition and structure of cartilage-like tissues formed by MSCs are far from those of native cartilage. Thus, there is an urgent need to develop strategies that promote MSC chondrogenic differentiation to give rise to durable and phenotypically correct regenerated cartilage. This review provides an overview of recent advances in enhancement strategies for MSC chondrogenic differentiation, including optimization of bioactive factors, culture conditions, cell type selection, coculture, gene editing, scaffolds, and physical stimulation. This review will aid the further understanding of the MSC chondrogenic differentiation process and enable improvement of MSC-based cartilage tissue engineering.

Analysis of the Differential Gene and Protein Expression Profiles of Corneal Epithelial Cells Stimulated with Alternating Current Electric Fields

In cells, intrinsic endogenous direct current (DC) electric fields (EFs) serve as morphogenetic cues and are necessary for several important cellular responses including activation of multiple signaling pathways, cell migration, tissue regeneration and wound healing. Endogenous DC EFs, generated spontaneously following injury in physiological conditions, directly correlate with wound healing rate, and different cell types respond to these EFs via directional orientation and migration. Application of external DC EFs results in electrode polarity and is known to activate intracellular signaling events in specific direction. In contrast, alternating current (AC) EFs are known to induce continuous bidirectional flow of charged particles without electrode polarity and also minimize electrode corrosion. In this context, the present study is designed to study effects of AC EFs on corneal epithelial cell gene and protein expression profiles in vitro. We performed gene and antibody arrays, analyzed the data to study specific influence of AC EFs, and report that AC EFs has no deleterious effect on epithelial cell function. Gene Ontology results, following gene and protein array data analysis, showed that AC EFs influence similar biological processes that are predominantly responsive to organic substance, chemical, or external stimuli. Both arrays activate cytokine–cytokine receptor interaction, MAPK and IL-17 signaling pathways. Further, in comparison to the gene array data, the protein array data show enrichment of diverse activated signaling pathways through several interconnecting networks.

Electric field stimulation for tissue engineering applications

Electric fields are involved in numerous physiological processes, including directional embryonic development and wound healing following injury. To study these processes in vitro and/or to harness electric field stimulation as a biophysical environmental cue for organised tissue engineering strategies various electric field stimulation systems have been developed. These systems are overall similar in design and have been shown to influence morphology, orientation, migration and phenotype of several different cell types. This review discusses different electric field stimulation setups and their effect on cell response.

Changing Expression Profiles and Inclination to Competing Endogenous RNA Networks on MAPK Signaling Pathways of Human Adipose-Derived Stem Cells in a Direct Current Electric Field

Adipose-derived stem cells (ADSCs) are an abundant cell source and provide an easy way to harvest mesenchymal stem cells, which are the focus of considerable attention in regenerative medicine. Electric fields (EF) play roles in many biological events and have been reported to promote cell proliferation, migration, and differentiation. In this study, ADSCs were treated with a direct current electric field (DCEF) of either 0 (control group) or 300 mV/mm (EF group) for six hours. RNA screening and analysis revealed that 66, 164, 26, and 1310 circRNAs, lncRNAs, miRNAs, and mRNAs, respectively, were differentially expressed in the DCEF-treated ADSCs compared with untreated ADSCs. Differentially expressed mRNAs were enriched in the MAPK signaling pathway, TNF signaling pathway, and some other pathways. ANXA1, ERRFI1, JAG1, EPHA2, PRR9, and H2AFY2 were related to the keratinocyte differentiation process. Competing endogenous RNA (ceRNA) networks were constructed on the basis of genes in the MAPK signaling pathway. Twenty-one RNAs in the above networks were randomly chosen, and their expression was validated using qRT-PCR, which showed the same expression trends as the RNA sequencing analysis. The MAPK signaling pathway is of great importance in the ADSC processes that occur in a DCEF, including keratinocyte differentiation. Several ceRNAs may participate in the regulation of MAPK signaling. This study may give new insight into the proliferation, migration, and differentiation of ADSCs, which will be valuable for tissue engineering and regenerative medicine.

Alternating Electric Fields Modify the Function of Human Osteoblasts Growing on and in the Surroundings of Titanium Electrodes

Endogenous electric fields created in bone tissue as a response to mechanical loading are known to influence the activity and differentiation of bone and precursor cells. Thus, electrical stimulation offers an adjunct therapy option for the promotion of bone regeneration. Understanding the influence of electric fields on bone cell function and the identification of suitable electrical stimulation parameters are crucial for the clinical success of stimulation therapy. Therefore, we investigated the impact of alternating electric fields on human osteoblasts that were seeded on titanium electrodes, which delivered the electrical stimulation. Moreover, osteoblasts were seeded on collagen-coated coverslips near the electrodes, representing the bone stock surrounding the implant. Next, 0.2 V, 1.4 V, or 2.8 V were applied to the in vitro system with 20 Hz frequency. After one, three, and seven days, the osteoblast morphology and expression of osteogenic genes were analysed. The actin organisation, as well as the proliferation, were not affected by the electrical stimulation. Changes in the gene expression and protein accumulation after electrical stimulation were voltage-dependent. After three days, the osteogenic gene expression and alkaline phosphatase activity were up to 2.35-fold higher following the electrical stimulation with 0.2 V and 1.4 V on electrodes and coverslips compared to controls. Furthermore, collagen type I mRNA, as well as the amount of the C-terminal propeptide of collagen type I were increased after the stimulation with 0.2 V and 1.4 V, while the higher electrical stimulation with 2.8 V led to decreased levels, especially on the electrodes.

Investigation of The Cellular Response to Bone Fractures: Evidence for Flexoelectricity

The recent discovery of bone flexoelectricity (strain-gradient-induced electrical polarization) suggests that flexoelectricity could have physiological effects in bones, and specifically near bone fractures, where flexoelectricity is theoretically highest. Here, we report a cytological study of the interaction between crack stress and bone cells. We have cultured MC3T3-E1 mouse osteoblastic cells in biomimetic microcracked hydroxyapatite substrates, differentiated into osteocytes and applied a strain gradient to the samples. The results show a strong apoptotic cellular response, whereby mechanical stimulation causes those cells near the crack to die, as indicated by live-dead and caspase staining. In addition, analysis two weeks post-stimulation shows increased cell attachment and mineralization around microcracks and a higher expression of osteocalcin –an osteogenic protein known to be promoted by physical exercise. The results are consistent with flexoelectricity playing at least two different roles in bone remodelling: apoptotic trigger of the repair protocol, and electro-stimulant of the bone-building activity of osteoblasts.

Self-Activated Electrical Stimulation for Effective Hair Regeneration via a Wearable Omnidirectional Pulse Generator

Hair loss, a common and distressing symptom, has been plaguing humans. Various pharmacological and nonpharmacological treatments have been widely studied to achieve the desired effect for hair regeneration. As a nonpharmacological physical approach, physiologically appropriate alternating electric field plays a key role in the field of regenerative tissue engineering. Here, a universal motion-activated and wearable electric stimulation device that can effectively promote hair regeneration via random body motions was designed. Significantly facilitated hair regeneration results were obtained from Sprague-Dawley rats and nude mice. Higher hair follicle density and longer hair shaft length were observed on Sprague-Dawley rats when the device was employed compared to conventional pharmacological treatments. The device can also improve the secretion of vascular endothelial growth factor and keratinocyte growth factor and thereby alleviate hair keratin disorder, increase the number of hair follicles, and promote hair regeneration on genetically defective nude mice. This work provides an effective hair regeneration strategy in the context of a nonpharmacological self-powered wearable electronic device.

Electrical stimulation promotes the angiogenic potential of adipose-derived stem cells

Autologous fat transfer (AFT) is limited by post-operative volume loss due to ischemia-induced cell death in the fat graft. Previous studies have demonstrated that electrical stimulation (ES) promotes angiogenesis in a variety of tissues and cell types. In this study we investigated the effects of ES on the angiogenic potential of adipose-derived stem cells (ASC), important progenitor cells in fat grafts with proven angiogenic potential. Cultured human ASC were electrically stimulated for 72 hours after which the medium of stimulated (ES) and non-stimulated (control) ASC was analysed for angiogenesis-related proteins by protein array and ELISA. The functional effect of ES on angiogenesis was then assessed in vitro and in vivo. Nine angiogenesis-related proteins were detected in the medium of electrically (non-)stimulated ASC and were quantified by ELISA. The pro-angiogenic proteins VEGF and MCP-1 were significantly increased following ES compared to controls, while the anti-angiogenic factor Serpin E1/PAI-1 was significantly decreased. Despite increased levels of anti-angiogenic TSP-1 and TIMP-1, medium of ES-treated ASC significantly increased vessel density, total vessel network length and branching points in chorio-allantoic membrane assays. In conclusion, our proof-of-concept study showed that ES increased the angiogenic potential of ASC both in vitro and in vivo.

Human Neural Tissues from Neural Stem Cells Using Conductive Biogel and Printed Polymer Microelectrode Arrays for 3D Electrical Stimulation

Electricity is important in the physiology and development of human tissues such as embryonic and fetal development, and tissue regeneration for wound healing. Accordingly, electrical stimulation (ES) is increasingly being applied to influence cell behavior and function for a biomimetic approach to in vitro cell culture and tissue engineering. Here, the application of conductive polymer (CP) poly(3,4-ethylenedioxythiophene)-polystyrenesulfonate (PEDOT:PSS) pillars is described, direct-write printed in an array format, for 3D ES of maturing neural tissues that are derived from human neural stem cells (NSCs). NSCs are initially encapsulated within a conductive polysaccharide-based biogel interfaced with the CP pillar microelectrode arrays (MEAs), followed by differentiation in situ to neurons and supporting neuroglia during stimulation. Electrochemical properties of the pillar electrodes and the biogel support their electrical performance. Remarkably, stimulated constructs are characterized by widespread tracts of high-density mature neurons and enhanced maturation of functional neural networks. Formation of tissues using the 3D MEAs substantiates the platform for advanced clinically relevant neural tissue induction, with the system likely amendable to diverse cell types to create other neural and non-neural tissues. The platform may be useful for both research and translation, including modeling tissue development, function and dysfunction, electroceuticals, drug screening, and regenerative medicine.

Primary Cilia Exhibit Mechanosensitivity to Cyclic Tensile Strain and Lineage-Dependent Expression in Adipose-Derived Stem Cells

Non-motile primary cilia are dynamic cellular sensory structures and are expressed in adipose-derived stem cells (ASCs). We have previously shown that primary cilia are involved in chemically-induced osteogenic differentiation of human ASC (hASCs) in vitro. Further, we have reported that 10% cyclic tensile strain (1 Hz, 4 hours/day) enhances hASC osteogenesis. We hypothesize that primary cilia respond to cyclic tensile strain in a lineage dependent manner and that their mechanosensitivity may regulate the dynamics of signaling pathways localized to the cilium. We found that hASC morphology, cilia length and cilia conformation varied in response to culture in complete growth, osteogenic differentiation, or adipogenic differentiation medium, with the longest cilia expressed in adipogenically differentiating cells. Further, we show that cyclic tensile strain both enhances osteogenic differentiation of hASCs while it suppresses adipogenic differentiation as evidenced by upregulation of RUNX2 gene expression and downregulation of PPARG and IGF-1, respectively. This study demonstrates that hASC primary cilia exhibit mechanosensitivity to cyclic tensile strain and lineage-dependent expression, which may in part regulate signaling pathways localized to the primary cilium during the differentiation process. We highlight the importance of the primary cilium structure in mechanosensing and lineage specification and surmise that this structure may be a novel target in manipulating hASC for in tissue engineering applications.

Dual functional approaches for osteogenesis coupled angiogenesis in bone tissue engineering

Bone fracture healing is a multistep and overlapping process of inflammation, angiogenesis and osteogenesis. It is initiated by inflammation, causing the release of various cytokines and growth factors. It leads to the recruitment of stem cells and formation of vasculature resulting in the functional bone formation. This combined phenomenon is used by bone tissue engineers from past few years to address the problem of vasculature and osteogenic differentiation during bone regeneration. In this review, we have discussed all major studies reporting the dual functioning approach to promote osteogenesis coupled angiogenesis using various scaffolds. These scaffolds are broadly classified into four types based on the nature of their structural and functional components. The functionality of the scaffold is either due to the structural components or the loaded cargo which conducts or induces the coupled functionality. Dual delivery system for osteoinductive and angioinductive factors ensures the co-delivery of two different types of molecules to induce osteogenesis and angiogenesis. Single delivery scaffold for angioinductive and osteoinductive molecule releases single type of molecules which could induce both angiogenesis and osteogenesis. Osteoconductive scaffold consisted of bone constituents releases angioinductive factors. Osteoconductive and angioconductive scaffold composed of components which provide the native substrate features for osteogenesis and angiogenesis. This review article also discusses the studies highlighting the synergism of physico-chemical stimuli as dual functioning feature to enhance angiogenesis and osteogenesis simultaneously. In addition, this article covers one of the least discussed area of the bone regeneration i.e. 'cartilage formation as a median between angiogenesis and osteogenesis'.

Physical Stimulations for Bone and Cartilage Regeneration

A wide range of techniques and methods are actively invented by clinicians and scientists who are dedicated to the field of musculoskeletal tissue regeneration. Biological, chemical, and physiological factors, which play key roles in musculoskeletal tissue development, have been extensively explored. However, physical stimulation is increasingly showing extreme importance in the processes of osteogenic and chondrogenic differentiation, proliferation and maturation through defined dose parameters including mode, frequency, magnitude, and duration of stimuli. Studies have shown manipulation of physical microenvironment is an indispensable strategy for the repair and regeneration of bone and cartilage, and biophysical cues could profoundly promote their regeneration. In this article, we review recent literature on utilization of physical stimulation, such as mechanical forces (cyclic strain, fluid shear stress, etc.), electrical and magnetic fields, ultrasound, shock waves, substrate stimuli, etc., to promote the repair and regeneration of bone and cartilage tissue. Emphasis is placed on the mechanism of cellular response and the potential clinical usage of these stimulations for bone and cartilage regeneration.

Calcium Spike Patterns Reveal Linkage of Electrical Stimulus and MSC Osteogenic Differentiation

Mesenchymal stromal/stem cells (MSCs) are easily obtained multipotent cells that are widely applied in regenerative medicine. Electrical stimulation (ES) has a promoting effect on bone healing and osteogenic differentiation of MSCs. Direct and alternating currents (AC) are extensively used to promote the osteogenic differentiation of MSCs in vivo and in vitro. However, information on conducting effective differentiation remains scarce. In this paper, we propose a method to optimize ES parameters based on calcium spike patterns of MSCs. Calcium spike frequency decreases as the osteogenic differentiation of MSC progresses. Furthermore, we tested various ES parameters through the real-time monitoring of calcium spike patterns. We efficiently initiated the process of osteogenic differentiation in MSCs by using the optimal parameters of AC, including voltage, signal shapes, frequency, and duty time. This method provides a new approach to optimize osteogenic differentiation and is potentially useful in clinical treatment such as of bone fractures.

The Role of Physical Stimuli on Calcium Channels in Chondrogenic Differentiation of Mesenchymal Stem Cells

Human mesenchymal stem cells (hMSC) are becoming increasingly popular in tissue engineering. They are the most frequently used stem cell source for clinical applications due to their high potential to differentiate into several lineages. Cartilage is known for its low capacity for self-maintenance and currently there are no efficient methods to improve cartilage repair. Chondrogenic differentiation of hMSC isolated from different tissues is widely employed due to a high clinical demand for the improvement of cartilage regeneration. Calcium channels that are regulated by physical stimuli seem to play a pivotal role in chondrogenic differentiation of MSCs. These channels increase intracellular calcium concentration, which leads to the initiation of the relevant cellular processes that are required for differentiation. This review will focus on the impact of different physical stimuli, including electrical, electromagnetic/magnetic and mechanical on various calcium channels and calcium signaling mechanisms during chondrogenic differentiation of hMSC.

Osteogenic Effect and Cell Signaling Activation of Extremely Low-Frequency Pulsed Electromagnetic Fields in Adipose-Derived Mesenchymal Stromal Cells

Extremely low-frequency pulsed electromagnetic field (ELF-PEMF) devices have been used in the clinic for the treatment of bone disorders over the past 30 years. However, the underlying mechanism of which ELF-PEMFs exert an effect on tissues at a cellular level is not well understood. Hence, in this study, we explored the potential of different ELF-PEMF signals in modulating human adipose-derived mesenchymal stromal cells' (hAMSC) osteogenic capability. The cell proliferation rate was assessed using carboxyfluorescein succinimidyl ester (CFSE) method. The osteogenesis potential of cells was determined by alkaline phosphatase (ALP) activity, Alizarin-Red S staining, and RT-qPCR. Finally, the intracellular signaling pathway of a selected ELF-PEMF signal was examined using the PathScan Intracellular Signaling Array. Among the tested ELF-PEMF signals, program 20 (26 Hz) showed activation of the Akt and MAPK/ERK signaling cascade and significant upregulations of collagen I, alkaline phosphatase, and osteocalcin when compared to nonstimulated cells. This study demonstrates the potential of certain ELF-PEMF signal parameters to induce osteogenic differentiation of hAMSC and provides important clues in terms of the molecular mechanisms for the stimulation of osteogenic effects by ELF-PEMF on hAMSC.

Modulating Surface Potential by Controlling the β Phase Content in Poly(vinylidene fluoridetrifluoroethylene) Membranes Enhances Bone Regeneration

Bioelectricity plays a vital role in living organisms. Although electrical stimulation is introduced in the field of bone regeneration, the concept of a dose-response relationship between surface potential and osteogenesis is not thoroughly studied. To optimize the osteogenic properties of different surface potentials, a flexible piezoelectric membrane, poly(vinylidene fluoridetrifluoroethylene) [P(VDF-TrFE)], is fabricated by annealing treatment to control its β phases. The surface potential and piezoelectric coefficients (d₃₃ ) of the membranes can be regulated by increasing β phase contents. Compared with d₃₃  = 20 pC N^-1 (surface potential = -78 mV) and unpolarized membranes, bone marrow mesenchymal stem cells (BM-MSCs) cultured on the d₃₃  = 10 pC N^-1 (surface potential = -53 mV) membranes have better osteogenic properties. In vivo, d₃₃  = 10 pC N^-1 membranes result in rapid bone regeneration and complete mature bone-structure formation. BM-MSCs on d₃₃  = 10 pC N^-1 membranes have the lowest reactive oxygen species level and the highest mitochondrial membrane electric potential, implying that these membranes provide the best electrical qunantity for BM-MSCs' proliferation and energy metabolism. This study establishes an effective method to control the surface potential of P(VDF-Trfe) membranes and highlights the importance of optimized electrical stimulation in bone regeneration.

Charge injection based electrical stimulation on polypyrrole planar electrodes to regulate cellular osteogenic differentiation

This study reveals that the Q_inj on electrodes is a more significant factor than applied voltage for electrical stimulation to regulate cellular osteogenic differentiation, and the charge injection capacity can be tuned by thickness of Ppy.

The effect of electrical stimulation on cortical cells in 3D nanofibrous scaffolds

Cellular behaviors are significantly affected by cellular microenvironment, including mechanical supports, electrical and chemical cues, etc. Three dimensional conductive nanofibers (3D-CNFs) provide the capability to regulate cellular behaviors using mechanical, geometrical and electrical cues together, which are especially important in neural tissue engineering. However, very few studies were conducted to address combined effects of 3D nanofibrous scaffolds and electrical stimulation (ES) on cortical cell cultures. In the present study, polypyrrole (PPy)-coated electrospun polyacrylonitrile (PAN) nanofibers with a 3D structure were successfully prepared for the cortical cell culture, which was compared to cells cultured in the 2D-CNFs meshes, as well as that in the bare PAN nanofibers, both in 2D and 3D. While smooth PAN 3D nanofibers showed dispersive cell distribution, PPy coated 3D-CNFs showed clusters of cortical cells. The combined effects of 3D conductive nanofibers and ES on neurons and glial cells were studied. Different from previous observations on 2D substrates, pulsed electrical stimulations could prevent formation of cell clusters if applied at the beginning of culture, but could not disperse the clusters of cortical cells already formed. Furthermore, the electrical stimulations improved the proliferation of glial cells and accelerate neuron maturation. This study enriched the growing body of evidence for using electrical stimulation and 3D conductive nanofibers to control the culture of cortical cells, which have broad applications in neural engineering, such as implantation, biofunctional in vitro model, etc.

Cellular behaviors are significantly affected by cellular microenvironment, including mechanical supports, electrical and chemical cues, etc.

Mediation of cellular osteogenic differentiation through daily stimulation time based on polypyrrole planar electrodes

In electrical stimulation (ES), daily stimulation time means the interacting duration with cells per day, and is a vital factor for mediating cellular function. In the present study, the effect of stimulation time on osteogenic differentiation of MC3T3-E1 cells was investigated under ES on polypyrrole (Ppy) planar interdigitated electrodes (IDE). The results demonstrated that only a suitable daily stimulation time supported to obviously upregulate the expression of ALP protein and osteogenesis-related genes (ALP, Col-I, Runx2 and OCN), while a short or long daily stimulation time showed no significant outcomes. These might be attributed to the mechanism that an ES induced transient change in intracellular calcium ion concentration, which was responsible for activating calcium ion signaling pathway to enhance cellular osteogenic differentiation. A shorter daily time could lead to insufficient duration for the transient change in intracellular calcium ion concentration, and a longer daily time could give rise to cellular fatigue with no transient change. This work therefore provides new insights into the fundamental understanding of cell responses to ES and will have an impact on further designing materials to mediate cell behaviors.

Unraveling the mechanistic effects of electric field stimulation towards directing stem cell fate and function: A tissue engineering perspective

Electric field (EF) stimulation can play a vital role in eliciting appropriate stem cell response. Such an approach is recently being established to guide stem cell differentiation through osteogenesis/neurogenesis/cardiomyogenesis. Despite significant recent efforts, the biophysical mechanisms by which stem cells sense, interpret and transform electrical cues into biochemical and biological signals still remain unclear. The present review critically analyses the variety of EF stimulation approaches that can be employed to evoke appropriate stem cell response and also makes an attempt to summarize the underlying concepts of this notion, placing special emphasis on stem cell based tissue engineering and regenerative medicine. This review also discusses the major signaling pathways and cellular responses that are elicited by electric stimulation, including the participation of reactive oxygen species and heat shock proteins, modulation of intracellular calcium ion concentration, ATP production and numerous other events involving the clustering or reassembling of cell surface receptors, cytoskeletal remodeling and so on. The specific advantages of using external electric stimulation in different modalities to regulate stem cell fate processes are highlighted with explicit examples, in vitro and in vivo.

Three-dimensional piezoelectric fibrous scaffolds selectively promote mesenchymal stem cell differentiation

The discovery of electric fields in biological tissues has led to efforts in developing technologies utilizing electrical stimulation for therapeutic applications. Native tissues, such as cartilage and bone, exhibit piezoelectric behavior, wherein electrical activity can be generated due to mechanical deformation. Yet, the use of piezoelectric materials have largely been unexplored as a potential strategy in tissue engineering, wherein a piezoelectric biomaterial acts as a scaffold to promote cell behavior and the formation of large tissues. Here we show, for the first time, that piezoelectric materials can be fabricated into flexible, three-dimensional fibrous scaffolds and can be used to stimulate human mesenchymal stem cell differentiation and corresponding extracellular matrix/tissue formation in physiological loading conditions. Piezoelectric scaffolds that exhibit low voltage output, or streaming potential, promoted chondrogenic differentiation and piezoelectric scaffolds with a high voltage output promoted osteogenic differentiation. Electromechanical stimulus promoted greater differentiation than mechanical loading alone. Results demonstrate the additive effect of electromechanical stimulus on stem cell differentiation, which is an important design consideration for tissue engineering scaffolds. Piezoelectric, smart materials are attractive as scaffolds for regenerative medicine strategies due to their inherent electrical properties without the need for external power sources for electrical stimulation.

Enhancement of mesenchymal stem cell chondrogenesis with short-term low intensity pulsed electromagnetic fields

Pulse electromagnetic fields (PEMFs) have been shown to recruit calcium-signaling cascades common to chondrogenesis. Here we document the effects of specified PEMF parameters over mesenchymal stem cells (MSC) chondrogenic differentiation. MSCs undergoing chondrogenesis are preferentially responsive to an electromagnetic efficacy window defined by field amplitude, duration and frequency of exposure. Contrary to conventional practice of administering prolonged and repetitive exposures to PEMFs, optimal chondrogenic outcome is achieved in response to brief (10 minutes), low intensity (2 mT) exposure to 6 ms bursts of magnetic pulses, at 15 Hz, administered only once at the onset of chondrogenic induction. By contrast, repeated exposures diminished chondrogenic outcome and could be attributed to calcium entry after the initial induction. Transient receptor potential (TRP) channels appear to mediate these aspects of PEMF stimulation, serving as a conduit for extracellular calcium. Preventing calcium entry during the repeated PEMF exposure with the co-administration of EGTA or TRP channel antagonists precluded the inhibition of differentiation. This study highlights the intricacies of calcium homeostasis during early chondrogenesis and the constraints that are placed on PEMF-based therapeutic strategies aimed at promoting MSC chondrogenesis. The demonstrated efficacy of our optimized PEMF regimens has clear clinical implications for future regenerative strategies for cartilage.

Electrical stimulation of adipose-derived mesenchymal stem cells and endothelial cells co-cultured in a conductive scaffold for potential orthopaedic applications

Electrical stimulation (ES) has emerged as a useful tool to regulate cell behaviour, but the effect of ES on mesenchymal stem cell (MSC)/vasculogenic cell co-culture has not been investigated. Herein, human adipose-derived MSCs (AD-MSCs) and umbilical vein endothelial cells (HUVECs) were co-cultured in an electrically conductive polypyrrole/chitosan scaffold. Compared with AD-MSC monoculture, calcium deposition in the co-culture without and with ES (200 μA for 4 h/day) was 139% and 346% higher, respectively, after 7 days. As the application of ES to AD-MSC monoculture only increased calcium deposition by 56% compared with that without ES after 7 days, these results indicate that ES and co-culture with HUVECs have synergistic effects on AD-MSCs' osteogenic differentiation. ES application also significantly enhanced CD31 expression of HUVECs. In HUVEC monoculture, application of ES increased CD31 expression by 224%, whereas the corresponding increase in AD-MSC/HUVEC co-culture with ES application was 62%. The gene expression results indicate that ES enhanced the cellular functions in AD-MSC and HUVEC monoculture via autocrine bone morphogenetic protein-2 (BMP-2) and vascular endothelial growth factor (VEGF), respectively. In co-culture, crosstalk between AD-MSCs and HUVECs due to paracrine BMP-2 and VEGF enhanced the cellular functions compared with the respective monoculture. With application of ES to the AD-MSC/HUVEC co-culture, autocrine signalling was enhanced, resulting in further promotion of cellular functions. These findings illustrate that co-culturing AD-MSC/HUVEC in a conductive scaffold with ES offers potential benefits for bone defect therapy.

Electrical brain stimulation induces dendritic stripping but improves survival of silent neurons after optic nerve damage

Repetitive transorbital alternating current stimulation (rtACS) improves vision in patients with chronic visual impairments and an acute treatment increased survival of retinal neurons after optic nerve crush (ONC) in rodent models of visual system injury. However, despite this protection no functional recovery could be detected in rats, which was interpreted as evidence of “silent survivor” cells. We now analysed the mechanisms underlying this “silent survival” effect. Using in vivo microscopy of the retina we investigated the survival and morphology of fluorescent neurons before and after ONC in animals receiving rtACS or sham treatment. One week after the crush, more neurons survived in the rtACS-treated group compared to sham-treated controls. In vivo imaging further revealed that in the initial post-ONC period, rtACS induced dendritic pruning in surviving neurons. In contrast, dendrites in untreated retinae degenerated slowly after the axonal trauma and neurons died. The complete loss of visual evoked potentials supports the hypothesis that cell signalling is abolished in the surviving neurons. Despite this evidence of “silencing”, intracellular free calcium imaging showed that the cells were still viable. We propose that early after trauma, complete dendritic stripping following rtACS protects neurons from excitotoxic cell death by silencing them.

In vitro effect of direct current electrical stimulation on rat mesenchymal stem cells

Background

Electrical stimulation (ES) has been successfully used to treat bone defects clinically. Recently, both cellular and molecular approaches have demonstrated that ES can change cell behavior such as migration, proliferation and differentiation.

Methods

In the present study we exposed rat bone marrow- (BM-) and adipose tissue- (AT-) derived mesenchymal stem cells (MSCs) to direct current electrical stimulation (DC ES) and assessed temporal changes in osteogenic differentiation. We applied 100 mV/mm of DC ES for 1 h per day for three, seven and 14 days to cells cultivated in osteogenic differentiation medium and assessed viability and calcium deposition at the different time points. In addition, expression of osteogenic genes, Runx2, Osteopontin, and Col1A2 was assessed in BM- and AT-derived MSCs at the different time points.

Results

Results showed that ES changed osteogenic gene expression patterns in both BM- and AT-MSCs, and these changes differed between the two groups. In BM-MSCs, ES caused a significant increase in mRNA levels of Runx2, Osteopontin and Col1A2 at day 7, while in AT-MSCs, the increase in Runx2 and Osteopontin expression were observed after 14 days of ES.

Discussion

This study shows that rat bone marrow- and adipose tissue-derived stem cells react differently to electrical stimuli, an observation that could be important for application of electrical stimulation in tissue engineering.

Primary cilia are sensors of electrical field stimulation to induce osteogenesis of human adipose-derived stem cells

In this study, we report for the first time that the primary cilium acts as a crucial sensor for electrical field stimulation (EFS)-enhanced osteogenic response in osteoprogenitor cells. In addition, primary cilia seem to functionally modulate effects of EFS-induced cellular calcium oscillations. Primary cilia are organelles that have recently been implicated to play a crucial sensor role for many mechanical and chemical stimuli on stem cells. Here, we investigate the role of primary cilia in EFS-enhanced osteogenic response of human adipose-derived stem cells (hASCs) by knocking down 2 primary cilia structural proteins, polycystin-1 and intraflagellar protein-88. Our results indicate that structurally integrated primary cilia are required for detection of electrical field signals in hASCs. Furthermore, by measuring changes of cytoplasmic calcium concentration in hASCs during EFS, our findings also suggest that primary cilia may potentially function as a crucial calcium-signaling nexus in hASCs during EFS.-Cai, S., Bodle, J. C., Mathieu, P. S., Amos, A., Hamouda, M., Bernacki, S., McCarty, G., Loboa, E. G. Primary cilia are sensors of electrical field stimulation to induce osteogenesis of human adipose-derived stem cells.

Hyaluronic acid doped-poly(3,4-ethylenedioxythiophene)/chitosan/gelatin (PEDOT-HA/Cs/Gel) porous conductive scaffold for nerve regeneration

Conducting polymer, as a "smart" biomaterial, has been increasingly used to construct tissue engineered scaffold for nerve tissue regeneration. In this study, a novel porous conductive scaffold was prepared by incorporating conductive hyaluronic acid (HA) doped-poly(3,4-ethylenedioxythiophene) (PEDOT-HA) nanoparticles into a chitosan/gelatin (Cs/Gel) matrix. The physicochemical characteristics of Cs/Gel scaffold with 0-10wt% PEDOT-HA were analyzed and the results indicated that the incorporation of PEDOT-HA into scaffold increased the electrical and mechanical properties while decreasing the porosity and water absorption. Moreover, in vitro biodegradation of scaffold displayed a declining trend with the PEDOT-HA content increased. About the biocompatibility of conductive scaffold, neuron-like rat phaeochromocytoma (PC12) cells were cultured in scaffold to evaluate cell adhesion and growth. 8% PEDOT-HA/Cs/Gel scaffold had a higher cell adhesive efficiency and cell viability than the other conductive scaffolds. Furthermore, cells in the scaffold with 8wt% PEDOT-HA expressed higher synapse growth gene of GAP43 and SYP compared with Cs/Gel control group. These results suggest that 8%PEDOT-HA/Cs/Gel scaffold is an attractive cell culture conductive substrate which could support cell adhesion, survival, proliferation, and synapse growth for the application in nerve tissue regeneration.

Fabrication and characterization of conductive poly (3,4-ethylenedioxythiophene) doped with hyaluronic acid/poly (l-lactic acid) composite film for biomedical application

Poly 3,4-ethylenedioxythiophene (PEDOT), a polythiophene derivative, has been proved to be modified by chemical process as biocompatible conductive polymer for biomedical applications. In this study, novel hyaluronic acid (HA)-doped PEDOT nanoparticles were synthesized by the method of chemical oxidative polymerization, then conductive PEDOT-HA/poly(l-lactic acid) (PLLA) composite films were prepared. The physicochemical characteristics and biocompatibility of films were further investigated. FTIR, Raman and EDX analysis demonstrated that HA was successfully doped into PEDOT particles. Cyclic voltammograms indicated PEDOT-HA particles had favorable electrochemical stability. PEDOT-HA/PLLA films showed lower surface contact angle and faster degradation degree compared with PLLA films. Moreover, the cytotoxicity test of PEDOT-HA/PLLA films showed that neuron-like pheochromocytoma (PC12) cells adhered and spread well on the surface of PEDOT-HA/PLLA films and cell viability denoted by MTT assay had a significant increase. PEDOT-HA/PLLA films modified with laminin (LN) also exhibited an efficiently elongated cell morphology observed by fluorescent microscope and metallographic microscope. Furthermore, PEDOT-HA/PLLA films were subjected to different current intensity to elucidate the effect of electrical stimulation (ES) on neurite outgrowth of PC12 cells. ES (0.5 mA, 2 h) significantly promoted neurite outgrowth with an average value length of 122 ± 5 μm and enhanced the mRNA expression of growth-associated protein (GAP43) and synaptophysin (SYP) in PC12 cells when compared with other ES groups. These results suggest that PEDOT-HA/PLLA film combined with ES are conducive to cell growth and neurite outgrowth, indicating the conductive PEDOT-HA/PLLA film may be an attractive candidate with ES for enhancing nerve regeneration in nerve tissue engineering.

Stretchable Silver Nanowire Microelectrodes for Combined Mechanical and Electrical Stimulation of Cells

The use of stretchable electrodes interfaced with the human body has enabled a new frontier in biomedical engineering, and the miniaturization of such electrodes can allow for a more precise spatial control to monitor or stimulate tissues. The understanding of the response of cells or tissues to combined electromechanical stimulation, as made possible by stretchable electrodes, is essential to improve medical devices and therapies. Cheap to produce and easy to use platforms for in vitro cell studies are thus urgently needed. This study reports the successful implementation of silver nanowires (AgNWs) into an integrated miniaturized electromechanical stimulator, which is compatible with cell culture. The innovative steps include a lithography-based lift-off method to micropattern AgNWs onto an elastic silicone membrane. These stretchable microelectrodes are then integrated into a microfluidic device for cell culture, which enables the synchronous electromechanical stimulation of cells. In a proof-of-concept study, it is furthermore shown that fibroblasts respond uniquely to mechanical stretching, electrical stimulation, and combined electromechanical stimulations in terms of cell alignment and morphology, as well as by producing the extracellular matrix protein collagen. This proof-of-concept study illustrates the functionality and usability of these stretchable AgNWs microelectrodes for either basic research or future biomedical applications.

The Regulation of Osteogenesis Using Electroactive Polypyrrole Films

To evaluate the effect of electrical conductivity of biomaterials on osteogenesis, polypyrrole (PPy) was fabricated by oxidative chemical polymerization as substrates for cell culture. Through adjusting the concentrations of monomer and initiator, polypyrrole films with different electrical conductivities were fabricated. These fabricated polypyrrole films are transparent enough for easy optical microscopy. Fourier transform infrared spectroscopy, X-ray spectroscopy and four-point probe were used to assess the microstructures, surface chemical compositions and electrical sheet resistance of films, respectively. Results indicate that higher monomer and initiator concentration leads to highly-branched PPy chains and thus promotes the electron mobility and electrical conductivity. Selected polypyrrole films then were applied for culturing rat bone marrow stromal cells. Cell viability and mineralization assays reveal that not only these films are biocompatible, but also capable of enhancing the calcium deposition into the extra cellular matrix by the differentiated cells.

Development and Characterization of Organic Electronic Scaffolds for Bone Tissue Engineering

Bones have been shown to exhibit piezoelectric properties, generating electrical potential upon mechanical deformation and responding to electrical stimulation with the generation of mechanical stress. Thus, the effects of electrical stimulation on bone tissue engineering have been extensively studied. However, in bone regeneration applications, only few studies have focused on the use of electroactive 3D biodegradable scaffolds at the interphase with stem cells. Here a method is described to combine the bone regeneration capabilities of 3D-printed macroporous medical grade polycaprolactone (PCL) scaffolds with the electrical and electrochemical capabilities of the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT). PCL scaffolds have been highly effective in vivo as bone regeneration grafts, and PEDOT is a leading material in the field of organic bioelectronics, due to its stability, conformability, and biocompatibility. A protocol is reported for scaffolds functionalization with PEDOT, using vapor-phase polymerization, resulting in a conformal conducting layer. Scaffolds' porosity and mechanical stability, important for in vivo bone regeneration applications, are retained. Human fetal mesenchymal stem cells proliferation is assessed on the functionalized scaffolds, showing the cytocompatibility of the polymeric coating. Altogether, these results show the feasibility of the proposed approach to obtain electroactive scaffolds for electrical stimulation of stem cells for regenerative medicine.

Facilitated Neural Differentiation of Adipose Tissue–Derived Stem Cells by Electrical Stimulation and Nurr-1 Gene Transduction

Neuron-like cells derived from adipose tissue-derived stem cells (ADSCs) have been considered one of the most promising cells for the treatment of neurodegenerative diseases and neurotrauma in the central nervous system (CNS). Thus far, extensive efforts have been made to facilitate neuronal differentiation of ADSCs, but limited progress has been achieved. In the present study, we tested the possibility of using a combination of electrical stimulation (ES) with Nurr-1 gene transduction to promote neuronal differentiation of ADSCs. The tolerance of ADSCs to ES was first examined by a cell apoptosis assay. The proliferation of cells was characterized using a CCK-8 assay. The morphology of cells was examined by scanning electron microscopy (SEM). The differentiation of ADSCs into neuron-like cells was examined by immunocytochemistry (ICC)–immunofluorescence staining, quantitative real-time polymerase chain reaction (qRT-PCR), Western blotting, and enzyme linked immunosorbent assay (ELISA). The gene expression of microtubule-associated protein 2 (MAP-2), β-tubulin, neurofilament 200 (NF-200), octamer binding transcription factor 4 (OCT-4), and glial fibrillary acidic protein (GFAP) after stimulation was examined by qRT-PCR. We found that the optimal intensity of ES for neuronal differentiation of ADSCs was 1 V/cm. In addition, ES combined with Nurr-1 gene transduction increased the neuronal differentiation rate of ADSCs, the length of neurite-like processes, and the secretion of dopamine. Further studies showed that a combination of ES with Nurr-1 gene transduction was capable of promoting the expression of MAP-2, β-tubulin, and NF-200 but decreased the expression of OCT-4 and GFAP. All of these findings indicate that a combination of ES with Nurr-1 gene transduction could facilitate neuronal differentiation of ADSCs, which raises the possibility of its application in the treatment of neurodegenerative diseases and neurotrauma in the CNS.

Induction of chondrogenic differentiation of human adipose-derived stem cells by low frequency electric field

BACKGROUND

Since when the cartilage damage (e.g., with the osteoarthritis) it could not be repaired in the body, hence for its reconstruction needs cell therapy. For this purpose, adipose-derived stem cells (ADSCs) is one of the best cell sources because by the tissue engineering techniques it can be differentiated into chondrocytes. Chemical and physical inducers is required order to stem cells to chondrocytes differentiating. We have decided to define the role of electric field (EF) in inducing chondrogenesis process.

MATERIALS AND METHODS

A low frequency EF applied the ADSCs as a physical inducer for chondrogenesis in a 3D micromass culture system which ADSCs were extracted from subcutaneous abdominal adipose tissue. Also enzyme-linked immunosorbent assay, methyl thiazolyl tetrazolium, real time polymerase chain reaction and flowcytometry techniques were used for this study.

RESULTS

We found that the 20 minutes application of 1 kHz, 20 mv/cm EF leads to chondrogenesis in ADSCs. Although our results suggest that application of physical (EF) and chemical (transforming growth factor-β3) inducers at the same time, have best results in expression of collagen type II and SOX9 genes. It is also seen EF makes significant decreased expression of collagens type I and X genes.

CONCLUSION

The low frequency EF can be a good motivator to promote chondrogenic differentiation of human ADSCs.

Effects of electric fields on human mesenchymal stem cell behaviour and morphology using a novel multichannel device

The intrinsic piezoelectric nature of collagenous-rich tissues, such as bone and cartilage, can result in the production of small, endogenous electric fields (EFs) during applied mechanical stresses. In vivo, these EFs may influence cell migration, a vital component of wound healing. As a result, the application of small external EFs to bone fractures and cutaneous wounds is actively practiced clinically. Due to the significant regenerative potential of stem cells in bone and cartilage healing, and their potential role in the observed improved healing in vivo post applied EFs, using a novel medium throughput device, we investigated the impacts of physiological and aphysiological EFs on human bone marrow-derived mesenchymal stem cells (hBM-MSCs) for up to 15 hours. The applied EFs had significant impacts on hBM-MSC morphology and migration; cells displayed varying degrees of conversion to a highly elongated phenotype dependent on the EF strength, consistent perpendicular alignment to the EF vector, and definitive cathodal migration in response to EF strengths ≥0.5 V cm(-1), with the fastest migration speeds observed at between 1.7 and 3 V cm(-1). We observed variability in hBM-MSC donor-to-donor responses and overall tolerances to applied EFs. This study thus confirms hBM-MSCs are responsive to applied EFs, and their rate of migration towards the cathode is controllable depending on the EF strength, providing new insight into the physiology of hBM-MSCs and possibly a significant opportunity for the utilisation of EFs in directed scaffold colonisation in vitro for tissue engineering applications or in vivo post implantation.

Biodegradable triboelectric nanogenerator as a life-time designed implantable power source

Transient electronics built with degradable organic and inorganic materials is an emerging area and has shown great potential for in vivo sensors and therapeutic devices. However, most of these devices require external power sources to function, which may limit their applications for in vivo cases. We report a biodegradable triboelectric nanogenerator (BD-TENG) for in vivo biomechanical energy harvesting, which can be degraded and resorbed in an animal body after completing its work cycle without any adverse long-term effects. Tunable electrical output capabilities and degradation features were achieved by fabricated BD-TENG using different materials. When applying BD-TENG to power two complementary micrograting electrodes, a DC-pulsed electrical field was generated, and the nerve cell growth was successfully orientated, showing its feasibility for neuron-repairing process. Our work demonstrates the potential of BD-TENG as a power source for transient medical devices.

Designing a novel nanocomposite for bone tissue engineering using electrospun conductive PBAT/polypyrrole as a scaffold to direct nanohydroxyapatite electrodeposition

Electrospinning is a well-recognized technique for producing nanostructured fibers with different functionalities, generating materials that are able to support cell adhesion and further proliferation.

Built-in microscale electrostatic fields induced by anatase-rutile-phase transition in selective areas promote osteogenesis

Bone has a built-in electric field because of the presence of piezoelectric collagen. To date, only externally applied electric fields have been used to direct cell behavior; however, these fields are not safe or practical for in vivo use. In this work, for the first time, we use a periodic microscale electric field (MEF) built into a titanium implant to induce osteogenesis. Such a MEF is generated by the periodic organization of a junction made of two parallel semiconducting TiO₂ zones: anatase and rutile with lower and higher electron densities, respectively. The junctions were formed through anatase-rutile-phase transition in selective areas using laser irradiation on the implants. The in vitro and in vivo studies confirmed that the built-in MEF was an efficient electrical cue for inducing osteogenic differentiation in the absence of osteogenic supplements and promoted bone regeneration around the implants. Our work opens up a new avenue toward bone repair and regeneration using built-in MEF.