Electrical Cell-Substrate Impedance Spectroscopy Can Monitor Age-Grouped Human Adipose Stem Cell Variability During Osteogenic Differentiation

Association between Donor Age and Osteogenic Potential of Human Adipose Stem Cells in Bone Tissue Engineering

Adipose stem cells (ASCs) have multilineage differentiation capacity and hold great potential for regenerative medicine. Compared to bone marrow-derived mesenchymal stem cells (bmMSCs), ASCs are easier to isolate from abundant sources with significantly higher yields. It is generally accepted that bmMSCs show age-related changes in their proliferation and differentiation potentials, whereas this aspect is still controversial in the case of ASCs. In this review, we evaluated the existing data on the effect of donor age on the osteogenic potential of human ASCs. Overall, a poor agreement has been achieved because of inconsistent findings in the previous studies. Finally, we attempted to delineate the possible reasons behind the lack of agreements reported in the literature. ASCs represent a heterogeneous cell population, and the osteogenic potential of ASCs can be influenced by donor-related factors such as age, but also gender, lifestyle, and the underlying health and metabolic state of donors. Furthermore, future studies should consider experimental factors in in vitro conditions, including passaging, cryopreservation, culture conditions, variations in differentiation protocols, and readout methods.

Advances in TEER measurements of biological barriers in microphysiological systems

Biological barriers are multicellular structures that precisely regulate the transport of ions, biomolecules, drugs, cells, and other organisms. Transendothelial/epithelial electrical resistance (TEER) is a label-free method for predicting the properties of biological barriers. Understanding the mechanisms that control TEER significantly enhances our knowledge of the physiopathology of different diseases and aids in the development of new drugs. Measuring TEER values within microphysiological systems called organ-on-a-chip devices that simulate the microenvironment, architecture, and physiology of biological barriers in the body provides valuable insight into the behavior of barriers in response to different drugs and pathogens. These integrated systems should increase the accuracy, reproducibility, sensitivity, resolution, high throughput, speed, cost-effectiveness, and reliable predictability of TEER measurements. Implementing advanced micro and nanoscale manufacturing techniques, surface modification methods, biomaterials, biosensors, electronics, and stem cell biology is necessary for integrating TEER measuring systems with organ-on-chip technology. This review focuses on the applications, advantages, and future perspectives of integrating organ-on-a-chip technology with TEER measurement methods for studying biological barriers. After briefly reviewing the role of TEER in the physiology and pathology of barriers, standard techniques for measuring TEER, including Ohm's law and impedance spectroscopy, and commercially available devices are described. Furthermore, advances in TEER measurement are discussed in multiple barrier-on-a-chip system models representing different organs. Finally, we outline future trends in implementing advanced technologies to design and fabricate nanostructured electrodes, complicated microfluidic chips, and membranes for more advanced and accurate TEER measurements.

Combining Electrostimulation with Impedance Sensing to Promote and Track Osteogenesis within a Titanium Implant

(1) Background: Electrical stimulation is a promising alternative to promote bone fracture healing but with the limitation of tracking the osteogenesis progress in vivo. To overcome this issue, we present an opportunity to combine the electrical stimulation of a commercial titanium implant, which promotes osteogenesis within the fracture, with a real-time readout of the osteogenic progress by impedance sensing. This makes it possible to adjust the electrical stimulation modalities to the individual patient’s fracture healing process. (2) Methods: In detail, osteogenic differentiation of several cell types was monitored under continuous or pulsatile electrical stimulation at 0.7 V AC/20 Hz for at least seven days on a titanium implant by electric cell-substrate impedance sensing (ECIS). For control, chemical induction of osteogenic differentiation was induced. (3) Results: The most significant challenge was to discriminate impedance changes caused by proliferation events from those initiated by osteogenic differentiation. This discrimination was achieved by remodeling the impedance parameter Alpha (α), which increases over time for pulsatile electrically stimulated stem cells. Boosted α-values were accompanied by an increased formation of actin stress fibers and a reduced expression of the focal adhesion kinase in the cell periphery; morphological alterations known to occur during osteogenesis. (4) Conclusions: This work provided the basis for developing an effective fracture therapy device, which can induce osteogenesis on the one hand, and would allow us to monitor the induction process on the other hand.

A non-invasive smart scaffold for bone repair and monitoring

Existing strategies for bone defect repair are difficult to monitor. Smart scaffold materials that can quantify the efficiency of new bone formation are important for bone regeneration and monitoring. Carbon nanotubes (CNT) have promising bioactivity and electrical conductivity. In this study, a noninvasive and intelligent monitoring scaffold was prepared for bone regeneration and monitoring by integrating carboxylated CNT into chemically cross-linked carboxymethyl chitosan hydrogel. CNT scaffold (0.5% w/v) demonstrated improved mechanical properties with good biocompatibility and electrochemical responsiveness. Cyclic voltammetry and electrochemical impedance spectroscopy of CNT scaffold responded sensitively to seed cell differentiation degree in both cellular and animal levels. Interestingly, the CNT scaffold could make up the easy deactivation shortfall of bone morphogenetic protein 2 by sustainably enhancing stem cell osteogenic differentiation and new bone tissue formation through CNT roles. This research provides new ideas for the development of noninvasive and electrochemically responsive bioactive scaffolds, marking an important step in the development of intelligent tissue engineering.

•

Existing strategies for bone defect repair are difficult to monitor.

•

In this study, a noninvasive and intelligent monitoring scaffold was prepared for bone regeneration and monitoring.

•

This scaffold was a combination of CNT integrated into a chemically cross-linked carboxymethyl chitosan hydrogel.

•

CNT scaffold showed improved mechanical properties with biocompatibility and electrochemical responsiveness.

Oscillation-Based Spectroscopy for Cell-Culture Monitorization

Biological Impedance is a physical property related to the state and inherent evolution of biological samples. Among the existing impedance measurement methods, Oscillation-Based (OB) tests are a simple and smart solution to indirectly measure impedance correlated with the amplitude and frequency of the generated oscillation which are proportional to the sample under test. An OB test requires tuning of the system blocks to specifications derived from every measurement problem. The OB setup must be done to obtain the optimum measurement sensitivity for the specific constraints imposed by the system under test, electronic interfaces, and electrodes employed for test. This work proposes the extension of OB measurement systems to spectroscopy test, enabling a completely new range of applications for this technology without the restrictions imposed by setting a fixed frequency on the electrical oscillator. Some examples will be presented to the measurement of cell cultures samples, considering the corresponding circuit interfaces and electric models for the electrode-cell system. The proposed analysis method allows the selection of the best oscillator elements for optimum sensitivity range in amplitude and frequency oscillation values, when a specific cell culture is monitored for the OB system.

The evaluation of a multiphasic 3D-bioplotted scaffold seeded with adipose derived stem cells to repair osteochondral defects in a porcine model

There is a need for the development of effective treatments for focal articular cartilage injuries. We previously developed a multiphasic 3D-bioplotted osteochondral scaffold design that can drive site-specific tissue formation when seeded with adipose-derived stem cells (ASC). The objective of this study was to evaluate this scaffold in a large animal model. Osteochondral defects were generated in the trochlear groove of Yucatan minipigs and repaired with scaffolds that either contained or lacked an electrospun tidemark and were either unseeded or seeded with ASC. Implants were monitored via computed tomography (CT) over the course of 4 months of in vivo implantation and compared to both open lesions and autologous explants. ICRS II evaluation indicated that defects with ASC-seeded scaffolds had healing that most closely resembled the aulogous explant. Scaffold-facilitated subchondral bone repair mimicked the structure of native bone tissue, but cartilage matrix staining was not apparent within the scaffold. The open lesions had the highest volumetric infill detected using CT analysis (p < 0.05), but the repair tissue was largely disorganized. The acellular scaffold without a tidemark had significantly more volumetric filling than either the acellular or ASC seeded groups containing a tidemark (p < 0.05), suggesting that the tidemark limited cell infiltration into the cartilage portion of the scaffold. Overall, scaffold groups repaired the defect more successfully than an open lesion but achieved limited repair in the cartilage region. With further optimization, this approach holds potential to treat focal cartilage lesions in a highly personalized manner using a human patient's own ASC cells.

Direct and Label-Free Cell Status Monitoring of Spheroids and Microcarriers Using Microfluidic Impedance Cytometry

3D cellular spheroids/microcarriers (100 µm-1 mm) are widely used in biomanufacturing, and non-invasive biosensors are useful to monitor cell quality in bioprocesses. In this work, a novel microfluidic approach for label-free and continuous-flow monitoring of single spheroid/microcarrier (hydrogel and Cytodex) based on electrical impedance spectroscopy using co-planar Field's metal electrodes is reported. Through numerical simulation and experimental validation, two unique impedance signatures (|Z_LF | (60 kHz), |Z_HF | (1 MHz)) which are optimal for spheroid growth and viability monitoring are identified. Using a closed-loop recirculation system, it is demonstrated that |Z_LF | increases with breast cancer (MCF-7) spheroid biomass, while higher opacity (impedance ratio |Z_HF |/|Z_LF |) indicates cell death due to compromised cell membrane. Anti-cancer drug (paclitaxel)-treated spheroids also exhibit lower |Z_LF | with increased cell dissociation. Interestingly, impedance characterization of adipose-derived mesenchymal stem cell differentiation on Cytodex microcarriers reveals that adipogenic cells (higher intracellular lipid content) exhibit higher impedance than osteogenic cells (more conductive due to calcium ions) for both microcarriers and single cell level. Taken together, the developed platform offers great versatility for multi-parametric analysis of spheroids/microcarriers at high throughput (≈1 particle/s), and can be readily integrated into bioreactors for long-term and remote monitoring of biomass and cell quality.

Differentiation potential and mRNA profiles of human dedifferentiated adipose cells and&nbsp;adipose‑derived stem cells from young donors

Dedifferentiated adipose cells (DAs) and adipose-derived stem cells (ADSCs) are two of the primary types of stem cells derived from adipose tissue, which have been reported to possess similar characteristics, but also exhibit unique phenotypic and functional advantages. However, several reports have described inconsistent results regarding their differences in multilineage differentiation function. Moreover, to the best of our knowledge, there are no studies assessing their myogenic ability, or the differences in the transcriptome between the two cell types derived from lipoaspirates via tumescent liposuction from the same donors. The aim of the present study was to compare the properties and expression profiles of these cell types. Subcutaneous adipose tissue of three female patients (aged 23–30 years) with a physiological BMI (19.1–23.9 kg/m²) were obtained during tumescent liposuction of the abdomen or the thigh. The stromal vascular fraction and mature adipocytes were obtained via collagenase digestion, and ADSCs and DAs were cultured successively. To determine the differences between DAs and ADSCs after 6–7 passages, cell proliferation assays, phenotypic assessment, differentiation assays and high-throughput RNA sequencing (seq) were used. Similar cell morphologies, proliferation dynamics, surface markers and transcriptome expression profiles were observed between the DAs and ADSCs. Whilst there were notable individual differences in the osteogenic, lipogenic, chondrogenic and myogenic abilities of the DAs and ADSCs, it was difficult to determine their differentiation potential based only on the cell source. Interestingly, the myogenic ability was relatively stronger in cells with relatively weaker lipogenic ability. Only 186 differentially expressed genes between the two groups were identified using RNAseq. Several of these genes were involved in biological functions such as transcription regulation, protein translation regulation, cytokine interactions and energy metabolism regulation. The results of the present study suggested a similar functional potential of DAs and ADSCs from young donors undergoing tumescent liposuction operation in regeneration areas and the balance of the differentiative ability of the same cell populations. These data may provide a foundation for further clinical administration of stem cells derived from adipose tissues in therapy.

Long-term and label-free monitoring for osteogenic differentiation of mesenchymal stem cells using force sensor and impedance measurement

Stem cells have attracted increasing research interest in the field of regenerative medicine due to their unique abilities to differentiate into multiple cell lineages. Label-free, real-time, and long-term monitoring for stem cell differentiation is requisite in studying directional differentiation and development mechanisms for tissue engineering applications, but a great challenge because of the rigorous demands for sensitivity, stability and biocompatibility of devices. In this article, a label-free and real-time monitoring approach using a zinc oxide (ZnO) nanorod field effect transistor (FET) is proposed to detect cell traction forces (CTFs) exerted by cells on underlying substrates. The ZnO nanorod FET with the approach of difference-frequency lock-in detection achieves high sensitivity, good stability, and excellent biocompatibility, by which real-time and long-term (over 20 days) monitoring of cellular mechanical changes in osteogenic differentiation of mesenchymal stem cells (MSCs) is successfully achieved. We also employ electrical impedance monitoring using microelectrode array chips and microscopic observation to investigate cell migration and nodular aggregation behaviors of MSCs in osteogenic differentiation. Various biochemical assays including alkaline phosphatase (ALP), osteopontin expression and alizarin red staining are utilized to verify osteogenic differentiation of MSCs. We propose a combination of cell traction force measurement, impedance measurement and microscopic observation to provide multimodal profiling of cell morphology, and cellular biomechanical and electrophysiological phenotypes, which can track cellular dynamics in stem cell development and help to deeply understand the mechanism of osteogenic differentiation.

Microchip with Single-Cell Impedance Measurements for Monitoring Osteogenic Differentiation of Mesenchymal Stem Cells under Electrical Stimulation

Effective induction methods and in situ monitoring are essential for studying the mechanism of biological responses in stem cell differentiation. This article proposes an induction method incorporating electrical stimulation under an inhomogeneous field with single-cell impedance monitoring for studying osteogenic differentiation of mesenchymal stem cells (MSCs) using a microchip. The microchip contains an array of sextupole-electrode units for implementing a combination of controllable electrical stimulation and single-cell impedance measurements. MSCs are inducted to osteogenic differentiation under electrical stimulation using quadrupole electrodes and single-cell impedances are monitored in situ using a pair of microelectrodes at each unit center. The proposed microchip adopts an array design to monitor a number of MSCs in parallel, which improves measurement throughput and facilitates to carry out statistic tests. We perform osteogenic differentiation of MSCs on the microchip with and without electrical stimulation meanwhile monitoring single-cell impedance in real time for 21 days. The recorded impedance results show the detailed characteristic change of MSCs at the single-cell level during osteogenic differentiation, which demonstrates a significant difference between the conditions with and without electrical stimulation. The cell morphology and various staining analyses are also used to validate osteogenesis and correlate with the impedance expression. Correlation analysis of the impedance measurement, cell morphology, and various staining assays proves the great acceleration effect of the proposed electrical stimulation on osteogenic differentiation of MSCs. The proposed impedance method can monitor the dynamic process of cell development and study heterogeneity of stem cell differentiation at the single-cell level.

3D bioprinting using hollow multifunctional fiber impedimetric sensors

3D bioprinting is an emerging biofabrication process for the production of adherent cell-based products, including engineered tissues and foods. While process innovations are rapidly occurring in the area of process monitoring, which can improve fundamental understanding of process-structure-property relations as well as product quality by closed-loop control techniques, in-line sensing of the bioink composition remains a challenge. Here, we report that hollow multifunctional fibers enable in-line impedimetric sensing of bioink composition and exhibit selectivity for real-time classification of cell type, viability, and state of differentiation during bioprinting. Continuous monitoring of the fiber impedance magnitude and phase angle response from 102 to 106 Hz during microextrusion 3D bioprinting enabled compositional and quality analysis of alginate bioinks that contained fibroblasts, neurons, or mouse embryonic stem cells (mESCs). Fiber impedimetric responses associated with the bioinks that contained differentiated mESCs were consistent with differentiation marker expression characterized by immunocytochemistry. 3D bioprinting through hollow multifunctional fiber impedimetric sensors enabled classification of stem cells as stable or randomly differentiated populations. This work reports an advance in monitoring 3D bioprinting processes in terms of in-line sensor-based bioink compositional analysis using fiber technology and provides a non-invasive sensing platform for achieving future quality-controlled bioprinted tissues and injectable stem-cell therapies.

Use of Discrete Wavelet Transform to Assess Impedance Fluctuations Obtained from Cellular Micromotion

Electric cell–substrate impedance sensing (ECIS) is an attractive method for monitoring cell behaviors in tissue culture in real time. The time series impedance fluctuations of the cell-covered electrodes measured by ECIS are the phenomena accompanying cellular micromotion as cells continually rearrange their cell–cell and cell–substrate adhesion sites. Accurate assessment of these fluctuations to extract useful information from raw data is important for both scientific and practical purposes. In this study, we apply discrete wavelet transform (DWT) to analyze the concentration-dependent effect of cytochalasin B on human umbilical vein endothelial cells (HUVECs). The sampling rate of the impedance time series is 1 Hz and each data set consists of 2048 points. Our results demonstrate that, in the Daubechies (db) wavelet family, db1 is the optimal mother wavelet function for DWT-based analysis to assess the effect of cytochalasin B on HUVEC micromotion. By calculating the energy, standard deviation, variance, and signal magnitude area of DWT detail coefficients at level 1, we are able to significantly distinguish cytotoxic concentrations of cytochalasin B as low as 0.1 μM, and in a concentration-dependent manner. Furthermore, DWT-based analysis indicates the possibility to decrease the sampling rate of the micromotion measurement from 1 Hz to 1/16 Hz without decreasing the discerning power. The statistical measures of DWT detail coefficients are effective methods for determining both the sampling rate and the number of individual samples for ECIS-based micromotion assays.

Electrical Modeling of the Growth and Differentiation of Skeletal Myoblasts Cell Cultures for Tissue Engineering

In tissue engineering, of utmost importance is the control of tissue formation, in order to form tissue constructs of clinical relevance. In this work, we present the use of an impedance spectroscopy technique for the real-time measurement of the dielectric properties of skeletal myoblast cell cultures. The processes involved in the growth and differentiation of these cell cultures in skeletal muscle are studied. A circuit based on the oscillation-based test technique was used, avoiding the use of high-performance circuitry or external input signals. The effect of electrical pulse stimulation applied to cell cultures was also studied. The technique proved useful for monitoring in real-time the processes of cell growth and estimating the fill factor of muscular stem cells. Impedance spectroscopy was also useful to study the real-time monitoring of cell differentiation, obtaining different oscillation amplitude levels for differentiated and undifferentiated cell cultures. Finally, an electrical model was implemented to better understand the physical properties of the cell culture and control the tissue formation process.

Integration of biological systems with electronic-mechanical assemblies

Biological systems continuously interact with the surrounding environment because they are dynamically evolving. The interaction is achieved through mechanical, electrical, chemical, biological, thermal, optical, or a synergistic combination of these cues. To provide a fundamental understanding of the interaction, recent efforts that integrate biological systems with the electronic-mechanical assemblies create unique opportunities for simultaneous monitoring and eliciting the responses to the biological system. Recent innovations in materials, fabrication processes, and device integration approaches have created the enablers to yield bio-integrated devices to interface with the biological system, ranging from cells and tissues to organs and living individual. In this short review, we will provide a brief overview of the recent development on the integration of the biological systems with electronic-mechanical assemblies across multiple scales, with applications ranging from healthcare monitoring to therapeutic options such as drug delivery and rehabilitation therapies. STATEMENT OF SIGNIFICANCE: An overview of the recent progress on the integration of the biological system with both electronic and mechanical assemblies is discussed. The integration creates the unique opportunity to simultaneously monitor and elicit the responses to the biological system, which provides a fundamental understanding of the interaction between the biological system and the electronic-mechanical assemblies. Recent innovations in materials, fabrication processes, and device integration approaches have created the enablers to yield bio-integrated devices to interface with the biological system, ranging from cells and tissues to organs and living individual.

CMOS based whole cell impedance sensing: Challenges and future outlook

With the increasing need for multi-analyte point-of-care diagnosis devices, cell impedance measurement is a promising technique for integration with other sensing modalities. In this comprehensive review, the theory underlying cell impedance sensing, including the history, complementary metal-oxide-semiconductor (CMOS) based implementations, and applications are critically assessed. Whole cell impedance sensing, also known as electric cell-substrate impedance sensing (ECIS) or electrical impedance spectroscopy (EIS), is an approach for studying and diagnosing living cells in in-vitro and in-vivo environments. The technique is popular since it is label-free, non-invasive, and low cost when compared to standard biochemical assays. CMOS cell impedance measurement systems have been focused on expanding their applications to numerous aspects of biological, environmental, and food safety applications. This paper presents and evaluates circuit topologies for whole cell impedance measurement. The presented review compares several existing CMOS designs, including the classification, measurement speed, and sensitivity of varying topologies.

Impedance-based cellular assays for regenerative medicine

Therapies based on regenerative techniques have the potential to radically improve healthcare in the coming years. As a result, there is an emerging need for non-destructive and label-free technologies to assess the quality of engineered tissues and cell-based products prior to their use in the clinic. In parallel, the emerging regenerative medicine industry that aims to produce stem cells and their progeny on a large scale will benefit from moving away from existing destructive biochemical assays towards data-driven automation and control at the industrial scale. Impedance-based cellular assays (IBCA) have emerged as an alternative approach to study stem-cell properties and cumulative studies, reviewed here, have shown their potential to monitor stem-cell renewal, differentiation and maturation. They offer a novel method to non-destructively assess and quality-control stem-cell cultures. In addition, when combined with in vitro disease models they provide complementary insights as label-free phenotypic assays. IBCA provide quantitative and very sensitive results that can easily be automated and up-scaled in multi-well format. When facing the emerging challenge of real-time monitoring of three-dimensional cell culture dielectric spectroscopy and electrical impedance tomography represent viable alternatives to two-dimensional impedance sensing.This article is part of the theme issue 'Designer human tissue: coming to a lab near you'.

Transplantation of Adipose-derived Cells for Periodontal Regeneration: A Systematic Review

This systematic review evaluated the transplantation of cells derived from adipose tissue for applications in dentistry. SCOPUS, PUBMED and LILACS databases were searched for in vitro studies and pre-clinical animal model studies using the keywords "ADIPOSE", "CELLS", and "PERIODONTAL", with the Boolean operator "AND". A total of 160 titles and abstracts were identified, and 29 publications met the inclusion criteria, 14 in vitro and 15 in vivo studies. In vitro studies demonstrated that adipose- derived cells stimulate neovascularization, have osteogenic and odontogenic potential; besides adhesion, proliferation and differentiation on probable cell carriers. Preclinical studies described improvement of bone and periodontal healing with the association of adipose-derived cells and the carrier materials tested: Platelet Rich Plasma, Fibrin, Collagen and Synthetic polymer. There is evidence from the current in vitro and in vivo data indicating that adipose-derived cells may contribute to bone and periodontal regeneration. The small quantity of studies and the large variation on study designs, from animal models, cell sources and defect morphology, did not favor a meta-analysis. Additional studies need to be conducted to investigate the regeneration variability and the mechanisms of cell participation in the processes. An overview of animal models, cell sources, and scaffolds, as well as new perspectives are provided for future bone and periodontal regeneration study designs.

Combining stem cell-derived hepatocytes with impedance sensing to better predict human drug toxicity

Background: The liver plays a central role in human drug metabolism. To model drug metabolism, the major cell type of the liver, the hepatocyte, is commonly used. Hepatocytes can be derived from human and animal sources, including pluripotent stem cells. Cell-based models have shown promise in modeling human drug exposure. The assays used in those studies are normally 'snap-shot' in nature, and do not provide the complete picture of human drug exposure. Research design and methods: In this study, we employ stem cell-derived hepatocytes and impedance sensing to model human drug toxicity. This impedance-based stem cell assay reports hepatotoxicity in real time after treatment with compounds provided by industry. Results: Using electric cell-substrate impedance Sensing (ECIS), we were able to accurately measure drug toxicity post-drug exposure in real time and more quickly than gold standard biochemical assays. Conclusions: ECIS is robust and non-destructive methodology capable of monitoring human drug exposure with superior performance to current gold standard 'snapshot' assays. We believe that the methodology presented within this article could prove valuable in the quest to better predict off-target effects of drugs in humans.

Corin is a key regulator of endochondral ossification and bone development via modulation of vascular endothelial growth factor A expression

Corin has been studied extensively within the vascular system and is known to regulate blood pressure. We have shown that corin is one of the most highly upregulated genes during osteogenic differentiation of human adipose-derived stem cells (hASCs). This study tested the hypothesis that, through modulation of angiogenic signalling pathways, corin is a critical regulator of osteogenic differentiation and endochondral ossification. In vitro, corin expression in hASC was suppressed via siRNA knockdown and vascular endothelial growth factor A (VEGF-A) expression was quantified via reverse transcription polymerase chain reaction. In vivo, a murine corin knockout model (female, 10 weeks) was used to determine the effect of corin deficiency on long bone development. Wild-type and corin knockout long bones were compared via haematoxylin and eosin staining to assess tissue characteristics and cellular organization, three-point bending to assess mechanical characteristics, and immunohistochemistry to visualize VEGF-A expression patterns. Corin knockdown significantly (p < 0.05) increased VEGF-A mRNA expression during osteogenic differentiation. In vivo, corin knockout reduced tibial growth plate thickness (p < 0.01) and severely diminished the hypertrophic region. Corin knockout femurs had significantly increased stiffness (p < 0.01) and maximum loads (p < 0.01) but reduced postyield deflections (p < 0.01). In corin knockout mice, VEGF-A expression was increased near the growth plate but was reduced throughout the tibial shaft and distal head of the tibiae. This is the first study to show that corin is a key regulator of bone development by modulation of VEGF-A expression. Further elucidation of this mechanism will aid in the development of optimized bone tissue engineering and regenerative medicine therapies.

Label free process monitoring of 3D bioprinted engineered constructs via dielectric impedance spectroscopy

Biofabrication processes can affect biological quality attributes of encapsulated cells within constructs. Currently, assessment of the fabricated constructs is performed offline by subjecting the constructs to destructive assays that require staining and sectioning. This drawback limits the translation of biofabrication processes to industrial practice. In this work, we investigate the dielectric response of viable cells encapsulated in bioprinted 3D hydrogel constructs to an applied alternating electric field as a label-free non-destructive monitoring approach. The relationship between β-dispersion parameters (permittivity change-Δε, Cole-Cole slope factor-α, critical polarization frequency-f _c ) over the frequency spectrum and critical cellular quality attributes are investigated. Results show that alginate constructs containing a higher number of viable cells (human adipose derived stem cells-hASC and osteosarcoma cell line-MG63) were characterized by significantly higher Δε and α (both p < 0.05). When extended to bioprinting, results showed that changes in hASC proliferation and viability in response to changes in critical bioprinting parameters (extrusion pressure, temperature, processing time) significantly affected ∆ε, α, and f _c . We also demonstrated monitoring of hASC distribution after bioprinting and changes in proliferation over time across the cross-section of a bioprinted medial knee meniscus construct. The trends in ∆ε over time were in agreement with the alamarBlue assay results for the whole construct, but this measurement approach provided a localized readout on the status of encapsulated cells. The findings of this study support the use of dielectric impedance spectroscopy as a label-free and non-destructive method to characterize the critical quality attributes of bioprinted constructs.

The Effects of a Pulsed Electromagnetic Field on the Proliferation and Osteogenic Differentiation of Human Adipose-Derived Stem Cells

Background

A low frequency pulsed electromagnetic field (PEMF) has been confirmed to play an important role in promoting the osteogenic differentiation of human bone marrow stem cells (BMSCs). Adipose-derived stem cells (ASCs) possess some attractive characteristics for clinical application compared to BMSCs, such as abundant stem cells from lipoaspirates, faster growth, less discomfort and morbidity during surgery. ASCs can become adipocytes, osteoblasts, chondrocytes, myocytes, neurocytes, and other cell types. Thus, ASCs might be a good alternative in clinical work involving treatment with PEMF.

Material/Methods

Human ASCs (hASCs)were divided into a control group (without PEMF exposure) and an experimental group (PEMF for two hours per day). We examined the effect of PEMF on promoting cell proliferation and osteogenic differentiation from several aspects: CCK-8 proliferation assay, RNA extraction, qRT-PCR detection, western blotting, and immunofluorescence staining experiments.

Results

PEMF could promote cell proliferation of human ASCs (hASCs) at an early stage as determined by CCK-8 assay. A specific intensity (1 mT) and frequency (50 Hz) of PEMF promoted osteogenic differentiation in hASCs in alkaline phosphatase (ALP) staining experiments. In addition, bone-related gene expression increased after two weeks of PEMF exposure, the protein expression of OPN, OCN, and RUNX-2 also increased after a longer period (three weeks) of PEMF treatment as determined by western blotting and immunofluorescence staining.

Conclusions

We found for the first time that PMEF has a role in stimulating cell proliferation of hASCs at an early period, subsequently promoting bone-related gene expression and inducing the expression of related proteins to stimulate osteogenic differentiation.

Label-free and real-time monitoring of human mesenchymal stem cell differentiation in 2D and 3D cell culture systems using impedance cell sensors

Three dimensional (3D) stem cell culture has recently received considerable attention because it may enable the development of in vitro 3D tissue models. In particular, label-free and real-time monitoring of stem cell differentiation is of importance for tissue engineering applications; however, only a few non-invasive monitoring methods are available, especially for 3D cell culture. Here, we describe impedance cell sensors that allowed the monitoring of cellular behaviors in 2D and 3D cell cultures in real-time. Specifically, apparent capacitance peaks appeared in both 2D and 3D cell culture systems when human mesenchymal stem cells (hMSCs) were cultured in osteogenic induction medium. In contrast, when hMSCs were cultured in adipogenic induction medium, the capacitance increased monotonically. In addition, distinct characteristics were noted in the plots of capacitance versus conductance for the cells cultured in osteogenic and adipocyte induction media. These results demonstrated that the differentiation of hMSCs toward osteoblasts and adipocytes in 2D and 3D cell culture systems could be discriminated non-invasively by measuring the real-time capacitance and conductance. Furthermore, the vertical distribution of cellular activities in 3D cell cultures could be monitored in real-time using the 3D impedance cell sensors. Thus, these sensors may be suitable for monitoring the differentiation of various stem cells into different types of cells with distinct dielectric properties for tissue engineering applications.

3D impedance cell sensors are developed to monitor hMSC differentiation in label-free and real-time. Analyzing capacitance and conductance with these sensors shows that osteoblast and adipocyte lineages can be discriminated non-invasively in 3D cell culture systems.

Applications of Bioimpedance Measurement Techniques in Tissue Engineering

Rapid development in the field of tissue engineering necessitates implementation of monitoring methods for evaluation of the viability and characteristics of the cell cultures in a real-time, non-invasive and non-destructive manner. Current monitoring techniques are mainly histological and require labeling and involve destructive tests to characterize cell cultures. Bioimpedance measurement technique which benefits from measurement of electrical properties of the biological tissues, offers a non-invasive, label-free and real-time solution for monitoring tissue engineered constructs. This review outlines the fundamentals of bioimpedance, as well as electrical properties of the biological tissues, different types of cell culture constructs and possible electrode configuration set ups for performing bioimpedance measurements on these cell cultures. In addition, various bioimpedance measurement techniques and their applications in the field of tissue engineering are discussed.

Fabrication of Fine Electrodes on the Tip of Hypodermic Needle Using Photoresist Spray Coating and Flexible Photomask for Biomedical Applications

We have introduced a fabrication method for electrical impedance spectroscopy (EIS)-on-a-needle (EoN: EIS-on-a-needle) to locate target tissues in the body by measuring and analyzing differences in the electrical impedance between dissimilar biotissues. This paper describes the fabrication method of fine interdigitated electrodes (IDEs) at the tip of a hypodermic needle using a photoresist spray coating and flexible film photomask in the photolithography process. A polyethylene terephthalate (PET) heat shrink tube (HST) with a wall thickness of 25 µm is employed as the insulation and passivation layer. The PET HST shows a higher mechanical durability compared with poly(p-xylylene) polymers, which have been widely used as a dielectric coating material. Furthermore, the HST shows good chemical resistance to most acids and bases, which is advantageous for limiting chemical damage to the EoN. The use of the EoN is especially preferred for the characterization of chemicals/biomaterials or fabrication using acidic/basic chemicals. The fabricated gap and width of the IDEs are as small as 20 µm, and the overall width and length of the IDEs are 400 µm and 860 µm, respectively. The fabrication margin from the tip (distance between the tip of hypodermic needle and starting point of the IDEs) of the hypodermic needle is as small as 680 µm, which indicates that unnecessarily excessive invasion into biotissues can be avoided during the electrical impedance measurement. The EoN has a high potential for clinical use, such as for thyroid biopsies and anesthesia drug delivery in a spinal space. Further, even in surgery that involves the partial resection of tumors, the EoN can be employed to preserve as much normal tissue as possible by detecting the surgical margin (normal tissue that is removed with the surgical excision of a tumor) between the normal and lesion tissues.

Role of the protease corin in chondrogenic differentiation of human bone marrow-derived mesenchymal stem cells

Mesenchymal stem cells (MSCs) have the potency to differentiate into chondrocytes, osteocytes and adipocytes. Corin is a cardiac protease that activates the natriuretic peptides, thereby regulating blood volume and pressure. In addition to the heart, corin gene upregulation was reported in bone marrow- and adipose tissue-derived MSCs that underwent osteogenic differentiation. To date, the biological significance of corin expression in MSC differentiation remains unknown. In this study we isolated and cultured human bone marrow-derived MSCs that were capable of undergoing chondrogenic, osteogenic and adipogenic lineage differentiation. By reverse transcription polymerase chain reaction (RT-PCR) and immunostaining, we found that corin expression was upregulated when these MSCs underwent chondrogenic, osteogenic and adipogenic differentiation. The upregulation of corin expression was most significant in the cells undergoing chondrogenic lineage differentiation. Silencing corin gene expression by small hairpin RNA in the MSCs inhibited chondrogenic, but not osteogenic and adipogenic, differentiation. These results suggest a novel function of corin in MSC differentiation and chondrocyte development.