Microscale tissue engineering using gravity-enforced cell assembly

Neural Differentiation of Spheroids Derived from Human Induced Pluripotent Stem Cells-Mesenchymal Stem Cells Coculture

Organoids, the condensed three-dimensional (3D) tissues emerged at the early stage of organogenesis, are a promising approach to regenerate functional and vascularized organ mimics. While incorporation of heterotypic cell types, such as human mesenchymal stem cells (hMSCs) and human induced pluripotent stem cells (hiPSCs)-derived neural progenitors aid neural organ development, the interactions of secreted factors during neurogenesis have not been well understood. The objective of this study is to investigate the impact of the composition and structure of 3D hybrid spheroids of hiPSCs and hMSCs on dorsal cortical differentiation and the secretion of extracellular matrices and trophic factors in vitro. The hybrid spheroids were formed at different hiPSC:hMSC ratios (100:0, 75:25, 50:50, 25:75, 0:100) using direct mixing or pre-hiPSC aggregation method, which generated dynamic spheroid structure. The cellular organization, proliferation, neural marker expression, and the secretion of extracellular matrix proteins and the cytokines were characterized. The incorporation of MSCs upregulated Nestin and β-tubulin III expression (the dorsal cortical identity was shown by Pax6 and TBR1 expression), matrix remodeling proteins, and the secretion of transforming growth factor-β1 and prostaglandin E2. This study indicates that the appropriate composition and structure of hiPSC-MSC spheroids promote neural differentiation and trophic factor and matrix secretion due to the heterotypic cell-cell interactions.

Fast fabrication of stable cartilage-like tissue using collagen hydrogel microsphere culture

Mesenchymal stem cells (MSCs) had been increasingly regarded as a potent cell source for cartilage repair. However, due to the instability of MSC-derived chondrocyte phenotype and ossification of the synthesised cartilage matrix, regenerating a stable cartilage tissue by MSCs is still challenging. The fate of chondrogenesis from MSCs is regulated by their local microenvironment, which is of vital importance to the cell behaviours, chondrogenic phenotype and matrix synthesis. In this study, we fabricated cartilage-like tissues by the chondrogenesis of MSC in three different microenvironments, including cell pellets, collagen hydrogel bulk (CHB) and collagen hydrogel microspheres (CHMs) in vitro. After 15 days in culture, the cell number was increased to 472.6% in CHMs, compared to a 58.6% decrease in CHB and a 46.6% decrease in pellets; resulting in a 230% increase in CHM size, but a 36.8% decrease in CHB and only a 20.1% increase in pellets. Histological staining demonstrated a more intensive but less homogeneous glycosaminoglycan (GAG) pattern in pellets than in CHMs. The outer area of CHB showed a stronger GAG staining than its inner area from day 5 to day 15, but the staining was weaker than that in both pellets and CHMs. The PCR results showed that CHMs achieved a significantly higher chondrogenic gene (AGG, COL2A1, SOX9) expression and a lower hypertrophic gene (COL10A1) expression than pellets and CHB, suggesting a better chondrogenic differentiation potential with a more stable phenotype in CHMs. In summary, this study highlights the advantages of CHM microenvironments over those of CHB and pellets by a better mimicking of the natural MSC proliferation process and enhancing mass exchange in vitro. The CHM culture demonstrated potential to fabricate stable cartilage-like tissue in MSC based cartilage tissue regeneration.

Comparative analysis of tumor spheroid generation techniques for differential in vitro drug toxicity

Multicellular tumor spheroids are powerful in vitro models to perform preclinical chemosensitivity assays. We compare different methodologies to generate tumor spheroids in terms of resultant spheroid morphology, cellular arrangement and chemosensitivity. We used two cancer cell lines (MCF7 and OVCAR8) to generate spheroids using i) hanging drop array plates; ii) liquid overlay on ultra-low attachment plates; iii) liquid overlay on ultra-low attachment plates with rotating mixing (nutator plates). Analysis of spheroid morphometry indicated that cellular compaction was increased in spheroids generated on nutator and hanging drop array plates. Collagen staining also indicated higher compaction and remodeling in tumor spheroids on nutator and hanging drop arrays compared to conventional liquid overlay. Consequently, spheroids generated on nutator or hanging drop plates had increased chemoresistance to cisplatin treatment (20-60% viability) compared to spheroids on ultra low attachment plates (10-20% viability). Lastly, we used a mathematical model to demonstrate minimal changes in oxygen and cisplatin diffusion within experimentally generated spheroids. Our results demonstrate that in vitro methods of tumor spheroid generation result in varied cellular arrangement and chemosensitivity.

Spontaneous hair follicle germ (HFG) formation in vitro, enabling the large-scale production of HFGs for regenerative medicine

Hair follicle morphogenesis is triggered by reciprocal interactions between hair follicle germ (HFG) epithelial and mesenchymal layers. Here, we developed a method for large-scale preparation of HFGs in vitro via self-organization of cells. We mixed mouse epidermal and mouse/human mesenchymal cells in suspension and seeded them in microwells of a custom-designed array plate. Over a 3-day culture period, cells initially formed a randomly distributed single cell aggregate and then spatially separated from each other, exhibiting typical HFG morphological features. These self-sorted hair follicle germs (ssHFGs) were shown to be capable of efficient hair-follicle and shaft generation upon intracutaneous transplantation into the backs of nude mice. This finding facilitated the large-scale preparation of approximately 5000 ssHFGs in a microwell-array chip made of oxygen-permeable silicone. We demonstrated that the integrity of the oxygen supply through the bottom of the silicone chip was crucial to enabling both ssHFG formation and subsequent hair shaft generation. Finally, spatially aligned ssHFGs on the chip were encapsulated into a hydrogel and simultaneously transplanted into the back skin of nude mice to preserve their intervening spaces, resulting in spatially aligned hair follicle generation. This simple ssHFG preparation approach is a promising strategy for improving current hair-regenerative medicine techniques.

Multiscale cytometry and regulation of 3D cell cultures on a chip

Three-dimensional cell culture is emerging as a more relevant alternative to the traditional two-dimensional format. Yet the ability to perform cytometry at the single cell level on intact three-dimensional spheroids or together with temporal regulation of the cell microenvironment remains limited. Here we describe a microfluidic platform to perform high-density three-dimensional culture, controlled stimulation, and observation in a single chip. The method extends the capabilities of droplet microfluidics for performing long-term culture of adherent cells. Using arrays of 500 spheroids per chip, in situ immunocytochemistry and image analysis provide multiscale cytometry that we demonstrate at the population scale, on 10⁴ single spheroids, and over 10⁵ single cells, correlating functionality with cellular location within the spheroids. Also, an individual spheroid can be extracted for further analysis or culturing. This will enable a shift towards quantitative studies on three-dimensional cultures, under dynamic conditions, with implications for stem cells, organs-on-chips, or cancer research.3D cell culture is more relevant than the two-dimensional format, but methods for parallel analysis and temporal regulation of the microenvironment are limited. Here the authors develop a droplet microfluidics system to perform long-term culture of 3D spheroids, enabling multiscale cytometry of individual cells within the spheroid.

Development of a 3D angiogenesis model to study tumour - endothelial cell interactions and the effects of anti-angiogenic drugs

The tumour microenvironment and tumour angiogenesis play a critical role in the development and therapy of many cancers, but in vitro models reflecting these circumstances are rare. In this study, we describe the development of a novel tri-culture model, using non-small cell lung cancer (NSCLC) cell lines (A549 and Colo699) in combination with a fibroblast cell line (SV 80) and two different endothelial cell lines in a hanging drop technology. Endothelial cells aggregated either in small colonies in Colo699 containing microtissues or in tube like structures mainly in the stromal compartment of microtissues containing A549. An up-regulation of hypoxia and vimentin, ASMA and a downregulation of E-cadherin were observed in co- and tri-cultures compared to monocultures. Furthermore, a morphological alteration of A549 tumour cells resembling "signet ring cells" was observed in tri-cultures. The secretion of proangiogenic growth factors like vascular endothelial growth factor (VEGF) was measured in supernatants. Inhibition of these proangiogenic factors by using antiangiogenic drugs (bevacizumab and nindetanib) led to a significant decrease in migration of endothelial cells into microtissues. We demonstrate that our method is a promising tool for the generation of multicellular tumour microtissues and reflects in vivo conditions closer than 2D cell culture.

The ascendance of microphysiological systems to solve the drug testing dilemma

The development of drugs is a process obstructed with manifold security and efficacy concerns. Although animal models are still widely used to meet the diligence required, they are regarded as outdated tools with limited predictability. Novel microphysiological systems intend to create systemic models of human biology. Their ability to host 3D organoid constructs in a controlled microenvironment with mechanical and electrophysiological stimuli enables them to create and maintain homeostasis. These platforms are, thus, envisioned to be superior tools for testing and developing substances such as drugs, cosmetics and chemicals. We will present reasons why microphysiological systems are required for the emerging demands, highlight current technological and regulatory obstacles, and depict possible solutions from state-of-the-art platforms from major contributors.

Microphysiological systems are devices constructed for the cocultivation of miniaturized human organ equivalents. They are commonly placed into a continuous stream of nutrient solution. The microphysiological tools aim to reshape current development, toxicity testing and efficacy assessment of therapeutic agents, food additives, chemicals and environmental pollutants. We are on the verge of initiating a paradigm shift away from established, but often misleading animal and single tissue culture techniques toward the generation of predictive data for a compound's safety and efficacy prior to its exposure to humans.

Laser irradiated fluorescent perfluorocarbon microparticles in 2-D and 3-D breast cancer cell models

Perfluorocarbon (PFC) droplets were studied as new generation ultrasound contrast agents via acoustic or optical droplet vaporization (ADV or ODV). Little is known about the ODV irradiated vaporization mechanisms of PFC-microparticle complexs and the stability of the new bubbles produced. In this study, fluorescent perfluorohexane (PFH) poly(lactic-co-glycolic acid) (PLGA) particles were used as a model to study the process of particle vaporization and bubble stability following excitation in two-dimensional (2-D) and three-dimensional (3-D) cell models. We observed localization of the fluorescent agent on the microparticle coating material initially and after vaporization under fluorescence microscopy. Furthermore, the stability and growth dynamics of the newly created bubbles were observed for 11 min following vaporization. The particles were co-cultured with 2-D cells to form 3-D spheroids and could be vaporized even when encapsulated within the spheroids via laser irradiation, which provides an effective basis for further work.

Nanoengineered implant as a new platform for regenerative nanomedicine using 3D well-organized human cell spheroids

In tissue engineering, it is still rare today to see clinically transferable strategies for tissue-engineered graft production that conclusively offer better tissue regeneration than the already existing technologies, decreased recovery times, and less risk of complications. Here a novel tissue-engineering concept is presented for the production of living bone implants combining 1) a nanofibrous and microporous implant as cell colonization matrix and 2) 3D bone cell spheroids. This combination, double 3D implants, shows clinical relevant thicknesses for the treatment of an early stage of bone lesions before the need of bone substitutes. The strategy presented here shows a complete closure of a defect in nude mice calvaria after only 31 days. As a novel strategy for bone regenerative nanomedicine, it holds great promises to enhance the therapeutic efficacy of living bone implants.

Dielectric spectroscopy platform to measure MCF10A epithelial cell aggregation as a model for spheroidal cell cluster analysis

A platform using planar electrodes to non-invasively monitor cell aggregation in a 3-dimensional extracellular matrix with dielectric spectroscopy.

21st Century Cell Culture for 21st Century Toxicology

There is no good science in bad models. Cell culture is especially prone to artifacts. A number of novel cell culture technologies have become more broadly available in the 21st century, which allow overcoming limitations of traditional culture and are more physiologically relevant. These include the use of stem-cell derived human cells, cocultures of different cell types, scaffolds and extracellular matrices, perfusion platforms (such as microfluidics), 3D culture, organ-on-chip technologies, tissue architecture, and organ functionality. The physiological relevance of such models is further enhanced by the measurement of biomarkers (e.g., key events of pathways), organ specific functionality, and more comprehensive assessment cell responses by high-content methods. These approaches are still rarely combined to create microphysiological systems. The complexity of the combination of these technologies can generate results closer to the in vivo situation but increases the number of parameters to control, bringing some new challenges. In fact, we do not argue that all cell culture needs to be that sophisticated. The efforts taken are determined by the purpose of our experiments and tests. If only a very specific molecular target to cell response is of interest, a very simple model, which reflects this, might be much more suited to allow standardization and high-throughput. However, the less defined the end point of interest and cellular response are, the better we should approximate organ- or tissue-like culture conditions to make physiological responses more probable. Besides these technologic advances, important progress in the quality assurance and reporting on cell cultures as well as the validation of cellular test systems brings the utility of cell cultures to a new level. The advancement and broader implementation of Good Cell Culture Practice (GCCP) is key here. In toxicology, this is a major prerequisite for meaningful and reliable results, ultimately supporting risk assessment and product development decisions.

Elaboration of a finite element model of pancreatic islet dielectric response to gap junction expression and insulin release

Dielectric spectroscopy could potentially be a powerful tool to monitor isolated human pancreatic islets for applications in diabetes therapy and research. Isolated intact human islets provide the most relevant means to understand the cellular and molecular mechanisms associated with diabetes. The advantages of dielectric spectroscopy for continuous islet monitoring are that it is a non-invasive, inexpensive and real-time technique. We have previously assessed the dielectric response of human islet samples during stimulation and differentiation. Because of the complex geometry of islets, analytical solutions are not sufficiently representative to provide a pertinent model of islet dielectric response. Here, we present a finite element dielectric model of a single intact islet that takes into account the tight packing of islet cells and intercellular junctions. The simulation yielded dielectric spectra characteristic of cell aggregates, similar to those produced with islets. In addition, the simulation showed that both exocytosis, such as what occurs during insulin secretion, and differential gap junction expression have significant effects on islet dielectric response. Since the progression of diabetes has some connections with dysfunctional islet gap junctions and insulin secretion, the ability to monitor these islet features with dielectric spectroscopy would benefit diabetes research.

Reversible Monolayer/Spheroid Cell Culture Switching by UCST-Type Thermoresponsive Ureido Polymers

Multicellular spheroids have been studied in the fields of oncology, stem cell biology, and tissue engineering. In this study, we found a new polymer material for thermo-controlled spheroid/monolayer cell culture switching. The polymers that have pendant ureido groups (ureido polymers) exhibited upper critical solution temperature-type phase separation behavior. Cells in monolayer culture were converted to spheroids by the addition of ureido polymers below phase separation temperature (T_p). Time-lapse observations indicated that cells began to migrate and aggregate to form the spheroids to avoid contact with phase-separated polymer (coacervates) on the surface of the culture dish. We supposed that the coacervates seemingly suppressed interaction between cell and the dish surface or extracellular matrices. By increasing culture temperature above T_p, the spheroids began to collapse into a monolayer of cells due to dissolution of the coacervates. These results indicated that cell morphology could be repeatedly switched by changing the culture temperature in the presence of ureido polymers.

Automated, Multiplexed Electrical Impedance Spectroscopy Platform for Continuous Monitoring of Microtissue Spheroids

Microtissue spheroids in microfluidic devices are increasingly used to establish novel in vitro organ models of the human body. As the spheroids are comparably sizable, it is difficult to monitor larger numbers of them by optical means. Therefore, electrical impedance spectroscopy (EIS) emerges as a viable alternative to probing spheroid properties. Current spheroid EIS systems are, however, not suitable for investigating multiple spheroids in parallel over extended time in an automated fashion. Here we address this issue by presenting an automated, multiplexed EIS (AMEIS) platform for impedance analysis in a microfluidic setting. The system was used to continuously monitor the effect of the anticancer drug fluorouracil (5-FU) on HCT116 cancer spheroids. Simultaneous EIS monitoring of up to 15 spheroids was performed in parallel over 4 days at a temporal resolution of 2 min without any need for pumps. The measurements were continuous in nature, and the setup was kept in a standard incubator under controlled conditions during the measurements. A baseline normalization method to improve robustness and to reduce the influence of slow changes in the medium conductivity on the spheroid EIS readings has been developed and validated by experiments and means of a finite-element model. The same method and platform was then used for online monitoring of cardiac spheroids. The beating frequency of each cardiac spheroid could be read out in a completely automated fashion. The developed system constitutes a promising method for simultaneously evaluating drug impact and/or toxic effects on multiple microtissue spheroids.

A 3D co-culture microtissue model of the human placenta for nanotoxicity assessment

There is increasing evidence that certain nanoparticles (NPs) can overcome the placental barrier, raising concerns on potential adverse effects on the growing fetus. But even in the absence of placental transfer, NPs may pose a risk to proper fetal development if they interfere with the viability and functionality of the placental tissue. The effects of NPs on the human placenta are not well studied or understood, and predictive in vitro placenta models to achieve mechanistic insights on NP-placenta interactions are essentially lacking. Using the scaffold-free hanging drop technology, we developed a well-organized and highly reproducible 3D co-culture microtissue (MT) model consisting of a core of placental fibroblasts surrounded by a trophoblast cell layer, which resembles the structure of the in vivo placental tissue. We could show that secretion levels of human chorionic gonadotropin (hCG) were significantly higher in 3D than in 2D cell cultures, which indicates an enhanced differentiation of trophoblasts grown on 3D MTs. NP toxicity assessment revealed that cadmium telluride (CdTe) and copper oxide (CuO) NPs but not titanium dioxide (TiO₂) NPs decreased MT viability and reduced the release of hCG. NP acute toxicity was significantly reduced in 3D co-culture MTs compared to 2D monocultures. Taken together, 3D placental MTs provide a new and promising model for the fast generation of tissue-relevant acute NP toxicity data, which are indispensable for the safe development of NPs for industrial, commercial and medical applications.

Well-organized spheroids as a new platform to examine cell interaction and behaviour during organ development

We present an experimental method allowing the production of three-dimensional organ-like structures, namely microtissues (MTs), in vitro without the need for exogenous extracellular matrix (ECM) or growth factors. Submandibular salivary glands (embryonic day ED14), kidneys (ED13) and lungs (ED13) were harvested from mouse embryos and dissociated into single cells by enzyme treatment. Single cells were seeded into special hanging drop culture plates (InSphero) and cultured for up to 14 days to obtain MTs. This strategy permitted full control of the quantity of seeded cells. The development of the MTs into organs was followed histologically and immunohistochemically. Well-organized epithelial structures surrounded by a basal lamina were formed, as confirmed by transmission electron microscopy. Expression of E-cadherin, vimentin, fibronectin and α-SMA was compared in organs and corresponding MTs by real-time quantitative polymerase chain reaction. Branching morphogenesis was induced in MTs (as shown by histology and immunostaining for fibronectin and perlecan) and was conserved even after 14 days of culture. MTs continued their development and their epithelial structures were comparable with those of the physiological organ at postnatal day 2 (PN2). Expression of aquaporins was investigated to obtain better support for the functional differentiation of epithelial cells. Histogenesis proceeded and led to the start of organogenesis. This experimental model might improve our knowledge of epithelial-mesenchymal histogenesis and can be employed to study development or cellular organization during the embryonic formation of organs.

Superporous Poly(ethylene glycol) Diacrylate Cryogel with a Defined Elastic Modulus for Prostate Cancer Cell Research

The physical and mechanical properties of the tumor microenvironment are crucial for the growth, differentiation and migration of cancer cells. However, such microenvironment is not found in the geometric constraints of 2D cell culture systems used in many cancer studies. Prostate cancer research, in particular, suffers from the lack of suitable in vitro models. Here a 3D superporous scaffold is described with thick pore walls in a mechanically stable and robust architecture to support prostate tumor growth. This scaffold is generated from the cryogelation of poly(ethylene glycol) diacrylate to produce a defined elastic modulus for prostate tumor growth. Lymph node carcinoma of the prostate (LNCaP) cells show a linear growth over 21 d as multicellular tumor spheroids in such a scaffold with points of attachments to the walls of the scaffold. These LNCaP cells respond to the growth promoting effects of androgens and demonstrate a characteristic cytoplasmic-nuclear translocation of the androgen receptor and androgen-dependent gene expression. Compared to 2D cell culture, the expression or androgen response of prostate cancer specific genes is greatly enhanced in the LNCaP cells in this system. This scaffold is therefore a powerful tool for prostate cancer studies with unique advantages over 2D cell culture systems.

Electrical Impedance Spectroscopy for Microtissue Spheroid Analysis in Hanging-Drop Networks

Electrical impedance spectroscopy (EIS) as a label free and noninvasive analysis method receives growing attention for monitoring three-dimensional tissue constructs. In this Article, we present the integration of an EIS readout function into the hanging-drop network platform, which has been designed for culturing microtissue spheroids in perfused multitissue configurations. Two pairs of microelectrodes have been implemented directly in the support of the hanging drops by using a small glass inlay inserted in the microfluidic structure. The pair of bigger electrodes is sensitive to the drop size and allows for drop size control over time. The pair of smaller electrodes is capable of monitoring, on the one hand, the size of microtissue spheroids to follow, for example, the growth of cancer microtissues, and, on the other hand, the beating of cardiac microtissues in situ. The presented results demonstrate the feasibility of an EIS readout within the framework of multifunctional hanging-drop networks.

Active implant combining human stem cell microtissues and growth factors for bone-regenerative nanomedicine

AIMS

Mesenchymal stem cells (MSCs) from adult bone marrow provide an exciting and promising stem cell population for the repair of bone in skeletal diseases. Here, we describe a new generation of collagen nanofiber implant functionalized with growth factor BMP-7 nanoreservoirs and equipped with human MSC microtissues (MTs) for regenerative nanomedicine.

MATERIALS & METHODS

By using a 3D nanofibrous collagen membrane and by adding MTs rather than single cells, we optimize the microenvironment for cell colonization, differentiation and growth.

RESULTS & CONCLUSION

Furthermore, in this study, we have shown that by combining BMP-7 with these MSC MTs in this double 3D environment, we further accelerate bone growth in vivo. The strategy described here should enhance the efficiency of therapeutic implants compared with current simplistic approaches used in the clinic today based on collagen implants soaked in bone morphogenic proteins.

Adipose regeneration and implications for breast reconstruction: update and the future

The evolution of breast reconstruction and management of breast cancer has evolved significantly since the earliest descriptions in the Edwin Smith Papyrus (3,000 BC). The development of surgical and scientific expertise has changed the way that women are managed, and plastic surgeons are now able to offer a wide range of reconstructive options to suit individual needs. Beyond the gold standard autologous flap based reconstructions, regenerative therapies promise the elimination of donor site morbidity whilst providing equivalent aesthetic and functional outcomes. Future research aims to address questions regarding ideal cell source, optimisation of scaffold composition and interaction of de novo adipose tissue in the microenvironment of breast cancer.

Microtissues in Cardiovascular Medicine: Regenerative Potential Based on a 3D Microenvironment

More people die annually from cardiovascular diseases than from any other cause. In particular, patients who suffer from myocardial infarction may be affected by ongoing adverse remodeling processes of the heart that may ultimately lead to heart failure. The introduction of stem and progenitor cell-based applications has raised substantial hope for reversing these processes and inducing cardiac regeneration. However, current stem cell therapies using single-cell suspensions have failed to demonstrate long-lasting efficacy due to the overall low retention rate after cell delivery to the myocardium. To overcome this obstacle, the concept of 3D cell culture techniques has been proposed to enhance therapeutic efficacy and cell engraftment based on the simulation of an in vivo-like microenvironment. Of great interest is the use of so-called microtissues or spheroids, which have evolved from their traditional role as in vitro models to their novel role as therapeutic agents. This review will provide an overview of the therapeutic potential of microtissues by addressing primarily cardiovascular regeneration. It will accentuate their advantages compared to other regenerative approaches and summarize the methods for generating clinically applicable microtissues. In addition, this review will illustrate the unique properties of the microenvironment within microtissues that makes them a promising next-generation therapeutic approach.

Nanoparticle transport across the placental barrier: pushing the field forward!

The human placenta is a multifunctional organ constituting the barrier between maternal and fetal tissues. Nanoparticles can cross the placental barrier, and there is increasing evidence that the extent of transfer is dependent on particle characteristics and functionalization. While translocated particles may pose risks to the growing fetus particles may also be engineered to enable new particle-based therapies in pregnancy. In both cases, a comprehensive understanding of nanoparticle uptake, accumulation and translocation is indispensable and requires predictive placental transfer models. We examine and evaluate the current literature to draw first conclusions on the possibility to steer translocation of nanoparticles. In addition, we discuss if current placental models are suitable for nanoparticle transfer studies and suggest strategies to improve their predictability.

Three-dimensional Micro-culture System for Tooth Tissue Engineering

The arrangement of cells within a tissue plays an essential role in organogenesis, including tooth development. Progress is being made to regenerate teeth by reassociating dissociated embryonic dental cells and implanting them in vivo. In the present study, we tested the hanging drop method to study mixed epithelial-mesenchymal cell reorganization in a liquid instead of semisolid medium to see whether it could lead to tooth histogenesis and organogenesis. This method allowed the control of the proportion and number of cells to be used, and the forming microtissues showed homogeneous size. The liquid environment favored cell migrations as compared with collagen gels. Three protocols were compared. The one that sequentially combined the hanging drop and semisolid medium cultures prior to in vivo implantation gave the best results. Indeed, after implantation, teeth developed, showing a well-formed crown, mineralization of dentin and enamel, and the initiation of root formation. Vascularization and the cellular heterogeneity in the mesenchyme were similar to what was observed in developing molars. Finally, after coimplantation with a trigeminal ganglion, the dental mesenchyme, including the odontoblast layer, became innervated. The real advantage of this technique is the small number of cells required to make a tooth. This experimental model can be employed to study the development, physiology, metabolism, or toxicology in forming teeth and test other cell sources.

Novel technologies and emerging biomarkers for personalized cancer immunotherapy

The culmination of over a century's work to understand the role of the immune system in tumor control has led to the recent advances in cancer immunotherapies that have resulted in durable clinical responses in patients with a variety of malignancies. Cancer immunotherapies are rapidly changing traditional treatment paradigms and expanding the therapeutic landscape for cancer patients. However, despite the current success of these therapies, not all patients respond to immunotherapy and even those that do often experience toxicities. Thus, there is a growing need to identify predictive and prognostic biomarkers that enhance our understanding of the mechanisms underlying the complex interactions between the immune system and cancer. Therefore, the Society for Immunotherapy of Cancer (SITC) reconvened an Immune Biomarkers Task Force to review state of the art technologies, identify current hurdlers, and make recommendations for the field. As a product of this task force, Working Group 2 (WG2), consisting of international experts from academia and industry, assembled to identify and discuss promising technologies for biomarker discovery and validation. Thus, this WG2 consensus paper will focus on the current status of emerging biomarkers for immune checkpoint blockade therapy and discuss novel technologies as well as high dimensional data analysis platforms that will be pivotal for future biomarker research. In addition, this paper will include a brief overview of the current challenges with recommendations for future biomarker discovery.

Novel technologies and emerging biomarkers for personalized cancer immunotherapy

The culmination of over a century’s work to understand the role of the immune system in tumor control has led to the recent advances in cancer immunotherapies that have resulted in durable clinical responses in patients with a variety of malignancies. Cancer immunotherapies are rapidly changing traditional treatment paradigms and expanding the therapeutic landscape for cancer patients. However, despite the current success of these therapies, not all patients respond to immunotherapy and even those that do often experience toxicities. Thus, there is a growing need to identify predictive and prognostic biomarkers that enhance our understanding of the mechanisms underlying the complex interactions between the immune system and cancer. Therefore, the Society for Immunotherapy of Cancer (SITC) reconvened an Immune Biomarkers Task Force to review state of the art technologies, identify current hurdlers, and make recommendations for the field. As a product of this task force, Working Group 2 (WG2), consisting of international experts from academia and industry, assembled to identify and discuss promising technologies for biomarker discovery and validation. Thus, this WG2 consensus paper will focus on the current status of emerging biomarkers for immune checkpoint blockade therapy and discuss novel technologies as well as high dimensional data analysis platforms that will be pivotal for future biomarker research. In addition, this paper will include a brief overview of the current challenges with recommendations for future biomarker discovery.

Combined Effect of Cryogel Matrix and Temperature-Reversible Soluble-Insoluble Polymer for the Development of in Vitro Human Liver Tissue

Hepatic cell culture on a three-dimensional (3D) matrix or as a hepatosphere appears to be a promising in vitro biomimetic system for liver tissue engineering applications. In this study, we have combined the concept of a 3D scaffold and a spheroid culture to develop an in vitro model to engineer liver tissue for drug screening. We have evaluated the potential of poly(ethylene glycol)-alginate-gelatin (PAG) cryogel matrix for in vitro culture of human liver cell lines. The synthesized cryogel matrix has a flow rate of 7 mL/min and water uptake capacity of 94% that enables easy nutrient transportation in the in vitro cell culture. Young's modulus of 2.4 kPa and viscoelastic property determine the soft and elastic nature of synthesized cryogel. Biocompatibility of PAG cryogel was evaluated through MTT assay of HepG2 and Huh-7 cells on matrices. The proliferation and functionality of the liver cells were enhanced by culturing hepatic cells as spheroids (hepatospheres) on the PAG cryogel using temperature-reversible soluble-insoluble polymer, poly(N-isopropylacrylamide) (PNIPAAm). Pore size of the cryogel above 100 μm modulated spheroid size that can prevent hypoxia condition within the spheroid culture. Both the hepatic cells have shown a significant difference (P < 0.05) in terms of cell number and functionality when cultured with PNIPAAm. After 10 days of culture using 0.05% PNIPAAm, the cell number increased by 11- and 7-fold in case of HepG2 and Huh-7 cells, respectively. Similarly, after 10 days of hepatic spheroids culture on PAG cryogel, the albumin production, urea secretion, and CYP450 activity were significantly higher in case of culture with PNIPAAm. The developed tissue mass on the PAG cryogel in the presence of PNIPAAm possess polarity, which was confirmed using F-actin staining and by presence of intercellular bile canalicular lumen. The developed cryogel matrix supports liver cells proliferation and functionality and therefore can be used for in vitro and in vivo drug testing.

Seamless Combination of Fluorescence-Activated Cell Sorting and Hanging-Drop Networks for Individual Handling and Culturing of Stem Cells and Microtissue Spheroids

Open microfluidic cell culturing devices offer new possibilities to simplify loading, culturing, and harvesting of individual cells or microtissues due to the fact that liquids and cells/microtissues are directly accessible. We present a complete workflow for microfluidic handling and culturing of individual cells and microtissue spheroids, which is based on the hanging-drop network concept: The open microfluidic devices are seamlessly combined with fluorescence-activated cell sorting (FACS), so that individual cells, including stem cells, can be directly sorted into specified culturing compartments in a fully automated way and at high accuracy. Moreover, already assembled microtissue spheroids can be loaded into the microfluidic structures by using a conventional pipet. Cell and microtissue culturing is then performed in hanging drops under controlled perfusion. On-chip drop size control measures were applied to stabilize the system. Cells and microtissue spheroids can be retrieved from the chip by using a parallelized transfer method. The presented methodology holds great promise for combinatorial screening of stem-cell and multicellular-spheroid cultures.

A mechanistic study on tumour spheroid formation in thermosensitive hydrogels: experiments and mathematical modelling

Thermo-reversible microgels to culture and harvest uniform-sized tumour spheroids with a narrow size-distribution.

TGF-β1, GDF-5, and BMP-2 stimulation induces chondrogenesis in expanded human articular chondrocytes and marrow-derived stromal cells

Replacement of degenerated cartilage with cell-based cartilage products may offer a long-term solution to halt arthritis' degenerative progression. Chondrocytes are frequently used in cell-based FDA-approved cartilage products; yet human marrow-derived stromal cells (hMSCs) show significant translational potential, reducing donor site morbidity and maintaining their undifferentiated phenotype with expansion. This study sought to investigate the effects of transforming growth factor β1 (TGF-β1), growth/differentiation factor 5 (GDF-5), and bone morphogenetic protein 2 (BMP-2) during postexpansion chondrogenesis in human articular chondrocytes (hACs) and to compare chondrogenesis in passaged hACs with that of passaged hMSCs. Through serial expansion, chondrocytes dedifferentiated, decreasing expression of chondrogenic genes while increasing expression of fibroblastic genes. However, following expansion, 10 ng/mL TGF-β1, 100 ng/mL GDF-5, or 100 ng/mL BMP-2 supplementation during three-dimensional aggregate culture each upregulated one or more markers of chondrogenic gene expression in both hACs and hMSCs. Additionally, in both cell types, the combination of TGF-β1, GDF-5, and BMP-2 induced the greatest upregulation of chondrogenic genes, that is, Col2A1, Col2A1/Col1A1 ratio, SOX9, and ACAN, and synthesis of cartilage-specific matrix, that is, glycosaminoglycans (GAGs) and ratio of collagen II/I. Finally, TGF-β1, GDF-5, and BMP-2 stimulation yielded mechanically robust cartilage rich in collagen II and GAGs in both cell types, following 4 weeks maturation. This study illustrates notable success in using the self-assembling method to generate robust, scaffold-free neocartilage constructs using expanded hACs and hMSCs.

Magnetic engineering of stable rod-shaped stem cell aggregates: circumventing the pitfall of self-bending

A current challenge for tissue engineering while restoring the function of diseased or damaged tissue is to customize the tissue according to the target area. Scaffold-free approaches usually yield spheroid shapes with the risk of necrosis at the center due to poor nutrient and oxygen diffusion. Here, we used magnetic forces developed at the cellular scale by miniaturized magnets to create rod-shaped aggregates of stem cells that subsequently matured into a tissue-like structure. However, during the maturation process, the tissue-rods spontaneously bent and coiled into sphere-like structures, triggered by the increasing cell-cell adhesion within the initially non-homogeneous tissue. Optimisation of the intra-tissular magnetic forces successfully hindered the transition, in order to produce stable rod-shaped stem cells aggregates.

Integrating Microtissues in Nanofiber Scaffolds for Regenerative Nanomedicine

A new generation of biomaterials focus on smart materials incorporating cells. Here, we describe a novel generation of synthetic nanofibrous implant functionalized with living microtissues for regenerative nanomedicine. The strategy designed here enhances the effectiveness of therapeutic implants compared to current approaches used in the clinic today based on single cells added to the implant.

3D liver models on a microplatform: well-defined culture, engineering of liver tissue and liver-on-a-chip

The liver, the largest organ in the human body, is a multi-functional organ with diverse metabolic activities that plays a critical role in maintaining the body and sustaining life. Although the liver has excellent regenerative and recuperative properties, damages caused by chronic liver diseases or viral infection may lead to permanent loss of liver functions. Studies of liver disease mechanism have focused on drug screening and liver tissue engineering techniques, including strategies based on in vitro models. However, conventional liver models are plagued by a number of limitations, which have motivated the development of 'liver-on-a-chip' and microplatform-based bioreactors that can provide well-defined microenvironments. Microtechnology is a promising tool for liver tissue engineering and liver system development, as it can mimic the complex in vivo microenvironment and microlevel ultrastructure, by using a small number of human cells under two-dimensional (2D) and three-dimensional (3D) culture conditions. These systems provided by microtechnology allow improved liver-specific functions and can be expanded to encompass diverse 3D culture methods, which are critical for the maintenance of liver functions and recapitulation of the features of the native liver. In this review, we provide an overview of microtechnologies that have been used for liver studies, describe biomimetic technologies for constructing microscale 2D and 3D liver models as well as liver-on-a-chip systems and microscale bioreactors, and introduce applications of liver microtechnology and future trends in the field.

Double compartmented and hybrid implant outfitted with well-organized 3D stem cells for osteochondral regenerative nanomedicine

AIM

Articular cartilage repair remains challenging, because most clinical failures are due to the lack of subchondral bone regeneration. We report an innovative approach improving cartilage repair by regenerating a robust subchondral bone, supporting articular cartilage.

MATERIALS & METHODS

We developed a compartmented living implant containing triple-3D structure: stem cells as microtissues for embryonic endochondral development mimic, nanofibrous collagen to enhance mineralization for subchondral bone and alginate hydrogel for cartilage regeneration.

RESULTS & CONCLUSION

This system mimics the natural gradient of the osteochondral unit, using only one kind of stem cell, targeting their ability to express specific bone or cartilage proteins. Mineralization gradient of articular cartilage and the natural 'glue' between subchondral bone and cartilage were reproduced in vitro.

The use of optical trap and microbeam to investigate the mechanical and transport characteristics of tunneling nanotubes in tumor spheroids

The use of optical trap and microbeam for investigating mechanical and transport properties of inter cellular tunneling nanotubes (TnTs) in tumor spheroids has been demonstrated. TnTs in tumor spheroids have been visualized by manipulating TnT connected cells using optical tweezers. Functionality of the TnTs for transferring cytoplasmic vesicles and injected dye molecules by optoporation method has been studied. Further, the TnTs could be longitudinally stretched by manipulating the connected cells and their elastic response was studied. Manipulation of cells at the surface of tumor spheroid using optical tweezers and injection of fluorescent dye into a trapped cell using optoporation technique.

Epidermal stem cells and skin tissue engineering in hair follicle regeneration

The reconstitution of a fully organized and functional hair follicle from dissociated cells propagated under defined tissue culture conditions is a challenge still pending in tissue engineering. The loss of hair follicles caused by injuries or pathologies such as alopecia not only affects the patients' psychological well-being, but also endangers certain inherent functions of the skin. It is then of great interest to find different strategies aiming to regenerate or neogenerate the hair follicle under conditions proper of an adult individual. Based upon current knowledge on the epithelial and dermal cells and their interactions during the embryonic hair generation and adult hair cycling, many researchers have tried to obtain mature hair follicles using different strategies and approaches depending on the causes of hair loss. This review summarizes current advances in the different experimental strategies to regenerate or neogenerate hair follicles, with emphasis on those involving neogenesis of hair follicles in adult individuals using isolated cells and tissue engineering. Most of these experiments were performed using rodent cells, particularly from embryonic or newborn origin. However, no successful strategy to generate human hair follicles from adult cells has yet been reported. This review identifies several issues that should be considered to achieve this objective. Perhaps the most important challenge is to provide three-dimensional culture conditions mimicking the structure of living tissue. Improving culture conditions that allow the expansion of specific cells while protecting their inductive properties, as well as methods for selecting populations of epithelial stem cells, should give us the necessary tools to overcome the difficulties that constrain human hair follicle neogenesis. An analysis of patent trends shows that the number of patent applications aimed at hair follicle regeneration and neogenesis has been increasing during the last decade. This field is attractive not only to academic researchers but also to the companies that own almost half of the patents in this field.

Photo-cross-linkable methacrylated gelatin and hydroxyapatite hybrid hydrogel for modularly engineering biomimetic osteon

Modular tissue engineering holds great potential in regenerating natural complex tissues by engineering three-dimensional modular scaffolds with predefined geometry and biological characters. In modular tissue-like construction, a scaffold with an appropriate mechanical rigidity for assembling fabrication and high biocompatibility for cell survival is the key to the successful bioconstruction. In this work, a series of composite hydrogels (GH0, GH1, GH2, and GH3) based on a combination of methacrylated gelatin (GelMA) and hydroxyapatite (HA) was exploited to enhance hydrogel mechanical rigidity and promote cell functional expression for osteon biofabrication. These composite hydrogels presented a lower swelling ratio, higher mechanical moduli, and better biocompatibility when compared to the pure GelMA hydrogel. Furthermore, on the basis of the composite hydrogel and photolithograph technology, we successfully constructed an osteon-like concentric double-ring structure in which the inner ring encapsulating human umbilical vascular endothelial cells (HUVECs) was designed to imitate blood vessel tubule while the outer ring encapsulating human osteoblast-like cells (MG63s) acts as part of bone. During the coculture period, MG63s and HUVECs exhibited not only satisfying growth status but also the enhanced genic expression of osteogenesis-related and angiogenesis-related differentiations. These results demonstrate this GelMA-HA composite hydrogel system is promising for modular tissue engineering.

3D spheroid cultures improve the metabolic gene expression profiles of HepaRG cells

Apo (Apolipoprotein)B secretion, as well as albumin secretion, increased in 3D HepG2 and HepaRG spheroids. Liver metabolic gene expression was up-regulated in 3D HepaRG spheroids. These results suggest that hanging drop 3D cultures can improve hepatocellular responses as a functional liver.

3D (three-dimensional) cultures are considered to be an effective method for toxicological studies; however, little evidence has been reported whether 3D cultures have an impact on hepatocellular physiology regarding lipid or glucose metabolism. In the present study, we conducted physiological characterization of hepatoma cell lines HepG2 and HepaRG cells cultured in 3D conditions using a hanging drop method to verify the effect of culture environment on cellular responses. Apo (Apolipoprotein)B as well as albumin secretion was augmented by 3D cultures. Expression of genes related to not only drug, but also glucose and lipid metabolism were significantly enhanced in 3D cultured HepaRG spheroids. Furthermore, mRNA levels of CYP (cytochrome P450) enzymes following exposure to corresponding inducers increased under the 3D condition. These data suggest that this simple 3D culture system without any special biomaterials can improve liver-specific characteristics including lipid metabolism. Considering that the system enables high-throughput assay, it may become a powerful tool for compound screening concerning hepatocellular responses in order to identify potential drugs.

The multi-organ chip--a microfluidic platform for long-term multi-tissue coculture

The ever growing amount of new substances released onto the market and the limited predictability of current in vitro test systems has led to a high need for new solutions for substance testing. Many drugs that have been removed from the market due to drug-induced liver injury released their toxic potential only after several doses of chronic testing in humans. However, a controlled microenvironment is pivotal for long-term multiple dosing experiments, as even minor alterations in extracellular conditions may greatly influence the cell physiology. We focused within our research program on the generation of a microengineered bioreactor, which can be dynamically perfused by an on-chip pump and combines at least two culture spaces for multi-organ applications. This circulatory system mimics the in vivo conditions of primary cell cultures better and assures a steadier, more quantifiable extracellular relay of signals to the cells. For demonstration purposes, human liver equivalents, generated by aggregating differentiated HepaRG cells with human hepatic stellate cells in hanging drop plates, were cocultured with human skin punch biopsies for up to 28 days inside the microbioreactor. The use of cell culture inserts enables the skin to be cultured at an air-liquid interface, allowing topical substance exposure. The microbioreactor system is capable of supporting these cocultures at near physiologic fluid flow and volume-to-liquid ratios, ensuring stable and organotypic culture conditions. The possibility of long-term cultures enables the repeated exposure to substances. Furthermore, a vascularization of the microfluidic channel circuit using human dermal microvascular endothelial cells yields a physiologically more relevant vascular model.

AnaSP: a software suite for automatic image analysis of multicellular spheroids

Today, more and more biological laboratories use 3D cell cultures and tissues grown in vitro as a 3D model of in vivo tumours and metastases. In the last decades, it has been extensively established that multicellular spheroids represent an efficient model to validate effects of drugs and treatments for human care applications. However, a lack of methods for quantitative analysis limits the usage of spheroids as models for routine experiments. Several methods have been proposed in literature to perform high throughput experiments employing spheroids by automatically computing different morphological parameters, such as diameter, volume and sphericity. Nevertheless, these systems are typically grounded on expensive automated technologies, that make the suggested solutions affordable only for a limited subset of laboratories, frequently performing high content screening analysis. In this work we propose AnaSP, an open source software suitable for automatically estimating several morphological parameters of spheroids, by simply analyzing brightfield images acquired with a standard widefield microscope, also not endowed with a motorized stage. The experiments performed proved sensitivity and precision of the segmentation method proposed, and excellent reliability of AnaSP to compute several morphological parameters of spheroids imaged in different conditions. AnaSP is distributed as an open source software tool. Its modular architecture and graphical user interface make it attractive also for researchers who do not work in areas of computer vision and suitable for both high content screenings and occasional spheroid-based experiments.

Stem cell-derived systems in toxicology assessment

Industrial sectors perform toxicological assessments of their potential products to ensure human safety and to fulfill regulatory requirements. These assessments often involve animal testing, but ethical, cost, and time concerns, together with a ban on it in specific sectors, make appropriate in vitro systems indispensable in toxicology. In this study, we summarize the outcome of an EPAA (European Partnership of Alternatives to Animal Testing)-organized workshop on the use of stem cell-derived (SCD) systems in toxicology, with a focus on industrial applications. SCD systems, in particular, induced pluripotent stem cell-derived, provide physiological cell culture systems of easy access and amenable to a variety of assays. They also present the opportunity to apply the vast repository of existing nonclinical data for the understanding of in vitro to in vivo translation. SCD systems from several toxicologically relevant tissues exist; they generally recapitulate many aspects of physiology and respond to toxicological and pharmacological interventions. However, focused research is necessary to accelerate implementation of SCD systems in an industrial setting and subsequent use of such systems by regulatory authorities. Research is required into the phenotypic characterization of the systems, since methods and protocols for generating terminally differentiated SCD cells are still lacking. Organotypical 3D culture systems in bioreactors and microscale tissue engineering technologies should be fostered, as they promote and maintain differentiation and support coculture systems. They need further development and validation for their successful implementation in toxicity testing in industry. Analytical measures also need to be implemented to enable compound exposure and metabolism measurements for in vitro to in vivo extrapolation. The future of SCD toxicological tests will combine advanced cell culture technologies and biokinetic measurements to support regulatory and research applications. However, scientific and technical hurdles must be overcome before SCD in vitro methods undergo appropriate validation and become accepted in the regulatory arena.

Is Trichomonas tenax a Parasite or a Commensal?

Trichomonas tenax is considered a commensal organism found under poor oral hygiene conditions. T. tenax presents morphological similarities with T. vaginalis, and there are doubts concerning whether this protist is a parasite and whether it is a genetic variant of T. vaginalis. This study aimed to investigate the capacity of T. tenax to cause mammalian cell damage and compare its cytotoxicity with that of T. vaginalis. Protozoan-host cell interaction assays were performed with Madin-Darby canine kidney, HeLa, and gum cells and 3D spheroids, which were examined by scanning electron and transmission electron microscopy. Cellular viability experiments were also performed. T. tenax attached and had different forms when interacting with mammalian cells and caused damage with time-dependent host-cell viability. We observed that T. tenax produced plasma membrane projections and phagocytosed portions of the mammalian cells. In addition, T. tenax caused membrane blebbing and apoptotic bodies in HeLa cells, thus inducing cell death. Spheroids were also used in interaction assays with T. tenax and they were damaged by these cells. This study shows that T. tenax fulfills the requisites of a parasite, causing damage to different mammalian cells and behaving similarly to T. vaginalis when in contact with target cells in vitro.

In vitro analysis of scaffold-free prevascularized microtissue spheroids containing human dental pulp cells and endothelial cells

INTRODUCTION

Scaffolds often fail to mimic essential functions of the physiologic extracellular matrix (ECM) that regulates cell-cell communication in tissue microenvironments. The development of scaffold-free microtissues containing stem cell-derived ECM may serve as a successful alternative to the use of artificial scaffolds. The current study aimed to fabricate 3-dimensional microtissue spheroids of dental pulp cells (DPCs) prevascularized by human umbilical vein endothelial cells (HUVECs) and to characterize these scaffold-free spheroids for the in vitro formation of pulplike tissue constructs.

METHODS

Three-dimensional microtissue spheroids of DPC alone and DPC-HUVEC co-cultures were fabricated using agarose micro-molds. Cellular organization within the spheroids and cell viability (live/dead assay) were assessed at days 1, 7, and 14. Microtissue spheroids were allowed to self-assemble into macrotissues, induced for odontogenic differentiation (21 days), and examined for expression levels of osteo/odontogenic markers: alkaline phosphatase, bone sialoprotein and RUNX2 (Real-time PCR), mineralization (von-Kossa), and prevascularisation (immunohistochemistry for CD31).

RESULTS

The DPC microtissue microenvironment supported HUVEC survival and capillary network formation in the absence of a scaffolding material and external angiogenic stimulation. Immunohistochemical staining for CD31 showed the capillary network formed by HUVECs did sustain-for a prolonged period-even after the microtissues transformed into a macrotissue. Induced, prevascularized macrotissues showed enhanced differentiation capacity compared with DPC alone macrotissues, as shown by higher osteo/odontogenic gene expression levels and mineralization.

CONCLUSIONS

These findings provide insight into the complex intercellular cross talk occurring between DPCs and HUVECs in the context of angiogenesis and pulp regeneration and highlight the significance of developing a favorable 3-dimensional microenvironment that can, in turn, contribute toward successful pulp regeneration strategies.

Cancer multicellular spheroids: volume assessment from a single 2D projection

Volume is one of the most important features for the characterization of a tumour on a macroscopic scale. It is often used to assess the effectiveness of care treatments, thus making its correct evaluation a crucial issue for patient care. Similarly, volume is a key feature on a microscopic scale. Multicellular cancer spheroids are 3D tumour models widely employed in pre-clinical studies to test the effects of drugs and radiotherapy treatments. Very few methods have been proposed to estimate the tumour volume arising from a 2D projection of multicellular spheroids, and even fewer have been designed to provide a 3D reconstruction of the tumour shape. In this work, we propose Reconstruction and Visualization from a Single Projection (ReViSP), an automatic method conceived to reconstruct the 3D surface and estimate the volume of single cancer multicellular spheroids, or even of spheroid cultures. As the input parameter ReViSP requires only one 2D projection, which could be a widefield microscope image. We assessed the effectiveness of our method by comparing it with other approaches. To this purpose, we used a new strategy that allowed us to achieve accurate volume measurements based on the analysis of home-made 3D objects, built by mimicking the spheroid morphology. The results confirmed the effectiveness of our method for both 3D reconstruction and volume assessment. ReViSP software is distributed as an open source tool.

3D spherical microtissues and microfluidic technology for multi-tissue experiments and analysis

Rational development of more physiologic in vitro models includes the design of robust and flexible 3D-microtissue-based multi-tissue devices, which allow for tissue-tissue interactions. The developed device consists of multiple microchambers interconnected by microchannels. Pre-formed spherical microtissues are loaded into the microchambers and cultured under continuous perfusion. Gravity-driven flow is generated from on-chip reservoirs through automated chip-tilting without any need for additional tubing and external pumps. This tilting concept allows for operating up to 48 devices in parallel in order to test various drug concentrations with a sufficient number of replicates. For a proof of concept, rat liver and colorectal tumor microtissues were interconnected on the chip and cultured during 8 days in the presence of the pro-drug cyclophosphamide. Cyclophosphamide has a significant impact on tumor growth but only after bio-activation by the liver. This effect was only observed in the perfused and interconnected co-cultures of different microtissue types on-chip, whereas the discontinuous transfer of supernatant via pipetting from static liver microtissues that have been treated with cyclophosphamide did not significantly affect tumor growth. The results indicate the utility and multi-tissue functionality of this platform. The importance of continuous medium circulation and tissue interaction is highlighted.

Soluble CD54 induces human endothelial cells ex vivo expansion useful for cardiovascular regeneration and tissue engineering application

Aim

Consistent expansion of primary human endothelial cells in vitro is critical in the development of engineered tissue. A variety of complex culture media and techniques developed from different basal media have been reported with alternate success. Incongruous results are further confounded by donor-to-donor variability and cellular source of derivation. Our results demonstrate how to overcome these limitations using soluble CD54 (sCD54) as additive to conventional culture medium.

Methods and results

Isolated primary fragment of different vessel types was expanded in Ham's F12 DMEM, enriched with growth factors, Fetal Calf Serum and conditioned medium of Human Umbilical Vein Endothelial Cells (HUVEC) collected at different passages. Cytokine content of culture media was analyzed in order to identify the soluble factors correlating with better proliferation profile. sCD54 was found to induce the in vitro expansion of human endothelial cells (HECs) independently from the vessels source and even in the absence of HUVEC-conditioned medium. The HECs cultivated in the presence of sCD54 (50 ng/ml), resulted positive for the expression of CD146 and negative for CD45, and lower fibroblast contamination. Cells were capable to proliferate with an S phase of 25%, to produce vascular endothelial growth factor, VEGF, (10 ng/ml) and to give origin to vessel-like tubule in vitro.

Conclusion

Our results demonstrate that sCD54 is an essential factor for the in-vitro expansion of HECs without donor and vessel-source variability. Resulting primary cultures can be useful, for tissue engineering in regenerative medicine (e.g. artificial micro tissue generation, coating artificial heart valve etc.) and bio-nanotechnology applications.