Strategies for improving the physiological relevance of human engineered tissues

Vascularised organoids: Recent advances and applications in cancer research

Organoids are three-dimensional (3D) cellular models designed to replicate human tissues and organs while preserving their physiological complexity and functionality. Among these, vascularised organoids represent a groundbreaking advancement in 3D tissue engineering, incorporating vascular networks into engineered tissues to more accurately mimic the in vivo tumour microenvironment. These models offer significantly improved physiological relevance compared to conventional two-dimensional cultures or animal models, positioning them as invaluable tools in cancer research. Despite their potential, the rapid proliferation of techniques and materials for developing vascularised organoids presents challenges for researchers navigating this dynamic field. This systematic review provides a comprehensive examination of methodologies for fabricating vascularised organoids, with a focus on strategies that enhance vascularisation and support organoid growth. It critically evaluates the materials used, emphasising those that effectively mimic the extracellular matrix and facilitate vascular network formation. Key advancements in engineered organoids models are highlighted, emphasising their potential for studying interactions between vasculature and cancer cells, conducting drug screening, and understanding cytokine regulation. In summary, this review provides an in-depth overview of the current landscape of vascularised organoid fabrication and functionality, addressing challenges and opportunities within the field. A detailed understanding of the scope and future trajectories is essential for advancing organoid development and expanding their applications in both basic cancer research and clinical practice. KEY POINTS: Comparative analysis: Evaluation of organoids, animal models, and 2D models, highlighting their respective strengths and limitations in replicating physiological conditions and studying disease processes. Vascularisation techniques: Comparative evaluation of vascularised organoid fabrication methods, emphasising their efficiency, scalability and ability to replicate physiological vascular networks. Material selection: Thorough evaluation of materials for vascularised organoid culture system, focusing on those that effectively mimic the extracellular matrix and support vascular network formation. Applications: Overview of organoid applications in basic cancer research and clinical settings, with an emphasis on their potential in drug discovery, disease modelling and exploring complex biological processes.

Engineering considerations in the design of tissue specific bioink for 3D bioprinting applications

Over eight million surgical procedures are conducted annually in the United Stats to address organ failure or tissue losses. In response to this pressing need, recent medical advancements have significantly improved patient outcomes, primarily through innovative reconstructive surgeries utilizing tissue grafting techniques. Despite tremendous efforts, repairing damaged tissues remains a major clinical challenge for bioengineers and clinicians. 3D bioprinting is an additive manufacturing technique that holds significant promise for creating intricately detailed constructs of tissues, thereby bridging the gap between engineered and actual tissue constructs. In contrast to non-biological printing, 3D bioprinting introduces added intricacies, including considerations for material selection, cell types, growth, and differentiation factors. However, technical challenges arise, particularly concerning the delicate nature of living cells in bioink for tissue construction and limited knowledge about the cell fate processes in such a complex biomechanical environment. A bioink must have appropriate viscoelastic and rheological properties to mimic the native tissue microenvironment and attain desired biomechanical properties. Hence, the properties of bioink play a vital role in the success of 3D bioprinted substitutes. This review comprehensively delves into the scientific aspects of tissue-centric or tissue-specific bioinks and sheds light on the current challenges of the translation of bioinks and bioprinting.

Supercooled preservation of cultured primary rat hepatocyte monolayers

Supercooled preservation (SCP) is a technology that involves cooling a substance below its freezing point without initiating ice crystal formation. It is a promising alternative to prolong the preservation time of cells, tissues, engineered tissue products, and organs compared to the current practices of hypothermic storage. Two-dimensional (2D) engineered tissues are extensively used in in vitro research for drug screening and development and investigation of disease progression. Despite their widespread application, there is a lack of research on the SCP of 2D-engineered tissues. In this study, we presented the effects of SCP at -2 and -6°C on primary rat hepatocyte (PRH) monolayers for the first time and compared cell viability and functionality with cold storage (CS, + 4°C). We preserved PRH monolayers in two different commercially available solutions: Hypothermosol-FRS (HTS-FRS) and the University of Wisconsin (UW) with and without supplements (i.e., polyethylene glycol (PEG) and 3-O-Methyl-Α-D-Glucopyranose (3-OMG)). Our findings revealed that UW with and without supplements were inadequate for the short-term preservation of PRH monolayers for both SCP and CS with high viability, functionality, and monolayer integrity. The combination of supplements (PEG and 3-OMG) in the HTS-FRS solution outperformed the other groups and yielded the highest viability and functional capacity. Notably, PRH monolayers exhibited superior viability and functionality when stored at -2°C through SCP for up to 3 days compared to CS. Overall, our results demonstrated that SCP is a feasible approach to improving the short-term preservation of PRH monolayers and enables readily available 2D-engineered tissues to advance in vitro research. Furthermore, our findings provide insights into preservation outcomes across various biological levels, from cells to tissues and organs, contributing to the advancement of bioengineering and biotechnology.

Robot-based 6D bioprinting for soft tissue biomedical applications

Within this interdisciplinary study, we demonstrate the applicability of a 6D printer for soft tissue engineering models. For this purpose, a special plant was constructed, combining the technical requirements for 6D printing with the biological necessities, especially for soft tissue. Therefore, a commercial 6D robot arm was combined with a sterilizable housing (including a high-efficiency particulate air (HEPA) filter and ultraviolet radiation (UVC) lamps) and a custom-made printhead and printbed. Both components allow cooling and heating, which is desirable for working with viable cells. In addition, a spraying unit was installed that allows the distribution of fine droplets of a liquid. Advanced geometries on uneven or angled surfaces can be created with the use of all six axes. Based on often used bioinks in the field of soft tissue engineering (gellan gum, collagen, and gelatin methacryloyl) with very different material properties, we could demonstrate the flexibility of the printing system. Furthermore, cell-containing constructs using primary human adipose-derived stem cells (ASCs) could be produced in an automated manner. In addition to cell survival, the ability to differentiate along the adipogenic lineage could also be demonstrated as a representative of soft tissue engineering.

Silk Fibroin Materials: Biomedical Applications and Perspectives

The golden rule in tissue engineering is the creation of a synthetic device that simulates the native tissue, thus leading to the proper restoration of its anatomical and functional integrity, avoiding the limitations related to approaches based on autografts and allografts. The emergence of synthetic biocompatible materials has led to the production of innovative scaffolds that, if combined with cells and/or bioactive molecules, can improve tissue regeneration. In the last decade, silk fibroin (SF) has gained attention as a promising biomaterial in regenerative medicine due to its enhanced bio/cytocompatibility, chemical stability, and mechanical properties. Moreover, the possibility to produce advanced medical tools such as films, fibers, hydrogels, 3D porous scaffolds, non-woven scaffolds, particles or composite materials from a raw aqueous solution emphasizes the versatility of SF. Such devices are capable of meeting the most diverse tissue needs; hence, they represent an innovative clinical solution for the treatment of bone/cartilage, the cardiovascular system, neural, skin, and pancreatic tissue regeneration, as well as for many other biomedical applications. The present narrative review encompasses topics such as (i) the most interesting features of SF-based biomaterials, bare SF's biological nature and structural features, and comprehending the related chemo-physical properties and techniques used to produce the desired formulations of SF; (ii) the different applications of SF-based biomaterials and their related composite structures, discussing their biocompatibility and effectiveness in the medical field. Particularly, applications in regenerative medicine are also analyzed herein to highlight the different therapeutic strategies applied to various body sectors.

The Evolution of Current Concept of the Reconstructive Ladder in Plastic Surgery: The Emerging Role of Translational Medicine

Plastic surgeons have used the reconstructive ladder for many decades as a standard directory for complex trauma reconstruction with the goal of repairing body structures and restoring functionality. This consists of different surgical maneuvers, such as secondary intention and direct tissue closure, as well as more complex methods such as local tissue transfer and free flap. The reconstructive ladder represents widely known options achievable for tissue reconstruction and wound closure that puts at the bottom rung the simplest methods of reconstruction and strengthens the complexity by moving upward. Regenerative medicine and surgery constitute a quickly spreading area of translational research that can be employed by minimally invasive surgical strategies, with the aim of regenerating cells and tissues in vivo in order to reestablish normal function through the intrinsic potential of cells, in combination with biomaterials and appropriate biochemical stimuli. These translational procedures have the aim of creating an appropriate microenvironment capable of supporting the physiological cellular function to generate the desired cells or tissues and to generate parenchymal, stromal, and vascular components on demand, and above all to produce intelligent materials capable of determining the fate of cells. Smart technologies have been grown that give extra "rungs" on the classic reconstructive ladder to integrate a more holistic, patient-based approach with improved outcomes. This commentary presents the evolution of the traditional concept of the reconstructive ladder in the field of plastic surgery into a new course with the aim of achieving excellent results for soft tissue reconstruction by applying innovative technologies and biologically active molecules for a wide range of surgical diseases.

High throughput microscopy and single cell phenotypic image-based analysis in toxicology and drug discovery

Measuring single cell responses to the universe of chemicals (drugs, natural products, environmental toxicants etc.) is of paramount importance to human health as phenotypic variability in sensing stimuli is a hallmark of biology that is considered during high throughput screening. One of the ways to approach this problem is via high throughput, microscopy-based assays coupled with multi-dimensional single cell analysis methods. Here, we will summarize some of the efforts in this vast and growing field, focusing on phenotypic screens (e.g., Cell Painting), single cell analytics and quality control, with particular attention to environmental toxicology and drug screening. We will discuss advantages and limitations of high throughput assays with various end points and levels of complexity.

A Bioglass-Poly(lactic-co-glycolic Acid) Scaffold@Fibrin Hydrogel Construct to Support Endochondral Bone Formation

Bone tissue engineering using stem cells to build bone directly on a scaffold matrix often fails due to lack of oxygen at the injury site. This may be avoided by following the endochondral ossification route; herein, a cartilage template is promoted first, which can survive hypoxic environments, followed by its hypertrophy and ossification. However, hypertrophy is so far only achieved using biological factors. This work introduces a Bioglass-Poly(lactic-co-glycolic acid@fibrin (Bg-PLGA@fibrin) construct where a fibrin hydrogel infiltrates and encapsulates a porous Bg-PLGA. The hypothesis is that mesenchymal stem cells (MSCs) loaded in the fibrin gel and induced into chondrogenesis degrade the gel and become hypertrophic upon reaching the stiffer, bioactive Bg-PLGA core, without external induction factors. Results show that Bg-PLGA@fibrin induces hypertrophy, as well as matrix mineralization and osteogenesis; it also promotes a change in morphology of the MSCs at the gel/scaffold interface, possibly a sign of osteoblast-like differentiation of hypertrophic chondrocytes. Thus, the Bg-PLGA@fibrin construct can sequentially support the different phases of endochondral ossification purely based on material cues. This may facilitate clinical translation by decreasing in-vitro cell culture time pre-implantation and the complexity associated with the use of external induction factors.

Gut-on-a-Chip Research for Drug Development: Implications of Chip Design on Preclinical Oral Bioavailability or Intestinal Disease Studies

The gut plays a key role in drug absorption and metabolism of orally ingested drugs. Additionally, the characterization of intestinal disease processes is increasingly gaining more attention, as gut health is an important contributor to our overall health. The most recent innovation to study intestinal processes in vitro is the development of gut-on-a-chip (GOC) systems. Compared to conventional in vitro models, they offer more translational value, and many different GOC models have been presented over the past years. Herein, we reflect on the almost unlimited choices in designing and selecting a GOC for preclinical drug (or food) development research. Four components that largely influence the GOC design are highlighted, namely (1) the biological research questions, (2) chip fabrication and materials, (3) tissue engineering, and (4) the environmental and biochemical cues to add or measure in the GOC. Examples of GOC studies in the two major areas of preclinical intestinal research are presented: (1) intestinal absorption and metabolism to study the oral bioavailability of compounds, and (2) treatment-orientated research for intestinal diseases. The last section of this review presents an outlook on the limitations to overcome in order to accelerate preclinical GOC research.

A state-of-the-art guide about the effects of sterilization processes on 3D-printed materials for surgical planning and medical applications: A comparative study

Surgeons use different medical devices in the surgery, such as patient-specific anatomical models, cutting and positioning guides, or implants. These devices must be sterilized before being used in the operation room. There are many sterilization processes available, with autoclave, hydrogen peroxide, and ethylene oxide being the most common in hospital settings. Each method has both advantages and disadvantages in terms of mechanics, chemical interaction, and post-treatment accuracy. The aim of the present study is to evaluate the dimensional and mechanical effect of the most commonly used sterilization techniques available in clinical settings, i.e., Autoclave 121, Autoclave 134, and hydrogen peroxide (HPO), on 11 of the most used 3D-printed materials fabricated using additive manufacturing technologies. The results showed that the temperature (depending on the sterilization method) and the exposure time to that temperature influence not only the mechanical behavior but also the original dimensioning planned on the 3D model. Therefore, HPO is a better overall option for most of the materials evaluated. Finally, based on the results of the study, a recommendation guide on sterilization methods per material, technology, and clinical application is presented.

3D cancer models: One step closer to in vitro human studies

Cancer immunotherapy is the great breakthrough in cancer treatment as it displayed prolonged progression-free survival over conventional therapies, yet, to date, in only a minority of patients. In order to broad cancer immunotherapy clinical applicability some roadblocks need to be overcome, first among all the lack of preclinical models that faithfully depict the local tumor microenvironment (TME), which is known to dramatically affect disease onset, progression and response to therapy. In this review, we provide the reader with a detailed overview of current 3D models developed to mimick the complexity and the dynamics of the TME, with a focus on understanding why the TME is a major target in anticancer therapy. We highlight the advantages and translational potentials of tumor spheroids, organoids and immune Tumor-on-a-Chip models in disease modeling and therapeutic response, while outlining pending challenges and limitations. Thinking forward, we focus on the possibility to integrate the know-hows of micro-engineers, cancer immunologists, pharmaceutical researchers and bioinformaticians to meet the needs of cancer researchers and clinicians interested in using these platforms with high fidelity for patient-tailored disease modeling and drug discovery.

Effects of dragon fruit oligosaccharides on immunity, gut microbiome, and their metabolites in healthy adults – a randomized double-blind placebo controlled study

Healthy food has wide popularity and relates positively to health. Our previous studies have shown that dragon fruit oligosaccharides (DFO) have prebiotic activities, balancing the gut microbiota in a simulated human colon system, and are safe and stimulate the immune system in rats. The effects of DFO on immune stimulation gut microbe modulation and the correlation of gut microbiota and nutrients were investigated in a human trial. This clinical study was a randomized, double-blinded, placebo-controlled trial. The participants were 107 healthy adults, divided into 3 groups that received DFO in drinking waterdoses of 4 and 8 g/day, compared to the placebo group for 4 consecutive weeks. DFO consumption at 4 g/day increased IgA level (11.31 mg/dL or 10.95% from baseline) and 8 g/day outstandingly promoted the growth of Bifidobacterium spp. (8.41%) and Faecalibacterium (1.99%) and decreased harmful bacteria, especially, Escherichia coli (8.44%). The relationship between gut microbes and nutrient intake was explored and significant (p < 0.05) correlations between specific microbial groups and intakes of specific macro- and micronutrients were observed. The potential dose of DFO for healthy adults was established as 4 g/day for improving IgA level and 8 g/day for promoting beneficial gut microbiota.

Modelling acute myeloid leukemia (AML): What's new? A transition from the classical to the modern

Acute myeloid leukemia (AML) is a heterogeneous malignancy affecting myeloid cells in the bone marrow (BM) but can spread giving rise to impaired hematopoiesis. AML incidence increases with age and is associated with poor prognostic outcomes. There has been a disconnect between the success of novel drug compounds observed in preclinical studies of hematological malignancy and less than exceptional therapeutic responses in clinical trials. This review aims to provide a state-of-the-art overview on the different preclinical models of AML available to expand insights into disease pathology and as preclinical screening tools. Deciphering the complex physiological and pathological processes and developing predictive preclinical models are key to understanding disease progression and fundamental in the development and testing of new effective drug treatments. Standard scaffold-free suspension models fail to recapitulate the complex environment where AML occurs. To this end, we review advances in scaffold/matrix-based 3D models and outline the most recent advances in on-chip technology. We also provide an overview of clinically relevant animal models and review the expanding use of patient-derived samples, which offer the prospect to create more "patient specific" screening tools either in the guise of 3D matrix models, microphysiological "organ-on-chip" tools or xenograft models and discuss representative examples.

Co-Culture of THP-1 Cells and Normal Human Epidermal Keratinocytes (NHEK) for Modified Human Cell Line Activation Test (h-CLAT)

To improve the accuracy of skin sensitization prediction of chemicals by conventional alternative methods using cells, it is important to reproduce the environment of skin in vitro, such as the crosstalk between keratinocytes and dendritic cells (DCs). We developed a skin sensitization test system based on the markers and criteria of the human cell line activation test (h-CLAT), which combines THP-1 cells as a surrogate for DCs and keratinized normal human epidermal keratinocytes (NHEK). After exposure to chemicals via keratinized NHEK, the cell surface expression of CD54 and CD86 on THP-1 was measured by flow cytometry. This co-culture system evaluated 2,4-dinitrochlorobenzene (DNCB), a typical sensitizer, as positive, lactic acid (LA), a non-sensitizer, as negative, and isoeugenol (IE), a prohapten that requires biological activation to acquire skin sensitization, as positive. However, the expression levels of CD54 and CD86 in DNCB-treated THP-1 were lower than those in normal h-CLAT. Therefore, we investigated the effects of the medium and secretion by NHEK cells on THP-1 cells. CD54 and CD86 expression was enhanced in monocultured THP-1 in the medium for keratinized NHEK and in the conditioned medium of keratinized NHEK. The increase in CD54 and CD86 by changes in the medium type was higher than that by the NHEK secretion; therefore, it was found that the medium composition has a large effect on the evaluation index among the experimental parameters in the co-culture system. It is necessary to find the optimal medium for immunotoxicity assessment in the co-culture system.

Fabrication of biomimetic networks using viscous fingering in flexographic printing

Mammalian tissue comprises a plethora of hierarchically organized channel networks that serve as routes for the exchange of liquids, nutrients, bio-chemical cues or electrical signals, such as blood vessels, nerve fibers, or lymphatic conduits. Despite differences in function and size, the networks exhibit a similar, highly branched morphology with dendritic extensions. Mimicking such hierarchical networks represents a milestone in the biofabrication of tissues and organs. Work to date has focused primarily on the replication of the vasculature. Despite initial progress, reproducing such structures across scales and increasing biofabrication efficiency remain a challenge. In this work, we present a new biofabrication method that takes advantage of the viscous fingering phenomenon. Using flexographic printing, highly branched, inter-connective channel structures with stochastic, biomimetic distribution and dendritic extensions can be fabricated with unprecedented efficiency. Using gelatin (5%-35%) as resolvable sacrificial material, the feasability of the proposed method is demonstrated on the example of a vascular network. By selectively adjusting the printing velocity (0.2-1.5 m s^-1), the anilox roller dip volume (4.5-24 ml m^-2) as well as the shear viscosity of the printing material used (10-900 mPas), the width of the structures produced (30-400 µm) as well as their distance (200-600 µm) can be specifically determined. In addition to the flexible morphology, the high scalability (2500-25 000 mm²) and speed (1.5 m s^-1) of the biofabrication process represents an important unique selling point. Printing parameters and hydrogel formulations are investigated and tuned towards a process window for controlled fabrication of channels that mimic the morphology of small blood vessels and capillaries. Subsequently, the resolvable structures were casted in a hydrogel matrix enabling bulk environments with integrated channels. The perfusability of the branched, inter-connective structures was successfully demonstrated. The fabricated networks hold great potential to enable nutrient supply in thick vascularized tissues or perfused organ-on-a-chip systems. In the future, the concept can be further optimized and expanded towards large-scale and cost-efficient biofabrication of vascular, lymphatic or neural networks for tissue engineering and regenerative medicine.

Microfluidic Arrays of Breast Tumor Spheroids for Drug Screening and Personalized Cancer Therapies

One of the obstacles limiting progress in the development of effective cancer therapies is the shortage of preclinical models that capture the dynamic nature of tumor microenvironments. Interstitial flow strongly impacts tumor response to chemotherapy; however, conventional in vitro cancer models largely disregard this key feature. Here, a proof of principle microfluidic platform for the generation of large arrays of breast tumor spheroids that are grown under close-to-physiological flow in a biomimetic hydrogel is reported. This cancer spheroids-on-a-chip model is used for time- and labor-efficient studies of the effects of drug dose and supply rate on the chemosensitivity of breast tumor spheroids. The capability to grow large arrays of tumor spheroids from patient-derived cells of different breast cancer subtypes is shown, and the correlation between in vivo drug efficacy and on-chip spheroid drug response is demonstrated. The proposed platform can serve as an in vitro preclinical model for the development of personalized cancer therapies and effective screening of new anticancer drugs.

3D Cell Culture Models as Recapitulators of the Tumor Microenvironment for the Screening of Anti-Cancer Drugs

Today, innovative three-dimensional (3D) cell culture models have been proposed as viable and biomimetic alternatives for initial drug screening, allowing the improvement of the efficiency of drug development. These models are gaining popularity, given their ability to reproduce key aspects of the tumor microenvironment, concerning the 3D tumor architecture as well as the interactions of tumor cells with the extracellular matrix and surrounding non-tumor cells. The development of accurate 3D models may become beneficial to decrease the use of laboratory animals in scientific research, in accordance with the European Union's regulation on the 3R rule (Replacement, Reduction, Refinement). This review focuses on the impact of 3D cell culture models on cancer research, discussing their advantages, limitations, and compatibility with high-throughput screenings and automated systems. An insight is also given on the adequacy of the available readouts for the interpretation of the data obtained from the 3D cell culture models. Importantly, we also emphasize the need for the incorporation of additional and complementary microenvironment elements on the design of 3D cell culture models, towards improved predictive value of drug efficacy.

Rapid fabrication of gelatin-based scaffolds with prevascularized channels for organ regeneration

One of the biggest hinders in tissue engineering over the last decades was the complexity of the prevascularized channels of the engineered scaffold, which was still lower than that of human tissues. Another relative trouble was lacking precision molding capability, which restricted the clinical applications of the huge engineered scaffold. In this study, a promising approach was proposed to prepare hydrogel scaffold with prevascularized channels by liquid bath printing, which chitosan/β-sodium glycerophosphate (CS/β-GP) severed as the ink hydrogel, and gelation/nanoscale bacterial cellulose (Gel/BC) acted as the supporting hydrogel. Here, the ink hydrogel was printed by a versatile nozzle and embedded in the supporting hydrogel. Ink hydrogel transformed into liquid effluent at low temperature after cross-linking of gelatin by microbial transglutaminase (mTG). No residual template was seen on the channel surface after template removal. This preparation had a high degree of freedom in the geometry of the channel, which was demonstrated by making various prevascularized channels including circular, branched, and tree-shaped networks. The molding accuracy of the channel was detected by studying the roundness of the cross-section of the molded hollow channel, and the effect of the mechanical properties by adding BC to supporting hydrogel was analyzed. Human umbilical vein endothelial cells (HUVECs) were injected into the aforementioned channels and formed confluent and homogeneous distribution on the surface of channels. Altogether, these results showed that this approach can construct hydrogel scaffold with complex and accurate molding prevascularized channels, and had great potential to resolve urgent vascularization issue of bulk tissue-engineering scaffold.

Effect of the Addition Frequency of 5-Azacytidine in Both Micro- and Macroscale Cultures

INTRODUCTION

Human mesenchymal stem cells (hMSCs) have a great clinical potential for tissue regeneration purposes due to its multilineage capability. Previous studies have reported that a single addition of 5-azacytidine (5-AzaC) causes the differentiation of hMSCs towards a myocardial lineage. The aim of this work was to evaluate the effect of 5-AzaC addition frequency on hMSCs priming (i.e., indicating an early genetic differentiation) using two culture environments.

METHODS

hMSCs were supplemented with 5-AzaC while cultured in well plates and in microfluidic chips. The impact of 5-AzaC concentration (10 and 20 μM) and addition frequency (once, daily or continuously), as well as of culture period (2 or 5 days) on the genetic upregulation of PPARγ (adipocytes), PAX3 (myoblasts), SOX9 (chondrocytes) and RUNX2 (osteoblasts) was evaluated.

RESULTS

Daily delivering 5-AzaC caused a higher upregulation of PPARγ, SOX9 and RUNX2 in comparison to a single dose delivery, both under static well plates and dynamic microfluidic cultures. A particularly high gene expression of PPARγ (tenfold-change) could indicate priming of hMSCs towards adipocytes.

CONCLUSIONS

Both macro- and microscale cultures provided results with similar trends, where addition frequency of 5-AzaC was a crucial factor to upregulate several genes. Microfluidics technology was proven to be a suitable platform for the continuous delivery of a drug and could be used for screening purposes in tissue engineering research.

Three-Dimensional Human Cell Culture Models to Study the Pathophysiology of the Anterior Eye

In recent decades, the establishment of complex three-dimensional (3D) models of tissues has allowed researchers to perform high-quality studies and to not only advance knowledge of the physiology of these tissues but also mimic pathological conditions to test novel therapeutic strategies. The main advantage of 3D models is that they recapitulate the spatial architecture of tissues and thereby provide more physiologically relevant information. The eye is an extremely complex organ that comprises a large variety of highly heterogeneous tissues that are divided into two asymmetrical portions: the anterior and posterior segments. The anterior segment consists of the cornea, conjunctiva, iris, ciliary body, sclera, aqueous humor, and the lens. Different diseases in these tissues can have devastating effects. To study these pathologies and develop new treatments, the use of cell culture models is instrumental, and the better the model, the more relevant the results. Thus, the development of sophisticated 3D models of ocular tissues is a significant challenge with enormous potential. In this review, we present a comprehensive overview of the latest advances in the development of 3D in vitro models of the anterior segment of the eye, with a special focus on those that use human primary cells.

Trypsin-Free Cultivation of 3D Mini-Tissues in an Adaptive Membrane Bioreactor

The production of large scaffold-free tissues is a key challenge in regenerative medicine. Nowadays, temperature-responsive polymers allow intact tissue harvesting without needing proteolytic enzymes. This method is limited to tissue culture plastic with limited upscaling capacity and plain process control. Here, a thermoresponsive hollow fiber membrane bioreactor is presented to produce large scaffold-free tissues. Intact tissues, rich in cell-to-cell connections and ECM, are harvested from a poly(N-vinylcaprolactam) microgel functionalized poly(ether sulfone)/poly(vinylpyrrolidone) hollow fiber membrane by a temperature shift. The harvested 3D tissues adhere in successive cultivation and exhibit high vitality for several days. The facile adsorptive coating waives the need for extensive surface treatment. The research is anticipated to be a starting point for upscaling the production of interconnected tissues enabling new opportunities in regenerative medicine, large-scale drug screening on physiological relevant tissues, and potentially opening new chances in cell-based therapies.

The unique applicability of the human placenta to the Adverse Outcome Pathway (AOP) concept: the placenta provides fundamental insights into human organ functions at multiple levels of biological organization

Despite the short lifespan of the human placenta, the proper formation and function of the organ is of crucial importance for fetal development. Placental dysfunction increases the risk of complications for mother and child during pregnancy and childbirth and beyond as it predisposes to fetal programming. The placenta is an upstream organ of the fetus. It performs the functions of fetal lungs, liver, intestines, kidneys and glands as long as these organs are not fully functional. Furthermore, it is the only human organ that is non-invasively available either after elective abortion or after birth. This is a crucial point given that the conceptual framework of Adverse Outcome Pathway (AOP) requires data on organ function. In vitro and ex vivo placental studies, combined with epidemiological and clinical data on pregnant women, newborns, and infants can uniquely cover all levels of information needed to develop new AOPs and complement existing AOPs related to reproductive toxicity and beyond. To stimulate further research in this area and to support researchers in future studies dealing with the development of AOPs related to the placenta, this review first gives a brief description of placental structure, placental development and relevant pregnancy diseases. The state of knowledge about the available placental models, their particularities and limitations are briefly discussed. Finally, the use of placental research for the development of AOPs is presented with an illustrative example.

Indirect co-culture of lung carcinoma cells with hyperthermia-treated mesenchymal stem cells influences tumor spheroid growth in a collagen-based 3-dimensional microfluidic model

BACKGROUND

Mesenchymal stem cells (MSCs) have paradoxically been reported to exert either pro- or anti-tumor effects in vitro. Hyperthermia, in combination with chemotherapy, has tumor-inhibiting effects; however, its role, together with MSCs, so far is not well understood. Furthermore, a lot of research is conducted using conventional 2-dimensional in vitro models that do not mimic the actual tumor microenvironment.

AIM

In light of this fact, an indirect method of co-culturing human amniotic membrane-derived MSCs (AMMSCs) with collagen-encapsulated human lung carcinoma cells (A549) was performed using a 3-dimensional (3D) tumor-on-chip device.

METHODS

The conditioned medium of AMMSCs (AMMSC-CM) or heat-treated AMMSCs (heat-AMMSC-CM) was utilized to create indirect co-culture conditions. Tumor spheroid growth characterization, immunocytochemistry and cytotoxicity assays, and anti-cancer peptide (P1) screening were performed to determine the effects of the conditioned medium.

RESULTS

The A549 cells cultured inside the 3D microfluidic chip developed into multicellular tumor spheroids over five days of culture. The AMMSC-CM, contrary to previous reports claiming its tumor-inhibiting potential, led to significant proliferation of tumor spheroids. Heat-AMMSC-CM led to reductions in both spheroid diameter and cell proliferation. The medium containing the P1 peptide was found to be the least cytotoxic to tumor spheroids in co-culture compared with the monoculture and heat-co-culture groups.

CONCLUSIONS

Hyperthermia, in combination with the anticancer peptide, exhibited highest cytotoxic effects. This study highlights the growing importance of 3D microfluidic tumor models for testing stem-cell-based and other anti-cancer therapies.

Isolation and characterisation of nasoseptal cartilage stem/progenitor cells and their role in the chondrogenic niche

BACKGROUND

Since cartilage-derived stem/progenitor cells (CSPCs) were first identified in articular cartilage using differential adhesion to fibronectin, their self-renewal capacity and niche-specific lineage preference for chondrogenesis have propelled their application for cartilage tissue engineering. In many adult tissues, stem/progenitor cells are recognised to be involved in tissue homeostasis. However, the role of nasoseptal CSPCs has not yet been elucidated. Our aim was to isolate and characterise nasoseptal CSPCs alongside nasoseptal chondrocyte populations and determine chondrogenic capacity.

METHODS

Here, we isolated nasoseptal CSPCs using differential adhesion to fibronectin and assessed their colony forming efficiency, proliferation kinetics, karyotype and trilineage potential. CSPCs were characterised alongside non-fibronectin-adherent nasoseptal chondrocytes (DNCs) and cartilage-derived cells (CDCs, a heterogenous combination of DNCs and CSPCs) by assessing differences in gene expression profiles using PCR Stem Cell Array, immunophenotype using flow cytometry and chondrogencity using RT-PCR and histology.

RESULTS

CSPCs were clonogenic with increased gene expression of the neuroectodermal markers NCAM1 and N-Cadherin, as well as Cyclins D1 and D2, compared to DNCs. All three cell populations expressed recognised mesenchymal stem cell surface markers (CD29, CD44, CD73, CD90), yet only CSPCs and CDCs showed multilineage differentiation potential. CDC populations expressed significantly higher levels of type 2 collagen and bone morphogenetic protein 2 genes, with greater cartilage extracellular matrix secretion. When DNCs were cultured in isolation, there was reduced chondrogenicity and higher expression of type 1 collagen, stromal cell-derived factor 1 (SDF-1), CD73 and CD90, recognised markers of a fibroblast-like phenotype.

CONCLUSIONS

Fibronectin-adherent CSPCs demonstrate a unique gene expression profile compared to non-fibronectin-adherent DNCs. DNCs cultured in isolation, without CSPCs, express fibroblastic phenotype with reduced chondrogenicity. Mixed populations of stem/progenitor cells and chondrocytes were required for optimal chondrogenesis, suggesting that CSPCs may be required to retain phenotypic stability and chondrogenic potential of DNCs. Crosstalk between DNCs and CSPCs is proposed based on SDF-1 signalling.

Vertically-Aligned Functionalized Silicon Micropillars for 3D Culture of Human Pluripotent Stem Cell-Derived Cortical Progenitors

Silicon is a promising material for tissue engineering since it allows to produce micropatterned scaffolding structures resembling biological tissues. Using specific fabrication methods, it is possible to build aligned 3D network-like structures. In the present study, we exploited vertically-aligned silicon micropillar arrays as culture systems for human iPSC-derived cortical progenitors. In particular, our aim was to mimic the radially-oriented cortical radial glia fibres that during embryonic development play key roles in controlling the expansion, radial migration and differentiation of cortical progenitors, which are, in turn, pivotal to the establishment of the correct multilayered cerebral cortex structure. Here we show that silicon vertical micropillar arrays efficiently promote expansion and stemness preservation of human cortical progenitors when compared to standard monolayer growth conditions. Furthermore, the vertically-oriented micropillars allow the radial migration distinctive of cortical progenitors in vivo. These results indicate that vertical silicon micropillar arrays can offer an optimal system for human cortical progenitors' growth and migration. Furthermore, similar structures present an attractive platform for cortical tissue engineering.

3D Cell-Based Assays for Drug Screens: Challenges in Imaging, Image Analysis, and High-Content Analysis

The introduction of more relevant cell models in early preclinical drug discovery, combined with high-content imaging and automated analysis, is expected to increase the quality of compounds progressing to preclinical stages in the drug development pipeline. In this review we discuss the current switch to more relevant 3D cell culture models and associated challenges for high-throughput screening and high-content analysis. We propose that overcoming these challenges will enable front-loading the drug discovery pipeline with better biology, extracting the most from that biology, and, in general, improving translation between in vitro and in vivo models. This is expected to reduce the proportion of compounds that fail in vivo testing due to a lack of efficacy or to toxicity.

Piezo-bending actuators for isometric or auxotonic contraction analysis of engineered heart tissue

Engineered heart tissue (EHT) has proven as valuable tool for disease modelling, drug safety screening, and cardiac repair. Especially in combination with the stem cell technology, these in vitro models of the human heart have generated interest not only of basic cardiovascular researchers but also of regulatory authorities responsible for drug safety. A main limitation of 3D-based assays for evaluating cardiotoxicity is their limited throughput. We integrated piezo-bending actuators in a 24-well system for the generation of strip-like rat and human EHT attached to hollow, elastic silicone posts. Muscle contractions of EHTs induced a measurable electrical current in the piezo-bending actuators that could be analysed for contraction amplitude, frequency, and contraction and relaxation kinetics. Compared with the standard video-optical analysis of contractile activity, the new system allows for (a) the analysis of several tissues in parallel, (b) switching between auxotonic and isometric contractions by inserting a stiff metal post in the silicone post opposing the piezo actuator, (c) continuous measurement over days with low data volume (megabyte), (d) automated measurement without the necessity of adjustment of tissue position for video-optical analysis, (e) reduced complexity and costs, (f) high sensitivity of contraction detection, (g) calculation of absolute contraction force, and (h) suitability for variable tissue geometries. The new set-up for contraction analysis based on piezo-bending actuators is a promising new method for the parallel screening of EHT for pharmacological drug effects and other applications of muscle tissue engineering (e.g., skeletal muscle engineering or cardiac repair).

Microfluidic Cell Culture Platforms to Capture Hepatic Physiology and Complex Cellular Interactions

Animal models such as rats and primates provide body-wide information for drug and metabolite responses, including organ-specific toxicity and any unforeseen side effects on other organs. Although effective in the drug-screening process, their translatability to humans is limited because of the lack of high concordance and correlation among enzymatic mechanisms, cellular mechanisms, and resulting toxicities. A significant mode of failure for safety prediction in drug screening is hepatotoxicity, resulting in ∼30% of all safety-related drug failures and withdrawals from the market. The liver is a multifunctional organ with diverse metabolic, secretory, and inflammatory response roles and is essential for maintaining key body functions. Conventional cell culture platforms (such as multiwell plate cultures) and metabolic enzyme systems (microsomes, cytochrome P450 enzymes) have been routinely used to assess drug pharmacokinetics and metabolism. However, current in vitro models often fail to recapitulate the complexity and dynamic nature of human tissues, imposing a heavy reliance on in vivo testing using preclinical species that have metabolic processes, disease mechanisms, and modes of toxicity distinct from humans. Recently, microphysiological systems (MPS) have gained attention as powerful tools with the potential to generate human-relevant information that can supplant and fill the gap of knowledge between preclinical animal models and simpler, conventional in vitro cell culture systems. Developments in microfabrication technologies for generating complex microfluidic systems, along with the ability to establish and maintain multicellular models to capture dynamic, human-relevant behavior, have provided new avenues to generate such physiologically relevant systems. These MPS platforms, when designed and developed with in vivo-derived design parameters, have the potential to capture key aspects and better mimic organ functionality. In this review, we discuss developments in microtechnologies for fabricating, establishing, and maintaining hepatic cell culture systems, with a specific focus on models that aim to capture in vivo physiology in vitro. By designing microscale systems to impart specific in vivo physiologic parameters, it is possible to create a dynamic system that can capture multiple aspects of the hepatic microenvironment, bringing us closer to a comprehensive in vitro testing platform for hepatic responses and toxicities.

Vessel-on-a-chip with Hydrogel-based Microfluidics

Hydrogel structures equipped with internal microchannels offer more in vivo-relevant models for construction of tissues and organs in vitro. However, currently used microfabrication methods of constructing microfluidic devices are not suitable for the handling of hydrogel. This study presents a novel method of fabricating hydrogel-based microfluidic chips by combining the casting and bonding processes. A twice cross-linking strategy is designed to obtain a bonding interface that has the same strength with the hydrogel bulk, which can be applied to arbitrary combinations of hydrogels. It is convenient to achieve the construction of hydrogel structures with channels in branched, spiral, serpentine, and multilayer forms. The experimental results show that the combination of gelatin and gelatin methacrylate (GelMA) owns the best biocompatibility and can promote cell functionalization. Based on these, a vessel-on-a-chip system with vascular function in both physiological and pathological situations is established, providing a promising model for further investigations such as vascularization, vascular inflammation, tissue engineering, and drug development. Taken together, a facile and cytocompatible approach is developed for engineering a user-defined hydrogel-based chip that can be potentially useful in developing vascularized tissue or organ models.

In vitro and ex vivo systems at the forefront of infection modeling and drug discovery

Bacterial infections and antibiotic resistant bacteria have become a growing problem over the past decade. As a result, the Centers for Disease Control predict more deaths resulting from microorganisms than all cancers combined by 2050. Currently, many traditional models used to study bacterial infections fail to precisely replicate the in vivo bacterial environment. These models often fail to incorporate fluid flow, bio-mechanical cues, intercellular interactions, host-bacteria interactions, and even the simple inclusion of relevant physiological proteins in culture media. As a result of these inadequate models, there is often a poor correlation between in vitro and in vivo assays, limiting therapeutic potential. Thus, the urgency to establish in vitro and ex vivo systems to investigate the mechanisms underlying bacterial infections and to discover new-age therapeutics against bacterial infections is dire. In this review, we present an update of current in vitro and ex vivo models that are comprehensively changing the landscape of traditional microbiology assays. Further, we provide a comparative analysis of previous research on various established organ-disease models. Lastly, we provide insight on future techniques that may more accurately test new formulations to meet the growing demand of antibiotic resistant bacterial infections.

Preclinical three-dimensional colorectal cancer model: The next generation of in vitro drug efficacy evaluation

Colorectal cancer (CRC), the third most common cancer diagnosed in both men and women in the United States, shows a highly ineffective therapeutic management. In these years neither substantial improvements nor new therapeutic approaches have been provided to patients. Performing the early lead discovery phases of new cancer drugs in cellular models, resembling as far as possible the real in vivo tumor environment, may be more effective in predicting their future success in the later clinical phases. In this review, we critically describe the most representative bioengineered models for anticancer drug screening in CRC from the conventional two-dimensional models to the new-generation three-dimensional scaffold-based ones. The scaffold aims to replace the extracellular matrix, thus influencing the biomechanical, biochemical, and biological properties of cells and tissues. In this scenario, we believe that reconstitution of tumor condition is mandatory for an alternative in vitro methods to study cancer development and therapeutic strategies.

Toward Immunocompetent 3D Skin Models

3D human skin models provide a platform for toxicity testing, biomaterials evaluation, and investigation of fundamental biological processes. However, the majority of current in vitro models lack an inflammatory system, vasculature, and other characteristics of native skin, indicating scope for more physiologically complex models. Looking at the immune system, there are a variety of cells that could be integrated to create novel skin models, but to do this effectively it is also necessary to understand the interface between skin biology and tissue engineering as well as the different roles the immune system plays in specific health and disease states. Here, a progress report on skin immunity and current immunocompetent skin models with a focus on construction methods is presented; scaffold and cell choice as well as the requirements of physiologically relevant models are elaborated. The wide range of technological and fundamental challenges that need to be addressed to successfully generate immunocompetent skin models and the steps currently being made globally by researchers as they develop new models are explored. Induced pluripotent stem cells, microfluidic platforms to control the model environment, and new real-time monitoring techniques capable of probing biochemical processes within the models are discussed.

Mimicking the 3D biology of osteochondral tissue with microfluidic-based solutions: breakthroughs towards boosting drug testing and discovery

The development of tissue-engineering (TE) solutions for osteochondral (OC) regeneration has been slowed by technical hurdles related to the recapitulation of their complex and hierarchical architecture. OC defects refer to damage of both the articular cartilage and the underlying subchondral bone. To repair an OC tissue defect, the complexity of the bone and cartilage must be considered. To help achieve this, microfluidics is converging with TE approaches to provide new treatment possibilities. Microfluidics uses precise micrometer-to-millimeter-scale fluid flows to achieve high-resolution and spatial and/or temporal control of the cell microenvironment, providing powerful tools for cell culturing. Herein, we overview the progress of microfluidics for developing 3D in vitro models of OC tissue, with a focus on cancer bone metastasis.

A Method for Prostate and Breast Cancer Cell Spheroid Cultures Using Gelatin Methacryloyl-Based Hydrogels

Modern tissue engineering technologies have delivered tools to recreate a cell's naturally occurring niche in vitro and to investigate normal and pathological cell-cell and cell-niche interactions. Hydrogel biomaterials mimic crucial properties of native extracellular matrices, including mechanical support, cell adhesion sites and proteolytic degradability. As such, they are applied as 3D cell culture platforms to replicate tissue-like architectures observed in vivo, allowing physiologically relevant cell behaviors. Here we review bioengineered 3D approaches used for prostate and breast cancer. Furthermore, we describe the synthesis and use of gelatin methacryloyl-based hydrogels as in vitro 3D cancer model. This platform is used to engineer the microenvironments for prostate and breast cancer cells to study processes regulating spheroid formation, cell functions and responses to therapeutic compounds. Collectively, these bioengineered 3D approaches provide cell biologists with innovative pre-clinical tools that integrate the complexity of the disease seen in patients to advance our knowledge of cancer cell physiology and the contribution of a tumor's surrounding milieu.

Organ-On-A-Chip Platforms: A Convergence of Advanced Materials, Cells, and Microscale Technologies

Significant advances in biomaterials, stem cell biology, and microscale technologies have enabled the fabrication of biologically relevant tissues and organs. Such tissues and organs, referred to as organ-on-a-chip (OOC) platforms, have emerged as a powerful tool in tissue analysis and disease modeling for biological and pharmacological applications. A variety of biomaterials are used in tissue fabrication providing multiple biological, structural, and mechanical cues in the regulation of cell behavior and tissue morphogenesis. Cells derived from humans enable the fabrication of personalized OOC platforms. Microscale technologies are specifically helpful in providing physiological microenvironments for tissues and organs. In this review, biomaterials, cells, and microscale technologies are described as essential components to construct OOC platforms. The latest developments in OOC platforms (e.g., liver, skeletal muscle, cardiac, cancer, lung, skin, bone, and brain) are then discussed as functional tools in simulating human physiology and metabolism. Future perspectives and major challenges in the development of OOC platforms toward accelerating clinical studies of drug discovery are finally highlighted.

Angiogenic and osteogenic regeneration in rats via calcium phosphate scaffold and endothelial cell co-culture with human bone marrow mesenchymal stem cells (MSCs), human umbilical cord MSCs, human induced pluripotent stem cell-derived MSCs and human embryonic stem cell-derived MSCs

Angiogenesis is a limiting factor in regenerating large bone defects. The objective of this study was to investigate angiogenic and osteogenic effects of co-culture on calcium phosphate cement (CPC) scaffold using human umbilical vein endothelial cells (hUVECs) and mesenchymal stem cells (MSCs) from different origins for the first time. hUVECs were co-cultured with four types of cell: human umbilical cord MSCs (hUCMSCs), human bone marrow MSCs (hBMSCs) and MSCs from induced pluripotent stem cells (hiPSC-MSCs) and embryonic stem cells (hESC-MSCs). Constructs were implanted in 8 mm cranial defects of rats for 12 weeks. CPC without cells served as control 1. CPC with hBMSCs served as control 2. Microcapillary-like structures were successfully formed on CPC in vitro in all four co-cultured groups. Microcapillary lengths increased with time (p < 0.05). Osteogenic and angiogenic gene expressions were highly elevated and mineralization by co-cultured cells increased with time (p < 0.05). New bone amount and blood vessel density of co-cultured groups were much greater than controls (p < 0.05) in an animal study. hUVECs co-cultured with hUCMSCs, hiPSC-MSCs and hESC-MSCs achieved new bone and vessel density similar to hUVECs co-cultured with hBMSCs (p > 0.1). Therefore, hUCMSCs, hiPSC-MSCs and hESC-MSCs could serve as alternative cell sources to hBMSCs, which require an invasive procedure to harvest. In conclusion, this study showed for the first time that co-cultures of hUVECs with hUCMSCs, hiPSC-MSCs, hESC-MSCs and hBMSCs delivered via CPC scaffold achieved excellent osteogenic and angiogenic capabilities in vivo. The novel co-culture constructs are promising for bone reconstruction with improved angiogenesis for craniofacial/orthopaedic applications. Copyright © 2017 John Wiley & Sons, Ltd.

Progress and Future Prospectives in Skin-on-Chip Development with Emphasis on the use of Different Cell Types and Technical Challenges

Understanding the healthy and diseased state of skin is important in many areas of basic and applied research. Although the field of skin tissue engineering has advanced greatly over the last years, current in vitro skin models still do not mimic the complexity of the human skin. Skin-on-chip and induced pluripotent stem cells (iPSC) might be key technologies to improve in vitro skin models. This review summarizes the state of the art of in vitro skin models with regard to cell sources (primary, cell line, iPSC) and microfluidic devices. It can be concluded that iPSC have the potential to be differentiated into many kinds of immunologically matched cells and skin-on-chip technology might lead to more physiologically relevant skin models due to the controlled environment, possible exchange of immune cells, and an increased barrier function. Therefore the combination of iPSC and skin-on-chip is expected to lead to superior healthy and diseased in vitro skin models.

Importance of endogenous extracellular matrix in biomechanical properties of human skin model

The physical and mechanical properties of cells modulate their behavior such proliferation rate, migration and extracellular matrix remodeling. In order to study cell behavior in a tissue-like environment in vitro, it is of utmost importance to develop biologically and physically relevant 3D cell models. Here, we characterized the physical properties of a single cell type growing in configurations of increasing complexity. From one human skin biopsy, primary dermal fibroblasts were isolated and seeded to give monolayer (2D model), spheroid (3D model poor in extracellular matrix) and tissue-engineered cell sheet (3D model rich in endogenous extracellular matrix). Living native human dermis tissue was used as a gold standard. Nanomechanical and viscoelastic properties at the cell scale were measured by atomic force microscopy (AFM) while biphoton microscopy allowed collagen detection by second harmonic generation and scanning electron microscopy helped in model morphological characterization. In all models, fibroblasts presented a similar typical elongated cell shape, with a cytoskeleton well-arranged along the long axis of the cell. However, elastic moduli of the tissue-engineered cell sheet and native dermis tissue were similar and statistically lower than monolayer and spheroid models. We successfully carried out AFM force measurements on 3D models such as spheroids and tissue-engineered cell sheets, as well as on living native human tissue. We demonstrated that a tissue-engineered dermal model recapitulates the mechanical properties of human native dermal tissue unlike the classically used monolayer and spheroid models. Furthermore, we give statistical evidence to indicate a correlation between cell mechanical properties and the presence of collagens in the models studied.

Reconfigurable microfluidic device with discretized sidewall

Various microfluidic features, such as traps, have been used to manipulate flows, cells, and other particles within microfluidic systems. However, these features often become undesirable in subsequent steps requiring different fluidic configurations. To meet the changing needs of various microfluidic configurations, we developed a reconfigurable microfluidic channel with movable sidewalls using mechanically discretized sidewalls of laterally aligned rectangular pins. The user can deform the channel sidewall at any time after fabrication by sliding the pins. We confirmed that the flow resistance of the straight microchannel could be reversibly adjusted in the range of 10¹-10⁵Pa s/μl by manually displacing one of the pins comprising the microchannel sidewall. The reconfigurable microchannel also made it possible to manipulate flows and cells by creating a segmented patterned culture of COS-7 cells and a coculture of human umbilical vein endothelial cells (HUVECs) and human lung fibroblasts (hLFs) inside the microchannel. The reconfigurable microfluidic device successfully maintained a culture of COS-7 cells in a log phase throughout the entire period of 216 h. Furthermore, we performed a migration assay of cocultured HUVEC and hLF spheroids within one microchannel and observed their migration toward each other.

Review: bioreactor design towards generation of relevant engineered tissues: focus on clinical translation

In tissue engineering and regenerative medicine, studies that utilize 3D scaffolds for generating voluminous tissues are mostly confined in the realm of in vitro research and preclinical animal model testing. Bioreactors offer an excellent platform to grow and develop 3D tissues by providing conditions that mimic their native microenvironment. Aligning the bioreactor development process with a focus on patient care will aid in the faster translation of the bioreactor technology to clinics. In this review, we discuss the various factors involved in the design of clinically relevant bioreactors in relation to their respective applications. We explore the functional relevance of tissue grafts generated by bioreactors that have been designed to provide physiologically relevant mechanical cues on the growing tissue. The review discusses the recent trends in non-invasive sensing of the bioreactor culture conditions. It provides an insight to the current technological advancements that enable in situ, non-invasive, qualitative and quantitative evaluation of the tissue grafts grown in a bioreactor system. We summarize the emerging trends in commercial bioreactor design followed by a short discussion on the aspects that hamper the 'push' of bioreactor systems into the commercial market as well as 'pull' factors for stakeholders to embrace and adopt widespread utility of bioreactors in the clinical setting. Copyright © 2017 John Wiley & Sons, Ltd.

Tissue-Engineered Solutions in Plastic and Reconstructive Surgery: Principles and Practice

Recent advances in microsurgery, imaging, and transplantation have led to significant refinements in autologous reconstructive options; however, the morbidity of donor sites remains. This would be eliminated by successful clinical translation of tissue-engineered solutions into surgical practice. Plastic surgeons are uniquely placed to be intrinsically involved in the research and development of laboratory engineered tissues and their subsequent use. In this article, we present an overview of the field of tissue engineering, with the practicing plastic surgeon in mind. The Medical Research Council states that regenerative medicine and tissue engineering “holds the promise of revolutionizing patient care in the twenty-first century.” The UK government highlighted regenerative medicine as one of the key eight great technologies in their industrial strategy worthy of significant investment. The long-term aim of successful biomanufacture to repair composite defects depends on interdisciplinary collaboration between cell biologists, material scientists, engineers, and associated medical specialties; however currently, there is a current lack of coordination in the field as a whole. Barriers to translation are deep rooted at the basic science level, manifested by a lack of consensus on the ideal cell source, scaffold, molecular cues, and environment and manufacturing strategy. There is also insufficient understanding of the long-term safety and durability of tissue-engineered constructs. This review aims to highlight that individualized approaches to the field are not adequate, and research collaboratives will be essential to bring together differing areas of expertise to expedite future clinical translation. The use of tissue engineering in reconstructive surgery would result in a paradigm shift but it is important to maintain realistic expectations. It is generally accepted that it takes 20–30 years from the start of basic science research to clinical utility, demonstrated by contemporary treatments such as bone marrow transplantation. Although great advances have been made in the tissue engineering field, we highlight the barriers that need to be overcome before we see the routine use of tissue-engineered solutions.

Electrophysiology, immunophenotype, and gene expression characterization of senescent and cryopreserved human amniotic fluid stem cells

We characterized human amniotic fluid stem cells (AFSC) in senescent cultures (6 weeks) versus cryopreserved cells using whole-cell patch-clamp, immunophenotyping, and differential gene expression profiling for senescence genes. We evidenced five ion current components (outward rectifier, A-type, inward rectifier, and big conductance Ca2+-dependent K+ currents, fast voltage-dependent Na+ currents). Senescent AFSC showed reduced expression of CD90, CD44, CD133, over 500-fold increase of interferon gamma and telomerase reverse transcriptase genes, increased cycle-dependent kinase 4 inhibitors, p53-binding protein 1, and decreased calreticulin and CD44. HLA-ABC immune expression was similar, and HLA-DR expression very low in both cell types. A subset of cryopreserved AFSC featured large inward rectifier K+ currents, voltage-dependent Na+ currents, and neural progenitor markers evidenced by immunophenotyping and RT-PCR. In all AFSC, in both culture conditions, at patch rupture the outward currents were very low, and they increased progressively over several minutes upon cytoplasm dialysis with pipette solution.

Microengineered platforms for co-cultured mesenchymal stem cells towards vascularized bone tissue engineering

Bone defects are common disease requiring thorough treatments since the bone is a complex vascularized tissue that is composed of multiple cell types embedded within an intricate extracellular matrix (ECM). For past decades, tissue engineering using cells, proteins, and scaffolds has been suggested as one of the promising approaches for effective bone regeneration. Recently, many researchers have been interested in designing effective platform for tissue regeneration by orchestrating factors involved in microenvironment around tissues. Among factors affecting bone formation, vascularization during bone development and after minor insults via endochondral and intramembranous ossification is especially critical for the long-term support for functional bone. In order to create vascularized bone constructs, the interactions between human mesenchymal stem cells (MSCs) and endothelial cells (ECs) have been investigated using both direct and indirect co-culture studies. Recently, various culture methods including micropatterning techniques, three dimensional scaffolds, and microfluidics have been developed to create micro-engineered platforms that mimic the nature of vascularized bone formation, leading to the creation of functional bone structures. This review focuses on MSCs co-cultured with endothelial cells and microengineered platforms to determine the underlying interplay between co-cultured MSCs and vascularized bone constructs, which is ultimately necessary for adequate regeneration of bone defects.

Gels prepared from egg yolk and its fractions for tissue engineering

New biomaterials prepared from egg yolk and its main fractions (plasma and granules) have been developed for use in tissue engineering. Protein gels obtained via transglutaminase cross-linking were characterized by rheometry, texturometry and scanning electron microscopy. All the gels exhibited suitable physical and mechanical characteristics for use as potential biomaterials in skin regeneration. Specifically, results showed that these materials presented a compact, uniform structure, with granular gel being found to be the most resistant as well as the most elastic material. Accordingly, these gels were subsequently evaluated as scaffolds for murine fibroblast growth. The best results were obtained with granule gels. Not only adhesion and cell growth were detected when using these gels, but also continuous coatings of cells growing on their surface. These findings can be attributed to the higher protein content of this fraction and to the particular structure of its proteins. Thus, granules have proved to be an interesting potential raw material for scaffold development. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:1577-1583, 2016.