Role of the extracellular matrix in morphogenesis

Searching molecular biomarkers correlating with BSID-III at 24 months in infants with neonatal hypoxic-ischemic encephalopathy

An early prediction of outcomes of neonatal hypoxic-ischemic encephalopathy (NE) is of key importance in reducing neonatal mortality and morbidity. The objectives were (i) to analyze the characteristics of miRNA expression and metabolic patterns of neonates with NE and (ii) to assess their predictive performance for neurodevelopmental outcomes. Plasma samples from moderate/severe NE patients (N = 92) of the HYPOTOP study were collected before, during, and after therapeutic hypothermia (TH) and compared to a control group (healthy term infants). The expression of miRNAs and concentrations of metabolites (hypoxia-related and energy, steroid, and tryptophan metabolisms) were analyzed. Neurodevelopmental outcomes were evaluated at 24 months postnatal age using Bayley Scales of Infant Development, ed. III, BSID-III. Differences in miRNA and metabolic profiles were found between NE vs. control infants, abnormal (i.e., mildly and moderately abnormal and severe) vs. normal, and severe vs. non-severe (i.e., normal and mildly and moderately abnormal) BSID-III. 4-Androstene-3,17-dione, testosterone, betaine, xanthine, and lactate were suitable for BSID-III outcome prediction (receiver operating characteristic areas under the curve (AUCs) ≥ 0.6), as well as 68 miRNAs (AUCs of 0.5-0.9). Significant partial correlations of xanthine and betaine levels and the expression of several miRNAs with BSID-III sub-scales were found. Conclusion: We have identified metabolites/miRNAs that might be useful to support the prediction of middle-term neurodevelopmental outcomes of NE. What is known and what is new: • The early prediction of outcomes of neonatal hypoxic-ischemic encephalopathy (NE) is of key importance in reducing neonatal mortality and morbidity. • Alterations of the metabolome and miRNAs had been observed in NE. • We performed miRNA sequencing and quantified selected metabolites (i.e., lactate, pyruvate, ketone bodies, Krebs cycle intermediates, tryptophan pathway, hypoxia-related metabolites, and steroids) by GC- and LC-MS. • Specific miRNAs and metabolites that allow prediction of middle-term neurodevelopmental outcomes of newborns with NE undergoing hypothermia treatment were identified.

Recent Advances in Graphene Oxide-Based on Organoid Culture as Disease Model and Cell Behavior - A Systematic Literature Review

Due to their ability to replicate the in vivo microenvironment through cell interaction and induce cells to stimulate cell function, three-dimensional cell culture models can overcome the limitations of two-dimensional models. Organoids are 3D models that demonstrate the ability to replicate the natural structure of an organ. In most organoid tissue cultures, matrigel made of a mouse tumor extracellular matrix protein mixture is an essential ingredient. However, its tumor-derived origin, batch-to-batch variation, high cost, and safety concerns have limited the usefulness of organoid drug development and regenerative medicine. Its clinical application has also been hindered by the fact that organoid generation is dependent on the use of poorly defined matrices. Therefore, matrix optimization is a crucial step in developing organoid culture that introduces alternatives as different materials. Recently, a variety of substitute materials has reportedly replaced matrigel. The purpose of this study is to review the significance of the latest advances in materials for cell culture applications and how they enhance build network systems by generating proper cell behavior. Excellence in cell behavior is evaluated from their cell characteristics, cell proliferation, cell differentiation, and even gene expression. As a result, graphene oxide as a matrix optimization demonstrated high potency in developing organoid models. Graphene oxide can promote good cell behavior and is well known for having good biocompatibility. Hence, advances in matrix optimization of graphene oxide provide opportunities for the future development of advanced organoid models.

Evaluation of the Recombinant Bacterial Chitinases as Anti-proliferative and Anti-migratory Agents for the Human Breast Cancer Cell Line, MCF-7

Chitinases, a glycosyl hydrolase family 18 members, have a wide distribution in both prokaryotes and eukaryotes, including humans. Regardless of the absence of endogenous chitin polymer, various chitinases and chitinase-like proteins (CLPs) have been reported in mammals. However, several other carbohydrate polymers, such as hyaluronic acid and heparan sulfate, show structural similarities with chitin, which could be a potential target of chitinase and CLPs. Heparan sulfate is part of the integral membrane proteins and involves in cell adherence and migration. Hence, to demonstrate the effect of chitinase on cancer cell progression, we selected two chitinases from Serratia marcescens, ChiB and ChiC, which function as exo- and endo-chitinase, respectively. The ChiB and ChiC proteins were produced recombinantly by cloning chiB and chiC genes from Serratia marcescens. The cell viability of the Michigan Cancer Foundation-7 (MCF-7) cells was studied using different concentrations of the purified recombinant proteins. Cell viability assay was performed using 3-(4, 5-dimethyl thiazolyl-2)-2, 5-diphenyltetrazolium bromide and water-soluble tetrazolium salt, and the effect of ChiB and ChiC on cell proliferation was studied by clonogenic assay. The cell migration study was analysed by wound healing, transwell migration, and invasion assays. Cell cycle analysis of propidium iodide-stained cells and cell proliferation markers such as pERK1/2, pAKT, and SMP30 were also done. It was observed that both ChiB and ChiC were able to impede cell viability, cell migration, and invasion significantly. These observations and our in silico molecular docking analysis suggest that ChiC is a potential anticancer agent and is more efficient than ChiB. Since the ChiC is able to inhibit both cancer cell proliferation and migration, it could be a potential candidate for the treatment of metastatic cancer.

Synthesis and characterization of a silk fibroin/placenta matrix hydrogel for breast reconstruction

Reconstructive surgery is a complex and demanding interdisciplinary field. One of the major challenges is the production of sizeable, implantable, inexpensive bioprostheses such as breast implants. In this study, porous hybrid hydrogels were fabricated by a combinatorial method using decellularized human placenta (dHplacenta) and silk fibroin. Histology was used to confirm the acellularity of the dHplacenta. The physio-chemical properties of the hydrogels were evaluated using SEM, FTIR, and rheological assays. The synthesized hydrogels exhibited a uniform 3-D microstructure with an interconnected porous network, and the hybrid hydrogels with a 30/70 ratio had improved mechanical properties compared to the other hydrogels. Hybrid hydrogels were also cultured with adipose-derived mesenchymal stem cells (ADSCs). Liposuction was used to obtain adipose tissue from patients, which was then characterized using flow cytometry and karyotyping. The results showed that CD34 and CD31 were downregulated, whereas CD105 and CD90 were upregulated in ADSCs, indicating a phenotype resembling to that of mesenchymal stem cells from the human bone marrow. Moreover, after re-cellularized hydrogel, the live/dead assay and SEM analysis confirmed that most viability and cellular expansion on the hydrogels contained higher ratios of dHplacenta (30/70) than the other two groups. All these findings recapitulated that the 30/70 dHplacenta/silk fibroin hydrogel can perform as an excellent substrate for breast tissue engineering applications.

Effect of substrate heterogeneity and topology on epithelial tissue growth dynamics

Tissue growth kinetics and interface dynamics depend on the properties of the tissue environment and cell-cell interactions. In cellular environments, substrate heterogeneity and geometry arise from a variety factors, such as the structure of the extracellular matrix and nutrient concentration. We used the CellSim3D model, a kinetic cell division simulator, to investigate the growth kinetics and interface roughness dynamics of epithelial tissue growth on heterogeneous substrates with varying topologies. The results show that the presence of quenched disorder has a clear effect on the colony morphology and the roughness scaling of the interface in the moving interface regime. In a medium with quenched disorder, the tissue interface has a smaller interface roughness exponent, α, and a larger growth exponent, β. The scaling exponents also depend on the topology of the substrate and cannot be categorized by well-known universality classes.

Disruptive 3D in vitro models for respiratory disease investigation: A state-of-the-art approach focused on SARS-CoV-2 infection

COVID-19, along with most respiratory diseases in the medical field, demonstrates significant ability to take its toll on global population. There is a particular difficulty in studying these conditions, which stems especially from the short supply of in vitro models for detailed investigation, the specific therapeutic knowledge required for disease scrutinization and the occasional need of BSL-3 [Biosafety Level 3] laboratories for research. Based on this, the process of drug development is hampered to a great extent. In the scenario of COVID-19, this difficulty is even more substantial on account of the current undefinition regarding the exact role of the ACE2 [Angiotensin-converting enzyme 2] receptor upon SARS-CoV-2 kinetics in human cells and the great level of demand in the investigation process of ACE2, which usually requires the laborious and ethically complicated usage of transgenic animal models overexpressing the receptor. Moreover, the rapid progression of the aforementioned diseases, especially COVID-19, poses a crucial necessity for adequate therapeutic solutions emergence. In this context, the work herein presented introduces a groundbreaking set of 3D models, namely spheroids and MatriWell cell culture inserts, whose remarkable ability to mimic the in vivo environment makes them highly suitable for respiratory diseases investigation, particularly SARS-CoV-2 infection. Using MatriWells, we developed an innovative platform for COVID-19 research: a pulmonary air-liquid interface [ALI] associated with endothelial (HUVEC) cells. Infection studies revealed that pulmonary (BEAS-2B) cells in the ALI reached peak viral load at 24h and endothelial cells, at 48h, demonstrating lung viral replication and subsequent hematogenous dissemination, which provides us with a unique and realistic framework for studying COVID-19. Simultaneously, the spheroids were used to address the understudied ACE2 receptor, aiming at a pronounced process of COVID-19 investigation. ACE2 expression not only increased spheroid diameter by 20% (p<0.001) and volume by 60% (p≤0.0001) but also led to a remarkable 640-fold increase in intracellular viral load (p≤0.01). The previously mentioned finding supports ACE2 as a potential target for COVID-19 treatment. Lastly, we observed a higher viral load in the MatriWells compared to spheroids (150-fold, p<0.0001), suggesting the MatriWells as a more appropriate approach for COVID-19 investigation. By establishing an advanced method for respiratory tract conditions research, this work paves the way toward an efficacious process of drug development, contributing to a change in the course of respiratory diseases such as COVID-19.

Maintenance of adult stem cells from human minor salivary glands via the Wnt signaling pathway

BACKGROUND

Xerostomia is a salivary gland dysfunction that negatively impacts the life quality of patients; however, there is no effective treatment for xerostomia. Bioengineered organs, generated using stem cells obtained from newborn salivary glands and ligated injury models, are a new organ transplantation strategy that could be feasible for xerostomia treatment. Reconstruction of salivary gland organoids by seed cells obtained from human minor salivary glands will offer theoretical fundaments and technology support for clinical application and organ regeneration research. Herein, we aimed to propose a new method for culturing and enriching adult human minor salivary gland stem cells in vitro in a three-dimensional (3D) environment via Wnt signaling activation.

METHODS

Obtained and characterized human minor salivary gland stem cells (hMSGSCs) with self-organization ability were 3D-cultured to generate organoids. We examined hMSGSCs proliferation and colony formation using MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assays. Telomerase reverse transcriptase staining, flow cytometry, immunofluorescence assay, RNA isolation, RT-PCR, and qPCR were performed to assess hMSGSCs structure and the function of reconstructive organoids in vitro.

RESULTS

hMSGSCs showed typical epithelial-like characteristics, such as positive for CD49f and cell KRT expression. hMSGSCs served as adult stem cells in salivary glands and could differentiate into acinar and duct cells. Upon the addition of Noggin, CHIR99021, and Wnt3A to the 3D culture system, hMSGSCs showed higher LGR5 expression and decreased AMY1B and MUC5B expression. Therefore, the Wnt and bone morphogenetic protein (BMP) pathways are important in regulating hMSGSCs self-organization and differentiation.

CONCLUSIONS

We showed that the stem cell properties of hMSGSCs in a 3D culture system can be maintained by activating the Wnt signaling pathway and inhibiting the BMP signaling pathway. Our findings contribute new insights on salivary gland organoid generation in vitro.

The challenge of making the right choice: patient avatars in the era of cancer immunotherapies

Immunotherapies are a key therapeutic strategy to fight cancer. Diverse approaches are used to activate tumor-directed immunity and to overcome tumor immune escape. The dynamic interplay between tumor cells and their tumor(immune)microenvironment (T(I)ME) poses a major challenge to create appropriate model systems. However, those model systems are needed to gain novel insights into tumor (immune) biology and a prerequisite to accurately develop and test immunotherapeutic approaches which can be successfully translated into clinical application. Several model systems have been established and advanced into so-called patient avatars to mimic the patient´s tumor biology. All models have their advantages but also disadvantages underscoring the necessity to pay attention in defining the rationale and requirements for which the patient avatar will be used. Here, we briefly outline the current state of tumor model systems used for tumor (immune)biological analysis as well as evaluation of immunotherapeutic agents. Finally, we provide a recommendation for further development to make patient avatars a complementary tool for testing and predicting immunotherapeutic strategies for personalization of tumor therapies.

Spinal Cord Organoids to Study Motor Neuron Development and Disease

Motor neuron diseases (MNDs) are a heterogeneous group of disorders that affect the cranial and/or spinal motor neurons (spMNs), spinal sensory neurons and the muscular system. Although they have been investigated for decades, we still lack a comprehensive understanding of the underlying molecular mechanisms; and therefore, efficacious therapies are scarce. Model organisms and relatively simple two-dimensional cell culture systems have been instrumental in our current knowledge of neuromuscular disease pathology; however, in the recent years, human 3D in vitro models have transformed the disease-modeling landscape. While cerebral organoids have been pursued the most, interest in spinal cord organoids (SCOs) is now also increasing. Pluripotent stem cell (PSC)-based protocols to generate SpC-like structures, sometimes including the adjacent mesoderm and derived skeletal muscle, are constantly being refined and applied to study early human neuromuscular development and disease. In this review, we outline the evolution of human PSC-derived models for generating spMN and recapitulating SpC development. We also discuss how these models have been applied to exploring the basis of human neurodevelopmental and neurodegenerative diseases. Finally, we provide an overview of the main challenges to overcome in order to generate more physiologically relevant human SpC models and propose some exciting new perspectives.

Alternative Culture Systems for Bovine Oocyte In Vitro Maturation: Liquid Marbles and Differentially Shaped 96-Well Plates

In vivo-matured oocytes exhibit higher developmental competence than those matured in vitro but mimicking the in vivo environment by in vitro conditions has been challenging. Until now, conventional two-dimensional (2D) systems have been used for in vitro maturation of bovine cumulus-oocytes-complexes (COCs). However, using such systems present certain limitations. Therefore, alternative low-cost methodologies may help to optimize oocyte in vitro maturation. Here, we used two different systems to culture COCs and evaluate their potential influence on embryo development and quality. In the first system, we used treated fumed silica particles to create a 3D microenvironment (liquid marbles; LM) to mature COCs. In the second system, we cultured COCs in 96-well plates with different dimensions (flat, ultra-low attachment round-bottom, and v-shaped 96-well plates). In both systems, the nuclear maturation rate remained similar to the control in 2D, showing that most oocytes reached metaphase II. However, the subsequent blastocyst rate remained lower in the liquid marble system compared with the 96-well plates and control 2D systems. Interestingly, a lower total cell number was found in the resulting embryos from both systems (LM and 96-well plates) compared with the control. In conclusion, oocytes matured in liquid marbles or 96-well plates showed no remarkable change in terms of meiotic resumption. None of the surface geometries influenced embryo development while oocyte maturation in liquid marbles led to reduced embryo development. These findings show that different geometry during maturation did not have a large impact on oocyte and embryo development. Lower embryo production after in vitro maturation in liquid marbles was probably detected because in vitro maturation was performed in serum-free medium, which makes oocytes more sensitive to possible toxic effects from the environment.

In vitro expansion of hematopoietic stem cells in a porous hydrogel-based 3D culture system

Hematopoietic stem cell (HSC) transplantation remains the most effective therapy for hematologic and lymphoid disorders. However, as the primary therapeutic cells, the source of HSCs has been limited due to the scarcity of matched donors and difficulties in ex vivo expansion. Here, we described a facile method to attempt the expansion of HSCs in vitro through a porous alginate hydrogel-based 3D culture system. We used gelatin powders as the porogen to create submillimeter-scaled pores in alginate gel bulk while pre-embedding naïve HSCs in the gel phase. The results indicated that this porous hydrogel system performed significantly better than those cultured via conventional suspension or encapsulation in non-porous alginate hydrogels in maintaining the phenotype and renewability of HSCs. Only the porous hydrogel system achieved a two-fold growth of CD34+ cells within seven days of culture, while the number of CD34+ cells in the suspension system and nonporous hydrogel showed different degrees of attenuation. The expansion efficiency of the porous hydrogel for CD34+CD38- cells was more than 2.2 times that of the other two systems. Mechanistic study via biophysical analysis revealed that the porous alginate system was competent to reduce the electron capture caused by biomaterials, decrease cellular oxygen stress, avoid oxidative protection, thus maintaining the cellular phenotype of the CD34+ cells. The transcriptomic analysis further suggested that the porous alginate system also upregulated the TNF signaling pathway and activated the NF-κB signaling pathway to promote the CD34+ cells' survival and maintain cellular homeostasis so that renewability was substantially favoured. STATEMENT OF SIGNIFICANCE: • The reported porous hydrogel system performs significantly better in terms of maintaining the phenotype and renewability of HSCs than those cultured via conventional suspension or encapsulation in non-porous alginate hydrogel. • The reported porous alginate system is competent to reduce the electron capture caused by biomaterials, decrease cellular oxygen stress, avoid oxidative protection, and therefore maintain the cellular phenotype of the CD34+ cells. • The reported porous alginate system can also upregulate the TNF signaling pathway and activate the NF-κB signaling pathway to promote the CD34+ cells' survival and maintain cellular homeostasis so that the renewability is substantially favored..

Matrigel: history/background, uses, and future applications

Basement membranes are thin sheets of extracellular matrix with many diverse roles in the body. Those in normal tissue are also highly insoluble and resist attempts to extract and characterize their components. A mouse tumor, the EHS tumor, has provided large amounts of basement membrane material, which has facilitated the structural and functional characterization of its components. An extract of the tumor, known as Matrigel, contains components which reconstitute into a solid gel at 37°. This solid basement membrane matrix has been used in both cell culture and in vivo. Matrigel has been utilized in some 12,000-plus publications for a variety of studies with embryonic, normal, and stem or malignant cells. Evidence presented in this Commentary suggests that Matrigel isolated from tumors grown in diverse hosts could exert unique effects that could be helpful in analyzing the causes of various pathologies and for screening possible therapeutic agents.

Patient-Derived Multiple Myeloma 3D Models for Personalized Medicine-Are We There Yet?

Despite the wide variety of existing therapies, multiple myeloma (MM) remains a disease with dismal prognosis. Choosing the right treatment for each patient remains one of the major challenges. A new approach being explored is the use of ex vivo models for personalized medicine. Two-dimensional culture or animal models often fail to predict clinical outcomes. Three-dimensional ex vivo models using patients' bone marrow (BM) cells may better reproduce the complexity and heterogeneity of the BM microenvironment. Here, we review the strengths and limitations of currently existing patient-derived ex vivo three-dimensional MM models. We analyze their biochemical and biophysical properties, molecular and cellular characteristics, as well as their potential for drug testing and identification of disease biomarkers. Furthermore, we discuss the remaining challenges and give some insight on how to achieve a more biomimetic and accurate MM BM model. Overall, there is still a need for standardized culture methods and refined readout techniques. Including both myeloma and other cells of the BM microenvironment in a simple and reproducible three-dimensional scaffold is the key to faithfully mapping and examining the relationship between these players in MM. This will allow a patient-personalized profile, providing a powerful tool for clinical and research applications.

Tunable Synthesis of Hydrogel Microfibers via Interfacial Tetrazine Ligation

Crosslinked, degradable, and cell-adhesive hydrogel microfibers were synthesized via interfacial polymerization employing tetrazine ligation, an exceptionally fast bioorthogonal reaction between strained trans-cyclooctene (TCO) and s-tetrazine (Tz). A hydrophobic trisTCO crosslinker and homo-difunctional poly(ethylene glycol) (PEG)-based macromers with the tetrazine group conjugated to PEG via a stable carbamate (PEG-bisTz1) bond or a labile hydrazone (PEG-bisTz2) linkage were synthesized. After laying an ethyl acetate solution of trisTCO over an aqueous solution of bisTz macromers, mechanically robust microfibers were continuously pulled from the oil-water interface. The resultant microfibers exhibited comparable mechanical and thermal properties but different aqueous stability. Combining PEG-bisTz2 and PEG-bisTz3 with a dangling arginine-glycine-aspartic acid (RGD) peptide in the aqueous phase yielded degradable fibers that supported the attachment and growth of primary vocal fold fibroblasts. The degradable and cell-adhesive hydrogel microfibers are expected to find utility in a wide array of tissue engineering applications.

The co-influence of hyaluronic acid and collagen on the development of an engineered annulus tissue model with bone marrow stromal cells

Inveterbral disc degeneration is a significant musculoskeletal disease that brings huge burden of pain, disability, psychological and social consequences to the affected population worldwide with treatments that only alleviate the pain but does not address the underlying biological problems. For the past decades, tissue engineering of the disc has been investigated with Annulus Fibrosus been one of the complicated disc component to be engineered. With the limited source of annulus cells, bone marrow stromal cells have been frequently investigated as a potental cell candidate to develop an annulus fibrosus-like tissue which often require a multi-disclipinary effort to achieve. The extracellular matrix of Annulus Fibrosus is largely make up of collagen and proteoglycan which is still unclear how these matrix proteins could influence the bone marrow stromal cells towards constructing a AF-like tissue. In this study, we adopted a coiled hydrogel microfiber that resembles the micro-architecture of the native AF tissue to encapsulate bone marrow stromal cells and incorporated collagen type 1 and hyaluronic acid which later demonstrated that the co-presence of hyaluronic acid and collagen could potentially upregulated AF-associated biomarkers and protease expression which are critical for later development of an engineered AF tissue construct.

Three-Dimensional 3D Culture Models in Gynecological and Breast Cancer Research

Traditional two-dimensional (2D) monolayer cell cultures have long been the gold standard for cancer biology research. However, their ability to accurately reflect the molecular mechanisms of tumors occurring in vivo is limited. Recent development of three-dimensional (3D) cell culture models facilitate the possibility to better recapitulate several of the biological and molecular characteristics of tumors in vivo, such as cancer cells heterogeneity, cell-extracellular matrix interactions, development of a hypoxic microenvironment, signaling pathway activities depending on contacts with extracellular matrix, differential growth kinetics, more accurate drugs response, and specific gene expression and epigenetic patterns. In this review, we discuss the utilization of different types of 3D culture models including spheroids, organotypic models and patient-derived organoids in gynecologic cancers research, as well as its potential applications in oncological research mainly for screening drugs with major physiological and clinical relevance. Moreover, microRNAs regulation of cancer hallmarks in 3D cell cultures from different types of cancers is discussed.

The ECM: To Scaffold, or Not to Scaffold, That Is the Question

The extracellular matrix (ECM) has pleiotropic effects, ranging from cell adhesion to cell survival. In tissue engineering, the use of ECM and ECM-like scaffolds has separated the field into two distinct areas-scaffold-based and scaffold-free. Scaffold-free techniques are used in creating reproducible cell aggregates which have massive potential for high-throughput, reproducible drug screening and disease modeling. Though, the lack of ECM prevents certain cells from surviving and proliferating. Thus, tissue engineers use scaffolds to mimic the native ECM and produce organotypic models which show more reliability in disease modeling. However, scaffold-based techniques come at a trade-off of reproducibility and throughput. To bridge the tissue engineering dichotomy, we posit that finding novel ways to incorporate the ECM in scaffold-free cultures can synergize these two disparate techniques.

3D Cell Culture Systems: Tumor Application, Advantages, and Disadvantages

The traditional two-dimensional (2D) in vitro cell culture system (on a flat support) has long been used in cancer research. However, this system cannot be fully translated into clinical trials to ideally represent physiological conditions. This culture cannot mimic the natural tumor microenvironment due to the lack of cellular communication (cell-cell) and interaction (cell-cell and cell-matrix). To overcome these limitations, three-dimensional (3D) culture systems are increasingly developed in research and have become essential for tumor research, tissue engineering, and basic biology research. 3D culture has received much attention in the field of biomedicine due to its ability to mimic tissue structure and function. The 3D matrix presents a highly dynamic framework where its components are deposited, degraded, or modified to delineate functions and provide a platform where cells attach to perform their specific functions, including adhesion, proliferation, communication, and apoptosis. So far, various types of models belong to this culture: either the culture based on natural or synthetic adherent matrices used to design 3D scaffolds as biomaterials to form a 3D matrix or based on non-adherent and/or matrix-free matrices to form the spheroids. In this review, we first summarize a comparison between 2D and 3D cultures. Then, we focus on the different components of the natural extracellular matrix that can be used as supports in 3D culture. Then we detail different types of natural supports such as matrigel, hydrogels, hard supports, and different synthetic strategies of 3D matrices such as lyophilization, electrospiding, stereolithography, microfluid by citing the advantages and disadvantages of each of them. Finally, we summarize the different methods of generating normal and tumor spheroids, citing their respective advantages and disadvantages in order to obtain an ideal 3D model (matrix) that retains the following characteristics: better biocompatibility, good mechanical properties corresponding to the tumor tissue, degradability, controllable microstructure and chemical components like the tumor tissue, favorable nutrient exchange and easy separation of the cells from the matrix.

Calcium-Enriched Nanofibrillated Cellulose/Poloxamer in-situ Forming Hydrogel Scaffolds as a Controlled Delivery System of Raloxifene HCl for Bone Engineering

PURPOSE

TEMPO-oxidized nanofibrillated cellulose (TONFC) originating from an agricultural waste (sugar cane) was utilized to prepare injectable in-situ forming hydrogel scaffolds (IHS) for regenerative medicine.

METHODS

TONFC was prepared and characterized for its morphology and chemical structure using TEM and FT-IR, respectively. The cold method was applied to prepare hydrogels. Various concentrations of poloxamer 407 were added to the prepared TONFC (0.5%w/w). Different sources of calcium, Fujicalin® (DCP) or hydroxyapatite (TCP), were used to formulate the aimed calcium-enriched raloxifene hydrochloride-loaded IHS. Gelation temperature, drug content, injectability and in-vitro drug release were evaluated along with the morphological characters. Cytocompatibility studies and tissue regeneration properties were assessed on Saos-2 cells.

RESULTS

TEM photograph of TONFC showed fibrous nanostructure. The selected formulation "Ca-IHS4" composed of TONFC+15% P407+10% TCP showed the most prolonged release pattern for 12 days with the least burst effect (about 25% within 24 h). SEM micro-photographs of the in-situ formed scaffolds showed a highly porous 3D structure. Cytocompatibility studies of formulation "Ca-IHS4" revealed the biocompatibility as well as improved cell adhesion, alkaline phosphatase enzyme activity and calcium ion deposition.

CONCLUSION

The outcomes suggest that Ca-IHS4 presents a simple, safe-line and non-invasive strategy for bone regeneration.

Collagen- and hyaluronic acid-based hydrogels and their biomedical applications

Hydrogels have been widely investigated in biomedical fields due to their similar physical and biochemical properties to the extracellular matrix (ECM). Collagen and hyaluronic acid (HA) are the main components of the ECM in many tissues. As a result, hydrogels prepared from collagen and HA hold inherent advantages in mimicking the structure and function of the native ECM. Numerous studies have focused on the development of collagen and HA hydrogels and their biomedical applications. In this extensive review, we provide a summary and analysis of the sources, features, and modifications of collagen and HA. Specifically, we highlight the fabrication, properties, and potential biomedical applications as well as promising commercialization of hydrogels based on these two natural polymers.

Fabrication of a novel 3D scaffold for cartilage tissue repair: In-vitro and in-vivo study

Self-repairing is not an advanced ability of articular cartilage. Tissue engineering has provided a novel way for reconstructing cartilage using natural polymers because of their biocompatibility and bio-functionality. The purpose of cartilage tissue engineering is to design a scaffold with proper pore structure and similar biological and mechanical properties to the native tissue. In this study, porous scaffolds prepared from gelatin, chitosan and silk fibroin were blended with varying ratios. Between the blends of chitosan (C), gelatin (G) and silk fibroin (S), the scaffold with the weight per volume ratio of 2:2:3 (w/v) showed the most favorable and higher certain properties than the other blends. The CGS 2:2:3 scaffold showed the best pore size that is between 100 μm and 300 μm. The water absorption and degradation rate of the CGS 2:2:3 scaffold were found suitable for cartilage tissue engineering. Cell culture study using human chondrocytes showed good cell adhesion and proliferation. To further study the effect of this scaffold on the living tissue, 36 rabbits were randomly assigned to CGS 2:2:3 scaffold with and without seeded chondrocytes and control groups. Hematoxylin and Eosin (H&E), Masson's trichrome (MT), and safranin O (SO) staining showed 65 ± 9.1% new cartilage tissue present in the defect filled with cell-seeded scaffold and most of the cartilaginous tissue was hyaline cartilage, while the control group showed no new cartilage tissue.

Impact of Porcine Pancreas Decellularization Conditions on the Quality of Obtained dECM

Due to the limited number of organ donors, 3D printing of organs is a promising technique. Tissue engineering is increasingly using xenogeneic material for this purpose. This study was aimed at assessing the safety of decellularized porcine pancreas, together with the analysis of the risk of an undesirable immune response. We tested eight variants of the decellularization process. We determined the following impacts: rinsing agents (PBS/NH₃·H₂O), temperature conditions (4 °C/24 °C), and the grinding method of native material (ground/cut). To assess the quality of the extracellular matrix after the completed decellularization process, analyses of the following were performed: DNA concentration, fat content, microscopic evaluation, proteolysis, material cytotoxicity, and most importantly, the Triton X-100 content. Our analyses showed that we obtained a product with an extremely low detergent content with negligible residual DNA content. The obtained results confirmed the performed histological and immuno-fluorescence staining. Moreover, the TEM microscopic analysis proved that the correct collagen structure was preserved after the decellularization process. Based on the obtained results, we chose the most favorable variant in terms of quality and biology. The method we chose is an effective and safe method that gives a chance for the development of transplant and regenerative medicine.

Development of a 3D spheroid cell culture system from fish cell lines for in vitro infection studies: Evaluation with Saprolegnia parasitica

Understanding the ways in which pathogens infect host cells is essential to improve and develop new treatment strategies. This study aimed to generate a novel in vitro infection model by establishing a reproducible 3D spheroid cell culture system that may lead to a reduced need for animals in fish disease research. 2D models (commonly cell lines) cannot replicate many key conditions of in vivo infections, but 3D spheroids have the potential to provide bridging technology between in vivo and in vitro systems. 3D spheroids were generated using cells from rainbow trout (Oncorhynchus mykiss) cell lines, RTG-2 and RTS-11. The RTG-2 spheroids were tested for their potential to be infected upon exposure to Saprolegnia parasitica spores. Positive infiltration of mycelia into the spheroids was verified by confocal microscopy. As a closer analogue of in vivo conditions encountered during infection, the straightforward model developed in this study shows promise as an additional tool that can be used to further our understanding of host-pathogen interactions for Saprolegnia and possibly a variety of other fish pathogens.

Progress in the mechanical modulation of cell functions in tissue engineering

In mammals, mechanics at multiple stages-nucleus to cell to ECM-underlie multiple physiological and pathological functions from its development to reproduction to death. Under this inspiration, substantial research has established the role of multiple aspects of mechanics in regulating fundamental cellular processes, including spreading, migration, growth, proliferation, and differentiation. However, our understanding of how these mechanical mechanisms are orchestrated or tuned at different stages to maintain or restore the healthy environment at the tissue or organ level remains largely a mystery. Over the past few decades, research in the mechanical manipulation of the surrounding environment-known as substrate or matrix or scaffold on which, or within which, cells are seeded-has been exceptionally enriched in the field of tissue engineering and regenerative medicine. To do so, traditional tissue engineering aims at recapitulating key mechanical milestones of native ECM into a substrate for guiding the cell fate and functions towards specific tissue regeneration. Despite tremendous progress, a big puzzle that remains is how the cells compute a host of mechanical cues, such as stiffness (elasticity), viscoelasticity, plasticity, non-linear elasticity, anisotropy, mechanical forces, and mechanical memory, into many biological functions in a cooperative, controlled, and safe manner. High throughput understanding of key cellular decisions as well as associated mechanosensitive downstream signaling pathway(s) for executing these decisions in response to mechanical cues, solo or combined, is essential to address this issue. While many reports have been made towards the progress and understanding of mechanical cues-particularly, substrate bulk stiffness and viscoelasticity-in regulating the cellular responses, a complete picture of mechanical cues is lacking. This review highlights a comprehensive view on the mechanical cues that are linked to modulate many cellular functions and consequent tissue functionality. For a very basic understanding, a brief discussion of the key mechanical players of ECM and the principle of mechanotransduction process is outlined. In addition, this review gathers together the most important data on the stiffness of various cells and ECM components as well as various tissues/organs and proposes an associated link from the mechanical perspective that is not yet reported. Finally, beyond addressing the challenges involved in tuning the interplaying mechanical cues in an independent manner, emerging advances in designing biomaterials for tissue engineering are also explored.

The Lack of a Representative Tendinopathy Model Hampers Fundamental Mesenchymal Stem Cell Research

Overuse tendon injuries are a major cause of musculoskeletal morbidity in both human and equine athletes, due to the cumulative degenerative damage. These injuries present significant challenges as the healing process often results in the formation of inferior scar tissue. The poor success with conventional therapy supports the need to search for novel treatments to restore functionality and regenerate tissue as close to native tendon as possible. Mesenchymal stem cell (MSC)-based strategies represent promising therapeutic tools for tendon repair in both human and veterinary medicine. The translation of tissue engineering strategies from basic research findings, however, into clinical use has been hampered by the limited understanding of the multifaceted MSC mechanisms of action. In vitro models serve as important biological tools to study cell behavior, bypassing the confounding factors associated with in vivo experiments. Controllable and reproducible in vitro conditions should be provided to study the MSC healing mechanisms in tendon injuries. Unfortunately, no physiologically representative tendinopathy models exist to date. A major shortcoming of most currently available in vitro tendon models is the lack of extracellular tendon matrix and vascular supply. These models often make use of synthetic biomaterials, which do not reflect the natural tendon composition. Alternatively, decellularized tendon has been applied, but it is challenging to obtain reproducible results due to its variable composition, less efficient cell seeding approaches and lack of cell encapsulation and vascularization. The current review will overview pros and cons associated with the use of different biomaterials and technologies enabling scaffold production. In addition, the characteristics of the ideal, state-of-the-art tendinopathy model will be discussed. Briefly, a representative in vitro tendinopathy model should be vascularized and mimic the hierarchical structure of the tendon matrix with elongated cells being organized in a parallel fashion and subjected to uniaxial stretching. Incorporation of mechanical stimulation, preferably uniaxial stretching may be a key element in order to obtain appropriate matrix alignment and create a pathophysiological model. Together, a thorough discussion on the current status and future directions for tendon models will enhance fundamental MSC research, accelerating translation of MSC therapies for tendon injuries from bench to bedside.

Fabrication of small-structure red-emissive fluorescent probes for plasma membrane enables quantification of nuclear to cytoplasmic ratio in live cells and tissues

Nuclear to cytoplasmic ratio is one of the vital parameters in diagnosis of cancer by means of hematoxylin-eosin (HE) stained histopathology. However, HE histopathology dependent on mechanical tissue slice damages biosamples and exhibits insufficient accuracy. Herein, we rationally prepared two small-molecule plasma membrane fluorescent probes with red-emitting fluorescence for visualizing plasma membrane in living cells and tissues. Their fluorescence intensities are strongly affected by environmental viscosity, which enables the exclusive imaging of plasma membrane in high fidelity. The probes can visualize plasma membrane in SiHa and rat blood red cells. Particularly, the probes are able to visualize T-tubule (transverse tubule) in skeletal muscle tissues successfully, suggesting their ability to image plasma membrane in tissues. In cooperation with Hoechst 33342, the nuclear to cytoplasmic ratio was successfully qualified in live cells and tissues. We believe these probes may have potential applications in facilitating the study on histopathology and the related areas.

Real-time monitoring of liver fibrosis through embedded sensors in a microphysiological system

Hepatic fibrosis is a foreshadowing of future adverse events like liver cirrhosis, liver failure, and cancer. Hepatic stellate cell activation is the main event of liver fibrosis, which results in excessive extracellular matrix deposition and hepatic parenchyma's disintegration. Several biochemical and molecular assays have been introduced for in vitro study of the hepatic fibrosis progression. However, they do not forecast real-time events happening to the in vitro models. Trans-epithelial electrical resistance (TEER) is used in cell culture science to measure cell monolayer barrier integrity. Herein, we explored TEER measurement's utility for monitoring fibrosis development in a dynamic cell culture microphysiological system. Immortal HepG2 cells and fibroblasts were co-cultured, and transforming growth factor β1 (TGF-β1) was used as a fibrosis stimulus to create a liver fibrosis-on-chip model. A glass chip-based embedded TEER and reactive oxygen species (ROS) sensors were employed to gauge the effect of TGF-β1 within the microphysiological system, which promotes a positive feedback response in fibrosis development. Furthermore, albumin, Urea, CYP450 measurements, and immunofluorescent microscopy were performed to correlate the following data with embedded sensors responses. We found that chip embedded electrochemical sensors could be used as a potential substitute for conventional end-point assays for studying fibrosis in microphysiological systems.

Mouse embryonic stem cells self-organize into trunk-like structures with neural tube and somites

Post-implantation embryogenesis is a highly dynamic process comprising multiple lineage decisions and morphogenetic changes that are inaccessible to deep analysis in vivo. We found that pluripotent mouse embryonic stem cells (mESCs) form aggregates that upon embedding in an extracellular matrix compound induce the formation of highly organized "trunk-like structures" (TLSs) comprising the neural tube and somites. Comparative single-cell RNA sequencing analysis confirmed that this process is highly analogous to mouse development and follows the same stepwise gene-regulatory program. Tbx6 knockout TLSs developed additional neural tubes mirroring the embryonic mutant phenotype, and chemical modulation could induce excess somite formation. TLSs thus reveal an advanced level of self-organization and provide a powerful platform for investigating post-implantation embryogenesis in a dish.

Hepatocytes and Endothelial Networks in a Fluid-Based In Vitro Model of Liver Drug Metabolism

Drug-induced liver toxicity remains a major cause of drug withdrawal from animal testing and human clinical trials. A functional liver culture model corresponding to the liver is urgently required; however, in previous liver models, it has proven difficult to stably maintain multiple liver functions. Previously reported fluid-based systems have some advantages for hepatocyte culture, but have insufficient liver-specific functions because they simply involve moving conventional hepatocyte cultures from a dish into a fluid-based system. Importantly, these cultures have no liver tissue-specific structures that construct liver-specific cellular polarities, such as apical, basolateral, and basal faces. In this study, we developed a fluid-based system for our liver tissue culture models. The liver tissues that were constructed in our originally designed fluid-based systems represent a tissue culture model for studying hepatic functions. Together, our findings show that by mimicking the structure of the liver in the body, our system effectively maintains multiple liver-specific functions. Impact statement A functional liver culture model corresponding to the liver is urgently required; however, in previous liver models, it has proven difficult to stably maintain multiple liver functions. In this study, we developed a fluid-based system for our liver tissue culture models. The liver tissues that were constructed in our originally designed fluid-based systems represent a tissue culture model for studying hepatic functions. Together, our findings show that by mimicking the structure of the liver in the body, our system effectively maintains multiple liver-specific functions.

Biomineralization process in hard tissues: The interaction complexity within protein and inorganic counterparts

Biomineralization can be considered as nature's strategy to produce and sustain biominerals, primarily via creation of hard tissues for protection and support. This review examines the biomineralization process within the hard tissues of the human body with special emphasis on the mechanisms and principles of bone and teeth mineralization. We describe the detailed role of proteins and inorganic ions in mediating the mineralization process. Furthermore, we highlight the various available models for studying bone physiology and mineralization starting from the historical static cell line-based methods to the most advanced 3D culture systems, elucidating the pros and cons of each one of these methods. With respect to the mineralization process in teeth, enamel and dentin mineralization is discussed in detail. The key role of intrinsically disordered proteins in modulating the process of mineralization in enamel and dentine is given attention. Finally, nanotechnological interventions in the area of bone and teeth mineralization, diseases and tissue regeneration is also discussed. STATEMENT OF SIGNIFICANCE: This article provides an overview of the biomineralization process within hard tissues of the human body, which encompasses the detailed mechanism innvolved in the formation of structures like teeth and bone. Moreover, we have discussed various available models used for studying biomineralization and also explored the nanotechnological applications in the field of bone regeneration and dentistry.

Current Advances in 3D Tissue and Organ Reconstruction

Bi-dimensional culture systems have represented the most used method to study cell biology outside the body for over a century. Although they convey useful information, such systems may lose tissue-specific architecture, biomechanical effectors, and biochemical cues deriving from the native extracellular matrix, with significant alterations in several cellular functions and processes. Notably, the introduction of three-dimensional (3D) platforms that are able to re-create in vitro the structures of the native tissue, have overcome some of these issues, since they better mimic the in vivo milieu and reduce the gap between the cell culture ambient and the tissue environment. 3D culture systems are currently used in a broad range of studies, from cancer and stem cell biology, to drug testing and discovery. Here, we describe the mechanisms used by cells to perceive and respond to biomechanical cues and the main signaling pathways involved. We provide an overall perspective of the most recent 3D technologies. Given the breadth of the subject, we concentrate on the use of hydrogels, bioreactors, 3D printing and bioprinting, nanofiber-based scaffolds, and preparation of a decellularized bio-matrix. In addition, we report the possibility to combine the use of 3D cultures with functionalized nanoparticles to obtain highly predictive in vitro models for use in the nanomedicine field.

In Vitro and In Vivo Tumor Models for the Evaluation of Anticancer Nanoparticles

Multiple studies about tumor biology have revealed the determinant role of the tumor microenvironment in cancer progression, resulting from the dynamic interactions between tumor cells and surrounding stromal cells within the extracellular matrix. This malignant microenvironment highly impacts the efficacy of anticancer nanoparticles by displaying drug resistance mechanisms, as well as intrinsic physical and biochemical barriers, which hamper their intratumoral accumulation and biological activity.Currently, two-dimensional cell cultures are used as the initial screening method in vitro for testing cytotoxic nanocarriers. However, this fails to mimic the tumor heterogeneity, as well as the three-dimensional tumor architecture and pathophysiological barriers, leading to an inaccurate pharmacological evaluation.Biomimetic 3D in vitro tumor models, on the other hand, are emerging as promising tools for more accurately assessing nanoparticle activity, owing to their ability to recapitulate certain features of the tumor microenvironment and thus provide mechanistic insights into nanocarrier intratumoral penetration and diffusion rates.Notwithstanding, in vivo validation of nanomedicines remains irreplaceable at the preclinical stage, and a vast variety of more advanced in vivo tumor models is currently available. Such complex animal models (e.g., genetically engineered mice and patient-derived xenografts) are capable of better predicting nanocarrier clinical efficiency, as they closely resemble the heterogeneity of the human tumor microenvironment.Herein, the development of physiologically more relevant in vitro and in vivo tumor models for the preclinical evaluation of anticancer nanoparticles will be discussed, as well as the current limitations and future challenges in clinical translation.

Tunable Hybrid Matrices Drive Epithelial Morphogenesis and YAP Translocation

Morphogenesis is a tightly-regulated developmental process by which tissues acquire the morphology that is critical to their function. For example, epithelial cells exhibit different 2D and 3D morphologies, induced by distinct biochemical and biophysical cues from their environment. In this work, novel hybrid matrices composed of a Matrigel and synthetic oligo(ethylene glycol)-grafted polyisocyanides (PICs) hydrogels are used to form a highly tailorable environment. Through precise control of the stiffness and cell-matrix interactions, while keeping other properties constant, a broad range of morphologies induced in Madin-Darby Canine Kidney (MDCK) cells is observed. At relatively low matrix stiffness, a large morphological shift from round hollow cysts to 2D monolayers is observed, without concomitant translocation of the mechanotransduction protein Yes-associated protein (YAP). At higher stiffness levels and enhanced cell-matrix interactions, tuned by controlling the adhesive peptide density on PIC, the hybrid hydrogels induce a flattened cell morphology with simultaneous YAP translocation, suggesting activation. In 3D cultures, the latter matrices lead to the formation of tubular structures. Thus, mixed synthetic and natural gels, such as the hybrids presented here, are ideal platforms to dissect how external physical factors can be used to regulate morphogenesis in MDCK model system, and in the future, in more complex environments.

A novel fluorescent probe with high photostability for imaging distribution of RNA in living cells and tissues

Herein, we have firstly developed a novel fluorescent probe based on 2,2′-bithiophene for imaging distribution of RNA in living cells and tissues.

Modeling mammalian trunk development in a dish

Mammalian post-implantation development comprises the coordination of complex lineage decisions and morphogenetic processes shaping the embryo. Despite technological advances, a comprehensive understanding of the dynamics of these processes and of the self-organization capabilities of stem cells and their descendants remains elusive. Building synthetic embryo-like structures from pluripotent embryonic stem cells in vitro promises to fill these knowledge gaps and thereby may prove transformative for developmental biology. Initial efforts to model the post-implantation embryo resulted in structures with compromised morphology (gastruloids). Recent approaches employing modified culture media, an extracellular matrix surrogate or extra-embryonic stem cells, however, succeeded in establishing embryo-like architecture. For example, embedding of gastruloids in Matrigel unlocked self-organization into trunk-like structures with bilateral somites and a neural tube-like structure, together with gut tissue and primordial germ cell-like cells. In this review, we describe the currently available models, discuss how these can be employed to acquire novel biological insights, and detail the imminent challenges for improving current models by in vitro engineering.

Hydrogels as Drug Delivery Systems: A Review of Current Characterization and Evaluation Techniques

Owing to their tunable properties, controllable degradation, and ability to protect labile drugs, hydrogels are increasingly investigated as local drug delivery systems. However, a lack of standardized methodologies used to characterize and evaluate drug release poses significant difficulties when comparing findings from different investigations, preventing an accurate assessment of systems. Here, we review the commonly used analytical techniques for drug detection and quantification from hydrogel delivery systems. The experimental conditions of drug release in saline solutions and their impact are discussed, along with the main mathematical and statistical approaches to characterize drug release profiles. We also review methods to determine drug diffusion coefficients and in vitro and in vivo models used to assess drug release and efficacy with the goal to provide guidelines and harmonized practices when investigating novel hydrogel drug delivery systems.

Matrigel-Free Laminin-Entactin Matrix to Induce Human Renal Proximal Tubule Structure Formation In Vitro

A successful in vitro tissue model must recapitulate the native tissue features while also being reproducible. Currently, Matrigel is the principal biomaterial used to induce the formation of proximal convoluted tubules (PCTs) in vitro, because of its similar composition and structure with the kidney tubular basement membrane and the presence of critical growth factors. However, Matrigel is not well-defined, and batch-to-batch variability is a significant issue. Here, we define a Matrigel-free method, using a laminin-entactin (L-E) matrix to support the formation of proximal tubular-like structures in vitro using immortalized human renal epithelial cells (RPTEC/TERT1) cocultured with murine fibroblast stromal cells (FOXD1^lacZ+). The matrix supports the presence of specific components of the tubular basement membrane (laminin, entactin/nidogen, and heparan sulfate proteoglycan) in addition to fibroblast growth factor 8a (FGF-8a). The matrix also induces tubulogenesis, leading to the formation of PCTs based on several key markers, including E-cadherin, aquaporin-1, and Na⁺/K⁺ ATPase. Moreover, these PCT structures displayed cell polarity and a well-defined lumen after 18 days in culture. This laminin-entactin (L-E) matrix constitutes a defined and consistent biomaterial that can be used in kidney tissue engineering for understanding in vitro proximal tubule development and for nephrotoxicity studies.

Comprehensive Survey on Nanobiomaterials for Bone Tissue Engineering Applications

One of the most important ideas ever produced by the application of materials science to the medical field is the notion of biomaterials. The nanostructured biomaterials play a crucial role in the development of new treatment strategies including not only the replacement of tissues and organs, but also repair and regeneration. They are designed to interact with damaged or injured tissues to induce regeneration, or as a forest for the production of laboratory tissues, so they must be micro-environmentally sensitive. The existing materials have many limitations, including impaired cell attachment, proliferation, and toxicity. Nanotechnology may open new avenues to bone tissue engineering by forming new assemblies similar in size and shape to the existing hierarchical bone structure. Organic and inorganic nanobiomaterials are increasingly used for bone tissue engineering applications because they may allow to overcome some of the current restrictions entailed by bone regeneration methods. This review covers the applications of different organic and inorganic nanobiomaterials in the field of hard tissue engineering.

Angiogenic biomaterials to promote therapeutic regeneration and investigate disease progression

The vasculature is a key component of the tissue microenvironment. Traditionally known for its role in providing nutrients and oxygen to surrounding cells, the vasculature is now also acknowledged to provide signaling cues that influence biological outcomes in regeneration and disease. These cues come from the cells that comprise vasculature, as well as the dynamic biophysical and biochemical properties of the surrounding extracellular matrix that accompany vascular development and remodeling. In this review, we illustrate the larger role of the vasculature in the context of regenerative biology and cancer progression. We describe cellular, biophysical, biochemical, and metabolic components of vascularized microenvironments. Moreover, we provide an overview of multidimensional angiogenic biomaterials that have been developed to promote therapeutic vascularization and regeneration, as well as to mimic elements of vascularized microenvironments as a means to uncover mechanisms by which vasculature influences cancer progression and therapy.

Tissue engineering of the biliary tract and modelling of cholestatic disorders

Our insight into the pathogenesis of cholestatic liver disease remains limited, partly owing to challenges in capturing the multitude of factors that contribute to disease pathogenesis in vitro. Tissue engineering could address this challenge by combining cells, materials and fabrication strategies into dynamic modelling platforms, recapitulating the multifaceted aetiology of cholangiopathies. Herein, we review the advantages and limitations of platforms for bioengineering the biliary tree, looking at how these can be applied to model biliary disorders, as well as exploring future directions for the field.

Developmental role of hyaluronic acid and its application in salivary gland tissue engineering

Dry mouth, or xerostomia, caused by salivary gland dysfunction significantly impacts oral/systemic health and quality of life. Although in vitro-generated artificial salivary glands have been considered as the fundamental solution, its structural complexity is difficult to reproduce using current biomaterials. Therefore, understanding and recapitulating the roles of biomacromolecules in salivary gland organogenesis is needed to solve these problems. Hyaluronic acid (HA) is a macromolecule abundant during salivary gland organogenesis, but its role remains unknown. Here, we verify the effects of HA on salivary gland organogenesis and artificial organ germ formation in solubilized and substrate-immobilized forms. In embryonic submandibular glands (eSMG), we found dense HA layers encapsulating proliferative c-Kit+ progenitor cells that were expressing CD44, an HA receptor. The blockage of HA synthesis, or degradation of HA, impaired eSMG growth by ablating the c-Kit+ progenitor cell population. We also found that high-molecular-weight (HMW) HA has a significant role in eSMG growth. Based on these findings, we discovered that HA is also crucial for in vitro formation of salivary gland organ germs, one of the most promising candidates for salivary gland tissue regeneration. We significantly enhanced salivary gland organ germ formation by supplementing HMW HA in solution; this effect was further increased when the HMW HA was immobilized on the substrate by polydopamine/HA co-immobilization. Our study suggests that the current use of HA in salivary gland tissue engineering can be further optimized.

Engineered tissues and strategies to overcome challenges in drug development

Current preclinical studies in drug development utilize high-throughput in vitro screens to identify drug leads, followed by both in vitro and in vivo models to predict lead candidates' pharmacokinetic and pharmacodynamic properties. The goal of these studies is to reduce the number of lead drug candidates down to the most likely to succeed in later human clinical trials. However, only 1 in 10 drug candidates that emerge from preclinical studies will succeed and become an approved therapeutic. Lack of efficacy or undetected toxicity represents roughly 75% of the causes for these failures, despite these parameters being the primary exclusion criteria in preclinical studies. Recently, advances in both biology and engineering have created new tools for constructing new preclinical models. These models can complement those used in current preclinical studies by helping to create more realistic representations of human tissues in vitro and in vivo. In this review, we describe current preclinical models to identify their value and limitations and then discuss select areas of research where improvements in preclinical models are particularly needed to advance drug development. Following this, we discuss design considerations for constructing preclinical models and then highlight recent advances in these efforts. Taken together, we aim to review the advances as of 2020 surrounding the prospect of biological and engineering tools for adding enhanced biological relevance to preclinical studies to aid in the challenges of failed drug candidates and the burden this poses on the drug development enterprise and thus healthcare.

In vitro generation of functional murine heart organoids via FGF4 and extracellular matrix

Our understanding of the spatiotemporal regulation of cardiogenesis is hindered by the difficulties in modeling this complex organ currently by in vitro models. Here we develop a method to generate heart organoids from mouse embryonic stem cell-derived embryoid bodies. Consecutive morphological changes proceed in a self-organizing manner in the presence of the laminin-entactin (LN/ET) complex and fibroblast growth factor 4 (FGF4), and the resulting in vitro heart organoid possesses atrium- and ventricle-like parts containing cardiac muscle, conducting tissues, smooth muscle and endothelial cells that exhibited myocardial contraction and action potentials. The heart organoids exhibit ultrastructural, histochemical and gene expression characteristics of considerable similarity to those of developmental hearts in vivo. Our results demonstrate that this method not only provides a biomimetic model of the developing heart-like structure with simplified differentiation protocol, but also represents a promising research tool with a broad range of applications, including drug testing.

Our understanding of the development of the heart has been limited by a lack of in vitro cellular models. Here, the authors treat mouse embryonic stem cell-derived embryoid bodies with laminin-entactin (to mimic the developing microenvironment) and FGF4 to form heart organoids, with atrial and ventricular-like parts.

Interaction of Staphylococcus aureus and Host Cells upon Infection of Bronchial Epithelium during Different Stages of Regeneration

The primary barrier that protects our lungs against infection by pathogens is a tightly sealed layer of epithelial cells. When the integrity of this barrier is disrupted as a consequence of chronic pulmonary diseases or viral insults, bacterial pathogens will gain access to underlying tissues. A major pathogen that can take advantage of such conditions is Staphylococcus aureus, thereby causing severe pneumonia. In this study, we investigated how S. aureus responds to different conditions of the human epithelium, especially nonpolarization and fibrogenesis during regeneration using an in vitro infection model. The infective process was monitored by quantification of the epithelial cell and bacterial populations, fluorescence microscopy, and mass spectrometry. The results uncover differences in bacterial internalization and population dynamics that correlate with the outcome of infection. Protein profiling reveals that, irrespective of the polarization state of the epithelial cells, the invading bacteria mount similar responses to adapt to the intracellular milieu. Remarkably, a bacterial adaptation that was associated with the regeneration state of the epithelial cells concerned the early upregulation of proteins controlled by the redox-responsive regulator Rex when bacteria were confronted with a polarized cell layer. This is indicative of the modulation of the bacterial cytoplasmic redox state to maintain homeostasis early during infection even before internalization. Our present observations provide a deeper insight into how S. aureus can take advantage of a breached epithelial barrier and show that infected epithelial cells have limited ability to respond adequately to staphylococcal insults.

Perspectives on Synthetic Materials to Guide Tissue Regeneration for Osteochondral Defect Repair

Regenerative engineering holds the potential to treat clinically pervasive osteochondral defects (OCDs). In a synthetic materials-guided approach, the scaffold's chemical and physical properties alone instruct cellular behavior in order to effect regeneration, referred to herein as "instructive" properties. While this alleviates the costs and off-target risks associated with exogenous growth factors, the scaffold must be potently instructive to achieve tissue growth. Moreover, toward achieving functionality, such a scaffold should also recapitulate the spatial complexity of the osteochondral tissues. Thus, in addition to the regeneration of the articular cartilage and underlying cancellous bone, the complex osteochondral interface, composed of calcified cartilage and subchondral bone, should also be restored. In this Perspective, we highlight recent synthetic-based, instructive osteochondral scaffolds that have leveraged new material chemistries as well as innovative fabrication strategies. In particular, scaffolds with spatially complex chemical and morphological features have been prepared with electrospinning, solvent-casting-particulate-leaching, freeze-drying, and additive manufacturing. While few synthetic scaffolds have advanced to clinical studies to treat OCDs, these recent efforts point to the promising use of the chemical and physical properties of synthetic materials for regeneration of osteochondral tissues.