The influence of matrix properties on growth and morphogenesis of human pancreatic ductal epithelial cells in 3D

Biomimetic hydrogels with mesoscale collagen architecture for patient-derived tumor organoids culture

Patient-derived tumor organoids (PDTOs) shows great potential as a preclinical model. However, the current methods for establishing PDTOs primarily focus on modulating local properties, such as sub-micrometer topographies. Nevertheless, they neglect to capture the global millimeter or intermediate mesoscale architecture that have been demonstrated to influence tumor response to therapeutic treatment and tumor progression. In this study, we present a rapid technique for generating collagen bundles with an average length of 90 ± 27 μm and a mean diameter of 5 ± 1.5 μm from tumor tissue debris that underwent mechanical agitation following enzymatic digestion. The collagen bundles were subsequently utilized for the fabrication of biomimetic hydrogels, incorporating microbial transglutaminase (mTG) crosslinked gelatin. These biomimetic hydrogels, referred to as MC-gel, were specifically designed for patient-derived tumor organoids. The lung cancer organoids cultured in MC-gel exhibited larger diameters and higher cell viability compared to those cultured in gels lacking the mesoscale collagen bundle; moreover, their irregular morphology more closely resembled that observed in vivo. The MC-gel-based lung cancer organoids effectively replicated the histology and mutational landscapes observed in the original donor patient's tumor tissue. Additionally, these lung cancer organoids showed a remarkable similarity in their gene expression and drug response across different matrices. This recently developed model holds great potential for investigating the occurrence, progression, metastasis, and management of tumors, thereby offering opportunities for personalized medicine and customized treatment options.

Orthogonally Crosslinked Gelatin-Norbornene Hydrogels for Biomedical Applications

The thiol-norbornene photo-click reaction has exceptionally fast crosslinking efficiency compared with chain-growth polymerization at equivalent macromer contents. The orthogonal reactivity between norbornene and thiol/tetrazine permits crosslinking of synthetic and naturally derived macromolecules with modularity, including poly(ethylene glycol) (PEG)-norbornene (PEGNB), gelatin-norbornene (GelNB), among others. For example, collagen-derived gelatin contains both cell adhesive motifs (e.g., Arg-Gly-Asp or RGD) and protease-labile sequences, making it an ideal macromer for forming cell-laden hydrogels. First reported in 2014, GelNB is increasingly used in orthogonal crosslinking of biomimetic matrices in various applications. GelNB can be crosslinked into hydrogels using multi-functional thiol linkers (e.g., dithiothreitol (DTT) or PEG-tetra-thiol (PEG4SH) via visible light or longwave ultraviolet (UV) light step-growth thiol-norbornene reaction or through an enzyme-mediated crosslinking (i.e., horseradish peroxidase, HRP). GelNB-based hydrogels can also be modularly crosslinked with tetrazine-bearing macromers via inverse electron-demand Diels-Alder (iEDDA) click reaction. This review surveys the various methods for preparing GelNB macromers, the crosslinking mechanisms of GelNB-based hydrogels, and their applications in cell and tissue engineering, including crosslinking of dynamic matrices, disease modeling, and tissue regeneration, delivery of therapeutics, as well as bioprinting and biofabrication.

Matrix Degradability Contributes to the Development of Salivary Gland Progenitor Cells with Secretory Functions

Synthetic matrices that are cytocompatible, cell adhesive, and cell responsive are needed for the engineering of implantable, secretory salivary gland constructs to treat radiation induced xerostomia or dry mouth. Here, taking advantage of the bioorthogonality of the Michael-type addition reaction, hydrogels with comparable stiffness but varying degrees of degradability (100% degradable, 100DEG; 50% degradable, 50DEG; and nondegradable, 0DEG) by cell-secreted matrix metalloproteases (MMPs) were synthesized using thiolated HA (HA-SH), maleimide (MI)-conjugated integrin-binding peptide (RGD-MI), and MI-functionalized peptide cross-linkers that are protease degradable (GIW-bisMI) or nondegradable (GIQ-bisMI). Organized multicellular structures developed readily in all hydrogels from dispersed primary human salivary gland stem cells (hS/PCs). As the matrix became progressively degradable, cells proliferated more readily, and the multicellular structures became larger, less spherical, and more lobular. Immunocytochemical analysis showed positive staining for stem/progenitor cell markers CD44 and keratin 5 (K5) in all three types of cultures and positive staining for the acinar marker α-amylase under 50DEG and 100DEG conditions. Quantitatively at the mRNA level, the expression levels of key stem/progenitor markers KIT, KRT5, and ETV4/5 were significantly increased in the degradable gels as compared to the nondegradable counterparts. Western blot analyses revealed that imparting matrix degradation led to >3.8-fold increase in KIT expression by day 15. The MMP-degradable hydrogels also promoted the development of a secretary phenotype, as evidenced by the upregulation of acinar markers α-amylase (AMY), aquaporin-5 (AQP5), and sodium-potassium chloride cotransporter 1 (SLC12A2). Collectively, we show that cell-mediated matrix remodeling is necessary for the development of regenerative pro-acinar progenitor cells from hS/PCs.

The Values and Perspectives of Organoids in the Field of Metabolic Syndrome

Metabolic syndrome (MetS) has become a global health problem, and the prevalence of obesity at all stages of life makes MetS research increasingly important and urgent. However, as a comprehensive and complex disease, MetS has lacked more appropriate research models. The advent of organoids provides an opportunity to address this issue. However, it should be noted that organoids are still in their infancy. The main drawbacks are a lack of maturity, complexity, and the inability to standardize large-scale production. Could organoids therefore be a better choice for studying MetS than other models? How can these limitations be overcome? Here, we summarize the available data to present current progress on pancreatic and hepatobiliary organoids and to answer these open questions. Organoids are of human origin and contain a variety of human cell types necessary to mimic the disease characteristics of MetS in their development. Taken together with the discovery of hepatobiliary progenitors in situ, the dedifferentiation of beta cells in diabetes, and studies on hepatic macrophages, we suggest that promoting endogenous regeneration has the potential to prevent the development of end-stage liver and pancreatic lesions caused by MetS and outline the direction of future research in this field.

Towards spatially-organized organs-on-chip: Photopatterning cell-laden thiol-ene and methacryloyl hydrogels in a microfluidic device

Micropatterning techniques for 3D cell cultures enable the recreation of tissue-level structures, but the combination of patterned hydrogels with organs-on-chip to generate organized 3D cultures under microfluidic perfusion remains challenging. To address this technological gap, we developed a user-friendly in-situ micropatterning protocol that integrates photolithography of crosslinkable, cell-laden hydrogels with a simple microfluidic housing, and tested the impact of crosslinking chemistry on stability and spatial resolution. Working with gelatin functionalized with photo-crosslinkable moieties, we found that inclusion of cells at high densities (≥ 107/mL) did not impede thiol-norbornene gelation, but decreased the storage moduli of methacryloyl hydrogels. Hydrogel composition and light dose were selected to match the storage moduli of soft tissues. To generate the desired pattern on-chip, the cell-laden precursor solution was flowed into a microfluidic chamber and exposed to 405 nm light through a photomask. The on-chip 3D cultures were self-standing and the designs were interchangeable by simply swapping out the photomask. Thiol-ene hydrogels yielded highly accurate feature sizes from 100 - 900 μm in diameter, whereas methacryloyl hydrogels yielded slightly enlarged features. Furthermore, only thiol-ene hydrogels were mechanically stable under perfusion overnight. Repeated patterning readily generated multi-region cultures, either separately or adjacent, including non-linear boundaries that are challenging to obtain on-chip. As a proof-of-principle, primary human T cells were patterned on-chip with high regional specificity. Viability remained high (> 85%) after 12-hr culture with constant perfusion. We envision that this technology will enable researchers to pattern 3D co-cultures to mimic organ-like structures that were previously difficult to obtain.

Biofunctional peptide-click PEG-based hydrogels as 3D cell scaffolds for corneal epithelial regeneration

Poly(ethylene glycol) (PEG)-based hydrogels as highly promising 3D cell scaffolds have been widely implemented in the field of tissue regrowth and regeneration, yet the functionalized PEG hydrogel providing dynamic, cell-instructive microenvironments is inherently difficult to obtain. Here, we have exploited the specificity of click reaction to develop a set of hydrogels based on 4-arm PEG tetraazide (4-arm-PEG-N₃) and di-propargylated peptides (GRGDG and GRDGG) with tunable physicochemical properties applicable for 3D cell scaffolds. The azide groups of PEG were reacted with the alkynyl groups of peptides, catalyzed by copper to form triazole rings, thus generating a cross-linked hydrogel. The gelation time and mechanical strength of the hydrogels varied according to the PEG/peptide feed ratio. The resulting hydrogel exhibited a typical porous microstructure and suitable swelling behavior. The in vitro cytotoxicity test indicated that the resulting hydrogels did not cause apparent cytotoxicity against human corneal epithelial cells (HCECs). After co-incubation with HCECs, the density of RGD as well as peptide sequence in the hydrogels remarkably affected the cell attachment, spreadability, and proliferation. Additionally, the proposed hydrogel showed high ocular biocompatibility after being embedded subconjunctivally into rabbit eyes. Overall, these findings highlighted that the biofunctional hydrogels formed by PEG and RGD motifs via a controllable click reaction might be promising 3D cell scaffolds for corneal epithelial regeneration.

Biomaterials for recruiting and activating endogenous stem cells in situ tissue regeneration

Over the past two decades in situ tissue engineering has emerged as a new approach where biomaterials are used to harness the body's own stem/progenitor cells to regenerate diseased or injured tissue. Immunomodulatory biomaterials are designed to promote a regenerative environment, recruit resident stem cells to diseased or injured tissue sites, and direct them towards tissue regeneration. This review explores advances gathered from in vitro and in vivo studies on in situ tissue regenerative therapies. Here we also examine the different ways this approach has been incorporated into biomaterial sciences in order to create customized biomaterial products for therapeutic applications in a broad spectrum of tissues and diseases. STATEMENT OF SIGNIFICANCE: Biomaterials can be designed to recruit stem cells and coordinate their behavior and function towards the restoration or replacement of damaged or diseased tissues in a process known as in situ tissue regeneration. Advanced biomaterial constructs with precise structure, composition, mechanical, and physical properties can be transplanted to tissue site and exploit local stem cells and their micro-environment to promote tissue regeneration. In the absence of cells, we explore the critical immunomodulatory, chemical and physical properties to consider in material design and choice. The application of biomaterials for in situ tissue regeneration has the potential to address a broad range of injuries and diseases.

Click-functionalized hydrogel design for mechanobiology investigations

The advancement of click-functionalized hydrogels in recent years has coincided with rapid growth in the fields of mechanobiology, tissue engineering, and regenerative medicine. Click chemistries represent a group of reactions that possess high reactivity and specificity, are cytocompatible, and generally proceed under physiologic conditions. Most notably, the high level of tunability afforded by these reactions enables the design of user-controlled and tissue-mimicking hydrogels in which the influence of important physical and biochemical cues on normal and aberrant cellular behaviors can be independently assessed. Several critical tissue properties, including stiffness, viscoelasticity, and biomolecule presentation, are known to regulate cell mechanobiology in the context of development, wound repair, and disease. However, many questions still remain about how the individual and combined effects of these instructive properties regulate the cellular and molecular mechanisms governing physiologic and pathologic processes. In this review, we discuss several click chemistries that have been adopted to design dynamic and instructive hydrogels for mechanobiology investigations. We also chart a path forward for how click hydrogels can help reveal important insights about complex tissue microenvironments.

Hydrogel Composites with Different Dimensional Nanoparticles for Bone Regeneration

The treatment of large segmental bone defects and complex types of fractures caused by trauma, inflammation, or tumor resection is still a challenge in the field of orthopedics. Various natural or synthetic biological materials used in clinical applications cannot fully replicate the structure and performance of raw bone. This highlights how to endow materials with multiple functions and biological properties, which is a problem that needs to be solved in practical applications. Hydrogels with outstanding biocompatibility, for their casting into any shape, size, or form, are suitable for different forms of bone defects. Therefore, they have been used in regenerative medicine more widely. In this review, versatile hydrogels are compounded with nanoparticles of different dimensions, and many desirable features of these materials in bone regeneration are introduced, including drug delivery, cell factor vehicle, cell scaffolds, which have potential in bone regeneration applications. The combination of hydrogels and nanoparticles of different dimensions encourages better filling of bone defect areas and has higher adaptability. This is due to the minimally invasive properties of the material and ability to match irregular defects. These biological characteristics make composite hydrogels with different dimensional nanoparticles become one of the most attractive options for bone regeneration materials.

Dual Functionalization of Gelatin for Orthogonal and Dynamic Hydrogel Cross-Linking

Gelatin-based hydrogels are widely used in biomedical fields because of their abundance of bioactive motifs that support cell adhesion and matrix remodeling. Although inherently bioactive, unmodified gelatin exhibits temperature-dependent rheology and solubilizes at body temperature, making it unstable for three-dimensional (3D) cell culture. Therefore, the addition of chemically reactive motifs is required to render gelatin-based hydrogels with highly controllable cross-linking kinetics and tunable mechanical properties that are critical for 3D cell culture. This article provides a series of methods toward establishing orthogonally cross-linked gelatin-based hydrogels for dynamic 3D cell culture. In particular, we prepared dually functionalized gelatin macromers amenable for sequential, orthogonal covalent cross-linking. Central to this material platform is the synthesis of norbornene-functionalized gelatin (GelNB), which forms covalently cross-linked hydrogels via orthogonal thiol-norbornene click cross-linking. Using GelNB as the starting material, we further detail the methods for synthesizing gelatin macromers susceptible to hydroxyphenylacetic acid (HPA) dimerization (i.e., GelNB-HPA) and hydrazone bonding (i.e., GelNB-CH) for on-demand matrix stiffening. Finally, we outline the protocol for synthesizing a gelatin macromer capable of adjusting hydrogel stress relaxation via boronate ester bonding (i.e., GelNB-BA). The combination of these orthogonal chemistries affords a wide range of gelatin-based hydrogels as biomimetic matrices in tissue engineering and regenerative medicine applications.

Comparative evaluation of methods for isolating small extracellular vesicles derived from pancreatic cancer cells

BACKGROUND

Small extracellular vesicles (sEVs) are nanosized vesicles involved in cell-to-cell communication. sEVs have been widely studied for clinical applications such as early detection of diseases and as therapeutics. Various methods for sEVs isolation are been using, but different methods may result in different qualities of sEVs and impact downstream analysis and applications. Here, we compared current isolation methods and performed a comparative analysis of sEVs from supernatant of cultured pancreatic cancer cells.

METHODS

Ultracentrifugation, ultrafiltration and co-precipitation as concentration methods were firstly evaluated for yield, size, morphology and protein level of pellets. Then, isolate sEVs obtained by four different purification methods: size exclusion chromatography, density gradient ultracentrifugation, ultracentrifugation, and immunoaffinity capturing, were analysed and compared.

RESULTS

For the concentration process, ultracentrifugation method obtained high quality and high concentration of pellets. For the purification process, immunoaffinity capturing method obtained the purest sEVs with less contaminants, while density gradient ultracentrifugation-based method obtained sEVs with the smallest size. Proteomic analysis revealed distinct protein contents of purified sEVs from different methods.

CONCLUSIONS

For isolating sEVs derived from supernatant of cultured pancreatic cancer cell line, ultracentrifugation-based method is recommended for concentration of sEVs, density gradient ultracentrifugation-based method may be applied for obtaining purified sEVs with controlled size, immunoaffinity capturing may be suitable for studies requiring sEVs with high purity but may loss subtypes of sEVs without specific protein marker.

Semi-interpenetrating polymer network cryogels based on poly(ethylene glycol) diacrylate and collagen as potential off-the-shelf platforms for cancer cell research

In the present work, we investigated the potential of novel semi-interpenetrating polymer network (semi-IPN) cryogels, obtained through ultraviolet exposure of aqueous mixtures of poly(ethylene glycol) diacrylate and type I collagen, as tunable off-the-shelf platforms for 3D cancer cell research. We synthesized semi-IPN cryogels with variable collagen amounts (0.1% and 1% w/v) and assessed the effect of collagen on key cryogel properties for cell culture, for example, porosity, degradation rate and mechanical stiffness. Then, we investigated the ability of the cryogels to sustain the long-term growth of two pancreatic ductal adenocarcinoma (PDAC) cell populations, the parenchymal Panc1 cells and their derived cancer stem cells. Results revealed that both cell lines efficiently infiltrated, attached and expanded in the cryogels over a period of 14 days. However, only when grown in the cryogels with the highest collagen concentration, both cell lines reproduced their characteristic growth pattern previously observed in collagen-enriched organotypic cultures, biomimetic of the highly fibrotic PDAC stroma. Cellular preembedding in Matrigel, that is, the classical approach to develop/grow organoids, interfered with an efficient intra-scaffold migration and growth. Although preliminary, these findings highlight the potential of the proposed cryogels as reproducible and tunable cancer cell research platforms.

Mammary epithelial morphogenesis in 3D combinatorial microenvironments

Human mammary epithelial cells can proliferate and reorganize into polarized multi-cellular constructs in-vitro, thereby functioning as an important model system in recapitulating key steps of in-vivo morphogenesis. Current approaches to constructing such three-dimensional mimics of the in-vivo microenvironment have involved the use of complex and ill-defined naturally derived matrices, whose properties are difficult to manipulate independently, and which have therefore limited our ability to understand the extrinsic regulation of morphogenesis. Here, we employ an automated, high-throughput approach to array modular building blocks of synthetic components, and develop a systematic approach to analyze colonies resulting from these varied microenvironmental combinations. This methodology allows us to systematically map the relationship between microenvironmental properties and ensuing morphogenetic phenotypes. Our analysis reveals that apico-basal polarity of mammary epithelial cells occurs within a narrow range of matrix stiffness, and that phenotypic homogeneity is favored in matrices which are insensitive to MMP-mediated degradation. Furthermore, combinations of extracellular proteins in the matrix finely tune the morphology of the mammary colonies, suggesting that subtle disregulations of the microenvironment may play a significant role in pathological disease states. This approach, which leverages the combinatorial possibilities of modular synthetic artificial extracellular matrices with an automated technology platform, demonstrates how morphogenesis can be assessed systematically in 3D, and provides new insights into mammary epithelial multicellularity.

Engineering of biomaterials for tumor modeling

Development of biomaterials mimicking tumor and its microenvironment has recently emerged for the use of drug discovery, precision medicine, and cancer biology. These biomimetic models have developed by reconstituting tumor and stroma cells within the 3D extracellular matrix. The models are recently extended to recapitulate the in vivo tumor microenvironment, including biological, chemical, and mechanical conditions tailored for specific cancer type and its microenvironment. In spite of the recent emergence of various innovative engineered tumor models, many of these models are still early stage to be adapted for cancer research. In this article, we review the current status of biomaterials engineering for tumor models considering three main aspects - cellular engineering, matrix engineering, and engineering for microenvironmental conditions. Considering cancer-specific variability in these aspects, our discussion is focused on pancreatic cancer, specifically pancreatic ductal adenocarcinoma (PDAC). In addition, we further discussed the current challenges and future opportunities to create reliable and relevant tumor models.

Stepwise Control of Crosslinking in a One-Pot System for Bioprinting of Low-Density Bioinks

Extrusion-based 3D bioprinting is hampered by the inability to print materials of low-viscosity. In this study, a single initiating system based on ruthenium (Ru) and sodium persulfate (SPS) is utilized for a sequential dual-step crosslinking approach: 1) primary (partial) crosslinking in absence of light to alter the bioink's rheological profile for print fidelity, and 2) subsequent secondary post-printing crosslinking for shape maintenance. Allyl-functionalized gelatin (Gel-AGE) is used as a bioink, allowing thiol-ene click reaction between allyl moieties and thiolated crosslinkers. A systematic investigation of primary crosslinking reveals that a thiol-persulfate redox reaction facilitates thiol-ene crosslinking, mediating an increase in bioink viscosity that is controllable by tailoring the Ru/SPS, crosslinker, and/or Gel-AGE concentrations. Thereafter, subsequent photoinitiated secondary crosslinking then facilitates maximum conversion of thiol-ene bonds between AGE and thiol groups. The dual-step crosslinking method is applicable to a wide biofabrication window (3-10 wt% Gel-AGE) and is demonstrated to allow printing of low-density (3 wt%) Gel-AGE, normally exhibiting low viscosity (4 mPa s), with high shape fidelity and high cell viability (>80%) over 7 days of culture. The presented approach can therefore be used as a one-pot system for printing low-viscous bioinks without the need for multiple initiating systems, viscosity enhancers, or complex chemical modifications.

A Novel Scaffold-Based Hybrid Multicellular Model for Pancreatic Ductal Adenocarcinoma-Toward a Better Mimicry of the in vivo Tumor Microenvironment

With a very low survival rate, pancreatic ductal adenocarcinoma (PDAC) is a deadly disease. This has been primarily attributed to (i) its late diagnosis and (ii) its high resistance to current treatment methods. The latter specifically requires the development of robust, realistic in vitro models of PDAC, capable of accurately mimicking the in vivo tumor niche. Advancements in the field of tissue engineering (TE) have helped the development of such models for PDAC. Herein, we report for the first time a novel hybrid, polyurethane (PU) scaffold-based, long-term, multicellular (tri-culture) model of pancreatic cancer involving cancer cells, endothelial cells, and stellate cells. Recognizing the importance of ECM proteins for optimal growth of different cell types, the model consists of two different zones/compartments: an inner tumor compartment consisting of cancer cells [fibronectin (FN)-coated] and a surrounding stromal compartment consisting of stellate and endothelial cells [collagen I (COL)-coated]. Our developed novel hybrid, tri-culture model supports the proliferation of all different cell types for 35 days (5 weeks), which is the longest reported timeframe in vitro. Furthermore, the hybrid model showed extensive COL production by the cells, mimicking desmoplasia, one of PDAC's hallmark features. Fibril alignment of the stellate cells was observed, which attested to their activated state. All three cell types expressed various cell-specific markers within the scaffolds, throughout the culture period and showed cellular migration between the two zones of the hybrid scaffold. Our novel model has great potential as a low-cost tool for in vitro studies of PDAC, as well as for treatment screening.

Biophysical Control of Bile Duct Epithelial Morphogenesis in Natural and Synthetic Scaffolds

The integration of bile duct epithelial cells (cholangiocytes) in artificial liver culture systems is important in order to generate more physiologically relevant liver models. Understanding the role of the cellular microenvironment on differentiation, physiology, and organogenesis of cholangiocytes into functional biliary tubes is essential for the development of new liver therapies, notably in the field of cholangiophaties. In this study, we investigated the role of natural or synthetic scaffolds on cholangiocytes cyst growth, lumen formation and polarization. We demonstrated that cholangiocyte cyst formation efficiency can be similar between natural and synthetic matrices provided that the mechanical properties of the hydrogels are matched. When using synthetic matrices, we also tried to understand the impact of elasticity, matrix metalloprotease-mediated degradation and integrin ligand density on cyst morphogenesis. We demonstrated that hydrogel stiffness regulates cyst formation. We found that controlling integrin ligand density was key in the establishment of large polarized cysts of cholangiocytes. The mechanism of lumen formation was found to rely on cell self-organization and proliferation. The formed cholangiocyte organoids showed a good MDR1 (multi drug resistance protein) transport activity. Our study highlights the advantages of fully synthetic scaffold as a tool to develop bile duct models.

Linkage Groups within Thiol-Ene Photoclickable PEG Hydrogels Control In Vivo Stability

Thiol-norbornene (thiol-ene) photoclickable poly(ethylene glycol) (PEG) hydrogels are a versatile biomaterial for cell encapsulation, drug delivery, and regenerative medicine. Numerous in vitro studies with these 4-arm ester-linked PEG-norbornene (PEG-4eNB) hydrogels demonstrate robust cytocompatibility and ability to retain long-term integrity with nondegradable crosslinkers. However, when transplanted in vivo into the subcutaneous or intraperitoneal space, these PEG-4eNB hydrogels with nondegradable crosslinkers rapidly degrade within 24 h. This characteristic limits the usefulness of PEG-4eNB hydrogels in biomedical applications. Replacing the ester linkage with an amide linkage (PEG-4aNB) mitigates this rapid in vivo degradation, and the PEG-4aNB hydrogels maintain long-term in vivo stability for months. Furthermore, when compared to PEG-4eNB, the PEG-4aNB hydrogels demonstrate equivalent mechanical properties, crosslinking kinetics, and high cytocompatibility with rat islets and human mesenchymal stem cells. Thus, the PEG-4aNB hydrogels may be a suitable replacement platform without necessitating critical design changes or sacrificing key properties relevant to the well-established PEG-4eNB hydrogels.

Enzymatically-degradable alginate hydrogels promote cell spreading and in vivo tissue infiltration

Enzymatically-degradable materials recapitulate the dynamic and reciprocal interactions between cells and their native microenvironment by allowing cells to actively shape the degradation process. In order to engineer a synthetic 3D environment enabling cells to orchestrate the degradation of the surrounding material, norbornene-modified alginate was crosslinked with two different peptide crosslinkers susceptible to cleavage by matrix metalloproteinases using UV-initiated thiol-ene chemistry. Resulting hydrogels were characterized for their initial mechanical and rheological properties, and their degradation behavior was measured by tracking changes in wet weight upon enzyme incubation. This process was found to be a function of the crosslinker type and enzyme concentration, indicating that degradation kinetics could be controlled and tuned. When mouse embryonic fibroblasts were encapsulated in 3D, cell number remained constant and viability was high in all materials, while cell spreading and extensive filopodia formation was observed only in the degradable gels, not in non-degradable controls. After implanting hydrogels into the backs of C57/Bl6 mice for 8 weeks, histological stainings of recovered gel remnants and surrounding tissue revealed higher tissue and cell infiltration into degradable materials compared to non-degradable controls. This alginate-based material platform with cell-empowered enzymatic degradation could prove useful in diverse tissue engineering contexts, such as regeneration and drug delivery.

In vitro differentiation of single donor derived human dental mesenchymal stem cells into pancreatic β cell-like cells

The present study was carried out to investigate and compare the in vitro differentiation potential of mesenchymal stem cells (MSCs) isolated from human dental tissues (pulp, papilla, and follicle) of the same donor. MSCs were isolated from dental tissues (pulp, papilla, and follicle) following digestion method and were analyzed for the expression of pluripotent markers and cell surface markers. All three types of MSCs were evaluated for their potential to differentiate into mesenchymal lineages. Further, the MSCs were differentiated into pancreatic β cell-like cells using multistep protocol and characterized for the expression of pancreatic lineage specific markers. Functional properties of differentiated pancreatic β cell-like cells were assessed by dithizone staining and glucose challenge test. All three types of MSCs showed fibroblast-like morphology upon culture and expressed pluripotent, and mesenchymal cell surface markers. These MSCs were successfully differentiated into mesenchymal lineages and transdifferentiated into pancreatic β cell-like cells. Among them, dental follicle derived MSCs exhibits higher transdifferentiation potency toward pancreatic lineage as evaluated by the expression of pancreatic lineage specific markers both at mRNA and protein level, and secreted higher insulin upon glucose challenge. Additionally, follicle-derived MSCs showed higher dithizone staining upon differentiation. All three types of MSCs from a single donor possess similar cellular properties and can differentiate into pancreatic lineage. However, dental follicle derived MSCs showed higher potency toward pancreatic lineage than pulp and papilla derived MSCs, suggesting their potential application in future stem cell based therapy for the treatment of diabetes.

In vivo imaging of insulin-secreting human pancreatic ductal cells using MRI reporter gene technique: A feasibility study

PURPOSE

The purpose of this study was to investigate the feasibility of in vivo imaging of human pancreatic ductal cells by OATP1B3 reporter gene under MRI.

METHODS

A human cell line (PANC-1) derived from the pancreatic ductal epithelium was used in this study. After transduction of OATP1B3, the cellular physiological functions and the ability of intracellular uptake of the MRI contrast medium (Gd-EOB-DTPA) were examined. Induced differentiation of the PANC-1 cells into hormone-secreting cells were performed to simulate pancreatic β-like cells. The hormone-secreting cells were implanted into rats and in vivo MRI was evaluated.

RESULTS

The mRNA and proteins of OATP1B3 were highly expressed. No significant change of cellular physiological functions was found after the expression. After induced differentiation, the hormone secretion capacities of the OATP1B3-expressing PANC-1 cells were confirmed. Intra-cellular uptake of Gd-EOB-DTPA was determined in vitro by inductively coupled plasma mass spectrometry and MRI. In vivo MRI of the OATP1B3-expressing xenograft revealed an increased signal intensity after contrast enhancement.

CONCLUSION

OATP1B3 can be used as a safe and feasible in vivo MRI gene reporter for human pancreatic ductal cells.

Cellular Behavior of RAW264.7 Cells in 3D Poly(ethylene glycol) Hydrogel Niches

Although macrophages undergo dynamic cellular responses in diverse extracellular environments, macrophage research has mostly relied on conventional culture methodologies such as two-dimensional and suspension cultures. In contrast, recent efforts have revealed evidence of the characteristic cellular behaviors of macrophages in actual tissues using a three-dimensional (3D) culture matrix. In this work, we exploited a poly(ethylene glycol)-based hydrogel as a macrophage culture matrix and observed cellular behaviors in 3D by manipulating the matrix properties. In the 3D microenvironment, macrophage-like RAW264.7 cells proliferated and formed spherical clusters by degrading the surrounding hydrogel network. Interestingly, we observed the significant upregulation of matrix metalloproteinases (MMPs) (i.e., MMP9 and MMP14) as well as M1 polarization markers (i.e., iNOS, COX2, TNF-α) in 3D, whereas M2 polarization markers (i.e., CD206, Arg1, TGF-β) were downregulated. Specifically, the expressions of both M1 and M2 markers were simultaneously increased in a stiff matrix compared to those of a soft matrix. In addition, matrix degradability significantly influenced the TNF-α secretion of encapsulated RAW264.7 cells. The MMP sensitivity of the hydrogel decreased TNF-α expression in a soft matrix, whereas it upregulated TNF-α in a stiff matrix compared to those of MMP-insensitive hydrogel. These findings suggest that the highly tunable poly(ethylene glycol) hydrogels can dictate macrophage behavior by altering the surrounding 3D microenvironment.

Generation of pancreatic β cells for treatment of diabetes: advances and challenges

Human embryonic stem cells (hESC) and induced pluripotent stem cells (hiPSC) are considered attractive sources of pancreatic β cells and islet organoids. Recently, several reports presented that hESC/iPSC-derived cells enriched with specific transcription factors can form glucose-responsive insulin-secreting cells in vitro and transplantation of these cells ameliorates hyperglycemia in diabetic mice. However, the glucose-stimulated insulin-secreting capacity of these cells is lower than that of endogenous islets, suggesting the need to improve induction procedures. One of the critical problems facing in vivo maturation of hESC/iPSC-derived cells is their low survival rate after transplantation, although this rate increases when the implanted pancreatic cells are encapsulated to avoid the immune response. Several groups have also reported on the generation of hESC/iPSC-derived islet-like organoids, but development of techniques for complete islet structures with the eventual generation of vascularized constructs remains a major challenge to their application in regenerative therapies. Many issues also need to be addressed before the successful clinical application of hESC/iPSC-derived cells or islet organoids. In this review, we summarize advances in the generation of hESC/iPSC-derived pancreatic β cells or islet organoids and discuss the limitations and challenges for their successful therapeutic application in diabetes.

Designer hydrogels: Shedding light on the physical chemistry of the pancreatic cancer microenvironment

Pancreatic ductal adenocarcinoma (PDAC) is currently the third leading cause of cancer mortality in the United States, with a 5-year survival of ∼8%. PDAC is characterized by a dense and hypo-vascularized stroma consisting of proliferating cancer cells, cancer-associated fibroblasts, macrophages and immune cells, as well as excess matrices including collagens, fibronectin, and hyaluronic acid. In addition, PDAC has increased interstitial pressures and a hypoxic/acidic tumor microenvironment (TME) that impedes drug delivery and blocks cancer-directed immune mechanisms. In spite of increasing options in targeted therapy, PDAC has mostly remained treatment recalcitrant. Owing to its critical roles on governing PDAC progression and treatment outcome, TME and its interplay with the cancer cells are increasingly studied. In particular, three-dimensional (3D) hydrogels derived from or inspired by components in the TME are progressively developed. When properly designed, these hydrogels (e.g., Matrigel, collagen gel, hyaluronic acid-based, and semi-synthetic hydrogels) can provide pathophysiologically relevant compositions, conditions, and contexts for supporting PDAC cell fate processes. This review summarizes recent efforts in using 3D hydrogels for fundamental studies on cell-matrix or cell-cell interactions in PDAC.

Design of synthetic extracellular matrices for probing breast cancer cell growth using robust cyctocompatible nucleophilic thiol-yne addition chemistry

Controlled, three-dimensional (3D) cell culture systems are of growing interest for both tissue regeneration and disease, including cancer, enabling hypothesis testing about the effects of microenvironment cues on a variety of cellular processes, including aspects of disease progression. In this work, we encapsulate and culture in three dimensions different cancer cell lines in a synthetic extracellular matrix (ECM), using mild and efficient chemistry. Specifically, harnessing the nucleophilic addition of thiols to activated alkynes, we have created hydrogel-based materials with multifunctional poly(ethylene glycol) (PEG) and select biomimetic peptides. These materials have definable, controlled mechanical properties (G' = 4-10 kPa) and enable facile incorporation of pendant peptides for cell adhesion, relevant for mimicking soft tissues, where polymer architecture allows tuning of matrix degradation. These matrices rapidly formed in the presence of sensitive breast cancer cells (MCF-7) for successful encapsulation with high cell viability, greatly improved relative to that observed with the more widely used radically-initiated thiol-ene crosslinking chemistry. Furthermore, controlled matrix degradation by both bulk and local mechanisms, ester hydrolysis of the polymer network and cell-driven enzymatic hydrolysis of cell-degradable peptide, allowed cell proliferation and the formation of cell clusters within these thiol-yne hydrogels. These studies demonstrate the importance of chemistry in ECM mimics and the potential thiol-yne chemistry has as a crosslinking reaction for the encapsulation and culture of cells, including those sensitive to radical crosslinking pathways.

Concise Review: Current Status of Three-Dimensional Organoids as Preclinical Models

Three-dimensional (3D) cultures use the property of some cells to self-organize in matrices and generate structures that can be programmed to represent an organ or a pathology. Organoid cultures are the 3D cultivation of source tissue (ranging from cells to tissue fragments) in a support matrix and specialized media that nearly resembles the physiological environment. Depending on the source tissue, growth factors, and inhibitors provided, organoids can be programmed to recapitulate the biology of a system and progression of pathology. Organoids are genetically stable, and genetically amenable, making them very suitable tools to study tissue homeostasis and cancer. In this Review, we focus on providing recent technical advances from published literature to efficiently use organoids as a tool for disease modeling and therapeutics. Also, we discuss stem cell biology principles used to generate multiple organoids and their characteristics, with a brief description of methodology. A major theme of this review is to expand organoid applications to the study disease progression and drug response in different cancers. We also discuss shortcomings, limitations, and advantages of developed 3D cultures, with the rationale behind the methodology. Stem Cells 2018;36:1329-1340.

A 3D bioinspired highly porous polymeric scaffolding system for in vitro simulation of pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma is an aggressive disease with an extremely low survival rate. This is due to the (i) poor prognosis and (ii) high resistance of the disease to current treatment options. The latter is partly due to the very complex and dense tissue/tumour microenvironment of pancreatic cancer, which contributes to the disease's progression and the inhibition of apoptotic pathways. Over the last years, advances in tissue engineering and the development of three-dimensional (3D) culture systems have shed more light into cancer research by enabling a more realistic recapitulation of the niches and structure of the tumour microenvironment. Herein, for the first time, 3D porous polyurethane scaffolds were fabricated and coated with fibronectin to mimic features of the structure and extracellular matrix present in the pancreatic cancer tumour microenvironment. The developed 3D scaffold could support the proliferation of the pancreatic tumour cells, which was enhanced with the presence of fibronectin, for a month, which is a significantly prolonged in vitro culturing duration. Furthermore, in situ imaging of cellular and biomarker distribution showed the formation of dense cellular masses, the production of collagen-I by the cells and the formation of environmental stress gradients (e.g. HIF-1α) with similar heterogeneity trends to the ones reported in in vivo studies. The results obtained in this study suggest that this bioinspired porous polyurethane based scaffold has great potential for in vitro high throughput studies of pancreatic cancer including drug and treatment screening.

Biomimetic and enzyme-responsive dynamic hydrogels for studying cell-matrix interactions in pancreatic ductal adenocarcinoma

The tumor microenvironment (TME) governs all aspects of cancer progression and in vitro 3D cell culture platforms are increasingly developed to emulate the interactions between components of the stromal tissues and cancer cells. However, conventional cell culture platforms are inadequate in recapitulating the TME, which has complex compositions and dynamically changing matrix mechanics. In this study, we developed a dynamic gelatin-hyaluronic acid hybrid hydrogel system through integrating modular thiol-norbornene photopolymerization and enzyme-triggered on-demand matrix stiffening. In particular, gelatin was dually modified with norbornene and 4-hydroxyphenylacetic acid to render this bioactive protein photo-crosslinkable (through thiol-norbornene gelation) and responsive to tyrosinase-triggered on-demand stiffening (through HPA dimerization). In addition to the modified gelatin that provides basic cell adhesive motifs and protease cleavable sequences, hyaluronic acid (HA), an essential tumor matrix, was modularly and covalently incorporated into the cell-laden gel network. We systematically characterized macromer modification, gel crosslinking, as well as enzyme-triggered stiffening and degradation. We also evaluated the influence of matrix composition and dynamic stiffening on pancreatic ductal adenocarcinoma (PDAC) cell fate in 3D. We found that either HA-containing matrix or a dynamically stiffened microenvironment inhibited PDAC cell growth. Interestingly, these two factors synergistically induced cell phenotypic changes that resembled cell migration and/or invasion in 3D. Additional mRNA expression array analyses revealed changes unique to the presence of HA, to a stiffened microenvironment, or to the combination of both. Finally, we presented immunostaining and mRNA expression data to demonstrate that these irregular PDAC cell phenotypes were a result of matrix-induced epithelial-mesenchymal transition (EMT).

Improving gelation efficiency and cytocompatibility of visible light polymerized thiol-norbornene hydrogels via addition of soluble tyrosine

Hydrogels immobilized with biomimetic peptides have been used widely for tissue engineering and drug delivery applications. Photopolymerization has been among the most commonly used techniques to fabricate peptide-immobilized hydrogels as it offers rapid and robust peptide immobilization within a crosslinked hydrogel network. Both chain-growth and step-growth photopolymerizations can be used to immobilize peptides within covalently crosslinked hydrogels. A previously developed visible light mediated step-growth thiol-norbornene gelation scheme has demonstrated efficient crosslinking of hydrogels composed of an inert poly(ethylene glycol)-norbornene (PEGNB) macromer and a small molecular weight bis-thiol linker, such as dithiothreitol (DTT). Compared with conventional visible light mediated chain-polymerizations where multiple initiator components are required, step-growth photopolymerized thiol-norbornene hydrogels are more cytocompatible for the in situ encapsulation of radical sensitive cells (e.g., pancreatic β-cells). This contribution explored visible light based crosslinking of various bis-cysteine containing peptides with macromer 8-arm PEGNB to form biomimetic hydrogels suitable for in situ cell encapsulation. It was found that the addition of soluble tyrosine during polymerization not only significantly accelerated gelation, but also improved the crosslinking efficiency of PEG-peptide hydrogels as evidenced by a decreased gel point and enhanced gel modulus. In addition, soluble tyrosine drastically enhanced the cytocompatibility of the resulting PEG-peptide hydrogels, as demonstrated by in situ encapsulation and culture of pancreatic MIN6 β-cells. This visible light based thiol-norbornene crosslinking mechanism provides an attractive gelation method for preparing cytocompatible PEG-peptide hydrogels for tissue engineering applications.

Enhanced differentiation of human pluripotent stem cells into pancreatic progenitors co-expressing PDX1 and NKX6.1

Background

Pancreatic progenitors (PPs) co-expressing the two transcription factors (TFs) PDX1 and NKX6.1 are recognized as the indispensable precursors of functional pancreatic β cells. Here, we aimed to establish an efficient protocol for maximizing generation of PDX1⁺/NKX6.1⁺ PPs from human pluripotent stem cells (hPSCs).

Methods

In order to enhance the PDX1⁺/NKX6.1⁺ population, we manipulated in vitro culture conditions during differentiation by dissociating densely formed endodermal cells and re-plating them at different densities. These dissociated cells were subjected to an augmented duration of retinoid and fibroblast growth factor (FGF)10 signaling to induce higher PDX1 and NKX6.1 expression.

Results

Our optimized protocol dramatically increased the expression of NKX6.1, leading to an increase in the proportion of PDX1⁺/NKX6.1⁺ progenitors (~90%) in monolayer, higher than the previously published protocols, as well as upregulated key TFs controlling pancreatic development. The improved efficiency of pancreatic differentiation was complemented by an inhibited hepatic specification and an increased proliferation of NKX6.1⁺ cells. Interestingly, we were able to enrich a novel PDX1^–/NKX6.1⁺ population by manipulating the re-plating density; these oriented themselves in three-dimensional clusters. Further differentiation validated the ability of our PDX1⁺/NKX6.1⁺ progenitors to generate NGN3⁺ endocrine progenitors.

Conclusions

We provide a novel technique that facilitates appropriate cellular rearrangement in monolayer culture to yield a high proportion of PDX1⁺/NKX6.1⁺ PPs with an elevated self-replicating capacity, thereby aiding scalable production of functional β cells from hPSCs in vitro. Our innovative method also enriches a novel NKX6.1⁺/PDX1^– population, with characteristics of proposed endocrine precursors, allowing further studies on deciphering routes to β-cell development.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-017-0759-z) contains supplementary material, which is available to authorized users.

Local remodeling of synthetic extracellular matrix microenvironments by co-cultured endometrial epithelial and stromal cells enables long-term dynamic physiological function

Mucosal barrier tissues, comprising a layer of tightly-bonded epithelial cells in intimate molecular communication with an underlying matrix-rich stroma containing fibroblasts and immune cells, are prominent targets for drugs against infection, chronic inflammation, and other disease processes. Although human in vitro models of such barriers are needed for mechanistic studies and drug development, differences in extracellular matrix (ECM) needs of epithelial and stromal cells hinder efforts to create such models. Here, using the endometrium as an example mucosal barrier, we describe a synthetic, modular ECM hydrogel suitable for 3D functional co-culture, featuring components that can be remodeled by cells and that respond dynamically to sequester local cell-secreted ECM characteristic of each cell type. The synthetic hydrogel combines peptides with off-the-shelf reagents and is thus accessible to cell biology labs. Specifically, we first identified a single peptide as suitable for initial attachment of both endometrial epithelial and stromal cells using a 2D semi-empirical screen. Then, using a co-culture system of epithelial cells cultured on top of gel-encapsulated stromal cells, we show that inclusion of ECM-binding peptides in the hydrogel, along with the integrin-binding peptide, leads to enhanced accumulation of basement membrane beneath the epithelial layer and more fibrillar collagen matrix assembly by stromal cells over two weeks in culture. Importantly, endometrial co-cultures composed of either cell lines or primary cells displayed hormone-mediated differentiation as assessed by morphological changes and secretory protein production. A multiplex analysis of apical cytokine and growth factor secretion comparing cell lines and primary cells revealed strikingly different patterns, underscoring the importance of using primary cell models in analysis of cell-cell communication networks. In summary, we define a "one-size-fits-all" synthetic ECM that enables long-term, physiologically responsive co-cultures of epithelial and stromal cells in a mucosal barrier format.

Versatile synthetic alternatives to Matrigel for vascular toxicity screening and stem cell expansion

The physiological relevance of Matrigel as a cell-culture substrate and in angiogenesis assays is often called into question. Here, we describe an array-based method for the identification of synthetic hydrogels that promote the formation of robust in vitro vascular networks for the detection of putative vascular disruptors, and that support human embryonic stem cell expansion and pluripotency. We identified hydrogel substrates that promoted endothelial-network formation by primary human umbilical vein endothelial cells and by endothelial cells derived from human induced pluripotent stem cells, and used the hydrogels with endothelial networks to identify angiogenesis inhibitors. The synthetic hydrogels show superior sensitivity and reproducibility over Matrigel when evaluating known inhibitors, as well as in a blinded screen of a subset of 38 chemicals, selected according to predicted vascular disruption potential, from the Toxicity ForeCaster library of the US Environmental Protection Agency. The identified synthetic hydrogels should be suitable alternatives to Matrigel for common cell-culture applications.

Designing a bio-inspired biomimetic in vitro system for the optimization of ex vivo studies of pancreatic cancer

Pancreatic cancer is one of the most aggressive and lethal human malignancies. Drug therapies and radiotherapy are used for treatment as adjuvants to surgery, but outcomes remain disappointing. Advances in tissue engineering suggest that 3D cultures can reflect the in vivo tumor microenvironment and can guarantee a physiological distribution of oxygen, nutrients, and drugs, making them promising low-cost tools for therapy development. Here, we review crucial structural and environmental elements that should be considered for an accurate design of an ex vivo platform for studies of pancreatic cancer. Furthermore, we propose environmental stress response biomarkers as platform readouts for the efficient control and further prediction of the pancreatic cancer response to the environmental and treatment input.

Encapsulation of primary salivary gland cells in enzymatically degradable poly(ethylene glycol) hydrogels promotes acinar cell characteristics

Radiation therapy for head and neck cancers leads to permanent xerostomia due to the loss of secretory acinar cells in the salivary glands. Regenerative treatments utilizing primary submandibular gland (SMG) cells show modest improvements in salivary secretory function, but there is limited evidence of salivary gland regeneration. We have recently shown that poly(ethylene glycol) (PEG) hydrogels can support the survival and proliferation of SMG cells as multicellular spheres in vitro. To further develop this approach for cell-based salivary gland regeneration, we have investigated how different modes of PEG hydrogel degradation affect the proliferation, cell-specific gene expression, and epithelial morphology within encapsulated salivary gland spheres. Comparison of non-degradable, hydrolytically-degradable, matrix metalloproteinase (MMP)-degradable, and mixed mode-degradable hydrogels showed that hydrogel degradation by any mechanism is required for significant proliferation of encapsulated cells. The expression of acinar phenotypic markers Aqp5 and Nkcc1 was increased in hydrogels that are MMP-degradable compared with other hydrogel compositions. However, expression of secretory acinar proteins Mist1 and Pip was not maintained to the same extent as phenotypic markers, suggesting changes in cell function upon encapsulation. Nevertheless, MMP- and mixed mode-degradability promoted organization of polarized cell types forming tight junctions and expression of the basement membrane proteins laminin and collagen IV within encapsulated SMG spheres. This work demonstrates that cellularly remodeled hydrogels can promote proliferation and gland-like organization by encapsulated salivary gland cells as well as maintenance of acinar cell characteristics required for regenerative approaches. Investigation is required to identify approaches to further enhance acinar secretory properties.

STATEMENT OF SIGNIFICANCE

Regenerative strategies to replace damaged salivary glands require the function and organization of acinar cells. Hydrogel-based approaches have shown promise to control cell function and phenotype. However, little is known about how specific parameters, such as the mechanism of hydrogel degradation (e.g., hydrolytic or enzymatic), influence the viability, proliferation, organization, and phenotype of salivary gland cells. In this work, it is shown that hydrogel-encapsulated primary salivary gland cell proliferation is dependent upon hydrogel degradation. Hydrogels crosslinked with enzymatically degradable peptides promoted the expression of critical acinar cell markers, which are typically downregulated in primary cultures. Furthermore, salivary gland cells encapsulated in enzymatically- but not hydrolytically-degradable hydrogels displayed highly organized and polarized salivary gland cell markers, which mimics characteristics found in native gland tissue. In sum, results indicate that salivary gland cells respond to cellularly remodeled hydrogels, resulting in self-assembly and organization akin to acini substructures of the salivary gland.

Biomimetic Hydrogels Incorporating Polymeric Cell-Adhesive Peptide To Promote the 3D Assembly of Tumoroids

Toward the goal of establishing physiologically relevant in vitro tumor models, we synthesized and characterized a biomimetic hydrogel using thiolated hyaluronic acid (HA-SH) and an acrylated copolymer carrying multiple copies of cell adhesive peptide (PolyRGD-AC). PolyRGD-AC was derived from a random copolymer of tert-butyl methacrylate (tBMA) and oligomeric (ethylene glycol) methacrylate (OEGMA), synthesized via atom transfer radical polymerization (ATRP). Acid hydrolysis of tert-butyl moieties revealed the carboxylates, through which acrylate groups were installed. Partial modification of the acrylate groups with a cysteine-containing RGD peptide generated PolyRGD-AC. When PolyRGD-AC was mixed with HA-SH under physiological conditions, a macroscopic hydrogel with an average elastic modulus of 630 Pa was produced. LNCaP prostate cancer cells encapsulated in HA-PolyRGD gels as dispersed single cells formed multicellular tumoroids by day 4 and reached an average diameter of ∼95 μm by day 28. Cells in these structures were viable, formed cell-cell contacts through E-cadherin (E-CAD), and displayed cortical organization of F-actin. Compared with the control gels prepared using PolyRDG, multivalent presentation of the RGD signal in the HA matrix increased cellular metabolism, promoted the development of larger tumoroids, and enhanced the expression of E-CAD and integrins. Overall, hydrogels with multivalently immobilized RGD are a promising 3D culture platform for dissecting principles of tumorigenesis and for screening anticancer drugs.

Loss of E-cadherin disrupts ovarian epithelial inclusion cyst formation and collective cell movement in ovarian cancer cells

Increased inclusion cyst formation in the ovary is associated with ovarian cancer development. We employed in vitro three-dimensional (3D) organotypic models formed by normal human ovarian surface epithelial (OSE) cells and ovarian cancer cells to study the morphologies of normal and cancerous ovarian cortical inclusion cysts and the molecular changes during their transitions into stromal microenvironment. When compared with normal cysts that expressed tenascin, the cancerous cysts expressed high levels of laminin V and demonstrated polarized structures in Matrigel; and the cancer cells migrated collectively when the cyst structures were positioned in a stromal-like collagen I matrix. The molecular markers identified in the in vitro 3D models were verified in clinical samples. Network analysis of gene expression of the 3D structures indicates concurrent downregulation of transforming growth factor beta pathway genes and high levels of E-cadherin and microRNA200 (miR200) expression in the cancerous cysts and the migrating cancer cells. Transient silencing of E-cadherin expression in ovarian cancer cells disrupted cyst structures and inhibited collective cell migration. Taken together, our studies employing 3D models have shown that E-cadherin is crucial for ovarian inclusion cyst formation and collective cancer cell migration.

Heralding a new paradigm in 3D tumor modeling

Numerous studies to date have contributed to a paradigm shift in modeling cancer, moving from the traditional two-dimensional culture system to three-dimensional (3D) culture systems for cancer cell culture. This led to the inception of tumor engineering, which has undergone rapid advances over the years. In line with the recognition that tumors are not merely masses of proliferating cancer cells but rather, highly complex tissues consisting of a dynamic extracellular matrix together with stromal, immune and endothelial cells, significant efforts have been made to better recapitulate the tumor microenvironment in 3D. These approaches include the development of engineered matrices and co-cultures to replicate the complexity of tumor-stroma interactions in vitro. However, the tumor engineering and cancer biology fields have traditionally relied heavily on the use of cancer cell lines as a cell source in tumor modeling. While cancer cell lines have contributed to a wealth of knowledge in cancer biology, the use of this cell source is increasingly perceived as a major contributing factor to the dismal failure rate of oncology drugs in drug development. Backing this notion is the increasing evidence that tumors possess intrinsic heterogeneity, which predominantly homogeneous cancer cell lines poorly reflect. Tumor heterogeneity contributes to therapeutic resistance in patients. To overcome this limitation, cancer cell lines are beginning to be replaced by primary tumor cell sources, in the form of patient-derived xenografts and organoids cultures. Moving forward, we propose that further advances in tumor engineering would require that tumor heterogeneity (tumor variants) be taken into consideration together with tumor complexity (tumor-stroma interactions). In this review, we provide a comprehensive overview of what has been achieved in recapitulating tumor complexity, and discuss the importance of incorporating tumor heterogeneity into 3D in vitro tumor models. This work carves out the roadmap for 3D tumor engineering and highlights some of the challenges that need to be addressed as we move forward into the next chapter.

Biomaterials-based strategies for salivary gland tissue regeneration

The salivary gland is a complex, secretory tissue that produces saliva and maintains oral homeostasis. Radiation induced salivary gland atrophy, manifested as "dry mouth" or xerostomia, poses a significant clinical challenge. Tissue engineering recently has emerged as an alternative, long-term treatment strategy for xerostomia. In this review, we summarize recent efforts towards the development of functional and implantable salivary glands utilizing designed polymeric substrates or synthetic matrices/scaffolds. Although the in vitro engineering of a complex implantable salivary gland is technically challenging, opportunities exist for multidisciplinary teams to assemble implantable and secretory tissue modules by combining stem/progenitor cells found in the adult glands with biomimetic and cell-instructive materials.

Advancing biomaterials of human origin for tissue engineering

Biomaterials have played an increasingly prominent role in the success of biomedical devices and in the development of tissue engineering, which seeks to unlock the regenerative potential innate to human tissues/organs in a state of deterioration and to restore or reestablish normal bodily function. Advances in our understanding of regenerative biomaterials and their roles in new tissue formation can potentially open a new frontier in the fast-growing field of regenerative medicine. Taking inspiration from the role and multi-component construction of native extracellular matrices (ECMs) for cell accommodation, the synthetic biomaterials produced today routinely incorporate biologically active components to define an artificial in vivo milieu with complex and dynamic interactions that foster and regulate stem cells, similar to the events occurring in a natural cellular microenvironment. The range and degree of biomaterial sophistication have also dramatically increased as more knowledge has accumulated through materials science, matrix biology and tissue engineering. However, achieving clinical translation and commercial success requires regenerative biomaterials to be not only efficacious and safe but also cost-effective and convenient for use and production. Utilizing biomaterials of human origin as building blocks for therapeutic purposes has provided a facilitated approach that closely mimics the critical aspects of natural tissue with regard to its physical and chemical properties for the orchestration of wound healing and tissue regeneration. In addition to directly using tissue transfers and transplants for repair, new applications of human-derived biomaterials are now focusing on the use of naturally occurring biomacromolecules, decellularized ECM scaffolds and autologous preparations rich in growth factors/non-expanded stem cells to either target acceleration/magnification of the body's own repair capacity or use nature's paradigms to create new tissues for restoration. In particular, there is increasing interest in separating ECMs into simplified functional domains and/or biopolymeric assemblies so that these components/constituents can be discretely exploited and manipulated for the production of bioscaffolds and new biomimetic biomaterials. Here, following an overview of tissue auto-/allo-transplantation, we discuss the recent trends and advances as well as the challenges and future directions in the evolution and application of human-derived biomaterials for reconstructive surgery and tissue engineering. In particular, we focus on an exploration of the structural, mechanical, biochemical and biological information present in native human tissue for bioengineering applications and to provide inspiration for the design of future biomaterials.

In Situ "Clickable" Zwitterionic Starch-Based Hydrogel for 3D Cell Encapsulation

Three-dimensional (3D) cell encapsulation in hydrogel provides superb methods to investigate the biochemical cues in directing cellular fate and behaviors outside the organism, the primary step of which is to establish suitable "blank platform" to mimic and simplify native ECM microenvironment. In this study, zwitterionic starch-based "clickable" hydrogels were fabricated via a "copper- and light- free" Michael-type "thiol-ene" addition reaction between acylated-modified sulfobetaine-derived starch (SB-ST-A) and dithiol-functionalized poly(ethylene glycol) (PEG-SH). By incorporating antifouling SB-ST and PEG, the hydrogel system would be excellently protected from nontarget protein adsorption to act as a "blank platform". The hydrogels could rapidly gel under physiological conditions in less than 7 min. Dynamic rheology experiments suggested the stiffness of the hydrogel was close to the native tissues, and the mechanical properties as well as the gelation times and swelling behaviors could be easily tuned by varying the precursor proportions. The protein and cell adhesion assays demonstrated that the hydrogel surface could effectively resist nonspecific protein and cell adhesion. The degradation study in vitro confirmed that the hydrogel was biodegradable. A549 cells encapsulated in the hydrogel maintained high viability (up to 93%) and started to proliferate in number and extend in morphology after 2 days' culture. These results indicated the hydrogel presented here could be a potential candidate as "blank platform" for 3D cell encapsulation and biochemical cues induced cellular behavior investigation in vitro.

Dual mode gelation behavior of silk fibroin microgel embedded poly(ethylene glycol) hydrogels

Hydrogel formation by more than two cross-linking mechanisms is preferred for the sophisticated manipulation of hydrogel properties.

Synthetic matrices reveal contributions of ECM biophysical and biochemical properties to epithelial morphogenesis

Epithelial cells cultured within collagen and laminin gels proliferate to form hollow and polarized spherical structures, recapitulating the formation of a rudimentary epithelial organ. However, the contributions of extracellular matrix (ECM) biochemical and biophysical properties to morphogenesis are poorly understood because of uncontrolled presentation of multiple adhesive ligands, limited control over mechanical properties, and lot-to-lot compositional variability in these natural ECMs. We engineered synthetic ECM-mimetic hydrogels with independent control over adhesive ligand density, mechanical properties, and proteolytic degradation to study the impact of ECM properties on epithelial morphogenesis. Normal cyst growth, polarization, and lumen formation were restricted to a narrow range of ECM elasticity, whereas abnormal morphogenesis was observed at lower and higher elastic moduli. Adhesive ligand density dramatically regulated apicobasal polarity and lumenogenesis independently of cell proliferation. Finally, a threshold level of ECM protease degradability was required for apicobasal polarity and lumen formation. This synthetic ECM technology provides new insights into how cells transduce ECM properties into complex morphogenetic behaviors.

Integrin-specific hydrogels as adaptable tumor organoids for malignant B and T cells

Non-Hodgkin lymphomas are a heterogeneous group of lymphoproliferative disorders of B and T cell origin that are treated with chemotherapy drugs with variable success rate that has virtually not changed over decades. Although new classes of chemotherapy-free epigenetic and metabolic drugs have emerged, durable responses to these conventional and new therapies are achieved in a fraction of cancer patients, with many individuals experiencing resistance to the drugs. The paucity in our understanding of what regulates the drug resistance phenotype and establishing a predictive indicator is, in great part, due to the lack of adequate ex vivo lymphoma models to accurately study the effect of microenvironmental cues in which malignant B and T cell lymphoma cells arise and reside. Unlike many other tumors, lymphomas have been neglected from biomaterials-based microenvironment engineering standpoint. In this study, we demonstrate that B and T cell lymphomas have different pro-survival integrin signaling requirements (αvβ3 and α4β1) and the presence of supporting follicular dendritic cells are critical for enhanced proliferation in three-dimensional (3D) microenvironments. We engineered adaptable 3D tumor organoids presenting adhesive peptides with distinct integrin specificities to B and T cell lymphoma cells that resulted in enhanced proliferation, clustering, and drug resistance to the chemotherapeutics and a new class of histone deacetylase inhibitor (HDACi), Panobinostat. In Diffuse Large B cell Lymphomas, the 3D microenvironment upregulated the expression level of B cell receptor (BCR), which supported the survival of B cell lymphomas through a tyrosine kinase Syk in the upstream BCR pathway. Our integrin specific ligand functionalized 3D organoids mimic a lymphoid neoplasm-like heterogeneous microenvironment that could, in the long term, change the understanding of the initiation and progression of hematological tumors, allow primary biospecimen analysis, provide prognostic values, and importantly, allow a faster and more rational screening and translation of therapeutic regimens.