A microenvironment-inspired synthetic three-dimensional model for pancreatic ductal adenocarcinoma organoids

A bioactive calcium silicate nanowire-containing hydrogel for organoid formation and functionalization

Organoids, which are 3D multicellular constructs, have garnered significant attention in recent years. Existing organoid culture methods predominantly utilize natural and synthetic polymeric hydrogels. This study explored the potential of a composite hydrogel mainly consisting of calcium silicate (CS) nanowires and methacrylated gelatin (GelMA) as a substrate for organoid formation and functionalization, specifically for intestinal and liver organoids. Furthermore, the research delved into the mechanisms by which CS nanowires promote the structure formation and development of organoids. It was discovered that CS nanowires can influence the stiffness of the hydrogel, thereby regulating the expression of the mechanosensory factor yes-associated protein (YAP). Additionally, the bioactive ions released by CS nanowires in the culture medium could accelerate Wnt/β-catenin signaling, further stimulating organoid development. Moreover, bioactive ions were found to enhance the nutrient absorption and ATP metabolic activity of intestinal organoids. Overall, the CS/GelMA composite hydrogel proves to be a promising substrate for organoid formation and development. This research suggested that inorganic biomaterials hold significant potential in organoid research, offering bioactivities, biosafety, and cost-effectiveness.

A Pump-Free Strategy for the Controllable Generation of Alginate Microgels as Cellular Microcarriers

Microgels are advanced scaffolds for tissue engineering due to their proper biodegradability, good biocompatibility, and high specific surface area for effective oxygen and nutrient transfer. However, most of the current monodispersed microgel fabrication systems rely heavily on various precision pumps, which highly increase the cost and complexity of their downstream application. In this work, we developed a simple and facile system for the controllable generation of uniform alginate microgels by integrating a gas-shearing strategy into a glass microfluidic device. Importantly, the cell-laden microgels can be rapidly prepared in a pump-free manner under an all-aqueous environment. The three-dimensional cultured green fluorescent protein-human A549 cells in alginate microgels exhibited enhanced stemness and drug resistance compared to those under two-dimensional conditions. The pancreatic cancer organoids in alginate microgels exhibited some of the key features of pancreatic cancer. The proposed microgels showed decent monodispersity, biocompatibility, and versatility, providing great opportunities in various biomedical applications such as microcarrier fabricating, organoid engineering, and high-throughput drug screening.

Dual-crosslinking gelatin-hyaluronic acid methacrylate based biomimetic PDAC desmoplastic niche enhances tumor-associated macrophages recruitment and M2-like polarization

The tumor microenvironment (TME) of pancreatic ductal adenocarcinoma (PDAC) is characterized by deposition of desmoplastic matrix (including collagen and hyaluronic acid). And the interactions between tumor-associated macrophages (TAMs) and tumor cells play a crucial role in progression of PDAC. Hence, the appropriate model of tumor cell-macrophage interaction within the unique PDAC TME is of significantly important. To this end, a 3D tumor niche based on dual-crosslinking gelatin methacrylate and hyaluronic acid methacrylate hydrogels was constructed to simulate the desmoplastic tumor matrix with matching compressive modulus and composition. The bionic 3D tumor niche creates an immunosuppressive microenvironment characterized by the downregulation of M1 markers and upregulation of M2 markers in TAMs. Mechanistically, RNA-seq analysis revealed that the PI3K-AKT signaling pathway might modulate the phenotypic balance and recruitment of macrophages through regulating SELE and VCAM-1. Furthermore, GO and GSEA revealed the biological process of leukocyte migration and the activation of cytokine-associated signaling were involved. Finally, the 3D tumor-macrophage niches with three different ratios were fabricated which displayed increased M2-like polarization and stemness. The utilization of the 3D tumor niche has the potential to provide a more accurate investigation of the interplay between PDAC tumor cells and macrophages within an in vivo setting.

Optimising a self-assembling peptide hydrogel as a Matrigel alternative for 3-dimensional mammary epithelial cell culture

Three-dimensional (3D) organoid models have been instrumental in understanding molecular mechanisms responsible for many cellular processes and diseases. However, established organic biomaterial scaffolds used for 3D hydrogel cultures, such as Matrigel, are biochemically complex and display significant batch variability, limiting reproducibility in experiments. Recently, there has been significant progress in the development of synthetic hydrogels for in vitro cell culture that are reproducible, mechanically tuneable, and biocompatible. Self-assembling peptide hydrogels (SAPHs) are synthetic biomaterials that can be engineered to be compatible with 3D cell culture. Here we investigate the ability of PeptiGel® SAPHs to model the mammary epithelial cell (MEC) microenvironment in vitro. The positively charged PeptiGel®Alpha4 supported MEC viability, but did not promote formation of polarised acini. Modifying the stiffness of PeptiGel® Alpha4 stimulated changes in MEC viability and changes in protein expression associated with altered MEC function, but did not fully recapitulate the morphologies of MECs grown in Matrigel. To supply the appropriate biochemical signals for MEC organoids, we supplemented PeptiGels® with laminin. Laminin was found to require negatively charged PeptiGel® Alpha7 for functionality, but was then able to provide appropriate signals for correct MEC polarisation and expression of characteristic proteins. Thus, optimisation of SAPH composition and mechanics allows tuning to support tissue-specific organoids.

Hydrogel/microcarrier cell scaffolds for rapid expansion of satellite cells from large yellow croakers: Differential analysis between 2D and 3D cell culture

Cell culture meat is based on the scaled-up expansion of seed cells. The biological differences between seed cells from large yellow croakers in the two-dimensional (2D) and three-dimensional (3D) culture systems have not been explored. Here, satellite cells (SCs) from large yellow croakers (Larimichthys crocea) were grown on cell climbing slices, hydrogels, and microcarriers for five days to analyze the biological differences of SCs on different cell scaffolds. The results exhibited that SCs had different cell morphologies in 2D and 3D cultures. Cell adhesion receptors (Itgb1andsdc4) and adhesion spot markervclof the 3D cultures were markedly expressed. Furthermore, myogenic decision markers (Pax7andmyod) were significantly enhanced. However, the expression of myogenic differentiation marker (desmin) was significantly increased in the microcarrier group. Combined with the transcriptome data, this suggests that cell adhesion of SCs in 3D culture was related to the integrin signaling pathway. In contrast, the slight spontaneous differentiation of SCs on microcarriers was associated with rapid cell proliferation. This study is the first to report the biological differences between SCs in 2D and 3D cultures, providing new perspectives for the rapid expansion of cell culture meat-seeded cells and the development of customized scaffolds.

Synergistic Effects of Matrix Biophysical Properties on Gastric Cancer Cell Behavior via Integrin-Mediated Cell-ECM Interactions

The biophysical properties of the extracellular matrix (ECM) play a pivotal role in modulating cancer progression via cell-ECM interactions. However, the biophysical properties specific to gastric cancer (GC) remain largely unexplored. Pertinently, GC ECM shows significantly heterogeneous metamorphoses, such as matrix stiffening and intricate restructuring. By combining collagen I and alginate, this study designs an in vitro biomimetic hydrogel platform to independently modulate matrix stiffness and structure across a physiological stiffness spectrum while preserving consistent collagen concentration and fiber topography. With this platform, this study assesses the impacts of matrix biophysical properties on cell proliferation, migration, invasion, and other pivotal dynamics of AGS. The findings spotlight a compelling interplay between matrix stiffness and structure, influencing both cellular responses and ECM remodeling. Furthermore, this investigation into the integrin/actin-collagen interplay reinforces the central role of integrins in mediating cell-ECM interactions, reciprocally sculpting cell conduct, and ECM adaptation. Collectively, this study reveals a previously unidentified role of ECM biophysical properties in GC malignant potential and provides insight into the bidirectional mechanical cell-ECM interactions, which may facilitate the development of novel therapeutic horizons.

Converging bioprinting and organoids to better recapitulate the tumor microenvironment

Bioprinting shows excellent potential for preclinical tumor modeling, with significant advantages over 2D cell cultures in replicating the tumor microenvironment (TME). Recently, the use of tumor organoids in bioprinting models has emerged as a groundbreaking approach to simulate volumetric tumor tissues. This synergetic fabrication method leverages the advantages of the spatial and geometric control of bioprinting to assemble heterogeneous TME components, while tumor organoids maintain collective cell behaviors. In this review, we provide a landscape of the latest progress on the convergence of 3D bioprinting and tumor organoids. Furthermore, we discuss the potential to incorporate organ-on-a-chip with bioprinting tumor organoids to improve the biomimicry and predictability of therapeutic performance. Lastly, we address the challenges to personalized medicine and predictive clinical integration.

Bioengineering toolkits for potentiating organoid therapeutics

Organoids are three-dimensional, multicellular constructs that recapitulate the structural and functional features of specific organs. Because of these characteristics, organoids have been widely applied in biomedical research in recent decades. Remarkable advancements in organoid technology have positioned them as promising candidates for regenerative medicine. However, current organoids still have limitations, such as the absence of internal vasculature, limited functionality, and a small size that is not commensurate with that of actual organs. These limitations hinder their survival and regenerative effects after transplantation. Another significant concern is the reliance on mouse tumor-derived matrix in organoid culture, which is unsuitable for clinical translation due to its tumor origin and safety issues. Therefore, our aim is to describe engineering strategies and alternative biocompatible materials that can facilitate the practical applications of organoids in regenerative medicine. Furthermore, we highlight meaningful progress in organoid transplantation, with a particular emphasis on the functional restoration of various organs.

Microphysiological systems as models for immunologically 'cold' tumors

The tumor microenvironment (TME) is a diverse milieu of cells including cancerous and non-cancerous cells such as fibroblasts, pericytes, endothelial cells and immune cells. The intricate cellular interactions within the TME hold a central role in shaping the dynamics of cancer progression, influencing pivotal aspects such as tumor initiation, growth, invasion, response to therapeutic interventions, and the emergence of drug resistance. In immunologically 'cold' tumors, the TME is marked by a scarcity of infiltrating immune cells, limited antigen presentation in the absence of potent immune-stimulating signals, and an abundance of immunosuppressive factors. While strategies targeting the TME as a therapeutic avenue in 'cold' tumors have emerged, there is a pressing need for novel approaches that faithfully replicate the complex cellular and non-cellular interactions in order to develop targeted therapies that can effectively stimulate immune responses and improve therapeutic outcomes in patients. Microfluidic devices offer distinct advantages over traditional in vitro 3D co-culture models and in vivo animal models, as they better recapitulate key characteristics of the TME and allow for precise, controlled insights into the dynamic interplay between various immune, stromal and cancerous cell types at any timepoint. This review aims to underscore the pivotal role of microfluidic systems in advancing our understanding of the TME and presents current microfluidic model systems that aim to dissect tumor-stromal, tumor-immune and immune-stromal cellular interactions in various 'cold' tumors. Understanding the intricacies of the TME in 'cold' tumors is crucial for devising effective targeted therapies to reinvigorate immune responses and overcome the challenges of current immunotherapy approaches.

Stepwise Stiffening/Softening of and Cell Recovery from Reversibly Formulated Hydrogel Double Networks

Biomechanical contributions of the ECM underpin cell growth and proliferation, differentiation, signal transduction, and other fate decisions. As such, biomaterials whose mechanics can be spatiotemporally altered - particularly in a reversible manner - are extremely valuable for studying these mechanobiological phenomena. Herein, we introduce a poly(ethylene glycol) (PEG)-based hydrogel model consisting of two interpenetrating step-growth networks that are independently formed via largely orthogonal bioorthogonal chemistries and sequentially degraded with distinct bacterial transpeptidases, affording reversibly tunable stiffness ranges that span healthy and diseased soft tissues (e.g., 500 Pa - 6 kPa) alongside terminal cell recovery for pooled and/or single-cell analysis in a near "biologically invisible" manner. Spatiotemporal control of gelation within the primary supporting network was achieved via mask-based and two-photon lithography; these stiffened patterned regions could be subsequently returned to the original soft state following sortase-based secondary network degradation. Using this approach, we investigated the effects of 4D-triggered network mechanical changes on human mesenchymal stem cell (hMSC) morphology and Hippo signaling, as well as Caco-2 colorectal cancer cell mechanomemory at the global transcriptome level via RNAseq. We expect this platform to be of broad utility for studying and directing mechanobiological phenomena, patterned cell fate, as well as disease resolution in softer matrices.

Nascent matrix deposition supports alveolar organoid formation from aggregates in synthetic hydrogels

Human induced pluripotent stem cell (iPSC) derived alveolar organoids have emerged as a system to model the alveolar epithelium in homeostasis and disease. However, alveolar organoids are typically grown in Matrigel, a mouse-sarcoma derived basement membrane matrix that offers poor control over matrix properties, prompting the development of synthetic hydrogels as a Matrigel alternative. Here, we develop a two-step culture method that involves pre-aggregation of organoids in hydrogel-based microwells followed by embedding in a synthetic hydrogel that supports alveolar organoid growth, while also offering considerable control over organoid and hydrogel properties. We find that the aggregated organoids secrete their own nascent extracellular matrix (ECM) both in the microwells and upon embedding in the synthetic hydrogels. Thus, the synthetic gels described here allow us to de-couple exogenous and nascent ECM in order to interrogate the role of ECM in organoid formation.

Patient-Derived Organoids as Therapy Screening Platforms in Cancer Patients

Patient-derived organoids (PDOs) developed ex vivo and in vitro are increasingly used for therapeutic screening. They provide a more physiologically relevant model for drug discovery and development compared to traditional cell lines. However, several challenges remain to be addressed to fully realize the potential of PDOs in therapeutic screening. This paper summarizes recent advancements in PDO development and the enhancement of PDO culture models. This is achieved by leveraging materials engineering and microfabrication technologies, including organs-on-a-chip and droplet microfluidics. Additionally, this work discusses the application of PDOs in therapy screening to meet diverse requirements and overcome bottlenecks in cancer treatment. Furthermore, this work introduces tools for data processing and analysis of organoids, along with their microenvironment. These tools aim to achieve enhanced readouts. Finally, this work explores the challenges and future perspectives of using PDOs in drug development and personalized screening for cancer patients.

Chemotherapy Assessment in Advanced Multicellular 3D Models of Pancreatic Cancer: Unravelling the Importance of Spatiotemporal Mimicry of the Tumor Microenvironment

Pancreatic ductal adenocarcinoma (PDAC) is a challenge for global health with very low survival rate and high therapeutic resistance. Hence, advanced preclinical models for treatment screening are of paramount importance. Herein, chemotherapeutic (gemcitabine) assessment on novel (polyurethane) scaffold-based spatially advanced 3D multicellular PDAC models is carried out. Through comprehensive image-based analysis at the protein level, and expression analysis at the mRNA level, the importance of stromal cells is confirmed, primarily activated stellate cells in the chemoresistance of PDAC cells within the models. Furthermore, it is demonstrated that, in addition to the presence of activated stellate cells, the spatial architecture of the scaffolds, i.e., segregation/compartmentalization of the cancer and stromal zones, affect the cellular evolution and is necessary for the development of chemoresistance. These results highlight that, further to multicellularity, mapping the tumor structure/architecture and zonal complexity in 3D cancer models is important for better mimicry of the in vivo therapeutic response.

Rethinking the Roles of Cancer-Associated Fibroblasts in Pancreatic Cancer

Bearing a dismal 5-year survival rate, pancreatic ductal adenocarcinoma (PDAC) is a challenging disease that features a unique fibroinflammatory tumor microenvironment. As major components of the PDAC tumor microenvironment, cancer-associated fibroblasts are still poorly understood and their contribution to the several hallmarks of PDAC, such as resistance to therapies, immunosuppression, and high incidence of metastasis, is likely underestimated. There have been encouraging advances in the understanding of these fascinating cells, but many controversies remain, leaving the field still actively exploring the full scope of their contributions in PDAC progression. Here we pose several important considerations regarding PDAC cancer-associated fibroblast functions. We posit that transcriptomic analyses be interpreted with caution, when aiming to uncover the functional contributions of these cells. Moreover, we propose that normalizing these functions, rather than eliminating them, will provide the opportunity to enhance therapeutic response. Finally, we propose that cancer-associated fibroblasts should not be studied in isolation, but in conjunction with its extracellular matrix, because their respective functions are coordinated and concordant.

Graphene Oxide Nanoparticles and Organoids: A Prospective Advanced Model for Pancreatic Cancer Research

Pancreatic cancer, notorious for its grim 10% five-year survival rate, poses significant clinical challenges, largely due to late-stage diagnosis and limited therapeutic options. This review delves into the generation of organoids, including those derived from resected tissues, biopsies, pluripotent stem cells, and adult stem cells, as well as the advancements in 3D printing. It explores the complexities of the tumor microenvironment, emphasizing culture media, the integration of non-neoplastic cells, and angiogenesis. Additionally, the review examines the multifaceted properties of graphene oxide (GO), such as its mechanical, thermal, electrical, chemical, and optical attributes, and their implications in cancer diagnostics and therapeutics. GO's unique properties facilitate its interaction with tumors, allowing targeted drug delivery and enhanced imaging for early detection and treatment. The integration of GO with 3D cultured organoid systems, particularly in pancreatic cancer research, is critically analyzed, highlighting current limitations and future potential. This innovative approach has the promise to transform personalized medicine, improve drug screening efficiency, and aid biomarker discovery in this aggressive disease. Through this review, we offer a balanced perspective on the advancements and future prospects in pancreatic cancer research, harnessing the potential of organoids and GO.

Nano- and Microstructures of Collagen-Nanocellulose Hydrogels as Engineered Extracellular Matrices

The extracellular matrix (ECM) is the fundamental acellular element of human tissues, providing their mechanical structure while delivering biomechanical and biochemical signals to cells. Three-dimensional (3D) tissue models commonly use hydrogels to recreate the ECM in vitro and support the growth of cells as organoids and spheroids. Collagen-nanocellulose (COL-NC) hydrogels rely on the blending of both polymers to design matrices with tailorable physical properties. Despite the promising application of these biomaterials in 3D tissue models, the architecture and network organization of COL-NC remain unclear. Here, we investigate the structural effects of incorporating NC fibers into COL hydrogels by small-angle neutron scattering (SANS) and ultra-SANS (USANS). The critical hierarchical structure parameters of fiber dimensions, interfiber distance, and coassembled open structures of NC and COL in the absence and presence of cells were determined. We found that NC expanded and increased the homogeneity in the COL network without affecting the inherent fiber properties of both polymers. Cells cultured as spheroids in COL-NC remodeled the hydrogel network without a significant impact on its architecture. Our study reveals the polymer organization of COL-NC hydrogels and demonstrates SANS and USANS as exceptional techniques to reveal nano- and micron-scale details on polymer organization, which leads to a better understanding of the structural properties of hydrogels to engineer novel ECMs.

Harnessing 3D in vitro systems to model immune responses to solid tumours: a step towards improving and creating personalized immunotherapies

In vitro 3D models are advanced biological tools that have been established to overcome the shortcomings of oversimplified 2D cultures and mouse models. Various in vitro 3D immuno-oncology models have been developed to mimic and recapitulate the cancer-immunity cycle, evaluate immunotherapy regimens, and explore options for optimizing current immunotherapies, including for individual patient tumours. Here, we review recent developments in this field. We focus, first, on the limitations of existing immunotherapies for solid tumours, secondly, on how in vitro 3D immuno-oncology models are established using various technologies - including scaffolds, organoids, microfluidics and 3D bioprinting - and thirdly, on the applications of these 3D models for comprehending the cancer-immunity cycle as well as for assessing and improving immunotherapies for solid tumours.

Engineering Heterogeneous Tumor Models for Biomedical Applications

Tumor tissue engineering holds great promise for replicating the physiological and behavioral characteristics of tumors in vitro. Advances in this field have led to new opportunities for studying the tumor microenvironment and exploring potential anti-cancer therapeutics. However, the main obstacle to the widespread adoption of tumor models is the poor understanding and insufficient reconstruction of tumor heterogeneity. In this review, the current progress of engineering heterogeneous tumor models is discussed. First, the major components of tumor heterogeneity are summarized, which encompasses various signaling pathways, cell proliferations, and spatial configurations. Then, contemporary approaches are elucidated in tumor engineering that are guided by fundamental principles of tumor biology, and the potential of a bottom-up approach in tumor engineering is highlighted. Additionally, the characterization approaches and biomedical applications of tumor models are discussed, emphasizing the significant role of engineered tumor models in scientific research and clinical trials. Lastly, the challenges of heterogeneous tumor models in promoting oncology research and tumor therapy are described and key directions for future research are provided.

Revolutionizing digestive system tumor organoids research: Exploring the potential of tumor organoids

Digestive system tumors are the leading cause of cancer-related deaths worldwide. Despite ongoing research, our understanding of their mechanisms and treatment remain inadequate. One promising tool for clinical applications is the use of gastrointestinal tract tumor organoids, which serve as an important in vitro model. Tumor organoids exhibit a genotype similar to the patient's tumor and effectively mimic various biological processes, including tissue renewal, stem cell, and ecological niche functions, and tissue response to drugs, mutations, or injury. As such, they are valuable for drug screening, developing novel drugs, assessing patient outcomes, and supporting immunotherapy. In addition, innovative materials and techniques can be used to optimize tumor organoid culture systems. Several applications of digestive system tumor organoids have been described and have shown promising results in related aspects. In this review, we discuss the current progress, limitations, and prospects of this model for digestive system tumors.

Bioengineering Approaches for the Pancreatic Tumor Organoids Research and Application

Pancreatic cancer is a highly lethal form of digestive malignancy that poses significant health risks to individuals worldwide. Chemotherapy-based comprehensive treatment is the primary therapeutic approach for midlife and late-life patients. Nevertheless, the heterogeneity of the tumor and individual genetic backgrounds result in substantial variations in drug sensitivity among patients, rendering a single treatment regimen unsuitable for all patients. Conventional pancreatic cancer tumor organoid models are capable of emulating the biological traits of pancreatic cancer and are utilized in drug development and screening. However, these tumor organoids can still not mimic the tumor microenvironment (TME) in vivo, and the poor controllability in the preparation process hinders translation from essential drug screening to clinical pharmacological therapy. In recent years, many engineering methods with remarkable results have been used to develop pancreatic cancer organoid models, including bio-hydrogel, co-culture, microfluidic, and gene editing. Here, this work summarizes and analyzes the recent developments in engineering pancreatic tumor organoid models. In addition, the future direction of improving engineered pancreatic cancer organoids is discussed for their application prospects in clinical treatment.

Addressing Key Questions in Organoid Models: Who, Where, How, and Why?

Organoids are three-dimensional cellular structures designed to recreate the biological characteristics of the body's native tissues and organs in vitro. There has been a recent surge in studies utilizing organoids due to their distinct advantages over traditional two-dimensional in vitro approaches. However, there is no consensus on how to define organoids. This literature review aims to clarify the concept of organoids and address the four fundamental questions pertaining to organoid models: (i) What constitutes organoids?-The cellular material. (ii) Where do organoids grow?-The extracellular scaffold. (iii) How are organoids maintained in vitro?-Via the culture media. (iv) Why are organoids suitable in vitro models?-They represent reproducible, stable, and scalable models for biological applications. Finally, this review provides an update on the organoid models employed within the female reproductive tract, underscoring their relevance in both basic biology and clinical applications.

Biophysics in tumor growth and progression: from single mechano-sensitive molecules to mechanomedicine

Evidence from physical sciences in oncology increasingly suggests that the interplay between the biophysical tumor microenvironment and genetic regulation has significant impact on tumor progression. Especially, tumor cells and the associated stromal cells not only alter their own cytoskeleton and physical properties but also remodel the microenvironment with anomalous physical properties. Together, these altered mechano-omics of tumor tissues and their constituents fundamentally shift the mechanotransduction paradigms in tumorous and stromal cells and activate oncogenic signaling within the neoplastic niche to facilitate tumor progression. However, current findings on tumor biophysics are limited, scattered, and often contradictory in multiple contexts. Systematic understanding of how biophysical cues influence tumor pathophysiology is still lacking. This review discusses recent different schools of findings in tumor biophysics that have arisen from multi-scale mechanobiology and the cutting-edge technologies. These findings range from the molecular and cellular to the whole tissue level and feature functional crosstalk between mechanotransduction and oncogenic signaling. We highlight the potential of these anomalous physical alterations as new therapeutic targets for cancer mechanomedicine. This framework reconciles opposing opinions in the field, proposes new directions for future cancer research, and conceptualizes novel mechanomedicine landscape to overcome the inherent shortcomings of conventional cancer diagnosis and therapies.

Recent advances in defined hydrogels in organoid research

Organoids are in vitro model systems that mimic the complexity of organs with multicellular structures and functions, which provide great potential for biomedical and tissue engineering. However, their current formation heavily relies on using complex animal-derived extracellular matrices (ECM), such as Matrigel. These matrices are often poorly defined in chemical components and exhibit limited tunability and reproducibility. Recently, the biochemical and biophysical properties of defined hydrogels can be precisely tuned, offering broader opportunities to support the development and maturation of organoids. In this review, the fundamental properties of ECM in vivo and critical strategies to design matrices for organoid culture are summarized. Two typically defined hydrogels derived from natural and synthetic polymers for their applicability to improve organoids formation are presented. The representative applications of incorporating organoids into defined hydrogels are highlighted. Finally, some challenges and future perspectives are also discussed in developing defined hydrogels and advanced technologies toward supporting organoid research.

Embedded Bioprinting of Breast Tumor Cells and Organoids Using Low-Concentration Collagen-Based Bioinks

Bioinks for 3D bioprinting of tumor models should not only meet printability requirements but also accurately maintain and support phenotypes of tumor surrounding cells to recapitulate key tumor hallmarks. Collagen is a major extracellular matrix protein for solid tumors, but low viscosity of collagen solution has made 3D bioprinted cancer models challenging. This work produces embedded, bioprinted breast cancer cells and tumor organoid models using low-concentration collagen I based bioinks. The biocompatible and physically crosslinked silk fibroin hydrogel is used to generate the support bath for the embedded 3D printing. The composition of the collagen I based bioink is optimized with a thermoresponsive hyaluronic acid-based polymer to maintain the phenotypes of both the noninvasive epithelial and invasive breast cancer cells, as well as cancer-associated fibroblasts. Mouse breast tumor organoids are bioprinted using optimized collagen bioink to mimic in vivo tumor morphology. A vascularized tumor model is also created using a similar strategy, with significantly enhanced vasculature formation under hypoxia. This study shows the great potential of embedded bioprinted breast tumor models utilizing a low-concentration collagen-based bioink for advancing the understanding of tumor cell biology and facilitating drug discovery research.

Establishment of organoid models for pancreatic ductal adenocarcinoma and screening of individualized therapy strategy

BACKGROUND

Patients with pancreatic ductal adenocarcinoma (PDAC) who undergo surgical resection and receive effective chemotherapy have the best chance for long-term survival. Unfortunately, because of the heterogeneity of pancreatic cancer, it is difficult to find a personalized treatment strategy for patients. Organoids are ideal preclinical models for personalized medicine. Therefore, we explore the cultivation conditions and construction methods of PDAC organoid models to screen the individualized therapy strategy.

METHODS

Fresh PDAC tissues from surgical resection were collected and digested with digestive enzymes; then the tumor cells were embedded in Matrigel with a suitable medium to establish the PDAC organoid models. The genetic stability of the organoids was analyzed using whole exon sequencing; hematoxylin and eosin staining and immunohistochemistry of organoids were performed to analyze their consistency with the pathological morphology of the patient's tumor tissue; After 2 days of organoid culture, we selected four commonly used clinical chemotherapy drugs for single or combined treatment to analyze drug sensitivity.

RESULTS

Two cases of PDAC organoid models were successfully established, and the results of their pathological characteristics and exome sequencing were consistent with those of the patient's tumor tissue. Both PDAC organoids showed more sensitivity to gemcitabine and cisplatin, and the combined treatment was more effective than monotherapy.

CONCLUSION

Both organoids better retained the pathological characteristics, genomic stability, and heterogeneity with the original tumor. Individual PDAC organoids exhibited different sensitivities to the same drugs. Thus, this study provided ideal experimental models for screening individualized therapy strategy for patients with PDAC.

Exploring New Dimensions of Tumor Heterogeneity: The Application of Single Cell Analysis to Organoid-Based 3D In Vitro Models

Modeling the heterogeneity of the tumor microenvironment (TME) in vitro is essential to investigating fundamental cancer biology and developing novel treatment strategies that holistically address the factors affecting tumor progression and therapeutic response. Thus, the development of new tools for both in vitro modeling, such as patient-derived organoids (PDOs) and complex 3D in vitro models, and single cell omics analysis, such as single-cell RNA-sequencing, represents a new frontier for investigating tumor heterogeneity. Specifically, the integration of PDO-based 3D in vitro models and single cell analysis offers a unique opportunity to explore the intersecting effects of interpatient, microenvironmental, and tumor cell heterogeneity on cell phenotypes in the TME. In this review, the current use of PDOs in complex 3D in vitro models of the TME is discussed and the emerging directions in the development of these models are highlighted. Next, work that has successfully applied single cell analysis to PDO-based models is examined and important experimental considerations are identified for this approach. Finally, open questions are highlighted that may be amenable to exploration using the integration of PDO-based models and single cell analysis. Ultimately, such investigations may facilitate the identification of novel therapeutic targets for cancer that address the significant influence of tumor-TME interactions.

Can Organoid Model Reveal a Key Role of Extracellular Vesicles in Tumors? A Comprehensive Review of the Literature

Extracellular vesicles (EVs) are small membrane-bound vesicles that are released by cells into the extracellular environment. The role of EVs in tumors has been extensively studied, and they have been shown to play a crucial role in tumor growth, progression, and metastasis. Past research has mainly used 2D-cultured cell line models to investigate the role of EVs in tumors, which poorly simulate the tumor microenvironment. Organoid technology has gradually matured in recent years. Organoids are similar in composition and behavior to physiological cells and have the potential to recapitulate the architecture and function of the original tissue. It has been widely used in organogenesis, drug screening, gene editing, precision medicine and other fields. The integration of EVs and organoids has the potential to revolutionize the field of cancer research and represents a promising avenue for advancing our understanding of cancer biology and the development of novel therapeutic strategies. Here, we aimed to present a comprehensive overview of studies using organoids to study EVs in tumors.

Flourishing tumor organoids: History, emerging technology, and application

Malignant tumors are one of the leading causes of death which impose an increasingly heavy burden on all countries. Therefore, the establishment of research models that closely resemble original tumor characteristics is crucial to further understanding the mechanisms of malignant tumor development, developing safer and more effective drugs, and formulating personalized treatment plans. Recently, organoids have been widely used in tumor research owing to their advantages including preserving the structure, heterogeneity, and cellular functions of the original tumor, together with the ease of manipulation. This review describes the history and characteristics of tumor organoids and the synergistic combination of three-dimensional (3D) culture approaches for tumor organoids with emerging technologies, including tissue-engineered cell scaffolds, microfluidic devices, 3D bioprinting, rotating wall vessels, and clustered regularly interspaced short palindromic repeats-CRISPR-associated protein 9 (CRISPR-Cas9). Additionally, the progress in research and the applications in basic and clinical research of tumor organoid models are summarized. This includes studies of the mechanism of tumor development, drug development and screening, precision medicine, immunotherapy, and simulation of the tumor microenvironment. Finally, the existing shortcomings of tumor organoids and possible future directions are discussed.

Tricolor visible wavelength-selective photodegradable hydrogel biomaterials

Photodynamic hydrogel biomaterials have demonstrated great potential for user-triggered therapeutic release, patterned organoid development, and four-dimensional control over advanced cell fates in vitro. Current photosensitive materials are constrained by their reliance on high-energy ultraviolet light (<400 nm) that offers poor tissue penetrance and limits access to the broader visible spectrum. Here, we report a family of three photolabile material crosslinkers that respond rapidly and with unique tricolor wavelength-selectivity to low-energy visible light (400-617 nm). We show that when mixed with multifunctional poly(ethylene glycol) macromolecular precursors, ruthenium polypyridyl- and ortho-nitrobenzyl (oNB)-based crosslinkers yield cytocompatible biomaterials that can undergo spatiotemporally patterned, uniform bulk softening, and multiplexed degradation several centimeters deep through complex tissue. We demonstrate that encapsulated living cells within these photoresponsive gels show high viability and can be successfully recovered from the hydrogels following photodegradation. Moving forward, we anticipate that these advanced material platforms will enable new studies in 3D mechanobiology, controlled drug delivery, and next-generation tissue engineering applications.

Organoid co-culture model of the human endometrium in a fully synthetic extracellular matrix enables the study of epithelial-stromal crosstalk

BACKGROUND

The human endometrium undergoes recurring cycles of growth, differentiation, and breakdown in response to sex hormones. Dysregulation of epithelial-stromal communication during hormone-mediated signaling may be linked to myriad gynecological disorders for which treatments remain inadequate. Here, we describe a completely defined, synthetic extracellular matrix that enables co-culture of human endometrial epithelial and stromal cells in a manner that captures healthy and disease states across a simulated menstrual cycle.

METHODS

We parsed cycle-dependent endometrial integrin expression and matrix composition to define candidate cell-matrix interaction cues for inclusion in a polyethylene glycol (PEG)-based hydrogel crosslinked with matrix metalloproteinase-labile peptides. We semi-empirically screened a parameter space of biophysical and molecular features representative of the endometrium to define compositions suitable for hormone-driven expansion and differentiation of epithelial organoids, stromal cells, and co-cultures of the two cell types.

FINDINGS

Each cell type exhibited characteristic morphological and molecular responses to hormone changes when co-encapsulated in hydrogels tuned to a stiffness regime similar to the native tissue and functionalized with a collagen-derived adhesion peptide (GFOGER) and a fibronectin-derived peptide (PHSRN-K-RGD). Analysis of cell-cell crosstalk during interleukin 1B (IL1B)-induced inflammation revealed dysregulation of epithelial proliferation mediated by stromal cells.

CONCLUSIONS

Altogether, we demonstrate the development of a fully synthetic matrix to sustain the dynamic changes of the endometrial microenvironment and support its applications to understand menstrual health and endometriotic diseases.

FUNDING

This work was supported by The John and Karine Begg Foundation, the Manton Foundation, and NIH U01 (EB029132).

Matrix scaffolds for endometrium-derived organoid models

The uterus-lining endometrium is essential to mammalian reproduction, receiving and accommodating the embryo for proper development. Despite its key role, mechanisms underlying endometrial biology (menstrual cycling, embryo interaction) and disease are not well understood. Its hidden location in the womb, and thereby-associated lack of suitable research models, contribute to this knowledge gap. Recently, 3D organoid models have been developed from both healthy and diseased endometrium. These organoids closely recapitulate the tissue's epithelium phenotype and (patho)biology, including in vitro reproduction of the menstrual cycle. Typically, organoids are grown in a scaffold made of surrogate tissue extracellular matrix (ECM), with mouse tumor basement membrane extracts being the most commonly used. However, important limitations apply including their lack of standardization and xeno-derivation which strongly hinder clinical translation. Therefore, researchers are actively seeking better alternatives including fully defined matrices for faithful and efficient growth of organoids. Here, we summarize the state-of-the-art regarding matrix scaffolds to grow endometrium-derived organoids as well as more advanced organoid-based 3D models. We discuss remaining shortcomings and challenges to advance endometrial organoids toward defined and standardized tools for applications in basic research and translational/clinical fields.

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.

Advances in biomimetic hydrogels for organoid culture

An organoid is a 3-dimensional (3D) cell culture system that mimics the structural and functional characteristics of organs, and it has promising applications in regenerative medicine, precision drug screening and personalised therapy. However, current culture techniques of organoids usually use mouse tumour-derived scaffolds (Matrigel) or other animal-derived decellularised extracellular matrices as culture systems with poorly defined components and undefined chemical and physical properties, which limit the growth of organoids and the reproducibility of culture conditions. In contrast, some synthetic culture materials have emerged in recent years with well-defined compositions, and flexible adjustment and optimisation of physical and chemical properties, which can effectively support organoid growth and development and prolong survival time of organoid in vitro. In this review, we will introduce the challenge of animal-derived decellularised extracellular matrices in organoid culture, and summarise the categories of biomimetic hydrogels currently used for organoid culture, and then discuss the future opportunities and perspectives in the development of advanced hydrogels in organoids. We hope that this review can promote academic communication in the field of organoid research and provide some assistance in advancing the development of organoid cultivation technology.

The role of organoids in cancer research

Organoids are established through in vitro 3D culture, and they can mimic the structure and physiological functions of organs or tissues in vivo. Organoids have attracted much attention in recent years. They can provide a reliable technology platform for cancer research and treatment and are a valuable preclinical model for academic research and personalized medicine. A number of studies have confirmed that organoids have great application prospects in new drug development, drug screening, tumour mechanism research, and precision medicine. In this review, we mainly focus on recent advances in the application of organoids in cancer research. We also discussed the opportunities and challenges facing organoids, hoping to indicate directions for the development of organoids in the future.

Dynamic modulation of matrix adhesiveness induces epithelial-to-mesenchymal transition in prostate cancer cells in 3D

Synthetic matrices with dynamic presentation of cell guidance cues are needed for the development of physiologically relevant in vitro tumor models. Towards the goal of mimicking prostate cancer progression and metastasis, we engineered a tunable hyaluronic acid-based hydrogel platform with protease degradable and cell adhesive properties employing bioorthogonal tetrazine ligation with strained alkenes. The synthetic matrix was first fabricated via a slow tetrazine-norbornene reaction, then temporally modified via a diffusion-controlled method using trans-cyclooctene, a fierce dienophile that reacts with tetrazine with an unusually fast rate. The encapsulated DU145 prostate cancer single cells spontaneously formed multicellular tumoroids after 7 days of culture. In situ modification of the synthetic matrix via covalent tagging of cell adhesive RGD peptide induced tumoroid decompaction and the development of cellular protrusions. RGD tagging did not compromise the overall cell viability, nor did it induce cell apoptosis. In response to increased matrix adhesiveness, DU145 cells dynamically loosen cell-cell adhesion and strengthen cell-matrix interactions to promote an invasive phenotype. Characterization of the 3D cultures by immunocytochemistry and gene expression analyses demonstrated that cells invaded into the matrix via a mesenchymal like migration, with upregulation of major mesenchymal markers, and down regulation of epithelial markers. The tumoroids formed cortactin positive invadopodia like structures, indicating active matrix remodeling. Overall, the engineered tumor model can be utilized to identify potential molecular targets and test pharmacological inhibitors, thereby accelerating the design of innovative strategies for cancer therapeutics.

Biomechanical and Biological Characterization of XGel, a Human-Derived Hydrogel for Stem Cell Expansion and Tissue Engineering

Hydrogels are 3D scaffolds used as alternatives to in vivo models for disease modeling and delivery of cells and drugs. Existing hydrogel classifications include synthetic, recombinant, chemically defined, plant- or animal-based, and tissue-derived matrices. There is a need for materials that can support both human tissue modeling and clinically relevant applications requiring stiffness tunability. Human-derived hydrogels are not only clinically relevant, but they also minimize the use of animal models for pre-clinical studies. This study aims to characterize XGel, a new human-derived hydrogel as an alternative to current murine-derived and synthetic recombinant hydrogels that features unique physiochemical, biochemical, and biological properties that support adipocyte and bone differentiation. Rheology studies determine the viscosity, stiffness, and gelation features of XGel. Quantitative studies for quality control support consistency in the protein content between lots. Proteomics studies reveal that XGel is predominantly composed of extracellular matrix proteins, including fibrillin, collagens I-VI, and fibronectin. Electron microscopy of the hydrogel provides phenotypic characteristics in terms of porosity and fiber size. The hydrogel demonstrates biocompatibility as a coating material and as a 3D scaffold for the growth of multiple cell types. The results provide insight into the biological compatibility of this human-derived hydrogel for tissue engineering.

3D Biomimetic Models to Reconstitute Tumor Microenvironment In Vitro: Spheroids, Organoids, and Tumor-on-a-Chip

Decades of efforts in engineering in vitro cancer models have advanced drug discovery and the insight into cancer biology. However, the establishment of preclinical models that enable fully recapitulating the tumor microenvironment remains challenging owing to its intrinsic complexity. Recent progress in engineering techniques has allowed the development of a new generation of in vitro preclinical models that can recreate complex in vivo tumor microenvironments and accurately predict drug responses, including spheroids, organoids, and tumor-on-a-chip. These biomimetic 3D tumor models are of particular interest as they pave the way for better understanding of cancer biology and accelerating the development of new anticancer therapeutics with reducing animal use. Here, the recent advances in developing these in vitro platforms for cancer modeling and preclinical drug screening, focusing on incorporating hydrogels are reviewed to reconstitute physiologically relevant microenvironments. The combination of spheroids/organoids with microfluidic technologies is also highlighted to better mimic in vivo tumors and discuss the challenges and future directions in the clinical translation of such models for drug screening and personalized medicine.

Chitin nanocrystal-assisted 3D bioprinting of gelatin methacrylate scaffolds

In recent years, there has been an increasing focus on the application of hydrogels in tissue engineering. The integration of 3D bioprinting technology has expanded the potential applications of hydrogels. However, few commercially available hydrogels used for 3D biological printing exhibit both excellent biocompatibility and mechanical properties. Gelatin methacrylate (GelMA) has good biocompatibility and is widely used in 3D bioprinting. However, its low mechanical properties limit its use as a standalone bioink for 3D bioprinting. In this work, we designed a biomaterial ink composed of GelMA and chitin nanocrystal (ChiNC). We explored fundamental printing properties of composite bioinks, including rheological properties, porosity, equilibrium swelling rate, mechanical properties, biocompatibility, effects on the secretion of angiogenic factors and fidelity of 3D bioprinting. The results showed that adding 1% (w/v) ChiNC to 10% (w/v) GelMA improved the mechanical properties and printability of the GelMA hydrogels, promoted cell adhesion, proliferation and vascularization and enabled the printing of complex 3D scaffolds. This strategy of incorporating ChiNC to enhance the performance of GelMA biomaterials could potentially be applied to other biomaterials, thereby expanding the range of materials available for use. Furthermore, in combination with 3D bioprinting technology, this approach could be leveraged to bioprint scaffolds with complex structures, further broadening the potential applications in tissue engineering.

Trends in mechanobiology guided tissue engineering and tools to study cell-substrate interactions: a brief review

Sensing the mechanical properties of the substrates or the matrix by the cells and the tissues, the subsequent downstream responses at the cellular, nuclear and epigenetic levels and the outcomes are beginning to get unraveled more recently. There have been various instances where researchers have established the underlying connection between the cellular mechanosignalling pathways and cellular physiology, cellular differentiation, and also tissue pathology. It has been now accepted that mechanosignalling, alone or in combination with classical pathways, could play a significant role in fate determination, development, and organization of cells and tissues. Furthermore, as mechanobiology is gaining traction, so do the various techniques to ponder and gain insights into the still unraveled pathways. This review would briefly discuss some of the interesting works wherein it has been shown that specific alteration of the mechanical properties of the substrates would lead to fate determination of stem cells into various differentiated cells such as osteoblasts, adipocytes, tenocytes, cardiomyocytes, and neurons, and how these properties are being utilized for the development of organoids. This review would also cover various techniques that have been developed and employed to explore the effects of mechanosignalling, including imaging of mechanosensing proteins, atomic force microscopy (AFM), quartz crystal microbalance with dissipation measurements (QCMD), traction force microscopy (TFM), microdevice arrays, Spatio-temporal image analysis, optical tweezer force measurements, mechanoscanning ion conductance microscopy (mSICM), acoustofluidic interferometric device (AID) and so forth. This review would provide insights to the researchers who work on exploiting various mechanical properties of substrates to control the cellular and tissue functions for tissue engineering and regenerative applications, and also will shed light on the advancements of various techniques that could be utilized to unravel the unknown in the field of cellular mechanobiology.

User-Controlled 4D Biomaterial Degradation with Substrate-Selective Sortase Transpeptidases for Single-Cell Biology

Stimuli-responsive biomaterials show great promise for modeling disease dynamics ex vivo with spatiotemporal control over the cellular microenvironment. However, harvesting cells from such materials for downstream analysis without perturbing their state remains an outstanding challenge in 3/4-dimensional (3D/4D) culture and tissue engineering. In this manuscript, a fully enzymatic strategy for hydrogel degradation that affords spatiotemporal control over cell release while maintaining cytocompatibility is introduced. Exploiting engineered variants of the sortase transpeptidase evolved to recognize and selectively cleave distinct peptide sequences largely absent from the mammalian proteome, many limitations implicit to state-of-the-art methods to liberate cells from gels are sidestepped. It is demonstrated that evolved sortase exposure has minimal impact on the global transcriptome of primary mammalian cells and that proteolytic cleavage proceeds with high specificity; incorporation of substrate sequences within hydrogel crosslinkers permits rapid and selective cell recovery with high viability. In composite multimaterial hydrogels, it is shown that sequential degradation of hydrogel layers enables highly specific retrieval of single-cell suspensions for phenotypic analysis. It is expected that the high bioorthogonality and substrate selectivity of the evolved sortases will lead to their broad adoption as an enzymatic material dissociation cue and that their multiplexed use will enable newfound studies in 4D cell culture.

Impact of hydrogel biophysical properties on tumor spheroid growth and drug response

The extracellular matrix (ECM) plays a critical role in regulating cell-matrix interactions during tumor progression. These interactions are due in large part to the biophysical properties responding to cancer cell interactions. Within in vitro models, the ECM is mimicked by hydrogels, which possess adjustable biophysical properties that are integral to tumor development. This work presents a systematic and comparative study on the impact of the biophysical properties of two widely used natural hydrogels, Matrigel and collagen gel, on tumor growth and drug response. The biophysical properties of Matrigel and collagen including complex modulus, loss tangent, diffusive permeability, and pore size, were characterised. Then the spheroid growth rates in these two hydrogels were monitored for spheroids with two different sizes (140 μm and 500 μm in diameters). An increased migratory growth was observed in the lower concentration of both the gels. The effect of spheroid incorporation within the hydrogel had a minimal impact on the hydrogel's complex modulus. Finally, 3D tumor models using different concentrations of hydrogels were applied for drug treatment using paclitaxel. Spheroids cultured in hydrogels with different concentrations showed different drug response, demonstrating the significant effect of the choice of hydrogels and their concentrations on the drug response results despite using the same spheroids. This study provides useful insights into the effect of hydrogel biophysical properties on spheroid growth and drug response and highlights the importance of hydrogel selection and in vitro model design.

The application of pancreatic cancer organoids for novel drug discovery

INTRODUCTION

Pancreatic ductal adenocarcinoma presents with a dismal prognosis. Personalized therapy is urgently warranted to overcome the treatment limitations of the "one-size-fits-all" scheme. Organoids have emerged as fundamental novel tools to study tumor biology and heterogeneity, hence overcoming limitations of other model systems by better-reflecting tissue heterogeneity and recapitulating in-vivo processes. Besides their crucial role in basic research, they have evolved as tools for translational drug discovery and patient stratification.

AREAS COVERED

This review highlights the achievements of an organoid-based drug investigation and discovery. The authors present an overview of studies using organoids for drug testing. Further, they pinpoint studies correlating the in vitro prediction of organoids to the actual patient`s response. Furthermore, the authors describe novel model systems and take a thorough overlook of microfluidic chips, synthetic matrices, multicellular systems, bioprinting, and stem cell-derived pancreatic organoid systems.

EXPERT OPINION

Organoid systems promise great potential for future clinical applications. Indeed, they may be implemented into informed decision-making for guiding therapies. However, validation by randomized trials is mandatory. Additionally, organoids in combination with other cellular compartments may be exploited for drug discovery by studying niche-tumor interaction. Yet, several precautions must be kept in mind, such as standardization and reproducibility.

Middle-out methods for spatiotemporal tissue engineering of organoids

Organoids recapitulate many aspects of the complex three-dimensional (3D) organization found within native tissues and even display tissue and organ-level functionality. Traditional approaches to organoid culture have largely employed a top-down tissue engineering strategy, whereby cells are encapsulated in a 3D matrix, such as Matrigel, alongside well-defined biochemical cues that direct morphogenesis. However, the lack of spatiotemporal control over niche properties renders cellular processes largely stochastic. Therefore, bottom-up tissue engineering approaches have evolved to address some of these limitations and focus on strategies to assemble tissue building blocks with defined multi-scale spatial organization. However, bottom-up design reduces the capacity for self-organization that underpins organoid morphogenesis. Here, we introduce an emerging framework, which we term middle-out strategies, that relies on existing design principles and combines top-down design of defined synthetic matrices that support proliferation and self-organization with bottom-up modular engineered intervention to limit the degrees of freedom in the dynamic process of organoid morphogenesis. We posit that this strategy will provide key advances to guide the growth of organoids with precise geometries, structures and function, thereby facilitating an unprecedented level of biomimicry to accelerate the utility of organoids to more translationally relevant applications.

A 3D Ex Vivo Tumor-Immune Coculture System Mimicking In Vivo Tumor Environmental Stress on CD8+ T Cells Exhaustion

Dissection of exhaustion trajectories of immune cells under tumor selection pressure in the tumor microenvironment (TME) elucidates the underlying machinery in anti-tumor immunity, which still lacks easy-to-use models to decipher. Herein, gelatin methacryloyl (GelMA)-poly (ethylene oxide) (PEO) based 3D hydrogel microspheroids are constructed with non-immunogenicity and controllable macroporous structure to establish a tumor-immune cell coculture (3D-HyGTIC) system. In 3D-HyGTIC system, when immune cells embarked, stepwise up-regulation of main immune checkpoints (ICs) molecules is observed with compromised cytokine production in CD8⁺ T cells, the trajectory of which is in lineage correlation with in vivo grafted tumors. Reinvigoration of CD8⁺ T cells is more obvious with the addition of an anti-PD-1 regimen at the early time point, which is recapitulated during the coculture of patient-derived tumor fragments (PDTF) and autologous T cells. Moreover, the upregulation of LAG-3 on CD8⁺ T cells after anti-PD-1 treatment is uncovered. Sequential addition of anti-LAG-3 successfully rescues the otherwise failed reactivation of CD8⁺ T cells. Therefore, the 3D-HyGTIC system is not only inclined to mimic the early differentiation trajectories of tumor-infiltrating CD8⁺ T cells but also may facilitate an evaluation of the efficacy of IC blockades and guide the designing of combination immunotherapy.

Combining preclinical tools and models to unravel tumor complexity: Jump into the next dimension

Tumors are complex and heterogeneous diseases characterized by an intricate milieu and dynamically in connection with surrounding and distant tissues. In the last decades, great efforts have been made to develop novel preclinical models able to recapitulate the original features of tumors. However, the development of an in vitro functional and realistic tumor organ is still utopic and represents one of the major challenges to reproduce the architecture of the tumor ecosystem. A strategy to decrypt the whole picture and predict its behavior could be started from the validation of simplified biomimetic systems and then proceed with their integration. Variables such as the cellular and acellular composition of tumor microenvironment (TME) and its spatio-temporal distribution have to be considered in order to respect the dynamic evolution of the oncologic disease. In this perspective, we aim to explore the currently available strategies to improve and integrate in vitro and in vivo models, such as three-dimensional (3D) cultures, organoids, and zebrafish, in order to better understand the disease biology and improve the therapeutic approaches.

Engineered hydrogels for mechanobiology

Cells' local mechanical environment can be as important in guiding cellular responses as many well-characterized biochemical cues. Hydrogels that mimic the native extracellular matrix can provide these mechanical cues to encapsulated cells, allowing for the study of their impact on cellular behaviours. Moreover, by harnessing cellular responses to mechanical cues, hydrogels can be used to create tissues in vitro for regenerative medicine applications and for disease modelling. This Primer outlines the importance and challenges of creating hydrogels that mimic the mechanical and biological properties of the native extracellular matrix. The design of hydrogels for mechanobiology studies is discussed, including appropriate choice of cross-linking chemistry and strategies to tailor hydrogel mechanical cues. Techniques for characterizing hydrogels are explained, highlighting methods used to analyze cell behaviour. Example applications for studying fundamental mechanobiological processes and regenerative therapies are provided, along with a discussion of the limitations of hydrogels as mimetics of the native extracellular matrix. The article ends with an outlook for the field, focusing on emerging technologies that will enable new insights into mechanobiology and its role in tissue homeostasis and disease.

Tunable PEG Hydrogels for Discerning Differential Tumor Cell Response to Biomechanical Cues

Increased extracellular matrix (ECM) density in the tumor microenvironment has been shown to influence aspects of tumor progression such as proliferation and invasion. Increased matrix density means cells experience not only increased mechanical properties, but also a higher density of bioactive sites. Traditional in vitro ECM models like Matrigel and collagen do not allow these properties to be investigated independently. In this work, a poly(ethylene glycol)-based scaffold is used which modifies with integrin-binding sites for cell attachment and matrix metalloproteinase 2 and 9 sensitive sites for enzyme-mediated degradation. The polymer backbone density and binding site concentration are independently tuned and the effect each of these properties and their interaction have on the proliferation, invasion, and focal complex formation of two different tumor cell lines is evaluated. It is seen that the cell line of epithelial origin (Hs 578T, triple negative breast cancer) proliferates more, invades less, and forms more mature focal complexes in response to an increase in matrix adhesion sites. Conversely, the cell line of mesenchymal origin (HT1080, fibrosarcoma) proliferates more in 2D culture but less in 3D culture, invades less, and forms more mature focal complexes in response to an increase in matrix stiffness.

Organoids

Organoids have attracted increasing attention because they are simple tissue-engineered cell-based in vitro models that recapitulate many aspects of the complex structure and function of the corresponding in vivo tissue. They can be dissected and interrogated for fundamental mechanistic studies on development, regeneration, and repair in human tissues. Organoids can also be used in diagnostics, disease modeling, drug discovery, and personalized medicine. Organoids are derived from either pluripotent or tissue-resident stem (embryonic or adult) or progenitor or differentiated cells from healthy or diseased tissues, such as tumors. To date, numerous organoid engineering strategies that support organoid culture and growth, proliferation, differentiation and maturation have been reported. This Primer serves to highlight the rationale underlying the selection and development of these materials and methods to control the cellular/tissue niche; and therefore, structure and function of the engineered organoid. We also discuss key considerations for generating robust organoids, such as those related to cell isolation and seeding, matrix and soluble factor selection, physical cues and integration. The general standards for data quality, reproducibility and deposition within the organoid community is also outlined. Lastly, we conclude by elaborating on the limitations of organoids in different applications, and key priorities in organoid engineering for the coming years.

Next generation patient derived tumor organoids

Patient-derived tumor organoids (PDTOs) have emerged as exceptional pre-clinical models as they preserved, in most of the cases, the mutational landscape and tumor-clonal heterogeneity of the primary tumors. Despite being extensively used in disease modelling as well as in precision medicine for drug testing and discovery, they still have some limitations. The main limitation is that during their establishment they lose all components of the tumor microenvironment (TME) which are known modulators of tumor response to therapeutic treatment as well as disease progression. In this review we address the effects of different players of the TME such as immune cells, fibroblasts, endothelial cells and the extracellular matrix composition on tumor behavior and response to treatment as well as the different culture and co-culture strategies that could improve PDTOs value as pre-clinical models leading to the development of next generation PDTOs.

A Tumor Microenvironment Model of Pancreatic Cancer to Elucidate Responses toward Immunotherapy

Pancreatic cancer is a devastating malignancy with minimal treatment options. Standard-of-care therapy, including surgery and chemotherapy, is unsatisfactory, and therapies harnessing the immune system have been unsuccessful in clinical trials. Resistance to therapy and disease progression are mediated by the tumor microenvironment, which contains excessive amounts of extracellular matrix and stromal cells, acting as a barrier to drug delivery. There is a lack of preclinical pancreatic cancer models that reconstruct the extracellular, cellular, and biomechanical elements of tumor tissues to assess responses toward immunotherapy. To address this limitation and explore the effects of immunotherapy in combination with chemotherapy, a multicellular 3D cancer model using a star-shaped poly(ethylene glycol)-heparin hydrogel matrix is developed. Human pancreatic cancer cells, cancer-associated fibroblasts, and myeloid cells are grown encapsulated in hydrogels to mimic key components of tumor tissues, and cell responses toward treatment are assessed. Combining the CD11b agonist ADH-503 with anti-PD-1 immunotherapy and chemotherapy leads to a significant reduction in tumor cell viability, proliferation, metabolic activity, immunomodulation, and secretion of immunosuppressive and tumor growth-promoting cytokines.