3D bioengineered tissue model of the large intestine to study inflammatory bowel disease

In vitro co-culture models for studying organoids-macrophages interaction: the golden technology of cancer immunotherapy

Macrophages, as the largest immune cell group in tumour tissues, play a crucial role in influencing various malignant behaviours of tumour cells and tumour immune evasion. As the research on macrophages and cancer immunotherapy develops, the importance of appropriate research models becomes increasingly evident. The development of organoids has bridged the gap between traditional two-dimensional (2D) cultures and animal experiments. Recent studies have demonstrated that organoids exhibit similar physiological characteristics to the source tissue and closely resemble the in vivo genome and molecular markers of the source tissue or organ. However, organoids still lack an immune component. Developing a co-culture model of organoids and macrophages is crucial for studying the interaction and mechanisms between tumour cells and macrophages. This paper presents an overview of the establishment of co-culture models, the current research status of organoid macrophage interactions, and the current status of immunotherapy. In addition, the application prospects and shortcomings of the model are explained. Ultimately, it is hoped that the co-culture model will offer a preclinical testing platform for maximising a precise cancer immunotherapy strategy.

The application of organoids in colorectal diseases

Intestinal organoids are a three-dimensional cell culture model derived from colon or pluripotent stem cells. Intestinal organoids constructed in vitro strongly mimic the colon epithelium in cell composition, tissue architecture, and specific functions, replicating the colon epithelium in an in vitro culture environment. As an emerging biomedical technology, organoid technology has unique advantages over traditional two-dimensional culture in preserving parental gene expression and mutation, cell function, and biological characteristics. It has shown great potential in the research and treatment of colorectal diseases. Organoid technology has been widely applied in research on colorectal topics, including intestinal tumors, inflammatory bowel disease, infectious diarrhea, and intestinal injury regeneration. This review focuses on the application of organoid technology in colorectal diseases, including the basic principles and preparation methods of organoids, and explores the pathogenesis of and personalized treatment plans for various colorectal diseases to provide a valuable reference for organoid technology development and application.

Impact of Micro- and Nano-Plastics on Human Intestinal Organoid-Derived Epithelium

The development of patient-derived intestinal organoids represents an invaluable model for simulating the native human intestinal epithelium. These stem cell-rich cultures outperform commonly used cell lines like Caco-2 and HT29-MTX in reflecting the cellular diversity of the native intestinal epithelium after differentiation. In our recent study examining the effects of polystyrene (PS), microplastics (MPs), and nanoplastics (NPs), widespread pollutants in our environment and food chain, on the human intestinal epithelium, these organoids have been instrumental in elucidating the absorption mechanisms and potential biological impacts of plastic particles. Building on previously established protocols in human intestinal organoid culture, we herein detail a streamlined protocol for the cultivation, differentiation, and generation of organoid-derived monolayers. This protocol is tailored to generate monolayers incorporating microfold cells (M cells), key for intestinal particle uptake but often absent in current in vitro models. We provide validated protocols for the characterization of MPs/NPs via scanning electron microscopy (SEM) for detailed imaging and their introduction to intestinal epithelial monolayer cells via confocal immunostaining. Additionally, protocols to test the impacts of MP/NP exposure on the functions of the intestinal barrier using transendothelial electrical resistance (TEER) measurements and assessing inflammatory responses using cytokine profiling are detailed. Overall, our protocols enable the generation of human intestinal organoid monolayers, complete with the option of including or excluding M cells, offering crucial techniques for observing particle uptake and identifying inflammatory responses in intestinal epithelial cells to advance our knowledge of the potential effects of plastic pollution on human gut health. These approaches are also amendable to the study of other gut-related chemical and biological exposures and physiological responses due to the robust nature of the systems. © 2024 Wiley Periodicals LLC. Basic Protocol 1: Human intestinal organoid culture and generation of monolayers with and without M cells Support Protocol 1: Culture of L-WRN and production of WRN-conditioned medium Support Protocol 2: Neuronal cell culture and integration into intestinal epithelium Support Protocol 3: Immune cell culture and integration into intestinal epithelium Basic Protocol 2: Scanning electron microscopy: sample preparation and imaging Basic Protocol 3: Immunostaining and confocal imaging of MP/NP uptake in organoid-derived monolayers Basic Protocol 4: Assessment of intestinal barrier function via TEER measurements Basic Protocol 5: Cytokine profiling using ELISA post-MP/NP exposure.

Three-Dimensional Scaffolds for Intestinal Cell Culture: Fabrication, Utilization, and Prospects

The intestine is a visceral organ that integrates absorption, metabolism, and immunity, which is vulnerable to external stimulus. Researchers in the fields such as food science, immunology, and pharmacology have committed to developing appropriate in vitro intestinal cell models to study the intestinal absorption and metabolism mechanisms of various nutrients and drugs, or pathogenesis of intestinal diseases. In the past three decades, the intestinal cell models have undergone a significant transformation from conventional two-dimensional cultures to three-dimensional (3D) systems, and the achievements of 3D cell culture have been greatly contributed by the fabrication of different scaffolds. In this review, we first introduce the developing trend of existing intestinal models. Then, four types of scaffolds, including Transwell, hydrogel, tubular scaffolds, and intestine-on-a-chip, are discussed for their 3D structure, composition, advantages, and limitations in the establishment of intestinal cell models. Excitingly, some of the in vitro intestinal cell models based on these scaffolds could successfully mimic the 3D structure, microenvironment, mechanical peristalsis, fluid system, signaling gradients, or other important aspects of the original human intestine. Furthermore, we discuss the potential applications of the intestinal cell models in drug screening, disease modeling, and even regenerative repair of intestinal tissues. This review presents an overview of state-of-the-art scaffold-based cell models within the context of intestines, and highlights their major advances and applications contributing to a better knowledge of intestinal diseases. Impact statement The intestine tract is crucial in the absorption and metabolism of nutrients and drugs, as well as immune responses against external pathogens or antigens in a complex microenvironment. The appropriate experimental cell model in vitro is needed for in-depth studies of intestines, due to the limitation of animal models in dynamic control and real-time assessment of key intestinal physiological and pathological processes, as well as the "R" principles in laboratory animal experiments. Three-dimensional (3D) scaffold-based cell cultivation has become a developing tendency because of the superior cell proliferation and differentiation and more physiologically relevant environment supported by the customized 3D scaffolds. In this review, we summarize four types of up-to-date 3D cell culture scaffolds fabricated by various materials and techniques for a better recapitulation of some essential physiological and functional characteristics of original intestines compared to conventional cell models. These emerging 3D intestinal models have shown promising results in not only evaluating the pharmacokinetic characteristics, security, and effectiveness of drugs, but also studying the pathological mechanisms of intestinal diseases at cellular and molecular levels. Importantly, the weakness of the representative 3D models for intestines is also discussed.

Trends in 3D models of inflammatory bowel disease

Inflammatory bowel disease (IBD) encompasses a set of chronic inflammatory conditions, namely Crohn's disease and ulcerative colitis. Despite all advances in the management of IBD, a definitive cure is not available, largely due to a lack of a holistic understanding of its etiology and pathophysiology. Several in vitro, in vivo, and ex vivo models have been developed over the past few decades in order to abbreviate remaining gaps. The establishment of reliable and predictable in vitro intestinal inflammation models may indeed provide valuable tools to expedite and validate the development of therapies for IBD. Three-dimensional (3D) models provide a more accurate representation of the different layers of the intestine, contributing to a stronger impact on drug screening and research on intestinal inflammation, and bridging the gap between in vitro and in vivo research. This work provides a critical overview on the state-of-the-art on existing 3D models of intestinal inflammation and discusses the remaining challenges, providing insights on possible pathways towards achieving IBD mimetic models. We also address some of the main challenges faced by implementing cell culture models in IBD research while bearing in mind clinical translational aspects.

Advances in the Generation of Constructed Cardiac Tissue Derived from Induced Pluripotent Stem Cells for Disease Modeling and Therapeutic Discovery

The human heart lacks significant regenerative capacity; thus, the solution to heart failure (HF) remains organ donation, requiring surgery and immunosuppression. The demand for constructed cardiac tissues (CCTs) to model and treat disease continues to grow. Recent advances in induced pluripotent stem cell (iPSC) manipulation, CRISPR gene editing, and 3D tissue culture have enabled a boom in iPSC-derived CCTs (iPSC-CCTs) with diverse cell types and architecture. Compared with 2D-cultured cells, iPSC-CCTs better recapitulate heart biology, demonstrating the potential to advance organ modeling, drug discovery, and regenerative medicine, though iPSC-CCTs could benefit from better methods to faithfully mimic heart physiology and electrophysiology. Here, we summarize advances in iPSC-CCTs and future developments in the vascularization, immunization, and maturation of iPSC-CCTs for study and therapy.

Advancements in Nanoparticle Characterization

Nanotechnology for drug delivery has made significant advancements over the last two decades. Innovations have been made in cancer research and development, including chemotherapies, imaging agents, and vaccine strategies, as well as other therapeutic areas, e.g., the recent commercialization of mRNA lipid nanoparticles as vaccines against the SARS-CoV-2 virus. The field has also seen technological advancements to aid in addressing the complex questions posed by these novel therapies. In this latest edition of protocols and methods for nanoparticle characterization, we highlight both old and new methodologies for defining physicochemical properties, present both in vitro and in vivo methods to test for a variety of immunotoxicities, and describe assays used for pharmacological studies to assess drug release and tissue distribution.

Microphysiological Constructs and Systems: Biofabrication Tactics, Biomimetic Evaluation Approaches, and Biomedical Applications

In recent decades, microphysiological constructs and systems (MPCs and MPSs) have undergone significant development, ranging from self-organized organoids to high-throughput organ-on-a-chip platforms. Advances in biomaterials, bioinks, 3D bioprinting, micro/nanofabrication, and sensor technologies have contributed to diverse and innovative biofabrication tactics. MPCs and MPSs, particularly tissue chips relevant to absorption, distribution, metabolism, excretion, and toxicity, have demonstrated potential as precise, efficient, and economical alternatives to animal models for drug discovery and personalized medicine. However, current approaches mainly focus on the in vitro recapitulation of the human anatomical structure and physiological-biochemical indices at a single or a few simple levels. This review highlights the recent remarkable progress in MPC and MPS models and their applications. The challenges that must be addressed to assess the reliability, quantify the techniques, and utilize the fidelity of the models are also discussed.

Recent Advances in Cell-Based In Vitro Models to Recreate Human Intestinal Inflammation

Inflammatory bowel disease causes a major burden to patients and healthcare systems, raising the need to develop effective therapies. Technological advances in cell culture, allied with ethical issues, have propelled in vitro models as essential tools to study disease aetiology, its progression, and possible therapies. Several cell-based in vitro models of intestinal inflammation have been used, varying in their complexity and methodology to induce inflammation. Immortalized cell lines are extensively used due to their long-term survival, in contrast to primary cultures that are short-lived but patient-specific. Recently, organoids and organ-chips have demonstrated great potential by being physiologically more relevant. This review aims to shed light on the intricate nature of intestinal inflammation and cover recent works that report cell-based in vitro models of human intestinal inflammation, encompassing diverse approaches and outcomes.

Therapeutic effect of bromelain and papain on intestinal injury induced by indomethacin in male rats

Objectives

Inflammatory bowel diseases (IBDs) are a multiple inflammatory status in small intestines and colon. Bromelain and Papain were cysteine proteases enzymes extracted from pineapple and papaya, and possess antioxidant and anti-inflammatory characteristics. Therefore, this comparative work aimed to examine the anti-inflammatory and antioxidant effect of bromelain and papain in intestinal inflammation of rats and to evaluate the most potent effect of both types of enzymes.

Methods

Forty rats were used in this study (8 rats/group), G1: control group, G2: (Indo group) intestinal inflammation was induced by two doses of Indomethacin (7.5 mg/kg body weight) apart 24 h. G3: (Indomethacin + Bromelain) intestinal inflamed rats treated by oral dose of bromelain (1000 mg/kg/day). G4: (Indomethacin + Papain) intestinal inflamed rats treated by oral dose of papain (800 mg/kg/day). G5: (Indomethacin + Sulfasalazine) intestinal inflamed rats treated by oral dose of sulfasalazine (500 mg/kg/day). Oxidative stress and inflammatory markers were measured along with histological assessment.

Results

Indomethacin-induced intestinal inflammation (in both Jejunum and Ileum) characterized by increased oxidative stress biomarkers: Xanthine oxidase, Catalase, Glutathione reductase, and Protein carbonyl and Inflammatory biomarkers: Tumor necrosis factor-α, Interleukin-10, Monocyte chemoattractant protein-1, Nuclear factor-kappa β, C-reactive protein, and Prostaglandin E2, as compared to control rats. On the other hand, administering either bromelain or Papain would effectively decrease symptoms of intestinal inflammation and modulate biomarkers of oxidative stress and pro-inflammatory cytokines.

Conclusion

Comparing results revealed that bromelain showed the most potent protective effect and possesses an apparent role in protection against the development of intestinal inflammation.

Biological effects of polystyrene micro- and nano-plastics on human intestinal organoid-derived epithelial tissue models without and with M cells

Micro- and nano-plastics (MPs and NPs) released from plastics in the environment can enter the food chain and target the human intestine. However, knowledge about the effects of these particles on the human intestine is still limited due to the lack of relevant human intestinal models to validate data obtained from animal studies or tissue models employing cancer cells. In this study, human intestinal organoids were used to develop epithelia to mimic the cell complexity and functions of native tissue. Microfold cells (M cells) were induced to distinguish their role when exposure to MPs and NPs. During the exposure, the M cells acted as sensors, capturers and transporters of larger sized particles. The epithelial cells internalized the particles in a size-, concentration-, and time-dependent manner. Importantly, high concentrations of particles significantly triggered the secretion of a panel of inflammatory cytokines linked to human inflammatory bowel disease (IBD).

Give Them Vasculature and Immune Cells: How to Fill the Gap of Organoids

Valid and relevant models are critical for research to have biological relevance or to proceed in the right path. As well-established two-dimensional cell cultures lack niches and cues and rodent models differ in species, three-dimensional organoids emerged as a powerful platform for research. Cultured in vitro from stem cells, organoids are heterogeneous in cells and closely resemble the in vivo settings. Organoids also recapitulate the unique human features if cultured from a human source and are subjected to genetic modification. However, one type of organoid possesses only a limited selection of cells. In particular, the absence of vasculature and immune cells restricts the organoids from nutrition, cues, or critical interactions, undermining the validity of organoids as physiological or pathological models. To fill the current gap, there is an urgent need to provide organoids with vasculature and immune cells. In this paper, we review the methods to generate physiological and pathological organoid models and summarize ways to vascularize or immunize them. Our discussion continues with some advantages and disadvantages of each method and some emerging solutions to current problems.

Investigation of silk as a phantom material for ultrasound and photoacoustic imaging

Comprehensive characterization of biomedical imaging systems require phantoms that are easy to fabricate and can mimic human tissue. Additionally, with the arrival of engineered tissues, it is key to develop phantoms that can mimic bioengineered samples. In ultrasound and photoacoustic imaging, water-soluble phantom materials such as gelatin undergo rapid degradation while polymer-based materials such as polyvinyl alcohol are not conducive for generating bioengineered tissues that can incorporate cells. Here we propose silk protein-based hydrogels as an ultrasound and photoacoustic phantom material that has potential to provide a 3D environment for long-term sustainable cell growth. Common acoustic, optical, and biomechanical properties such as ultrasound attenuation, reduced scattering coefficient, and Young's modulus were measured. The results indicate that silk acoustically mimics many tissue types while exhibiting similar reduced optical scattering in the wavelength range of 400-1200 nm. Furthermore, silk-based materials can be stored long-term with no change in acoustic and optical properties, and hence can be utilized to assess the performance of ultrasound and photoacoustic systems.

Mechanical stretching boosts expansion and regeneration of intestinal organoids through fueling stem cell self-renewal

Intestinal organoids, derived from intestinal stem cell self-organization, recapitulate the tissue structures and behaviors of the intestinal epithelium, which hold great potential for the study of developmental biology, disease modeling, and regenerative medicine. The intestinal epithelium is exposed to dynamic mechanical forces which exert profound effects on gut development. However, the conventional intestinal organoid culture system neglects the key role of mechanical microenvironments but relies solely on biological factors. Here, we show that adding cyclic stretch to intestinal organoid cultures remarkably up-regulates the signature gene expression and proliferation of intestinal stem cells. Furthermore, mechanical stretching stimulates the expansion of SOX9+ progenitors by activating the Wnt/β-Catenin signaling. These data demonstrate that the incorporation of mechanical stretch boosts the stemness of intestinal stem cells, thus benefiting organoid growth. Our findings have provided a way to optimize an organoid generation system through understanding cross-talk between biological and mechanical factors, paving the way for the application of mechanical forces in organoid-based models.

Suspended Collagen Hydrogels to Replicate Human Colonic Epithelial Cell Interactions with Immune Cells

The human colon plays a critical role in fluid and salt absorption and harbors the largest immune compartment. There is a widespread need for in vitro models of human colon physiology with its innate immune system. A method is described to produce a cassette with a network of struts supporting a suspended, non-chemically cross-linked collagen hydrogel scaffold compatible with the co-culture of primary gastrointestinal epithelium and migratory inflammatory cells. The epithelial monolayer cultured on the suspended collagen possesses a population of polarized and differentiated cells similar to that present in vivo. This epithelial layer displays proper barrier function with a transepithelial electrical resistance (TEER) ≥ 1,500 Ω cm2 and an apparent permeability ≤10-5 cm2 s-1 . Immune cells plated on the basal face of the scaffold transmigrated over a period of 24 h to the epithelial layer in response to epithelial production of IL-8 induced by luminal stimulation of Clostridium difficile Toxin A. These studies demonstrate that this in vitro platform possesses a functional primary colonic epithelial layer with an immune cell compartment capable of recruitment in response to pro-inflammatory cues coming from the epithelium.

Crypt-Villus Scaffold Architecture for Bioengineering Functional Human Intestinal Epithelium

Crypt-villus architecture in the small intestine is crucial for the structural integrity of the intestinal epithelium and maintenance of gut homeostasis. We utilized three-dimensional (3D) printing and inverse molding techniques to form three-dimensional (3D) spongy scaffold systems that resemble the intestinal crypt-villus microarchitecture. The scaffolds consist of silk fibroin protein with curved lumens with rows of protruding villi with invaginating crypts to generate the architecture. Intestinal cell (Caco-2, HT29-MTX) attachment and growth, as well as long-term culture support were demonstrated with cell polarization and tissue barrier properties compared to two-dimensional (2D) Transwell culture controls. Further, physiologically relevant oxygen gradients were generated in the 3D system. The various advantages of this system may be ascribed to the more physiologically relevant 3D environment, offering a system for the exploration of disease pathogenesis, host-microbiome interactions, and therapeutic discovery.

Regenerative medicine technologies applied to transplant medicine.an update

Regenerative medicine (RM) is changing how we think and practice transplant medicine. In regenerative medicine, the aim is to develop and employ methods to regenerate, restore or replace damaged/diseased tissues or organs. Regenerative medicine investigates using tools such as novel technologies or techniques, extracellular vesicles, cell-based therapies, and tissue-engineered constructs to design effective patient-specific treatments. This review illustrates current advancements in regenerative medicine that may pertain to transplant medicine. We highlight progress made and various tools designed and employed specifically for each tissue or organ, such as the kidney, heart, liver, lung, vasculature, gastrointestinal tract, and pancreas. By combing both fields of transplant and regenerative medicine, we can harbor a successful collaboration that would be beneficial and efficacious for the repair and design of de novo engineered whole organs for transplantations.

Recent advances in biofabricated gut models to understand the gut-brain axis in neurological diseases

Increasing evidence has accumulated that gut microbiome dysbiosis could be linked to neurological diseases, including both neurodegenerative and psychiatric diseases. With the high prevalence of neurological diseases, there is an urgent need to elucidate the underlying mechanisms between the microbiome, gut, and brain. However, the standardized aniikmal models for these studies have critical disadvantages for their translation into clinical application, such as limited physiological relevance due to interspecies differences and difficulty interpreting causality from complex systemic interactions. Therefore, alternative in vitro gut–brain axis models are highly required to understand their related pathophysiology and set novel therapeutic strategies. In this review, we outline state-of-the-art biofabrication technologies for modeling in vitro human intestines. Existing 3D gut models are categorized according to their topographical and anatomical similarities to the native gut. In addition, we deliberate future research directions to develop more functional in vitro intestinal models to study the gut–brain axis in neurological diseases rather than simply recreating the morphology.

Donor-to-donor variability of a human three-dimensional bronchial epithelial model: A case study of cigarette smoke exposure

Three-dimensional (3D) cultured primary cells are used to predict the toxicity of substances towards humans because these 3D cultures closely mimic the physiological architecture of tissues. Nonetheless, it is important to consider primary-cell-specific variability for endpoint selection and appropriate evaluation of toxicity because donor-dependent characteristics may be retained even in in vitro cell cultures. In this report, 3D differentiated bronchial epithelial cells from three donors were used to investigate donor-to-donor variability, with an aqueous extract of cigarette smoke (CS) used as the test substance. Ciliary function, cytokine secretion, and histopathology, which are affected by CS, were examined, and transcriptomic analysis was also performed. The results revealed that interleukin-8 secretion and oxidative stress-related gene expression were consistently altered for all donors; however, their amplitudes varied. Moreover, one of the donors showed unique responses to CS, suggesting that this donor was an outlier. This donor showed intrinsic differences in histology, cytokine secretion, and gene expression profile. Such donors may help evaluate potential toxicological concerns and aid our understanding of disease pathogenesis. Conversely, these donors may confound toxicological assessment and endpoint selection. Fit-for-purpose handling of inter-donor variability is warranted.

Bioengineered 3D Tissue Model of Intestine Epithelium with Oxygen Gradients to Sustain Human Gut Microbiome

The human gut microbiome is crucial to hosting physiology and health. Therefore, stable in vitro coculture of primary human intestinal cells with a microbiome community is essential for understanding intestinal disease progression and revealing novel therapeutic targets. Here, a three-dimensional scaffold system is presented to regenerate an in vitro human intestinal epithelium that recapitulates many functional characteristics of the native small intestines. The epithelium, derived from human intestinal enteroids, contains mature intestinal epithelial cells and possesses selectively permeable barrier functions. Importantly, by properly positioning the scaffolds cultured under normal atmospheric conditions, two physiologically relevant oxygen gradients, a proximal-to-distal oxygen gradient along the gastrointestinal (GI) tract, and a radial oxygen gradient across the epithelium, are distinguished in the tissues when the lumens are faced up and down in cultures, respectively. Furthermore, the presence of the low oxygen gradients supported the coculture of intestinal epithelium along with a complex living commensal gut microbiome (including obligate anaerobes) to simulate temporal microbiome dynamics in the native human gut. This unique silk scaffold platform may enable the exploration of microbiota-related mechanisms of disease pathogenesis and host-pathogen dynamics in infectious diseases including the potential to explore the human microbiome-gut-brain axis and potential novel microbiome-based therapeutics.

Transcytosis of IgA Attenuates Salmonella Invasion in Human Enteroids and Intestinal Organoids

Secretory IgA (SIgA) is the most abundant antibody type in intestinal secretions where it contributes to safeguarding the epithelium from invasive pathogens like the Gram-negative bacterium, Salmonella enterica serovar Typhimurium (STm). For example, we recently reported that passive oral administration of the recombinant monoclonal SIgA antibody, Sal4, to mice promotes STm agglutination in the intestinal lumen and restricts bacterial invasion of Peyer's patch tissues. In this report, we sought to recapitulate Sal4-mediated protection against STm in human Enteroids and human intestinal organoids (HIOs) as models to decipher the molecular mechanisms by which antibodies function in mucosal immunity in the human gastrointestinal tract. We confirm that Enteroids and HIO-derived monolayers are permissive to STm infection, dependent on HilD, the master transcriptional regulator of the SPI-I type three secretion system (T3SS). Stimulation of M-like cells in both Enteroids and HIOs by the addition of RANKL further enhanced STm invasion. The apical addition of Sal4 mouse IgA, as well as recombinant human Sal4 dimeric IgA (dIgA) and SIgA resulted a dose-dependent reduction in bacterial invasion. Moreover, basolateral application of Sal4 dIgA to Enteroid and HIO monolayers gave rise to SIgA in the apical compartment via a pathway dependent on expression of the polymeric immunoglobulin receptor (pIgR). The resulting Sal4 SIgA was sufficient to reduce STm invasion of Enteroid and HIO epithelial cell monolayers by ~20-fold. Recombinant Sal4 IgG was also transported in the Enteroid and HIOs, but to a lesser degree and via a pathway dependent on the neonatal Fc receptor (FCGRT). The models described lay the foundation for future studies into detailed mechanisms of IgA and IgG protection against STm and other pathogens.

Extracellular matrix bioink boosts stemness and facilitates transplantation of intestinal organoids as a biosafe Matrigel alternative

Organoids hold inestimable therapeutic potential in regenerative medicine and are increasingly serving as an in vitro research platform. Still, their expanding applications are critically restricted by the canonical culture matrix and system. Synthesis of a suitable bioink of bioactivity, biosecurity, tunable stiffness, and printability to replace conventional matrices and fabricate customized culture systems remains challenging. Here, we envisaged a novel bioink formulation based on decellularized extracellular matrix (dECM) from porcine small intestinal submucosa for organoids bioprinting, which provides intestinal stem cells (ISCs) with niche-specific ECM content and biomimetic microstructure. Intestinal organoids cultured in the fabricated bioink exhibited robust generation as well as a distinct differentiation pattern and transcriptomic signature. This bioink established a new co-culture system able to study interaction between epithelial homeostasis and submucosal cells and promote organoids maturation after transplantation into the mesentery of immune-deficient NODSCID-gamma (NSG) mice. In summary, the development of such photo-responsive bioink has the potential to replace tumor-derived Matrigel and facilitate the application of organoids in translational medicine and disease modeling.

Untangling Mucosal Drug Delivery: Engineering, Designing, and Testing Nanoparticles to Overcome the Mucus Barrier

Mucus is a complex viscoelastic gel and acts as a barrier covering much of the soft tissue in the human body. High vascularization and accessibility have motivated drug delivery to various mucosal surfaces; however, these benefits are hindered by the mucus layer. To overcome the mucus barrier, many nanomedicines have been developed, with the goal of improving the efficacy and bioavailability of drug payloads. Two major nanoparticle-based strategies have emerged to facilitate mucosal drug delivery, namely, mucoadhesion and mucopenetration. Generally, mucoadhesive nanoparticles promote interactions with mucus for immobilization and sustained drug release, whereas mucopenetrating nanoparticles diffuse through the mucus and enhance drug uptake. The choice of strategy depends on many factors pertaining to the structural and compositional characteristics of the target mucus and mucosa. While there have been promising results in preclinical studies, mucus-nanoparticle interactions remain poorly understood, thus limiting effective clinical translation. This article reviews nanomedicines designed with mucoadhesive or mucopenetrating properties for mucosal delivery, explores the influence of site-dependent physiological variation among mucosal surfaces on efficacy, transport, and bioavailability, and discusses the techniques and models used to investigate mucus-nanoparticle interactions. The effects of non-homeostatic perturbations on protein corona formation, mucus composition, and nanoparticle performance are discussed in the context of mucosal delivery. The complexity of the mucosal barrier necessitates consideration of the interplay between nanoparticle design, tissue-specific differences in mucus structure and composition, and homeostatic or disease-related changes to the mucus barrier to develop effective nanomedicines for mucosal delivery.

Engineering in vitro immune-competent tissue models for testing and evaluation of therapeutics

Advances in 3D cell culture, microscale fluidic control, and cellular analysis have enabled the development of more physiologically-relevant engineered models of human organs with precise control of the cellular microenvironment. Engineered models have been used successfully to answer fundamental biological questions and to screen therapeutics, but these often neglect key elements of the immune system. There are immune elements in every tissue that contribute to healthy and diseased states. Including immune function will be essential for effective preclinical testing of therapeutics for inflammatory and immune-modulated diseases. In this review, we first discuss the key components to consider in designing engineered immune-competent models in terms of physical, chemical, and biological cues. Next, we review recent applications of models of immunity for screening therapeutics for cancer, preclinical evaluation of engineered T cells, modeling autoimmunity, and screening vaccine efficacy. Future work is needed to further recapitulate immune responses in engineered models for the most informative therapeutic screening and evaluation.

3D Microvascularized Tissue Models by Laser-Based Cavitation Molding of Collagen

3D tissue models recapitulating human physiology are important for fundamental biomedical research, and they hold promise to become a new tool in drug development. An integrated and defined microvasculature in 3D tissue models is necessary for optimal cell functions. However, conventional bioprinting only allows the fabrication of hydrogel scaffolds containing vessel-like structures with large diameters (>100 µm) and simple geometries. Recent developments in laser photoablation enable the generation of this type of structure with higher resolution and complexity, but the photo-thermal process can compromise cell viability and hydrogel integrity. To address these limitations, the present work reports in situ 3D patterning of collagen hydrogels by femtosecond laser irradiation to create channels and cavities with diameters ranging from 20 to 60 µm. In this process, laser irradiation of the hydrogel generates cavitation gas bubbles that rearrange the collagen fibers, thereby creating stable microchannels. Such 3D channels can be formed in cell- and organoid-laden hydrogel without affecting the viability outside the lumen and can enable the formation of artificial microvasculature by the culture of endothelial cells and cell media perfusion. Thus, this method enables organs-on-a-chip and 3D tissue models featuring complex microvasculature.

Mast Cells Tryptase Promotes Intestinal Fibrosis in Natural Decellularized Intestinal Scaffolds

BACKGROUND

Standard two-dimensional (2D) culture has confirmed the mechanism of mast cells (MCs) in the pathogenesis of inflammatory bowel disease (IBD), but the regulation of signaling responses of MCs may well differ in three-dimensional (3D) microenvironments. The aim of the study was to develop a 3D culture model based on decellularized intestinal scaffolds (DIS) and verify how MCs influenced fibroblasts phenotype in the 3D model.

METHODS

DIS were achieved using the detergent technique and extracellular matrix (ECM) components were verified by histologic analysis, quantification and scanning electron microscope. After human colon fibroblasts recellularized into the scaffolds and activated by MCs tryptase and TGFβ1, the changes in genes and signaling pathways during fibroblasts activation in 3D were studied and compared with the changes in 2D cell culture on plastic plates.

RESULTS

Decellularization process effectively removed native cell debris while retaining natural ECM components and structure. The engrafted fibroblasts could penetrate into the scaffolds and maintain its phenotype. No matter whether fibroblasts were cultured in 2D or 3D, MCs tryptase and transforming growth factor β1 (TGF-β1) could promote the differentiation of fibroblasts into fibrotic-phenotype myofibroblasts through Akt and Smad2/3 signaling pathways. Furthermore, the pro-collagen1α1 and fibronectin synthesis of myofibroblasts in 3D was higher than in 2D culture.

CONCLUSION

Our results demonstrated that the DIS can be used as a bioactive microenvironment for the study of intestinal fibrosis, providing an innovative platform for future intestinal disease modeling and screening of genes and signaling pathways.

Processing-Structure-Properties Relationships of Glycerol-Plasticized Silk Films

Silk possesses excellent mechanical properties and biocompatibility due to its unique protein sequences and hierarchical structures. Thus, it has been widely used as a biomaterial in a broad spectrum of biomedical applications. In this study, an in-depth investigation of glycerol-plasticized silk films was carried out to understand the processing-structure-properties relationships. A series of glycerol-plasticized silk films with glycerol contents in the range of 0 to 30% (w/w) were prepared. The molecular structures and organizations of silk proteins and the interactions between glycerol and proteins were studied using FTIR, XRD, and DSC. At a low glycerol content (<12%), DSC revealed that the glass transition temperature and thermally induced crystallization temperature decreased as the glycerol content increased, implying that glycerol mainly interacts with silk proteins through hydrogen bonding. As the glycerol content further increased, the chain mobility of the silk proteins was promoted, leading to the formation of β-sheet structures, water insolubility, and increased crystallinity. In addition, the stretchability and toughness of the films were significantly enhanced. The role of glycerol as a plasticizer in regulating the silk protein structures and determining the properties of the films was thoroughly discussed.

Versatile human in vitro triple coculture model coincubated with adhered gut microbes reproducibly mimics pro-inflammatory host-microbe interactions in the colon

The colonic epithelial barrier is vital to preserve gut and host health by maintaining the immune homeostasis between host and microbes. The mechanisms underlying beneficial or harmful host-microbe interactions are poorly understood and impossible to study in vivo given the limited accessibility and ethical constraints. Moreover, existing in vitro models lack the required cellular complexity for the routine, yet profound, analysis of the intricate interplay between different types of host and microbial cells. We developed and characterized a broadly applicable, easy-to-handle in vitro triple coculture model that combines chemically-induced macrophage-like, goblet and epithelial cells covered by a mucus layer, which can be coincubated with complex human-derived gut microbiota samples for 16 h. Comparison with a standard epithelial monolayer model revealed that triple cocultures produce thicker mucus layers, morphologically organize in a network and upon exposure to human-derived gut microbiota samples, respond via pro-inflammatory cytokine production. Both model systems, however, were not suffering from cytotoxic stress or different microbial loads, indicating that the obtained endpoints were caused by the imposed conditions. Addition of the probiotic Lactobacillus rhamnosus GG to assess its immunomodulating capacity in the triple coculture slightly suppressed pro-inflammatory cytokine responses, based on transcriptomic microarray analyses. TNF conditioning of the models prior to microbial exposure did not cause shifts in cytokines, suggesting a strong epithelial barrier in which TNF did not reach the basolateral side. To conclude, the triple coculture model is tolerable towards manipulations and allows to address mechanistic host-microbe research questions in a stable in vitro environment.

Current knowledge on the multiform reconstitution of intestinal stem cell niche

The development of “mini-guts” organoid originates from the identification of Lgr5⁺ intestinal stem cells (ISCs) and circumambient signalings within their specific niche at the crypt bottom. These in vitro self-renewing “mini-guts”, also named enteroids or colonoids, undergo perpetual proliferation and regulated differentiation, which results in a high-performance, self-assembling and physiological organoid platform in diverse areas of intestinal research and therapy. The triumphant reconstitution of ISC niche in vitro also relies on Matrigel, a heterogeneous sarcoma extract. Despite the promising prospect of organoids research, their expanding applications are hampered by the canonical culture pattern, which reveals limitations such as inaccessible lumen, confine scale, batch to batch variation and low reproducibility. The tumor-origin of Matrigel also raises biosafety concerns in clinical treatment. However, the convergence of breakthroughs in cellular biology and bioengineering contribute to multiform reconstitution of the ISC niche. Herein, we review the recent advances in the microfabrication of intestinal organoids on hydrogel systems.

Magnetically-propelled fecal surrogates for modeling the impact of solid-induced shear forces on primary colonic epithelial cells

The colonic epithelium is continuously exposed to an array of biological and mechanical stimuli as its luminal contents are guided over the epithelial surface through regulated smooth muscle contraction. In this report, the propulsion of solid fecal contents over the colonic epithelium is recapitulated through noninvasive actuation of magnetic agarose hydrogels over primary intestinal epithelial cultures, in contrast to the vast majority of platforms that apply shear forces through liquid microflow. Software-controlled magnetic stepper motors enable experimental control over the frequency and velocity of these events to match in vivo propulsive contractions, while the integration of standardized well plate spacing facilitates rapid integration into existing assay pipelines. The application of these solid-induced shear forces did not deleteriously affect cell monolayer surface coverage, viability, or transepithelial electrical resistance unless the device parameters were raised to a 50× greater contraction frequency and 4× greater fecal velocity than those observed in healthy humans. At a frequency and velocity that is consistent with average human colonic motility, differentiation of the epithelial cells into absorptive and goblet cell phenotypes was not affected. Protein secretion was modulated with a two-fold increase in luminal mucin-2 secretion and a significant reduction in basal interleukin-8 secretion. F-actin, zonula occludens-1, and E-cadherin were each present in their proper basolateral locations, similar to those of static control cultures. While cellular height was unaffected by magnetic agarose propulsion, several alterations in lateral morphology were observed including decreased circularity and compactness, and an increase in major axis length, which align with surface epithelial cell morphologies observed in vivo and may represent early markers of luminal exfoliation. This platform will be of widespread utility for the investigation of fecal propulsive forces on intestinal physiology, shedding light on how the colonic epithelium responds to mechanical cues.

Modeling Immunity In Vitro: Slices, Chips, and Engineered Tissues

Modeling immunity in vitro has the potential to be a powerful tool for investigating fundamental biological questions, informing therapeutics and vaccines, and providing new insight into disease progression. There are two major elements to immunity that are necessary to model: primary immune tissues and peripheral tissues with immune components. Here, we systematically review progress made along three strategies to modeling immunity: ex vivo cultures, which preserve native tissue structure; microfluidic devices, which constitute a versatile approach to providing physiologically relevant fluid flow and environmental control; and engineered tissues, which provide precise control of the 3D microenvironment and biophysical cues. While many models focus on disease modeling, more primary immune tissue models are necessary to advance the field. Moving forward, we anticipate that the expansion of patient-specific models may inform why immunity varies from patient to patient and allow for the rapid comprehension and treatment of emerging diseases, such as coronavirus disease 2019.

A Dietary Cholesterol-Based Intestinal Inflammation Assay for Improving Drug-Discovery on Inflammatory Bowel Diseases

Inflammatory bowel diseases (IBD) with chronic infiltration of immune cells in the gastrointestinal tract are common and largely incurable. The therapeutic targeting of IBD has been hampered by the complex causality of the disease, with environmental insults like cholesterol-enriched Western diets playing a critical role. To address this drug development challenge, we report an easy-to-handle dietary cholesterol-based in vivo assay that allows the screening of immune-modulatory therapeutics in transgenic zebrafish models. An improvement in the feeding strategy with high cholesterol diet (HCD) selectively induces a robust and consistent infiltration of myeloid cells in larvae intestines that is highly suitable for compound discovery efforts. Using transgenics with fluorescent reporter expression in neutrophils, we take advantage of the unique zebrafish larvae clarity to monitor an acute inflammatory response in a whole organism context with a fully functional innate immune system. The use of semi-automated image acquisition and processing combined with quantitative image analysis allows categorizing anti- or pro-inflammatory compounds based on a leukocytic inflammation index. Our HCD gut inflammation (HCD-GI) assay is simple, cost- and time-effective as well as highly physiological which makes it unique when compared to chemical-based zebrafish models of IBD. Besides, diet is a highly controlled, selective and targeted trigger of intestinal inflammation that avoids extra-intestinal outcomes and reduces the chances of chemical-induced toxicity during screenings. We show the validity of this assay for a screening platform by testing two dietary phenolic acids, namely gallic acid (GA; 3,4,5-trihydroxybenzoic acid) and ferulic acid (FA; 4-hydroxy-3-methoxycinnamic acid), with well described anti-inflammatory actions in animal models of IBD. Analysis of common IBD therapeutics (Prednisolone and Mesalamine) proved the fidelity of our IBD-like intestinal inflammation model. In conclusion, the HCD-GI assay can facilitate and accelerate drug discovery efforts on IBD, by identification of novel lead molecules with immune modulatory action on intestinal neutrophilic inflammation. This will serve as a jumping-off point for more profound analyses of drug mechanisms and pathways involved in early IBD immune responses.

A Tissue-Engineered Tracheobronchial In Vitro Co-Culture Model for Determining Epithelial Toxicological and Inflammatory Responses

Translation of novel inhalable therapies for respiratory diseases is hampered due to the lack of in vitro cell models that reflect the complexity of native tissue, resulting in many novel drugs and formulations failing to progress beyond preclinical assessments. The development of physiologically-representative tracheobronchial tissue analogues has the potential to improve the translation of new treatments by more accurately reflecting in vivo respiratory pharmacological and toxicological responses. Herein, advanced tissue-engineered collagen hyaluronic acid bilayered scaffolds (CHyA-B) previously developed within our group were used to evaluate bacterial and drug-induced toxicity and inflammation for the first time. Calu-3 bronchial epithelial cells and Wi38 lung fibroblasts were grown on either CHyA-B scaffolds (3D) or Transwell® inserts (2D) under air liquid interface (ALI) conditions. Toxicological and inflammatory responses from epithelial monocultures and co-cultures grown in 2D or 3D were compared, using lipopolysaccharide (LPS) and bleomycin challenges to induce bacterial and drug responses in vitro. The 3D in vitro model exhibited significant epithelial barrier formation that was maintained upon introduction of co-culture conditions. Barrier integrity showed differential recovery in CHyA-B and Transwell® epithelial cultures. Basolateral secretion of pro-inflammatory cytokines to bacterial challenge was found to be higher from cells grown in 3D compared to 2D. In addition, higher cytotoxicity and increased basolateral levels of cytokines were detected when epithelial cultures grown in 3D were challenged with bleomycin. CHyA-B scaffolds support the growth and differentiation of bronchial epithelial cells in a 3D co-culture model with different transepithelial resistance in comparison to the same co-cultures grown on Transwell® inserts. Epithelial cultures in an extracellular matrix like environment show distinct responses in cytokine release and metabolic activity compared to 2D polarised models, which better mimic in vivo response to toxic and inflammatory stimuli offering an innovative in vitro platform for respiratory drug development.

Primate Organoids and Gene-Editing Technologies toward Next-Generation Biomedical Research

The improved ability to organize pluripotent stem cells (PSCs) into 3D structures in vitro has shed light on organoid technology to recapitulate organs and tumors in vivo. Advances in gene-editing technologies, particularly CRISPR-mediated techniques, offer tremendous potential in facilitating organoid research, including the study of development, disease modeling, and personalized medicine. This review discusses how the combination of two novel technologies - organoids and gene editing - not only contributes to revealing molecular events taking place during development and tumorigenesis but also has implications for biobanking, precision medicine, and other diverse biomedical applications.

Advances in Engineering Human Tissue Models

Research in cell biology greatly relies on cell-based in vitro assays and models that facilitate the investigation and understanding of specific biological events and processes under different conditions. The quality of such experimental models and particularly the level at which they represent cell behavior in the native tissue, is of critical importance for our understanding of cell interactions within tissues and organs. Conventionally, in vitro models are based on experimental manipulation of mammalian cells, grown as monolayers on flat, two-dimensional (2D) substrates. Despite the amazing progress and discoveries achieved with flat biology models, our ability to translate biological insights has been limited, since the 2D environment does not reflect the physiological behavior of cells in real tissues. Advances in 3D cell biology and engineering have led to the development of a new generation of cell culture formats that can better recapitulate the in vivo microenvironment, allowing us to examine cells and their interactions in a more biomimetic context. Modern biomedical research has at its disposal novel technological approaches that promote development of more sophisticated and robust tissue engineering in vitro models, including scaffold- or hydrogel-based formats, organotypic cultures, and organs-on-chips. Even though such systems are necessarily simplified to capture a particular range of physiology, their ability to model specific processes of human biology is greatly valued for their potential to close the gap between conventional animal studies and human (patho-) physiology. Here, we review recent advances in 3D biomimetic cultures, focusing on the technological bricks available to develop more physiologically relevant in vitro models of human tissues. By highlighting applications and examples of several physiological and disease models, we identify the limitations and challenges which the field needs to address in order to more effectively incorporate synthetic biomimetic culture platforms into biomedical research.

The Role of Organoids as a Novel Platform for Modeling of Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is a chronic relapsing-remitting immune-mediated disorder affecting the gut. It is common in Westernized regions and is increasing in incidence in developing countries. At a molecular level, intrinsic deficiencies in epithelial integrity, mucosal barrier function, and mechanisms of immune response and resolution contribute to the development of IBD. Traditionally two platforms have been utilized for disease modeling of IBD; in-vitro monolayer cell culture and in-vivo animal models. Both models have limitations, including cost, lack of representative cell types, lack of complexity of cellular interactions in a living organism, and xenogeneity. Organoids, three-dimensional cellular structures which recapitulate the basic architecture and functional processes of the organ of origin, hold potential as a third platform with which to investigate the pathogenesis and molecular defects which give rise to IBD. Organoids retain the genetic and transcriptomic profile of the tissue of origin over time and unlike monolayer cell culture can be induced to differentiate into most adult intestinal cell types. They may be used to model intestinal host-microbe interactions occurring at the mucosal barrier, are amenable to genetic manipulation and can be co-cultured with other cell lines of interest. Bioengineering approaches may be applied to render a more faithful representation of the intestinal epithelial niche. In this review, we outline the concept of intestinal organoids, discuss the advantages and disadvantages of the platform comparative to alternative models, and describe the translational applications of organoids in IBD.

Engineering organoids

Organoids are in vitro miniaturized and simplified model systems of organs that have gained enormous interest for modelling tissue development and disease, and for personalized medicine, drug screening and cell therapy. Despite considerable success in culturing physiologically relevant organoids, challenges remain to achieve real-life applications. In particular, the high variability of self-organizing growth and restricted experimental and analytical access hamper the translatability of organoid systems. In this Review, we argue that many limitations of traditional organoid culture can be addressed by engineering approaches at all levels of organoid systems. We investigate cell surface and genetic engineering approaches, and discuss stem cell niche engineering based on the design of matrices that allow spatiotemporal control of organoid growth and shape-guided morphogenesis. We examine how microfluidic approaches and lessons learnt from organs-on-a-chip enable the integration of mechano-physiological parameters and increase accessibility of organoids to improve functional readouts. Applying engineering principles to organoids increases reproducibility and provides experimental control, which will, ultimately, be required to enable clinical translation.

Immunocompetent Human Intestinal Models in Preclinical Drug Development

The intestinal epithelial barrier, together with the microbiome and local immune system, is a critical component that maintains intestinal homeostasis. Dysfunction may lead to chronic inflammation, as observed in inflammatory bowel diseases. Animal models have historically been used in preclinical research to identify and validate new drug targets in intestinal inflammatory diseases. Yet, limitations about their biological relevance to humans and advances in tissue engineering have forced the development of more complex three-dimensional reconstructed intestinal epithelium. By introducing immune and commensal microbial cells, these models more accurately mimic the gut's physiology and the pathophysiological changes occurring in vivo in the inflamed intestine. Specific advantages and limitations of two-dimensional (2D) and three-dimensional (3D) intestinal models such as coculture systems, organoids, and microfluidic devices to study inflammatory and immune-related responses are highlighted. While current cell culture models lack the cellular and molecular complexity observed in vivo, the emphasis is put on how these models can be used to improve preclinical drug development for inflammatory diseases of the intestine.

From 3D Back to 2D Monolayer Stomach Organoids-on-a-Chip

2D monolayer gastric organoids (2DMGOs)-on-a-chip have consistent structures and can live for more than a year in culture. This state-of-the-art cell physiological system in a microfluidic device provides a way to investigate biomedically relevant, stimuli-dependent cellular responses in a variety of differentiated 2DMGOs.

Building Scaffolds for Tubular Tissue Engineering

Hollow organs and tissue systems drive various functions in the body. Many of these hollow or tubular systems, such as vasculature, the intestines, and the trachea, are common targets for tissue engineering, given their relevance to numerous diseases and body functions. As the field of tissue engineering has developed, numerous benchtop models have been produced as platforms for basic science and drug testing. Production of tubular scaffolds for different tissue engineering applications possesses many commonalities, such as the necessity for producing an intact tubular opening and for formation of semi-permeable epithelia or endothelia. As such, the field has converged on a series of manufacturing techniques for producing these structures. In this review, we discuss some of the most common tissue engineered applications within the context of tubular tissues and the methods by which these structures can be produced. We provide an overview of the general structure and anatomy for these tissue systems along with a series of general design criteria for tubular tissue engineering. We categorize methods for manufacturing tubular scaffolds as follows: casting, electrospinning, rolling, 3D printing, and decellularization. We discuss state-of-the-art models within the context of vascular, intestinal, and tracheal tissue engineering. Finally, we conclude with a discussion of the future for these fields.

Organoid Models of Colorectal Pathology: Do They Hold the Key to Personalized Medicine? A Systematic Review

BACKGROUND

Colorectal cancer and IBD account for a large portion of the practice of colorectal surgery. Historical research models have provided insights into the underlying causes of these diseases but come with many limitations.

OBJECTIVE

The aim of this study was to systematically review the literature regarding the advantage of organoid models in modeling benign and malignant colorectal pathology.

DATA SOURCES

Sources included PubMed, Ovid-Medline, and Ovid Embase STUDY SELECTION:: Two reviewers completed a systematic review of the literature between January 2006 and January of 2020 for studies related to colon and intestinal organoids. Reviews, commentaries, protocols, and studies not performed in humans or mice were excluded.

RESULTS

A total of 73 articles were included. Organoid models of colorectal disease have been rising in popularity to further elucidate the genetic, transcriptomic, and treatment response of these diseases at the individual level. Increasingly complex models utilizing coculture techniques are being rapidly developed that allow in vitro recapitulation of the disease microenvironment.

LIMITATIONS

This review is only qualitative, and the lack of well utilized nomenclature in the organoid community may have resulted in the exclusion of articles.

CONCLUSIONS

Historical disease models including cell lines, patient-derived tumor xenografts, and animal models have created a strong foundation for our understanding of colorectal pathology. Recent advances in 3-dimensional cell cultures, in the form of patient-derived epithelial organoids and induced human intestinal organoids have opened a new avenue for high-resolution analysis of pathology at the level of an individual patient. Recent research has shown the potential of organoids as a tool for personalized medicine with their ability to retain patient characteristics, including treatment response.

InVitro Models of Intestine Innate Immunity

Animal models have delivered critical insights into mechanisms underlying the intestinal innate immune system; however, inherent differences exist between human and animal systems. To further understand the intestine innate immune system, there is a growing need for in vitro tissue model systems using human cells. A critical feature of in vitro cell and tissue models is the subepithelial environment, which contains additional cell types and includes 2D, microfluidic, organoid, and 3D tissue models. Where mouse models for the study of intestinal innate immune systems fall short, developments from in vitro models continue to grow in importance to aid efforts to understand this system in the context of disease and potential treatments.

Three-Dimensional Regeneration of Patient-Derived Intestinal Organoid Epithelium in a Physiodynamic Mucosal Interface-on-a-Chip

The regeneration of the mucosal interface of the human intestine is critical in the host-gut microbiome crosstalk associated with gastrointestinal diseases. The biopsy-derived intestinal organoids provide genetic information of patients with physiological cytodifferentiation. However, the enclosed lumen and static culture condition substantially limit the utility of patient-derived organoids for microbiome-associated disease modeling. Here, we report a patient-specific three-dimensional (3D) physiodynamic mucosal interface-on-a-chip (PMI Chip) that provides a microphysiological intestinal milieu under defined biomechanics. The real-time imaging and computational simulation of the PMI Chip verified the recapitulation of non-linear luminal and microvascular flow that simulates the hydrodynamics in a living human gut. The multiaxial deformations in a convoluted microchannel not only induced dynamic cell strains but also enhanced particle mixing in the lumen microchannel. Under this physiodynamic condition, an organoid-derived epithelium obtained from the patients diagnosed with Crohn's disease, ulcerative colitis, or colorectal cancer independently formed 3D epithelial layers with disease-specific differentiations. Moreover, co-culture with the human fecal microbiome in an anoxic-oxic interface resulted in the formation of stochastic microcolonies without a loss of epithelial barrier function. We envision that the patient-specific PMI Chip that conveys genetic, epigenetic, and environmental factors of individual patients will potentially demonstrate the pathophysiological dynamics and complex host-microbiome crosstalk to target a patient-specific disease modeling.

Tools for probing host-bacteria interactions in the gut microenvironment: From molecular to cellular levels

Healthy function of the gut microenvironment is dependent on complex interactions between the bacteria of the microbiome, epithelial and immune (host) cells, and the surrounding tissue. Misregulation of these interactions is implicated in disease. A range of tools have been developed to study these interactions, from mechanistic studies to therapeutic evaluation. In this Digest, we highlight select tools at the cellular and molecular level for probing specific cell-microenvironment interactions. Approaches are overviewed for controlling and probing cell-cell interactions, from transwell and microfluidic devices to engineered bacterial peptidoglycan fragments, and cell-matrix interactions, from three-dimensional scaffolds to chemical handles for in situ modifications.

Enzymatic Degradation of Bombyx mori Silk Materials: A Review

As a biomaterial, silk presents unique features with a combination of excellent mechanical properties, biocompatibility, and biodegradability. The biodegradability aspects of silk biomaterials, especially with options to control the rate from short (days) to long (years) time frames in vivo, make this protein-based biopolymer a good candidate for developing biodegradable devices used for tissue repairs and tissue engineering, as well as medical device implants. Silk materials, including native silk fibers and a broad spectrum of regenerated silk materials, have been investigated in vitro and in vivo to demonstrate degradation by proteolytic enzymes. In this Review, we summarize the findings on these studies on the enzymatic degradation of Bombyx mori (B. mori) silk materials. We also present a discussion on the factors that dictate the degradation properties of silk materials. Finally, in future perspectives, we highlight some key challenges and potential directions toward the future study of the degradation of silk materials.

Bi-layered Tubular Microfiber Scaffolds as Functional Templates for Engineering Human Intestinal Smooth Muscle Tissue

Designing biomimetic scaffolds with in vivo-like microenvironments using biomaterials is an essential component of successful tissue engineering approaches. The intestinal smooth muscle layers exhibit a complex tubular structure consisting of two concentric muscle layers in which the inner circular layer is orthogonally oriented to the outer longitudinal layer. Here, we present a three-dimensional (3D) bi-layered tubular scaffold based on flexible, mechanically robust and well aligned silk protein microfibers to mimic native human intestinal smooth muscle structure. The scaffolds were seeded with primary human intestinal smooth muscle cells to replicate human intestinal muscle tissues in vitro. Characterization of the tissue constructs revealed good biocompatibility and support for cell alignment and elongation in the different scaffold layers to enhance cell differentiation and functions. Furthermore, the engineered smooth muscle constructs supported oriented neurite outgrowth, a requisite step to achieve functional innervation. These results suggested these microfiber scaffolds as functional templates for in vitro regeneration of human intestinal smooth muscle systems. The scaffolding provides a crucial step toward engineering functional human intestinal tissue in vitro, as well as for the engineering of many other types of smooth muscles in terms of their similar phenotypes. Such utility may lead to a better understanding of smooth muscle associated diseases and treatments.

Organoids to study immune functions, immunological diseases and immunotherapy

Three-dimensional organoid culture systems show great promise as innovative physiological and pathophysiological models. Their applications in immunological research have been widely explored. For instance, immune organoids allow functional studies of immune system-related conditions, in a context that closely mimics the in vivo microenvironment, enabling an in-depth understanding of the immune tissue structures and functions. The newly developed coculture organoid and the air-liquid interface (ALI) systems also provided new insights for studying epithelia-immune cell interactions based on their endogenous distribution. Additionally, organoids have enabled the innovation of immunological disease models and exploration of the link between immunity and cancer, showing potential for personalized immunotherapy. This review is an overview of recent advances in the application of organoids in immunological research. Furthermore, the potential improvements for further utilization of organoids in personalized immunotherapy are discussed.

A simple three-dimensional gut model constructed in a restricted ductal microspace induces intestinal epithelial cell integrity and facilitates absorption assays

A new 3D gut-on-a-chip on a ductal scaffold induced a differentiated epithelial layer and allowed permeability and absorption assay.