类器官构建与培养：高级模型综合指南

以下为英文全文（English full text）

1. Introduction to Organoid Technology

Organoid technology has emerged as one of the most transformative and revolutionary advances in modern biomedical research, effectively bridging the persistent gap between traditional two-dimensional (2D) cell culture systems and complex in vivo animal models. Organoids are defined as three-dimensional (3D), self-organizing tissue structures that are derived from stem cells and that recapitulate key architectural, cellular, and functional features of their corresponding native organs in vivo. Unlike conventional immortalized cell lines, which often undergo genetic drift and fail to capture the full cellular diversity of tissues, organoids maintain the genetic stability of their donor tissues while simultaneously exhibiting remarkable cellular heterogeneity, tissue-level organization, and physiologically relevant structural complexity. These unique characteristics make organoids indispensable platforms for fundamental research in developmental biology, disease modeling, drug discovery, toxicity screening, personalized medicine, and regenerative medicine [1,2].

The concept of organoid culture is rooted in the pioneering understanding of stem cell biology and the identification of adult stem cell populations that reside within tissue-specific niches. The landmark publication by Sato and Clevers in 2009 demonstrated that single Lgr5-positive intestinal stem cells, when embedded in a basement membrane matrix (Matrigel) and provided with appropriate niche signals, could self-organize into complex crypt-villus structures that closely mimicked the native small intestinal epithelium [1]. This breakthrough not only established the feasibility of long-term 3D epithelial culture but also revealed that the essential components of the stem cell niche could be recapitulated in vitro using a defined set of growth factors and signaling molecules. Since this foundational work, the field has expanded exponentially, with organoid systems now established for virtually every major organ system, including the intestine, colon, stomach, brain, liver, lung, kidney, pancreas, prostate, breast, and retina [2,3].

2. Historical Development and Evolution of Organoid Technology

The historical trajectory of organoid technology can be traced through several distinct phases of innovation, each building upon advances in stem cell biology, developmental biology, and biomaterials science. The earliest precursors to modern organoid culture can be found in classical embryology experiments demonstrating that dissociated cells could re-aggregate and form organized structures. However, the modern era of organoid technology was inaugurated by the convergence of three critical advances: (1) the identification of specific adult stem cell markers such as Lgr5, (2) the development of defined basement membrane matrices that support 3D cell growth, and (3) the systematic elucidation of niche signaling pathways that govern stem cell self-renewal and differentiation.

The discovery of Lgr5 as a marker for active cycling stem cells in the intestinal epithelium by Hans Clevers and colleagues in 2007 provided the essential tool for isolating and characterizing the stem cell population responsible for the remarkable regenerative capacity of the intestinal epithelium [4]. This discovery was rapidly followed by the demonstration that single Lgr5+ cells could generate entire crypt-villus organoids in Matrigel when cultured with the appropriate combination of growth factors, as reported by Sato and colleagues in 2009 [1]. The culture conditions were based on a sophisticated understanding of the intestinal stem cell niche: Wnt signaling (provided by R-spondin 1, a potent Wnt pathway agonist), EGF signaling (essential for proliferation), and BMP inhibition (provided by Noggin, which prevents differentiation and maintains stemness). This foundational work was subsequently extended to human tissues, where Sato and colleagues in 2011 demonstrated that human intestinal crypts could similarly form organoid structures, though human organoids required additional small molecules including nicotinamide, A83-01 (a TGF-β receptor inhibitor), and SB202190 (a p38 MAPK inhibitor) to overcome the increased sensitivity of human epithelial cells to anoikis and culture-induced stress [3].

Parallel and complementary advances in pluripotent stem cell biology catalyzed the development of a second major branch of organoid technology: the generation of organoids from embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs). The landmark work by Lancaster and Knoblich in 2013 demonstrated that human PSCs, when cultured in a minimal medium under conditions that suppressed non-neural fates, could spontaneously differentiate into complex cerebral organoids that developed layered structures resembling the developing human cerebral cortex, complete with neural progenitors, neurons, and glial cells [5]. This self-patterning approach, which relies on the intrinsic developmental programs of PSCs rather than exogenous morphogen gradients, was rapidly adapted for other organ systems. For the liver, Huch and colleagues in 2013 established protocols for the expansion of bipotent adult hepatoblasts (liver progenitors) into organoids that could be maintained indefinitely and directed to differentiate into either functional hepatocytes or cholangiocytes (biliary epithelial cells) [6]. These advances demonstrated that organoid technology could be applied to both adult stem cells and pluripotent stem cells, each approach offering distinct advantages for different research applications.

3. Sources of Organoids: iPSCs versus Adult Stem Cells

Organoids can be generated from two fundamentally different cellular sources: pluripotent stem cells (PSCs), which encompass both embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), and adult stem cells (ASCs), which are tissue-resident stem cells responsible for physiological tissue turnover and regeneration. The choice between these two sources has profound implications for the experimental design, the time required for organoid generation, the genetic background of the resulting organoids, and the spectrum of research applications for which they are suited.

3.1 Pluripotent Stem Cell-Derived Organoids

Pluripotent stem cells provide a theoretically unlimited and renewable source of cells for organoid generation. ESCs are derived from the inner cell mass of blastocyst-stage embryos and represent the canonical pluripotent cell type, while iPSCs are generated by reprogramming somatic cells (such as skin fibroblasts or peripheral blood mononuclear cells) to a pluripotent state through the ectopic expression of transcription factors (typically Oct4, Sox2, Klf4, and c-Myc, collectively known as the Yamanaka factors) [7]. The capacity to generate iPSCs from any individual patient has revolutionized disease modeling, as it enables the creation of patient-specific organoids that carry the complete genetic background of the donor, including disease-causing mutations, protective alleles, and the full spectrum of genetic modifiers that influence disease phenotype and drug response [7,8].

The directed differentiation of PSCs into organoids follows a systematic recapitulation of embryonic developmental pathways. For endoderm-derived organs (intestine, liver, lung, pancreas), the differentiation protocol typically begins with the induction of definitive endoderm using Activin A, a TGF-β family member that activates Nodal signaling. This is followed by regional specification of the endoderm into anterior, posterior, or lateral domains through the application of specific morphogen combinations. For example, intestinal organoids from PSCs require Activin A to induce definitive endoderm, followed by FGF4 and Wnt3a (or the GSK-3β inhibitor CHIR99021) for hindgut specification, before the cells are embedded in Matrigel and cultured with EGF, Noggin, and R-spondin 1 to promote organoid outgrowth [9]. For the brain, PSCs exhibit an intrinsic neural bias, and cerebral organoids can be generated with minimal exogenous patterning, though specific regional identities (dorsal forebrain, ventral forebrain, midbrain, cerebellum) can be directed through the addition of morphogens such as sonic hedgehog (SHH), retinoic acid, or BMPs [5].

The primary advantages of PSC-derived organoids include: (1) the ability to model patient-specific genetic diseases, (2) access to developmental stages that are difficult to study in adult tissues, (3) the capacity for genetic engineering using CRISPR-Cas9 before differentiation, and (4) the generation of large numbers of organoids with consistent genetic backgrounds. However, PSC-derived organoids also have limitations: the differentiation process is lengthy (typically 30–90 days for mature organoids), the efficiency of directed differentiation can vary between cell lines, and the resulting organoids may not fully replicate the mature tissue architecture of adult organs.

3.2 Adult Stem Cell-Derived Organoids

Adult stem cell-derived organoids are established directly from tissue-resident stem cells that can be identified and isolated based on specific cell surface markers or anatomical location. In the intestine, Lgr5 marks the crypt base columnar cells that serve as active stem cells. In the liver, Sox9-positive ductal cells contain bipotent progenitors capable of generating both hepatocytes and cholangiocytes. In the lung, basal cells (p63-positive) serve as stem cells for the airway epithelium, while alveolar type 2 (AT2) cells function as stem cells for the alveolar epithelium [1,6,10].

The primary advantage of ASC-derived organoids is their direct derivation from mature, physiologically relevant tissue. Because they are generated from the native stem cell population that maintains the tissue in vivo, ASC organoids inherently recapitulate the adult tissue architecture, cell-type composition, and functional characteristics of the mature organ [3]. They can typically be established much more rapidly than PSC-derived organoids, often within 1–2 weeks of tissue collection, and they exhibit robust long-term expansion potential. Murine liver organoids, for example, have been maintained in continuous culture for over 24 months without loss of genetic stability or differentiation potential, and they retain normal karyotypes with polyploidy as the only deviation, which is a normal physiological feature of hepatocytes [6].

However, ASC-derived organoids are limited to tissues that contain identifiable and accessible stem cell populations. They cannot be easily generated from tissues with low stem cell abundance, from patients with severe tissue damage or fibrosis, or from organs where the stem cell niche is poorly understood. Furthermore, ASC organoids reflect the adult tissue state and may not be suitable for modeling developmental disorders or early embryonic processes. In cases where ASC-derived organoids are not feasible, PSC-derived organoids offer an alternative approach that can be engineered to carry specific genetic mutations or to model developmental stages [8].

4. Key Growth Factors and Signaling Pathways in Organoid Culture

The successful construction, maintenance, and directed differentiation of organoids depend fundamentally on the precise recapitulation of the stem cell niche signaling environment. The stem cell niche is the specialized microenvironment that provides the signals necessary for stem cell self-renewal, proliferation, and fate determination. In organoid culture, the niche is recreated through the addition of purified growth factors, small molecule inhibitors, and hormones to the culture medium. The following growth factors and signaling modulators constitute the essential components of most organoid culture systems, and their concentrations, combinations, and timing must be carefully optimized for each organoid type.

4.1 Wnt Signaling and R-spondin: The Master Regulators of Stemness

Wnt signaling is arguably the most critical pathway for stem cell self-renewal in epithelial tissues. In the canonical Wnt pathway, Wnt ligands bind to Frizzled receptors and LRP5/6 co-receptors, leading to the inhibition of the β-catenin destruction complex and the accumulation of nuclear β-catenin, which drives the transcription of target genes involved in proliferation and stem cell maintenance. In organoid culture, Wnt signaling is activated by the addition of Wnt3a (typically 100–200 ng/mL) and is dramatically amplified by R-spondin family proteins, which function as ligands for the Lgr family of receptors (Lgr4, Lgr5, Lgr6) and promote the clearance of Frizzled receptors from the cell surface, thereby sensitizing the cells to Wnt signals [1,11].

R-spondin 1 is the most commonly used family member in organoid culture, typically at concentrations of 0.5–1 µg/mL for human organoids. The concentration of R-spondin 1 must be carefully titrated: too little leads to stem cell exhaustion and organoid death, while too much can promote hyperproliferation and impaired differentiation. For many organoid types, conditioned medium from R-spondin-producing cell lines (such as the L-WRN cell line, which secretes Wnt3a, R-spondin 3, and Noggin) is used as a cost-effective alternative to purified recombinant proteins. However, conditioned medium contains undefined components that can introduce batch-to-batch variability. Recent advances have enabled the production of highly pure recombinant R-spondin 1 and Gremlin 1 from bacterial expression systems with defined cellular activities, improving the reproducibility of organoid culture media [11].

The strategic manipulation of Wnt signaling is also used to direct differentiation. For example, in liver organoid culture, the withdrawal of R-spondin 1 and Wnt3a drives hepatocyte differentiation, while maintaining Wnt signaling promotes the expansion of bipotent progenitors [6]. Similarly, in lung organoid culture, CHIR99021 (a GSK-3β inhibitor that activates Wnt signaling downstream of the receptor) is used at 3–10 µM during the initial stages of mesoderm specification and lung progenitor formation, but is subsequently withdrawn or reduced to promote terminal differentiation [12].

4.2 EGF and FGF Family Members: Mitogens for Proliferation and Patterning

Epidermal growth factor (EGF) is a universal mitogen for epithelial organoids and is required for the proliferation of stem cells and transit-amplifying cells across virtually all organoid systems. EGF binds to the EGF receptor (EGFR), a receptor tyrosine kinase that activates downstream MAPK/ERK signaling, promoting cell cycle progression and survival. In organoid culture, EGF is typically used at concentrations of 25–100 ng/mL, depending on the tissue type. Intestinal, liver, and pancreatic organoids all require EGF for sustained expansion [1,6,13].

Fibroblast growth factors (FGFs) play more specialized and context-dependent roles depending on the organ system. FGF10 is critical for the expansion of liver organoid progenitors (used at 100 ng/mL) and promotes the proliferation of hepatoblasts [6]. In lung organoid protocols, FGF7 and FGF10 are used to maintain airway and alveolar progenitors, respectively, with FGF10 promoting distal lung bud tip identity and FGF7 supporting airway epithelial expansion [12]. FGF9 is essential for kidney organoid differentiation, driving the specification of metanephric mesenchyme from intermediate mesoderm and maintaining nephron progenitor cells [14]. FGF4, in combination with Wnt signaling, is used to specify hindgut fate in PSC-derived intestinal organoids [9]. The specific FGF family member and concentration must be tailored to the organoid type and the desired developmental stage.

4.3 BMP Signaling and Noggin: The Brake on Differentiation

Bone morphogenetic protein (BMP) signaling promotes the differentiation of epithelial stem cells and the maturation of specialized cell types. In the native intestinal epithelium, BMP is expressed by the mesenchyme surrounding the crypt and acts as a gradient that prevents stem cell expansion outside the crypt base. In organoid culture, BMP signaling must be actively inhibited to maintain the stem cell state and prevent premature differentiation. Noggin, a potent secreted BMP antagonist that binds BMP ligands and prevents their interaction with receptors, is a staple component of virtually all organoid culture media, typically used at concentrations of 25–100 ng/mL [1,11].

Gremlin 1, another BMP inhibitor that acts through a distinct mechanism, can functionally substitute for Noggin in organoid culture. Urbischek and colleagues demonstrated that recombinant Gremlin 1 at 10–25 nM sustains intestinal organoid growth for at least 20 serial passages, and that bacterially-derived recombinant Gremlin 1 and R-spondin 1 can be produced with negligible endotoxin levels and defined cellular activities, providing a more reproducible and cost-effective alternative to eukaryotic expression systems [11].

The strategic withdrawal of BMP inhibition is used as a differentiation cue in many organoid systems. For example, removal of Noggin from liver organoid media promotes cholangiocyte differentiation, while removal from intestinal organoid media drives differentiation toward mature epithelial lineages including enterocytes, goblet cells, and enteroendocrine cells [6]. The timing and extent of BMP inhibition withdrawal must be carefully controlled to achieve the desired balance between stem cell maintenance and differentiation.

4.4 Additional Critical Components of Organoid Culture Media

• N-acetylcysteine (1–1.25 mM): A potent antioxidant and mucolytic agent that reduces oxidative stress and promotes organoid formation. N-acetylcysteine is particularly important for human organoids, which are more sensitive to oxidative stress than their murine counterparts [3].
• Nicotinamide (10 mM): A form of vitamin B3 that enhances organoid formation by suppressing sirtuin activity and promoting cellular metabolism. Nicotinamide is particularly important for the establishment and long-term culture of human liver and intestinal organoids, where it stabilizes cultures and extends organoid lifespan [6,13].
• Gastrin (1–10 nM): A gastrointestinal peptide hormone that stimulates the proliferation of gastric and intestinal stem cells. Gastrin is included in human intestinal and gastric organoid media to promote epithelial growth and crypt formation [3].
• A83-01 (0.5–5 µM): A selective inhibitor of the TGF-β type I receptor (ALK4/5/7) that prevents TGF-β-mediated epithelial-mesenchymal transition and apoptosis. A83-01 is essential for the culture of human intestinal, liver, and pancreatic organoids, where it stabilizes epithelial identity and prevents the acquisition of mesenchymal features [3,6].
• Y-27632 (10 µM): A pharmacological inhibitor of ROCK (Rho-associated coiled-coil-containing protein kinase) that prevents anoikis (detachment-induced apoptosis) during the initial seeding of single cells or small organoid fragments. Y-27632 is typically included only for the first 48 hours after passaging or single-cell plating [14,15].
• HGF (25–50 ng/mL): Hepatocyte growth factor is a potent mitogen for hepatocytes and a key component of liver organoid expansion media. HGF promotes hepatocyte proliferation and survival, and its withdrawal during differentiation promotes the maturation of hepatocyte-like cells [6].
• Forskolin (10 µM): An adenylate cyclase activator that increases intracellular cAMP levels. Forskolin is included in liver organoid initiation and expansion media to promote biliary differentiation and enhance organoid formation [6].
• DAPT (10 nM–10 µM): A γ-secretase inhibitor that indirectly inhibits Notch signaling. DAPT is used to promote hepatocyte differentiation in liver organoids and to drive goblet and enteroendocrine cell differentiation in intestinal organoids [6,13].
• Dexamethasone (1–30 µM): A synthetic glucocorticoid that activates the glucocorticoid receptor and drives terminal differentiation of hepatocytes. Dexamethasone is typically added during the final 3 days of hepatocyte differentiation to promote the expression of mature hepatocyte markers and functions [6].

5. Extracellular Matrix: The Role of Matrigel and Defined Alternatives

The three-dimensional extracellular matrix (ECM) is not merely a passive scaffold for organoid culture; it is an active signaling environment that provides biochemical cues, mechanical support, and spatial organization essential for cell polarization, lumen formation, and tissue-level morphogenesis. The choice of ECM profoundly influences organoid formation efficiency, morphology, and functional maturation.

5.1 Matrigel: The Gold Standard Basement Membrane Matrix

Matrigel, a solubilized basement membrane preparation derived from the Engelbreth-Holm-Swarm (EHS) mouse sarcoma, is the most widely used ECM for organoid culture [1,16]. Matrigel is rich in laminin (primarily laminin-111), collagen IV, entactin (nidogen), and heparan sulfate proteoglycans (including perlecan), and it polymerizes at 37°C to form a gel that supports cell adhesion, migration, polarization, and basement membrane deposition. The growth factor content of standard Matrigel includes TGF-β, EGF, IGF, FGF, and other bioactive molecules that can influence organoid behavior.

The typical working concentration for organoid culture is 50–100% Matrigel, with organoids embedded as droplets in 10–50 µL volumes per well of a 24-well plate. The Matrigel is kept on ice at all times before polymerization to prevent premature gelation, and it is polymerized at 37°C for 10–15 minutes before the addition of culture medium [1,3]. The thickness and shape of the Matrigel droplet can influence organoid morphology: thinner droplets promote the formation of monolayer-like structures, while thicker droplets favor the development of multilayered, cystic organoids.

However, Matrigel has several significant limitations that have motivated the development of alternative matrices. First, Matrigel is derived from mouse tumors, raising concerns about xenogeneic components and the potential for immune responses in transplantation applications. Second, Matrigel exhibits significant batch-to-batch variability in protein composition, growth factor content, and mechanical properties, which can introduce experimental variability and reduce reproducibility. Third, Matrigel contains undefined components that complicate the mechanistic interpretation of experimental results. Fourth, the ethical and regulatory concerns associated with tumor-derived products limit the suitability of Matrigel for clinical applications and regenerative medicine [16].

5.2 Growth Factor-Reduced and Phenol-Free Matrigel Variants

To address some of the limitations of standard Matrigel, growth factor-reduced (GFR) and phenol-free variants have been developed. GFR Matrigel has significantly reduced levels of TGF-β, EGF, and other growth factors, allowing researchers to control the signaling environment more precisely. Phenol-free Matrigel improves optical clarity for imaging applications. For most organoid applications, GFR Matrigel is the preferred substrate because it minimizes the confounding effects of undefined growth factors while retaining the essential basement membrane components [1,16].

5.3 Defined Basement Membrane Extracts

Cultrex UltiMatrix RGF BME is a growth factor-reduced basement membrane extract that has been developed as an alternative to Matrigel with reduced lot-to-lot variability and improved performance for certain organoid types. This matrix supports the growth of intestinal, liver, and kidney organoids and has been validated for both research and bioproduction applications [16].

5.4 Synthetic and Designer Hydrogels

The development of synthetic hydrogels represents a major advance toward fully defined, customizable, and clinically compatible organoid culture matrices. Peptide-based hydrogels, polyethylene glycol (PEG) hydrogels, and hyaluronic acid-based matrices can be engineered with specific mechanical properties (stiffness, elasticity), adhesion ligands (RGD peptides, laminin-derived sequences), and degradability profiles [17]. These designer matrices enable precise control over the biochemical and biophysical cues that govern organoid development.

For example, Gjorevski and colleagues demonstrated that a synthetic PEG hydrogel functionalized with laminin-derived peptides and RGD sequences could support intestinal stem cell and organoid culture with comparable efficiency to Matrigel, while providing independent control over stiffness, ligand density, and proteolytic degradability [17]. The stiffness of the ECM was found to profoundly influence organoid morphology: softer matrices (elastic modulus ~100–300 Pa) favored the formation of budding organoids with crypt-like domains, while stiffer matrices promoted cystic morphologies. This level of control is not achievable with Matrigel and opens new avenues for investigating the mechanobiology of organoid development.

Synthetic hydrogels are also essential for organoid-on-chip applications, where the matrix must be compatible with microfabrication processes and microfluidic perfusion. In organ-on-chip devices, the ECM is typically deposited as a thin layer on a porous membrane, and the mechanical properties of the matrix must be precisely tuned to support epithelial polarization and barrier formation while allowing tissue-tissue interaction and mechanical stimulation [18].

5.5 Laminin-511 and Other Defined Laminins

Laminin-511 is a specific laminin isoform that is highly expressed in the basement membrane of the intestinal epithelium and other tissues. Recombinant laminin-511 produced in mammalian cells has been shown to support intestinal organoid culture as a defined alternative to Matrigel. Laminin-511 provides the integrin-binding sites (primarily through the α5β1 integrin) that are essential for intestinal stem cell adhesion and survival, and it can be used as a clinical-grade substrate for applications involving patient-derived organoids or regenerative transplantation [17].

6. Standard Operating Procedures for Organoid Culture

The establishment and maintenance of organoid cultures require meticulous attention to sterile technique, reagent quality, timing, and environmental conditions. The following standard operating procedures (SOPs) provide a general framework that can be adapted for specific organoid types.

6.1 Tissue Procurement and Initial Processing

Fresh tissue samples should be processed as soon as possible after collection to maximize cell viability and minimize ischemic damage. For most tissues, a processing time of less than 6 hours is ideal, though acceptable results can be obtained with tissues processed within 24 hours if stored at 4°C in an appropriate transport medium. For intestinal organoids, the tissue is washed extensively with ice-cold PBS containing antibiotics, opened longitudinally, and the mucosal layer is either scraped or incubated with 10 mM EDTA in PBS at 4°C for 30–90 minutes to release crypts [3]. For solid tissues such as liver, pancreas, or tumor samples, enzymatic digestion with collagenase, dispase, or Liberase is required to dissociate the tissue into single cells or small epithelial fragments [6].

The transport medium for tissue specimens typically consists of Advanced DMEM/F12 supplemented with 10% fetal bovine serum (FBS), 1% Penicillin/Streptomycin, and 100 µg/mL Primocin (a broad-spectrum antibiotic effective against bacteria, fungi, and mycoplasmas). For extended transport times (>24 hours), specialized hypothermic storage solutions such as HypoThermosol FRS may provide improved cell viability compared to standard media [3].

6.2 Crypt and Stem Cell Isolation

After appropriate tissue processing, stem cells or crypts are isolated by mechanical and/or enzymatic methods. For intestinal tissues, EDTA chelation disrupts the calcium-dependent adhesion complexes that anchor crypts to the underlying basement membrane, allowing crypts to be released by mechanical agitation (vigorous pipetting or shaking). The crypt suspension is collected and passed through a 70–100 µm cell strainer to remove debris, tissue fragments, and single cells that may not efficiently form organoids. The filtered crypts are then collected by centrifugation at 200–300 × g for 5 minutes at 4°C, and the pellet is resuspended in cold Matrigel for embedding [3].

For tissues that require enzymatic dissociation, the digestion time and enzyme concentration must be carefully optimized to achieve the desired cell cluster size. Over-digestion can damage stem cells and reduce organoid formation efficiency, while under-digestion results in large tissue fragments that may not properly embed in the matrix. The digestion is typically stopped by adding an equal volume of cold DMEM/F12 containing 10% FBS, and the cells are filtered and collected by centrifugation.

6.3 Embedding and Plating

The embedding of cells in the ECM matrix is one of the most technically demanding steps in organoid culture and requires careful attention to temperature and timing. Matrigel and similar basement membrane extracts polymerize rapidly at temperatures above 10°C, so all pipette tips, tubes, and plates must be pre-cooled on ice. The isolated crypts or cells are resuspended in cold Matrigel at a density of 50–200 crypts per 30–50 µL droplet (for 24-well format). Higher densities can lead to overcrowding and fusion of organoids, while lower densities may result in poor organoid formation due to insufficient cell-cell signaling.

The cell-Matrigel suspension is plated as a dome in the center of each pre-warmed well of a 24-well plate. The dome should be compact and should not touch the sides of the well, as contact with the plastic surface can promote cell adhesion and disrupt 3D organization. The plate is immediately transferred to a 37°C incubator with 5% CO2 and incubated for 10–15 minutes to allow the Matrigel to polymerize. After polymerization, pre-warmed culture medium (500–750 µL per well for 24-well format) is gently added to the side of the well, taking care not to dislodge the Matrigel dome [1,3].

6.4 Culture Medium Formulation and Changes

The complete organoid medium is prepared from an Advanced DMEM/F12 base supplemented with B27 and N2 supplements (which provide essential fatty acids, cholesterol, antioxidants, and trace elements), GlutaMAX (a stabilized form of L-glutamine), HEPES (a buffer that maintains pH in ambient CO2 conditions during handling), and antibiotics. The specific growth factors, inhibitors, and hormones are added fresh to aliquots of basal medium immediately before use. Medium should be prepared in small batches to ensure freshness, and growth factors should be stored at −80°C in single-use aliquots to prevent repeated freeze-thaw cycles that degrade protein activity.

Medium changes are typically performed every 2–3 days by carefully aspirating the old medium from the side of the well and adding fresh pre-warmed medium. The Matrigel dome should not be disturbed during medium changes, as mechanical disruption can damage the organoids or cause them to detach from the matrix. For organoids that produce large amounts of mucus or debris (such as intestinal organoids), more frequent medium changes may be necessary to prevent accumulation of waste products and maintain optimal pH.

6.5 Passaging and Expansion

Organoids are passaged when they reach high density (typically filling 70–100% of the Matrigel dome) or when the culture medium begins to turn yellow due to acidification. The passaging interval varies by organoid type: intestinal organoids typically require passage every 5–10 days, liver organoids every 7–14 days, and brain organoids every 10–14 days. The passaging ratio (the ratio of old culture to new culture) is typically 1:3 to 1:6 for intestinal organoids and 1:3 to 1:4 for human organoids, though this can be adjusted based on the growth rate and experimental needs.

The passaging protocol involves mechanical disruption of the Matrigel dome followed by enzymatic or mechanical dissociation of the organoids into smaller fragments. For mechanical passaging, the Matrigel is broken into small pieces by scraping with a pipette tip, and the organoids are fragmented by vigorous pipetting in cold Advanced DMEM/F12. For enzymatic passaging, the organoids are incubated with TrypLE Express or Accutase at 37°C for 5–10 minutes to dissociate them into single cells or small clusters. After dissociation, the cells are centrifuged at 200–300 × g for 5 minutes, resuspended in fresh Matrigel, and re-plated at the desired ratio. For single-cell dissociation, 10 µM Y-27632 (ROCK inhibitor) should be included in the medium for the first 48 hours after plating to prevent anoikis and improve cell survival [3,15].

6.6 Cryopreservation and Banking

Organoid lines should be cryopreserved at regular intervals (typically every 5–10 passages) to create a backup stock and to facilitate the sharing of organoid lines between laboratories. Organoids at passages 2–10 are harvested by disrupting the Matrigel and collecting the organoids by centrifugation. The pellet is resuspended in cryopreservation medium consisting of 80% complete organoid medium, 10% fetal bovine serum (FBS), and 10% dimethyl sulfoxide (DMSO). The suspension is transferred to cryovials and placed in a freezing container at −80°C for a minimum of 24 hours before transfer to liquid nitrogen for long-term storage. The inclusion of Wnt3a, R-spondin, and Noggin in the freezing medium (via the use of 50% L-WRN conditioned medium as the base) improves post-thaw recovery by maintaining stem cell niche signals during the freeze-thaw process [3].

For thawing, cryovials are rapidly warmed in a 37°C water bath, and the contents are transferred to a tube containing pre-warmed complete medium. The cells are centrifuged, resuspended in fresh Matrigel, and plated as usual. Recovery rates vary by organoid type but typically range from 50–80% for well-established lines.

7. Quality Control and Quality Assurance in Organoid Culture

The implementation of rigorous quality control (QC) and quality assurance (QA) measures is essential for ensuring the reproducibility, reliability, and biological relevance of organoid-based experiments. Organoid cultures are living systems that can drift over time due to genetic instability, contamination, or selective pressures, and regular QC is necessary to detect and correct these issues before they compromise experimental results.

7.1 Morphological Assessment and Growth Monitoring

Organoid quality is first assessed by daily or every-other-day observation using an inverted brightfield microscope. Each organoid type has characteristic morphological features that indicate health and proper development. Healthy intestinal organoids exhibit a spherical or budding morphology with clearly defined crypt-like domains protruding from the surface. The central lumen indicates proper epithelial polarization and barrier formation. Liver organoids appear as compact, cystic, or solid structures depending on the differentiation state, with differentiated hepatocyte organoids becoming larger and more translucent [3,6]. Any signs of organoid darkening, fragmentation, vacuolization, or failure to form discrete structures indicate suboptimal culture conditions, contamination, or genetic instability.

Photographic documentation of organoid morphology at each passage provides a valuable record for tracking changes over time and identifying gradual drift in culture quality. Automated image analysis systems can be used to quantify organoid size, budding frequency, and other morphometric parameters for high-throughput monitoring.

7.2 Mycoplasma and Microbial Contamination Screening

All organoid cultures must be routinely tested for mycoplasma contamination using PCR-based detection, luminescence-based assays (such as MycoAlert), or direct culture methods. Mycoplasma contamination is a serious and often insidious problem in cell culture because the bacteria are too small to be detected by standard microscopy and do not cause obvious changes in medium pH. However, mycoplasma infection can profoundly alter cellular metabolism, gene expression, and growth characteristics, compromising the validity of experimental results. Organoid cultures should be tested monthly, and any contaminated cultures should be immediately discarded [3].

Bacterial and fungal contamination is prevented by the inclusion of antibiotics (Primocin, 100 µg/mL, or Penicillin/Streptomycin) during the initial culture period and by strict adherence to aseptic technique. However, long-term antibiotic use is not recommended for established cultures, as it can mask low-level contamination and promote the development of antibiotic-resistant organisms. All media and reagents should be filtered through 0.22 µm filters before use, and all equipment should be regularly sterilized.

7.3 Genetic Stability and Authentication

Long-term organoid cultures should be periodically monitored for chromosomal stability by karyotyping, fluorescence in situ hybridization (FISH), or single-nucleotide polymorphism (SNP) array analysis. While some degree of genetic drift is expected in rapidly proliferating cultures, significant aneuploidy or chromosomal rearrangements can alter organoid behavior and invalidate experimental comparisons. Murine liver organoids have been demonstrated to maintain normal diploid karyotypes after 24 months of continuous culture, with polyploidy (a normal physiological feature of hepatocytes) as the only expected deviation [6].

Organoid lines should be authenticated by short tandem repeat (STR) profiling and matched to the donor tissue to prevent cross-contamination or misidentification. For disease models, routine sequencing of the relevant mutation sites (e.g., KRAS, APC, TP53 for colorectal cancer organoids) is essential to confirm that the disease-causing genotype is maintained throughout passaging. Whole-exome sequencing (WES) can be performed at baseline and after extended culture to identify any acquired mutations that may have been selected during in vitro expansion [3,6].

7.4 Functional Validation and Phenotypic Characterization

Differentiated organoids must be validated for tissue-specific functions to ensure biological relevance. The specific validation assays depend on the organoid type and the intended application. For intestinal organoids, functional validation includes:

• Transepithelial Electrical Resistance (TEER): Measures the electrical resistance across the epithelial barrier, indicating the integrity of tight junctions. Normal intestinal organoids exhibit TEER values of 200–500 Ω·cm² [3].
• Forskolin-Induced Swelling (FIS): A functional assay for cystic fibrosis transmembrane conductance regulator (CFTR) activity. Addition of forskolin (10 µM) activates CFTR, leading to chloride secretion and water influx, causing visible organoid swelling within 1–4 hours. CFTR-deficient organoids from cystic fibrosis patients do not swell, while organoids with functional CFTR exhibit robust swelling that can be quantified by image analysis [3].
• Mucus Secretion and Barrier Function: Goblet cell differentiation can be assessed by mucin staining (MUC5AC, MUC2), and barrier integrity can be evaluated by permeability assays using fluorescent dextrans of different molecular weights [3].

For liver organoids, functional validation includes:

• Albumin Secretion: Measured by ELISA in the culture supernatant. Differentiated hepatocyte organoids should produce albumin at rates comparable to primary human hepatocytes (typically 1–10 µg/mL per day per 10^6 cells) [6].
• Urea Synthesis: Measured by colorimetric assay in the supernatant. Hepatocyte organoids should convert ammonia to urea via the urea cycle, demonstrating functional nitrogen metabolism [6].
• Cytochrome P450 Activity: Assessed using specific substrates for CYP1A2, CYP3A4, and CYP2C9. Activity should be inducible by prototypical inducers such as rifampicin (CYP3A4), 3-methylcholanthrene (CYP1A2), and phenobarbital (CYP2C9), demonstrating that the organoids possess functional drug metabolism capabilities [6,13].
• Bile Acid Transport: Assessed using taurocholate uptake and efflux assays. The apical efflux of bile acids via the bile salt export pump (BSEP) and the multidrug resistance protein 2 (MRP2) can be visualized by fluorescence microscopy and quantified by HPLC [6].
• Glycogen Storage: Detected by Periodic Acid-Schiff (PAS) staining in hepatocyte organoids, demonstrating the ability to store carbohydrates [6].

For brain organoids, functional validation includes electrophysiological recordings (patch-clamp to demonstrate action potential firing and spontaneous synaptic activity), calcium imaging (to reveal network-level spontaneous activity), and single-cell RNA sequencing (to confirm the presence of diverse neural and glial cell types) [5,15].

8. Applications of Organoid Technology in Biomedical Research

Organoid technology has found transformative applications across diverse fields of biomedical research, from fundamental developmental biology to clinical translational medicine. The following sections highlight the major application domains and their scientific and clinical significance.

8.1 Disease Modeling and Mechanistic Research

Patient-derived organoids recapitulate the histopathology, molecular features, and cellular heterogeneity of genetic diseases and cancers, providing unprecedented access to human disease biology. For genetic diseases, iPSC-derived organoids carrying disease-causing mutations can be generated and compared to isogenic control lines (corrected by CRISPR-Cas9) to identify disease mechanisms in a genetically controlled system. Examples include:

• Cystic Fibrosis: Intestinal organoids from CF patients exhibit defective CFTR function, as demonstrated by the absence of forskolin-induced swelling. These organoids have been used to validate CFTR modulators (ivacaftor, lumacaftor, tezacaftor) and to demonstrate genotype-specific drug responses [3].
• Polycystic Kidney Disease: Kidney organoids from PKD patients develop large cystic structures in proximal tubules and collecting ducts, providing a platform for screening cyst growth inhibitors such as octreotide, rapamycin, and CFTR inhibitors [14].
• Microcephaly: Brain organoids from microcephaly patients (e.g., with CDK5RAP2 mutations) exhibit reduced progenitor proliferation and premature neuronal differentiation, recapitulating the reduced brain size observed in patients [5].
• Familial Adenomatous Polyposis: Colorectal organoids from FAP patients with APC mutations exhibit constitutive Wnt activation and can be used to model adenoma progression and test chemopreventive strategies [1].

8.2 Drug Discovery and Toxicity Screening

Organoids provide physiologically relevant platforms for high-throughput drug screening that bridge the gap between 2D cell-based assays and animal models. The key advantages of organoids for drug screening include:

• Cellular Heterogeneity: Organoids contain multiple cell types, enabling the assessment of drug effects on both target cells and bystander cells, as well as the identification of off-target toxicities [2].
• Tissue Architecture: The 3D organization of organoids allows for the assessment of drug penetration, distribution, and local metabolism, which are not captured in 2D cultures [2].
• Patient-Specific Responses: Patient-derived organoids (PDOs) enable the prediction of individual patient responses to chemotherapy, targeted therapy, and immunotherapy, supporting personalized treatment selection [8,19].
• Genetic Context: The ability to generate isogenic organoid pairs (disease and corrected) enables the identification of genotype-specific drug sensitivities and resistance mechanisms [8].

High-throughput screening platforms have been developed for intestinal, liver, brain, and tumor organoids, using 96-well and 384-well formats compatible with automated liquid handling and imaging systems. Drug responses are typically assessed by viability assays (CellTiter-Glo, ATP assays), live/dead staining, or functional readouts (e.g., CFTR swelling for intestinal organoids, albumin secretion for liver organoids) [3,6].

8.3 Regenerative Medicine and Transplantation

The therapeutic potential of organoid transplantation is being actively explored for a range of tissue repair applications. The advantages of organoids over single-cell suspensions for transplantation include their pre-formed tissue architecture, which promotes survival and integration at the transplant site, and their cellular heterogeneity, which may provide the paracrine signals necessary for tissue regeneration. Current research directions include:

• Intestinal Organoid Transplantation: Small intestinal organoids have been transplanted into mouse models of necrotizing enterocolitis and radiation-induced mucosal injury, where they engraft and differentiate into functional epithelium, improving survival and mucosal integrity [3].
• Liver Organoid Transplantation: Hepatocyte-differentiated liver organoids have been transplanted into mouse models of metabolic liver disease (e.g., tyrosinemia, Wilson disease), where they partially correct the metabolic defect and improve liver function [6].
• Retinal Organoid Transplantation: Photoreceptor precursors derived from retinal organoids have been shown to integrate into the degenerating mouse retina and restore light responses, providing a proof-of-concept for cell replacement therapy in retinal degenerative diseases [2].

8.4 Organoid-on-Chip and Advanced Model Systems

The integration of organoids with microfluidic organ-on-chip devices represents a major frontier in the development of more physiologically relevant in vitro models. Organoid-on-chip systems combine the cellular complexity of organoids with the dynamic microenvironmental control of microfluidics, enabling the modeling of:

• Tissue-Tissue Interfaces: Co-culture of organoids with endothelial cells, fibroblasts, or immune cells in adjacent microchannels separated by porous membranes allows the study of cell-cell interactions, paracrine signaling, and barrier function [18].
• Mechanical Forces: Application of fluid shear stress, cyclic stretch, or compression to organoids mimics the mechanical environment of native tissues (e.g., blood flow in vessels, peristalsis in the intestine, breathing in the lung) and can profoundly influence cell behavior and differentiation [18].
• Vascular Perfusion: Microfluidic perfusion of organoids with culture medium or blood analogs improves nutrient delivery and oxygenation, reducing the necrosis that commonly occurs in the cores of large organoids and enabling extended culture for weeks to months [18].
• Multi-Organ Systems: Interconnection of multiple organoid-on-chip devices in a fluidic network allows the study of organ-organ interactions, drug absorption, distribution, metabolism, and excretion (ADME) in a human-relevant system [18].

GBiowit provides comprehensive organoid-on-chip platforms, including microfluidic devices specifically designed for co-culture with endothelial cells, immune cells, and stromal components, as well as integrated multi-organ systems for pharmacokinetic and pharmacodynamic studies.

9. Conclusion and Future Perspectives

Organoid technology represents a paradigm shift in how we model human biology in vitro, combining the experimental accessibility and scalability of cell culture with the cellular complexity and tissue-level organization that were previously only achievable in animal models. By carefully controlling the source of stem cells, the composition of the culture medium, the properties of the extracellular matrix, and the environmental conditions, researchers can generate organoids that faithfully recapitulate the structure, function, and disease phenotypes of their native organs.

The continued refinement of organoid technology will be driven by several key advances: the development of fully defined, synthetic matrices that eliminate the variability and xenogeneic concerns of Matrigel; the creation of immune-competent organoid models that incorporate tumor-infiltrating lymphocytes, macrophages, and other immune cells; the integration of organoids with advanced microfluidic and biosensor platforms for real-time monitoring of organoid physiology; and the establishment of clinical-grade organoid production pipelines that meet regulatory standards for cell therapy applications. As these technologies mature, organoids will play an increasingly central role in basic research, drug development, and personalized medicine.

GBiowit is committed to supporting the organoid research community with comprehensive solutions that span the entire organoid workflow. Our product portfolio includes defined culture media formulations with verified growth factor activities, Matrigel and synthetic matrix alternatives, complete organoid kits for major organ systems, and specialized reagents for quality control and functional validation. Our services include expert organoid modeling and culture support, high-throughput drug screening platforms, advanced organ-on-chip model development, and organoid biobanking solutions. For more information about our products and services, please visit www.gbiowit.com or contact our technical support team.

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