The technique, called continuous chaotic printing, relies on static mixers: passive elements with no moving parts that are inserted into extrusion printheads. As two or more inks flow through these elements under laminar conditions, the flow is repeatedly split, stretched, and reoriented. Each mixing element duplicates existing material interfaces, so the number of internal layers grows exponentially along the length of the mixer. Unlike approaches that demand microstructured nozzles, optical patterning systems, or external electric, magnetic, or acoustic fields, chaotic printing is inexpensive, scalable, and mathematically predictable—and it is gentle enough to handle fragile mammalian cells.

In the new study, the researchers pushed the platform beyond the traditional Kenics static mixer, testing three additional geometries borrowed from industrial chemical engineering: the Ross mixer, the Mini-SMX, and the full SMX. Each geometry stamps a distinctive microarchitectural fingerprint onto the printed filament. Kenics elements produce the familiar aligned, multilayered lamellae, reaching feature sizes of about 60 micrometers with four elements yielding 16 layers within roughly a millimeter. Ross-based constructs display asymmetric, wave- or flame-like architectures, while the Mini-SMX generates symmetric motifs reminiscent of flowers or radiant forms. The SMX mixer, evaluated with one and two elements, produces flame-like structures with pronounced segregation of the two ink phases toward opposite sides of the cross-section.

Critically, these patterns are not accidents. Computational fluid dynamics simulations of the flow at each mixer outlet closely mirrored the experimentally observed cross-sections of printed hydrogel fibers, confirming that chaotic advection under laminar flow is deterministic rather than stochastic. Complex spatial patterns emerge from repeated stretching and folding of fluid streams despite the absence of turbulence or any moving mechanical components. Under the printing conditions used—fluid viscosities close to that of water—the resulting microarchitectures are dictated primarily by mixer geometry and topology, not by random perturbations. That predictability means researchers can design an internal structure on a computer and expect to see it materialize in the printed filament.

The team also demonstrated the flexibility of the approach across three distinct deposition modes. In continuous wet-printing, filaments are extruded directly into a calcium chloride bath that crosslinks alginate. In dripping, discrete spherical constructs form by droplet detachment, yet the internal architecture survives the formation process intact. In direct ink writing, viscoelastic materials are patterned by pressure-driven extrusion into grid-like constructs, each filament retaining discernible internal microstructure. Reproducing such interleaved architectures by conventional extrusion printing would require ultra-fine nozzles and sequential layer-by-layer deposition of distinct domains, which is impractical for continuous filament fabrication. Chaotic printing achieves the same result in a single, high-throughput step.

Because the goal of chaotic printing differs fundamentally from classical mixing, the researchers reframed how mixer performance should be judged. In conventional applications, a static mixer is judged by how completely it homogenizes fluids, and mixers with higher Lyapunov exponents—measures of how rapidly neighboring fluid elements separate—such as the SMX are considered superior. In chaotic printing, the objective is not homogenization but the rapid generation of controlled interfacial area over short residence lengths. Quantifying the intermaterial perimeter separating red and green domains in printed cross-sections, the team found that interface growth is often approximately linear over the few mixing elements relevant to biofabrication, rather than exponential. The Kenics mixer was a notable exception, showing clear exponential growth consistent with its deterministic 2-to-the-n lamellar multiplication mechanism.

The fluid dynamics analysis revealed a fundamental trade-off. SMX-type mixers, with their intersecting baffle structures, generate the highest instantaneous rates of interface proliferation and the finest features, but they impose significantly larger pressure drops due to repeated obstruction and redirection of flow. The Ross mixer produces the sharpest velocity transitions and localized zones of accelerated flow near blade edges, which promote strong interface stretching but also create aggressive shear peaks. The Kenics geometry achieves effective flow reorientation with comparatively moderate pressure penalties and smoother shear distributions, making it particularly attractive for shear-sensitive living cells. The Mini-SMX emerged as a compelling middle ground, capable of high interface densities with a lower pressure cost than the full SMX design. The choice of mixer, the authors argue, should follow the architectural objective—feature size, structural regularity, energetic efficiency—rather than classical mixing metrics alone.

To prove the concept has biological teeth, the team turned to living systems. Caco-2 intestinal epithelial cells were printed within a blend of alginate and GelMA using a hollow tube, a three-element Kenics mixer, and a one-element SMX mixer. Cell viability remained high across all conditions at day one and day twenty after printing. More strikingly, constructs printed with the single-element SMX spontaneously developed organized multicellular clusters over three weeks, and immunofluorescence staining revealed expression of tissue-relevant markers including Villin and Vimentin, along with F-actin and nuclei. The chaotic microenvironment was permissive enough to support long-term culture, self-organization, and functional marker expression—from a minimal setup with no external fields or complex optics.

Bacteria provided an even more vivid demonstration of spatial control. Using a Mini-SMX printhead with two inlets and a single mixing element, the researchers printed Escherichia coli, a facultative anaerobe expressing green fluorescent protein, in the outer regions of fibers while confining Bifidobacterium bifidum, a strict anaerobe, to the core. The peripheral E. coli shielded the oxygen-sensitive B. bifidum from ambient oxygen, and after 48 hours the anaerobe reached approximately ten to the ninth colony-forming units per gram in structured constructs—significantly higher than in pre-mixed controls, where populations homogenized completely. This rational compartmentalization of a synthetic microbial consortium points toward gut-mimetic systems, controlled cross-feeding platforms, and engineered biofilms in which gradients of nutrients, metabolites, or mechanical properties can be designed into the material itself.

The third proof of concept moved from biology to chemistry. Phosphate-rich and calcium-rich gelatin inks were co-extruded through a printhead containing three Ross mixing elements, generating interdigitated domains with distinct ionic compositions embedded in a single continuous gelatin matrix. Calcium phosphate precipitated precisely at the internal interfaces between the domains, visualized by tetracycline-based fluorescence staining. Because both inks share the same polymeric matrix and are crosslinked throughout by transglutaminase, the construct remains mechanically integrated despite its chemically distinct microregions. This capacity to spatially program chemical transformations within soft materials opens routes to biomineralization, catalysis, and bioinspired composites with functional gradients or hybrid living-nonliving features.

Taken together, the work establishes static mixer geometry as a genuine design parameter—one that simultaneously controls microarchitecture, interface generation, shear exposure, and pressure loss. By expanding the chaotic printing toolbox beyond Kenics elements to Ross, Mini-SMX, and SMX geometries, and by validating the platform across wet-spinning, dripping, and direct writing, the researchers have broadened the design space available to bioprinting, soft matter, catalysis, and synthetic biology. The broader promise is seductive in its simplicity: complex, nature-like internal organization encoded passively within a printhead, in a single continuous fabrication step, using equipment that many laboratories already own. As the authors suggest, future directions may include interfacial reactivity for sensing, directed nutrient diffusion, and even the synthesis of inorganic phases within hydrogel scaffolds—turning chaos itself into a tool for structuring complexity.

Subject of Research: Chaotic bioprinting of microarchitected soft materials using different static mixer geometries

Article Title: From Flow to Function: Using Different Static Mixers to Fabricate Microarchitected Materials Via Chaotic Printing

Article References: Bolívar‐Monsalve, E. J., Ceballos‐González, C. F., Quevedo‐Moreno, D. A., Rendón‐Moreno, I. I., Cantoral‐Sánchez, A., Ambriz‐González, H., Alvarez, M. M., & Trujillo‐de Santiago, G. (2026). From Flow to Function: Using Different Static Mixers to Fabricate Microarchitected Materials Via Chaotic Printing. Advanced Science, 13(55), Article e76626. https://doi.org/10.1002/advs.76626

Image Credits: AI Generated

DOI: 10.1002/advs.76626

Keywords: chaotic printing, static mixers, bioprinting, microarchitecture, hydrogels, chaotic advection, computational fluid dynamics, synthetic microbial consortia, biomineralization, direct ink writing, soft materials, Caco-2 cells

The challenge the researchers set out to solve is one of geometry and biology combined. Most laboratory studies of Kawasaki disease rely on flat, two-dimensional sheets of endothelial cells, the thin lining that coats the inside of blood vessels. Such cultures are easy to grow and easy to analyze, but they bear little resemblance to the real thing. A coronary artery is a hollow, curved, multilayered tube in which endothelial cells interface with blood on one side and smooth muscle cells wrap the exterior, providing structural support. Animal models, particularly mice, have been used for decades, but the differences between mouse and human vascular and immune biology often limit how well findings translate to the clinic. The team, led by Xuting Zhang and colleagues at Wenzhou Medical University and collaborating institutions, hypothesized that recreating the true three-dimensional, bilayered architecture of a coronary artery would yield a far more faithful model of the disease.

Their manufacturing method of choice was microfluidic coaxial bioprinting, an elegant technique that exploits the same principle as a pipe within a pipe. The researchers assembled a device from glass capillaries and injection needles, aligning an inner capillary concentrically inside an outer one. Two fluids were pumped through this coaxial nozzle: an outer bioink containing 10 percent gelatin methacryloyl, or GelMA, blended with polyethylene glycol diacrylate, or PEGDA, and an inner sacrificial stream of 10 percent polyvinyl alcohol. When the co-flowing streams emerged from the capillary tip, ultraviolet light at 405 nanometers triggered photopolymerization of the outer hydrogel, locking in a continuous tube. The uncrosslinked PVA core was then simply washed away, leaving behind a hollow hydrogel microfiber with an open lumen running its entire length.

The precision achievable with this setup is remarkable. By adjusting the relative flow rates of the inner and outer fluids, the team could dial in the dimensions of the fibers at will. Holding the inner flow at 15 milliliters per hour and raising the outer flow from 15 to 35 milliliters per hour shifted the ratio of inner to outer diameter from about 65.5 percent down to 58.4 percent, while the outer diameter swelled from roughly 712 to 911 micrometers. Reversing the adjustment, by accelerating the inner stream while holding the outer one constant, enlarged both the overall caliber and the relative lumen. Throughput was equally impressive: a single milliliter of bioink yielded between roughly 4 and 6.5 meters of continuous hollow fiber, depending on the diameter chosen, underscoring the scalability of the approach.

Mechanical tuning came from the PEGDA content. Three formulations containing 2.5, 5, and 7.5 percent PEGDA in 10 percent GelMA produced hydrogels with Young’s moduli of approximately 73, 153, and 221 kilopascals respectively, and rheological testing confirmed the same trend in storage modulus. Swelling behavior plateaued within 24 hours, and the matrices retained more than 95 percent of their mass after a day in culture medium, yet dissolved completely within 24 hours when exposed to the enzyme collagenase, showing that degradation is enzymatically controllable rather than a product of passive hydrolysis. Importantly, the softest formulation, 10 percent GelMA with 2.5 percent PEGDA, proved best for early cell attachment, because PEGDA, while excellent for structural strength, tends to resist cell adhesion. That formulation was selected for all subsequent vascular constructs.

With the scaffold optimized, the researchers populated it with human cells in a deliberate sequence. First, human umbilical vein endothelial cells, or HUVECs, at a density of 10 million cells per milliliter were injected into the lumen and allowed 72 hours to engraft, forming a continuous endothelial monolayer with uniform circumferential alignment. Then human coronary artery smooth muscle cells, at 100 million cells per milliliter, were applied to the outer surface, where they colonized the exterior and formed a distinct smooth muscle layer. Confocal microscopy of the cytoskeleton and immunostaining confirmed the architecture: the endothelial marker CD31 lined the luminal surface, while alpha-smooth muscle actin was confined to the outer layer, faithfully reproducing the bilayered organization of a native coronary artery.

Crucially, the model was more than a structural mimic. When the team perfused fluorescent dextran molecules of 4 and 70 kilodaltons through the lumen, the endothelialized constructs allowed far less leakage into the surrounding hydrogel than acellular controls, demonstrating that the engineered endothelium functioned as a selective barrier to both small solutes and large plasma proteins, just as a real vessel does. As a positive control, exposure to the inflammatory molecule TNF-alpha for six hours triggered a cascade of endothelial activation: elevated lactate dehydrogenase release signaling membrane injury, increased oxidative stress, upregulation of the adhesion molecules ICAM-1, VCAM-1, and E-selectin, a surge of inflammatory cytokines and chemokines including IL-1beta, IL-6, IL-8, CX3CL1, CCL5, and MCP-1, and clear activation of the NF-kappaB signaling pathway, traced by the phosphorylation of I-kappaB-alpha and the p65 subunit.

The decisive test came when the constructs were bathed in serum drawn from children during the acute phase of Kawasaki disease, before intravenous immunoglobulin therapy, mixed at a 10 percent volume ratio into the culture medium, with serum from age-matched healthy children as the control. Within six hours, the patient serum drove the engineered arteries into a state that mirrored the disease: heightened endothelial injury and oxidative stress, intensified expression of all three adhesion molecules, a broad transcriptional inflammatory response, and robust NF-kappaB activation. The serum also triggered pyroptosis, a fiery form of programmed cell death, evidenced by upregulation of the inflammasome sensor NLRP3, the executioner protein gasdermin D, and caspase-1. This finding aligns with growing evidence that pyroptotic endothelial death contributes to the coronary artery lesions that make Kawasaki disease dangerous, and it suggests that NF-kappaB signaling and the NLRP3 inflammasome operate in a reinforcing loop rather than as separate, sequential events.

The platform then proved its worth as a drug-testing instrument. Pretreating the constructs with atorvastatin, the widely used statin, at a non-toxic concentration of 10 micromolar significantly blunted the inflammatory response to Kawasaki serum, suppressing adhesion molecule and cytokine expression and dampening NF-kappaB phosphorylation, consistent with the statin’s known anti-inflammatory, lipid-independent pleiotropic effects and with early clinical trials of atorvastatin in Kawasaki patients with coronary aneurysms. The selective NLRP3 inhibitor MCC950, also tested at 10 micromolar, likewise reduced ICAM-1 expression and inflammatory mediator transcripts, and it specifically shut down the pyroptotic machinery, lowering NLRP3, gasdermin D, caspase-1, and IL-1beta. Because intravenous immunoglobulin resistance remains a major clinical problem, the ability to distinguish these two mechanistically distinct protective strategies within a single human tissue model is exactly the kind of preclinical capability the field has lacked.

The authors are candid about the model’s current limits. The constructs were cultured under static conditions, without the fluid flow and shear stress that shape endothelial behavior in living arteries, and future versions will incorporate dynamic perfusion. The endothelial layer consists of HUVECs rather than coronary-specific endothelial cells, a pragmatic choice driven by the robust proliferation needed to form an intact barrier in a bioprinted scaffold. Even so, the achievement stands out. In a single platform, the team has combined tunable biofabrication, native-like multilayered architecture, functional barrier properties, patient-derived disease induction, and mechanistically resolved drug evaluation. For a disease that strikes young children, has no known cause, and can leave permanent cardiac damage, this bioprinted coronary artery equivalent offers a powerful new window into pathogenesis and a versatile testing ground for the therapies of tomorrow.

Subject of Research: Biomimetic 3D bioprinted coronary artery models for Kawasaki disease modeling and drug screening

Article Title: Engineering biomimetic coronary artery equivalents for Kawasaki disease modeling and drug screening

Article References: Zhang, X., Shao, C., Wang, Y., Liu, A., Rong, X., Jia, C., Yu, W., Zhang, H., Wu, R., Zhang, J., Zhang, L., Ye, F., & Chu, M. (2026). Engineering biomimetic coronary artery equivalents for Kawasaki disease modeling and drug screening. Materials Today Bio, 41, Article 103701. https://doi.org/10.1016/j.mtbio.2026.103701

Image Credits: AI Generated

DOI: 10.1016/j.mtbio.2026.103701

Keywords: Kawasaki disease, coronary artery, bioprinting, microfluidics, GelMA, endothelial dysfunction, NF-kB, pyroptosis, NLRP3, atorvastatin, MCC950, drug screening

The problem the researchers set out to solve is deceptively simple to state. In tissue engineering, scaffolds are the porous structures that support cell attachment and guide new tissue formation, and in craniofacial applications, where surgeons aim to reconstruct complex bones of the skull and face, the pore size, shape and spatial distribution of a scaffold are decisive for regenerative success. Additive manufacturing has made it possible to print scaffolds with predefined porosity, but what comes out of the printer does not always match what went into the design file. Bioinks, the cell-laden hydrogel mixtures used in bioprinting, can shear, spread or rearrange during extrusion, degrading shape fidelity. Verifying the printed result has traditionally meant laborious manual image analysis in software such as ImageJ or CellProfiler, an approach that is slow and, crucially, vulnerable to user bias.

The new platform couples custom 3D-printed hardware with a dedicated image-processing pipeline written in MATLAB. The imaging rig consists of a 12.3-megapixel Raspberry Pi High Quality Camera built around the Sony IMX477 sensor, fitted with a 6 mm wide-angle CS-mount lens and mounted on an adjustable 3D-printed monopod. A NeoPixel 12-LED RGB ring, held in a flexible thermoplastic polyurethane adapter, bathes the sample in homogeneous white light against a high-contrast black-and-white background, sharpening the contours of scaffold edges and suppressing the shadows that would otherwise corrupt segmentation. A Raspberry Pi 3 Model B+ and an Arduino Uno handle communication between the camera, the lighting and the host computer, and the structural parts of the mount were printed in polylactic acid, the workhorse polymer of desktop 3D printing.

The software side is where the engineering becomes genuinely distinctive. The pipeline takes a single zenithal image of the scaffold and processes it through a fixed sequence of operations: rotation, correction of the barrel distortion introduced by the wide-angle lens using a radial distortion model with an empirically determined coefficient of −0.15, grayscale conversion, interactive cropping, and automated segmentation by Otsu’s global thresholding, which chooses the black-and-white cutoff that maximises inter-class variance in the image histogram. Connected-component labelling with 8-connectivity then identifies each pore, and blob analysis filters out objects that are too small or too large to be genuine pores. The system outputs the number, area, perimeter and compactness of every pore in the uppermost printed layer, exporting the results to a spreadsheet alongside an annotated overlay image.

One of the most elegant technical contributions is the compactness metric. Rather than using the classical isoperimetric quotient, which anchors a circle at unity, the authors square-normalise the measure so that a perfect square pore scores exactly one, matching the orthogonal geometry that most printed scaffolds are designed to have. A penalty function then converts deviations in either direction, pores that round off or become convoluted, into a percentage quality score between 0 and 100 percent, with a perfect square yielding 100 percent and a perfectly circular pore scoring 72.7 percent. The authors note that their metric is the reciprocal of the printability index commonly used to assess bioink shape fidelity, which allows their values to be compared directly with the existing bioprinting literature. A colour-indexed graph maps each pore’s score onto a gradient, giving researchers an at-a-glance map of where a print went wrong.

The validation strategy was deliberately staged across four assays. First, a printed reference grid with known 0.5 cm square cells established the system’s trueness and repeatability. The platform proved remarkably repeatable, with a coefficient of variation of just 1.33 percent, but it systematically underestimated pore area by 11.6 percent, measuring a mean of 0.221 square centimetres against a nominal 0.250. The authors trace this bias to the manual pixel-per-centimetre calibration and to the segmentation threshold placing the detected edge slightly inside the true pore boundary. Because the error is systematic and reproducible, it can be removed by calibrating against a reference of certified area, a straightforward fix that turns a flaw into a documented, correctable offset.

The second assay delivered the headline comparison. On a 3D-printed polylactic acid scaffold containing three classes of pores, five repeated acquisitions by the platform agreed to within a coefficient of variation of 0.01 to 2.48 percent. The same specimen was then measured manually by three experienced tissue engineering researchers, and the results were striking: inter-user coefficients of variation ranged from 11.5 to 22.8 percent, and intra-user variability from 0 to 12.7 percent. Counterintuitively, the manual measurements diverged most on the larger pores, the opposite of the pixel-resolution sensitivity shown by the automated system on small features. The authors argue this exposes a systemic problem in collaborative laboratories, where measurement quality depends on individual attention and experience, and where dispersion between operators can exceed an order of magnitude.

Feasibility was then demonstrated on materials far harder to image than rigid plastic. Two self-setting silica–gelatin hybrid bioinks, differing only in their gelatin-to-sol volume ratio, were printed into 16-pore scaffolds on a Cellink BioX bioprinter; because the inks are transparent, they were dyed with methylene blue to create contrast. The software successfully segmented the complex, non-linear pore boundaries of these hydrated hydrogel constructs, where manual measurement is most error-prone, and revealed a printing resolution error of 0.0051 square centimetres relative to the design ground truth. A final assay on a brittle silica-based scaffold showed the compactness output flagging shape deviations that the printer’s settings were supposed to prevent. The authors are careful to note that these last assays were feasibility demonstrations without independent reference measurements, not full accuracy validations.

The platform does not attempt to replace micro-computed tomography, the gold standard for resolving a scaffold’s internal three-dimensional architecture, pore interconnectivity and through-thickness geometry. Micro-CT remains expensive, slow, with acquisition and reconstruction reaching 19.5 hours and 166 gigabytes per specimen at the finest pixel sizes, and it introduces dehydration and staining artefacts in hydrated hydrogels. The optical platform instead quantifies the two-dimensional projected macrotopography of the top printed layer, positioning itself as a rapid, non-destructive screening complement to volumetric imaging. Its limitations are candidly acknowledged: the workflow is semi-automated, with focus, aperture, monopod height, illumination and crop region set by the operator, the distortion coefficient must be redetermined for any different optical configuration, and low-contrast specimens may require staining.

What makes the work resonate beyond its immediate niche is its accessibility. The entire bill of materials comes to approximately €170 excluding VAT, the source code and 3D-printable STL files are openly available under an MIT licence, and the pipeline relies only on standard image-processing primitives, meaning it can be reproduced without a commercial MATLAB licence using GNU Octave or Python with OpenCV. By demonstrating that repeatability can be made independent of operator experience, the team offers laboratories a practical route to objective quality control in scaffold fabrication. The authors emphasise that no craniofacial-specific or clinical specimen was evaluated in this study, and that establishing utility in that demanding setting will require dedicated validation. But as patient-specific scaffolds for skull and facial bone reconstruction move closer to the clinic, the ability to verify, cheaply and reproducibly, that what was printed matches what was designed is exactly the kind of unglamorous infrastructure that turns promising biofabrication into reliable medicine.

Subject of Research: A low-cost semi-automated imaging platform for quantitative characterisation of 3D-printed scaffold surface macrotopography in tissue engineering

Article Title: A low-cost imaging platform for quantitative characterisation of scaffold surface macrotopography with potential application in craniofacial tissue engineering

Article References: Marimon, X., Saman-Sakkal, E., Rodriguez, R., Portela, A., Cerrolaza, M., Mateos, M. A., & Pérez, R. (2026). A low-cost imaging platform for quantitative characterisation of scaffold surface macrotopography with potential application in craniofacial tissue engineering. Medical & Biological Engineering & Computing. https://doi.org/10.1007/s11517-026-03661-6

Image Credits: AI Generated

DOI: 10.1007/s11517-026-03661-6

Keywords: tissue engineering, scaffolds, 3D printing, bioprinting, image processing, pore analysis, craniofacial regeneration, Raspberry Pi, shape fidelity, quality control, bioinks, computer vision

The tumor microenvironment, or TME, is far more than a passive backdrop for malignant cells. It is a dense, dynamic ecosystem of endothelial cells, immune cells, neurons, stromal cells, and secreted signaling molecules, all woven into an extracellular matrix composed of structural proteins such as collagen and elastin, adhesive glycoproteins like fibronectin and laminin, and charged polysaccharide chains. This matrix does not merely hold cells in place; it actively determines how fast tumors progress, how readily they metastasize, and how they respond to therapy. Proteoglycans within the matrix, for example, can remodel the biochemical landscape to open pathways through which cancer cells invade the bloodstream, a metastatic step known as intravasation. Once malignant cells reach distant tissues, they may even enter a quiescent, dormant state in the G0 phase of the cell cycle, evading both immune surveillance and chemotherapy until conditions favor renewed growth.

Hydrogels, the focus of the new review, are three-dimensional polymer networks formed by chemically or physically crosslinking hydrophilic building blocks such as hydroxyl, carboxyl, sulfonic acid, and amine groups. Their capacity to absorb large quantities of water gives them a softness and fluidity remarkably similar to soft biological tissue, which is precisely why tissue engineers have embraced them as extracellular matrix mimics. The choice of polymer backbone and crosslinking strategy directly dictates the mechanical strength, porosity, and degradation rate of the resulting material, allowing researchers to tune stiffness and biochemistry with a precision that animal models and plastic dishes cannot match. Hydrogels enable cells to interact with their surroundings on all sides, preserving the dynamic cell-matrix conversations that drive proliferation, migration, and intercellular communication.

The review classifies hydrogels into natural, synthetic, smart, and hybrid categories, each with distinct trade-offs. Natural polymers, including collagen, fibrin, alginate, hyaluronic acid, and chitosan, offer inherent bioactivity and enzymatic biodegradability because they resemble the extracellular matrix the body already knows how to process. Collagen, the most abundant structural protein in skin, cartilage, and bone, remains the workhorse of natural hydrogel matrices. Synthetic polymers such as polyethylene glycol, polyvinyl alcohol, and polyacrylic acid, by contrast, provide adjustable stiffness, reproducible composition, and regulatory pedigree, but they lack natural cell-binding sites and must be decorated with adhesive proteins. Concerns also persist about cytotoxic degradation products; PLGA, for instance, breaks down into acidic by-products that can lower local pH and provoke inflammation, while PEG can yield reactive species under long-term oxidative stress.

Hybrid systems attempt to capture the best of both worlds. PEG-heparin hydrogels, which combine a synthetic backbone with an anionic glycosaminoglycan, have emerged as strong alternatives to Matrigel, the widely used but compositionally ill-defined protein mixture derived from tumor cells. Compared with Matrigel, PEG-heparin platforms offer defined composition, greater reproducibility, and easier modification, and several have already advanced into preclinical and early clinical studies for drug delivery and tissue regeneration. Crosslinking chemistry adds another layer of control: physical crosslinking produces reversible, stimuli-responsive, and cytocompatible networks with modest mechanical strength, whereas covalent strategies such as photopolymerization, Michael addition, click chemistry, and enzymatic crosslinking deliver superior structural integrity and more predictable degradation kinetics.

The practical payoff of these materials is already visible across the five major cancer types examined in the review. In lung cancer, which claimed roughly one hundred twenty thousand American lives in 2024, a temperature-sensitive hydrogel integrating realgar arsenic sulfide with Fe3O4 magnetic nanoparticles created a combined imaging and thermotherapy platform, the first hydrogel formulation of its kind for that compound. Separately, an injectable hydrogel delivering the anti-angiogenic drug anlotinib through a hyaluronic acid-tyramine matrix inhibited endothelial cell proliferation and produced tumor suppression rates ten to twenty percent higher than the free drug across all tested doses, while reducing systemic toxicity. Matrigel-based cultures have even been used to test combined MEK inhibition and anti-PD-L1 immunotherapy in patient-derived three-dimensional spheroids, probing the tumor immune landscape outside the body.

Liver cancer models show a similar leap in physiological relevance. A three-dimensional culture system built from decellularized liver extracellular matrix hydrogel enhanced the self-renewal, migration, and drug resistance of HepG2 cells, unmasking cancer stem cell properties that flat cultures conceal and opening a route to stem cell-targeted drug discovery. A thermosensitive Pluronic F127 hydrogel co-delivering resveratrol microspheres and cisplatin enabled localized intraperitoneal chemotherapy, with resveratrol counteracting cisplatin’s side effects and prolonging drug retention in the abdominal cavity. Synthetic PEG-cysteine hydrogels and organic-inorganic PDMS-TEOS scaffolds, meanwhile, boosted albumin synthesis and urea production in hepatocyte-like cultures, markers of genuine liver function that monolayer systems routinely fail to sustain.

In breast cancer, a chitosan-based thermosensitive hydrogel seeded with 4T1 mouse mammary carcinoma cells produced tumors in mice that grew approximately 2.5-fold larger and weighed twice as much as those from conventional two-dimensional injections, while markedly elevating the cancer stem cell markers CD44 and CD24, demonstrating that the hydrogel platform genuinely replicates the in vivo niche. pH-sensitive chitosan nanocarriers extended the bioactivity of curcumin, a polyphenol crippled by poor solubility, and an L-alanine-derived hydrogel released doxorubicin specifically at acidic pH values characteristic of tumor tissue. An injectable, temperature-sensitive hydrogel loaded with titanium carbide nanoparticles even enabled laser-triggered photothermal therapy, heating tumors locally to kill cancer cells while sparing surrounding tissue.

Prostate and colon cancer applications extend the technology from disease modeling to clinical devices and microbiome engineering. Injectable hydrogel spacers such as SpaceOAR, placed between the prostate and rectum during radiotherapy, physically shield the bowel from radiation for three to six months before dissolving harmlessly, reducing rectal pain, bleeding, and other treatment toxicities. Matching hydrogel stiffness to the bone-like mechanical environment of prostate metastases, around 25 to 40 kilopascals, has proven essential for studying invasion and drug resistance. In colorectal cancer, pH-sensitive alginate beads reinforced with hydroxyapatite and magnetic nanoparticles protected the chemotherapy drug 5-fluorouracil from stomach acid and released it in the intestine, while hyaluronan-based organoid co-cultures combining patient-derived tumor cells with cancer-associated fibroblasts delivered personalized drug-testing platforms. Perhaps most strikingly, a living hydrogel embedded with the bacterium Thiobacillus denitrificans metabolizes immunosuppressive hydrogen sulfide in the colon tumor microenvironment into harmless sulfate, normalizing tumor vasculature and amplifying the efficacy of co-delivered camptothecin.

The review’s authors are candid about the obstacles that stand between these laboratory triumphs and routine clinical use. Natural hydrogels suffer from batch-to-batch variability, weak mechanical strength, and rapid, uneven degradation; synthetic ones raise questions about long-term biodegradation and residual monomer toxicity. Smart, stimuli-responsive hydrogels depend on environmental triggers whose values shift between individuals, disease states, and tissue locations, making therapeutic outcomes difficult to predict. Reproducibility, standardization, and clinical validation remain stubborn hurdles, and manufacturing dual-responsive systems under Good Manufacturing Practice conditions is still rare. Yet the trajectory is unmistakable: 3D bioprinting and photopolymerization are giving researchers precise spatial control over tumor architecture, artificial intelligence is accelerating polymer design, and injectable hydrogels are proving they can localize chemotherapy, immunotherapy, and even engineered bacteria directly at tumor sites. As the authors conclude, hydrogels have evolved from simple extracellular matrix mimics into powerful platforms for decoding tumor biology, and the models they enable may well define the next generation of precision oncology.

Subject of Research: Hydrogel-based three-dimensional models of the tumor microenvironment in cancer research

Article Title: Hydrogel applications in tumor microenvironment modeling

Article References: Karakaya, M., Karataş, R. B., Ayaz, F., & Aydemir, E. (2025). Hydrogel applications in tumor microenvironment modeling. Discover Biotechnology, 2(1), Article 21. https://doi.org/10.1007/s44340-025-00029-8

Image Credits: AI Generated

DOI: 10.1007/s44340-025-00029-8

Keywords: hydrogels, tumor microenvironment, 3D cell culture, extracellular matrix, drug delivery, cancer models, organoids, bioprinting, immunotherapy, biomaterials, precision oncology, spheroids

The authors argue that the term bone organoid has been applied far too loosely. Spheroids, which are useful modular building blocks that can enhance osteogenic differentiation, often lack tissue-level organization altogether. Engineered constructs can reproduce geometry or mechanical behavior yet remain dominated by an exogenous scaffold rather than by cells. Under the framework proposed in the review, a genuine bone organoid must satisfy four core criteria: it must be a viable cell-derived three-dimensional tissue that develops organization beyond simple aggregation; it must produce its own collagenous or osteoid-like matrix with spatially and temporally resolved mineralization; it must show that new mineral is biologically deposited rather than inherited from the material it was grown on; and it must display at least one dynamic skeletal function, such as regulated matrix formation, formation-resorption coupling or a controlled mechanobiological response. Engineered guidance is permitted, but only when it is transient or demonstrably permissive to endogenous organization.

The review goes further by proposing a tiered classification system with five categories: osteogenic spheroids, bone-like microtissues, engineered skeletal constructs, bone organoids and high-fidelity bone organoids. The top designation demands evidence across three interdependent domains. Structural mimicry requires hierarchical extracellular matrix organization and progressive mineralization that mirrors the sequence seen in native bone, where cells first deposit unmineralized osteoid and mineral then advances from discrete fronts. Functional fidelity requires coupled activity between osteoblast-lineage cells that build matrix and osteoclast-lineage cells that resorb it, linked through signaling pathways such as RANKL, RANK and osteoprotegerin. Biomechanical integrity requires that the construct maintain structural coherence and exhibit measurable mechanosensation, reflecting the fact that bone cells continuously convert mechanical loading, fluid flow and matrix stiffness into biological responses. Crucially, the authors stress that a sophisticated scaffold-dominated construct can be clinically useful while still falling outside the organoid class; placement is a statement about the source of organization, not about quality.

When the authors applied this classification to representative original studies, the results were sobering. Of the ten studies examined in their evidence map, several constructs labeled organoids by their original authors were reassigned as osteogenic spheroids because self-assembly was limited to the spheroid unit and tissue-level hierarchy was never demonstrated. Others were reclassified as engineered skeletal constructs because pre-existing material architecture dominated organization. Only a handful, including a 2021 woven bone organoid grown from human bone marrow stromal cells and a 2025 system using dynamic dual-network hydrogels in which cell migration generated spatiotemporal woven-bone architecture, met the core organoid criteria. Notably, no current model satisfies every high-fidelity domain, and the reviewers conclude that transparent reporting of what was tested, and what was not, is essential for the field to advance.

A recurring problem the review highlights is confounding between biological mineralization and material-derived mineral signals. Many popular bone engineering strategies incorporate nano-hydroxyapatite, bioactive glass or black-phosphorus nanosheets that release phosphate ions, and any of these can generate calcium deposits that look like bone formation on a stain but are actually chemical precipitation. The framework therefore demands that active, biologically regulated mineralization be distinguished from material contributions using acellular baselines, a requirement that several widely cited nanomaterial-based studies do not currently meet. The authors also emphasize that late osteogenic marker expression alone does not establish functional bone-like tissue; marker data must be interpreted alongside matrix organization and mineral distribution.

Beyond classification, the review provides a detailed account of the biology that a faithful model must capture. Osteoblasts deposit type I collagen-rich osteoid that later mineralizes as hydroxyapatite crystals grow; a subset of these cells becomes embedded as osteocytes, which sense strain through dendritic processes in canalicular networks and regulate both building and resorption through mediators such as sclerostin. Osteoclasts, formed by fusion of monocyte-macrophage precursors, acidify the resorption compartment and release enzymes that remove mineral and collagen while also releasing matrix-stored growth factors like TGF-beta and BMP-related signals. Meanwhile, endothelial cells provide angiocrine signaling that supports osteoprogenitor maintenance, and neural elements release calcitonin gene-related peptide and substance P, which influence osteoblast, osteoclast and vascular function. The review cautions that multilineage marker expression alone is insufficient; functional integration must be demonstrated with lineage-appropriate readouts such as lumen formation and perfusion for vessels, or innervation-dependent regulation of remodeling for nerves.

On the fabrication side, the authors take a clear-eyed view of bioprinting, distinguishing between printing preformed organoids and printing for organoid formation, with only the former deserving the label unless post-print self-organization is demonstrated. They survey the four major modalities: inkjet printing offers fine patterning but limited viscosity range, extrusion printing handles mineral-filled bioinks and is the most scalable but exposes cells to shear stress, laser-assisted printing achieves micrometer-scale nozzle-free patterning but is limited by throughput, and light-based stereolithography and digital light processing generate complex channels but suffer from optical attenuation in mineral-rich inks. Across all modalities, the review finds that evidence that printing improves organoid maturation remains substantially weaker than evidence that it improves initial geometry. Hybrid strategies, such as temporary scaffold-guided self-assembly, printed channels coupled with self-organized microvasculature, and modular assembly of developmentally primed cartilage microtissues, are highlighted as the most promising path forward, exemplified by recent bioprinted bone-organoid grafts with guided vascularization that matured after implantation.

The translational outlook is cautiously encouraging. Patient-derived chondrosarcoma organoids have faithfully recapitulated histological and genetic features of parental tumors and shown sensitivity to the SHH pathway inhibitor vismodegib, while a biobank of 44 sarcoma organoid lines has enabled high-throughput drug screening. A three-dimensional vascularized humanized bone organoid has revealed that estrogen withdrawal drives vessel-like structure formation and mineral deposition, offering mechanistic insight into postmenopausal osteoporosis that non-vascularized models could not capture. Induced pluripotent stem cell-derived jawbone organoids have reproduced phenotypic features of osteogenesis imperfecta, pointing toward precision modeling of genetic skeletal disease. For regenerative applications, engineered ossification center-like organoids and periosteum-derived organoids combined with printed scaffolds have achieved bone repair in rodent critical-sized defects, though the authors note that systematic comparison against autograft controls remains an essential next step.

The review closes with a series of practical proposals intended to move the field from anecdote to standard. These include a minimum reporting checklist covering cell source, passage number, matrix composition, induction schedules, regional rather than whole-construct viability, quantitative mineralization assessment and predefined exclusion criteria for poorly formed organoids, together with application-specific potency assays: coupled remodeling endpoints for osteoporosis models, reproducible dose-response data for drug screening platforms and vascularized bone formation for regenerative grafts. The authors also flag regulatory hurdles, noting that clinical-grade organoids will require good manufacturing practice compliance, validated potency assays and jurisdiction-specific pathways such as the European Advanced Therapy Medicinal Product framework. Their overarching message is that progress will come not from adding complexity indiscriminately but from controlling when and where complexity is introduced, with stimuli-responsive matrices that yield to endogenous tissue, machine-learning-optimized printing and microfluidic platforms that connect bone organoids to vascular, immune and metabolic modules. Bone organoids, the review concludes, occupy a genuinely valuable intermediate position between dish and animal, provided the label is reserved for constructs that can prove they deserve it.

Subject of Research: Development of an operational classification framework and biofabrication standards for engineering high-fidelity bone organoids

Article Title: Engineering high-fidelity bone organoids: Operational classification, multilineage crosstalk, biofabrication evidence, and translational validation

Article References: Huang, Y., Zhang, T., Chen, S., Zhou, H., Xu, H., Zhang, F., Li, L., & Lyu, F. (2026). Engineering high-fidelity bone organoids: Operational classification, multilineage crosstalk, biofabrication evidence, and translational validation. Materials Today Bio, 41, Article 103676. https://doi.org/10.1016/j.mtbio.2026.103676

Image Credits: AI Generated

DOI: 10.1016/j.mtbio.2026.103676

Keywords: bone organoids, organoid classification, bioprinting, osteoblasts, osteoclasts, mineralization, vascularization, hydrogels, disease modeling, drug screening, bone regeneration, bioinks