Bone fractures are one of the most common traumatic large-organ injuries and although many fractures can heal on their own, 2-12% of fractures are slow healing or do not heal (non-unions). Autologous grafts are currently used for treatment of non-unions but are associated with limited healthy bone tissue. Tissue engineered cell-based products have promise for an alternative treatment method. It was previously demonstrated that cartilaginous microspheroids of periosteum-derived cells could be assembled into scaffold-free constructs and heal murine critically-sized long bone defects (non-unions). However, the handleability of such scaffold-free implants can be compromised when scaling-up. In this work, cartilaginous spheroids were combined with melt electrowritten (MEW) meshes to create an engineered cell-based implant, able to induce in vivo bone formation. MEW polycaprolactone meshes were tailored to contain pores (116 ± 28 µm) of a size that captured microspheroids (180 ± 15 µm). Periosteum-derived microspheroids pre-cultured for 4 days, were seeded on MEW meshes and gene expression analysis demonstrated up-regulation of chondrogenic (SOX9, COL2) and prehypertrophic (VEGF) gene markers after 14 days, creating a biohybrid sheet. When implanted subcutaneously (4 weeks), the biohybrid sheets mineralized (23 ± 3% MV/TV) and formed bone and bone marrow. Bone formation was also observed when implanted in a murine critically-sized long bone defect, though a high variation between samples was detected. The high versatility of this biofabrication approach lies in the possibility to tailor the scaffolds to shape and dimensions corresponding to the large bone defects and the individual patient using robust bone forming building blocks. These strategies are instrumental in the development of personalized regenerative therapies with predictive clinical outcomes. STATEMENT OF SIGNIFICANCE: Successful treatments for healing of large long bone defects are still limited and 2-12% of fractures do not heal properly. We combined a novel biofabrication technique: melt electrowriting (MEW), with robust biology: bone forming cartilaginous spheroids to create biohybrid sheets able to form bone upon implantation. MEW enabled the fabrication of scaffolds with micrometer-sized fibers in defined patterns which allowed the capturing of and merging with cartilaginous spheroids which had the potency to mature into bone via the developmental process of endochondral ossification. The present study contributes to the rapidly growing field of "Biofabrication with Spheroid and Organoid Materials'' and demonstrates design considerations that are of great importance for biofabrication of functional tissues through the assembly of cellular spheroids.

The use of magnetic‐driven strategies for non‐contact manipulation of engineered living modules opens up new possibilities for tissue engineering. The integration of magnetic nanoparticles (MNPs) with cartilaginous microtissues enables model‐driven 4D bottom‐up biofabrication of remotely actuated assembloids, providing unique properties to mechanoresponsive tissues, particularly skeletal constructs. However, for clinical use, the long‐term effects of magnetic stimulation on phenotype and in vivo functionality need further exploration. Magnetic‐driven biofabrication includes both rapid processes, such as guided microtissue assembly, and slower biological processes, like extracellular matrix secretion. This work explores the interplay between magnetic fields and MNP‐loaded cartilaginous microtissues through mathematical modeling and experimental approaches, investigating long‐term stimulation effects on ECM maturation and chondrogenic hypertrophy. Transcriptomic analysis reveal that magnetic stimulation activated mechanosensitive pathways and catabolic processes, driving accelerated cartilage‐to‐bone transitions via endochondral ossification, outcomes not observed in non‐stimulated controls. This study paves the way for pre‐programmed, remotely actuated skeletal assembloids with superior bone‐forming capacity for regenerating challenging bone fractures.

Neural stem cells (NSCs) are crucial components of the nervous system, primarily located in the subventricular zone (SVZ) and subgranular zone (SGZ). The SVZ neural stem cell niche (NSCN) is a specialized microenvironment where growth factors and extracellular matrix (ECM) components collaborate to regulate NSC self-renewal and differentiation. Despite its importance, our understanding of the SVZ remains incomplete due to the inherent challenges of animal research, particularly given the tissue’s dynamic nature. To address these limitations, we developed a proof-of-concept, dynamic, and tissue-specific 3D organotypic SVZ model to reduce reliance on animal models. This static 3D organotypic model integrates a region-specific decellularized ECM derived from the SVZ, mimicking the native NSCN and supporting mouse-derived ependymal cells (ECs), radial glial cells (RGCs), astrocytes, and NSCs. To further improve physiological relevance, we incorporated a dynamic microfluidic culture system (SVZonChip), replicating cerebrospinal fluid (CSF) flow as observed in vivo. The resulting SVZonChip platform, combining region-specific ECM proteins with dynamic culture conditions, provides a sustainable and reproducible tool to minimize animal model use. It holds significant promise for studying SVZ-related diseases, such as congenital hydrocephalus, stroke, and post-stroke neurogenesis, while advancing translational research and enabling personalized medicine protocols.

Magnetic biofabrication enables rapid assembly of multicellular spheroids but still lacks a basis for predictive control over structure and mechanical environment. Here, we combine experiments and an individual spheroid-based model to study magnetic assembly of periosteum-derived spheroids. Spheroids are treated as discrete particles interacting through magnetic forces, contact mechanics, and interfacial friction, with parameters obtained from independent measurements. This model quantitatively captures assembly dynamics arising from magnetic force patterns and viscous drag with the well surface. The spatial distribution of magnetic forces, determined by magnet geometry and positioning, predicts the size and morphology of magnetic assembloids, including disk- and ring-like structures. Magnetic assembly further generates heterogeneous compressive stresses that depend on magnet geometry and spheroid number. Radial stresses arise collectively through inter-spheroid interactions, whereas vertical stresses are mainly determined by magnetic loading of individual spheroids. These results establish a minimal physical framework for magnetic biofabrication and provide a basis for predictive control of both tissue structure and mechanical microenvironment.

Magnetically driven biofabrication is emerging as a materials‐enabled extension of tissue engineering, integrating advances in magnetic nanoparticle (MNP) design with cells, spheroids, and biomaterial scaffolds to engineer responsive and remotely controllable living systems. Progress in nanoparticle engineering has yielded biocompatible and tunable MNP formulations that can be incorporated into hydrogels, spheroids, organoids, and scaffolds, where they influence cellular behavior, extracellular matrix organization, and mechanotransduction. Externally applied magnetic fields further enable non‐contact control over cell positioning, microtissue assembly, matrix alignment, and dynamic mechanical stimulation, expanding the design space of 3D and 4D biofabrication. This Review critically maps and unifies the multiscale design principles underlying magnetically driven biofabrication, spanning nanoparticle design, magnetic actuation strategies, and biological responses. We compare approaches ranging from single‐cell manipulation and magnetoactive bioinks to spheroid fusion and microfluidic systems with embedded magnetic actuation. We further discuss how physics‐based modeling, data‐informed optimization, and emerging digital twin concepts may help connect material properties, magnetic field design, and biological response. Finally, we examine translational considerations, including Good Manufacturing Practice (GMP)‐compatible nanoparticle formulations, mechanistic clarity, long‐term safety evaluation, and regulatory alignment, converging toward magnetically enabled tissue‐engineered advanced therapy medicinal products (Mag‐TE ATMPs).