Human Induced Pluripotent Spheroids' Growth Is Driven by Viscoelastic Properties and Macrostructure of 3D Hydrogel Environment

A polysaccharide-based hydrogel platform for tumor spheroid production and anticancer drug screening

Extracellular matrix mimics are still needed to grow cancer cells in 3D environments and study their evolution in vitro while precisely controlling relevant features. Most models currently use collagen, which is biomimetic but degrades quickly, or artificial polymers, which can be chemically modified but remain stiff. Herein we introduced a soft, non-adhesive, and resistant hydrogel platform for tumor spheroid production using a polysaccharide-based formulation. To ensure micro-structuring of the hydrogel and enable spheroid formation, 3D printed molds consisting of a network of 200-µm-diameter micropillars were used to generate microstructured hydrogel constructs that fit into a multi-well plate. This platform was validated for drug testing using three cancer cell lines (A673, MCF7 and U87) and 2 anticancer drugs (doxorubicin and paclitaxel). Drug response was assessed through bright-field microscopy monitoring and viability measurements after 48 h of treatment. This study validates the use of pullulan-dextran hydrogels for spheroid formation, combined with in situ drug screening.

Viscoelastic hydrogel combined with dynamic compression promotes osteogenic differentiation of bone marrow mesenchymal stem cells and bone repair in rats

A biomechanical environment constructed exploiting the mechanical property of the extracellular matrix and external loading is essential for cell behaviour. Building suitable mechanical stimuli using feasible scaffold material and moderate mechanical loading is critical in bone tissue engineering for bone repair. However, the detailed mechanism of the mechanical regulation remains ambiguous. In addition, TRPV4 is involved in bone development. Therefore, this study aims to construct a viscoelastic hydrogel combined with dynamic compressive loading and investigate the effect of the dynamic mechanical environment on the osteogenic differentiation of stem cells and bone repair in vivo. The role of TRPV4 in the mechanobiology process was also assessed. A sodium alginate-gelatine hydrogel with adjustable viscoelasticity and good cell adhesion ability was obtained. The osteogenic differentiation of BMSCs was obtained using the fast stress relaxation hydrogel and a smaller compression strain of 1.5%. TRPV4 was activated in the hydrogel with fast stress relaxation time, followed by the increase in intracellular Ca2+ level and the activation of the Wnt/β-catenin pathway. The inhibition of TRPV4 induced a decrease in the intracellular Ca2+ level, down-regulation of β-catenin and reduced osteogenesis differentiation of BMSCs, suggesting that TRPV4 might be the key mechanism in the regulation of BMSC osteogenic differentiation in the viscoelastic dynamic mechanical environment. The fast stress relaxation hydrogel also showed a good osteogenic promotion effect in the rat femoral defect model. The dynamic viscoelastic mechanical environment significantly induced the osteogenic differentiation of BMSCs and bone regeneration, which TRPV4 being involved in this mechanobiological process. Our study not only provided important guidance for the mechanical design of new biomaterials, but also provided a new perspective for the understanding of the interaction between cells and materials, the role of mechanical loading in tissue regeneration and the use of mechanical regulation in tissue engineering.

Future perspectives: advances in bone/cartilage organoid technology and clinical potential

Bone and cartilage tissues are essential for movement and structure, yet diseases like osteoarthritis affect millions. Traditional therapies have limitations, necessitating innovative approaches. Organoid technology, leveraging stem cells' regenerative potential, offers a novel platform for disease modelling and therapy. This review focuses on advancements in bone/cartilage organoid technology, highlighting the role of stem cells, biomaterials, and external factors in organoid development. We discuss the implications of these organoids for regenerative medicine, disease research, and personalised treatment strategies, presenting organoids as a promising avenue for enhancing cartilage repair and bone regeneration. Bone/cartilage organoids will play a greater role in the treatment of bone/cartilage diseases in the future, and promote the progress of biological tissue engineering.

Tuning viscoelasticity and stiffness in bioprinted hydrogels for enhanced 3D cell culture: A multi-scale mechanical analysis

Bioprinted hydrogels are extensively studied to provide an artificial matrix for 3D cell culture. The success of bioprinting hydrogels relies on fine-tuning their rheology and composition to achieve shear-thinning behavior. However, a challenge arises from the limited viscoelastic and stiffness range accessible from a single hydrogel formulation. Nevertheless, hydrogel mechanical properties are recognized as essential cues influencing cell phenotype, migration, and differentiation. Thus, it is crucial to develop a system to easily modulate bioprinted hydrogels' mechanical behaviors. In this work, we modulated the viscoelastic properties and stiffness of bioprinted hydrogels composed of fibrinogen, alginate, and gelatin by tuning the crosslinking bath solution. Various concentrations of calcium ionically crosslinked alginate, while transglutaminase crosslinked gelatin. Subsequently, we characterized the mechanical behavior of our bioprinted hydrogels from the nanoscale to the macroscale. This approach enabled the production of diverse bioprinted constructs, either with similar elastic behavior but different elastic moduli or with similar elastic moduli but different viscoelastic behavior from the same hydrogel formulation. Culturing fibroblasts in the hydrogels for 33 days revealed a preference for cell growth and matrix secretion in the viscoelastic hydrogels. This work demonstrates the suitability of the method to decouple the effects of material mechanical from biochemical composition cues on 3D cultured cells.

A Co-Culture System for Studying Cellular Interactions in Vascular Disease

Cardiovascular diseases (CVDs) are leading causes of morbidity and mortality globally, characterized by complications such as heart failure, atherosclerosis, and coronary artery disease. The vascular endothelium, forming the inner lining of blood vessels, plays a pivotal role in maintaining vascular homeostasis. The dysfunction of endothelial cells contributes significantly to the progression of CVDs, particularly through impaired cellular communication and paracrine signaling with other cell types, such as smooth muscle cells and macrophages. In recent years, co-culture systems have emerged as advanced in vitro models for investigating these interactions and mimicking the pathological environment of CVDs. This review provides an in-depth analysis of co-culture models that explore endothelial cell dysfunction and the role of cellular interactions in the development of vascular diseases. It summarizes recent advancements in multicellular co-culture models, their physiological and therapeutic relevance, and the insights they provide into the molecular mechanisms underlying CVDs. Additionally, we evaluate the advantages and limitations of these models, offering perspectives on how they can be utilized for the development of novel therapeutic strategies and drug testing in cardiovascular research.

Method for Large-scale Production of hIPSC Spheroids

Stem cell spheroids are rapidly becoming essential tools for a diverse array of applications ranging from tissue engineering to 3D cell models and fundamental biology. Given the increasing prominence of biotechnology, there is a pressing need to develop more accessible, efficient, and reproducible methods for producing these models. Various techniques such as hanging drop, rotating wall vessel, magnetic levitation, or microfluidics have been employed to generate spheroids. However, none of these methods facilitate the easy and efficient production of a large number of spheroids using a standard 6-well plate. Here, we present a novel method based on pellet culture (utilizing U-shaped microstructures) using a silicon mold produced through 3D printing, along with a detailed and illustrated manufacturing protocol. This technique enables the rapid production of reproducible and controlled spheroids (for 1× 106 cells, spheroids = 130 ± 10 μm) from human induced pluripotent stem cells (hIPSCs) within a short time frame (24 h). Importantly, the method allows the production of large quantities (2 × 104 spheroids for 1 × 106 cells) in an accessible and cost-effective manner, thanks to the use of a reusable mold. The protocols outlined herein are easily implementable, and all the necessary files for the method replication are freely available. Key features • Provision of 3D mold files (STL) to produce silicone induction device of spheroids using 3D printing. • Cost-effective, reusable, and autoclavable device capable of generating up to 1.2 × 104 spheroids of tunable diameters in a 6-well plate. • Spheroids induction with multiple hIPSC cell lines. • Robust and reproducible production method suitable for routine laboratory use.