Engineering Large-Scale Self-Mineralizing Bone Organoids with Bone Matrix-Inspired Hydroxyapatite Hybrid Bioinks.

Addressing large bone defects remains a significant challenge owing to the inherent limitations in self-healing capabilities, resulting in prolonged recovery and suboptimal regeneration. Although current clinical solutions are available, they have notable shortcomings, necessitating more efficacious approaches to bone regeneration. Organoids derived from stem cells show great potential in this field; however, the development of bone organoids has been hindered by specific demands, including the need for robust mechanical support provided by scaffolds and hybrid extracellular matrices (ECM). In this context, bioprinting technologies have emerged as powerful means of replicating the complex architecture of bone tissue. The research focused on the fabrication of a highly intricate bone ECM analog using a novel bioink composed of gelatin methacrylate/alginate methacrylate/hydroxyapatite (GelMA/AlgMA/HAP). Bioprinted scaffolds facilitate the long-term cultivation and progressive maturation of extensive bioprinted bone organoids, foster multicellular differentiation, and offer valuable insights into the initial stages of bone formation. The intrinsic self-mineralizing quality of the bioink closely emulates the properties of natural bone, empowering organoids with enhanced bone repair for both in vitro and in vivo applications. This trailblazing investigation propels the field of bone tissue engineering and holds significant promise for its translation into practical applications.

The Application of Organoids in the Research of Skeletal Diseases: Current Status and Prospects.

Organoids, which are clumps of cells formed after in vitro 3D culture utilizing autologous tissue and stem cells, possess the 3D structure and corresponding functional and genetic features of the original tissue and organ. This model has immense potential in modeling the ontogeny of specific organismal organs, as well as in drug screening and studying molecular mechanisms. The newly developed concept of bone organoids, a special type of complex hard tissues that can be created in vitro using tissue engineering 3D culture technology, mimics the complex biological functions of bone tissue in vivo. These bone organoids are highly useful in elucidating the regulatory mechanisms of bone regeneration, screening tissue engineering materials, and promoting bone regeneration and repair. They offer promising applications in bone regeneration research.

Organoids as Innovative Models for Bone and Joint Diseases.

Bone is one of the key components of the musculoskeletal system. Bone and joint disease are the fourth most widespread disease, in addition to cardiovascular disease, cancer, and diabetes, which seriously affect people's quality of life. Bone organoids seem to be a great model by which to promote the research method, which further could improve the treatment of bone and joint disease in the future. Here, we introduce the various bone and joint diseases and their biology, and the conditions of organoid culture, comparing the in vitro models among 2D, 3D, and organoids. We summarize the differing potential methods for culturing bone-related organoids from pluripotent stem cells, adult stem cells, or progenitor cells, and discuss the current and promising bone disease organoids for drug screening and precision medicine. Lastly, we discuss the challenges and difficulties encountered in the application of bone organoids and look to the future in order to present potential methods via which bone organoids might advance organoid construction and application.

432A perspective on light-based bioprinting of DNA hydrogels for advanced bone regeneration: Implication for bone organoids.

Light-based three-dimensional (3D) printing of hydrogels has been widely adopted for accelerating bone regeneration. However, the design principles of traditional hydrogels do not take into consideration the biomimetic regulation of multiple stages throughout the bone healing, and the hydrogels made cannot effectively induce sufficient osteogenesis, which in turn greatly limits their capacity in guiding bone regeneration. The recent progress achieved in DNA hydrogel, which is based on synthetic biology, could facilitate the innovation of the current strategy due to its advantages, such as resistance to enzymatic degradation, programmability, structural controllability, and mechanical properties. However, 3D printing of DNA hydrogel is not well defined and appears to have a few distinct early forms. In this article, a perspective on the early development of 3D printing of DNA hydrogels is presented, and a potential implication of the hydrogel-based bone organoids built-up for bone regeneration is proposed.

Ontogenic Identification and Analysis of Mesenchymal Stromal Cell Populations during Mouse Limb and Long Bone Development.

Bone-derived mesenchymal stromal cells (MSCs) differentiate into multiple lineages including chondro- and osteogenic fates and function in establishing the hematopoietic compartment of the bone marrow. Here, we analyze the emergence of different MSC types during mouse limb and long bone development. In particular, PDGFRαposSCA-1pos (PαS) cells and mouse skeletal stem cells (mSSCs) are detected within the PDGFRαposCD51pos (PαCD51) mesenchymal progenitors, which are the most abundant progenitors in early limb buds and developing long bones until birth. Long-bone-derived PαS cells and mSSCs are most prevalent in newborn mice, and molecular analysis shows that they constitute distinct progenitor populations from the earliest stages onward. Differential expression of CD90 and CD73 identifies four PαS subpopulations that display distinct chondro- and osteogenic differentiation potentials. Finally, we show that cartilage constructs generated from CD90pos PαS cells are remodeled into bone organoids encompassing functional endothelial and hematopoietic compartments, which makes these cells suited for bone tissue engineering.