Antonios G. Mikos

Infection is the most common complication of osteoporotic fractures, often characterized by bacterial resistance and intracellular infection, posing a major challenge in the treatment of osteoporotic fractures. Here, we developed a multifunctional biomimetic Trojan horse nanosystem based on hydroxyapatite nanotubes (NT‐HA) for microenvironment remodeling. The NT‐HA exhibits a dual‐stage antimicrobial peptide (AMP) delivery strategy, in which surface‐adsorbed AMPs are rapidly released to eliminate extracellular bacteria, while NT‐HA is internalized via endocytosis to release encapsulated AMPs for efficient intracellular bacterial clearance. After releasing AMPs, the NT‐HA can regulate the PI3K‐AKT signaling cascade, promoting the directed osteogenic differentiation of osteoporotic bone marrow mesenchymal stem cells (OBMSCs). In the repair of infected osteoporotic bone defects in vivo, this Trojan horse nanosystem not only enhances bone regeneration by eliminating cellular infections and inducing OBMSCs osteogenesis but also reduces peri‐implant bone loss and strengthens bone strength, ultimately remodeling the regenerative microenvironment to achieve optimal bone defect repair and functional reconstruction.

The osteochondral unit has a complex hierarchical structure where cartilage and subchondral bone show different physical, chemical, and functional properties. Replicating this structure remains a major challenge in osteochondral tissue engineering. Among various scaffold design factors, surface topography has emerged as a powerful regulator of cell behavior, but its rational integration into osteochondral constructs is still limited. This review systematically explores how topographical features affect cartilage and bone regeneration, focusing especially on feature size and anisotropy. Evidence across in vitro and in vivo studies indicates that nanoscale topographies better support chondrogenic differentiation and cartilage-like extracellular matrix formation by resembling natural cartilage, with isotropic features helping maintain chondrocyte shape. In contrast, microscale features tend to promote osteogenic differentiation, mineralization, and bone tissue organization, although osteogenic responses have also been observed on certain nanoscale topographies that mimic trabecular bone spaces. Anisotropic topographies further improve tissue-specific responses by guiding cell alignment and promoting organized matrix deposition across both cartilage and bone regions. Overall, these results highlight surface topography as a key design parameter for coordinating osteochondral regeneration. These complementary effects suggest that combining multi-scale and spatially graded topographies could imitate natural tissue architecture, enabling coordinated regeneration of cartilage and bone and offering a promising approach for functional osteochondral repair. Therefore, this review outlines practical design principles to guide the development of next-generation biomaterials for functional osteochondral repair.

Background and objectives: Bone is a multicellular organ that is the site of complex pathophysiological events (such as cancer). 3D confocal and multiphoton microscopy, followed by manual analysis and quantification, allow the identification of molecular, cellular, and tissue mechanisms in their original context, enabling the investigation of spatial biology at subcellular level. The automation of these analyses is becoming increasingly important due to their time-consuming nature, lack of standardization, and inter-subject variability. Methods: Deep learning applied to image analysis could overcome current limitations and optimize preclinical research. This includes automatic semantic segmentation of bone cells (osteoblasts, osteoclasts, and blood vessels) and mineral component, followed by parameter extraction and quantification. Accordingly, fluorescence microscopy images were generated, pre-processed, and fed (total 21,395 images: 17,104 for training, 4291 for validation) into a neural network-based architecture named Bo-Net. Results: The fully automatic Bo-Net achieved strong performance across the tested metrics and segmentation accuracy similar to experienced biologists (R = 0.81–0.99 for parameters tested) and improved analysis time from days to seconds in a variety of experimental conditions, confirming its relevance in different biologically relevant contexts. Conclusions: As a result, a fully automated, yet reliable, tool to optimize the analysis of multiparametric fluorescence microscopy images available to the bone research community was generated.

Whitlockite (WH), a natural magnesium-containing calcium phosphate second in abundance only to hydroxyapatite (HAp) in the inorganic phase of bone tissue, has attracted great attention in bone repair recently. Previous studies have shown that porous structures play a pivotal role in bone defect repair using biomaterials. However, the traditional fabrication process of porous ceramic through high-temperature sintering frequently results in the dehydration and breakdown of WH. To overcome this challenge, we develop an innovative fabrication of porous whitlockite ceramic via in-situ phase transformation from calcium phosphate ceramic. Furthermore, we perform molecular dynamics (MD) and determine intermediates to delve into a comprehensive exploration of the underpinning mechanism of the transformation. In-vitro cellular responses reveal the superior cell proliferation, adhesion, spreading, migration, and osteogenic and angiogenic differentiation of porous WH ceramic. Mechanistically, our results reveal that the Mg²⁺-mediated regulation of ATP levels activates the AMPK-FoxO signaling axis, which enhances osteogenesis through autophagy. Intramuscular implantation evaluation confirms the satisfactory osteoinduction, and further rat mandibular defect implantation reveals significant bone regeneration in comparison to calcium phosphate ceramic. Together, the porous WH ceramic encompasses enhanced potential for the regenerative amelioration of bone defects.

The mandible is the largest craniofacial bone and plays a crucial role in speech, mastication, swallowing, and facial aesthetics. The form or function of the mandible can be altered by defects as a result of tumors, trauma, infection, and congenital conditions. This paper covers the evolution of biomaterials-based approaches to the reconstruction of critical size mandibular defects. Historically the gold standard for critical size mandibular defect repair has been autologous fibula grafts. The emergence of the field of tissue engineering has led to the current research on biomaterial scaffolds, cells, and biological factors to design highly tunable, bio-inspired, tissue regenerative implants. Scaffold materials can be synthetic or natural and can be fabricated using a variety of additive manufacturing techniques. Mesenchymal stem cells, bone morphogenetic proteins, and transforming growth factor-β are frequently added to scaffolds. While great progress has been made, there are still barriers to translating this research to patients, ranging from insufficient bone regeneration in animal studies to the feasibility of establishing a good manufacturing practice. To address these challenges, the future of mandibular tissue engineering will look toward improving implant vascularization and innervation, personalizing implant shape and biology, and enhancing spatiotemporal control of drug release. With these goals in mind, researchers will ultimately develop biomaterials that can regenerate bone that is structurally and biologically identical to native mandibular tissue, improving both function and quality of life for patients.

Supplementary Table 1 from Mapping the Single-Cell Differentiation Landscape of Osteosarcoma

Cell cycle score for each cluster in the MTL