Bone regeneration and repair are crucial to ambulation and quality of life. Factors such as poor general health, serious medical comorbidities, chronic inflammation, and ageing can lead to delayed healing and nonunion of fractures, and persistent bone defects. Bioengineering strategies to heal bone often involve grafting of autologous bone marrow aspirate concentrate (BMAC) or mesenchymal stem cells (MSCs) with biocompatible scaffolds. While BMAC shows promise, variability in its efficacy exists due to discrepancies in MSC concentration and robustness, and immune cell composition. Understanding the mechanisms by which macrophages and lymphocytes – the main cellular components in BMAC – interact with MSCs could suggest novel strategies to enhance bone healing. Macrophages are polarized into pro-inflammatory (M1) or anti-inflammatory (M2) phenotypes, and influence cell metabolism and tissue regeneration via the secretion of cytokines and other factors. T cells, especially helper T1 (Th1) and Th17, promote inflammation and osteoclastogenesis, whereas Th2 and regulatory T (Treg) cells have anti-inflammatory pro-reconstructive effects, thereby supporting osteogenesis. Crosstalk among macrophages, T cells, and MSCs affects the bone microenvironment and regulates the local immune response. Manipulating the proportion and interactions of these cells presents an opportunity to alter the local regenerative capacity of bone, which potentially could enhance clinical outcomes.Cite this article: Bone Joint Res 2024;13(9):462–473.

To investigate the interaction among the cells thought to be foundational to inflammation, fibrosis, and angiogenesis in the synovial membrane. We encapsulated fibroblasts, polarized macrophages, and endothelial cells in a 3D culture system. We used this model to determine the cellular transcriptional profiles, cytokine secretion, and vascular formation associated with different macrophage phenotype conditions. Neo-angiogenesis reached its maximum level at approximately day 21 in the presence of pro-inflammatory macrophages conditions, but was sustained in the presence of anti-inflammatory macrophages. RNA sequencing revealed an influence of macrophage phenotype on gene expression associated with fibrosis and angiogenesis. Furthermore, by including lipopolysaccharides-coated polyethylene particles (lcPE), an inflammatory stimulus replicating wear debris from joint replacements into our system, insights into the local reaction to byproducts of different biomaterials can be ascertained. Chronic inflammation and fibrosis of the synovial membrane are often present in osteoarthritis and post-total joint arthroplasty. Our results suggest that the progression of inflammatory synovial diseases is influenced by macrophage phenotypes.

Establish alternative strategies to standard animal experiments decrease animal utilization and simultaneously enhance the reliability of biological and disease models. This review highlights advancements in three areas: in vitro culture platforms, disease modeling, and in silico simulations. We first discuss the innovative in vitro approaches, including 2D coculture systems, 3D spheroids, organoids, and organ-on-chip models, which facilitate the creation of physiologically relevant environments. Then, we focus on cell selection and characterization in disease modeling, with a particular focus on bone fracture healing and inflammation. We further review the potential of in silico simulations, including molecular docking, machine learning (ML) approaches, and pharmacokinetics-pharmacodynamics (PK/PD) modeling, to predict drug efficacy, interactions, and biological outcomes. These alternative strategies provide the potential for obtaining accurate and consistent results, thereby enhancing biomedical research and decreasing dependence on animal models. The Translational Potential of this Article: This review examines in vitro organoids, microphysiological systems, and computational models as alternatives to animal testing. These methods enhance our understanding of biological mechanisms. They also reduce the requirement for animal models. Ultimately, they help accelerate drug discovery that can directly benefit patients.

This study establishes a murine model of corticosteroid-associated osteonecrosis of the femoral head (ONFH) using a sustained-release prednisolone pellet and evaluates mitochondrial stress using ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography (PET/CT) and changes in key histologic markers of bone over a 6-week period. Sixteen 12-week-old Balb/C mice were divided into two groups: a prednisolone group (PRED) and a control group (SHAM). The PRED group received a subcutaneous 60-day sustained-release pellet containing 2.5 mg of prednisolone, while the SHAM group received placebo pellets. PET/CT imaging was performed at 1, 3, and 6 weeks. Bone mineral density (BMD) measurements, and histomorphological analyses for the number of empty lacunae, osteoblasts, osteoclasts, and NADPH oxidase (NOX) 2, a marker for oxidative stress, were conducted at 4 or 6 weeks. PET/CT imaging demonstrated increased uptake in the femoral head at 3 weeks in the PRED group. This was accompanied by increased numbers of empty lacunae and osteoclasts, increased oxidative stress, and decreased alkaline phosphatase staining at 4 weeks in the PRED group. We have successfully established and validated a small murine model of ONFH. The findings of this preclinical study suggest a critical timeline for potential interventions to mitigate the early adverse effects of continuous corticosteroid exposure on bone.