Chao Liu

Osteoarthritis (OA) is a heterogeneous disorder affecting multiple joint tissues, in which structural degeneration may be accompanied by varying degrees of synovial inflammation and immune–stromal dysregulation. Mesenchymal stem/stromal cells (MSCs) have demonstrated immunomodulatory and tissue-protective properties, increasingly linked to paracrine signaling. Comparative studies suggest that extracellular vesicles (EVs) make an important, but not exclusive, contribution to MSC paracrine activity, with soluble secretome components providing potentially complementary effects. Drawing on literature identified primarily through PubMed and Scopus and clinical trial records from ClinicalTrials.gov (updated through September 2026), this narrative review examines the immunomodulatory role of MSC-derived EVs (MSC-EVs) in OA, with emphasis on their interactions with the joint immune microenvironment and their contribution to tissue protection. Across experimental OA models, MSC-EVs have been reported to reduce synovitis, cartilage degeneration, subchondral bone alterations, and pain-related outcomes, although responses vary with MSC source, EV composition, engineering strategies, disease context, and treatment regimen. Mechanistically, the most consistent evidence supports modulation of macrophage-associated inflammatory responses, whereas effects on adaptive immune populations remain less established and are largely derived from non-OA models. Clinical evidence remains limited and currently provides mainly preliminary information on feasibility and short-term tolerability, with insufficient evidence to establish therapeutic efficacy. Overall, MSC-EVs represent a potential cell-free immunomodulatory approach for OA, but standardized manufacturing, product characterization, dosing, and rigorously controlled clinical trials are required to define their therapeutic value.

Inflammation is a key driver of cardiac disease progression, including heart failure and myocardial infarction, with macrophage‐cardiomyocyte interactions playing a central role in shaping the local inflammatory microenvironment. Prolonged exposure to pro‐inflammatory cytokines, many produced by macrophages, induces cardiomyocyte stress, dysfunction, and pathological tissue remodeling. However, the spatial and temporal dynamics of this crosstalk remain poorly understood, limiting the development of targeted therapies. To address this gap, we developed an in vitro cardiac inflammation model that enables controlled investigation of macrophage‐cardiomyocyte interactions. Cardiomyocytes were transduced with an NF‐κB‐responsive fluorescent reporter to allow real‐time monitoring of inflammatory signaling. MATLAB‐based simulations were used to optimize medium delivery and cell densities by modeling TNFα diffusion. Using a multiplex microfluidic co‐culture chip, we identified the TNFα threshold of 50 ng mL ^{− 1} with a 6‐h exposure as sufficient to activate cardiomyocyte NF‐κB signaling. Both macrophage‐conditioned medium and direct co‐culture significantly increased NF‐κB activation, indicating enhanced cardiomyocyte inflammatory stress. Dexamethasone markedly suppressed NF‐κB activation when administered at onset of co‐culture to both cell types, whereas IL‐10 showed limited efficacy. Overall, this cardiac inflammation model provides a versatile platform for dissecting immune‐cardiac crosstalk and supports future studies of multicellular crosstalk, spatiotemporal signaling dynamics, and therapeutic screening.

Microfluidic platforms offer controlled microenvironments for studying cell migration such as haptotaxis. In many gradient-based assays, protein gradients are first visualized using higher concentrations of fluorescent labels, since gradients formed at biologically relevant ligand densities often fall below the detection limits of conventional imaging methods. In this study, we demonstrate the feasibility of characterizing fibronectin gradients using a more sensitive, high-resolution approach with Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). Our methods increase analytical sensitivity to fibronectin gradients formed on commonly used synthetic surfaces to better elucidate physiological mechanisms and ensure experimental reproducibility. We utilized a microfluidic chip with a silicone housing placed on an optically clear plastic microscope slide designed for live-cell microscopy. Slides were coated with fibronectin incorporating surrogate labels for ToF-SIMS analysis to investigate spatial distribution. To enhance signal detection, fibronectin was labeled or conjugated with copper, bromine, and fluorine-containing BODIPY as surrogate elements. Among the tested labels, BODIPY-fibronectin (BODIPY-FN) provided the lowest background signal, enabling fluorescence-based detection at concentrations of 10 µg mL⁻¹ or higher, whereas ToF-SIMS demonstrated greater sensitivity, detecting fibronectin gradients at concentrations of 1 µg mL⁻¹ or higher. Semi-quantitative measurements using imaging mass spectrometry confirmed a graded distribution of fibronectin within the physiologically relevant “haptotaxis zone”, with detection sensitivity exceeding the limits of standard fluorescent microscopy. These results establish ToF-SIMS as a valid method for detecting surrogate-labeled ligand gradients, providing a reliable approach for future quantitative ligand measurements.

Skull morphogenesis is a complex, dynamic process involving two different germ layers and progressing to the coordinated, directional growth of individual bones. The mechanisms underlying directional growth toward the apex are not completely understood. Here, a microfluidic chip‐based approach is utilized to test whether calvarial osteoblast progenitors undergo haptotaxis on a gradient of Fibronectin1 (FN1) via lamellipodia. Mimicking the embryonic cranial mesenchyme's FN1 pattern, FN1 gradients is established in the chip using computer modeling and fluorescent labeling. Primary mouse calvarial osteoblast progenitors are plated in the chip along an array of segmented gradients of adsorbed FN1. The study performs single‐cell tracking and measures protrusive activity. Haptotaxis is observed at an intermediate FN1 concentration, with an average directional migration index (yFMI) of 0.07, showing a significant increase compared to the control average yFMI of ‐0.01. A significant increase in protrusive activity is observed during haptotaxis. Haptotaxis is an Arp2/3‐dependent, lamellipodia‐mediated process. Calvarial osteoblast progenitors treated with the Arp2/3 (Actin Related Protein 2/3 complex) inhibitor CK666 show significantly diminished haptotaxis, with an average yFMI of 0.01. Together, these results demonstrate haptotaxis on an FN1 gradient as a new mechanism in the apical expansion of calvarial osteoblast progenitors during development and shed light on the etiology of calvarial defects.

Paracrine signaling is challenging to study in vitro, as conventional culture tools dilute soluble factors and offer little to no spatiotemporal control over signaling. Microfluidic chips offer potential to address both of these issues. However, few solutions offer both control over onset and duration of cell–cell communication, and high throughput. We have developed a microfluidic chip designed to culture cells in adjacent chambers, separated by valves to selectively allow or prevent exchange of paracrine signals. The chip features 16 fluidic inputs and 128 individually-addressable chambers arranged in 32 sets of 4 chambers. Media can be continuously perfused or delivered by diffusion, which we model under different culture conditions to ensure normal cell viability. Immunocytochemistry assays can be performed in the chip, which we modeled and fine-tuned to reduce total assay time to 1 h. Finally, we validate the use of the chip for co-culture studies by showing that HEK293Ta cells respond to signals secreted by RAW 264.7 immune cells in adjacent chambers, only when the valve between the chambers is opened.