Microdroplets Encapsulated with NFATc1-siRNA and Exosomes-Derived from MSCs Onto 3D Porous PLA Scaffold for Regulating Osteoclastogenesis and Promoting Osteogenesis

Introduction

Osteoporotic-related fractures remains a significant public health concern, thus imposing substantial burdens on our society. Excessive activation of osteoclastic activity is one of the main contributing factors for osteoporosis-related fractures. While polylactic acid (PLA) is frequently employed as a biodegradable scaffold in tissue engineering, it lacks sufficient biological activity. Microdroplets (MDs) have been explored as an ultrasound-responsive drug delivery method, and mesenchymal stem cell (MSC)-derived exosomes have shown therapeutic effects in diverse preclinical investigations. Thus, this study aimed to develop a novel bioactive hybrid PLA scaffold by integrating MDs-NFATc1-silencing siRNA to target osteoclast formation and MSCs-exosomes (MSC-Exo) to influence osteogenic differentiation (MDs-NFATc1/PLA-Exo).

Methods

Human bone marrow-derived mesenchymal stromal cells (hBMSCs) were used for exosome isolation. Transmission electron microscopy (TEM) and confocal laser scanning microscopy were used for exosome and MDs morphological characterization, respectively. The MDs-NFATc1/PLA-Exo scaffold was fabricated through poly(dopamine) and fibrin gel coating. Biocompatibility was assessed using RAW 264.7 macrophages and hBMSCs. Osteoclast formations were examined via TRAP staining. Osteogenic differentiation of hBMSCs and cytokine expression modulation were also investigated.

Results

MSC-Exo exhibited a cup-shaped structure and effective internalization into cells, while MDs displayed a spherical morphology with a well-defined core-shell structure. Following ultrasound stimulation, the internalization study demonstrated efficient delivery of bioactive MDs into recipient cells. Biocompatibility studies indicated no cytotoxicity of MDs-NFATc1/PLA-Exo scaffolds in RAW 264.7 macrophages and hBMSCs. Both MDs-NFATc1/PLA and MDs-NFATc1/PLA-Exo treatments significantly reduced osteoclast differentiation and formation. In addition, our results further indicated MDs-NFATc1/PLA-Exo scaffold significantly enhanced osteogenic differentiation of hBMSCs and modulated cytokine expression.

Discussion

These findings suggest that the bioactive MDs-NFATc1/PLA-Exo scaffold holds promise as an innovative structure for bone tissue regeneration. By specifically targeting osteoclast formation and promoting osteogenic differentiation, this hybrid scaffold may address key challenges in osteoporosis-related fractures.

Fabrication of Interleukin-4 Encapsulated Bioactive Microdroplets for Regulating Inflammation and Promoting Osteogenesis

Background

Despite the inherent regenerative ability of bone, large bone defect regeneration remains a major clinical challenge for orthopedic surgery. Therapeutic strategies medicated by M2 phenotypic macrophages or M2 macrophage inducer have been widely used to promote tissue remodeling. In this study, ultrasound-responsive bioactive microdroplets (MDs) encapsulated with bioactive molecule interleukin-4 (IL4, hereafter designated MDs-IL4) were fabricated to regulate macrophage polarization and potentiate the osteogenic differentiation of human mesenchymal stem cells (hBMSCs).

Materials and Methods

The MTT assay, live and dead staining, and phalloidin/DAPI dual staining were used to evaluate biocompatibility in vitro. H&E staining was used to evaluate biocompatibility in vivo. Inflammatory macrophages were further induced via lipopolysaccharide (LPS) stimulation to mimic the pro-inflammatory condition. The immunoregulatory role of the MDs-IL4 was tested via macrophage phenotypic marker gene expression, pro-inflammatory cytokine level, cell morphological analysis, and immunofluorescence staining, etc. The immune-osteogenic response of hBMSCs via macrophages and hBMSCs interactions was further investigated in vitro.

Results

The bioactive MDs-IL4 scaffold showed good cytocompatibility in RAW 264.7 macrophages and hBMSCs. The results confirmed that the bioactive MDs-IL4 scaffold could reduce inflammatory phenotypic macrophages, as evidenced by changing in morphological features, reduction in pro-inflammatory marker gene expression, increase of M2 phenotypic marker genes, and inhibition of pro-inflammatory cytokine secretion. Additionally, our results indicate that the bioactive MDs-IL4 could significantly enhance the osteogenic differentiation of hBMSCs via its potential immunomodulatory properties.

Conclusion

Our results demonstrate that the bioactive MDs-IL4 scaffold could be used as novel carrier system for other pro-osteogenic molecules, thus having potential applications in bone tissue regeneration.