Long-lasting, controlled-release, and minimally invasive injectable platforms that provide a stable blood concentration to promote bone regeneration are less well developed. Using hexagonal mesoporous silica (HMS) loaded with dexamethasone (DEX) and poly(lactic-co-glycolic acid) (PLGA), we prepared porous DEX/HMS/PLGA microspheres (PDHP). In contrast to HMS/PLGA microspheres (HP), porous HMS/PLGA microspheres (PHP), DEX/PLGA microspheres (DP), and DEX/HMS/PLGA microspheres (DHP), PDHP showed notable immuno-coordinated osteogenic capabilities and were best at promoting bone mesenchymal stem cell proliferation and osteogenic differentiation. PDHP were combined with methacrylated silk (SilMA) and sodium alginate (SA) to form an injectable photocurable dual-network hydrogel platform that could continuously release the drug for more than 4 months. By adjusting the content of the microspheres in the hydrogel, a zero-order release hydrogel platform was obtained in vitro for 48 days. When the microsphere content was 1%, the hydrogel platform exhibited the best biocompatibility and osteogenic effects. The expression levels of the osteogenic gene alkaline phosphatases, BMP-2 and OPN were 10 to 15 times higher in the 1% group than in the 0% group, respectively. In addition, the 1% microsphere hydrogel strongly stimulated macrophage polarization to the M2 phenotype, establishing an immunological milieu that supports bone regrowth. The aforementioned outcomes were also observed in vivo. The most successful method for correcting cranial bone abnormalities in SD rats was to use a hydrogel called SilMA/SA containing 1% drug-loaded porous microspheres (PDHP/SS). The angiogenic and osteogenic effects of this treatment were also noticeably greater in the PDHP/SS group than in the control and blank groups. In addition, PDHP/SS polarized M2 macrophages and suppressed M1 macrophages in vivo, which reduced the local immune-inflammatory response, promoted angiogenesis, and cooperatively aided in situ bone healing. This work highlights the potential application of an advanced hydrogel platform for long-term, on-demand, controlled release for bone tissue engineering.

Mitochondrial network architecture, which is closely related to mitochondrial function, is mechanically sensitive and regulated by multiple stimuli. However, the effects of microtopographic cues on mitochondria remain poorly defined. Herein, polycaprolactone (PCL) surfaces were used as models to investigate how micropatterns regulate mitochondrial network architecture and function in rat adipose-derived stem cells (rASCs). It was found that large pit (LP)-induced rASCs to form larger and more complex mitochondrial networks. Consistently, the expression of key genes related to mitochondrial dynamics revealed that mitochondrial fusion (MFN1 and MFN2) and midzone fission (DRP1 and MFF) were increased in rASCs on LP. In contrast, the middle pit (MP)-enhanced mitochondrial biogenesis, as evidenced by the larger mitochondrial area and higher expression of PGC-1. Both LP and MP promoted ATP production in rASCs. It is likely that LP increased ATP levels through modulating mitochondrial network architecture while MP stimulated mitochondria biogenesis to do so. Our study clarified the regulation of micropatterned surfaces on mitochondria, highlighting the potential of LP and MP as a simple platform to stimulate mitochondria and the subsequent cellular function of MSCs.

Osteopontin (OPN) is a key mediator of cell interactions with biomaterials. However, few studies have been dedicated to studying cell adhesion on OPN-adsorbed substrates with controlled charge and wettability. Here, amino–carboxyl (NH₂/COOH) and hydroxyl–methyl (OH/CH₃) mixed self-assembled monolayers (SAMs) of varying charges and wettability, respectively, were used as controllable model surfaces to study OPN adsorption and subsequent mesenchymal stem cell (MSC) adhesion. The amount of OPN adsorbed onto the NH₂/COOH mixed SAMs appeared to monotonically depend on the surface charge, whereas only a moderately hydrophilic surface was conducive to OPN adsorption on OH/CH₃ mixed SAMs. The results correlated well with cell spreading on OPN-coated surfaces in a serum-free medium culture. In addition, the OH/CH₃ mixed SAMs with moderate wettability tended to promote β₁, β₃, α_v and α₅ integrins, indicating that wettability may guide cell adhesion by mediating the integrins signaling pathway. This work will have reference value for designing biologically responsive substrate surfaces.

Aims: This study aimed to examine the differences in bone induction and osseointegration performance of acellular extracellular matrix bone at different sites.Methods: We decellularized bone from bovine epiphysis near the marrow cavity (NMC), the middle of the cancellous bone (MCB), and near the cartilage (NC). The characterization, physicochemical properties, and effectiveness of the decellularization process of decellularized extracellular matrix (dECM) were analyzed. The proliferation, adhesion, seeding efficiency, and osteogenic differentiation properties of bone marrow mesenchymal stem cells (BMSCs) on decellularized extracellular matrix were investigated. The osteogenicity and osteointegration of dECM from different sources were verified in vivo by animal experiments, and the compatibility of dECM in vivo was also verified.Results: The NC group had the most significant compressive properties, where the compressive strength was about 1.62 times higher than that of the MCB group (p = 0.022) and 1.34 times higher than that of the NMC group (p < 0.001). dECM scaffolds had good histocompatibility and supported the adhesion and proliferation of BMSCs. In vitro, compared with the remaining two groups, the MCB group significantly upregulated the expression of osteogenic genes (alkaline phosphatase (ALP), runt-related transcription factor 2 (RUNX2), osteopontin (OPN), collagen type 1 (COL1), and bone morphogenetic protein 2 (BMP2)) and marker proteins (ALP, BMP2), whereas the NC group showed the weakest osteoinductive properties. In vivo, we confirmed that the MCB group possessed the most significant osteogenic and osseointegrative properties, followed by the NMC group, and the NC group proved to be the weakest. In particular, the MCB group possessed the ability to endogenously immunomodulate macrophage M1 phenotype to M2 phenotype polarization, creating the most favourable immune microenvironment for osteogenesis.Conclusion: Our data indicated that the xenogenic dECM scaffolds in MCB position possess the most significant biocompatibility and in vitro and in vivo induced osteogenesis and osseointegration properties. This study provides a more complete basis for the selection of dECM scaffolds in bone defect repair. In future studies of dECM composites applied to bone tissue engineering (BTE), utilizing the middle part of cancellous bone may be the best solution.Cite this article: Bone Joint Res 2025;14(4):292–308.