Sequential Dual-Biofactor Release from the Scaffold of Mesoporous HA Microspheres and PLGA Matrix for Boosting Endogenous Bone Regeneration

Ultrasound-triggered functional hydrogel promotes multistage bone regeneration

The dysfunction of bone mesenchymal stem cells (BMSCs), caused by the physical and chemical properties of the inflammatory and repair phases of bone regeneration, contributes to the failure of bone regeneration. To meet the spatiotemporal needs of BMSCs in different phases, designing biocompatible materials that respond to external stimuli, improve migration in the inflammatory phase, reduce apoptosis in the proliferative phase, and clear the hurdle in the differentiation phase of BMSCs is an effective strategy for multistage repair of bone defects. In this study, we designed a cascade-response functional composite hydrogel (Gel@Eb/HA) to regulate BMSCs dysfunction in vitro and in vivo. Gel@Eb/HA improved the migration of BMSCs by upregulating the expression of chemokine (C-C motif) ligand 5 (CCL5) during the inflammatory phase. Ultrasound (US) triggered the rapid release of Ebselen (Eb), eliminating the accumulation of reactive oxygen species (ROS) in BMSCs, and reversing apoptosis under oxidative stress. Continued US treatment accelerated the degradation of the materials, thereby providing Ca2+ for the osteogenic differentiation of BMSCs. Altogether, our study highlights the prospects of US-controlled intelligent system, that provides a novel strategy for addressing the complexities of multistage bone repair.

Rapid fabrication of biomimetic PLGA microsphere incorporated with natural porcine dermal aECM for bone regeneration

Bioactive microspheres coated with acellular extracellular matrix (aECM) have received extensive attention in bone tissue engineering. In this work, biomimetic microspheres with different aECM ratios, uniform size and controllable size were prepared easily by blending natural porcine dermal aECM and poly (lactic-co-glycolic acid) (PLGA) using electrohydrodynamic spraying and solidification actuated by solvent extraction method. In this work, the appropriate polymer concentration and preparation voltage were investigated, and the surface morphology of the microspheres was observed by scanning electron microscope. Sirius red was used to visualize aECM exposure on the surface of the microspheres. The in vitro and in vivo experiments were carried out to evaluate the bioactivity and osteogenic properties of the microspheres. The results showed that the morphology and size of PLGA microspheres had little influence on the aECM blending. In vitro experiments showed that the higher the content of aECM, the better the cell adhesion performance. In vivo, rat calvarial defect models were observed and characterized at 4 and 8 weeks postoperatively, and the values of BV/TV of 50aECM/PLGA were 47.57 ± 1.14% and 72.92 ± 2.19%, respectively. The results showed that the skull healing effect was better in aECM-containing microspheres. In conclusion, aECM/PLGA composite microspheres can increase cell adhesion performance through the addition of aECM. Moreover, in vivo experiments have proved that aECM/PLGA microspheres are beneficial to bone repair, which means the aECM/PLGA microspheres are a promising bone tissue engineering material.

A bilayer bioengineered patch with sequential dual-growth factor release to promote vascularization in bladder reconstruction

Bladder tissue engineering holds promise for addressing bladder defects resulting from congenital or acquired bladder diseases. However, inadequate vascularization significantly impacts the survival and function of engineered tissues after transplantation. Herein, a novel bilayer silk fibroin (BSF) scaffold was fabricated with the capability of vascular endothelial growth factor (VEGF) and platelet derived growth factor-BB (PDGF-BB) sequential release. The outer layer of the scaffold was composed of compact SF film with waterproofness to mimic the serosa of the bladder. The inner layer was constructed of porous SF matrix incorporated with SF microspheres (MS) loaded with VEGF and PDGF-BB. We found that the 5% (w/v) MS-incorporated scaffold exhibited a rapid release of VEGF, whereas the 0.2% (w/v) MS-incorporated scaffold demonstrated a slow and sustained release of PDGF-BB. The BSF scaffold exhibited good biocompatibility and promoted endothelial cell migration, tube formation and enhanced endothelial differentiation of adipose derived stem cells (ADSCs) in vitro. The BSF patch was constructed by seeding ADSCs on the BSF scaffold. After in vivo transplantation, not only could the BSF patch facilitate the regeneration of urothelium and smooth muscle, but more importantly, stimulate the regeneration of blood vessels. This study demonstrated that the BSF patch exhibited excellent vascularization capability in bladder reconstruction and offered a viable functional bioengineered patch for future clinical studies.

A Novel Strategy for Fabrication of Polyamide 66/Nanohydroxyapatite Composite Bone Repair Scaffolds by Low-Temperature Three-Dimensional Printing

Due to the decomposition temperature of Polyamide 66 (PA66) in the environment is close to its thermoforming temperature, it is difficult to construct porous scaffolds of PA66/nanohydroxyapatite (PA66/HAp) by fused deposition modeling (FDM) three-dimensional (3D) printing. In this study, we demonstrated for the first time a method for 3D printing PA66/HAp composites at room temperature, prepared PA66/HAp printing ink using a mixed solvent of formic acid/dichloromethane (FA/DCM), and constructed a series of composite scaffolds with varying HAp content. This printing system can print composite materials with a high HAp content of 60 wt %, which is close to the mineral content in natural bone. The physicochemical evaluation presented that the hydroxyapatite was uniformly distributed within the PA66 matrix, and the PA66/HAp composite scaffold with 30 wt % HAp content exhibited optimal mechanical properties and printability. The results of in vitro cell culture experiments indicated that the incorporation of HAp into the PA66 matrix significantly improved the cell adhesion, proliferation, and osteogenic differentiation of bone marrow stromal cells (BMSCs) cultured on the scaffold. In vivo animal experiments suggested that the PA66/HAp composite material with 30 wt % HAp content had the best structural maintenance and osteogenic performance. The three-dimensional PA66/HAp composite scaffold prepared by low temperature printing in the current study holds great potential for the repair of large-area bone defects.

M2 macrophage-derived exosome-functionalized topological scaffolds regulate the foreign body response and the coupling of angio/osteoclasto/osteogenesis

Designing scaffolds that can regulate the innate immune response and promote vascularized bone regeneration holds promise for bone tissue engineering. Herein, electrospun scaffolds that combined physical and biological cues were fabricated by anchoring reparative M2 macrophage-derived exosomes onto topological pore structured nanofibrous scaffolds. The topological pore structure of the fiber and the immobilization of exosomes increased the nanoscale roughness and hydrophilicity of the fibrous scaffold. In vitro cell experiments showed that exosomes could be internalized by target cells to promote cell migration, tube formation, osteogenic differentiation, and anti-inflammatory macrophage polarization. The activation of fibrosis, angiogenesis, and macrophage was elucidated during the exosome-functionalized fibrous scaffold-mediated foreign body response (FBR) in subcutaneous implantation in mice. The exosome-functionalized nanofibrous scaffolds also enhanced vascularized bone formation in a critical-sized rat cranial bone defect model. Importantly, histological analysis revealed that the biofunctional scaffolds regulated the coupling effect of angiogenesis, osteoclastogenesis, and osteogenesis by stimulating type H vessel formation. This study elaborated on the complex processes within the cell microenvironment niche during fibrous scaffold-mediated FBR and vascularized bone regeneration to guide the design of implants or devices used in orthopedics and maxillofacial surgery. STATEMENT OF SIGNIFICANCE: How to design scaffold materials that can regulate the local immune niche and truly achieve functional vascularized bone regeneration still remain an open question. Here, combining physical and biological cues, we proposed new insight to cell-free and growth factor-free therapy, anchoring reparative M2 macrophage-derived exosomes onto topological pore structured nanofibrous scaffolds. The exosomes functionalized-scaffold system mitigated foreign body response, including excessive fibrosis, tumor-like vascularization, and macrophage activation. Importantly, the biofunctional scaffolds regulated the coupling effect of angiogenesis, osteoclastogenesis, and osteogenesis by stimulating type H vessel formation.

Neuro-bone tissue engineering: emerging mechanisms, potential strategies, and current challenges

The skeleton is a highly innervated organ in which nerve fibers interact with various skeletal cells. Peripheral nerve endings release neurogenic factors and sense skeletal signals, which mediate bone metabolism and skeletal pain. In recent years, bone tissue engineering has increasingly focused on the effects of the nervous system on bone regeneration. Simultaneous regeneration of bone and nerves through the use of materials or by the enhancement of endogenous neurogenic repair signals has been proven to promote functional bone regeneration. Additionally, emerging information on the mechanisms of skeletal interoception and the central nervous system regulation of bone homeostasis provide an opportunity for advancing biomaterials. However, comprehensive reviews of this topic are lacking. Therefore, this review provides an overview of the relationship between nerves and bone regeneration, focusing on tissue engineering applications. We discuss novel regulatory mechanisms and explore innovative approaches based on nerve-bone interactions for bone regeneration. Finally, the challenges and future prospects of this field are briefly discussed.