Branched Channels in Porous β-Tricalcium Phosphate Scaffold Promote Vascularization

Rapid and efficient vascularization is still considerably challenging for a porous β-tricalcium phosphate (β-TCP) scaffold to achieve. To overcome this challenge, branched channels were created in the porous β-TCP scaffold by using 3D printing and a template-casting method to facilitate the instant flow of blood supply. Human bone mesenchymal stem cells (hBMSCs) and human umbilical vein endothelial cells (HUVECs) were seeded in the channeled porous scaffolds and characterized through a double-stranded DNA (dsDNA) assay, alkaline phosphatase (ALP) assay, and cell migration. Channeled porous β-TCP scaffolds were then implanted in the subcutaneous pockets of mice. Histological staining and immunohistochemical staining on vascularization and bone-related markers were carried out on the embedded paraffin sections. Results from in vitro experiments showed that branched channels significantly promoted HUVECs' infiltration, migration, proliferation, and angiogenesis, and also promoted the proliferation and osteogenesis differentiation of hBMSCs. In vivo implantation results showed that, in the early stage after implantation, cells significantly migrated into branched channeled scaffolds. More matured blood vessels formed in the branched channeled scaffolds compared to that in nonchanneled and straight channeled scaffolds. Beside promoting vascularization, the branched channels also stimulated the infiltration of bone-related cells into the scaffolds. These results suggested that the geometric design of branched channels in the porous β-TCP scaffold promoted rapid vascularization and potentially stimulated bone cells recruitment.

Manipulating Mesenchymal Stem Cell Differentiation on Nanopattern Constructed through Cell-Mediated Mineralization

The extracellular matrix microenvironment, including chemical constituents and topological structure, plays key role in regulating the cell behavior, such as adhesion, proliferation, differentiation, apoptosis, etc. Until now, to investigate the relationship between surface texture and cell response, various ordered patterns have been prepared on the surface of different matrixes, whereas almost all these strategies depend on advanced instruments or severe synthesis conditions. Herein, cell-mediated mineralization method has been applied to construct nanopattern on the surface of β-TCP scaffold. The formation process, morphology, and composition of the final pattern were characterized, and a possible mineralization mechanism has been proposed. Moreover, the cell behavior on the nanopattern has been investigated, and the results showed that the mouse bone marrow mesenchyme stem cells (mBMSCs) display good affinity with the nanopattern, which was manifested by the good proliferation and osteogenic differentiation status of cells. The synthetic strategy may shed light to construct advanced topological structures on other matrixes for bone repair.

Engineering Porous β-Tricalcium Phosphate (β-TCP) Scaffolds with Multiple Channels to Promote Cell Migration, Proliferation, and Angiogenesis

Inadequate oxygen and nutrient diffusion in a porous scaffold often resulted in insufficient formation of branched vasculatures, which hindered bone regeneration. In this study, interconnected porous β-tricalcium phosphate (β-TCP) scaffolds with different geometric designs of channels were fabricated and compared to discover the functionality of structure on facilitating nutrient diffusion for angiogenesis. In vitro fluid transportation and degradation of the scaffolds were performed. Cell infiltration, migration, and proliferation of human umbilical vein endothelial cells (HUVECs) on the scaffolds were carried out under both static and dynamic culture conditions. A computational simulation model and a series of immunofluorescent staining were implemented to understand the mechanism of cell behavior in response to different types of scaffolds. Results showed that geometry with multiple channels significantly accelerated the release of Ca²⁺ and increased the fluid diffusion efficiency. Moreover, multiple channels promoted HUVECs' infiltration and migration in vitro. The ex vivo implantation results showed that the channels promoted cells from the rats' calvarial bone explants to infiltrate into the implanted scaffold. Multiple channels also stimulated HUVECs' proliferation prominently at both static and dynamic culturing conditions. The expression of both cell migration-related protein α5 and angiogenesis-related protein CD31 on multiple-channeled scaffolds was upregulated compared to that on the other two types of scaffolds, implying that multiple channels reinforced cell migration and angiogenesis. All the findings suggested that the geometric design of multiple channels in the porous β-TCP scaffold has promising potential to promote cell infiltration, migration, and further vascularization when implanted in vivo.

Evaluation of the role of autogenous bone-marrow-derived mesenchymal stem cell transplantation for the repair of mandibular bone defects in rabbits

The repair of craniofacial bony defects by traditional grafting techniques requires substantial time and effort, with associated morbidity. Tissue engineering has therefore become a novel approach targeting application for bone regeneration. This study used the rabbit model for radiographic and histological evaluation of bone bioengineering for mandibular defects reconstruction using only β-tricalcium phosphate (β-TCP) and, when loaded with autogenous; bone marrow-derived undifferentiated mesenchymal stem cells (BM-MSCs). Critical-sized defects (10 × 15 mm) were created unilaterally in the mandibular body region of each rabbit (n = 16), to be filled with the BM-MSCs/β-TCP constructs for the study group (group I) (n1 = 8) and with scaffold devoid of cells for the control group (group II) (n2 = 8). Two rabbits from each group were sacrificed after healing periods of 2, 4, 12, and 24 weeks. The results revealed that the BM-MSCs endowed β-TCP scaffold with a better and more rapid bone regenerating potential: since the first evaluation period of 2 weeks, the regenerated bone tissue in group I was more mature, denser and homogeneously distributed. From these findings we could infer that the bone regeneration process was jump-started within the study group cases, which led to better quality of regenerated bone.