Introduction: Developing cartilage constructs with injectability, appropriate matrix composition and persistent cartilaginous phenotype remains an enduring challenge in cartilage repair. Bone marrow derived mesenchymal stem cells (BMSCs) have chondrogenic potential. Current approaches to drive their chondrogenic differentiation require extensive cell manipulation ex vivo and using exogenous growth factors. However, preventing hypertrophic transition of BMSCs in vivo and maintaining persistent chondrogenesis remain bottlenecks in clinical application. This study aimed to develop completely biological, injectable constructs to generate cartilage by co-transplanting chondrocyte and BMSCs. Methods: We fabricated fragmented chondrocyte macroaggregate (cell bricks) and mixed them with platelet rich plasma (PRP); BMSCs were mixed into the above constructs, allowed to clot and then subcutaneously injected into nude mice. Gross morphology observation, histological and immunohistochemical assay, immunofluorescence assay, biochemical analysis and gene expression analysis were used to compare the properties of BMSC-cell bricks-PRP complex with BMSC in PRP or BMSC/chondrocytes in PRP. Results: The constructs of BMSCs-cell bricks-PRP that were subcutaneously injected resulted in persistent chondrogenesis with appropriate morphology, adequate central nutritional perfusion without central necrosis or ossification, and further augmented nasal dorsum without obvious contraction and deformation. Conclusions: We concluded that cell bricks-enriched PRP clotting provides an autologous substance derived niche for chondrogenic differentiation of BMSCs in vivo, which suggests that such an injectable, completely biological system is a suitable stem cell carrier for micro-invasive cartilage repair.

Sox9 is an intrinsic transcription factor related to the determination and maintenance of chondrogenic lineage of bone marrow mesenchymal stem cells (BMSCs). In recent research, we have proved that fragmented chondrocyte aggregates (cell bricks) could promote chondrogenesis of BMSCs in vivo. However, it is still unknown whether the ratio of BMSCs/chondrocyte bricks has a significant influence on 3-D cartilage regeneration and related molecular mechanism. To address this issue, the current study subcutaneously injected three groups of cell complex with different rabbit BMSCs/chondrocyte bricks’ ratios (1 : 2, 1 : 1, and 2 : 1) into nude mice. Gross morphology observation, histological and immunohistochemical assays, biochemical analysis, gene expression analysis, and western blot were used to compare the influence of different BMSCs/chondrocyte bricks’ ratios on the properties of tissue-engineered cartilage and explore the related molecular mechanism. The constructs of 1 : 1 BMSCs/chondrocyte bricks, (B1CB1) group resulted in persistent chondrogenesis with appropriate morphology and adequate central nutritional perfusion without ossification. The related mechanism is that increased expression of Sox9 in the B1C1 group promoted chondrogenesis and inhibited the osteogenesis of BMSCs through upregulating Col-II as well as downregulating RUNX2 and downstream of Col-X and Col-I by upregulating Nkx3.2. This study demonstrated that BMSCs/chondrocyte bricks 1:1 should be a suitable ratio and the Sox9-Nkx3.2-RUNX2 pathway was a related mechanism which played an important role in the niche for stable chondrogenesis of BMSCs constructed by chondrocyte bricks and PRP.

Background: The lack of the ability to flexibly and accurately apply theoretical knowledge learned in the classroom to clinical diagnosis and treatment has been one of the biggest barriers preventing dental undergraduates transition into competent dentists. The flipped classroom model and simulation training system supporting self-directed learning have been a significant shift in medical education. Literatures about these topics are abundant, however, there are few practical flipped-classroom models which could help dental undergraduates adapt to the status of dentists quickly. This study proposed a novel extended flipped classroom model (P-I-T-D-S Flipped Classroom Model) assisted by the simulation training system and verified its effectiveness. Methods: The scores of sophomores majored in the Fundamentals of Stomatology at Air Force Medical University participated in the novel extended flipped classroom model and those participated in the traditional lecture model are compared. Moreover, a total of 39 participants (2023 cohort) were stratified and randomly assigned into a pre-class group and a post-class group to explore better flipped classroom model. We descriptively analysed the quantitative data and thematically analysed the qualitative data. Results: The scores of the undergraduates enrolled in the P-I-T-D-S Flipped Classroom Model (2023) are significantly higher than those taught under the Traditional Lecture-Based Model (2022). Notably, the scores in the pre-class group raised significantly higher than those in the post-class group, which might be related to the active learning model. Additionally, the undergraduates in the P-I-T-D-S Flipped Classroom Model showed higher willingness to participate in and satisfaction of the class. Conclusion: The P-I-T-D-S flipped classroom medical education model, through active learning, can effectively stimulate the learning enthusiasm of dental students, thereby improving their learning efficiency of basic dental knowledge and clinical practice ability.