Adapting to the acidic environment of the NP: RADA16-PLGA (TGF-β3) induces chondrogenic differentiation of BMSCs

<b>Aim:</b> RADA16-PLGA composite scaffolds constructed with simultaneous loading of BMSCs and TGF-β3 and explored their ability for chondrogenic differentiation <i>in vitro</i>. <b>Methods:</b> The performance of the composite scaffolds is assessed by rheometer assay, electron microscopic structural observation and ELISA release assay. The biosafety of the composite scaffolds is assessed by cytocompatibility assay and cell migration ability. The chondrogenic differentiation ability of composite scaffolds is evaluated by Alisin blue staining, PCR and immunofluorescence staining. <b>Results:</b> The composite scaffold has a good ECM-like structure, the ability to control the release of TGF-β3 and good biocompatibility. More importantly, the composite scaffolds can induce the differentiation of BMSCs to chondrocytes. <b>Conclusion:</b> Composite scaffolds are expected to enhance the endogenous NP repair process. RADA16 aqueous solution, PLGA microspheres and BMSCs are mixed to form a composite aqueous solution. The aqueous solution is injected into the body and exposed to the acidic environment of the NP. The nucleus pulposus pH induces gelation of the aqueous solution to form a composite scaffold. The composite scaffold can function <i>in vivo</i>. It induces the differentiation of BMSCs into chondrocytes and subsequently secretes a large amount of ECM such as Collagen II, GAGAs and SOX-9. In addition, it also enhances the self-repair of endogenous BMSCs, which is to replenish the reduction of nucleus pulposus cells and the loss of ECM. There is an endogenous repair process during myeloid degeneration, but there is an insufficient number of stem cells and a lack of sustained release of growth factors. BMSCs can differentiate into chondrocytes and secrete extracellular matrix in response to TGFβ3. The physico-mechanical properties and ultrastructure of the RADA16 hydrogel meet the requirements of the target material. The suitable conditions for RADA16 are 1% w/v and pH = 7.0. The RADA16-PLGA hydrogel-microsphere composite scaffold structure can encapsulate TGF-β3 to form a good controlled release system. The suitable conditions for the composite scaffold are 1% w/v and pH = 7.0. Composite scaffolds have good cytocompatibility. Composite scaffolds can recruit BMSCs for migration to the composite scaffold. The composite scaffold can adapt to the acidic environment of the degenerated disc, inducing the differentiation of BMSCs to chondrocyte-like cells while secreting large amounts of ECM. Composite scaffolds are expected to enhance the endogenous NP repair process and are promising tissue-engineered scaffolds for IVDD repair.