Repair Of Cartilage Defects With Human Umbilical Cord Mesenchymal Stem Cells And Cartilage Extracellular Matrix Scaffold In A Rabbit Model

Objective:To investigate the feasibility of human umbilical cord mesenchymal stem cells (hUCMSCs)as seed cells of cartilage tissue engineering. The study mainly includes four parts: the firstpart was aimed to study the biological characteristics of hUCMSCs and construct tissueengineered cartilage with hUCMSCs and cartilage extracellular matrix scaffold in vitro andin nude rats; the second part was aimed to repair articular cartilage defects in nude rat wit hhUCMSCs encapsulated in fibrin gel; the third part was aimed to repair articular cartilagedefects in rabbits with hUCMSCs and cartilage extracellular matrix scaffold; the fourthpart was aimed to fabricate scaffolds that can release two growth factors for cartilage tissueengineering and detect the release profile in vitro.Methods:(1) the4th generation of hUCMSCs was selected for differentiation into chondrocytes,osteoblasts and adipocytes in vitro and flow cytometry analysis. Tissue engineeredcartilage was constructed with hUCMSCs and cartilage extracellular matrix scaffold invitro and implanted subcutaneously in the back of nude rats. After4weeks, the compositeswere harvested for histological analysis.(2) hUCMSCs encapsulated in fibrin gel werecultured with or without TGF-β1. After two weeks, the Dead/Live assay was performed.the composites were implanted into cartilage defects (2.0mm×1.0mm) in the patellargroove of distal femur of nude rats.4weeks post-implantation, nude rats were sacrificedfor histological analysis.(3) A full-thickness cartilage defect (4.0mm×1.0mm) wascreated in the patellar grove of distal femur of rabbits. The treatments were divided into four groups:①scaffolds without hUCMSCs,②scaffolds with undifferentiated hUCMSCs,③scaffolds with chondrogeneic differentiated hUCMSCs, and④control group with notreatment. Specimen were harvested at3,6,12,16months postoperatively followed bymacroscopic observation, histological analysis and GAG content measurement.Macroscopic appearance was evaluated according to the International Cartilage RepairSociety (ICRS) score, and histological appearance was scored according to a ModifiedO’Driscoll (MODS) score.(4) Double emulsion solvent evaporation technique was used toencapsulate insulin-like growth factor (IGF-1) into PLGA microspheres. Tissueengineering cartilage scaffolds were prepared by thermal-induced phase separation (TIPS)technique with cartilage extracellular matrix mixed with PLGA microspheres. TGF-β1wasbinded to the scaffold through plasma treatment technique.Results:1、 hUCMSCs could differentiate into chondrocytes, osteoblasts and adipocytes underspecific culture condition. Flow cytometry revealed that the P4passage of the cellsexpressed CD105，CD90，CD73，CD44and HLA-ABC, but did not express CD34,CD45and HLA-DPDQDR. Ectopic cartilage formation was verified with toluidineblue and safranin O staining positive in both the pre-differentiated and undifferentiatedgroup with the pre-differentiated group strong positive and the undifferentiated groupweak positive.2、 hUCMSCs encapsulated in fibrin gel differentiated into cartilage tissue in cartilagedefects of nude rats in both the pre-differentiated and undifferentiated group.3、 Undifferentiated group yielded higher ICRS score and MODS score thanpre-differentiated group at each time point. In both the undifferentiated andpre-differentiated group, the highest score was achieved at6months post-implantation,with decreasing scores at12months and16months post-implantation. At6monthspost-implantation, the undifferentiated group demonstrated higher GAG contents thanthe pre-differentiated group.4、 The diameter of PLGA microspheres range from3to10μm, with spherical shape, smooth surface, multi-cavity in the inner hollow structure. The two growth factors canbe entrapped in the cartilage extracellular matrix scaffold and released in a sustainedmanner lasting for over30days.Conclusion:1、 hUCMSCs own the capacity of ectopic cartilage formation. In vitro chondrogeneicdifferentiation of hUCMSCs is conducive for cartilage matrix formation in vivo.2、 hUCMSCs encapsulated in fibrin gel can differentiate into cartilage tissue inarticular cartilage defects in nude rats.3、 The articular cartilage defects can be repaired with hUCMSCs and cartilageextracellular matrix scaffolds. The repair effects by undifferentiated hUCMSCs wasbetter than by pre-differentiated hUCMSCs. The repair tissue began degeneration after16months post-implantation.4、 Insulin-like growth factor can be entrapped in the PLGA microspheres using W/O/Wdouble emulsion solvent evaporation technique; Both growth factors can be entrappedinto the scaffold by microspheres and plasma anchorage technique.