Study On Microspheres Loaded With RhBMP-2Derived Oligopeptide And Related Scaffolds

Bone morphogenetic protein (BMP) is labile and expensive protein whichprevents its extensive application in bone repair. So, it is necessary to loadthem into some veichles. In this contribution, poly (lactide-co-glycolide)microspheres (abbreviated as PLGA microspheres), PLGA/chitosanmicrospheres (abbreviated as PLGA/CS microspheres) and PLGAmicrospheres/nano-hydroxyapatite-collagen/chitosan scaffold (abbreviated asPLGA microspheres/nHAC/chitosan scaffold) were individually preparedrespectively for delivering the oligopeptide derived from BMP-2(Peptide-24).PLGA microspheres were prepared for delivering Peptide-24withre-emulsification. The morphology and diameter of five kinds of PLGAmicrospheres were detected, and their drug-loading rates and encapsulationrates were compared. Five kinds of PLGA microspheres were incubated for3and30days to obtain the release supernatant and study the stability andbioactivity of released Peptide-24. The structure integrity and molecularweight retention of the Peptide-24in released fluids were confirmed. Thereleased Peptide-24was also proved to retaining perfect bioactivity by thecellular activity and the alkaline phosphatase (ALP) test.PLGA/CS microspheres with spheres-in-sphere structure were prepared.The PLGA microspheres and PLGA/CS microspheres were characterized interms of their size distribution, morphology, drug-loading rate, zeta potentialand physical-chemical properties. The incubation experiments of PLGAmicrospheres and PLGA/CS microspheres were manipulated in PBS solutionat pH7.4,37℃to monitor the release of model protein and the vehicledegradation. External CS crusts were proved to strikingly reduce initial burstrelease, extend continuous release and avoid the decrease of pH value inmiro-milieu.PLGA/CS microspheres were successfully constructed through adjustingthe amount of Peptide-24in twice delivery. Comparing with chitosan microspheres, the PLGA/CS microspheres have excellent release curves withzero-order kinetics and controllable model. The released Peptide-24kept itsoriginal structure and relative molecular weight. The changes of the matrixmolecular weight can explain the changes of pH value in micro-milieu whileincorporating the changes of the matrix morphology. Additionally, two kindsof bone growth factors (rhBMP-2,Peptide-24) were separately loaded in theinner PLGA microspheres and chitosan crusts of PLGA/CS microspheres.While in vivo repairing condyles of femur of SD rats, PLGA/CS microspheresloaded with rhBMP-2and Peptide-24have optimal concrescence. PLGA/CSmicrospheres are novel veichles for delivering two kinds of factors.Nano-hydroxyapatite-collagen (nHAC) and PLGA microspheres wereincorporated into chitosan matrix to form a kind of PLGAmicrospheres/nHAC/chitosan scaffold. The homogenicity, high porosity, goodhydrophilicity and excellent compressive strength of the scaffold wereverified. In vivo, PLGA microspheres/nHAC/chitosan scaffolds showedexcellent osteoinductive property and promoted the concrescence of5mm cranialdefects of rats.