| In clinic,it has been difficult to repair the large critical size defects arising from trauma,infection,tumor resection.Autologous bone is still the gold standard in bone reconstructive surgery because of its osteoconductivity, osteoinductivity,osteogenic potential and lack of immunogenicity as well.However,this standard auto graft has its own share of problems like inadequate amount,at least10%morbidity and potential complications in bone surgery.And it will take a long time to creep substitution. The bone allograft and xenograft has antigenicity, especially in large bone graft, often fail in the graft due to severe immune rejection, and has danger in the spread of pathogens as well. Therefore, in recent years with the emergence of tissue engineering, people began to use the principles and techniques of tissue engineering to plant the cells which have the osteogenic potential in the scaffold after differentiation, proliferation. And at last the engineered artificial bone has been made and can promote a large segmental bone defect repair. In cultivating tissue engineered bone in vitro, specially in large tissue engineered bone, the currently used bone substitutes still face many unsolved problems including incomplete formation of new bone tissue, failure of neovascularization, and slow growth of the capillary network. Meanwhile, drug is ofen used for better bone healing in clinical.However, due to bone tissue, such as in the biological density, low blood flow, permeability and poor specificity, the traditional methods of drug administration is difficult to arrive at the ideal site of the lesion, and thus its efficacy is low.Hydroxyapatite (HA) has very similar composition and structure to natural bone and with good biocompatibility, bone osteoconductivity and osteoinductivity.It has been widely used as bone substitute materials. HA can absorb chemical molecules and biological macromolecules such as proteins, so as a drug carrier has been widely studied. But it has problems with adsorption of impurities, low drug loading and burst release.A novel scaffold with large size and controlled porous structure has been designed and prepared for the aim of massive tissue engineered bone in previous experiment of our group. It was composed of HA spherules and porous HA tube.HA spherules can easily compound with biological active substance before being filled into the HA tubes. This study was designed to load the biological active substances promoting bone growth, neovasculariztion on the scaffold and get a new drug delivery system.This system can release the biological active substances in a sustained and effective manner in order to promote bone growth and healing in the repair of bone defects.HA spherules were prepared by the method of sol-gel and water/oil emulsification technology and the porous structures were characterized. Sal B,the major water-soluble components of the traditional Chinese medicine radix salviae miltiorrhizae, was investigated on osteoblast proliferation and differentiation and was loaded on the HA spherules.Then the drug-loaded spherules were wrapped with several different concentrations of PLA and several different concentrations of chitosan. The case of drug release and the best package substance with the right concentration were investigated. Finally,the influence of Sal B-loaded HA sustained-release spherules on the activity of osteoblasts cultured in vitro was studied.The main conclusions were obtained as follows:1. The HA spherules,prepared by the method of sol-gel and water/oil emulsification technology,possessed the porous structures can meet the organization growth.2. Sal B has been proven to be effective in promoting osteoblast proliferation and differentiation. SalB has the potential toameliorate bone healing by stimulating both the total metabolic activity and ALP activity of osteoblastic cells. It was suggested that Sal B at a mass concentration=160μg/mL significantly contributed to osteoblast proliferation. Moreover, the higher mass concentration indicated more obvious proliferation. However, Sal B at a mass concentration>160μg/mL had toxic effect on ostaoblasts. It showed that Sal B can promote bone growth and healing as the biological active substances used in the repair of bone defects, and the best effective concentration was160μg/mL.3. The results showed that PLA can form film but can not be attached to surface of HA sperules due to its hydrophobicity.So it was easy to come off and wrappd poor.However,it were explored that chitosan has good hydrophilicity,good film-formed and good cell compatibility,which was used to wrap on the surface of the HA spherules to get the Sal B-loaded HA sustained release spherules and2%concentration percentage was choosen in this study.4.The chitosan-coated Sal B-loaded HA sustained-release spherules prepared in this study can release Sal-B in vitro for a long period, effectively promoted osteoblast proliferation, maintained biological activity of osteoblasts, contributed to osteoblast differentiation and proliferation, increased utilization rate of drug in local region, decreased adverse reaction, and persistently contributed to bone formation. It is helpful for construction and repair of bioceramic scaffolds and is of high clinical value in treatment of large segmental bone defects. |
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