| Osteoporosis is one of the common clinical problems in postmenopausal women and the elderly,who are prone to bone defects.For osteoporotic bone defects,bone repair slows down due to slow bone regeneration and reduced bone mass.Bone repair materials are needed to assist bone tissue remodeling and promote bone defect healing in osteoporotic bone.Poly（lactic-co-glycolic acid）（PLGA）is a biological material approved by U.S.Food and Drug Administration.It has good biocompatibility and has been widely used in clinical and scientific research as drug carrier and bone repair scaffold.However,it is highly hydrophobic,and the acid products resulting from degradation prone to inflammatory responses.Hydroxyapatite（HA）,one of the components of human bone,has good biological activity and is an excellent bone replacement material.In addition,ion doping endows HA more functionality,strontium（Sr）and magnesium（Mg）have been widely used in the modification of hydroxyapatite.It has been reported that Sr has dual effects on bone tissue regeneration,which can both promote bone regeneration and inhibit bone resorption.Mg not only plays a role in the regeneration of bone tissue,but also promotes the regeneration of blood vessels.Because the separate inorganic or organic scaffolds cannot meet the complex requirements of bone tissue regeneration,the composite biomaterials composed of organic and inorganic materials are of great significance in bone tissue engineering.In order to prepare multifunctional materials that can promote the repair of osteoporotic bone defects,PLGA cage structure loaded with Sr and Mg doped HA（Sr/Mg@HA/PLGA-CAS）were prepared inspired by the role of dandelion’s umbrella-shaped structure in carrying seeds.Sr and Mg doped HA particles on Sr/Mg@HA/PLGA-CAS play a role in osteogenesis,angiogenesis and inhibiting osteoclast differentiation,thus effectively promoting the repair of osteoporotic bone defects.The main research content is as follows:In the preparation of materials,firstly,PLGA cage structure particles（PLGA-CAS）were prepared by double emulsion（W/O/W）.Then,Sr doped hydroxyapatite（Sr@HA）and Mg doped hydroxyapatite（Mg@HA）were prepared by hydrothermal reaction.Then,PLGA-CAS were treated with alkali to produce more carboxyl groups on its surface.Finally,the doped hydroxyapatite particles were loaded onto PLGA-CAS by ion interaction,and Sr/Mg@HA/PLGA-CAS particles were obtained after rinsing and lyophilization.The physicochemical properties,biocompatibility and biofunction of Sr/Mg@HA/PLGA-CAS were investigated.In terms of physical and chemical properties,the results showed that Sr/Mg@HA/PLGA-CAS had large pore size,high porosity,suitable particle size for cell adhesion and growth,and could be injected.After Sr/Mg@HA particles were successfully loaded,the hydrophilicity of Sr/Mg@HA/PLGA-CAS was significantly improved,and the degradation of Sr/Mg@HA/PLGA-CAS was in line with expectations,at the same time the p H of the microenvironment was stable.Sr/Mg@HA/PLGA-CAS could continuously release Sr2+and Mg2+within 15 days,which would facilitate their biological function.In terms of biocompatibility,Sr/Mg@HA/PLGA-CAS was favorable for protein adsorption.Gradient concentration hemolysis test and cytotoxicity test showed that the preparation process of Sr/Mg@HA/PLGA-CAS did not affect the biocompatibility.Osteoblast precursor cells（MC3T3-E1）co-culture with Sr/Mg@HA/PLGA-CAS and directly seeded on Sr/Mg@HA/PLGA-CAS kept great cell viability and normal proliferation.In terms of biofunction,Sr/Mg@HA/PLGA-CAS was beneficial to the early adhesion and propagation of MC3T3-E1,and the release of Sr2+and Mg2+enhanced the osteogenic activity of MC3T3-E1,including increasing the activity and expression of alkaline phosphatase,promoting osteogenic mineralization and up-regulating the expression of osteogenic genes.It also promoted vascular regeneration,such as promoting HUVECs migration,vascular formation and up-regulation of angiogenesis related gene expression.In addition,Sr/Mg@HA/PLGA-CAS particles also inhibited the osteoclast differentiation of RAW 264.7 cells and reduced the expression level of osteoclast related genes.Our study suggests that Sr/Mg@HA/PLGA-CAS can promote osteogenic differentiation,angiogenesis and inhibit osteoclast differentiation,which may have potential application value in the treatment of osteoporotic bone defects. |
