Alendronate Loaded Electrospun Plga Fiber Reinforcement Of Calcium Phosphate Cement

Calcium phosphates cement (CPC) is widely applied in bone regeneration due to its good biocompatibility, osteoconductivity, mouldability and injectability. Additionally, CPC is also an attractive candidate as the local delivery of skeletal drug, because its preparing procedure avoids sintering and heating release, and thus allows incorporation of drug and biologically active molecules. However, the poor mechanical strength of CPC has limited its applicability to only non-stress-bearing bone defects, prohibit its usage in many clinical applications. Therefore the mechanical strength of CPC is necessary to be improved to satisfy the requirement of clinical applications. Fiber reinforcement composites is more successful approaches to toughen brittle materials due to the role of the fibers bridging, crack deflection and fibers pullout through the composites. Electrospun fiber have been widely used as tissue engineering scaffolds due to its versatility and similarity to human native extracellular matrix.In the present study, Alendronate (ALN)-loaded electrospun poly lactide-co-glycolide (PLGA) fibers were incorporated into CPC. ALN not only act as the model drug due to its ability to suppress osteoclast-mediated bone resorption and promote osteoblast proliferation, but also as the surfactant due to its great affinity with calcium and hydroxyapatite. The aim of study is to improve the early mechanical properties of CPC and realize the local release of ALN.PLGA fibers and drug-loaded PLGA fibers were electrospun into a non-woven based on parameters respectively. The diameters, morphology, the drug loading ratio and contact angle of electrospun fibers were examined by scanning electron microscopy(SEM), microplate reader and contact angle goniometer. Biocement D cements was used as carrier, the different weight fractions of PLGA fibers were randomly mixed with the CPC paste. A liquid/powder ratio of0.45mL/g was applied. The setting time, mechanical properties and phase composition were characterized by Gilmore Needle, X-ray diffraction(XRD), SEM and Universal Testing Machine etc. Orthogonal experimental method was used to optimize the PLGA fiber weight, the arrays of fiber and the fiber with or without drug in terms of the work-of-fracture of CPC with PLGA fibers. The setting time, mechanical properties, phase composition, vitro degradation experiment and the drug release profile of the Optimal Group in orthogonal experiment were characterized. In addition, Osteoblasts(MC3T3-E1) were used to evaluate the biological behaviors (Cell morphology, proliferation and differentiation) of the drug-loaded fiber CPC composites.Morphology of electrospun fibers showed both of PLGA fibers and drug-loaded PLGA fibers were continuous, generally separate from each other and had a highly aligned fibrous morphology. With the addition of ALN, the morphology of PLGA fibers were not significantly different, but the surface contact angles of PLGA fibers decreased. The mean diameters of PLGA fibers and drug-load PLGA fibers were1.25±0.18μm and1.16±0.20μm respectively. The drug loading ratio of PLGA fibers was56.20±0.99%.The results of mechanical properties showed the flexural strength and elastic modulus of the composites were increased, but there was no significant difference between different fibers weight fraction and pristine CPC. In contrast, the work-of-fracture of the composites increased dramatically with the increasing PLGA fibers fraction. The results of orthogonal experiment showed the Optimal Group was7wt.%randomly arrays drug-loaded fiber CPC. The drug-loaded fibers can significantly improve the work-of-fracture of the composites due to great affinity of ALN with calcium and hydroxyapatite, which would improve the fibers wettability in CPC. Fracture surface and load-displacement curves of drug-load PLGA fiber CPC composite indicated CPC composite exhibited quasi-brittle behavior, which were similar to that of ductile materials due to the role of the fibers bridging, crack deflection and fibers pullout through CPC. Gilmore Needle results showed that both the initial and the final setting time decreased with the addition PLGA fibers and drug-loaded PLGA fibers. Drug-loaded PLGA fibers in CPC inhabited the conversion of DCPD and a-TCP due to the reduce of liquid/powder ratio. After24h hydrolysis, the phase of all CPC samples were mainly HA and a-TCP, small amounts of CaCO3and DCPD.After90days immersion in PBS, the local release of ALN from drug-loaded PLGA fiber CPC was achieved. The ALN was released rapidly in the first day, then sustained slower release. The release of ALN followed the matrix diffusion Higuchi’s law. The results of XRD showed the reaction products mainly converted to needle-like HA. The results of SEM and Infrared spectrum showed drug-loaded PLGA fibers completely degraded after immersed in PBS for90days. The macroporosity increased due to the PLGA fibers degradation. The results of SEM and fluorescence showed abundant cells adhered and mainly presented as the polygonal morphology on all samples after co-cultured with MC3T3-E1osteoblasts. Also many cells spread with filopodia and formed cell-cell junctions on all samples. It indicated that the cells kept their normal functional state. There was not significantly difference among Alamar Blue activities of cells co-cultured with all CPC samples. ALP assay showed drug-loaded PLGA fiber CPC have the positive effect on differentiation of osteoblasts.In this study, drug-loaded PLGA fibers were incorporated into CPC and increased the work-of-fracture of CPC composites dramatically. Furthermore, the drug-loaded PLGA fiber CPC locally released ALN which have a positive effect on differentiation of osteoblasts. Therefore the drug-loaded PLGA fiber CPC composites may provide the promising approach for bone fillers.