Study On Properities And In Vivo Biocompatibility Of Mussel-Inspired Calcium Phosphate Cement

In this study, polydopamine (PDA) was added to calcium phosphate cement (CPC) to enhance CPC compressive strength, which was inspired by the excellent adhesive property of mussel adhesive protein. The effect of PDA on the mineralization on CPC, the ability of osteogenesis and the bonding strength of CPC with host bone were investigated.In this study, PDA was used as cement solution, which was obtained by dissolving dopamine (DA) in Tris-HC1buffer and exposing to air for2d to oxidize and crosslink. CPC was prepared by mixing the PDA-contained cement solution with starting powder. Orthogonal test and compressive strength tests were applied to optimize the preparation of CPC with respect to the DA concentration, the ratio of liquid to solid and pH values. X-ray diffraction (XRD), Gilmore needle tests and Fourier transform infrared spectroscopy (FTIR) were employed to study the physiochemical properties of CPC. Scanning electron microscope (SEM) was used to observe the morphology of CPC and UV-Vis spectrophotometry was applied to study in vitro release of DA from CPC. Orthogonal analysis demonstrated that the optimal combination CPC was DA concentration40mg/mL, the ratio of liquid to solid0.3mL/g and pH value8.5, which had the highest compressive strength with significant difference compared with that of CPC control. XRD and FTIR indicated that the incorporation of PDA promoted the conversion of dicalcium phosphate dehydrate (DCPD). Setting time (including initial and final setting time) of the optimal combination CPC decreased slightly and satisfied with the clinical demands. SEM indicated that there were lots of nubbly crystals, more platy structure and less porosity in optimal combination CPC compared with those of CPC control. Cumulative release of un-polymerized DA from CPC was29.7%during in vitro degradation. Meanwhile, the pH values of the immersion solution were safe for human body.Optimal combination CPC (named PDA-CPC) was soaked in simulated body fluid to study the effect of PDA on the mineralization on CPC. XRD, FTIR and X-ray photoelectron spectroscopy (XPS) were used to identify the crystalline phases, the functional groups and relative contents of different elements of the CPC surface, respectively. SEM and Transmission electron microscopy (TEM) were used to characterize the morphology and crystal structure of calcium phosphate (CaP) formed on the surface of the PDA-CPC, respectively. CPC without PDA was used as control (named control-CPC). XRD indicated that PDA promoted the conversion of DCPD and a-tricalcium phosphate to hydroxyapatite (HA) at an early stage (0,1,3,5and7d) but subsequently inhibited this conversion (10and14d). The diffraction peaks of DCPD and CaCO3of both PDA-CPC and the control-CPC disappeared after soaking in SBF for1and3d, respectively. FTIR showed that the v3vibration of P-O of PDA-CPC surface appeared the obvious red shift after soaking for7d, which was similar to that of natural bone. SEM showed that PDA promoted rapid mineralization on PDA-CPC to form a nanoscale CaP layer after1d of soaking. This nanoscale CaP layer was similar to that of natural bone and could be always observed during the soaking, whereas the mineralization layer was observed on control-CPC surface after7d of soaking. XPS showed that the peak of C=O of PDA existed in the newly formed CaP on PDA-CPC, indicating the co-precipitation of CaP with PDA. Furthermore, transmission electron microscopy demonstrated that the newly formed nanocrystalline CaP on PDA-CPC was HA which precipitated in association with PDA. Therefore, PDA increased the mineralization capacity and promoted the formation of nanocrystalline bone-like apatite on PDA-CPC. Thus, this provides a simple and effective route for surface modification on CPC.PDA-CPC was implanted into skull, femurs and muscle of the back of New Zealand rabbits for2,4and8w. Blood testing after3d of implanting was used to study the inflammatory response of PDA-CPC, and X-ray detection was applied to observe the position and degradation of implants. Push-out was used to investigate the bonding strength of PDA-CPC with host bone. XRD and SEM were used to identify the crystalline phases and characterize the morphology of implants. Laser scanning confocal microscope (LSCM) and histology analysis (decalcified and undecalcified sections) were applied to observe the formation of new bone. Blood testing showed that the inflammatory cell of PDA-CPC was similar to that of control-CPC, indicating PDA was non-toxic. X-ray detection showed that the position of PDA-CPC implanted into skull and femurs did not change, whereas that of in muscle were changed slightly. Push-out testing indicated that PDA increased the bonding strength of PDA-CPC with host bone. XRD demonstrated that the diffraction peaks of DCPD and CaCO3disappeared after2w of implanting, and diffraction peaks of octacalcium phosphate (OCP) was found. Meanwhile, the intensities of HA diffraction peaks increased with implanted time. SEM showed that lots of cells adhered on the interface of PDA-CPC and host bone and spherical particles consisting of nano-wire CaP like that of mineralization in vitro was found in PDA-CPC. LSCM indicated that the formation of new bone was more than that of control-CPC after8w of implanting. The histology analysis of undecalcified sections of skull and muscle implants of PDA-CPC indicated that the lamellar bone with high maturity was found and PDA-CPC was not harmful to surrounding tissue. The histology analysis of decalcified sections of skull implants of PDA-CPC showed that lots of marrow cavities, red blood cells, osteoblasts and osteoclasts were found after2w of implanting. The maturity of bone increased after4w of implanting, and new bone was formed under periosteum, which was according to the mechanism of intramembranous ossification. After implanted for8w, tissue grew into PDA-CPC, and its morphology was integrated than that of control-CPC. Meanwhile, it could be observed that PDA was biodegradable.This study provides a new approach to develop CPC with high compressive strength, high bioactivity and high ability for bone repairing, and it can also provide a useful guidance for application of CPC in clinical.