Study On Porous Calcium Phosphate Cement Scaffold Reinforced By Mechanical Activation And Polydopamine

Calcium phosphate cement (CPC) has been widely used as bone substitutes in clinic, due to its excellent biocompatibility and self-setting. However, its poor mechanical property has limited its applicability to be non-stress-bearing bone filling material. In addition, the lack of porous structure for CPC, which is beneficial to the growth of cell and tissue, restricts its application in tissue engineering. Mechanical activation is a kind of methods aiming at improving the physical and chemical reactivity of substance by transforming the mechanical energy to internal energy. Polydopamin (PDA) is a cohesive material, which is polymerized by dopamine monomer in oxidation environment. Studies show that PDA is biocompatibility due to the catechol group. Therefore, porous calcium phosphate cement scaffold (CPC-S) is prepared, which was reinforced by mechanical activation and PDA. The influence and mechanism of mechanical activation and PDA on the mechanical strength, composition and biocompatibility of PDA/BCPC-S were studied furthermore.BCPC-S with porous was prepared by H2O2 gas foaming, which Biocement-D formula powder was mechanical activated by ball milling. Results showed that the particle size and density of mechanical activated CPC powder (BCPC-P) decreased while the specific surface area increased compared to those of CPC powder without mechanical activated. There were plenty of reactive sites and pores inside the powder or between the powder, which would promot the hydration of BCPC, result in the bonding among CPC particles much tighter, and improve the mechical strength, injectabiliby and anti-collapsibility of BCPC-S. SEM photos showed that there were two types of pores with dimension of a few micron and a few hundreds micron in both activated BCPC-S and the unactivated CPC-S (porosity were 77.98 ± 0.58%,65.50 ± 2.22% respectivly). However, the compression strength (4.11 ± 0.46 MPa) of BCPC-S was remarkablely higher than that of CPC-S(1.99 ± 0.43 MPa). XRD and TEM indicated that the mechanical activation provided the energy to decrease the grain size and crystallinity of calcium phosphate and improve the transforming of DCPD into DCPA. The deposition of calcium phosphate was promoted by mechanical activation, and the BCPC-S hydrated more completely which lead to the enhancing of compression strength.PDA improved the mechanical property of BCPC-S while shortening the setting time (initial time:20.15±1.75 min, final time:50.35±4.05 min) according to its cohesive ability between the particles during the polymerization. The reinforcement was best when the oxidation time and the concentration of PDA were 2 d and 40 mg/mL respectively, and the high porosity was maintained (77.5 ± 2.54%). XRD indicated that the crystallinity of HA in PDA/BCPC-S was higher than that in BCPC-S after mineralization in the SBF. SEM showed there was a kind of micro/nano multi-scale structure on the surface of PDA/BCPC-S. It might because of that catechol groups chelated with the Ca2+ and provided nucleation sites for crystallization of HA. The the nucleation energy decreased and a heterogeneous nucleation occured, which promoted the nucleation, crystallization and growth of HA finally.The adsorption of BSA (bovine serum albumin) on PDA/BCPC-S was upgraded due to the micro/nano structure of PDA/BCPC-S after mineralization. The adsoption isothermal curves and the fitting equations demanstated that the adsorption confroms to the Langmuir model (R2=0.999). The adsorption thermodynamics datas showed that the adsorption was endothermic reaction, and the adsorption of BSA on PDA/BCPC-S was easier to take place. The adsorption kinetic curves according with the second-order kinetic equation (R2=0.999), which means it was a chemical adsorption. The PDA increased the rate of the adsorption of BSA on PDA/BCPC-S.PDA/BCPC-S was co-cultured with the MSC (mesenchymal stem cell), and the biologiacal assessment was carried out in vitro. MTT (methyl thiazolyl tetrazolium) results showed the PDA/BCPC-S was friendly to the cells and promoting the proliferation of MSC all along the time, while RGR (relative growth rate) of BCPC and BCPC-S were low but became non-cytotoxic to the MSC after 5 ds. MSC were observed on the surfaces of all scaffolds with variety of mohpologies according to the Fluorescence staining and SEM photos, and the parapodiums of the cells stetched to spread out on the materal surface, indicating the beneficial biocompatibility. Quantity of MSC on PDA/BCPC-S was highest compared to BCPC and BCPC-S, demonstrating that the micro/nano structure was in favor of the adhesion and proliferation of cells. ALP (alkaline phosphate) showed that the proliferation and osteogenic differentiation ability of MSC improved along with co-culture time. PDA/BCPC-S could promote the osteogenic differentiation of MSC. ARS (alizarin reds) staining showed that PDA played a role of osteogenisis induction medium, causing the MSC differentiate into osteoblast and facilitating the mineralization of MSC.In this study, PDA/BCPC-S that reinforced by mechanical activation and PDA was investigated and optimized, and provided a promising bone substitute material with higher compression strength and porosity, the admirable adsorbability of BSA and cytocompatibility.