Synthesis Of Poor Crystalline Nanosized Zinc Silicate Via Microwave Hydrothermal Method And Its Application In Promoting The Performance Of Degradable Inorganic Biomaterials

Silicon (Si) and zinc (Zn) play a great role in bone metabolism, so the materialscontaining Si or Zn have become one of the hottest research points in the field of the bonerepair. Zinc silicate simultaneously contains Si and Zn elements, but it is so stable that Si andZn are hard to be dissolved out from the zinc silicate. The solubility of zinc silicate may beimproved via reducing its crystallinity and crystal size. Therefore, The poor crystallinenanosized zinc silicate (nano-ZS) powders were firstly synthesized via the microwavehydrothermal method. Among all the degradable inorganic biomaterials, calcium silicatebioceramics (CS) and calcium phosphate cements (CPC) were considered having the mostpotentials for the clinical bone repair owing to their respective excellent properties. However,they also have some disadvantages, such as the rapid degradation of CS, the lack ofosteoinductivity of CPC, and the lack of osteogenic functional ions released from CPC, whichneed to be resolved. Subsequently, nano-ZS powders were used as the modified materials forthe preparation of the CS with the Zn-containing surface layer (Zn-CS) via the surfacemodification, the preparation of core-shell structured wollastonite/nano-ZS (W/nano-ZS)composite microspheres via the ionic crosslink, and the preparation of the nano-ZS dopedCPC composite (ZS/CPC) via directly adding the nano-ZS into CPC, respectively, providingnew routes to improve the biological performances of the CS and CPC.Microwave hydrothermal method was used for the synthesis of the willemite phasenano-ZS with the low crystallinity. The nano-ZS powders displayed the submicron ellipsoidalshape, which were piled up with many nanocrystals. The crystal growth of the nano-ZS wasconsistent with the “multi-core growth” mechanism. With the decrease of the reactiontemperature, the crystallinity of the nano-ZS would gradually become poor. As nano-ZSpowders were soaked in the simulated body fluids (SBF), Si and Zn could be long-termreleased from the nano-ZS, and its release profile would be altered with the change of thereaction temperature. The relative low concentration of the nano-ZS powders extract causedno cytotoxicity on the mouse osteoblast-like cells (MC3T3-E1).Nano-ZS powders were spin-coated on the surface of the CS, and then the modified CSwas sintered to obtain the Zn-CS, which had a Zn-containing layer on its surface. The Zn-CS had the same surface phase as the CS, moreover, the Zn-containing surface layer couldeffectively slow down the dissolution of Ca and Si from the CS substrate. MC3T3-E1cellswell adhered and spread on the the Zn-containing surface layer, and Zn-CS could promote theproliferation of MC3T3-E1cells. Nevertheless, the structure of the Zn-containing surfacelayer is too stable, less mineralized hydroxyapatite (HA) would form on its surface, and lessZn could be released from the Zn-containing surface layer.In order to increase the dissolution of the Zn-containing surface layer, differentconcentrations of the well dispersed sodium alginate/nano-ZS (SA/nano-ZS) suspensionswere used for the surface modification of the CS. Subsequently, the modified CS was sinteredto obtain the Na/Zn-CS, which had a surface layer containing Zn and Na. Compared to theZn-CS, the surface composition of the Na/Zn-CS changed. Owing to the incorporation of Na+into the Zn-containing surface layer originally prepared by only using the nano-ZS, thesolubility of this surface layer increased. At this time, Zn2+could also be released from thesurface layer containing Zn and Na. Furthermore, the surface layer containing Zn and Nacould not only induce the rapid deposition of HA on its surface, but also effectively controlthe dissolution of the ions from the CS substrate. The rat bone marrow mesenchymal stemcells (rBMSCs) obviously proliferated when they were cultured on the surface of theNa/Zn-CS for7days. The rBMSCs cultured on the surfaces of the CS modified with0.1g/mLSA/nano-ZS suspensions had better differentiation performance than that of the pure CS.Using the liquid-droplet method, the core-shell structured W/nano-ZS compositemicrospheres were obtained after the two-step ionic crosslink. With the concentration of theSA/nano-ZS suspension increasing, the shell of the W/nano-ZS would become thicker. Owingto the influence of the alginate, the dissolution of the wollastonite particles in the W/nano-ZScomposite microspheres was obviously slowed. The mineralized HA could not be found onthe surfaces of the W/nano-ZS composite microspheres, but some gelatinous depositionscontaining Ca and P were found on their surfaces, which might be the amorphous calciumphosphate-calcium alginate gelatins. As soaking in the SBF, hierarchical porous structurewould be gradually formed in the shell of the W/nano-ZS composite microspheres, it’sshowed that the W/nano-ZS composite microspheres had the potential for simultaneouslyreleasing drugs during the in-situ bone repair. Different amounts of nano-ZS powders were added into the CPC to prepare the ZS/CPCcomposite. Although the initial setting time and the final setting time would be delayed whenthe nano-ZS were added into CPC, it still met the clinical operation requirements. Thecompressive strength of the CPC increased when the nano-ZS were added into the CPC. Bycomparing with the pure CPC, the ZS/CPC could obviously promote the proliferation anddifferentiation of the rBMSCs. Moreover, the ZS/CPC also had the ability to induce Ca and Pdepositing on the surface of the rBMSCs, indicating the osteoinductivity of the CPC may beimproved by the addition of the nano-ZS. Furthermore, in the initial hydration stage, largeamounts of Zn2+released from the Zn-carrier would affect the hydration of the CPC, whichcould further influence the phase composition, the crystal morphology, and the crystal size ofthe CPC hydration products. The releasing behavior of the Zn-carrier in CPC would affect thefollowing releasing behavior of the CPC hydration products. In our study, as51.88μM ofZn2+released into the cell culture medium, the proliferation of rBMSCs was the best. Whenthe concentration of the released Zn2+in the cell culture medium ranged from0μM to28.75μM, it could distinctly promote the ALP activity of the rBMSCs, and in this range, the ALPactivity of the rBMSCs would gradually increase with the raise of the concentration of thereleased Zn2+. However, when the concentration of the released Zn2+in the cell culturemedium exceeded28.75μM, the ALP activity of the rBMSCs would decrease.