【作者】 熊昆；

【导师】 叶建东；

【作者基本信息】 华南理工大学 ， 材料学， 2013， 博士

【摘要】 硅（Si）与锌（Zn）在骨的新陈代谢中发挥着重要的作用，故含有这两种痕量元素的材料成为了当前骨修复领域研究的热点之一。硅酸锌的化学组分中同时含有Si和Zn，但其结构过于稳定，Si和Zn很难溶出。鉴于降低结晶性和减小晶粒尺寸可改善材料的溶解性，本研究采用微波水热法，合成可同时释放Si与Zn的弱结晶纳米硅酸锌（nano-ZS）粉体。硅酸钙生物陶瓷（CS）和磷酸钙骨水泥（CPC）因其各自优异的特性，被认为是应用于骨修复的极有潜力的无机可降解生物材料。针对目前CS降解过快、CPC缺乏骨诱导性及缺乏能促进成骨的相关功能性离子溶出的问题，本研究以nano-ZS粉体为改性材料，分别采用表面修饰、离子交联、共混掺杂的方式，通过制备具有含Zn表面涂层的CS、具有核壳结构的硅灰石-纳米硅酸锌复合微球（W/nano-ZS），以及nano-ZS粉体掺杂CPC复合材料（ZS/CPC），为解决CS和CPC生物材料存在的问题提供新的途径。本文采用微波水热法合成了硅锌矿相（Willemite）的弱结晶nano-ZS粉体，其形貌呈亚微米椭球状，由众多的纳米晶聚集而成，符合“多核生长”的机制。随着合成温度的降低，nano-ZS粉体的结晶度逐渐变弱。nano-ZS粉体能够在人体模拟体液中长时间释放Si、Zn，而且，其释放曲线可通过改变合成温度来调节。较低浓度的nano-ZS粉体的浸提液与小鼠成骨样细胞（MC3T3-E1）共同培养24h后，不会产生细胞毒性。将nano-ZS粉体悬涂于CS表面，随后共烧制备出带有含Zn表面涂层的硅酸钙复合陶瓷（Zn-CS）。Zn的掺入并未改变CS的表面物相组成，而且，含Zn表面涂层能有效地减缓CS基底材料中Ca、Si的溶出速度。研究发现，MC3T3-E1能很好地在含Zn表面涂层上粘附、铺展，且Zn-CS还能促进MC3T3-E1的增殖。不过，由于此含Zn涂层的结构过于稳定，造成Zn-CS表面矿化沉积羟基磷灰石的速度较慢，且Zn也很难从含Zn涂层中释放出来。为了解决上述含Zn涂层溶解过慢的问题，采用不同浓度的海藻酸钠/纳米硅酸锌粉体（SA/nano-ZS）悬浮液来表面修饰CS（Na/Zn-CS），并成功在CS表面制备出含有Na、Zn两种元素的表面涂层。与Zn-CS瓷片相比，Na/Zn-CS瓷片表面的物相发生改变。Na+的掺入，提高了单纯用nano-ZS粉体制备的含Zn表面涂层的溶解性，而且，此时的表面涂层还能溶出Zn2+。含有Na、Zn两种元素的表面涂层，既可以诱导CS表面快速沉积HA，又能够控制CS整体的离子溶出。研究发现，小鼠骨髓间质干细胞（rBMSCs）在Na/Zn-CS瓷片表面培养7天后，能显著性增殖。经0.1g/mL的SA/nano-ZS悬浮液表面修饰过的CS比纯CS更能促进rBMSCs的分化。借鉴上述研究思路，采用液滴法，经两次离子交联后成功制备出具有核壳结构的W/nano-ZS复合微球。SA/nano-ZS悬浮液的浓度越大，形成的微球壳层即越厚。离子溶出与体外矿化实验结果显示，由于海藻酸盐的作用，W/nano-ZS复合微球中的硅灰石颗粒溶解明显减缓。W/nano-ZS复合微球表面未发现有羟基磷灰石晶体矿化。但是，微球表面沉积了一层含有Ca、P元素的胶态物质，此胶态物质可能是无定形磷酸钙—海藻酸钙凝胶。浸泡在SBF溶液中，W/nano-ZS复合微球的壳层会逐渐形成多级孔结构，显示其具备在骨修复的同时原位缓释药物的潜力。将不同质量的nano-ZS粉体添加到CPC中制备出ZS/CPC复合材料。虽然，nano-ZS粉体的加入会延长CPC的初凝和终凝时间，但仍在临床应用可接受的范围。而且，ZS/CPC复合材料的抗压强度较纯CPC材料有明显的提高。细胞研究表明，相比于纯CPC材料，ZS/CPC复合材料能显著促进rBMSCs的增殖、分化，而且还可诱导rBMSCs表面形成含Ca、P元素的晶体，表明nano-ZS粉体的加入可提高CPC材料的成骨诱导能力。此外，研究还发现，在CPC水化初期，大量的Zn2+溶出会影响CPC的水化进程，进而改变CPC水化产物的物相组成、结晶形貌以及晶粒尺寸。CPC中含Zn载体的Zn2+的溶出行为，会影响下一阶段CPC水化产物中Zn2+的溶出行为。本研究中，当Zn2+在培养基中溶出的浓度为51.88μM时，促进rBMSCs增殖的效果最佳。当溶出到培养基中的Zn2+浓度介于0~28.75μM之间时，rBMSCs的ALP活性随着Zn2+浓度的升高而逐渐上升，能显著提高rBMSCs的ALP活性表达。当Zn2+浓度大于28.75μM时，rBMSCs的ALP活性又会降低。更多还原

【Abstract】 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.更多还原