Study On Preparation And Properties Of A Novel Bioactive Dicalcium Silicate Material As Bone Substitutes

In recent years, a variety of bioactive inorganic materials have been studied as important bone substitutes, and the results showed that the CaO-SiO2-based materials such as bioglass and glass-ceramics are bioactive and biocompatible. However, the bioactive glasses such as 45S5 Bioglass? are too brittle to be fabricated the block parts, which limits their clinical applications. The glass-ceramics with high strength, i.e. A-W Cerabone?, are hardly used in large bone defect because of the mismatch of the elastic modulus between the implant and the host bone. Therefore, it is important to fabricate new bioactive materials with excellent bioactivity, biodegradability and mechanical properties for human bone prosthesis. In this dissertation, a novel bioactive dicalcium silicate (Ca₂SiO₄) material, similar in the components of CaO-SiO2-based bioactive glasses and glass-ceramics, was developed and studied for bone repair.Firstly, the superfineβ-, andγ-Ca₂SiO₄ powders with high purity (free CaO<0.22%) were prepared by a sol-gel and hydrothermal method with some modification, respectively. The powders could induce a bonelike carbonated hydroxyapatite (CHA) layer on their surface, and furthermore, were able to degrade continuously in simulated body fluid (SBF), indicating good bioactivity and degradability. In particular, the ionic products (Ca & Si ions) of the powder dissolution enhanced proliferation of fibroblasts and osteoblasts, suggesting good cell compatibility of Ca₂SiO₄ materials.Secondly, the new bioactive dicalcium silicate ceramics were fabricated by sinteringβ-Ca₂SiO₄ greens at different temperatures after compacting with cold isostatic pressure. The phase transition fromβ- toγ-phase of polymorphic ceramics occurred at 1100-1300℃, the increase of sintering temperature resulted in improved densification. The mechanical properties of theγ-Ca₂SiO₄ ceramic were improved remarkably when the ceramics were sintered at 1450℃for 2 hours, corresponding to a bending strength of 97.1±6.7 MPa, a fracture toughness of 1.80 MPa.m1/2 and an elastic modulus of 40.2±3.2 GPa, respectively. The results of in vitro studies showed that the Ca₂SiO₄ ceramics could induce CHA deposition in SBF and supported mesenchymal stem cells (MSCs) adhesion, spreading and growth. These findings indicate that theγ-Ca₂SiO₄ ceramic possesses good bioactivity, biocompatibility and mechanical properties, and is a potential bioceramic for hard tissue repair.Furthermore, self-setting property of theβ-Ca₂SiO₄ as novel biocement filler was investigated. The hydration reaction ofβ-Ca₂SiO₄ with water at 37℃leaded to the formation of calcium silicate hydrate(CSH) and small amount of calcium hydroxide (Ca(OH)2) (<1.5%), and the process included five stages: preinduction, induction, acceleration, deceleration, and diffusion. The hydration reaction revealed slow exothermal behavior with a maximal heat flux 1.78 mW.g-1 and temperature fluctuation within 3℃. The injectability, setting time and mechanical properties ofβ-Ca₂SiO₄ paste were correlated with the liquid to powder ratio (L/P). The workableβ-Ca₂SiO₄ pastes with a L/P ratio of 1.0¹.2 could be injected but enabled a prolonged initial setting time. The set paste showed cellular structures with compressive strength of 4.8 MPa at 2 days and up to 28.8 MPa at 28 days. The hydration products ofβ-Ca₂SiO₄ in the early setting stage showed fiber gel morphology in porous area, and the better crystallized lamina with directional growth located in the compact area. Particularly, the hydration and setting process was affected heavily by the condition of the preparation. The smaller was the granularity, the faster was the hydration and setting process, which would also lead to an increase in the compressive strength of the hardened body. Similarly, the initial setting speed and strength of the material could be improved by adding some gypsum in the raw powders or using CaCl2 solution as liquid phase.The degradability of the hydratedβ-Ca₂SiO₄ cements was evaluated by soaking in SBF and the results demonstrated that the consolidated paste exhibited a moderate degradation and induced bonelike CHA formation. In addition, the ionic products of the paste dissolution promoted proliferation of fibroblasts and osteoblasts remarkably. This hardened body could also support adhesion and spreading of the MSCs. Using gentamicin as a model drug, it was found that a high dose of drug release maintained 10 days and associated with a sustained release over 4 weeks from the paste. In conclusion, the results indicate that theβ-Ca₂SiO₄ is an excellent candidate as bioactive self-setting biomaterial for potential applications in the biomedical field, including the injectable implant material for bone/dental repair and controlled drug-delivery system.The globular paraffin porogen were fabricated into three-dimensionally (3D) macroporous negative replicas of desirable architectures and theβ-Ca₂SiO₄ andβ-Ca₂SiO₄/gelatin composite scaffolds were fabricated at low temperature with well-controlled architecture and inter-pore connectivity. The results showed that the composite scaffolds possessed a higher compressive strength (1.35±0.21 MPa) as compared to theβ-Ca₂SiO₄ scaffolds (0.71±0.13 MPa). In vitro Si release from the composite scaffold in SBF indicated that the porous architecture was favorable for its dissolution, nearly 16.3% and 39.6% of which degraded within 3 and 28 d, respectively, and the surface of the composite scaffold induced a bonelike CHA layer in SBF. These studies suggest that the 3D macro-porousβ-Ca₂SiO₄/gelatin composite scaffolds are potential materials for guided bone regeneration due to its desirable architecture and bioactive property.In conclusion, the results of this study indicate that the Ca₂SiO₄ materials possessed excellent bioactivity, degradability, and cell compatibility. In particular,γ-Ca₂SiO₄ ceramics showed improved mechanical properties as compared to sintered HA ceramics, andβ-Ca₂SiO₄ paste exhibited good self-setting properties and injectability. In addition, the consolidated paste possessed good bioactivity, degradability and cell compatibility. All these findings indicate that Ca₂SiO₄ are potential bioactive materials for bone repair.