| Autogenous bone is not always available or suitable for large areas of bone defect or in patients who have already had multiple procedures for bone reconstruction. In these cases, artificial bone substitutes can be chosen, with improved biocompatibility, safety, and osteoconductivity. Bioactive ceramics, which can bond with bone spontaneously, have been considered for use as bone graft substitutes for over 30 years. It is time to consider a shift towards a more biologically based method termed as"Third-Generation Biomedical Materials"designed to be both bioactive and resorbable. As one of the most important part of"Third-Generation Biomedical Materials", calcium silicate has been in study in recent years. This research focused on the in vivo performance of calcium silicate in the biomedical application, especially in the preclinical experiment. Materials and fabrication technologies are critically important in designing temporary scaffolds for bone tissue engineering. The methods manual-based fabrication techniques produce poorly controlled architecture. Especially, the microscopic parameters, such as pore size and interconnectivity, are fully uncontrollable. To our knowledge, no reports about porous calcium silicate scaffolds fabricated by rapid prototyping have been published until now. So, much attention has been paid in this research on fabricating porous calcium silicate scaffolds with controlled architecture and on evaluating the in vitro and in vivo performance of the prepared scaffolds.Four main experiments were involved in this research as follows:1. In Vivo Study of Porous Calcium Silicate Bioceramic in Subfascial SitesPorous calcium silicate (CS) andβ-tricalcium phosphate (β-TCP) bioceramics were obtained by sintering polymeric sponges infiltrated with ceramic slurry. They were implanted in rabbit subfascial sites and the biological characteristics were investigated. At 1, 2 and 4 weeks after implantation, specimens were harvested and analyzed by SPECT, Von Gieson staining, Micro-CT, SEM and EDX. There is no obvious toxic reaction in porous CS ceramics, showing the excellent biocompatibility of CS ceramics. In SPECT scanning, the ROI of CS andβ-TCP is 53.95±15.14 and 9.81±3.64 respectively (p<0.01), showing higher vascularization for CS. In Micro-CT analysis, the percentage of residual material volume fraction of CS andβ-TCP after 4 weeks is 16.41%±1.96% and 30.72%±0.69% respectively (p<0.01). In semi-quantitative analysis of histological observation, the percentage of residual material in CS is obviously lower than that inβ-TCP. These results show that the biodegradation of CS is higher than that ofβ-TCP. The deposition of the bone-like hydroxyapatite layer at 2 week after implantation show good bioactivity of CS in vivo. In conclusion, compared withβ-TCP, porous CS bioceramics have superiority in vascularization, ingrowth of new tissue and degradation in early stage. Therefore, porous CS bioceramics may be potential candidates as biocompatible, bioactive and biodegradable scaffolds for hard tissue repair and tissue engineering applications.2. Comprative study of in vivo performance of five porous bioactive glass/ceramics after implantation in muscle Five porous scaffolds were fabricated by the addition of porogens, including porousβ-calcium silicate,α-calcium silicate,β-tricalcium phosphate, hydroxyapatite and Bioglass. After 4, 8, 12 and 16 weeks of implantation into muscles of rabbit back, specimens were harvested and analyzed. Characterization of porous ceramic showed that the resulting porous calcium silicates had suitable porosity and mechanical properties. By Micro-CT, Histomorphometric analysis, RT-PCR, SEM and EDX, it was found that the fabricated calcium silicates were bioactive in mucle and can formed hydroxyapatite layer on the surface. Compared with other three porous scaffolds, the porous calcium silicates in the study showed higher in vivo resorption. No bone tissue formation could be observed in all five scaffols. However, the mRNA expression of BMP in calcium silicate group should be emphasized via Reverse-Transcription Polymerase Chain Reaction. Therefore, it is promising for calcium silicate for application on bone defect reconstruction and bone tissue engineering.3. Reconstruction of calvarial defect using porous calcium silicate bioactive ceramics in RabbitsThe porousβ-CS andβ-TCP ceramics were implanted in rabbit calvarial defects and the specimens were harvested after 4, 8 and 16 weeks, and evaluated by Micro-CT and histomorphometric analysis. The Micro-CT and histomorphometric analysis showed that the resorption ofβ-CS was much higher than that ofβ-TCP. The TRAP-positive multinucleated cells were observed on the surface ofβ-CS, suggested a cell-mediated process involved in the degradation ofβ-CS in vivo. The amount of newly formed bone was also measured, and more bone formation was observed withβ-CS as compared withβ-TCP (p<0.05).Histological observation demonstrated that newly formed bone tissue grew into the porousβ-CS, and a bone-like apatite layer was identified between the bone tissue andβ-CS materials. This study showed that the porousβ-CS ceramics could stimulate bone regeneration and may be used as bioactive and biodegradable materials for hard tissue repair and tissue engineering applications.4. Fabrication, in vitro and in vivo evaluation of a novel calcium silicate scaffolds with controlled architecture by rapid prototypingPorous calcium silicate scaffolds with controlled architecture (RP-CS) were fabricated by rapid prototyping and gel-casting. After immersion into SBF, a hydroxyapatite layer was precipitated on the surface of RP-CS, which showed its bioactivity. Co-cultured with rabbit bone marrow cells, RP-CS demonstrated suiiable biocompratibility. Futhermore, MTT tests and ALP activity tests showed the ability of RP-CS on bone marrow cells to osteogenic differentiation. Implanted into 12 mm bone defect of rabbit radius up to 24 weeks, RP-CS showed faster mineral apopsitional rate and higher resorption than RP-TCP. The study demonstrated the possibility of fabricating CS scaffolds with controlled architecture and further in vivo research.
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