Research On 3D Printed Bioactive Ceramic Bone Repair Scaffold

The demand for bone implants is increasing rapidly with the bone defect caused by more frequent trauma and tumor resection. The ideal bone repair material should satisfy a controllable porosity, pore structure with fully interconnectivity, the same shape with the bone defect area, the mechanical properties comparable to the natural bone, a degradation rate comparable to the rate of a newly formed bone. To realize the controllable fabrication of scaffolds, this doctoral thesis is intended to do some research studies on structure, mechanical strength and degradation properties.This thesis uses the 3D printed scaffold with high mechanical strength, high bioactivity,controllable biodegradation as its main line, and realizes the controlling of shape and properties of bioactive bone scaffold. The personalized customization of the bone defect repair is also realized by 3D printing from geometric shape to property (the customization of degradation property and degradation rate).The main contribution of the thesis is summarized as follows.(1) 3D print the calcium silicate (CSi) porous scaffold. The printability of inks for fabricating scaffolds are investigated systematically. And the effect of sintering temperature, bioactive glass(BG) content and pore morphology on the mechanical properites of scaffolds are also investigated.When the content of BG is 1%,the compressive strength of CSi-BG1 scaffolds with rectangular and honeycomb pore morphology sintered at 1080? are 48 MPa and 88 MPa, respectively. The surface of the scaffolds are covered by a layer of HA mineral after soaking in simulated body fluid,which indicates that the scaffolds have good bioactivity. And after soaking for 3 weeks,the scaffolds still have high mechanical strength over 60 MPa.(2) Although the mechanical strength of the CSi-BG scaffold is high, but it is still smaller than the strength of human cortical bone (100-150 MPa). For better mechanical property, the magnesium-doped wollastonite (CSi-Mg) ceramic porous scaffolds are fabricated, and the CSi-Mg scaffolds have high strength (120 MPa) comparable to that of cortical bone. The bioactivity tests in vitro indicate that the CSi-Mg scaffolds are beneficial for ALP activity, proliferation and differentiation of MC3T3 cells. The results of the long term animal experiment show that the scaffolds have good new bone regeneration capacity after implantation in rabbit calvarial defects for 12 weeks.(3) In consideration of the individual difference of the bone degradation rate in vivo, the personalized customization of the bone scaffold can be achieved by controllable degradation rate.Due to the good biocompatibility of tricalcium phosphate ((3-TCP), the CSi-Mg scaffolds doping with (3-TCP (CSi-Mg/TCP) are investigated further. The effect of P-TCP content, pore size,sintering process on the mechanical strength of scaffolds are investigated. The scaffolds with 10%and 20-30% content of ?-TCP possess high compressive strength (120-140 MPa or 80-100 MPa)after undergoing one- or two-step sintering. Meanwhile, the CSi-Mg/TCPx (x=10, 20) scaffolds with medium pore (?320 ?m) have over 100 MPa in compression and ?52% in porosity. In particular, the composite scaffolds still have high mechanical strength (over 50 MPa) after immersion in Tris buffer for 6 weeks. Moreover, the degradation rate of the composite scaffolds is decreased with the increase of ?-TCP content. These findings demonstrate that the scaffolds with controllable degradation rate can be achieved by controlling the content of (3-TCP and using the optimized sintering method, which providing feasible research approach for personalized customization of bone scaffold with degradation rate comparable to the rate of a newly formed bone.(4) Approach of both optimizing the pore structure of scaffold and doping with TCP for fabricating the bioceramic scaffold with better osteogenic performance are proposed. The scaffolds with improved host bone/scaffold interface pore morphology structure are fabricated.The scaffolds with improved pore structure have better osteogenic capacity than conventional scaffolds after implanted in rabbit calvarial defect for 8 and 12 weeks. With these considerations,the CSi-Mg10/TCP composite scaffolds with improved pore structure are fabricated further. The composite scaffolds have good osteogenic capability after implanted in defects for 8 weeks, and the percentage of newly formed bone reaches 33.8 ± 1.2% at 12 weeks postoperatively. These findings demonstrate that the bone regeneration repair capacity of scaffolds can be improved by controlling the interior pore structure of scaffold and doping with appropriate content of TCP,which provide feasible research approach for fabricating scaffolds with high newly formed bone regeneration capacity.(5) Taking the customized repair of rabbit mandibular defect as an example, the enormous potential of 3D printing technique using in the personalized customization of bone repair in the clinic is showed through Micro-CT scanning, three dimensional reconstruction and printing of bone scaffolds. The effect of Mg content on the bone regeneration capacity of scaffolds in vivo is investigated. The results indicate that CSi-Mg10 scaffolds have good bone regeneration repair capacity, and the percentage of newly formed bone reaches 29.1 ± 1.1% after implantation for 16 weeks. Moreover,the early good osseointegration between scaffolds and host bone is observed due to the good match in macro and micro between scaffolds and bone defect, which achieves the personalized customized repair of bone defect.This thesis investigates some keys systematically in the mechanical properties, degradation property and osteogenic performance of scaffolds and displays the enormous potential of 3D printing in the personalized repair of bone defect based on the requirement of bone defect repair in the clinic. The research above would lay foundations for the subsequent fabrication of artificial bone which satisfies with personalized requirement of customized shape and property in the clinic.