| Background:Tumor, trauma, congenital defects and other factors can result in mandibular defects, which caused facial deformity and disfunction affects, leading to varying degrees of physical and mental health of the patients and the mood of anxiety, nervousness, restlessness when communicating with others. Therefore, the jaw bone defect repair is a hot area of research for several years. Bone grafting is an important means for the treatment of bone defects. Autograft is considered to be "gold standard" for bone repair and has a high cure rate, which could complete the repair and regeneration of bone defects after in 3-6 months post transplantation.There are some shortcomings about autologous bone graft, such as the limited bone source and secondary trauma of donor site, which restricted its clinical application. Allograft, xenograft, decalcified bone matrix avoid the additional damage and pain to patients, but immune rejection, ethical issues and potential pathogens(such as the HIV virus, HBV virus) were simultaneously evoked. In recent years, the development of the research on tissue engineering provides a new idea and method for the progress of tissue defect repair and regeneration. Seed cells with a multiple differentiation potential are injected into scaffolds after in vitro proliferation, then the complex is implanted into the body to achieve the ultimate goals of regenerating functioning bioengineered organs to rebuild or repair tissue defects. This concept has brought a new gospel for bone tissue defect repair and showed a good development prospects of oral and maxillofacialbone defects.The development of bone tissue engineering based on our understanding on biological bone, stem cell biology and tissue engineering technology. There are three important factors about bone tissue engineering sacffolds-seed cells and bone growth factors. The scaffold and seed cells together constitute a three-dimensional complex, which is the core of tissue engineering. The bone engineering scaffolds not only provide a stable support for allowing bone cell attachment onto the surface as well as provide sufficient space for cell proliferation and differentiation, but also play a crucial role in guiding bone formation and controlling the structure. At the same time, the scaffold should have adequate mechanical strength for maintaining normal physiological movement. To study an ideal scaffold material with excellent biocompatibility and the certain extent of strength is one of the hot topics on bone tissue engineering at present. Currently, the materials for bone tissue engineering scaffold consist of biological materials and synthetic materials. The former mainly contains natural bone, coral bone and natural polymers, et al. Such materials have similar structures with human bone. The later includes probably organic polymers, inorganic biological ceramics and composite materials.Reticulated porous scaffolds(RPSs) have recently been more noticeable which have a well-interconnected pore network with large pore volume and an average pore connection size in the field of bone tissue engineering. Ceramic zirconia(ZrO2) has been shown to have excellent mechanical strength and good biocompatibility, which has been applied to the study of bone tissue engineering scaffolds. Several ceramic processing techniques have been used for preparing porous scaffolds, such as soild free form technique, combined gel-casting and freeze-drying method, sol-gel technique, replication technique and so on. The most convenient and feasible procedure is the replication technique, which was firstly invented by Schwartzwalder and Somers. The polyurethane sponge template is immersed in ceramic slurries. After the removal of the extra slurry and desiccation, the polymer template is burned out and the remaining ceramic framework continues to be sintered at certain temperature. However, nano-zirconia porous scaffolds prepared by this technique had low strength and would be easily destroyed for the reason that thin and defective struts such as cracks, pores and other large flaws remained on the surface after the sponge was burned out, which limited their use for the bone tissue engineering. The microstructural defects might have related to the preparation of the slurry, the pretreatment methods of the sponge template, the temperature and time of drying and sintering, the process of dipping and so on. Objective:The objective of our study is to evaluate the effect of using alkali for the pretreatment of template sponge and the influence of adding polyvinyl butyral (PVB) as the dispersant on the properties of ZrO2 slurry, to study the capability of bone regeneration and vascularization of three-dimensional nano-zirconia porous scaffolds with canine bone marrow stromal cells in vivo and evaluate the feasibility of bone tissue engineering. Methods:1. The effect of using alkali for the pretreatment of template sponge and slurry removal technology standardizationThe polyurethane sponges were pretreated by using the sodium hydroxide solution for different times, then we judge the suitable processing time by the comparison of the loading content and scanning electron microscope(SEM). We need to determine the basic time of the excess slurry removal and the drying time at low temperature, in order to achieve their goal of the standardization of production process.2. Influence of PVB on the properties of three-dimensional nano-zirconia porous scaffoldsThe slurries were prepared which contained different amounts of PVB. The improvement on the mechanical properties of the scaffolds prepared the sullry containing the dispersant was evaluated by sediment experiment, the loading content of slurry, compressive strength and SEM. Template duplication was taken to fabricate porous ZrO2 scaffold by the new slurry. The addition of PVB whether effect the compressive strength and porosity was evaluated.3. In vivo study ofnano-ZrO2 scaffolds compounds with canine bone marrow stromal cellsCanine bone marrow stromal cells(BMSCs) were obtained by total bone marrow adherent culture method, and then were subcultured and expanded to P3 in vitro. The surface treated nano-ZrO2 scaffold was seeded with bone marrow stromal cells and cultured for 3 days. Lastly, scaffolds seeded with canine BMSCs were implanted into an adult beagle’s mandibular for bone repair test.Results:1. The effect of using alkali for the pretreatment of template sponge and slurry removal technology standardizationThe most suitable time of using 2 mol/L sodium hydroxide solution for the pretreatment of template sponge is 8h. The polyurethane sponge pretreatment can corrode the surface and increase the surface roughness, which can achieve the purpose of increasing the adhesion between the slurry and the template and improving the loading content of slurry. Finally we got the standardization of production process.2. Influence of PVB on the properties of three-dimensional nano-zirconia porous scaffoldsThe test result showed that the new slurry has better stability by taking 0.2% polyvinyl butyral as the dispersant, which could be used to prepare the new scaffolds with higher compressive strength(0.32±0.030Mpa). The scaffolds prepared by the slurry with the dispersant content of 0.2% had a complete structure, which the amount of surface cracks significantly decreased than other groups. There were a little of lateral and longitudinal cracks on the strut walls and intersections. The addition of PVB had no negative effect on the compressive strength and porosity.3. In vivo study of nano-ZrO2 scaffolds compounds with canine bone marrow stromal cellsBone formation was studied by general observation and 3-dimensional CT reconstruction at 4 and 12 weeks after operation. There was bone defect repair which was implanted different scaffolds.Conclusions:1. The pretreatment of template sponge by using the alkali solution and the standardization of production process can improve the success rate after the first sintering and reduce the occurrence of the collapse of bloom phenomenon.2. The addition of PVB can improve the compressive strength of three-dimensional nano-zirconia porous scaffolds, which make the scaffolds more suitable for in vitro and in vivo study.3. After the three-dimensional nano-ZrO2 porous scaffold seeded with canine bone marrow stromal cells was implanted in vivo, it showed well bone repair in an adult beagle. In other words, the nano-ZrO2 porous scaffold was able to act as scaffold for bone tissue engineering. |
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