Preparation And Properties Of Modified HAP-based Porous Bioceramics

As a new kind of functional material, porous hydroxyapatite(HAP) bioceramics have been developed and some of them are now applied to repair and reconstruct diseased or damaged bones or tissues. At present, the porous HAP-based ceramic has extended to use as drug carrier and antitumor activity, due to it not only possess good biocompatiblity but also can modulate cellular activities, including cell adhesion, migration, DNA synthesis, and protein secretion, implying a promising application in biomedical field. In this dissertation, A novel porous bioceramics with the good bioactivity, biocompatibility and degradablility were designed and synthesized for bone regeneration and drug delivery. The structure and properties of the synthesized porous body were characterized by different methods. Biological evaluation of materials was carried out, via soaked simulated body fluid(SBF), by cultivating RSC96Schwann cells on the surface of the materials. The major work is summarized as the following:The ball,rod and fibrous HAP nanoparticles were synthesized successfully in this part.The influences of reaction temperature, dropping speed of solution,the change of pH value and stirring speed on the particle morphology were investigated.Nanophase HAP particles were coated with silica via the hydrolysis of tetraethyl orthosilicate after a dodecyl alcohol based esterification reaction. The silicate-coated HAP(HAPSi050) particles were characterized by TEM, SEM, XRD, FTIR, thermogravimetry and differential scanning calorimetry (DSC), sedimentation time and zeta potential (ξ) studies. A sequential change in infrared spectral features characteristic of HAP was accompanied by an increase in features characteristic of silica as revealed by FTIR. The results indicate that the SiO2Coating thickness is about3nm. The silica coating enhanced the colloidal stability of HAP in aqueous suspensions and antiacid dissolving capacity. This behavior can be explained based on a heterocoagulation coating mechanism in which silica clusters adsorb onto the HAP particle surface.The system of SiO2-CaO-O5bioactive glasses (BG) with a particle size less than100nm were successfully synthesized by W/O microemulsion approach.XRD, SEM and EDX analyses,X-ray fluorescence (XRF), laser particle size analyzer,TEM,FTIR, BET N2gas adsorption analysis techniques were utilized in order to evaluate the phase composition, dimension,morphology,interconnectivity of pores and particle size of the synthesized BG respectiveely. The measured BET specific surface area and pore volume was137.9cm2/g and0.37cm3/g respectively.The results of the degradation in vitro show that the pH value of degradation medium tended to rise but still in the range of neutral during the whole degradation time. That improved the BG is biodegradable.MTT assay showed that BG has been shown to have good biocompatibility and is also beneficial to the survival of Schwann cells,which can promote cell proliferation.During the preparation of porous HAPSi050-based ceramics with carbon powder, which was used as pore producer, and the SiO2-CaO-P2O5system bioglass as the reinforced phase.the calcinations temperatures,bioglass content,carbon powder content and the holding time were analyzed. The phase composition and microstructure of porous body were investigated by XRD and SEM. The universal testing machine, hardness tester, and permeability tester were used to determine the mechanical properties and fluid permeability of porous body. Result indicates that The bending strength would improve along with the increase of sintering temperature and bioglass content, the porosity and thepermeability were lower as a result. With the increase of carbon powder content, the porosity and permeability increases, but the bending strength gradually reduce as a result.The number of shapeless inter-agglomerate pores decreased and amount of spherical intra-agglomerate pores increased on increasing the sintering temperature from1100℃to1250℃. The shape of pores also changed with thermal treatment of specimens; the small pores remained spherical while the larger pores became more spherical in shape, as was proved by image analysis. A three-dimensional, finite element unit cell model was applied to evaluate the influence of pore shape on the mechanical strength of HAPSi050-based ceramics. By analyzing the effect of the shape of pores to the fracture toughness of sintered porous bioceramics, it was observed that the more spherical the pores were, the tougher became the bioceramics. After sintering at1250℃for2h, measured toughness was1.29MPa m1/2, which is a relatively high value for this type of bioceramics.The sample,which was soaked in SBF solution,lost the mass quickly in the beginning because of the dissolution.The dissolution reduced the decrease of the bending strength.After5days,the bone-like hydroxyapatite layer emerged,and it existed in the form of tiny crystallite,which size was30～50nm,and the mass of sample was growing.The bending strength should increase with the longer time,and the bone-like hydroxyapatite layer over-covered the sample surface completely after25days. After cultivating RSC96Schwann cells on the surface of porous materials, Biological evaluation were carried out through cell proliferation, cytotoxicity and SEM observation. The viability using MTT assay of RSC96cells seeded on porous ceramics disc showed that porous ceramics could promote cells adhesion and proliferation. Giemsa test and Fluorescent probe technology indicated that cytotoxicity of porous ceramics is similar to HAP, which suggested it is non-toxic. The SEM results showed that porous samples has better cell affinity than HAP. All of the above results suggested that the porous ceramic was non-toxic and could support the cell attachment and proliferation.