Manufacture And Properties Improvement Of Foam-Like Bioceramics Scaffold For Bone Tissue Engineering

Porous hydroxyapatite (HA) ceramic scaffolds are universally used for bone repair and replacement, and for serving functions to support the adhesion, transfer, proliferation and differentiation of cells due to the three-dimensional (3D) interconnected structure. Due to the brittleness of HA bioceramics, these scaffolds are not suitable to clinical load-bearing sites with the poor strength. Therefore, the application of porous HA bioceramics have been restricted. It is significant to improve the mechanical properties of porous HA bioceramics while maintained the high porosity.The polymer impregnating method was firstly adopted to produce porous hydroxyapatite (HA) ceramic scaffolds with 3D porous structures. The preparation process of porous HA bioceramics are optimized by investigating the concentrations of HA slurry, coating times and particle morphologies. Then, the Hot Isostatic Pressing (HIP) and polymer-coating methods were used to enhance the mechanical strength of porous HA bioceramics. At the same time, considering the biological properties, biomineralization technique was employed for porous Titanium (Ti), HA/PCL and HA/PDLLA scaffolds to improve the affinity to cell. The effect of some bioactive phases including HA, CaSO₄ and CS are investigated by introducing into the polymer coating. Besides, the interconnectivity of porous HA bioceramics fabricated by particle leaching are successfully improved by using extrusion method. The results show that the prepared HA bioceramics scaffolds possess excellent foam-like structure and mechanical properties. Nanoindenter, rotating viscosimeter, stereomicroscope, scanning electron microscopy (SEM), X-ray diffractometer (XRD) and mechancail tester were used to study the properties of porous HA bioceramics scaffold. Main conclusions are drawn as follows: 1. The porous HA scaffold with highly porous structure are successfully prepared by polymer impregnating method. The influence of particle morphologies on mechanical strength of porous HA bioceramics scaffold were investigated. The results showed that the porous HA bioceramics made from spherical HA particles held a higher compressive strength and sintering properties than when using other HA particles morphologies. The use of spherical particles in the preparation process of porous HA bioceramics proved to form the most homogeneous slurry with a higher viscosity, and held more coating on the PU template for the same impregnating process.2. HIP, PCL-coating and PDLLA-coating methods were used to enhance the mechanical properties of porous HA bioceramics scaffold. The strength mechanism of different methods was studies in detail. The results showed that: 1) All three methods are useful to enhance the mechanical properties of porous HA bioceramics, which is better by using the polymer-coating method. 2) As a technique to enhance the sintering and densification of ceramics, the HIP treatment is effective to improve the mergence between grains during the sintering process. Micropores and microcracks decrease significantly in struts of HIP-treated HA scaffolds. 3) PCL lining and PDLLA lining can serve to protect and support the scaffold in the initial stage of use after its implantation in vivo under different load bearing conditions, while the intergranular polymer can strengthen the bridge connection between the particles to prevent the crack propagation or the alteration of its pathway.3. The biomimetic mineralization technique was employed to modify the biological properties of porous structure by depositing Ca-P coating. 1) The nano net-like structure of Ca-P was deposited on the porous Ti scaffold by immersed in simulated body fluid (SBF) and had no influence on the interconnectivity of Ti scaffold. 2) The plate-like Ca-P was successfully deposited on the HA/PCL composite scaffold by immersed in supersaturation calcium phosphate solution (SCPS). 3) The introduction of bioactive phase (HA,CaSO₄ and CS) into PDLLA coating effectively enhanced the bioactivity of composite scaffold. After 7 and 14 days immersion in SBF, a nano net-like Ca-P coating were found on the surface of composite scaffolds. The bioactivity of the composite scaffolds with CaSO₄ is higher than the other composite scaffolds. With the increase of the concentration of SBF, the morphologies of deposited apatite are plate-like different from the net-like apatite immersed in 1SBF.4. Extrusion method is significant to improve the interconnectivity of porous HA bioceramics scaffold prepared by particle leaching method that hold excellent mechanical properties. The size of pore former of wax has no influence on the porosity (about 86%) of porous HA bioceramics. The shrinkage ratio (56%) of the three sinter porous HA bioceramics scaffolds have nothing to do with the particle size and chitin formagen except the HA concentration. With the increase of HA concentration, the shrinkage ratio of scaffold is descendent. The particle size have obvious effect on the compressive strength: with the increase of the size of wax, the compressive strength of porous HA bioceramics scaffold present a gradual decreasing tendency.