The Preparation And Characterization Of Porous Hydroxyapatite Ceramic Scaffold With Interconnectivity

The key of tissue engineering is manufacturing a bioactive and biodegradation scaffold to either maintain existing tissue structures or enable tissue growth for supporting growth, proliferation, transplanting and adhering of tissue cell. The scaffold must be osteoconductive and osteointegrative, and have enough mechanical strength to provide structural support during the bone growth and remodeling. All kinds of the scaffold are porous materials. The porosity and interconnectivity are important factors for the scaffold and also is propitious to more bone cell growth, the intensity of reconstructing bone has higher strength but that of the scaffold itself should reduce on the contrary.Hydroxyapatite (HA, Ca10(PO4)6(OH)2) is found in hard tissues of the body such as bone and teeth, has had some success as a bone replacement material.The porous HA ceramic should fulfil requests about tissue cells penetrating, transplanting, adhering and developing. The structural property of porous HA is more resorbable and more osteoconductive than dense HA.Based on early studies, the minimum requirement for pore size is considered to be～100μm due to cell size, migration requirements and transport. However, pore sizes >300μm are recommended, due to enhanced new bone formation.Some new techniques of fabricating porous HA ceramic scaffolds are introduced in this study. Comparing the samples manufactured and trying to discover the method about technique on preparation of porous ceramic with higher interconnection and favorable strength and also being controlled artificially. The shape, size, distributing, interconnecting of pores in samples were observed by Scanning electron micrograph. XRD patterns of sample indicated that the samples produced have no introduced heterogeneity and security of the techniques. The mechanical parameters of the samples were test by mechanical universal testing machine. The technique to manufacture porous HA ceramic with high interconnectivity and satisfied for mechanical performance was ensured besides the configuration of samples may be controlled artificially.1. The preparation of porous 3-D HA ceramic using chitin for carrier.It was claimed that a minimum pore size of (?)200μm was necessary for bone ingrowth into the porous implant materials. It is suspected that the size of interconnection is the main limiting factor of osteoconduction rather than the size of the pores themselves.In initial experiment, the ceramic slurry was prepared by chitin used as carrier, Hydroxyapatite ceramics with controlled porosity and pore size were prepared by adding sugar particles as pore-making agent (PMA). The scaffolds prepared have an open, uniform and interconnected porous structure. The pore morphology was characterized using a scanning electron microscope and light microscopy. The porosity and rate of open pore were measured for a series of samples. Two kinds of acid as corrosive agent to HA were respectively used to outspread the windows between pores within half-sintered blocks. It was found that LiCl has an effect on densification of HA ceramic during sintering. Micro rigidity of the HA ceramic doped has increased and changed steadily in different testing point. XRD patterns indicated the introducing of LiCl has no resulted decomposing of HA. The transport of cells in porous ceramic represent directional. Two kinds of slurry preparation, DMAc/LiCl/CT/HA and PVA/HA, were used for forming HA ceramic tube with using different core stick to conglutinate the slurry. SEM indicated the two slurry forming system could result distinctly in various appearances to HA tube. The techniques about improving interconnectivity between pores within porous HA ceramic blocks has become emphases of the experiment. Every factor of influencing on pore forming and linking among pores of the fabricated porous HA ceramic and artificially controlling method of inner structure were analysed.2. Fabricating porous bioceramics with interconnectivity by fibers pre-treated.Fibre yarns pre-treated coated by special macromolecule glue were weaved into mould with HA slurry blending with Polyvinyl Alcohol (PVA) to fabricate porous bioceramic. Stripe saved on surface of fiber was expressly charactered on channel in the ceramic block. SEM micrographs showed that channels have directional connecting, distributing equally, intact configuration and existence of thin stripes on inner-face. XRD patterns indicated the crystalline structure.The results indicated that the solidified fiber yarn could establish channel or pore in porous bioceramic. The structure should satisfy request about tissue engineering scaffold.3. Study on the process for modeling hydroxyapatite ceramic fiber and fabricating the porous ceramic by fiber self-filling.Hydroxyapatite slurry were adhere to surface of silk and simultaneously to be consolidated. The short HA ceramic fibres with preferable tropism were prepared through reasonable design of sintering process. N. N. Dimethyl Acetamide, LiCl and chitin were used for preparation of sol-gel systems of spinning fluid blended HA powder to make initial fiber. The concentration of each component of spinning fluid, the size of HA powders, temperature and flow speed of solidification bath would influence to fiber configuration and diameter. These infection factors also include the temperature of sintering process and confirming area of constant temperature. The experiment obtained fiber with diameter of 100-150μm and sequential length. On second thoughts, the method of fabricating porous HA ceramic by using HA powders and short HA fiber. By changing amount of fiber and pore-forming agent, Porous HA ceramic with porosities ranging from 60% to 80% were produced.4.The analysis about influence of mechanical performance to porous HA ceramic.The test and analysis on mechanical performance to porous HA ceramic samples manufactured by various methods were carried. The results showed that the strength of porous block etched by acid had reduced. Variation coefficient of strengths among the samples with same porosity increased along with porosity. Porosity, size and distribution of pores and channels in ceramic block made from directional fiber were optimized in the condition of low porosity. Arrange consistency of fiber yarn should be controlled well and truly when the porosity is over 70%. The size of HA powder should be less than 10μm when the HA ceramics with high porosity were required. Increasing sintering temperature can enhance the strength of whole porous ceramic block. The porous block filled by HA fiber actualized strength enhancing at certain porosity and the effect of strength increasing was very obvious standing open pore ratio. The method suits for preparation of porous HA ceramic with porosity of less than 80%.