Bioceramic porosity

For bone substitutes, it is very important that bioceramics have a considerable degree of porosity and particularly interconnected pores so that living bone grows rapidly into the pores. Special bone remodeling cells called osteoclasts and osteoblasts play an extremely important part of the process of rebuilding or repairing the bone. 

In Fig. 7, electron microscope photographs of two different types of high-po-rosity bioceramics are shown. The bone material on the left has 250- j. pore size with a background of micropores [Fig. 7(a)], The specimen on the right-hand side has 400- i pores with a background of 250-p pores as well as displaying micro-porosity within the pores [Fig. 7( >)]. We are also able to regulate the size and distribution of porosity in our bioceramic materials. 

The biological properties of fluoridated bioceramics depend on numerous factors besides the amount of fluoride (porosity, surface roughness, surface properties, degradation process) and it is often difficult to discern the specific role of fluoride. It seems useful to begin by summarising the biological properties of fluoride ions in solution. 

Inoue, O., Shimabukura, H., Shingaki, Y., and Ibaraki, K., Our application of high porosity hydroxyapatite cubes for the treatment of non-cystic benign tumors. Bioceramics 5,411-418 (1992). 

Bone is an anisotropic and viscoelastic ceramic matrix composite and is distinct from conventional ceramics. Its mechanical properties depend on its porosity, degree of mineralization, collagen fiber orientation, and other structural details. The data in Table 18.1 may be used to compare the physical and mechanical properties of bone, hydroxyapatite (the major mineral in bone, and hence, the most relevant material as a bioceramic), and CBPCs. 

The porosity is a critical factor for growth and integration of a tissue into the bioceramic implant. In particular the open porosity, that which is connected to the outside surface, is critical to the integration of tissue into the ceramic especially if the bioceramic is inert. Several methods have been developed to form porous ceramics, two of these are starch consolidation and drip casting. 

Lemons J.E., Bajpai P.K., Patka P, Bonel G., Starling L.B., Rosenstiel T., Muschler G, Kampnier S., and Timmermans T. 1988. Significance of the porosity and physical chemistry of calcium phosphate ceramics orthopaedic uses. In Bioceramics Material Characteristics Versus In Vivo Behavior. Annals of New York Academy of Sciences, Vol. 523, pp. 190-197. 

The Vycor process described in Chapter 8 uses the principle of phase separation. The resulting glass is 96% SiOz and 4% pores and is used as a filter and a bioceramic where porosity is important. It can be densified (after shaping) to allow processing of a pure SiOz shape at a lower temperature than for pure quartz glass. 

In reverse, the porosity of Ni/P alloys obtained by electroless plating on to bioceramic materials, may allow the temporary housing of drugs, and so on [70],... 

Active enzymes were encapsulated into a sol-gel matrix for the first time in 1990 719 About 60 different types of hybrid bioceramic materials with inotganic matrices made from silicon, titanium, and zirconium oxides Ti02-cellulose composites etc. were described. Recentiy, bioceramic sensors, solid electrolytes, electrochemical biosensors, etc. have been surveyed in a review. The moderate temperatures and mild hydrolytic and polymerization conditions in sol-gel reactions of alkoxides make it possible to trap proteins during matrix formation. This prevent proteins denaturation. The high stability of the trapped biomolecules, the inertness, the large specific surface, the porosity, and the optical transparency of the matrix facilitate use of sol-gel immobilization. The principal approaches ate considered below. 

Kinnari TJ, et al. Influence of smface porosity and pH on bacterial adherence to hydroxyapatite and biphasic calcium phosphate bioceramics. J Med Microbiol 2009 58(l) 132-7. 

Dense and inert bioceramics They are materials without porosity. The bond to the bone is morphologic by growth of the tissue in the superficial irregularities of the implants or bond through acrylic cement or by fit the implant in a defect by pressure. Typical example of this group is monocrystalline as much as polycrystalline alumina. 

De Groot, K. Le Geros, R.(1988). Significance of Porosity and Physical Chemistry of Calcium Phosphate Ceramics. In Ducheyne, P. Lemons editors. Bioceramics Material Characteristics Versus In Vivo Behaviour. (268-277). New York Publ. J. Am. Acad. Sci. 

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