Bioceramics

Sol-gel derived ceramic materials have many applications in various fields. Bioceramics is one of the most promising and interesting 

The sol-gel process starting from a liquid phase enables an easy control of the pore structure of the material and an introduction of other components in different kinds of composites, especially, in the case of silica-based materials. Processing of sol-gel derived silica fibers is weU established. 

The main parameters controlling the process are the functionality of the silica precursors and the degree of branching of the sdica clusters. The latter critically affects the spinnabUity and has commonly been characterized by rheological measurements. 

The biodegradation of silica fibers can be controlled by controlling the viscosity of the spinning solution and, thus, the biodegradation of the silica fibers can be varied even when the same recipe is used (79). 

Factors affecting the viscosity are the stage of spinnabiUty, the temperature of the silica sol and the amoimt of solvent in the spinning sol. The silica sol remains spinnable within a certain period of time. The viscosity of the silica sol increases continuously during that period of time. 

Biomedical-grade zirconia was introduced 20 years ago to solve the problem of alumina brittleness, and the consequent potential failure of implants. The reason for this is that biomedical-grade zirconia exhibits the best mechanical properties of oxide ceramics as a consequence of transformation toughening, which increases its resistance to crack propagation. Likewise, partially stabilized zirconia shows excellent biocompatibility, and it has therefore been applied to orthopedic uses such as hip and knee joints [255]. 

On 20 May 1992, a Dutch periodical published an article in which they mentioned the possibility of healing fractures with mother-of-pearl and coral. With this method painful operations could be avoided. The article was illustrated with an ancient Maya skull which showed a hole filled with mother-of-pearl. The ancient Mayas were well ahead of their time. 

By the end of the 1980s this method had surfaced again in medicine. A group of French scientists discovered that coral is very useful when healing fractures. The French firm Inoteb now obtains coral from seas all over the world, cleans it and prepares it for implantation into the body. 

Yet another product of the sea is a huge oyster found south of the Philippine island Palawan. It is called Pinctada maxima and can weigh up to ten kilogrammes. This oyster produces a shell which is as strong as reinforced vibrated concrete. Like coral, this shell is made of calcium carbonate. The inside is covered with mother-of-pearl which cannot be digested by human bone cells. Mother-of-pearl consists for approximately 66% of calcium carbonate and for about 31% of water. The rest is conchioline, a though and homy product. 

The surface of the mother-of-pearl is somewhat permeable for human cells and consequently these cells can form a strong bond between the mother-of-pearl and the bone. Mother-of-pearl is also used in the manufacture of artificial dental roots. These can be attached to the jaw much more firmly than any metal whatsoever. It is thought that mother-of-pearl contains certain natural substances which accelerate the production of human bone. 

Thus it appears that nature teaches us how certain defects in the human body can be mended in a natural way. 

HA-autogenous bone composite Trisodium phosphate, calcium and phosphate salts AI2O3, HA, glass-ceramics AI2O3, HA, HA-PLA composites, surface active glasses 

Bioactive glass-ceramics PLA-carbon fibre composites AI2O3, HA-PLA composites 

Orthopaedic loadbearing applications Dental implants Coating for chemical bonding Alveolar ridge augmentations Temporary bone space fillers 

Coatings for tissues intergrowth Percutaneous access devices Artificial tendons and ligaments Periodontal pocket obliteration 

Ceramic materials Structural building materials Refractory materials Non- structural products Structural products Earthen ware Stone ware Porcelain Technical ceramics 

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Tamura, K. et al. (2004) Effects of micro/ nano particle size on cell function and morphology, Bioceramics 26 (eds Barbosa, M.A., et al.), Trans Tech Publications, Uetikon-Zurich, pp. 919-922. 

Hench, L.L. (1991) Bioceramics from concept to clinic. Journal of the American Ceramic Society, 74, 1487-1510. 

Kamitakahara, M., Ohtsuki, C., Morihara, Y., Ogata, S. and Tanihara, M. (2005) Hydroxyapatite deposition on collagen-like polypeptide modified with silanol groups, in Archives of BioCeramics Research (eds F. Watari, T. Akazawa, M. Uo, T. Akasaka), Vol.5, pp. 210-213. 

Hench, L.L. and Andersson O. (1993) bioactive Glasses. An Introduction to Bioceramics (eds L.L. Hench and J. Wilson), World Scientific Publishing, Singapore, pp. 41. 

Bioceramics The First Weight Bearing, Completely Resorbable Synthetic Bone Replacement Materials... 

It was obvious to early researchers on synthetic bone material that a pure calcium phosphate bioceramic would be the optimum replacement for human and mammalian bone. The calcium phosphate in human bone is called hydroxyapatite (Fig. 1). It is an ionic substance having the formula Ca5(0H)(P04)3. 

HIGH-PERFORMANCE PURE CALCIUM PHOSPHATE BIOCERAMICS... 

We also have been able to prepare equally strong bioceramic materials of several pure calcium phosphates, which are resorbed much faster into the body as they are converted chemically to living bone by a process that we shall discuss (1-3). We have also synthesized an extremely strong (20,000-lb/in. 2 flexural strength) nonporous dental enamel material which is an excellent material for dental caps, crowns, and dentures (Fig. 3) (4). 

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. 

The secret to our success with hydroxyapatite and other strong calcium phosphates is that we seek syntheses for these bioceramics at temperatures on the order of400-800°C, where if hydroxyapatite is used as a reactant it does not decompose. Previously, most attempts failed to produce calcium phosphate bioceramic materials that were even 20% as strong as crystalline hydroxyapatite. Most crumbled under even moderate crompession in vivo. 

Megagraft 1000, the calcium phosphate bioceramic, is synthesized by chemical reaction between calcium and phosphate ion sources (6-9). This synthesis is done by taking the mixture of a calcium and a phosphate source and heating it to a temperature below the starting melting point for an extended period of time. The calcium source can be from calcium phosphates, calcium hydroxide, calcium halides,... 

Our researchers have worked very hard to accomplish our goals by doing things we felt would enhance our synthetic bone materials and their performance to enable them to equal and often exceed the performance of autograft as implants as well as in other types of bone augmentation and replacement. The nonporous tooth enamel solid calcium phosphate materials have flexural strengths of over 20,000 lb in.2 However, without pores it would take an extremely long time to resorb this nonporous bioceramic. 

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. 

Neither autograft, allograft, nor other calcium phosphate bioceramic materials of which we are aware have these properties. Figure 9(a) shows living bone with healthy bone cells (gray) deposited by osteoblasts into the pores of our bioceramic (1-3). 

Figure 9. (a) First bone grows in and fills pores in the bioceramic, (b) Under higher magnification,... 

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