Calcium-based ceramics

The first feature discussed above has been well recognized, and much modern research has been focussed on developing biocompatible calcium-based ceramics. Manipulation of the microstructure, however, has not been attempted sufficiently, and much of the rapid prototyping has been to develop suitable macroscopic forms for sintered ceramics. 

Alexander H., Parsons J.R., Ricci J.L., Bajpai P.K., and Weiss A.B. 1987. Calcium-based ceramics and composites in bone reconstruction. Crit. Rev. 4 43—47. 

One great advantage with phosphate bonded ceramics in biomaterial or dental applications is the phosphate ions in their structure. Bones contain calcium phosphate, and hence phosphate bonded ceramics are generally biocompatible with bones. While chemically bonded calcium phosphate ceramics have been difficult to produce, magnesium and zinc based phosphate bonded ceramics have been more easily synthesized and used as structural and dental cements. 

Naturally occurring phosphate cements are also known. Krajewski [3] cites calcium-based phosphate cements in the Albeian condensed Glauconitic Limestone of the Tatra Mountains in Western Carpathians. In recent years methods have been developed to fabricate calcium phosphate ceramics by direct reaction of calcium compounds and either phosphoric acid or an acid phosphate. The mineralogy of the products has also been well studied. Most of these efforts are directed towards development of calcium-based bioceramics containing calcium phosphate compounds, such as hydroxyapatite. These developments are discussed below. 

The biocompatible CBPC development has occurred only in the last few years, and the recent trend has been to evaluate them as biocompatible ceramics. After all, biological systems form bone and dentine at room temperature, and it is natural to expect that biocompatible ceramics should also be formed at ambient temperature, preferably in a biological environment when placed in a body as a paste. CBPCs allow such placement. We have discussed such calcium phosphate-based cements in Chapter 13. Calcium-based CBPCs, especially those constituting hydroxyapatite (HAP), are a natural choice. HAP is a primary mineral in bone [3], and hence calcium phosphate cements can mimic natural bone. Some of these ceramics with tailored composition and microstructure are already in use, yet there is ample room for improvement. This Chapter focuses on the most recent biocompatible CBPCs and their testing in a biological environment. To understand biocompatible material and its biological environment, it is first necessary to understand the structure of bone and how it is formed. 

Inorganic particles have also been used to produce electrospun scaffolds. Hydroxyapatite (HA) is a calcium phosphate-based ceramic present in natural bone, which has been evaluated for the production of bone scaffolds. Electrospun scaffolds were produced from a blend of PLGA and nanosized HA. When MSC were cultivated on the scaffolds, their osteogenic differentiation was favored. 

Ooms, E. M., Wolke, J. G. C., van de Heuvel, R., Jeschke, B., and Jansen, J. A. 2003. Histological evaluation of the hone response to calcium phosphate cement implanted in cortical bone. Biomaterials 24 989-1000. Ooms, E. M., Wolke, J. G. C., van der Waerden, J. P. C. M., and Jansen, J. A. 2002. Trabecular bone response to injectable calcium phosphate (Ca-P) cement. Journal Biomedical Materials Research 61 9-18. Orlovskii, P. V., Komlev, V. S., and Barinov, S. M. 2002. Hydroxyapatite and hydroxyapatite based ceramics. Inorganic Materials 38 1159-72. 

For example, calcium copper titanate - CaCu3Ti40i2 (CCTO), ruthenium oxide RUO2 cobalt-nickel spinels, carbon-based ceramic composite films... 

Calcium phosphate-based ceramics constitute, at present, the preferred bone substitute in orthopedic and maxillofacial surgery. They are very sirttilar to the mineral phase of the bone, by their stracture and/or their chemical composition. Calcium phosphates usually found in ceramics are ... 

The development of calcium phosphate-based ceramics at high temperature requires taking into account the thermal stability of these compounds. We can distinguish two schemes of decomposition according to the temperature irreversible decompositions (condensation of hydrogenophosphate ions, decomposition of carbonate ions, of hydroxide ions, etc.) at low temperature (150-1,000°C) and reversible decomposition (decomposition of the apatite into TCP, TTCP and lime) at high temperatures (T > 1,000°C). 

Methyl vinyl ether is rapidly hydrolysed by contact with dilute acids to form acetaldehyde, which is more reactive and has wider flammability limits than the ether [1], Presence of base is essential during storage or distillation of the ether to prevent rapid acid-catalysed homopolymerisation, which is not prevented by antioxidants. Even mildly acidic solids (calcium chloride or some ceramics) will initiate exothermic polymerisation [2],... 

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