Calcium phosphate-based system

Calcium phosphate-based systems have wide applications in biomedical areas. Brown has outlined the similarities between the hydration of calcium silicates and calcium phosphates. The hydration products in both systems have high surface areas, variable composition, and poor crystallinity. Pozzolanic reactions and Hadley-like grains form in both systems. The primary cement-water reactions for C3S and tetracalcium phosphate are as follows ... 

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. 

SS/MA may be structured in different ratios of sulfonated styrene to maleic anhydride. Typically, it is 3 1 (20,000 MW) or 1 1 (15,000 MW). The application rates of all calcium phosphate scale/sludge inhibitors or stabilizers vary, based on the amount of calcium present in the cooling system, with increased calcium hardness leading to higher levels of polymer required. 

Bio-nanocomposites based on calcium phosphates can perform other innovative fundions such as acting as a reservoir for the controlled release of bioadive compounds once the material is implanted in the bone defect. For instance, the incorporation of a morphogenetic protein that promotes bone regeneration in an HAP-alginate-collagen system [110] or a vitamin in a Ca-deficient HAP-chitosan nanocomposite [111] are recent examples of this kind of application. 

Nature itself gives us a spectacular example of a biopolymer-based delivery system in the form of the native casein micelle of mammalian milk (Lemay et al, 2007). This is primarily a colloidal delivery system for calcium, where the micronutrient is in the form of calcium phosphate, which does not give a bitter taste, and which provides good bioavailability owing to its colloidal size, amorphous state and quick dissolution in gastric conditions (pH 1-2). Nevertheless, the casein micelle structure is unique there are no other readily available natural delivery systems for most nutraceuticals. Therefore some new designs are clearly required (Velikov and Pelan, 2008 McClements et al, 2008, 2009). 

For beef cattle pasture systems in the Amazon basin, only calcium, among the base cations, is normally added to the system via pasture management practices. This is because animal supplementation with bone meal or bicalcium phosphate is commonly practiced in most beef cattle systems throughout Amazonia. For a typical active pasture with a medium carrying capacity, the amount of calcium entering the system in one year through mineral supplementation would be around 4.0 kg per hectare which is close to the amount expected to be exported in animal products. 

Bioceramics as Bone Substitutes The development of the so-called bioceramics is based on the knowledge that native bone is essentially composed of a more or less carbonated hydroxyapatite (HA) Caio(P04)(,(OH)2. With respect to the need for low solubility or of a controllable resorption, different compounds of the calcium phosphate system Ca(OH)2-H3P04-H20 have been applied for bone substitutes or bone fillings (Table 5.1). 

Approximately 10% of the human population (with regional differences indicating both genetic and environmental factors [33]) is affected by the formation of stones or calculi in the urinary tract. Urolithiasis is not only a painful condition, but also causes annual costs to the health system in the order of billions of dollars in the USA alone [34, 35]. Based on their composition, structure and location in the urinary tract, renal stones have been classified into 11 groups and their formation mechanisms have been discussed together with alterations in urinary parameters and metabolic risk factors for renal lithiasis [35]. Approximately 70% of these stones contain calcium oxalate monohydrate (COM) and dihydrate as major components, while other calculi are composed of ammonium magnesium phosphate (struvite), calcium phosphates (hydroxyapatite and brushite), uric acid and urates, cystine and xanthine. An accurate knowledge of the solubilities of these substances is necessary to understand the cause of renal or bladder calculi formation and find ways towards its prevention and treatment [36]. 

Calcium phosphate sensors are commonly based on solvents with low permittivities, e.g. DOPP (s = 6.2), whereas neutral carrier types may require highly polar solvents, typically 2-nitrophenyl octylether (2-NPOE), e = 23.6 (28). Another characteristic feature of neutral carrier systems (Table 3.12) is the presence of lipophilic anions, e.g. tetraphenylborate (KTPB) which was first incorporated to reduce the interference by lipophilic sample anions (36) and so dislodge interferents from the membrane phase. Today tetrakis(4-chlorophenyl)borate, KTpClPB, is generally preferred because its water solubility is smaller than that of KTPB by a factor of about 1000, and its... 

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