Hydroxyapatite HAP

Hydroxyapatite (HAP), with basically the same crystal structure as Ca-deficient, carbonate-containing hydroxyapatite, is compatible with and reactive in a live human body. However, sintered HAP prepared by treating fine HAP particles under elevated temperature and pressure has insufficient mechanical properties, in particular fracture toughness, which greatly limits its commercial applicability. It is rarely implanted alone. On the other hand, zirconia, particularly partially stabilized zirconia (PSZ),... 

The research in this area builds on the earlier work of Haka et al. [57] who found that excised calcifications can be classified into two groups using Raman spectroscopy type I - calcium oxalate dihydrate (cod) and type II - calcium hydroxyapatite (hap). Calcium oxalate crystals are mainly found in benign ductal cysts while calcium hydroxyapatite is found in both carcinoma and in benign breast tissue the chemical specificity of Raman spectroscopy identifies... 

Hydroxyapatite (HAP), the molecular formula of which is Ca5(P04)3(0H) or Caio(P04)6(OH)2, is the major inorganic constituent in bone, teeth, etc. in the human body. HAP has essentially the same chemical composition and crystalline structure as those of human bone and so has good bio-compatibility. For a long time, it has been widely used as a sclerotin material in setting broken bone, filling teeth, etc. [215]. In addition, HAP can also be used as a food additive and moisture-sensitive element, etc. 

One of the important fields where carbohydrate polymer/inorganic hybrids may be successfully applied is bioactive materials, e.g., artificial bones expedient for surgery to accelerate the recovery of living bones. There has been increasing interest in hydroxyapatite (HAp) deposition onto the matrix surface of cellulose or related polysaccharide. HAp is a form of calcium phosphate, a main constituent of the inorganic phase of human bone. This kind of study is also a step on the way to exploitation of new biomimetic mineralization methods. 

In order to improve the properties and the spinnability, fibroin sometimes has been electrospun together with other natural or synthetic polymers (Jin et al., 2002 Park et al., 2004, 2006 Wang et al., 2004, 2006). For instance, Jin et al. (2002) developed an aqueous process for silk electrospinning in combination with PEO. More recently, Cao (2008) used PVA/Silk Fibroin (SF), Gelatin/SF, and Hydroxyapatite (HAP)/SF to produce double-layered (core-shell) nanofibers (mats) by coelectrospinning. 

Fig. 22 Top Modification of aqueous microgels by hydroxyapatite (HAp) nanocrystals, (a-d) TEM images of VCL/AAEM/VIm-HAp hybrid microgels containing different amounts of HAp (a) 0, (b) 7.9, (c) 34.2, and (d) 52.2 wt%. (e) EDX line scan of single microgel containing 52.2 wt% HAp with element distribution curves. Color of the lines in (e) corresponds to the color in the element distribution spectra. Reprinted from [149] with permission. Copyright 2008 American Chemical Society...

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. 

Hydroxyapatite (HAp) and its isomorphous modifications are important and prospective materials in bioceramics. There are some mechanochemical smdies on HAp. In [25] HAp was prepared from calcium hydrated orthophosphates and calcium hydroxide or oxide by mechanical activation of mixtures in planetary mill. The authors... 

As can be seen in Fig. 5.14D for crystallization of hydroxyapatite (HAp), increasing the L/S power decreases the particle size [144]. No HAp crystals formed above 300 W below... 

Sedimentation field-flow fractionation was used also for the kinetic study of hydroxyapatite (HAP) particles aggregation in the presence of various electrolytes to determine the rate constants for the bimol-ecular process of aggregation and to investigate the possible aggregation mechanisms describing the experimental data. The HAP sample contained polydis-perse, irregular colloidal particles with number-average diameter dys = 0.262 + 0.046 /rm. 

---