Hydroxyapatite mechanical properties

Hong Z, Zhang P, He C et al (2005) Nano-composite of poly(L-lactide) and surface grafted hydroxyapatite mechanical properties and biocompatibility. Biomaterials 26 6296-6304... 

Padilla, S., Vallet-Regi, M., Ginebra, M. P. and Gil, F.J. (2005) Processing and mechanical properties of hydroxyapatite pieces obtained by the gelcasting method. Journal of the European Ceramic Society, 25, 375-383. 

Bone and teeth in mammals and bony fishes all rely on calcium phosphates in the form of hydroxyapatite [Ca5(P04)30H]2, usually associated with around 5% carbonate (and referred to as carbonated apatite). The bones of the endoskeleton and the dentin and enamel of teeth have a high mineral content of carbonated apatite, and represent an extraordinary variety of structures with physical and mechanical properties exquisitely adapted to their particular function in the tissue where they are produced. We begin by discussing the formation of bone and then examine the biomineralization process leading to the hardest mineralized tissue known, the enamel of mammalian teeth. 

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 inorganic component of bone is primarily platelike (20 to 80 nm long and 2 to 5 nm thick) crystalhne hydroxyapatite, Ca5(P04)3(0H) or HA (Kaplan et al., 1994 Park and Lakes, 1992). Small amounts of impurities may be present in the mineralized HA matrix for example, carbonate may replace phosphate groups, whereas chloride and fluoride may replace hydroxyl groups. Because release of ions from the mineral bone matrix controls cell-mediated functions, the presence of impurities may impact important biological aspects (and, subsequently, affect chemical and mechanical properties of bone) that are critical to normal bone function for example, impurities present in the mineralized matrix may affect cellular function(s) that influence new bone formation (Kaplan et al., 1994 Park and Lakes, 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. 

Summary of Mechanical Properties of Bone, Dentine [3], Hydroxyapatite [3], and CBPCs. 

Whilst the use of enamel and dentine as test substrates is widespread, they are complex materials to work with due to the natural variability both within and between specimens. A number of authors have examined alternative materials, which have similar mechanical properties to enamel and dentine, to use as test substrates. Acrylic [19, 20] and synthetic hydroxyapatite [21] have been proposed as suitable materials for abrasion testing, where mechanical effects dominate. These materials have several advantages since they are available as relatively large, smooth samples and exhibit better intra- and inter-sample reproducibility than their natural counterparts. This may, therefore, give better discrimination between test products for formulation development. However, the use of natural enamel and dentine is preferred, particularly for studies that aim to understand interactions between toothpaste products and tooth hard tissues. Other methods for assessing toothpaste abrasivity to hard tissues include gravimetry [22], scanning electron microscopy [23] and laser reflection [24]. 

Next-generation metallic biomaterials include porous titanium alloys and porous CoCrMo with elastic moduli that more closely mimic that of human bone nickel-titanium alloys with shape-memory properties for dental braces and medical staples rare earth magnets such as the NdFeB family for dental fixatives and titanium alloys or stainless steel coated with hydroxyapatite for improved bioactivity for bone replacement. The corrosion resistance, biocompatibility, and mechanical properties of many of these materials still must be optimized for example, the toxicity and carcinogenic nature of nickel released from NiTi alloys is a concern. ... 

Special methods of incorporation fillers are frequently pre-dispersed in polyol (for better mechanical properties) or plasticizers (to dry while dispersing) hydroxyapatite was modified by reaction with hexamethylene diisocyanate " ... 

Inorganic carriers (e.g. glass, silica gel, alumina, bentonite, hydroxyapatite, nickel/nickel oxide, titania, zirconia) often show good mechanical properties,... 

Bertrand, G., Collonges, G., Combes, C., Parco, M., Braceras, I., Alexis, J., Balcaen, Y., and Rey, C. (2014b) Comparison of physical-chemical and mechanical properties of chlorapatite and hydroxyapatite plasma sprayed coatings. Open Bioeng. J., in press. 

Fahad Hasan, M., Wang, J., and Berndt, C. (2014) Evaluation of the mechanical properties of plasma sprayed hydroxyapatite coatings. Appl. Surf. Sci., 303, 155-162. 

Latka, L., Pawlowski, L., Chicot, D., Pierlot, C., and Petit, F. (2010a) Mechanical properties of suspension plasma sprayed hydroxyapatite coatings submitted to simulated body fluid. Surf. Coat. Technol, 205 (4), 954-960. 

---