Molecular mechanisms of crystallization impacting calcium phosphate cements

Abstract

The biomineral calcium hydrogen phosphate dihydrate (CaHPO 4 ·2H 2 O), known as brushite, is a malleable material that both grows and dissolves faster than most other calcium minerals, including other calcium phosphate phases, calcium carbonates and calcium oxalates. Within the body, this ready formation and dissolution can play a role in certain diseases, such as kidney stone and plaque formation. However, these same properties, along with brushite's excellent biocompatibility, can be used to great benefit in making resorbable biomedical cements. To optimize cements, additives are commonly used to control crystallization kinetics and phase transformation. This paper describes the use of in situ scanning probe microscopy to investigate the role of several solution parameters and additives in brushite atomic step motion. Surprisingly, this work demonstrates that the activation barrier for phosphate (rather than calcium) incorporation limits growth kinetics and that additives such as magnesium, citrate and bisphosphonates each influence step motion in distinctly different ways. Our findings provide details of how, and where, molecules inhibit or accelerate kinetics. These insights have the potential to aid in designing molecules to target specific steps and to guide synergistic combinations of additives.

Monetite promoting effect of citric acid on brushite cement setting kinetics

“…The (110) plane is terminated by a calcium ion, making it susceptible to adsorption of impurities like citrate group. 7 Water layer is also interrupted at the step edges on the (010) face, where oxygen atoms are not available from neighbouring phosphates, so that calcium and phosphate ions are able to interact with the surrounding medium, allowing the dissolution of these ions and impurity adsorption. 8 The growth kinetics is mainly controlled by phosphate incorporation, and additives interfering with this step regulate precipitation and crystal growth.…”

Effect on growth and osteoblast mineralization of hydroxyapatite-zirconia (HA-ZrO 2 ) obtained by a new low temperature system

“…In this case, the powder potassium phosphates and thermal annealed during 1 h and as a result, tetragonal zirconia was obtained. Giocondi et al obtained HA decomposition in OCP, ACP, DCPD y DCPA under similar acidic conditions [41].…”

Structural changes to resorbable calcium phosphate bioceramic aged in vitro

“…2-3. There also appeared to be small fragments of material exhibiting a non-crystalline morphology coating the crystals; this is attributed to adsorbed protein, to which a number of researchers have previously made reference [48]. Immersion in 20 % v/v FBS solution yielded a similar change in porosity as did immersion in S-DMEM and S-HAM, which contained 10 % v/v and 20 % v/v FBS respectively; a rapid increase in porosity accompanied by an order of magnitude increase in the dominant pore diameters, as shown in Fig.…”