Untitled

Abstract

Hydraulic calcium phosphate cements (CPCs) that are used as osseous substitutes, set by an acid-base reaction between an acid calcium phosphate and a basic calcium salt (often a phosphate). In order to gain a better understanding of the setting of the monocalcium phosphate monohydrate-calcium oxide cement that we developed and in the aim to improve its mechanical properties, the setting reaction was studied by pH-metry. The two methods described in the literature were used. In the first, cement samples were prepared then crushed after different storage periods at 37 degrees C, 100% RH. The powder was then immersed in pure water with stirring and the pH was measured after equilibration. In the second technique, the starting materials were poured into water while stirring and the pH were followed over time. The two methods gave different results. The first procedure provided information concerning the pH of the surrounding liquid following the partial dissolution of the cement components, rather than any information about pH changes during setting. The second method is more appropriate to follow the pH variations during setting. In this second procedure, the effects of different parameters such as crushing time, stirring rate, liquid-to-powder (L/P) ratio and temperature were investigated. These parameters may impact substantially on the shape and position of the pH=f(t) curves. One or three pH jumps were observed during the setting depending on the composition of the liquid phase. The time at which these pH jumps occurred depended on the pH of the liquid phase, the concentration of the buffer, the crushing of starting materials, the L/P ratio and the temperature. Good linear correlations were obtained (i) between the time of the pH jumps and the L/P ratio and the temperature and (ii) between the time of the first pH jump and the compressive strength and the final setting time of the cements prepared with different liquid phases. It may be assumed in view of these correlations that the results obtained in dilute solution may be extrapolated to the conditions of cement sample preparation and that the mechanical properties of the cement are directly related to the phenomena that occur at the first pH jump which corresponds to precipitation of dicalcium phosphate dihydrate.

Biodegradable Materials for Bone Repair and Tissue Engineering Applications

“…Sometimes other additives are included in the cement composition to alter the setting time and physical properties. Very basic alkaline sources such as calcium oxide [331] and calcium hydroxide [332] can be used to prepare DCP cements. Dicalcium phosphate dehydrate (DCPD), mineral name brushite (Figure 5c), has a calcium to phosphate (Ca/P) ratio of 1 and hence calcium phosphates with Ca/P ratio higher than 1 can be utilized to make brushites [44,333].…”

“…Since DCP cements have a Ca/P ratio of 1, so acidic calcium phosphate compounds used to prepare DCP cements need to have a Ca/P ratio lower than 1. The only two calcium phosphates with this low ratio are monocalcium phosphate anhydrous (MCPA), also known as monetite and monoclacium phosphate monohydrate (MCPM) [331,337]. MCPM is more commonly used to prepare DCP cements because it has a water molecule that it donates during the cement setting process [44].…”

Self-Setting Calcium Orthophosphate Formulations

“…The list of possible additives includes (but is not limited to) the following cations: Na + , K + , Mg 2+ , Ca 2+ , Sr 2+ , Zn 2+ , H + and anions: PO 4 3− , HPO 4 2− , H 2 PO 4 − , P 2 O 7 4− , CO 3 2− , HCO 3 − , SO 4 2− , HSO 4 − , Cl − , OH − , F − , silicates [46]. Therefore, mixed-type self-setting formulations consisting of calcium orthophosphates and other calcium salts, such as calcium sulfate [54,55,56,57,58,59,60,61,62,63], calcium pyrophosphate [64,65,66], calcium polyphosphates [67,68], calcium carbonates [16,26,28,30,50,69,70,71], calcium oxide [72,73,74,75,76,77], calcium hydroxide [78,79,80], calcium aluminates [43,81,82], calcium silicates [83,84,85,86,87,88,89], etc ., are available. In addition, other chemicals such as Sr-containing compounds [19,90,91,92,93], Mg-containing compounds [93,94,95,96,97,98,99,100], Zn-containing compounds [101,102], etc ., might be added to calcium orthophosphates as well.…”

Calcium Orthophosphate Cements and Concretes

“…The list of possible additives includes (but is not limited to) the following cations: Na + , K + , Mg 2+ , Ca 2+ , Sr 2+ , H + and anions: PO 4 3− , HPO 4 2− , H 2 PO 4 − , P 2 O 7 4− , CO 3 2− , HCO 3 − , SO 4 2− , HSO 4 − , Cl − , OH − , F − , SiO 4 4− [25]. Therefore, mixed-type cements consisting of calcium orthophosphates and other calcium salts ( e.g., gypsum [34,38,39], calcium sulfate hemihydrate [40], calcium pyrophosphate [41,42,43], calcium polyphosphates [44], calcium carbonate [29,45,46,47], calcium oxide [48,49,50,51,52,53], calcium hydroxide [54,55,56], calcium aluminate [57,58], calcium silicate [59,60,61,62], etc . ), strontium orthophosphate [63,64], magnesium orthophosphate [65,66,67], barium sulfate [68], as well as cements made of various ion substituted calcium orthophosphates ( e.g., Ca 2 KNa(PO 4 ) 2 , NaCaPO 4 , Na 3 Ca 6 (PO 4 ) 5 , magnesium substituted CDHA, strontium substituted CDHA, etc .)…”