Hydrothermal method for preparing calcium phosphate monoliths

Abstract

A new hydrothermal route for preparing biphasic calcium phosphate monoliths is proposed. Firstly, a slurry of beta-tricalcium phosphate/ortho-phosphoric acid (<FONT FACE=Symbol>b</font>-TCP/H3PO4) is cast into the desired final shape and size to obtain a block composed of dicalcium phosphate dihydrate (DCPD) and <FONT FACE=Symbol>b</font>-TCP. This block is then treated in 1.0 M Na2HPO4 at 60 °C in order to hydrolyze the DCPD into Ca10-x(HPO4)x(PO4) 6-x(OH)2-x (CDHA) and Ca8H2(PO4)6 .5H2O (OCP). The result is a monolithic piece which preserves the initial shape and size, but which is composed instead of CDHA, OCP, and <FONT FACE=Symbol>b</font>-TCP. During the initial stage, when the pH is slightly alkaline, the product of DCPD hydrolysis is CDHA. However, when a neutral or slightly acidic pH is reached OCP is formed. Test samples processed by this method showed complete conversion of DCPD into CDHA and OCP after 112 h of hydrolysis, and with a compressive strength of 16.2 MPa, similar to cancellous bone

Transformations in CDHA/OCP/β‐TCP scaffold during ageing in simulated body fluid at 36.5°C

“…During the preparation of the intermediate cement represented by Eq. (1), it was employed an excess of β‐TCP with regard to H 3 PO 4 to obtain the best properties of the set cement and the final scaffold 4…”

“…In a previous work,4 a new calcium phosphate scaffold composed of calcium‐deficient hydroxyapatite (CDHA, Ca 10 − x Na x (HPO) x (PO 4 ) 6 − x (OH) 2 ), octacalcium phosphate (OCP, Ca 8 H 2 (PO 4 ) 6 ·5H 2 O), and β‐TCP) has been described. It is obtained by a two‐step method that involves casting of a cement of dicalcium phosphate dihydrate (DCPD, CaHPO 4 ·2H 2 O) in a mould.…”

“…The outer layer of the monoliths thus obtained is composed of CDHA and β‐TCP, and the inner core of OCP and β‐TCP. The compressive strength of the new biomaterial is similar to cancellous bone and its porosity is over 50% 4. Two of the major component phases, CDHA and β‐TCP, are well known as bioactive and osteoconductive materials and most of the commercial calcium phosphate bioceramics available in the market are made of them 1–3.…”

“…On the other hand, sintered calcium phosphates are more crystalline and less biologically reactive than calcium phosphates obtained by aqueous precipitation or crystallization under similar conditions to those existing in the living body. 1 In a previous work, 4 a new calcium phosphate scaffold composed of calcium-deficient hydroxyapatite (CDHA, Ca 10Àx Na x (HPO) x (PO 4 ) 6Àx (OH) 2 ), octacalcium phosphate (OCP, Ca 8 H 2 (PO 4 ) 6 Á5H 2 O), and b-TCP) has been described. It is obtained by a two-step method that involves casting of a cement of dicalcium phosphate dihydrate (DCPD, CaH-PO 4 Á2H 2 O) in a mould.…”

Efeito do pH na calcificação in vitro de pele porcina

“…A Figura 5 mostra o difratograma de raios X da matriz de pele porcina calcificada a pH 7,4 (matriz C), a mais calciamostras calcificadas em pH 7,4 (Figura 3a) foi observando a maior porcentagem de resíduo inorgânico (obtido em 750°C), ao redor de 30%. No caso das matrizes calcificadas em pH 9,0 (Fig.3b) tensidade para valores de d menores que 3,0Å, sugerindo a presença de outros sais [13,14] . Uma avaliação macroscópica das matrizes mostrou que após a calcificação estas se tornam mais rígidas e com a presença de sais brancos em sua superfície.…”