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Calcium phosphate scaffolds fabricated via chemical bonding technique from different precursors

Calcium phosphate bulk materials were fabricated via chemical bonding technique with the use of α‐tricalcium (TCP) and amorphous calcium phosphates (ACP) as binders at temperatures below 90 °C. The bonding technique included preparation of pastes of the binders with water, pressing the pastes into dense cylinders, and then hardening the cylinders in hot water. During the last step, hydrolytic conversion of TCP and ACP into small interpenetrating hydroxyapatite (HAp) crystals took place, providing pressed pastes of the binders with appropriate strength. The kinetics of α‐TCP hydrolysis leads to two distinct scaffold microstructures composed of platelet or needle‐like HAp crystals. Under optimal conditions of the bonding, the resulting materials demonstrated compressive strengths up to 90 MPa (and up to 145 MPa, when sodium citrate modifier of the paste is used), which is close to that one of a cortical bone. In contrast to TCP, ACP‐based samples exhibited lower strength, limiting them to use as non‐load bearing implant materials. To enhance mechanical properties, composites containing crystalline phases of HAP, β‐TCP and CaCO3 bonded by ACP binder were proposed. Low value of strength obtained for ACP‐based materials was attributed to extensive cracking resulted from stresses developing under setting of ACP.