Scaffold microstructure evolution via freeze-casting and hydrothermal phase transformation of calcium phosphate

Abstract

Extensive research efforts have been focused on customizing the microstructure, macrostructure, and phase composition of calcium phosphate for enhanced biocompatibility and bioactivity in scaffolds for bone substitutes. Despite significant progress, achieving precise phase composition and microstructure remains a challenge, primarily due to the necessity of scaffold sintering. This study addresses the challenges in developing customized patient-specific bone substitutes by proposing a sequential approach that reduces processing steps while providing control over the phase and morphology of the scaffolds' structure. The methodology utilizes freeze-casting and sintering for highly porous the scaffolds' preparation, followed by hydrothermal treatment to modify the microstructure. The introduction of CaCO3 induces a phase transformation of tricalcium phosphate, increasing the hydroxyapatite content, while the overall macrostructure retains the characteristics of freeze-casting. The surface morphology undergoes a transition from equiaxial grains to whiskers-like structures and hexagonal rods, impacting compressive strength. Following hydrothermal treatment, the formation of whiskers-like hydroxyapatite grains leads to a notable strength increase from 2.8 to 5.7 MPa. Remarkably, the scaffolds undergo nearly complete phase transformation, shifting from 100% tricalcium phosphate to 99% hydroxyapatite, all while conserving the macrostructure. Scaffolds with enhanced porosity and altered surface morphologies were created through freeze-casting, sintering, and subsequent hydrothermal treatment. The modified scaffolds maintained their overall macrostructure, displaying high porosity (>= 60%), diverse hydroxyapatite phase ratios (0-99%), and a compressive strength of 5.7 MPa. This study introduces a novel approach employing hydrothermal treatment for microstructural and phase customization of sintered scaffolds. imageExtensive research efforts have been focused on customizing the microstructure, macrostructure, and phase composition of calcium phosphate for enhanced biocompatibility and bioactivity in scaffolds for bone substitutes. Despite significant progress, achieving precise phase composition and microstructure remains a challenge, primarily due to the necessity of scaffold sintering. This study addresses the challenges in developing customized patient-specific bone substitutes by proposing a sequential approach that reduces processing steps while providing control over the phase and morphology of the scaffolds' structure. The methodology utilizes freeze-casting and sintering for highly porous the scaffolds' preparation, followed by hydrothermal treatment to modify the microstructure. The introduction of CaCO3 induces a phase transformation of tricalcium phosphate, increasing the hydroxyapatite content, while the overall macrostructure retains the characteristics of freeze-casting. The surface morphology undergoes a transition from equiaxial grains to whiskers-like structures and hexagonal rods, impacting compressive strength. Following hydrothermal treatment, the formation of whiskers-like hydroxyapatite grains leads to a notable strength increase from 2.8 to 5.7 MPa. Remarkably, the scaffolds undergo nearly complete phase transformation, shifting from 100% tricalcium phosphate to 99% hydroxyapatite, all while conserving the macrostructure. Scaffolds with enhanced porosity and altered surface morphologies were created through freeze-casting, sintering, and subsequent hydrothermal treatment. The modified scaffolds maintained their overall macrostructure, displaying high porosity (>= 60%), diverse hydroxyapatite phase ratios (0-99%), and a compressive strength of 5.7 MPa. This study introduces a novel approach employing hydrothermal treatment for microstructural and phase customization of sintered scaffolds. image