Consolidation of Spray-Dried Amorphous Calcium Phosphate by Ultrafast Compression: Chemical and Structural Overview

Bone regeneration research often seeks materials that promote cell activity and tissue growth. Amorphous calcium phosphates (ACPs) are promising due to their similarity to bone mineral. However, their metastable nature limits their use in bulk forms. Current studies focus on developing 3D scaffolds that are both resorbable and bioactive. Prior research has shown that conventional sintering methods can alter the chemical structure of ACPs. This gap motivated the exploration of alternative consolidation techniques. The need for a process that preserves the amorphous state while enabling structural formation remains unmet. No prior work had resolved the challenge of maintaining ACP’s metastability during consolidation. This paper addresses that limitation through a novel cold sintering approach.

This study aimed to develop a method for consolidating amorphous calcium phosphates (ACPs) without compromising their metastable nature. The goal was to create a 3D scaffold suitable for bone regeneration. The specific problem addressed was the lack of a consolidation process that preserves the amorphous structure of ACPs. The motivation was to enable the fabrication of bioactive scaffolds for non-load bearing bone defects. The authors proposed using ultrafast low-pressure room temperature compaction as a solution. This method was selected to avoid the high temperatures that typically alter ACPs. The study sought to confirm that the process could maintain the material’s amorphous state. The outcome would allow for the production of scaffolds with tailored properties.

The study employed ultrafast low-pressure room temperature (RT) compaction to consolidate ACP powders. This cold sintering method avoided high-temperature treatments that could alter the material’s structure. X-ray diffraction (XRD) was used to confirm the preservation of the amorphous state. Fourier-transform infrared (FTIR) and Raman spectroscopy were applied to analyze chemical changes. Solid-state nuclear magnetic resonance (NMR) provided insights into local structural modifications. Thermal analyses were conducted to assess physicochemical stability. The resulting pellets were examined for porosity and mechanical resistance. The process was evaluated for its suitability in producing scaffolds for bone regeneration.

The ultrafast compaction method successfully consolidated ACP pellets while maintaining their amorphous structure. XRD confirmed no crystallization occurred during the process. Spectroscopic analyses revealed minor physicochemical changes, including partial water loss. Raman and FTIR data indicated shifts in the HPO₄²⁻ ion environment. Solid-state NMR supported the presence of local structural modifications. The pellets exhibited an open porous structure suitable for non-load bearing applications. Mechanical testing showed sufficient resistance for surgical handling and reshaping. The process enabled the fabrication of reactive ACP scaffolds with potential for drug combination.

The authors concluded that ultrafast cold sintering preserves the amorphous nature of ACPs during consolidation. The process allows for the creation of porous scaffolds suitable for bone regeneration. The material’s metastability was maintained, supporting its bioactive potential. The open structure observed is ideal for non-load bearing defects. Mechanical resistance was sufficient for surgical use and manipulation. The method enables tailorable scaffolds that can be combined with thermosensitive drugs. The findings suggest a promising route for developing biomaterials with tailored properties. The process aligns with the need for low-energy fabrication methods in biomedical engineering.