Researchers Develop Apatite Nanoparticles for Implanted Biodevice Biocompatibility

Medical implants have transformed healthcare, offering innovative solutions with advanced materials and technologies. However, many biomedical devices face challenges like insufficient cell adhesion, leading to inflammatory responses after their implantation in the body. 

Researchers at Nagaoka University of Technology, Japan, have developed a method for synthesizing surface-modified apatite nanoparticles that results in improved cell adhesion, offering new possibilities for the next generation of biocompatible medical implants. 

Led by Dr. Motohiro Tagaya, Associate Professor at the Department of Materials Science and Bioengineering at Nagaoka University of Technology, Japan, this research aims to enhance the performance of apatite coatings and advance the field of biocompatible materials for medical devices. Dr. Tagaya, Mr. Kazuto Sugimoto from Nagaoka University of Technology, Dr. Tania Guadalupe Peñaflor Galindo from Sophia University, and Mr. Ryota Akutsu from Nagaoka University of Technology were also a part of this research team.

Study findings were published online in ACS Applied Materials & Interfaces, on January 13, 2025, and in Volume 17, Issue 4 of the journal on January 29, 2025.”

Apatite coatings, particularly hydroxyapatite (HA)—a naturally occurring form of apatite found in bones, have been shown to promote better integration with surrounding tissues. However, the biocompatibility of artificially synthesized apatite nanoparticles often falls short of expectations, primarily due to the nanoparticles’ limited ability to bind effectively with biological tissues.

Recent studies have found that coating artificial joints and implants with apatite nanoparticles is a plausible solution for improving the biocompatibility of these biodevices. 

The team synthesized hydroxyapatite nanoparticles by mixing aqueous solutions of calcium and phosphate ions. The pH of the solution was controlled using three different bases, which included tetramethylammonium hydroxide (TMAOH), sodium hydroxide (NaOH), and potassium hydroxide (KOH). The precipitated nanoparticles were then evaluated for their surface layer characteristics and were further used for coating via electrophoretic deposition.

The results showed that pH was a key factor during synthesis since it affected the crystalline phases, surface properties, and electrophoretic deposition. Analysis of the crystalline phases of the nanoparticles showed that the choice of pH influenced the formation of different calcium phosphate phases. Higher pH favored the formation of carbonate-containing hydroxyapatite (CHA), leading to better crystallinity and a higher calcium-to-phosphorus (Ca/P) molar ratio.

The surface of the apatite nanoparticles shows three different layers. The inner apatite layer/core is characterized by the presence of the crystalline structure of the apatite. Above the apatite layer is the non-apatitic layer, which is rich in ions like phosphate ions and carbonate ions. This layer reacts with water molecules and forms the hydration layer. 

Analyzing the surface characteristics of these layers revealed that pH adjustments facilitated the formation of the non-apatitic layer rich in reactive ions, enhancing hydration properties, which was confirmed.

The study also revealed that while higher pH facilitates the formation of the non-apatitic layer, the presence of Na⁺ ions reduces the concentration of phosphate ions. The introduction of substantial ions by NaOH also affected the uniformity of electrophoretic deposition, as observed in scanning probe microscope studies. This effect was not observed with KOH, indicating that KOH was more suitable than NaOH for forming the non-apatitic layer and ensuring uniform coating.