Calcium phosphate materials (CaP) are known to be major constituents of mammalian bone and synthetic CaPs have been shown to be bioactive in vitro and in vivo. They are one of the most versatile biomaterials for orthopedic applications and have been shown to be effective scaffolds for bone regeneration and as gene delivery carriers. However, significant problems related to their synthesis have limited their clinical use.
Conventional processing produces CaP with low crystallinity and large particulates which contributes to the overall brittleness of formed products. This has largely restricted the use of synthetic CaPs to non load-bearing applications. Nanopowders can be used to produce products with smaller grain sizes and thus improved mechanical properties.
Traditional CaP transfection often results in the formation of large aggregates due to subsequent crystal growth. As such, synthesis of nano CaPs is of particular interest and importance in developing novel therapeutic strategies for orthopedic pathologies.
Calcium phosphate nanoparticles (CaPn) were synthesized utilizing two different methods—chemical precipitation and a microwave assisted combustion synthesis (MACS) method.
Microwave processing has been shown to homogenize the heating profiles of materials via bulk or volumetric heating, as well as reduce processing times. This results in more uniform particle formation and products with improved integrity. The precipitated CaPn were sintered via microwave heating while those produced with MACS required no further heat treatment. The as-synthesized materials were characterized using FTIR, XRD, SEM and TEM. In vitro results using mouse osteoblasts on microwaved scaffolds showed cell growth over a seven day time period, demonstrating the biocompatibility of the microwave samples.
The CaPn generated from MACS were highly nanocrystalline and had high aspect ratios. They were studied as possible nonviral gene delivery carriers. A hydroxyapatite variant with europium doping was also produced and its ability to be used as a fluorescent probe was demonstrated. Plasmid DNA encoding for green fluorescent protein (GFP) was used to confirm the ability of these particles to deliver the DNA. A therapeutic plasmid expressing a turbo GFP bone morphogenetic protein-2 (pCMV-GFP-BMP-2) fusion construct was used to test the efficacy of the delivery system for orthopedic pathologies.