Calcium phosphate coated nanoparticles for drug delivery: where are we now?

For three decades since the term 'biomaterial' was defined in the late 1960s, the interest of the biomaterials research community in calcium phosphates (CaPs) constantly increased. After this interest reached its peak in the mid-1990s, however, it has begun its steady decline, which lasts to this day, the reasons being manifold, many of which are explicated in this review piece. As of this turning point onwards, one solution for CaP to regain its relevance has involved its use in composite structures where properties of complementary components are intended to mitigate each other's weaknesses. A major type of such hybrid particulate structures has included CaP as a surface coating, the goal being to augment bioactivity, promote an intimate interaction with living tissues, facilitate cellular uptake and/or impart smart, pH-sensitive properties to the particles, among other intended effects.

In this review article, historical remarks, recent examples, challenges and opportunities pertaining to CaP-coated nanoparticles for drug delivery are elaborated. Discussion is supplemented with a bibliographic analysis and framed within a chronological timeline.

Phenomenal properties and functions are bound to be elicited by composite structures containing CaP coatings and it is imperative that the exploration of these hybrids continues in decades that follow.