Layered Double Hydroxide Nanostructures as Biocompatible Drug Release Agents: Synthesis, Fundamentals, Modification, and Recent Progress

Abstract

Layered double hydroxides, commonly known as hydrotalcite clays, belong to a family of anionic clays with the general formula M2+(1-X)Mn3+(X)(OH)2.An-(X/n) and a layered brucite-like structure, where M2+, M3+, and An− represent divalent and trivalent metal cations and an anion, respectively. Their versatile compositions, often incorporating benign metals such as Mg, Al, Ca, and Zn, along with their straightforward and low-cost synthesis methods, make them ideal candidates for biocompatible applications. Negatively charged bioactive compounds can be intercalated within the interlayer basal spaces of these synthetic clays and subsequently released within the human body as drugs for therapeutic purposes. Furthermore, fine-tuning the reaction conditions enables the production of layered double hydroxides with reduced particle size (down to 50 nm in diameter in certain studies), with specific dissolution pH and precise anionic exchange capacities, offering a high degree of variability in drug release mechanisms. This chapter aims to discuss the primary synthesis methods of layered double hydroxides, such as the coprecipitation, homogenous precipitation, and sol-gel techniques. It also examines the mechanisms used to effectively store bioactive compounds within the clay matrix, highlighting specific case studies that illustrate the current state of the art in this specialized field.