Mesoporous silica nanoparticles: Synthesis and multifaceted functionalization for controlled drug delivery

Inorganic mesoporous silica nanoparticles (MSN) are porous materials extensively studied for drug delivery due to their properties such as facile and diverse synthesis methods, uniform and tunable pore size, biocompatible, high loading efficiency and existence of abundant surface silanol groups which avails facile surface functionalization. This latter property aids characteristics to these materials to be utilized for controlled cargo delivery, controlling biological responses, enhance cytocompatibility along with colloidal stability and improve targetability. In this review various MSN synthesis approaches and functionalization strategies for active and passive targeting, including controlled drug delivery by capping pores with stimulus/stimuli-sensitive gatekeepers is discussed. These caps can be triggered by various indigenous and/or exogenous stimuli and release the payload where and when required. Various stimuli-responsive drug delivery approaches targeting pH, redox, enzyme, temperature, light, etc., are discussed. In addition, several research groups have constructed MSN based nanoparticles, able to release payload in response to dual and triple stimuli for enhancing on-demand triggered release, reducing non-specific drug leakage. While adding multi-drug delivery property, MSN is complexed with different nanocarriers, synergistically enhancing characteristics of both the complexed nanocarriers. Therefore, owing to its versatility, MSNs can be considered to have great potential as drug delivery vectors.