Supramolecular Synthon Approach in Designing Molecular Gels for Advanced Therapeutics

Low-molecular-weight gelators (LMWGs) are an important class of soft materials that offer various potential applications including drug delivery. Structural diversities of the reported LMWGs and lack of molecular-level understanding of the self-assembly process of gelation make it difficult to design a gelator a priori. Most often gelators are discovered in a serendipitous manner and second-generation gelators are designed by modifying known gelling scaffolds. Since gel network within which the solvent molecules are immobilized is often found to be crystalline, a supramolecular synthon approach in the context of crystal engineering is demonstrated to be quite effective in designing LMWGs for various applications including therapeutics. Self-drug-delivery systems, wherein the need for a delivery vehicle does not exist, are becoming an effective alternative to conventional drug delivery systems. In the form of a simple gel (for non-invasive topical application) or injectable gel (for invasive subcutaneous applications), LMWGs derived from drugs provide an effective way to develop self-drug-delivery systems. This review article encompasses the early development of LMWG research, describes gradual transition from discovering just a gelator to a gelator having potential material applications including drug delivery, and highlights the merit of supramolecular synthon approach in designing LMWGs for self-drug-delivery applications.