Implantable drug delivery systems formed upon injection offer a host of advantages, including localized drug administration, sustained release, minimized side effects, and enhanced patient compliance. Among the various techniques utilized for the development of in situ forming drug implants, solvent-induced phase inversion emerges as a particularly promising approach. However, synthetic polymer-based implants have been associated with undesirable effects arising from polymer degradation. In response to this challenge, a novel category of drug delivery systems, known as phospholipids-based phase separation gels (PPSGs), has emerged. These gels, characterized by their low initial viscosity, exhibit injectability and undergo rapid transformation into in situ implants when exposed to an aqueous environment. A typical PPSG formulation comprises biodegradable components, such as phospholipids, pharmaceutical oil, and a minimal amount of ethanol. The minimized organic solvents in the composition show good biocompatibility. And the relatively simple composition holds promise for industrial-scale manufacturing. This comprehensive review provides an overview of the principles and advancements in PPSG systems, with specific emphasis on their suitability as drug delivery systems for a wide range of active pharmaceutical ingredients (APIs), spanning from small molecules to peptides and proteins. Additionally, we explore the critical parameters and underlying principles governing the formulation of PPSG-based drug delivery strategies, offering valuable insights on optimization strategies.

Background: Activated hepatic stellate cells (aHSCs) play a significant role during the onset of hepatic fibrosis, ultimately leading to excessive deposition of extracellular matrix (ECM) and other typical pathological features, and thus have become a popular target for the treatment of hepatic fibrosis. However, current aHSC-centric therapy strategies achieve unsatisfactory results, mainly due to the lack of approved anti-fibrosis drugs and sufficiently efficient aHSC-targeted delivery systems. In this study, our aim was to develop an Imatinib-loaded nanoparticle delivery system based on a chondroitin sulfate derivative to enhance aHSC targeting efficiency, improve the therapeutic effect for hepatic fibrosis, and investigate the underlying mechanism. Methods: The carboxyl group of chondroitin sulfate and the amino group of 1-hexadecylamine were linked by an amide bond in this study to produce the amphiphilic carrier CS-HDA. Then, the Imatinib-loaded nanoparticles (IM-CS NPs) were designed to efficiently target aHSCs through CD44-mediated endocytosis and effectively inhibit HSC overactivation via PDGF and TGF-β signaling pathways. Results: Both in vitro cellular uptake experiments and in vivo distribution experiments demonstrated that CS-HDA-modified nanoparticles (IM-CS NPs) exhibited a better targeting ability for aHSCs, which were subsequently utilized to treat carbon tetrachloride-induced hepatic fibrosis mouse models. Finally, significant fibrosis resolution was observed in the carbon tetrachloride-induced hepatic fibrosis mouse models after tail vein injection of the IM-CS NPs, along with their outstanding biocompatibility and biological safety. Conclusions: IM-loaded NPs based on an amphiphilic CS derivative have remarkable antifibrotic effects, providing a promising avenue for the clinical treatment of advanced hepatic fibrosis.