Polymers for Improved Delivery of Iodinated Contrast Agents

Thrombin Immobilized Hemocompatible Radiopaque Polyurethane Microspheres for Topical Blood Coagulation

Over the past decade, there has been growing interest in developing microspheres for embolization procedures. However, the lack of noninvasive monitoring of the embolic agents and the occurrence of reflux phenomenon leading to unintentional occlusions has raised concerns regarding their compatibility/suitability for embolization therapy. Here we report the development of specialty microspheres having intrinsic radiopacity and surface functionality to tackle the existing complications that pave the way for more advanced solutions. To achieve the above goal, an iodinated monomer, termed "IBHV," capable of imparting radiopacity and functionality, was synthesized and used as a chain extender to make radiopaque polyurethane. Microspheres with a smooth surface and an average diameter of 474 ± 73 μm were fabricated from this polyurethane. The microspheres obtained were noncytotoxic, had a permissible hemolysis rate, and showed better traceability on x-ray imaging. Subsequent immobilization of thrombin onto microspheres improved their hemostatic effect. This study demonstrated that immobilization of thrombin would lead to microspheres with unique traits of radiopacity and hemostatic properties, which will undoubtedly enhance embolization efficiency.

Radiopaque, Self-Immolative Poly(benzyl ether) as a Functional X-ray Contrast Agent: Synthesis, Prolonged Visibility, and Controlled Degradation

A self-immolative radiocontrast polymer agent has been newly designed for this study. The polymer agent is composed of a degradable poly(benzyl ether)-based backbone that enables complete and spontaneous depolymerization upon exposure to a specific stimulus, with iodophenyl pendant groups that confer a radiodensity comparable to that of commercial agents. In particular, when incorporated into a biodegradable polycaprolactone matrix, the agent not only reinforces the matrix and provides prolonged radiopacity without leaching but also governs the overall degradation kinetics of the composite under basic aqueous conditions, allowing for X-ray tracking and exhibiting a predictable degradation until the end of its lifespan. Our design would be advanced with various other components to produce synergistic functions and extended for applications in implantable biodegradable devices and theragnostic systems.

Liposome-camouflaged iodinated mesoporous silica nanoparticles with high loading capacity, high hemodynamic stability, high biocompatibility and high radiopacity

Due to their low osmolality and high tolerability, the highly water-soluble nonionic iodinated contrast agents, such as Ioversol (IV), are widely used as clinical agents for CT imaging. However, their clinical applications still are severely limited by the rapid renal excretion, serious adverse effects especially contrast-induced nephropathy and inefficient targetability. Various nanocarriers have demonstrated tremendous potential for achieving high imaging efficiency and low side effects. However, few nanoparticulate contrast agents can simultaneously integrate the desirable functions for imaging, including high loading capacity of iodine, high structure stability for systemic circulation, high biocompatibility and high radiopacity. Herein, we designed and prepared a kind of new radiopaque liposome-camouflaged iodinated mesoporous silica nanoparticles (OIV-MSNs@Liposomes) as contrast agents in CT imaging. Their composition, structure, morphology, biocompatibility and physicochemical properties as well as in vitro radiopacity were investigated in detail. The results indicated that OIV-MSNs@Liposomes can integrate their individual advantages of liposomes and MSNs, thus exhibiting great potential for use in the CT imaging. Considering the simple preparation process and readily available starting materials as well as enhanced biosafety and high performance in X-ray attenuation, the strategy reported here offers a versatile route to efficiently deliver highly water-soluble nonionic iodinated contrast agents for enhanced CT imaging, which are unattainable by traditional means.

Self-Assembled Nano-CT Contrast Agent Leveraging Size Aggregation for Improved In Vivo Tumor CT Imaging

Computed tomography (CT) is a widely utilized noninvasive diagnostic tool in clinical practice. However, the commonly employed small molecular iodinated contrast agents (ICAs) in clinical CT imaging have limitations such as nonspecific distribution in body, rapid clearance through kidneys, etc., leading to a narrow imaging time window. In contrast, existing nano-sized ICAs face challenges like structural uncertainty, poor reproducibility, low iodine content, and uniformity issues. In this study, a novel approach is presented utilizing the aggregation-induced emission luminogen (AIEgen) to design and fabricate a kind of monocomponent nano-sized ICA (namely, BioDHU-CT NPs) that exhibits a unique aggregation effect upon activation. The small sized BioDHU-CT nanoparticles exhibit excellent tumor targeting capabilities and can release ICA modified with AIEgen with a high release efficiency up to 88.45%, under the activation of reactive oxygen species highly expressed in tumor regions. The released ICA performs in situ aggregation capability in the tumor region, which can enhance the retention efficiency of CT contrast agents, extending the imaging time window and improving the imaging quality in tumor regions.

Facilitated encapsulation of a nonionic contrast agent for X-ray computed tomography into lipid vesicles by the multiple emulsification-solvent evaporation method

We studied the encapsulation of iohexol (Ihex), a nonionic contrast agent used for X-ray computational tomography, into lipid vesicles using the multiple emulsification-solvent evaporation method to formulate a nanosized contrast agent. This lipid vesicle preparation method consists of three steps: (1) primary emulsification for producing water-in-oil (W/O) emulsions containing fine water droplets that will be converted to the internal water phase of the lipid vesicles, (2) secondary emulsification for formulating multiple water-in-oil-in-water (W/O/W) emulsions encapsulating the fine water droplets containing Ihex, and (3) solvent evaporation to remove the oil phase solvent (n-hexane) and to form lipid bilayers surrounding the fine inner droplets, resulting in the formation of lipid vesicles encapsulating Ihex. As the diameter and Ihex concentration of the primary W/O emulsion droplets decreased, a higher Ihex encapsulation yield was obtained for the final lipid vesicles. The entrapment yield of Ihex in the final lipid vesicles varied significantly with the emulsifier (Pluronic® F-68) concentration in the external water phase of W/O/W emulsion, and the highest yield (65%) was obtained when the emulsifier concentration was 0.1 wt%. We also investigated the powderization of lipid vesicles encapsulating Ihex via lyophilization. The powderized vesicles were dispersed in water after rehydration and maintained their controlled diameters. The entrapment yield of Ihex in powderized lipid vesicles was maintained for over 1 month at 25 ˚C, while significant leakage of Ihex was observed in the lipid vesicles suspended in the aqueous phase.