Cellular Uptake and Intracellular Cargo Release From Dextran Based Nanogel Drug Carriers

The versatility of NG makes them ideal candidates for drug delivery and bioimaging [1]. NG, often characterized as soft nanoparticles, are hydrophilic 3D networks that can absorb large amounts of water or biological fluids while maintaining their structure. In the swollen state, the low surface tension between the fluid and the NG minimizes nonspecific interactions, such as protein and cell adhesion, enhancing biocompatibility. In addition, the sub-micrometer size of the nanogels ensures that most nanogels are able to be taken up by cells, while their large surface area allows for tailoring to various in vitro/vivo applications and rapid responses to environment stimuli [2]. Research on drug delivery applications has mostly focused on core-shell NG. Generally, a hydrophilic shell stabilizes the NG in water/biological fluid and provides the NG with a “stealth” property, allowing them to avoid mononuclear phagocytic system (MPS) recognition as well as opsonization. The hydrophobic core allows for loading of cargo/drug via hydrophobic and electrostatic interactions. Polymers frequently used to prepare NG include polyethylene glycol-poly(ethylene imine) [3], poly(4-vinylpyridine)-poly(N-isopropylacrylamide) [4], and natural polymers. The use of polysaccharides, such as dextran, for the hydrophilic shell is particularly appealing for biomedical applications due to well-documented biocompatibility and biodegradability, multiple reactive sites for attachment of specific ligands, and steric protection against protein adsorption [5–13]. Common synthesis methods to prepare core-shell NG include (inverse) emulsion polymerization [14], precipitation polymerization [15], and photopolymerization [16]. Alternatively, core-shell NG can be prepared via two simple steps, Maillard reaction and heat gelation. The Maillard reaction is a natural nontoxic reaction that links a protein and a polysaccharide. Subsequent heat gelation ensures partial denaturation of the protein and stable formation of the NG. This technique has several notable advantages: it is low-cost, completely “green” (i.e., it takes place in an aqueous solution) and initiator-free. Following this methodology, Li et al. synthesized NG with a LDNG that could be tailored from 80 nm to 1 μm in diameter [7]. In particular, LDNG (200 nm diameter) were spherical in shape, stable across a broad range of pH values and ionic strength, and capable of loading ibuprofen. Similar methodology has been used to prepare other protein-polysaccharide core-shell NG, such as bovine serum albumin (BSA)-dextran [9], BSA-dextran-chitosan [17], and doxorubicin-BSA-dextran [18] core-shell nanoparticles. The latter NG was found to prolong the life of mice having hepatoma H22 tumors [18]. In this work, we prepare rhodamine-labeled LDNG (LRDNG) and demonstrate their potential for use as carriers for drug delivery. This was accomplished by loading a fluorescent molecular probe (HAF) into the core of the LRDNG to model a drug. HUVEC were used as a cell culture model to verify the uptake of the LRDNG and drug release, as well as to assess cytotoxicity. Finally, the “stealth” characteristics of the LRDNG were confirmed using differentiated macrophages (PMA-stimulated THP-1 cells), as a model for the MPS.