(525f) High Throughput Screening of Biodegradable Nanogels with Tunable Size and Swelling for Intracellular Drug Delivery

Authors: 
Spencer, D. S., The University of Texas at Austin
Luu, B. C., The University of Texas at Austin
Beckman, D. W., The University of Texas at Austin
Peppas, N. A., University of Texas at Austin
The design and synthesis of biodegradable, intelligently responsive polymeric nanomaterials in which size and swelling can be tuned without changing material composition is a distinct advantage of cross-linked nanomaterials synthesized by emulsion polymerization. Nanogels have enhanced stability to dilution and lower drug leakage compared to their self-assembled counterparts and emulsion polymerization offers the advantage of controlling nanogel size through surfactant choice and concentration. Furthermore, the use of controlled radical polymerization has the advantage of imparting non-statistical architectures through reaction from a macroinitiator or incorporation of functional initiators.

Recently, PEG graft monomers were shown to have poor conversion in organic solvents below their equilibrium monomer concentrations in atom transfer radical polymerization (ATRP) reactions. In this work, biodegradable cationic nanogels composed of 2-diethylaminoethyl methacrylate, methacrylate comonomers, and a biodegradable disulfide crosslinker (bis(2-methacryloyl)oxyethyl disulfide) were synthesized via activators regenerated by electron transfer (ARGET) ATRP in a high throughput format. First, nanogels were synthesized with or without PEG in an emulsion polymerization. Select nanogel formulations were then modified with PEG or PEG copolymers using copper-catalyzed alkyne-azide cycloaddition. Reaction parameters including surfactant hydrophilic-lipophilic balance, monomer hydrophobicity, crosslinking density, and monomer concentration were systematically investigated to synthesize nanoparticles with predictable size, swelling, and responsive behaviors. Following reaction parameter optimization, a library of nanogels containing a range of hydrophobic comonomers, PEG graft density, and architecture modifications were analyzed for their ability to load and release model chemotherapeutic agents and oligonucleotides. Leading candidates were evaluated in vitro for cytotoxic effects against a doxorubicin resistant cell line.

Nanogel composition was monitored as a function of time via purification and degradation of nanogels under reducing conditions followed by 1H NMR. Molecular weight of degraded nanogels was determined by GPC to be < 40 kDa. Nanogel hydrodynamic size was determined by dynamic light scattering and swelling volume was calculated as the cube of the ratio of swollen to collapsed hydrodynamic diameters. Nanogel collapsed hydrodynamic diameter was modulated from 50 – 150 nm with average polydispersity values < 0.100. Volume swelling ratios ranged from 1.5-9.1 in 1x PBS demonstrating the ease of tunability. Critical swelling pH onset ranged from pH 7.5 to 6.0 depending on the degree of hydrophobic modification. TEM was used to determine dry size, morphology and verify low polydispersity. Nanogel formulations were screened with respect to the loading of doxorubicin and siRNA. Loading and release profiles were related to materials properties to select a diverse set of candidate formulations for dose dependent cytotoxicity against a doxorubicin resistant cell line in vitro.

The use of controlled radical polymerization and click chemistry allowed for efficient synthesis of nanogels with either statistical or non-statistical architectures. Moreover, this approach demonstrates the ability to independently tune the responsive properties of a library of biodegradable nanogels for intracellular drug delivery.