Fine tuning the disassembly time of thermoresponsive polymer nanoparticles

Timed-released disassembly of nanoparticles without a remote trigger or environmental cues is demonstrated in this work. The reversible addition-fragmentation chain transfer (RAFT) polymerization allowed the fine-tuning of the chemical composition in the diblock copolymers, in which the first block consisted of a hydrophilic monomer (DMA) and the second random block consisted of three different monomers: (a) the thermoresponsive NIPAM, (b) the self-catalyzed hydrolyzable DMAEA, and (c) the hydrophobic BA. These diblock copolymers were solubilized in water below the lower critical solution temperature (LCST) of the thermoresponsive second block, and heated to 37 °C (i.e., >LCST) to form small micelle nanoparticles with a narrow particle size distribution. As DMAEA hydrolyzed to acrylic acid groups, the LCST of the diblock increased, and the time at the start of micelle disassembly (t(start)) corresponded to the point where the LCST was equal to the solution temperature (i.e., 37 °C). The high water content in the PNIPAM core allowed an even degradation of the core over time. The copolymer composition allowed fine control over t(start), as this time was linearly dependent upon the BA units in the second block. These nanoparticles could also be designed to be stable (i.e., not disassemble) over a wide pH range or disassemble below a pH of 7.3. Additionally, the time from the start of disassembly to full unimer formation (t(degrade)) could be controlled by the amount of DMAEA units in the second block. A longer t(degrade) (~5.5 h) was found when the number of DMAEA units was 42 compared to t(degrade) of 1.1 h for 25 units. The nanoparticles designed in this work, through fine control of the polymer chemical composition, have the potential for drug delivery purposes for timed-release of drugs and prodrugs and other wide-ranging applications where timed-release would be beneficial.