Microgel-Based Stretchable Reservoir Devices for Elongation Enhanced Small Molecule Release Rate

Abstract

Stretchable poly(N-isopropylacrylamide)-co-acrylic acid (pNIPAm-co-10% AAc) microgel-based reservoir devices were fabricated and used to control the release rate of the small molecule model drug tris(4-(dimethylamino)phenyl)methylium chloride (crystal violet, CV) to solution by varying the Au layer thickness coating the microgels and device elongation. Specifically, we showed that CV could be loaded into the microgel layer of the devices via electrostatic interactions at pH 6.5, and the release could be triggered upon exposure to a pH 3.0 solution, which breaks the microgel−CV electrostatic interactions. We demonstrated that the rate of release could be increased by decreasing the Au layer thickness coating microgels and by stretching, that is, thin Au and high elongation promoted the relatively fast release of CV from the device. We found that the Au overlayer thickness (and porosity) dominated the observed release rate profiles when the device was not stretched (or at low elongation), while elongation-induced cracks dominated the release rate at high elongation. We also showed that the CV release kinetics could transition from low ("off") to high ("on"), which enhanced when the devices are stretched. This behavior could be exploited in the future for autonomous release systems that release small molecules when stretched by natural processes, for example, movement of joints and muscles.

Cooling-Triggered Release from Mesoporous Poly(N-isopropylacrylamide) Microgels at Physiological Conditions

“…Porous and, as a result, very soft MM-gels can flatten to increase contact with the surface driven by an entropy increase because of the release of bound water and counterions. An understanding of the initial shape of the MM-gels is important for their possible use in microgel-based stretchable reservoir devices responsive to mechanical forces. , …”

Mechanically Resistant Poly(N‐vinylcaprolactam) Microgels with Sacrificial Supramolecular Catechin Hydrogen Bonds

“…Such mechanically resistant μgels might become useful for applications in biomedicine and engineering where shear forces are expected or for force‐actuated μgel materials. [ 59 , 60 ]…”

Surface‐Bound Microgels for Separation, Sensing, and Biomedical Applications

“…Zhang et al fabricated a similar system for CV delivery using P(NIPAm-co-AA) etalons, where CV was loaded into the microgel layer via electrostatic stabilization at pH 6.5 and released by breaking the electrostatic interactions through HCl addition to pH 3. [229] Most notably, the rate of CV release from the microgels was controlled either by varying the thickness of the sputtered gold overlayer or by stretching the etalon to expose microfractures in the overlayer. Guo et al followed this study by adding a self-assembled alkane-thiol coating on the gold overlayer to reduce the CV diffusion rate and enable accurate monitoring of the CV transport.…”