(A-29) Development of poly(ethylene) glycol hydrogel drug delivery device to study intramuscular adipose tissue signaling

Introduction:: The study of how inter-intramuscular adipose tissue (IMAT) signaling affects the transformation of white fat into brown fat is not well understood. To characterize these effects and create a basis for later translational therapies, a controlled-release, biodegradable system for the delivery of IMAT stimulatory molecules is needed. Here we developed a polyethylene glycol (PEG) hydrogel with embedded nanosilicates (NS) for the delivery of the small molecule drug Mirabegron to stimulate IMAT signaling to promote muscle regeneration.

PEG is a cost-effective, biocompatible, biodegradable material with tunable properties used in various drug delivery applications. By forming electrostatic complexes between the drug and NS particles, the release kinetics of the drug can be further slowed and burst release eliminated.


Materials and Methods:: 4-arm PEG-Acrylate and dithiol crosslinker were combined in Michael-type addition with an NS-Mirabegron solution, where the NS were incubated with the drug to form electrostatic complexes. The PEG, crosslinker, and complexes were mixed and dotted onto a glass slide. Silicone rubber spacers (0.5 mm) were placed on the edges of the slide and a second slide was placed on top.

To test the binding affinity of Mirabegron to the nanosilicates, laponite (LAP) and montmorillonite (MMT), the NS was combined with deionized water, incubated on a rocker for 1 hour, spun down, and the supernatant retrieved. Solutions of the NS-Mirabegron complexes were similarly prepared by adding the drug. The supernatant was measured through dynamic light scattering (DLS). Sustained release of Mirabegron from PEG-NS gels was quantified via bulk release experiments (285 nm absorbance of releasate vis spectrophotometry).


Results, Conclusions, and Discussions:: In measuring LAP, MMT, LAP-Mirabegron complex, and MMT-Mirabegron complexes in triplicate with DLS, a distinct size (nm) shift was observed between the nanosilicates in solutions and the complexes. Release profiles showed slower Mirabegron release from PEG-NS gels compared to PEG-only gels. Current work is focused on implanting the gels intramuscularly in mice and observing both inflammation caused by the gels and effect of Mirabegron release on muscle regeneration. Preliminary results show slight inflammation around the implanted gel, which seems to resolve by 2 weeks of implantation.

The IMAT stimulatory drug has been shown to bind to both nanosilicates, MMT and LAP, the foundation for the PEG sustained-release drug delivery system. Preliminary results also show inflammation around the gels upon implantation, which seems to resolve at 2 weeks. This indicates that the system will be adaptable for the intramuscular adipose tissue signaling study.

To show that the established system can be adapted for the drug, we first determined the affinity of the drug to the NS surface. Those experiments proved that the charged small molecule drug electrostatically binds to both nanosilicates, the crux of the sustained release drug delivery system. We then performed release experiments to show the effect of NS-Mirabegron drug complexation on slowing down drug release and minimizing burst release. The current work revolves around understanding the in vivo effects of the PEG and NS to optimize the drug delivery system formulation for intramuscular implantation.


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