Synthesis and Characterization of Temperature-Responsive Poly(ethylene glycol) -Based Hydrogel Nanocomposites

Temperature-responsive hydrogels are one of the most widely-studied types of responsive hydrogel systems, especially for biomedical applications. Their ability to perform in both swollen and collapsed states gives them the ability to be used in controlled drug delivery, microfluidic devices, and biosensors. Poly(ethylene glycol) (PEG) hydrogels are one of the most widely studied and utilized materials for biomedical applications. PEG hydrogels have been shown to be nontoxic, non-immunogenic, and approved by the US Food and Drug Administration for various clinical uses. Recent work has shown that poly(ethylene glycol) methyl methacrylate (PEGMA) polymers are temperature-responsive and exhibit a wide range of lower critical solution temperatures (LCST) based on the length of EG units in the macromer chain. PEG analogues with side-chains of intermediate length (2 < EG units < 10) generally exhibit a LCST in aqueous medium, where the polymers are soluble in water below the LCST but precipitated at temperatures above it. Furthermore, it has been shown that the LCST of these analogues can be tailored by varying copolymer solution of PEGMA of different EG chain lengths, and it is possible to shift the transition so that they will collapse around physiological temperatures. PEGMA analogues have the potential to act similarly to N-isopropylacrylamide (NIPAAm), and they could be an attractive alternative due to their biocompatible nature. The addition of iron oxide nanoparticles to the hydrogel matrix provides the systems the ability to heat remotely upon exposure to an alternating magnetic field (AMF). This along with the temperature-responsiveness of PEGMA may allow for local combination of hyperthermia and controlled drug delivery.

In this work, PEGMA hydrogel nanocomposites were fabricated with various molecular weight poly(ethylene glycol) dimethacrylates (PEGDMA) as the crosslinker to form insoluble hydrogel networks. Diethylene glycol methyl methacrylate (DEGMA, LCST = 26°C) and PEGMA (EG MW = 200, LCST = 60°C) copolymers were polymerized at various molar concentrations with 5 mole % EGDMA as the crosslinker along with 5 weight % iron oxide nanoparticles. Volumetric swelling studies were done from 22 to 65°C and confirm the temperature-responsive nature of the hydrogel systems. For a 52 mole% DEGMA, 43 mole% PEG200MA, 5 mole% TEGDMA hydrogel, the volume swelling ratio ranged from 3.2 at 22°C to 1.5 at 60°C. The volume swelling change around the LCST was broad which may be attributed to the significant crosslinking density of the hydrogel network. Current investigations are undergoing to look at the effect of longer PEGDMA crosslinkers on the volume swelling change and the LCSTs of the hydrogel systems. The ability of the gels to collapse in response to rapid temperature changes when exposed to an AMF is also being investigated along with cellular studies to show the biocompatible nature of the hydrogels.