Multi-Responsive Microgel Carrier for Intracellular Delivery of Biomacromolecular Drugs

As known, biological macromolecules have good curative effect and strong specificity, but cell transfection is difficult and easy to inactivate. In this paper, we developed a multifunctional microgel carrier for multi-drug co-loading and independent release in and out of cells. Firstly, poly(N-isopropylacrylamide) (COOH-PNIPAM-COOH) was prepared by reversible addition fragmentation chain transfer (RAFT) polymerization method and assembled with hyaluronic acid (HA) on the surface of ZIF-8 by electrostatic interaction. Then, microgel carrier ZIF@HA/PNIPAM(1:k)gel was obtained by cross-linking disulfide bonds. The microgel showed good anti-dilution stability and multi-stimulus response ability. They also have triple response of temperature, pH and glutathione (GSH) sensitivity with a low critical solubilization temperature (LCST) of 42 degree celsius and the pH-sensitive point of 5.89. The nuclear ZIF-8 could be dissolved in acid, the gel layer would shrink at high temperature and could be dissociated by glutathione (GSH) reduction. As drug models, small molecule proanthocyanidins (PC) and macromolecule bovine serum protein (FITC-BSA) were loaded in the gel layer and ZIF-8 respectively to study the release behavior of co-loaded two-drug. In vitro drug release experiments proved that the microgel could effectively prevent drug leakage under normal physiological environment, and the release amounts of PC and BSA were both below 15%. Meanwhile, the drug release behaviors in the simulated tumor microenvironment outside and inside cells were also studied. It was found that under specific conditions, the maximum release amounts could reach 74% for PC and 88% for BSA respectively, showing that the release of the two drugs had good controllability and independent. When high temperature is applied alone (simulating tumor extracellular environment), the gel layer shrinks, resulting in PC release. Under acidic and high GSH (mimicking the internal environment of tumor cells) conditions, both the gel and ZIF-8 dissociate, and FITC-BSA is released. The drug delivery system constructed in this work will contribute to the safe and effective delivery of biological macromolecules and solve the problem of multi-drug resistance. The research ideas will provide meaningful scientific guidance for the research of intracellular delivery of macromolecules required for chemotherapy of serious diseases and repair of damaged tissues.