Synthesis, characterization and biocompatibility of polypyrrole/Cu(II) metal-organic framework nanocomposites

The main objective of composite science is to fabricate new materials with desired properties such as high chemical, mechanical, and/or biological performances. In this research, new conductive nanocomposites of copper metal-organic frameworks (Cu-MOF) and polypyrrole (PPy) were fabricated with the aim of exploiting the electrical conductivity of polypyrrole and the porosity of MOFs in the final products. The prepared compounds (PPy/x%Cu-MOF, x = 20, 50, and 80) were investigated by FTIR, PXRD, SEM, TEM, DLS, BET, EDS mapping, cyclic voltammetry (CV), and zeta potential (ξ) measurements. Spherical morphology was confirmed by SEM and TEM analysis. The PPy/80%Cu-MOF nanocomposite showed the highest ξ potential (-40 mV), demonstrating the stability of dispersed particles. The CV results revealed that the nanocomposites have higher capacitance in comparison to the pure materials. In vitro degradation of the as-prepared compounds in simulated body fluid (SBF) was studied by EIS (electrochemical impedance spectroscopy) and Tafel polarization tests. Furthermore, in vitro biocompatibility of the PPy/x%Cu-MOF composite was evaluated on a group of cells including 3T3 fibroblasts, MCF-7 breast cancer cells, J774.A1 macrophages and red blood cells (RBCs). Viability of 3T3 fibroblasts, MCF-7, and J774.A1 cells, by Methylthiazolyldiphenyl-tetrazolium bromide (MTT) method, was dependent on Cu-MOF percent and amount of composites. Hemolytic assay for RBCs exposed to different amounts of the PPy/x%Cu-MOF composites showed hematological toxicity less than 5% in most concentrations. In addition, to investigate pro-inflammatory activity, J774.A1 macrophages were exposed to non-toxic concentrations of the PPy/x%Cu-MOF and no significant change in the expression of two inflammatory genes COX-2 and iNOS was observed. Injection of the PPy/x%Cu-MOF (5 mg kg^-1) into bloodstream of mice did not increase liver damage marker enzymes alanine transaminase (ALT) and aspartate transaminase (AST) level in serum 1 week post injection. Moreover, we observed slight but not significant increase in serum copper level in mice 1 week after injection. According to the results, the PPy/x%Cu-MOF nanocomposites exhibited a good in vitro and in vivo biocompatibility without inducing pro-inflammatory responses in macrophages and show promising potential for different biomedical applications such as biosensors and drug delivery. The release of curcumin from curcumin-loaded PPy/x%Cu-MOF nanocomposites was detectable in plasma of mice 4 days after administration.