Preparation and MRI performance of a composite contrast agent based on palygorskite pores and channels binding effect to prolong the residence time of water molecules on gadolinium ions.

Herein, gadolinium tannate was simply and conveniently coated on the surface of palygorskite by reaction of a coordination polymer formed between tannic acid and Gd. The palygorskite-tannate gadolinium-polyvinyl alcohol integrated composite (PAL@Gd@PVA) is successfully prepared after the introduction of polyvinyl alcohol onto the palygorskite-tannate gadolinium. The structure is characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray diffraction spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy analysis. The results show that TA-Gd and PVA are successfully loaded on the surface of palygorskite, and the rod crystal structure of palygorskite in the composite remains intact. Palygorskite fibres constitute the framework of the composite and play a key role in supporting and crosslinking the composite. The prepared compounds showed negligible cytotoxicity and low haemolysis rate, showing good biocompatibility. MRI results showed that the longitudinal and transverse relaxation rates of the composite are 59.56 and 340.81 mm s, respectively.