Composite mr contrast1/10/2024 13 A widely used strategy is appending Gd( III) complexes to a macromolecular platform, 14 such as dendrimers, 15 proteins, 16 and other kinds of slow rotating objects, 17,18 to prolong τ R for the enhancement of relaxivity. Based on the Solomon–Bloembergen–Morgen (SBM) theory, 12 the relaxivity can be significantly enhanced by tuning three important parameters: (i) the number of inner-sphere water molecules directly coordinated to the Gd( III) centre, q (ii) the residence time of the coordinated water molecule, τ M (iii) rotational correlation time representing the molecular tumbling time of a complex, τ R. 11 The development of MRI CAs with high relaxivity and high stability is of essential importance in both academic and clinical applications. 10 However, the commercially used Gd-based MRI CAs suffer low relaxivities and insufficient stability. Among them, the gadolinium (Gd) ion has seven unpaired electrons outside the nucleus, which exhibits the strongest paramagnetism and can enhance MRI signal intensity to the greatest extent and is widely used as a T1 type contrast agent. 7–9 It is mainly 1 contrast agents that enhance the signal that have been approved for clinical use. T2 contrast agents weaken the magnetic resonance imaging signal by reducing the transverse relaxation time of protons in water molecules around tissues, and are also known as negative contrast agents because of their effect on increasing the darkness of MRI images. T1 contrast agents enhance MRI signals by reducing the longitudinal relaxation time of protons in water molecules around tissues, and are also known as positive contrast agents because of their role in increasing brightness of MRI images. 5,6 MRI contrast agents can be divided into two types, namely T1 and T2. In order to increase the contrast of images of different tissues and improve the accuracy of diagnostic results, a contrast agent needs to be injected before MRI testing. 1–4 However, many organs and tissues in the human body are similar in density and relaxivity rate and other characteristics. It has attracted more and more attention for its advantages of high spatial resolution, having no limitation of tissue penetration ability and its harmlessness for the human body. Introduction Magnetic resonance imaging (MRI) is an imaging method based on the difference of relaxivity time between different tissues of the human body. In vitro MRI results showed that the longitudinal and transverse relaxation rates of the composite are 59.56 and 340.81 mm −1 s −1, respectively. The prepared compounds showed negligible cytotoxicity and low haemolysis rate, showing good biocompatibility. Palygorskite fibres constitute the framework of the composite and play a key role in supporting and crosslinking the composite. 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. 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 palygorskite–tannate gadolinium–polyvinyl alcohol integrated composite is successfully prepared after the introduction of polyvinyl alcohol onto the palygorskite–tannate gadolinium. Herein, gadolinium tannate was simply and conveniently coated on the surface of palygorskite by in situ reaction of a coordination polymer formed between tannic acid and Gd 3+.
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