Synthesis of microspherical cellulose particles and study of magnetic relaxation characteristics of their composites with Fe(III) ions

Abstract

The possibility of preparing microspherical cellulose particles was examined.Improvement of the image contrast is an urgent problem of the use of magnetic resonance imaging (MRI) in medicine. The tissue image contrast is determined not only by differences in the proton density in different areas of an organ being scanned, but also by differences in the magnetic relaxation times of water protons. To improve the image contrast, it is necessary to enhance the differentiation of proton relaxation times of water molecules along defi nite spatial coordinates. This can be attained by selective introduction of a paramagnetic impurity into the living body, because it is known that relaxation times of water protons sharply decrease in the presence of paramagnetic ions. Paramagnetic metal ions accelerate the relaxation to different extents. The highest relaxation effi ciency, i.e., the strongest ability to decrease the relaxation time at minimal concentration, is exhibited by ions of rare-earth elements, in particular, of Gd [1]. However, Gd exhibits pronounced toxicity [2]. Iron(III) ions, despite lower relaxation effi ciency, are preferable as contrast agents because of their lower toxicity and existence of metabolic pathways for the removal of excess iron from a living body. To reduce the toxicity, paramagnetic ions are bound with chelate ligands or encapsulated in biocompatible matrices. Incorporation of paramagnetic ions into biocompatible matrices ensures protection of the paramagnetic agent from redox factors of the internal medium of the living body and thus prolongs the effect of the contrast agent in an MRI experiment. However, encapsulation of a paramagnetic reduces its capability to decrease the relaxation time of protons of the aqueous surrounding. The magnitude of the negative effect of the thickness and morphochemical structure of the shell material depends on the rate of molecular diffusion of water protons between the external environment and sorbed water. To evaluate the effect of encapsulation on the contrasting properties of a paramagnetic, it is necessary to estimate how the rate of the diffusion exchange of water affects the magnetic relaxation rate of protons in a suspension of microcapsules.This study was aimed to prepare microspherical cellulose particles (MSCPs) [3], to determine the rate of diffusion of water molecules through the MSCP surface, and to examine the magnetic characteristics of an aqueous suspension of MSCPs with Fe(III) ions incorporated into them, in particular, the effect of such composites on the relaxation rate of water protons. EXPERIMENTALTo prepare microspherical cellulose particles, to an aqueous solution of calcium thiocyanate (density 1.40 ± 0.01 g ml -1 at 20°С) we added a defi nite amount of microcrystalline cellulose (MCC) (6 g per 100 ml) and left for 2 h for complete swelling. Then the mixture was placed in a desiccator and treated in a water-jet-

Nanostructured Cellulose II Gel Consisting of Spherical Particles

“…Hence, the production of TENCEL gel is highly energy-efficient: the required energy demand is significantly lower than unconventional CNF production. Cellulose micro- and nanoparticles can also be obtained by spraying a cellulose suspension into liquid nitrogen or by precipitation of dissolved cellulose and derivatives. − These methods are more time-consuming and produces only individual particles but not interacting particles forming a viscoelastic gel.…”