Carrier colloids

Cammas-Marion S, Okano T, Kataoka K. Functional and site-specific macromolecular micelles as high potential drug carriers. Colloids Surf B 1999 16 207-215. 

Sorption of radionuclides on particulates in solution is frequently observed. The particles may be coarsely or finely dispersed. Their surface properties (surface layer, charge, ion-exchange and sorption properties) play a major role. In general, they offer a great number of sorption sites on the surfaee, and microamounts of radionuclides may be found on the surface of these particles instead of in solution. Sorption of radionuclides on colloidal particles leads to formation of radioeolloids (carrier colloids, section 13.4). 

Formation of intrinsic colloids in natural waters can be excluded for radioisotopes of elements of groups 0, I and VII, and the probability that they may be formed is small for radioisotopes of elements of other groups as long as the concentration of the elements is low. In general, formation of carrier colloids by interaction of radionuclides with colloids already present in natural waters is most probable. Thus, clay particles have a high affinity for heavy alkali and alkaline-earth ions, which are bound by ion exchange. This leads to the formation of carrier colloids with Cs, Ra and °Sr. Formation of radiocolloids with hydrolysing species has already been discussed (section 13.4). 

Aquatic sediments are formed in all surface waters by the settling of coarse and fine inorganic and organic particles. They are present in rivers, in lakes and in the oceans, and radionuclides deposited on the surface of the earth will sooner or later come into contact with these sediments. They may enter the sediments by sorption of molecularly-dispersed species (ions, molecules), by precipitation or coprecipitation, by coagulation of colloids (in particular carrier colloids) followed by sedimentation of the particles formed, or by sedimentation of coarse particles (suspended matter). By desorption, the radionuclides may be remobilized and released again into the water. 

Radioactivity (activity) Property of matter exhibiting (radioactive) decay or isomeric transition of atomic nuclei and emission of nuclear radiation [Bq = s ] Radioanalysis Analysis by means of radioactive atoms (radionuclides) Radiocolloids Colloids (i.e. matter in the colloidal state) consisting of the radioactive matter considered (intrinsic colloids) or containing microamounts of radioactive matter (carrier colloids)... 

Two types of colloids are recognized in the literature. Intrinsic colloids (also called true colloids, type I colloids, precipitation colloids, or Eigencolloids ) consist of radioelements with very low solubility limits. Carrier colloids (also known as pseudocolloids, type II colloids or EremdkoIIoides ) consist of mineral or organic phases (in natural waters primarily organic complexes, silicates and oxides) to which radionuclides are sorbed. Both sparingly soluble and very soluble radionuclides can be associated with this type of colloid. In addition, radionuclides can be associated with microbial cells and be transported as biocolloids. 

Two different processes could be important for the initiation of radionuclide transport by carrier colloids (i) reversible sorption of radionuclides from solution onto pre-existing colloids and (ii) detachment of colloids from the host rock with high concentrations of previously sorbed irreversibly bound colloids. In both cases, radionuclides that sorb strongly to the rock matrix and would normally migrate very slowly will travel at a rapid rate while they are bound to colloids. 

Experimental studies. Sorption of radionuclides by colloids is affected by the same solution composition parameters discussed in the previous section on sorption processes. The important parameters include pH, redox conditions, the concentrations of competing cations such as Mg " " and K, and the concentrations of organic ligands and carbonate. The high surface area of colloids leads to relatively high uptake of radionuclides compared to the rock matrix. This means that a substantial fraction of mobile radionuclides could be associated with carrier colloids in some systems. The association of radionuclides with naturally occurring colloids and studies of radionuclide uptake by colloids in laboratory systems give some indication of the potential importance of colloid-facilitated radionuclide transport in the environment as discussed below. 

Due to the specificities of the RBS technique, model systems representative of colloids, heavy elements and surfaces encountered in natural systems relevant to radwaste disposal have been selected. Hence, investigations have been devoted to the study of i) colloids representative of those met in granitic or sedimentary formations (11, 16) such as silica, iron oxide and humic acids which may be considered as carrier colloids, ii) heavy elements as chemical analogues of radionuclides of interest such as Nd(III) or U(V1) as ionic species... 

A particular emphasis has been placed on the detachment rate of colloids from the mineral surface. Colloid sorption is irreversible (or at least shows very slow desorption kinetics regardless of solution composition either in electrolyte solution or in the presence of a carrier colloid such as silica or humic acids (Table ID) moreover, desorption tests up to three months have not shown any colloid detachment. No marked influence of temperature on the release of retained ceria colloids has been observed between 20 and 90°C. 

As for ternary systems, a study of the effect of the order of adding constituents has shown that when the carrier colloid is added after the colloid 1, there is no effect, whatever the systems. This is related to the irreversible character of the sorption of colloid 1. When a true colloid is added after interacting the surface with the carrier colloid, if the conditions are in favour of a presorbed layer (opposite charges), an increase of sorption is observed. When the pseudocolloid interacts with the mineral surface, the charge effect is important and can lead to a strong decrease in heavy element sorption (Figures 6-7). 

Koutsoukos, P.G. and Lycourghiotis, A.S., Regulation of the sorptive capacity of oxides used as catalyst carriers. Colloids Surf., 55, 297, 1991. 

M. G. Shalygin, A. Yu. Okunev, D. Roizard, E. Favre, V. V. Teplyakov, Gas permeability of combined membrane systems with mobile liquid carrier. Colloid J. 68 (2006) 518-525. 

Liu L, Tang Y, Gao C, Li Y, Chen S, Xiong T et al. Characterization and biodistribution in vivo of quercetin-loaded cationic nanostructured lipid carriers. Colloids SurfB Biointerfaces. 2014 115 125-131. 

Song, B., Zhang, W., Peng, R. et al. 2009. Synthesis and cell activity of novel galactosylated chitosan as a gene carrier. Colloids Surf. B Bioint. 70 181-186. 

Reprinted from T.S. Sampath Kumar, K. Madhumathi, B. Rajkamal, S. Zaheatha, A. Rajathi Malar, S. Alamelu Bai, Enhanced protein delivery by multi-ion containing eggshell derived apatitic-alginate composite nano-carriers. Colloids and Surfaces B Biointerfaces 123 (2014) 542-548. Copyright (2014), with permission from Elsevier. 

J. Zhang, M. Wu, J. Yang, Q. Wu, Z. JiiL Anionic poly(lactic acid)-polyurethane micelles as potential biodegradable drug dehvery carriers. Colloids Surf. Physicochem. Eng. Aspects 337 (2009) 200-204. 

Cammas-Marion, S., Okano, T. and Kataoka, K. (1999) Functional and site-specific macromole-cular micelles as high potential dmg carriers. Colloids and Surfaces B Biointerfaces, 16, 207-15. 

Jung J, Arnold RD, Wicker L (2013) Pectin and charge modified pectin hydrogel beads as a colon-targeted drug delivery carrier. Colloids Surf B Biointerfaces 104 116-121 Keplinger C, Sun J-Y, Foo CC et al (2013) Stretchable, transparent, ionic conductors. Science 341 984-987... 

Y.C. Kuo, J.F. Chung, Physicochemical properties of nevirapine-loaded solid lipid nanoparticles and nanostructured lipid carriers. Colloids Surf, B. 83 (2011) 299-300. 

Liang, J., Wu, W.-L., Xu, X.-D., Zhuo, R.-X., Zhang, X.-Z., 2014. pH Responsive micelle self-assembled from a new amphiphilic peptide as anti-tumor drug carrier. Colloids Surf. B Biointerfaces 114, 398 03. 

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