Preparation Of Novel Medical Adsorption Materials And Their Character For Uric Acid And Urea

Uremia is one kind of diseases which threatens seriously the life of patients. whenkidney failure occurs, there is a great deal of accumulations of uric acid and urea in the blood.Via blood purification, the accumulation of uric acid and urea can be removed effectively andalleviated the symptoms of patients. Except dialysis technique, hemoperfusion is another newtechnique to purify blood. The key of hemoperfusion technique is the adsorbent with highefficiency, great adsorption amount and blood compatibility. This paper investigates thesynthesis of novel adsorption materials for uric acid and urea ,and researches their adsorptioncharacter and mechanism.Polyethylenimine (PEI) was grafted on silica particles using by γ-chloropropyltrimethoxysilane as couplant, and the novel composite adsorption material of PEI/SiO₂ formedical application was prepared, which has strong adsorption ability toward uric acid. Staticadsorption experiment results show that the macromolecules of PEI on silica particles canproduce strong adsorption force for trihydroxyl purine that is the tautomer of uric acid byhydrogen bond interaction. The isothermal adsorption is accorded with Freundlich equation,and the saturated adsorption amount is able to reach 84.9 mg/g. The pH value of the aqueoussolution can exert great effect on the adsorption property of PEI/SiO₂, in neutral solution,PEI/SiO₂ has very strong adsorption ability for uric acid. in acidic solution, 70% of the Natoms on PEI chains are protonated, so the hydrogen bond interaction between PEI on thesurface of PEI/SiO₂ and 2,6,8-trihydroxypurine is very weak. These reasons result in smalladsorption capacity of uric acid on PEI/SiO₂ in acidic solution. However in basic solution theprotonation degree of PEI decrease sharply, and the electrostatic interaction between PEI/SiO2and uric acid is weak, so that in basic solution the adsorption capacity of uric acid onPEI/SiO2 is also small. Temperature has certain influence on the adsorption property ofPEI/SiO2, and the adsorption amount is increased with the increment of temperature. Thereason for this is that the physical adsorption is accompanied by chemical adsorption, whichis the chemical bonding process between uric acid and amino groups of PEI .This chemicaladsorption process is endothermic probably, so the adsorption amount increases with therising of tempereature.Polystyrene was transformer into chloromethylated polyotyrene via Friedel-Craftsreactions, then the polystyrene with aldehyde groups was obtained by Sommelet reaction,namely polyethylene benzaldehyde was abtained. The adsorption property of polyethylenebenzaldehyde towards urea was studied deeply. The experiment results show thatpolyethylene benzaldehyde has stranger chemical adsorption ability towards urea by right ofSchiff base reaction. The adsorption process is also a endotherm chemical reaction, so theadsorption amount in creases with temperature rising. The chemical instability of Schiff basecauses that polyethylene benzaldehyde has high adsorption capacity only in neutral medium,that is its adsorption ability for urea in acidic or basic medium is poorer.