Chitosan sulfate suspensions

The preparation for the activator-containing suspension The chitosan sulfate samples were immersed into the glycerin-methanol solution for 72 hours, to make sure the samples adsorb a certain amount of glycerin. The fraction of the adsorbed glycerin is determined by the weight method, and the glycerin content is 5wt%. After the removal of methanol, the chitosan sulfate suspension was made with the same procedures as the above-mentioned. 

Due to the instrumental limitations, the current density of the suspension without activator under the field strength less than 2000 V/mm couldn t be obtained. These experimental results indicate that the activator-firee chitosan sulfate suspension has very low conductivity, compared with other fluids (d, 75). 

Suspension Preparation. The preparation for the activator-fi suspension After drying, chitosan sulfate samples were dispersed in a certain amoxmt of silicone oil and ball-milled imtil microscopic examination indicated a mean particle size of 10 pm and the absence of particles > 20 pm. Particles were irregular in shape but without any tendency to anisometry. The silicone oil used is a colorless oil with the following physical properties density 0.97 g/cm, viscosity 100 mPa s at 20 C, dielectric constant 2.8, and boiling temperature 300 C. There was little tendency for these dispersions to separate in the short term, and such dispersions that had separated after lengthy standing readily redispersed on agitation. 

Effects of Field Strength and Particle Concentration. The shear stress of the activator-free suspensions containing chitosan sulfate particles at different... 

Co-administration of ofloxacin and chitosan in eyedrops increased the bioavailabUity of the antibiotic [290]. Trimethyl chitosan was more effective because of its solubility (plain chitosan precipitates at the pH of the tear fluid). On the other hand, N-carboxymethyl chitosan did not enhance the corneal permeability nevertheless it mediated zero-order ofloxacin absorption, leading to a time-constant effective antibiotic concentration [291]. Also W,0-carboxymethyl chitosan is suitable as an excipient in ophthalmic formulations to improve the retention and the bioavailability of drugs such as pilocarpine, timolol maleate, neomycin sulfate, and ephedrine. Most of the drugs are sensitive to pH, and the composition should have an acidic pH, to enhance stability of the drug. The delivery should be made through an anion exchange resin that adjusts the pH at around 7 [292]. Chitosan solutions do not lend themselves to thermal sterilization. A chitosan suspension, however. 

For this purpose, we have used Euphausia superba chitosan to prepare N-carboxymethyl chitosan, and then we have submitted it to sulfation. Glyoxylic acid crystals were added to an aqueous suspension of chitosan powder, to obtain a chitosan glyoxylate solution (pH 3.2). Upon pH adjustement to 4.5 - 5.0, Schiff reaction took place with formation of N-carboxymethylidene chitosan. The latter was then reduced with sodium cyanoborohydride and isolated by addition of acetone. The thus obtained N-carboxymethyl chitosan was subsequently submitted to sulfation in N,N-dimethylformamide. 

---