Mechanistic studies in the simultaneous flow and adsorption of polymer-coated latex particles on intestinal mucus I: Methods and physical model development
Teng C. L. C. ,; Ho, Norman F. H.
1987-12
Citation
Teng C. L. C., , Ho, N. F. H. (1987/12)."Mechanistic studies in the simultaneous flow and adsorption of polymer-coated latex particles on intestinal mucus I: Methods and physical model development." Journal of Controlled Release 6(1): 133-149. <http://hdl.handle.net/2027.42/26476>
Abstract
The adsorption of particles and concurrent steady-state flow of a dilute suspension from an infinite reservoir over the mucous surface of intestinal strips were quantitatively studied. The micronsize particle systems included negatively charged poly (vinyltoluene) and hydroxylated Dynosphere(R) particles with and without a positively charged polybrene polymer coated layer. The suspensoids were characterized by zeta potential measurements. An in vitro setup and technique likened to a thin falling liquid film system was developed wherein an excised intestinal segment cut lengthwise is spread on a plastic flute and positioned at an incline, and a suspension is allowed to flow down the intestinal strip. The falling liquid film was estimated to be 54 [mu]m in thickness from nonsteady-state flow kinetic experiments. Particle concentrations entering the segment from the dilute suspension reservoir and leaving the intestinal segment were determined with the Coulter counter to quantify the steady-state fraction of particles adsorbed as they relate to intestinal length, flow rate, ionic strength, zeta potential and particle concentration. The flowing liquid film technique was found to be quantitatively sensitive and, consequently, allowed one to focus on the mechanism of the approach of micron-size particles to the mucous surface without the major concern of particle flocculation in the bulk liquid.The logarithm of the fraction of nonadsorbed particles remaining in the liquid film decreased linearly with intestinal length at all flow rates employed. The fraction adsorbed decreased with increasing flow rates on account of the shorter transit times. The steady-state region of the fraction of nonadsorbed particles remaining versus time plots persisted for a relatively long time indicating the existence of a particle concentration gradient along the length of the intestinal strip. The fact that the fraction of particles adsorbed was not affected by particle concentrations ranging from 4.5-14 x 106 particles per ml suggests that there is sufficiently available unoccupied surface area for incoming particles to be adsorbed onto mucus. It has been estimated that no more than 5% of the area of the intestinal strip is occupied by adsorbed particles. Failure to desorb particles from the mucous surface by perfusing the intestinal segment indicates tight binding between the particles and mucus. A physical model was deduced from the experimental results wherein the steady-state fraction of adsorbed particles is related to length of the intestinal strip, flow rate and mass transfer-adsorption coefficient.The mass transfer resistances of negatively charged particles decreased with the addition of sodium chloride and approached the minimum resistance obtained by the positively charged, polybrenecoated latex particles, whose mass transfer resistance was independent of electrolyte concentration. This supports a mechanism involving the diffusion of the negatively charged particles within an electrostatic field of force as the particles approach the negatively charged mucous surface. Passage of particles over the potential energy barrier is required for the successful collision and tight binding with mucus.Publisher
Elsevier
Types
Article
URI
http://www.sciencedirect.com/science/article/B6T3D-475TCDK-RJ/2/87926dd44f727f8a4b6f11e5c6ac14e3Metadata
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