Enhanced Transscleral Iontophoretic Transport with Ion-Exchange Membrane

Abstract

The present study has demonstrated the potential of ion-exchange membranes for enhancing iontophoretic transport and drug delivery.

Influence of molecular shape, conformability, net surface charge, and tissue interaction on transscleral macromolecular diffusion

“…46 Although some studies have shown that molecules as large as 10 nm can traverse the sclera, 43 others suggest a pores size of 5 nm. 47 Therefore, although the pore sizes may be comparable to the glomerulus, the pathlength for diffusion is much higher in sclera. It is possible that this entraps linear or branching molecules such as dextan and ficoll.…”

“…47 In general, this would be expected to slow the diffusion of positively charged molecules, which may be retained in the scleral substrate. Unexpectedly, this was not the case with cationic dextrans in the present study.…”

Transport of arsenate through anion-exchange membranes in Donnan dialysis

“…Since the membrane is quite thick (43175 mm, Table 2), in order to allow for a high arsenate transport rate, the membrane should possess sufficiently ''open'' structure of the polymer backbone, which does not obstruct significantly the intra-membrane arsenate movement. Indeed, using experimentally determined permeability coefficients of neutral compounds, such as mannitol, and the hindered transport modelling approach, the effective (idealized) ''pore'' radius and the effective tortuosity values for this membrane were reported to be 0.8 70.1 nm and around 2, respectively [24]. These characteristics of the polymeric matrix appear to offset the opposite (arsenate retardation) effect of its relatively high thickness.…”

“…An effective ''pore'' radius value of 0.8 nm for Ionac MA3475, suggests that all water in the intra-molecular void spaces of the membrane polymeric matrix, is immobilized (''bonded''), since it is known that the region of ''bonded'' water in the curve of water distribution as a function of the effective membrane ''pore'' radius extends to r1.5 nm [25]. It could also be argued that since this effective ''pore'' radius has been estimated on the basis of transport measurements [24], and not by directly assessing the heterogeneous polymeric membrane matrix porosity, it could not reveal the presence of the second possible type of pores, being those constituted by the spaces between the anion-exchange resin particles and the linking polymer phase. The total volume of such spaces (large pores) is typically an order of magnitude lower than that of the intramolecular voids (small pores) within the ion-exchange particles [26].…”

“…It is known that for a given volume fraction of the solid the tortuosity factor in an homogeneous gel is usually greater than that in an heterogeneous polymeric matrix composed of particles [27]. Since membrane tortuosities usually range between two and six [28], an effective Ionac MA3475 tortuosity value of two [24] suggests that arsenate diffusion across this membrane should not be significantly retarded.…”