Hydrogels membrane permeability

The significance of the permeability depends upon the particular system at hand. If the hydrogel forms a barrier between a drug reservoir and a solution, the flux across the hydrogel membrane at steady state is simply... 

Permeability control of solutes through thermosensitive hydrogel membranes may be thought of in terms of the degree of hydration and kinetics of... 

Hydrogel membranes are particularly attractive because of high permeability and separation factor [300], and good stability for CO2/N2 separation [299], PVDF hollow fiber membrane modified by alkali was coated by PYA hydrogel on its surface and PVDF-PVA hydrogel membranes show better hydrophilic performance. For carbonate hydrogel (sodium carbonate concentration of 3.7 %) membrane, C02, concentration from 1.3 % to 0.6 % in feed gas could be decreased to 0.9-0.4 % at the outlet at 25 °C. 

J. P. Baker and R. A. Siegel, Hysteresis in the glucose permeability versus pH characteristic for a responsive hydrogel membrane, Macromol Rapid Commun., 17,409 15 (1996). 

Membranes made by interfacial polymerization have a dense, highly crosslinked polymer layer formed on the surface of the support membrane at the interface of the two solutions. A less crosslinked, more permeable hydrogel layer forms under this surface layer and fills the pores of the support membrane. The dense, crosslinked polymer layer, which can only form at the interface, is extremely thin, on the order of 0.1. im or less, so the membrane permeability is high. Because the polymer is highly crosslinked, its selectivity is also high. Although the crosslinked interfacial polymer layer determines membrane selectivity, the nature of the microporous support film affects membrane flux... 

Peptide delivery It has also been reported that a polycarbophil hydrogel formulation increased the vaginal membrane permeability of GnRH, in comparison to a solution, in rats. Co-administration of the GnRH loaded gel with various enzyme inhibitors (EDTA, sodium taurodihydrofusidate and sodium laurate) resulted in ovulation-inducing activity comparable with that of a sc injection. 

Figure 4.17 Schematic of pulsating drug delivery device based on feedback inhibition of glucose transport to glucose oxidase through a hydrogel membrane. Changes in permeability to glucose are accompanied by modulation of drug permeability. Reprinted from [97] with permission from American Institute of Physics.

Recently, we have examined solute permeation through hydrogel membranes in an effort to develop models which describe in detail the transport phenomena with particular emphasis on the role of water in this process. These studies have utilized p-HEMA and its copolymers, and both hydrophobic and hydrophilic solutes (7., i). It was determined that p-HEMA and its copolymers are permeable to both hydrophobic and hydrophilic solutes. 

The partition coefficients for water in p-HEMA and p-HEMA crosslinked with 1 mole % EGDMA are 0.52 and 0.51 respectively. However, from Sung s data (5), it is possible to define partition coefficients for water into the various subclasses of water in the hydrogel membranes. For p-HEMA, these values of Ko are bulk water 0.30, bulk + intermediate water 0.41, and bulk + intermediate + bound water 0.52. For p-HEMA with 1 mole % EGDMA, the values are bulk water 0.21, bulk + intermediate water 0.36, and bulk + intermediate + bound water 0.50. A comparison of these values with the experimental values found in Tables I and II indicates that the sugars partition primarily into bulk water of both membranes and, therefore, that the diffusion of these solutes occurs primarily in the bulk water of the membranes. This result is consistent with the observed very low permeability of inositol and raffinose in p-HEMA with 5 mole % EGDMA. These membranes have 1 i ttl e or no bul k water (5.). 

Step 3 When the hydrogel membrane becomes sufficiently charged, the membrane switches back to its swollen, high permeability state. The system is now poised at Step 1, and the cycle repeats. 

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