Osmotic Pressure beyond Concentration Restrictions

Ultrahigh Permeable C2N-Inspired Graphene Nanomesh Membranes versus Highly Strained C2N for Reverse Osmosis Desalination

The reverse osmosis (RO) desalination capability of hydrogenated and hydroxylated graphene nanomesh membranes (GNMs) inspired by the morphology of carbon nitride (C₂N) has been studied by using molecular dynamics simulation. As an advantage, water permeance of the GNMs is found to be several orders of magnitude higher than that of the available RO filters and comparable with highly strained C₂N (S-C₂N) as follows: 6,6-H,OH > 12-H > S-C₂N > 5,5-H,OH > 10-H. The reverse order is found for salt rejection, regardless of S-C₂N. The hydrophilic character of the incorporated -OH functional group is believed to be responsible for linking the water molecules in feed and permeate sides via the formation of strong hydrogen bonds. This leads to a remarkable reduction in resistance of water molecules during penetration across GNMs. In fact, water permeance and salt rejection of the GNMs are controllable by adjusting the effective size and chemistry of their nanopores, while these kinds of adjustments are principally impossible for C₂N, resulting in limiting the water permeance. More importantly, the C₂N nanofilter works efficiently only under high tensile strain, which is not so straightforward in practice. These observations are also verified by computing electrostatic potential map interaction and barrier energies for transportation of water molecules/ions through GNMs based on quantum chemistry aspects.

Experimental Estimation of Membrane Tension Induced by Osmotic Pressure

Osmotic pressure (Π) induces the stretching of plasma membranes of cells or lipid membranes of vesicles, which plays various roles in physiological functions. However, there have been no experimental estimations of the membrane tension of vesicles upon exposure to Π. In this report, we estimated experimentally the lateral tension of the membranes of giant unilamellar vesicles (GUVs) when they were transferred into a hypotonic solution. First, we investigated the effect of Π on the rate constant, k_p, of constant-tension (σ_ex)-induced rupture of dioleoylphosphatidylcholine (DOPC)-GUVs using the method developed by us recently. We obtained the σ_ex dependence of k_p in GUVs under Π and by comparing this result with that in the absence of Π, we estimated the tension of the membrane due to Π at the swelling equilibrium, σ_osm^eq. Next, we measured the volume change of DOPC-GUVs under small Π. The experimentally obtained values of σ_osm^eq and the volume change agreed with their theoretical values within the limits of the experimental errors. Finally, we investigated the characteristics of the Π-induced pore formation in GUVs. The σ_osm^eq corresponding to the threshold Π at which pore formation is induced is similar to the threshold tension of the σ_ex-induced rupture. The time course of the radius change of GUVs in the Π-induced pore formation depends on the total membrane tension, σ_t; for small σ_t, the radius increased with time to an equilibrium one, which remained constant for a long time until pore formation, but for large σ_t, the radius increased with time and pore formation occurred before the swelling equilibrium was reached. Based on these results, we discussed the σ_osm^eq and the Π-induced pore formation in lipid membranes.

Development and uniform evaluation of ropinirole osmotic pump tablets with REQUIP XL both in vitro and in beagle dogs

REQUIP XL, prolonged release formulation of ropinirole hydrochloride (RH) in market, could release ropinirole constantly and showed satisfactory therapeutic effect and good compliance. REQUIP XL was composed of more than 10 kinds of excipients and prepared by Geomatrix technology, which was complex and laborious. The purpose of this study was to obtain a dosage form of RH with similar in vitro release profile and bioequivalence in vivo compared to REQUIP XL. Osmotic pump tablet combined with fast release phase was selected as the delivery system of RH and similar release curves were obtained in different media. The tablets were also administered to beagle dogs and the pharmacokinetic parameters were calculated using a non-compartmental model. C_max, t_max, mean residence time (MRT), and area under the curve from 0 to 24 h (AUC_0-24) were 3.97 ± 0.53 ng/mL, 3.58 ± 0.49 h, 8.29 ± 0.93 h, and 35.20 ± 8.11 ng/mL ċ h for ropinirole osmotic pump tablets (ROPT) and 4.15 ± 1.07 ng/mL, 2.92 ± 0.49 h, 7.84 ± 1.09 h, and 34.34 ± 10.06 ng/mL ċ h for REQUIP XL. The log-transformed mean C_max and AUC_0-24 of ROPT were about 92.15% and 102.49% relative to that of REQUIP XL, respectively. The 90% confidence intervals of C_max and AUC_0-24 for ROPT were 75.69-115.31% and 88.89-122.30%, respectively. So it could be concluded that ROPT was uniform with REQUIP XL both in vitro and in beagles and the release profiles of Geomatrix technology may be obtained by osmotic pump combined with fast release technology.

Equilibrium and dynamic osmotic behaviour of aqueous solutions with varied concentration at constant and variable volume

Osmosis is essential for the living organisms. In biological systems the process usually occurs in confined volumes and may express specific features. The osmotic pressure in aqueous solutions was studied here experimentally as a function of solute concentration (0.05-0.5 M) in two different regimes: of constant and variable solution volume. Sucrose, a biologically active substance, was chosen as a reference solute for the complex tests. A custom made osmotic cell was used. A novel operative experimental approach, employing limited variation of the solution volume, was developed and applied for the purpose. The established equilibrium values of the osmotic pressure are in agreement with the theoretical expectations and do not exhibit any evident differences for both regimes. In contrast, the obtained kinetic dependences reveal striking divergence in the rates of the process at constant and varied solution volume for the respective solute concentrations. The rise of pressure is much faster at constant solution volume, while the solvent influx is many times greater in the regime of variable volume. The results obtained suggest a feasible mechanism for the way in which the living cells rapidly achieve osmotic equilibrium upon changes in the environment.

Osmotic micropumps for drug delivery

This paper reviews miniaturized drug delivery systems applying osmotic principles for pumping. Osmotic micropumps require no electrical energy and consequently enable drug delivery systems of smallest size for a broad field of new applications. In contrast to common tablets, these pumps provide constant (zero-order) drug release rates. This facilitates systems for long term use not limited by gastrointestinal transit time and first-pass metabolism. The review focuses on parenteral routes of administration targeting drug delivery either in a site-specific or systemic way. Osmotic pumps consist of three building blocks: osmotic agent, solvent, and drug. This is used to categorize pumps into (i) single compartment systems using water from body fluids as solvent and the drug itself as the osmotic agent, (ii) two compartment systems employing a separate osmotic agent, and (iii) multi-compartment architectures employing solvent, drug and osmotic agent separately. In parallel to the micropumps, relevant applications and therapies are discussed.