The effect of solute-membrane interaction on solute permeation under supersaturated conditions

Adsorption-electrochemical mediated precipitation for phosphorus recovery from sludge filter wastewater with a lanthanum-modified cellulose sponge filter

In this study, the sludge filter wastewater is confirmed to investigate the effects of adsorption-electrochemical mediated precipitation (EMP) driven phosphorus recovery on the basis of lanthanum-modified cellulose sponge filter (LCLM) material. The adsorption-EMP method relies on in situ recovery phosphate (P) from the used desorption agent (NaOH-NaCl binary solution) via the formation of Ca5(PO4)3OH all while preserving the alkalinity of the desorption agents which benefited long-term application. The lanthanum content of LCLM was 9.0 mg/g, and the adsorption capacity reached 226.1 ± 15.2 mg P/g La at an equilibrium concentration of 3.9 mg P/L. After adsorption, 55.7 % of P was recovered, and the corresponding alkalinity increased from 1.9 mmol/L to 2.2 mmol/L. Adsorption mechanism analysis revealed that the high lanthanum usage of LCLM was attributed to the synergistic effect of the lattice oxygen of LaO and LaPO4·0.5H2O crystallite formation. Additionally, the Ca5(PO4)3OH was found precipitated in the precipitation in the cathode chamber (P-CC) rather than on the surface/section of cation exchange membrane (CEM) and cathode indicating that the P recovery process was controlled by the saturation of CaP species in the EMP system and the electromigration effect. These findings present a new strategy to promote the effective utilization of rare earth elements for P adsorption and demonstrate the potential application of adsorption-EMP systems in dephosphorization for wastewater treatment.

Topical delivery of salicylates

Salicylates have a long history of use for pain relief. Salicylic acid and methyl salicylate are among the widely used topical salicylates namely for keratolytic and anti-inflammatory actions, respectively. The current review summarises both passive and active strategies, including emerging technologies employed to enhance skin permeation of these two salicylate compounds. The formulation design of topical salicylic acid targets the drug retention in and on the skin based on the different indications including keratolytic, antibacterial and photoprotective actions, while the investigations of topical delivery strategies for methyl salicylate are limited. The pharmacokinetics and metabolisms of both salicylate compounds are discussed. The current overview and future perspectives of the topical delivery strategies are also highlighted for translational considerations of formulation designs.

Skin models for the testing of transdermal drugs

The assessment of percutaneous permeation of molecules is a key step in the evaluation of dermal or transdermal delivery systems. If the drugs are intended for delivery to humans, the most appropriate setting in which to do the assessment is the in vivo human. However, this may not be possible for ethical, practical, or economic reasons, particularly in the early phases of development. It is thus necessary to find alternative methods using accessible and reproducible surrogates for in vivo human skin. A range of models has been developed, including ex vivo human skin, usually obtained from cadavers or plastic surgery patients, ex vivo animal skin, and artificial or reconstructed skin models. Increasingly, largely driven by regulatory authorities and industry, there is a focus on developing standardized techniques and protocols. With this comes the need to demonstrate that the surrogate models produce results that correlate with those from in vivo human studies and that they can be used to show bioequivalence of different topical products. This review discusses the alternative skin models that have been developed as surrogates for normal and diseased skin and examines the concepts of using model systems for in vitro–in vivo correlation and the demonstration of bioequivalence.

Acid-responsive polymeric nanocarriers for topical adapalene delivery

PURPOSE

The acne skin is characteristic of a relatively lower pH microenvironment compared to the healthy skin. The aim of this work was to utilize such pH discrepancy as a site-specific trigger for on-demand topical adapalene delivery.

METHODS

The anti-acne agent, adapalene, was encapsulated in acid-responsive polymer (Eudragit® EPO) nanocarriers via nanoprecipitation. The nanocarriers were characterized in terms of particle size, surface morphology, drug-carrier interaction, drug release and permeation.

RESULTS

Adapalene experienced a rapid release at pH 4.0 in contrast to that at pH 5.0 and 6.0. The permeation study using silicone membrane revealed a significant higher drug flux from the nanocarrier (6.5 ± 0.6 μg.cm(-2).h(-1)) in comparison to that (3.9 ± 0.4 μg.cm(-2).h(-1)) in the control vehicle (Transcutol®). The in vitro pig skin tape stripping study showed that at 24 h post dose-application the nanocarrier delivered the same amount of drug to the stratum corneum as the positive control vehicle did.

CONCLUSIONS

The acid-responsive nanocarriers hold promise for efficient adapalene delivery and thus improved acne therapy.

Rapid delivery of diazepam from supersaturated solutions prepared using prodrug/enzyme mixtures: toward intranasal treatment of seizure emergencies

Current treatments for seizure emergencies, such as status epilepticus, include intravenous or rectal administration of benzodiazepines. While intranasal delivery of these drugs is desirable, the small volume of the nasal cavity and low drug solubility pose significant difficulties. Here, we prepared supersaturated diazepam solutions under physiological conditions and without precipitation, using a prodrug/enzyme system. Avizafone, a peptide prodrug of diazepam, was delivered with--Aspergillus oryzae (A.O.) protease, an enzyme identified from a pool of hydrolytic enzymes in assay buffer, pH 7.4 at 32°C. This enzyme converted avizafone to diazepam at supersaturated concentrations. In vitro permeability studies were performed at various prodrug/enzyme ratios using Madin-Darby canine kidney II-wild type (MDCKII-wt) monolayers, a representative model of the nasal epithelium. Monolayer integrity was examined using TEER measurement and the lucifer yellow permeability assay. Prodrug/drug concentrations were measured using HPLC. Enzyme kinetics with avizafone-protease mixtures revealed K(M) = 1,501 ± 232 μM and V(max) = 1,369 ± 94 μM/s. Prodrug-protease mixtures, when co-delivered apically onto MDCKII-wt monolayers, showed 2-17.6-fold greater diazepam flux (S = 1.3-15.3) compared to near-saturated diazepam (S = 0.7). Data for prodrug conversion upstream (apical side) and drug permeability downstream (basolateral side) fitted reasonably well to a previously developed in vitro two compartment pharmacokinetic model. Avizafone-protease mixtures resulted in supersaturated diazepam in less than 5 min, with the rate and extent of supersaturation determined by the prodrug/enzyme ratio. Together, these results suggest that an intranasal avizafone-protease system may provide a rapid and alternative means of diazepam delivery.