Membraneless Method Research Articles

A facile membraneless method for detecting alkali-metal cations using organic electrochemical transistors

A facile membraneless method for detecting alkali-metal cations was developed by adding ionophores (crown ethers: 18C6 or 15C5) to a polymer matrix (p(g2T-TT)) as the active layer in organic electrochemical transistors.

Field trial of a membraneless vacuum preloading system for soft soil improvement

This paper reports a field trial of membraneless vacuum preloading and fill surcharge to improve a compressible clay layer below sand fill at a reclaimed land site in Singapore. The thickness of the soft clay layer varied from 4 to 17 m. Due to the sand fill, a vacuum was applied to the clay layer using a proprietary membraneless method. Four weeks after the vacuum load was applied, a 2·5 m thick layer of sand fill was added as surcharge. Ground settlements, settlements and pore pressures at different depths in the soil were measured during the soil improvement. The measured field settlements and pore-pressure data were used to compute the degree of consolidation. The calculated values were found to differ considerably, the reasons for which are discussed. Experiences and lessons learned from the project are also highlighted.

Membraneless water filtration using CO2

Water purification technologies such as microfiltration/ultrafiltration and reverse osmosis utilize porous membranes to remove suspended particles and solutes. These membranes, however, cause many drawbacks such as a high pumping cost and a need for periodic replacement due to fouling. Here we show an alternative membraneless method for separating suspended particles by exposing the colloidal suspension to CO2. Dissolution of CO2 into the suspension creates solute gradients that drive phoretic motion of particles. Due to the large diffusion potential generated by the dissociation of carbonic acid, colloidal particles move either away from or towards the gas–liquid interface depending on their surface charge. Using the directed motion of particles induced by exposure to CO2, we demonstrate a scalable, continuous flow, membraneless particle filtration process that exhibits low energy consumption, three orders of magnitude lower than conventional microfiltration/ultrafiltration processes, and is essentially free from fouling.

Influence of additives on a thermosensitive hydrogel for buccal delivery of salbutamol: Relation between micellization, gelation, mechanic and release properties

Thermosensitive hydrogels developed for buccal delivery of salbutamol were prepared using poloxamer analogs (Kolliphor(®) P407/P188), xanthan gum (Satiaxane(®) UCX930) and NaCl. P188 increased gelation temperature (Tsol-gel) by 2.5-5°C, micellization temperature (<1°C) and gelation time by >3s. To obtain a suitable Tsol-gel at 28-34°C, P407 and P188 concentrations were set to 18-19% and 1%. NaCl reduced Tsol-gel (>2°C) out of the optimal range. Six formulations containing 0.05-0.1% Satiaxane(®) fulfilled the temperature criteria. Concerning the gel strength, 1% P188 had no significant effect, NaCl increased it at 20°C, and Satiaxane(®) enhanced it at 20°C and 37°C. The release study using membrane-less (to mimic oral cavity) and membrane (to mimic buccal mucosa side) methods allowed a complete investigation showing that erosion and diffusion both contributed to the drug release but differed according to the formulation. In the membraneless method, simple P407 formulations had weak ability to retain salbutamol (T80=35 min). P188 accelerated drug release. NaCl accelerated release in the membraneless method by 5-11 min but slightly reduced it in the membrane method. The hydrogels containing Satiaxane(®) exhibited the slowest release. In the membrane method, combination of P407/P188/Satiaxane(®) provided a sustained diffusion with a burst effect (T25=9.6 min, T80=97.8 min), which provides potential clinical interests.

Enhanced brain targeting of curcumin by intranasal administration of a thermosensitive poloxamer hydrogel

The aim of this study was to develop a curcumin intranasal thermosensitive hydrogel and to improve its brain targeting efficiency. The hydrogel gelation temperature, gelation time, drug release and mucociliary toxicity characteristics as well as the nose-to-brain transport in the rat model were evaluated. The developed nasal hydrogel, composed of Pluronic F127 and Poloxamer 188, had shorter gelation time, longer mucociliary transport time and produced prolonged curcumin retention in the rat nasal cavity at body temperature. The hydrogel release mechanism was diffusion-controlled drug release, evaluated by the dialysis membrane method, but dissolution-controlled release when evaluated by the membraneless method. A mucociliary toxicity study revealed that the hydrogel maintained nasal mucosal integrity until 14 days after application. The drug-targeting efficiencies for the drug in the cerebrum, cerebellum, hippocampus and olfactory bulb after intranasal administration of the curcumin hydrogel were 1.82, 2.05, 2.07 and 1.51 times that after intravenous administration of the curcumin solution injection, respectively, indicating that the hydrogel significantly increased the distribution of curcumin into the rat brain tissue, especially into the cerebellum and hippocampus. A thermosensitive curcumin nasal gel was developed with favourable gelation, release properties, biological safety and enhanced brain-uptake efficiency.

Gallic Thermosensitive Gel

Gallic acid (G) is a natural phenolic compound that has potent antioxidant and antityrosinase activities. The solubility of gallic acid in aqueous system is rather poor. The purpose of this research is to develop the thermosensitive gel containing G based on Lutrol® F127 (L) and the antioxidant of prepared gels was determined using modified ABTS.+ method expressed as Vitamin C Equivalent Antioxidant Capacity (VCEAC) method. N-methyl pyrrolidone (N) could be used to effectively solubilize G into L aqueous systems. This developed thermosensitive system could convert from solution in the cool place to the firm gel under physiological condition on the skin to delivery an anti-aging agent such as gallic acid. Gallic acid gel prepared from hydroxypropyl methyl cellulose (HPMC, H) was employed to compare with the developed system. The developed gel containing 25% L, 25% N and 5% G (L25N25G5) showed the good physical appearances. In vitro release study was performed using the membrane-less method. The release of G from L25N25G5 into citrate-phosphate buffer pH 5.5 was faster than that of the gel containing 3% H, 25% N and 5% G (H3N25G5). From rheology study, L25N25G5 exhibited as a Newtonian flow at 4 °C and plastic flow at 28°C and 35 °C whereas H3N25G5 demonstrated as a pseudoplastic flow at all the three temperatures. Additionally, from VCEAC method, L25N25G5 exhibited a good antioxidant activity.

Analysis of in vitro skin permeation of 22-oxacalcitriol from ointments based on a two- or three-layer diffusion model considering diffusivity in a vehicle

In the present study, in vitro rat skin permeation of 22-oxacalcitriol (OCT) from ointments having differing compositions was determined and discussed based on a diffusion model. Diffusion coefficients of OCT in two ointments, one containing 3% (w/w) medium chain triglyceride (MCT) (3MO) and the other 30% (w/w) MCT (30MO), were determined using a modified membraneless method resulting in values of 0.89 × 10 −4 and 1.87 × 10 −4 cm 2/h, respectively. At 24 h after application with 3MO, 7% of the applied OCT dose permeated through full-thickness skin and 22% remained in the ointment, whereas with 30MO, 2% of the applied dose permeated through full-thickness skin and 65% remained in the ointment. The diffusion coefficient of OCT in 3MO was lower than 30MO but the cumulative amount of OCT permeated was higher. From analysis of skin permeation of OCT based on a diffusion model considering diffusivity in an ointment, the partition coefficient of OCT from the ointment to stratum corneum ( K SC/V) was calculated to be five-fold higher with 3MO than with 30MO. Our simulation study based on a diffusion model suggests that the diffusion coefficients of OCT in both ointments were high enough to have no affect on the skin permeation of OCT in the present case and that the difference in the skin permeations of the ointments was mainly caused by a difference in K SC/V.

Diffusion studies of methotrexate in Carbopol and Poloxamer gels

The diffusion properties of methotrexate (MTX) in two hydrogels, Carbopol 934 (Carbopol) and Poloxamer 407 (PF-127), were compared with those in PEG 1500 and white petrolatum ointments in order to evaluate various factors governing the diffusion of MTX in different semisolid vehicles. A new membraneless method, which employed an MTX gel as the donor phase, was used for the measurement of the diffusivity of MTX in the vehicles. The flux of MTX in the hydrogels was at least 20-fold faster than those found in the ointments. The diffusion coefficients ( D) of MTX were 3.58 (±0.31)×10 −6 cm 2/s in the 2% Carbopol gel and 1.03 (±0.01)×10 −6 cm 2/s in the 25% PF-127 gel at 34°C, despite similar bulk viscosities of the two gels. The activation energies for the diffusion of MTX in the Carbopol and PF-127 gels were 6.13 kcal/mol and 5.56 kcal/mol respectively, which were in the same order of magnitude as the diffusion of the small molecules in water, indicating that microviscosity rather than bulk viscosity of the gel was primarily responsible for the diffusion of MTX in the gels. D values of MTX in the PF-127 gel were significantly accelerated at higher temperatures, despite increased bulk viscosity of the gels due to the reverse thermal gelation property of PF-127. The diffusivity of MTX was the inverse function of polymer concentration, over the range of 20–30% of PF-127 and 1–3% of Carbopol at 34°C. Significant effects of pH and drug concentration on the diffusivity of MTX in the Carbopol gels were observed, while no such effects were found in the PF-127 gels.

Diffusion and Concentration Profiles of Drugs in Gels

A versatile membraneless method was used to study the diffusion of acetaminophen, ibuprofen, indomethacin, theophylline, and chlorpheniramine in thermoreversible gels. Two independent ways to calculate the diffusion coefficients and to verify Fickian transport are presented; the most sensitive criterion for Fickian transport being an agreement between the concentration profile for the drug in the gel and the free diffusion model. The diffusion of acetaminophen, ibuprofen, and indomethacin was studied at different temperatures in 1% (w/w) agarose gels. The diffusion coefficients for these drugs were found to be essentially the same as in water, and the apparent diffusion activation energies are close to that for self diffusion of water (4.62 kcal/mol), indicating a common mechanism for the diffusion of these drugs in the gel. The diffusivity of chlorpheniramine was also studied in 4% (w/w) agarose gels or with part of the agarose substituted with other polymers (e.g., chitosan and sodium alginate). These two oppositely charged polymers, mixed together, were found to occupy an “equivalent polymer volume” that was three times larger than the same amount of each of the constituents. When chitosan and gelatin-B were mixed into the agarose gel, non-Fickian transport resulted. Such non-Fickian transport was also observed with theophylline diffusing in a mixture of agarose, chitosan, and sodium alginate at a low pH.