Diffusion Apparatus Research Articles

Use of digital thruster to separate the cadmium and lead metals from mixture sample

The present work deals with the use of a digital thruster (DT) for the separation of cadmium and lead metals from mixture samples. Mixtures of lead and cadmium salts with varying concentrations were injected into a free electrolytic diffusion apparatus (FEDA). The microcathodes surrounding the central anode were programmed with a DT. The DT distributed the charge over the microcathodes at time intervals of 100–900 μs or at the frequency of 625–70 Hz. The microcathodes become electrodeposited with lead and cadmium metals, showing both separation and co-deposition. The purity of deposited metals was analyzed by Atomic Absorption Spectroscopy (AAS) using PerkinElmer and Aldrich AAS standards.

Erbium:YAG laser enhances transdermal peptide delivery and skin vaccination

Transdermal delivery of peptides and the related vaccines is attractive for treatment and prevention of diseases. However, this delivery method is limited by the low permeability of the stratum corneum (SC). The objective of this study was to enhance and control skin permeation of peptides and related vaccines using an erbium:yttrium–aluminum–garnet (Er:YAG) laser. The amount of peptide transported through nude mouse skin was measured using a Franz diffusion apparatus. The SC layer was partly ablated by an Er:YAG laser, resulting in a greater enhancement effect on peptide delivery. A thinned and discontinuous SC layer was observed after laser exposure. The flux of peptides across skin treated with a laser at various fluences was 3–140-fold higher than that across intact skin. The molecular size, lipophilicity, and sequence of the peptides were found to play important roles in modulating the enhancement of activity. The result of confocal laser scanning microscopy (CLSM) indicated a significant increase in the skin deposition of peptides into laser-treated skin. In an in vivo study, mouse skin was treated with the laser followed by skin vaccination with a lysozyme antigen. It was demonstrated for the first time that laser treatment with no adjuvant or penetration enhancer significantly enhanced the production of antibodies in the serum by 3-fold. To reveal the mechanisms underlying these changes, a proteomic technique combined with mass spectrometry was used. This is, to our knowledge, the first report of a laser being used to immunize intact animals.

Determination of the effective diffusion coefficient for 125I− in Beishan granite

With the policy of active development of nuclear energy in China in the following 20 years or more, the high-level radioactive wastes and spent fuels will increase considerably. In order to dispose of these wastes safely, China plans to construct a geological repository in the middle of the 21st century. Through more than 20 years of research and discussion in China, granite has been regarded as one of the most favorable candidate host rocks for a potential geological repository and 129 I has been recognized as one of the most important nuclides for the safety of the potential repository. In this paper, the diffusion of 125 I (as a surrogate of 129 I) in deep granite taken from Beishan, Gansu Province is investigated with the help of a small scale diffusion apparatus. The granite core sample was taken at the depth of about 300 m and cut into sections of 5∼20 mm. The granite section samples were weighted and the pore volume was determined with water immersion method. The chemical and elemental compositions of the granite are presented. Experimental results were treated with different methods, producing an effective diffusion coefficient of 125 I − in the granite of (2.44–2.72)×10 −12 m 2 s −1 .

Effect of chitosan, benzalkonium chloride and ethylenediaminetetraacetic acid on permeation of acyclovir across isolated rabbit cornea

The overall objective of this study was to evaluate the effect of chitosan, benzalkonium chloride (BAK) and disodium ethylendiaminetetraacetic acid (EDTA), alone and in combination, on permeation of acyclovir (ACV) across excised rabbit cornea. Corneas of male New Zealand White rabbits were used in these studies. Transcorneal permeation studies were conducted at 34 °C using a side-bi-side diffusion apparatus. In the presence of 0.01% BAK, transcorneal permeability of ACV was observed to increase almost 10.5-fold, from 3.5 × 10 −6 to 37.4 × 10 −6 cm/s. At 0.005% BAK, permeability of ACV was almost 3-fold higher than control. Combination of BAK 0.005% and EDTA 0.01% increased transcorneal penetration of ACV by 2.5-fold. Chitosan 0.2 and 0.1% increased corneal permeability of ACV by 5.8- and 3.1-fold, respectively, whereas, at 0.02%, chitosan did not exhibit a statistically significant effect. BAK at 0.005%, in combination with 0.01% EDTA and 0.1% chitosan, increased transcorneal ACV permeation by 5.5-fold. This study suggests that a judicious combination of chitosan, BAK and EDTA can lead to a significant increase in ACV's transcorneal permeability and that chitosan can enhance diffusion of hydrophilic agents across the corneal membrane. Further in vivo evaluation is warranted.

Metal‐Associated Forms and Speciation in Biosolid‐Amended Oxisols

The objective of this study was to determine the effects of pH and ionic strength on the distribution and speciation of zinc (Zn), copper (Cu), and cadmium (Cd) in surface soil samples from two Brazilian Oxisols amended with biosolids. Soils and biosolids were equilibrated in an experimental dual‐chamber diffusion apparatus that permits the soils and biosolids to react through a solution phase via diffusion across a membrane. After equilibrium was reached, soil and biosolids samples were sequentially fractionated to identify various solid forms of Zn, Cu, and Cd. Metal concentrations in the solution phase were determined and mass balance calculated. Equilibrating pH had no major effect on Cu solubility from biosolids and, at pH range from 4 to 7, most Cu remained in the biosolids. Soluble Zn and Cd concentration increased with decreasing pH because of the increased solubility of the biosolids. Copper and Zn were primarily associated with the residual fraction and Fe oxides in one soil, but were primarily associated with chemically unstable fractions, or adsorbed to the surface of oxides, in the other soil. In both soils, Cd was primarily associated with readily bioavailable fractions. The effect of pH on the metal distribution was more evident than the ionic strength effect. Free ions were the predominant metal species in solution, especially at lower pH values.

In Vitro Diffusion of the Immunosuppressant Tacrolimus Through Human and Rabbit Corneas

The aim of this study was to investigate the in vitro diffusion kinetics of tacrolimus (TAC) through rabbit and human corneas, and to evaluate the suitability of rabbit cornea as an in vitro permeability model for human cornea. A flow-through diffusion apparatus was used for all permeability experiments. The percentage of total (3)H-TAC diffusing across the corneas was determined over 24 h and fractions collected twice-hourly (20 degrees C; 1.5 mL/h). An F test was used for whole-curve comparisons, with a significance level of 5%. Steady-state values for TAC across both types of corneas were not reached. Although the percentage of TAC diffusing across rabbit cornea was higher than that found for human cornea up to 18 h, there were no statistically significant differences. The percentages of total TAC diffusing across human and rabbit cornea at the 24-h time points were 0.38% +/- 0.02% and 0.36% +/- 0.01%, respectively. Percentages of total TAC at the 24-h time points were approximately 4.9x and 4.1x higher than those found previously for cyclosporin A across human and rabbit corneas, respectively. Rabbit corneas are a suitable model for human corneas in in vitro permeability studies.

Resealing of electroporation of porcine epidermis using phospholipids and poloxamers

The resealing of porcine epidermis after electroporation is investigated. Porcine epidermis was subjected to electroporation (30 pulses at 100 V, 1 ms and at 1 Hz) in a vertical diffusion apparatus, in the presence of 2 mg/ml dimyristoylphosphatidylserine, to produce a long lasting permeable state. Resealing treatments include incubation in 0.0625–0.25 mM poloxamer 188 (P188), or incorporation of phosphatidylcholines (PC) and/or cationic lipids with additional pulses. The recovery of electric resistance of the epidermis samples after electroporation with or without resealing treatments was monitored. The transports of carboxyfluorescein and glucose were measured during the recovery process. Both P188 and PC were effective in resealing in terms of electric conductance and transport, with P188 reacting more rapidly and completely. P188 mediated lipid exchange between stratum corneum lipid particles was measured by fluorescence resonance energy transfer (FRET). Lipid reorganization facilitated by P188 and PC is suggested to be a major resealing mechanism of electroporation damage.

Sustained antibacterial effect of a hand rub gel incorporating chlorhexdine-loaded nanocapsules (Nanochlorex ®)

In the present study, an original chlorhexidine-loaded nanocapsule-based gel (Nanochlorex ®) was tested as hand rub gel against the resident skin flora in comparison with 2-propanol 60% (v/v) and 62% (v/v) ethanol-based gel (Purell ®). After 30-s hand rub, the immediate bactericidal effect of Nanochlorex ® was found comparable to 2-propanol 60% (v/v) (reduction factor, RF: 0.30 ± 0.35 versus 0.38 ± 0.55, P > 0.05) against aerobic bacteria, whereas the post-values of surviving anaerobes were shown significantly lower from Nanochlorex ® ( P < 0.001) and insignificant from 2-propanol 60% (v/v) ( P > 0.05). Sustained antibacterial effect of Nanochlorex ® was confirmed against the resident and transient hand flora in two sets of experiment. In the first, the results obtained with the glove-juice technique showed that the bactericidal effect induced by Nanochlorex ® hand rub persisted throughout 3-h period, while Purell ® failed to reduce significantly the post-values of surviving bacteria. In the second, repeated artificial contaminations with Staphylococcus epidermidis was carried out onto ex vivo human skin pre-treated by either Nanochlorex ® or Purell ® for 5 min, then maintained in cell diffusion apparatus for 4 h. The log 10 reduction of surviving bacteria was significantly higher with Nanochlorex ® than that determined with Purell ® after three successive contaminations (from ∼5.5 to 1.5 log 10 reduction for Nanochlorex ® between the first and the third contamination; ∼1 log 10 reduction for Purell ® throughout the experiment), confirming the sustained antibacterial effect of chlorhexidine-loaded nanocapsule-based gel. The immediate and sustained antibacterial effect of Nanochlorex ® was explained by chlorhexidine carrier system which improved the drug targeting to bacteria and reduced from osmotic gel further bacterial growth on the skin. Nanochlorex ® might constitute a promising approach for hygienic hand disinfection in care practice performing multiple procedures.

Lipid and Electroosmosis Enhanced Transdermal Delivery of Insulin by Electroporation

Transdermal transport of insulin and extraction of interstitial glucose under anodal iontophoresis (electroosmosis) following electroporation in the presence of 1,2-dimyristoylphophatidylserine (DMPS) was studied. An earlier study showed that DMPS increased the transport of insulin across porcine epidermis under electroporation by approximately fourfold. It was suggested that DMPS increased the lifetime of electropores in the epidermis resulting in an enhanced transport of permeants. When electroosmosis was applied across the epidermis following electroporation with DMPS, the enhancement of insulin transport was approximately 18-fold over electroporation alone. When the same strategy was applied to extract interstitial glucose, the enhancement was approximately 23-fold over electroporation alone. Real-time transdermal insulin transport kinetics was measured using FITC-labeled insulin and a custom-made vertical diffusion apparatus that had a fluorescence cuvette as the receiver compartment. Insulin transport by electroporation alone showed a nonlinear kinetics that is most likely due to the resealing of the electropores with time. The transport kinetics when electroporation was carried out in the presence of DMPS was more linear, confirming earlier studies that suggested the DMPS stabilizes transport paths formed by electroporation. The data suggests that in vivo, noninvasive insulin delivery to therapeutic levels and glucose extraction may be achieved by combining electroporation with anionic lipids and electroosmosis.

Characteristics of Substance P Transport Across the Blood–Brain Barrier

Substance P (SP; NH3(+)-Arg(+)-Pro-Lys(+)-Pro-Gln-Gln-Phe-Phe-Gly-Leu-Met-NH2) belongs to a group of neurokinins that are widely distributed in the central nervous system and peripheral nervous system. The biological effects mediated by SP in the central nervous system include regulation of affective behavior, emesis, and nociception. Many of these actions are believed to be the result of the binding of SP to the neurokinin-1 (NK-1) receptor and subsequent transport across the blood-brain barrier (BBB). The objective of the study was to investigate the involvement of the NK-1 receptor in the permeation of SP across the BBB. Transport of 3H SP (1-13 nM) was investigated using BBMEC monolayers grown on polycarbonate membranes mounted on a Side-bi-Side diffusion apparatus. 3H SP samples were analyzed by scintillation spectrometry. Liquid chromatography-tandem mass spectrometry was used to monitor the transport at higher concentrations (micromolar). SP transport across BBMEC monolayers was found to be saturable (Km = 8.57 +/- 1.59 nM, Vmax = 0.017 +/- 0.005 pmol min(-1) mg(-1) protein) in the concentration range of 0-13 nM. Significant (p < 0.05) decline in 3H SP permeation was observed in the presence of unlabeled SP and at 4 degrees C, indicating that the transport process is carrier-mediated. High-performance liquid chromatography analysis showed no significant metabolism of 3H SP in either the donor or receiver chambers. 3H SP transport was inhibited by 2-11 SP (p < 0.05) but not by any other fragments, indicating that both the C- and N-terminal regions are essential for molecular recognition by the receptor. Endocytic inhibitors (chloroquine, phenylarsine oxide, monensin, and brefeldin) did not inhibit SP transport, suggesting the involvement of a nonendocytic mechanism in SP permeation. Pro(9) SP, a high-affinity substrate for the NK-1 major subtype receptor, significantly (p < 0.05) inhibited the transport of SP. However, Sar(9)Met(O2)(11) SP, a high-affinity substrate for the NK-1 minor subtype receptor, septide, and neurokinin A, inhibitors of NK-1 and neurokinin-2 (NK-2) receptors, respectively, did not produce any inhibition of SP transport. Western blot analysis confirmed the presence of the NK-1 receptor in BBMEC monolayers. The above results provide functional and molecular evidence for the existence of a carrier-mediated mechanism in the transport of SP across the BBB. The effects of specific inhibitors and the results of Western blot analyses demonstrate the involvement of the NK-1 receptor in the transport of SP across the BBB.

Influence of the Non-Perfect Step Input Concentration at the Feed Side of the Membrane Surface on the Diffusion Coefficient Evaluation

Summary: Vapor diffusion coefficients in polymeric membranes were evaluated from dynamic permeation experiments. A membrane separated the diffusion cell into two parts – upstream and downstream. At the start of the experiment the concentration change in the upstream part (feed side) was made by substituting the input stream of pure nitrogen by the stream of permeant vapors. The solution of the Fick's second law with the step input concentration function is used for the evaluation of diffusion coefficients. The realization of the step input function can be difficult and its imperfection can negatively influence the evaluation process. This contribution deals with the description of the experimentally obtained input function and the study of its influence on evaluated values of diffusion coefficients. The mathematical model, which includes the non-perfect step input concentration function and the transport through a polymer was developed. The results of this study enable the estimation of diffusion coefficient evaluation errors as dependence on the experimental arrangements and on the membrane transport properties. Diffusion apparatus for measurement of the steady-state permeation process.

Porcine vaginal mucosa as an in vitro permeability model for human vaginal mucosa

The availability of human tissue for experimental purposes is often problematical and use is thus made of animal tissue as models of the human tissue. In this study, porcine vaginal mucosa was used as an in vitro permeability model for human vaginal mucosa using tritium-labelled permeants (17β-estradiol, r-arecoline, vasopressin, oxytocin and water). Fresh porcine and human vaginal tissues were frozen in liquid nitrogen and stored at −85 °C. In vitro permeability studies were performed using a flow-through diffusion apparatus (24 h, 20 °C, 1.5 ml/h). The mean steady state flux values for water, r-arecoline and vasopressin were approximately 4, 12 and 5% lower, while those for 17β-estradiol and oxytocin were approximately 17 and 53% higher, through porcine vaginal mucosa as compared to human vaginal mucosa, respectively. Using a F-test (comparing whole curves), statistically significant differences in the diffusion of 17β-estradiol, r-arecoline and oxytocin were indicated when comparing human and porcine vaginal mucosa. Generally, porcine vaginal mucosa seems a good in vitro permeability model for human vaginal mucosa. However, permeability of these two mucosa towards all permeants tested does not always correspond closely. These differences must always be considered when using porcine tissue as an in vitro permeability model for human vaginal mucosa.

Induction of cytotoxic T-lymphocytes by electroporation-enhanced needle-free skin immunization

A needle-free method based on transcutaneous electroporation is described for delivering peptide vaccines. The K b-binding OVA-peptide SIINFEKL was used as an example to induce the peptide-specific cytotoxic T-lymphocytes (CTL) response in mice. A saturated anionic lipid was added during electroporation, and post-pulse electroosmosis was applied to enhance the vaccine delivery. Electroporation was found to stimulate the exodus of Langerhans cells (LC) from the skin. The peptide transported into and through murine skin was measured using a Franz diffusion apparatus. Most peptide was retained in the skin rather than passing through the skin in the process. The peptide was delivered to the dorsal skin of mice by in vivo electroporation. An electroporation-transportable oligonucleotide with CpG motif was used as adjuvant. The efficacy of peptide delivery was comparable to that of intradermally injected with Freund's complete adjuvant (FCA). Peptide-specific CTL response to the vaccine delivered by needle-free electroporation/electroosmosis was equivalent to that delivered by intradermal injection, as determined by production of the peptide-specific IFN-γ in ELISPOT assay.

Measurement of drug release from microcarriers by microdialysis

The purpose of this study was to examine the feasibility of the microdialysis sampling technique as a method to precisely and conveniently measure drug release from microcarrier systems such as liposomes and microspheres. Release of 5-fluorouracil (5-FU) from liposomes and microspheres was evaluated in vitro using microdialysis. Retrodialysis calibration using 5-chlorouracil (5-CU) was performed in conjunction with on-line HPLC analysis. At a microdialysis perfusate flow rate of 0.5 μL/min, concurrent 5-FU gain and 5-CU loss ranged from 72% to 75%, while concurrent 5-FU loss and 5-CU ranged from 69% to 71%. After calibration, simultaneous 5-FU release profiles were obtained by continuous microdialysis and discrete equilibrium dialysis sampling using a side-by-side diffusion apparatus. Release rates were characterized by a first-order release model. The release rate constants for a representative liposomal formulation were 0.30 and 1.85/h by microdialysis in the acceptor and donor compartments, respectively, and 0.39/h by equilibrium dialysis in the acceptor compartment. The calculated release rate constant determined by equilibrium dialysis in the donor compartment (1.98/h) agrees with that determined by microdialysis (1.85/h) when the resistance of the equilibrium dialysis membrane with associated first-order rate constant of transfer of 0.42/h is taken into account. Release profiles of 5-FU from a number of different liposome and microsphere formulations were determined. The results indicate that a convenient and reproducible characterization of drug release from various liposome and microsphere formulations is readily obtainable by microdialysis. © 2005 Wiley-Liss, Inc. and the American Pharmacists Association.

Removal of Actinides from Acidic Solution via Carrier-Mediated Facilitated Transport Across Mesoporous Substrates with Nanoengineered Surfaces: Thiol Self-Assembled Monolayers with D(tBu)ΦD(iBu)CMPO Ligands

:The surface engineering of polycarbonate track-etched (PCTE) membranes was performed to create a permselective membrane for the removal of trace levels of fission products and transuranic metals from acidic streams. Electroless gold deposition was used to place a gold coating on the PCTE substrates. The gold coating was subsequently functionalized through the formation of a self-assembled monolayer of dodecanethiol, which was further functionalized with di-(4-t-butylphenyl)-N, N-diisobutylcarbamoylmethylphosphine oxide. Transport characteristics of metal ions, 137Cs, 85Sr, 241Am, and 239Pu, were obtained using a two-compartment diffusion apparatus. Transport studies showed that the functionalized membranes enhance the transport rates of 241 Am and 239Pu and inhibit the transport of 137Cs and 85Sr. Diffusion studies over an extended time revealed that the facilitated transport characteristics of 239Pu through the ligand-coated membranes are dependent on nitrate anion concentrations in the feed and sink cells.

Regional permeability of salmon calcitonin in isolated rat gastrointestinal tracts: Transport mechanism using Caco-2 cell monolayer

The objective of the study was to determine the region of maximum permeation of salmon calcitonin (sCT) through the gastrointestinal tract and to investigate the mechanism of permeation. For regional permeability determination, male Sprague-Dawley rats (250-300 g) were anesthetized and the gastrointestinal tissues were isolated. Stomach, duodenum, jejunum, ileum, or colon tissues were mounted on Navicyte side-by-side diffusion apparatus. Salmon calcitonin solutions (50 microm in phosphate-buffered saline, pH 7.4, 37 degrees C) were added to the donor side, and the samples were removed from the receiver compartment and analyzed by competitive radioimmunoassay (RIA). For mechanistic studies, Caco-2 cells were grown on Transwell inserts (0.4-microm pore size, 0.33 cm2 area) in a humidified 37 degrees C incubator (with 5% CO2). Transport experiments were conducted for sCT solutions (50 microm in Dulbecco's modified eagle's medium [DMEM], pH 7.4) from the apical-to-basolateral (A-to-B) direction and B-to-A direction at 37 degrees C and from the A-to-B direction at 4 degrees C. Cell monolayer integrity was monitored by mannitol permeability and transepithelial electrical resistance (TEER) measurements. The permeability coefficients (x 10(-9), cm/sec) for sCT through rat stomach, duodenum, jejunum, ileum, and colon tissues were 0.482 +/- 0.086, 0.718 +/- 0.025, 0.830 +/- 0.053, 1.537 +/- 0.32, and 0.934 +/- 0.15, respectively. The region of maximum sCT permeability is ileum followed by colon, jejunum, duodenum, and stomach. The permeability coefficients (x 10(-6), cm/sec) for sCT through Caco-2 cell monolayer were 8.57 +/- 2.34 (A-to-B, 37 degrees C), 8.01 +/- 1.22 (A-to-B, 4 degrees C), and 6.15 +/- 1.97 (B-to-A, 37 degrees C). The mechanism of its permeation is passive diffusion through the mucosa as determined from the Caco-2 monolayer permeability of sCT.

Diffusion of Metronidazole Released from Aqueous Solution and a Gel Through Human and Rabbit Corneas

Metronidazole has been suggested as an adjunct in the treatment of Acanthamoeba keratitis. This study involves the permeation of metronidazole from topically applied solutions and gels through human and rabbit corneas. The permeation of metronidazole, from the solutions and gels through the corneas, was determined using a flow-through diffusion apparatus. Human (32) and rabbit (54) corneas were obtained from an eye bank and animal nursery farm, respectively. Experiments were conducted at 20 degrees C and over a time period of 24 hours. High-performance liquid chromatography (HPLC) analysis was used as a detection method. Statistical tests used included an Analysis of Variance (ANOVA) and Duncan's multiple range test, for a determination of the steady state, and a nonlinear regression analysis, using an F test, was used to compare entire curves. Flux rates for 0.5% and 1% metronidazole solutions across human corneas were found to be 14% and 30% higher, respectively, than for rabbit corneas. However, the flux rates of the 0.5% and 0.8% metronidazole gels across rabbit corneas were found to be 7% and 25% higher than those for human corneas. The flux rates measured for at least the first 10 hours were not, statistically, significantly different between the metronidazole released from aqueous solutions and from the gel. Steady-state flux rates of the 0.5% metronidazole aqueous and gel formulations were approximately half those of the 0.8% and 1% preparations. Because of the longer corneal contact times, it may be therapeutically advantageous to use 0.8% metronidazole concentrations in gels for treating Acanthamoeba keratitis infestations. Further in vivo studies on the ocular compatibility of these formulations need to be performed. The use of rabbit corneas as an in vitro permeability model for human corneas is supported by these studies.

Theory of vapor diffusion in the high-density protein crystal growth device and its application to the measurement of the vapor pressures of aqueous solutions

A simple vapor transport model for a high-density protein crystal growth (HDPCG) microgravity vapor diffusion apparatus was developed to estimate the evaporation rate of a crystallizing solution including protein and precipitant. The independent variables were the precipitant concentrations and the solution volume. A series of experiments using aqueous sodium chloride with various initial conditions was carried out to verify the model. It was found that the experimental results were well reproduced by the theory. A method was introduced to estimate the parameter, k VP, which relates the precipitant concentration in the solution to the water vapor concentration in the air. For aqueous NaCl the determined value of k VP value coincided well with the known value. In addition, k VP values of some other precipitant systems were estimated, and tabulated.

Enhanced transdermal transport by electroporation using anionic lipids

Transdermal drug delivery is an attractive approach for either local or systemic treatment in medicine. In the last decade, different active transdermal delivery methods have been further investigated such as cationic liposomal delivery and electroporation-enhanced delivery. In light of gaining a synergistic effect of lipid and electroporation, a new method of using anionic lipids to enhance the transdermal transport of molecules under electroporation is reported here. Heat-stripped porcine epidermis was used for measurement of transdermal transport using an in vitro vertical diffusion apparatus. Lipid vesicles were prepared using a 1:1 mole ratio mixture of 1,2-dioleoyl-3-phosphatidylglycerol (DOPG) and 1,2-dioleoyl-3-phosphatidylcholine (DOPC). When the lipids were mixed with (but not encapsulating) the transport target molecule, the electroporation-induced transport through porcine epidermis was increased as compared to that without the lipids. The enhancement in transport was dependent upon the size and the charge of the transported molecule. Methylene blue (MB), protoporphyrin IX (PpIX) and dimethyl-protoporphyrin IX (DM-PpIX) were used as small target molecules, and FITC-dextrans (4 to 155 kDa) were used as large target molecules in our studies. Enhancement of transport, to varying degree, was observed for all three small molecules (molecular weights <1 kDa), in the presence of DOPG:DOPC vesicles. In the case of large molecules, lipid-enhanced transport was only observed for the 4 kDa dextran, and not for the larger ones ( M w>10 kDa). Neutral or cationic lipids alone did not enhance the transdermal transport under the electroporation conditions we used.

Transdermal insulin delivery using lipid enhanced electroporation

Transdermal insulin transport by electroporation was measured using porcine epidermis and fluorescein-labeled insulin. Previous studies have shown that anionic lipids can enhance the electroporative transport of molecules up to 10 kDa in size. It was also shown that it is the charge and not the type of the phospholipid head group that influences transdermal transport under electroporation. Moreover, phospholipids with saturated acyl chains enhance the transport of larger molecules more as compared to those with unsaturated chains. In the current study, based on those earlier findings, the effect of 1,2-dimyristoyl-3-phosphatidylserine (DMPS) on the transdermal transport of insulin by electroporation was examined. Porcine epidermis was used as a model for skin. Transport was measured using glass vertical diffusion apparatus in which the epidermis separated the donor and receiver compartments. Negative pulses were applied across the epidermis using platinum electrodes. Results show that when electroporation was carried out in the presence of DMPS, there was greater than 20-fold enhancement of insulin transport. Furthermore, while in the presence of the phospholipid, almost all the transported insulin was detected in the receiver compartment; in the absence of added lipids, only about half the insulin transported was in the receiver compartment and an almost equal amount of insulin remained in the epidermis. Fluorescence microscopy revealed that the insulin transport was mainly through the lipid multilayer regions that surround the corneocytes.