Passive and active strategies for transdermal delivery using co-encapsulating nanostructured lipid carriers: In vitro vs. in vivo studies

This work aimed at designing a formulation based on nanostructured lipid carriers (NLC) for transdermal co-administration of olanzapine and simvastatin, using passive and active strategies in a combined in vitro/in vivo development approach. NLC were prepared by two distinct methods, namely solvent emulsification–evaporation (SE/E) and high pressure homogenization (HPH). HPH was selected on the basis of a better performance in terms of drug loading and in vitro permeation rate. Several mathematical models were used to elucidate the release mechanisms from lipid nanoparticles. In vitro release kinetics was shown to be driven by diffusion, but other mechanisms were also present, and supported the feasibility of using NLC for sustained drug delivery. The in vitro skin studies showed that the chemical penetration enhancers, limonene and ethanol, added to the NLC formulations, promoted a synergistic permeation enhancement of both drugs, with olanzapine exhibiting a higher permeation than simvastatin. Transdermal administration to rats resulted in steady-state levels reached at around 10 h and maintained for 48 h, again with olanzapine exhibiting a better permeation rate. The pharmacokinetic parameters indicated that the NLC dispersion displayed a better in vivo performance than the gel, which was consistent with the in vitro results. These differences were, however, negligible in the flux values, supporting the use of gel as a final, more convenient, formulation. The in vivo experiments in rats correlated well with in vitro findings and revealed that the combined use of ethanol and limonene, incorporated in the NLC formulation, provided the main driving force for drug permeation. The Dermaroller® pretreatment did not significantly enhance drug permeation, supporting the use of passive methods as suitable for a transdermal delivery system. Furthermore, this work may provide a promising proof-of-concept for further clinical application in the treatment of schizophrenia and associated disorders, combined with dyslipidemia.     

Development of thermodynamically stable nanostructured lipid carrier system using central composite design for zero order permeation of Econazole nitrate through epidermis

The investigation was aimed at developing thermodynamically stable topical delivery system of nanostructured lipid carrier of econazole nitrate (EN) for the treatment of deep seated fungal infection by improving its permeability. Fifteen formulations (F1–F15) of nanostructured lipid carriers (NLCs) were prepared by solvent injection technique using central composite design and characterized for particle size and % entrapment efficiency. Closeness in the results, guided the selection of five NLC formulations which were formulated as hydrogels (G1–G5) using Carbopol 934. The permeation studies of gels demonstrated G3 with flux rate of 3.21?±?0.03 µg/cm²/min (> target flux of 1.46 µg/cm²/min) as the best formulation that exhibited zero order permeation. The amount of drug/unit area demonstrated linear dependency on flux rate. Confocal laser scanning microscopy demonstrated penetration of rhodamine red till the stratum basale due to hydration of stratum corneum. Hydrogel G3 containing NLC formulation (F5) was selected as the optimized topical gel. TEM of F5 revealed spherical particles that presented low recrystallization index of 72.35%. Stability profile for 90 days revealed insignificant change (p?<?0.05) in the particle size and zeta potential indicating substantial stability of the system. Thus, EN-loaded NLC indicated better permeability and thermodynamic stability as effective topical delivery system for deep seated fungal infection.     

Skin permeation of buprenorphine and its ester prodrugs from lipid nanoparticles: lipid emulsion,nanostructured lipid carriers and solid lipid nanoparticles

The aim of this study was to develop and characterize lipid nanoparticle systems for the transdermal delivery of buprenorphine and its prodrugs. A panel of three buprenorphine prodrugs with ester chains of various lengths was synthesized and characterized by solubility, capacity factor (log K′), partitioning between lipids and water and the ability to penetrate nude mouse skin. Colloidal systems made of squalene (lipid emulsion, LE), squalene + Precirol (nanostructured lipid carriers, NLC) and Precirol (solid lipid nanoparticles, SLN) as the lipid core material were prepared. Differential scanning calorimetry showed that the SLN had a more-ordered crystalline lattice in the inner matrix compared to the NLC. The particle size ranged from 220–300 nm, with NLC showing the smallest size. All prodrugs were highly lipophilic and chemically stable, but enzymatically unstable in skin homogenate and plasma. The in vitro permeation results exhibited a lower skin delivery of drug/prodrug with an increase in the alkyl chain length. SLN produced the highest drug/prodrug permeation, followed by the NLC and LE. A small inter-subject variation was also observed with SLN carriers. SLN with soybean phosphatidylcholine (SLN-PC) as the lipophilic emulsifier showed a higher drug/prodrug delivery across the skin compared to SLN with Myverol, a palmitinic acid monoglyceride. The in vitro permeation of the prodrugs occurred in a sustained manner for SLN-PC. The skin permeation of buprenorphine could be adjusted within a wide range by combining a prodrug strategy and lipid nanoparticles.     

固体脂质纳米粒作为水杨酸经皮给药载体的研究

目的 考察固体脂质纳米粒作为经皮给药载体对水杨酸经皮吸收的促渗透作用.方法 采用薄膜超声法制备水杨酸固体脂质纳米粒,以改良的Franz扩散池考察其体外透皮特性;并与水杨酸软膏剂比较,考察其促渗作用.结果 制备的水杨酸固体脂质纳米粒均匀圆整,包封率为46.4%,体外透皮特性优于普通软膏剂,24 h后皮肤药物累积透过量为654.3 μg/cm2,皮肤中药物残留量为22.99 μg,均分别显署高于软膏剂组(128.0 μg/cm2和0.84 μg,P<0.05).结论 固体脂质纳米粒作为水杨酸经皮给药载体,可有效促进药物透皮吸收和增加药物在皮肤中储留量,而且可延缓药物的释放,从而有效提高药物疗效及患者依从性.     

Potential Use of Nanostructured Lipid Carriers for Topical Delivery of Flurbiprofen

The potential use of nanostructured lipid carriers (NLC) composed of a fatty acid [stearic acid (SA)] or a triglyceride (glyceryl behenate) as solid lipids, and a mixture of medium chain triglycerides and castor oil as liquid lipids, for skin administration of flurbiprofen (FB), has been explored. Two different optimized NLC formulations (FB-SANLC based on SA vs. FB-C888NLC based on glyceryl behenate), with respect to the morphometrical properties (particle size and polydispersity index) and the entrapment efficiency, were used in this study. The ex vivo permeation profiles of FB-C888NLC, FB-SANLC and conventional FB solution were evaluated using human skin. An improved FB permeation was observed when the drug was delivered by skin application of FB-C888NLC, attributed to the particle size and matrix crystallinity. The differential scanning calorimetry and X-ray diffraction studies suggested major polymorphic transitions in the lipid matrix of FB-C888NLC. A good correlation between polymorphic transitions and increased drug permeation was observed. However, both NLC dispersions showed a penetration-enhancing ratio (ER) higher than conventional FB solution. The in vitro and in vivo irritancy and local tolerability were assessed by running, respectively, the SKINTEX? and Draize test. Both FB-C888NLC and FB-SANLC were classified as nonirritant.     

Pentapeptide modified ethosomes for enhanced skin retention and topical efficacy activity of indomethacin

Challenges associated with topical analgesics and anti-inflammatory drugs include poor drug penetration and retention at the desired lesion site. Therefore, improving these challenges would help to reduce the toxic and side effects caused by drug absorption into the systemic circulation and improve the therapeutic efficacy of topical therapeutic drugs. Pentapeptide (KTTKS) is a signal peptide in skin tissue, it can be recognized and bound by signal recognition particles. In the current study, we successfully prepared novel indomethacin (IMC) loaded KTTKS-modified ethosomes (IMC-KTTKS-Es), and the physicochemical properties and topical efficacy were investigated. Results showed that the prepared IMC-KTTKS-Es displayed a particle size of about 244 nm, a negative charge, good deformability, and encapsulation efficiency (EE) exceeding 80% for IMC, with a sustained release pattern. In vitro percutaneous permeation studies revealed that the skin retention was increased after the drug was loaded in the IMC-KTTKS-Es. Confocal laser scanning microscopy also showed improved skin retention of IMC-KTTKS-Es. In addition, IMC-KTTKS-Es showed improved topical analgesic and anti-inflammatory activity with no potentially hazardous skin irritation. This study suggested that the IMC-KTTKS-Es might be an effective drug carrier for topical skin therapy with a good safety profile.     

Nanostructured lipid carriers as novel ophthalmic delivery system for mangiferin: Improving in vivo ocular bioavailability

The aim of this study was to develop a novel nanostructured lipid carriers (NLCs) system to improve ocular bioavailability of mangiferin (MGN) for the potential treatment of cataract. The physicochemical properties of MGN‐loaded NLC (MGN‐NLC) formulation were characterized by particle size, polydispersity index, zeta potential, entrapment efficiency, drug loading, morphological property, and crystalline state. in vitro characteristics were investigated by drug release from NLC system, physical stability, and corneal permeation through excised rabbit cornea. Moreover, in vivo ocular tolerability was assessed by a modified Draize test and histological microscopy. Preocular retention capability was evaluated by slit‐lamp observation. Pharmacokinetic study in the aqueous humor was performed by microdialysis technique. Transmission electron microscopy depicted spherical and uniform morphology. Differential scanning calorimetry and X‐ray diffractometry displayed imperfect crystalline lattice. The optimized MGN‐NLC formulation exhibited a sustained drug release with 3 months stability and 4.31‐fold increase of in vitro corneal permeation. Furthermore, in vivo studies exhibited a high tolerance in the ocular tissues and prolonged drug retention capacity on the corneal surface. Finally, pharmacokinetic study suggested a 5.69‐fold increase of ocular bioavailability compared with MGN solution (MGN‐SOL). Therefore, NLC system is a promising approach for ocular delivery of MGN. © 2012 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 101:3833–3844, 2012     

余甘子软膏的制备及冰片促渗作用考察

目的:制备余甘子软膏并考察冰片对余甘子软膏经皮渗透的影响。方法:采用L₉(3⁴)正交试验,以耐寒试验、耐热试验、离心试验及感官评价为指标优选余甘子软膏的制备工艺,并进行皮肤刺激性考察;采用Franz扩散池法,以没食子酸、柯里拉京的体外透皮为指标,通过HPLC考察不同含量冰片对余甘子软膏的促渗作用;并对余甘子软膏经皮渗透及体外释放规律进行探究。结果:余甘子软膏的最佳处方为石蜡油0.5 g,凡士林1 g,羊毛脂5 g,硬脂酸3 g,纯净水1 g,丙三醇1 g,余甘子浸膏4 g;5%的冰片对余甘子软膏中没食子酸和柯里拉京的促渗效果最佳,24 h时的经皮累计渗透量分别为1.163 6,0.073 8 mg·cm^-2,经皮吸收速率为0.046 3,0.003 1 mg·cm^-2·h^-1,增渗倍数为1.738 0,1.822 5;24 h时余甘子软膏中没食子酸和柯里拉京的累计释放率分别为58.91%,45.47%;含5%冰片的余甘子软膏中没食子酸和柯里拉京的经皮渗透均符合一级方程,体外释放分别符合Higuchi方程、Hixson-Crowell方程;单次给药1,24 h后均无明显皮肤刺激性。结论:制得的余甘子软膏具有良好的性状及体外经皮渗透、体外释放性能,无明显皮肤刺激性。     

Nanosized ethosomes-based hydrogel formulations of methoxsalen for enhanced topical delivery against vitiligo: formulation optimization,in vitro evaluation and preclinical assessment

The present investigation aimed for the development and characterization of ethosomes-based hydrogel formulations of methoxsalen for enhanced topical delivery and effective treatment against vitiligo. The ethosomes were prepared by central composite design (CCD) and characterized for various quality attributes like vesicle shape, size, zeta potential, lamellarity, drug entrapment and drug leaching. The optimized ethosomes were subsequently incorporated int Carbopol® 934 gel and characterized for drug content, rheological behavior, texture profile, in vitro release, ex vivo skin permeation and retention, skin photosensitization and histopathological examination. Ethosomes were found to be spherical and multilamellar in structures having nanometric size range with narrow size distribution, and high encapsulation efficiency. Ethosomal formulations showed significant skin permeation and accumulation in the epidermal and dermal layers. The fluorescence microscopy study using 123 Rhodamine exhibited enhanced permeation of the drug-loaded ethosomes in the deeper layers of skin. Also, the developed formulation showed insignificant phototoxicity and erythema vis-à-vis the conventional cream. The results were cross-validated using histopathological examination of skin segments. In a nutshell, the ethosomes-based hydrogel formulation was found to be a promising drug delivery system demonstrating enhanced percutaneous penetration of methoxsalen with reduced phototoxicity and erythema, thus leading to improved patient compliance for the treatment against vitiligo.     

Topical delivery of Idebenone using nanostructured lipid carriers: evaluations of sun-protection and anti-oxidant effects

The objective of present study was to develop nanostructured lipid carriers (NLC) for topical delivery of antioxidant drug and evaluation of its sun protection efficacy. In the present study attempts have been made to formulate Idebenone loaded nanostructured lipid carriers (INLC) by using solvent precipitation method. Preformulation study evidenced for selection of Captex 500 P as an oil phase in which Idebenone has saturation solubility of 0.266 ± 0.032 g/ml. Compritol 888 ATO and ethanol were selected as solid lipid and solvent respectively. Surfactant and co-surfactant as Labrasol and Transcutol P have given stable formulations on the basis of HLB required for stabilization, respect to oil phase. INLC has particle size of 605 ± 4.01 nm and %EE of 82.58 ± 2.20 %. Optimized batches were subjected for crystallographic investigation, in vitro skin permeation study, drug deposition study, SPF determination and antioxidant activity. XRD, DSC studies illustrated that partial amorphization of Idebenone by molecularly dispersion within lipid blend leads for entrapment of drug. Permeation data showed that optimized INLC has flux value (Jss) of 7.87 μg cm^?2 h^?1. High significance (P < 0.001) of drug deposition in skin was observed between INLC and plain Idebenone gel. SPF value for INLC has 23 which represents that lipid nanocarriers have standards of blocking of 94–96 % of UVB rays. Such high skin deposition and SPF leads to more antioxidant effect of formulations. Hence lipid nanocarriers such as NLC have potential as an antioxidant and sun protection for topical drug delivery.     

An evaluation of crude palm oil (CPO) and tocotrienol rich fraction (TRF) of palm oil as percutaneous permeation enhancers using full-thickness human skin

The drawbacks associated with chemical skin permeation enhancers such as skin irritation and toxicity necessitated the research to focus on potential permeation enhancers with a perceived lower toxicity. Crude palm oil (CPO) is obtained by direct compression of the mesocarp of the fruit of the oil palm belonging to the genus Elaeis. In this research, CPO and tocotrienol-rich fraction (TRF) of palm oil were evaluated for the first time as skin permeation enhancers using full-thickness human skin. The in vitro permeation experiments were conducted using excised human skin mounted in static upright ‘Franz-type’ diffusion cells. The drugs selected to evaluate the enhancing effects of these palm oil derivatives were 5-fluorouracil, lidocaine and ibuprofen: compounds covering a wide range of Log p values. It was demonstrated that CPO and TRF were capable of enhancing the percutaneous permeation of drugs across full-thickness human skin in vitro. Both TRF and CPO were shown to significantly enhance the permeation of ibuprofen with flux values of 30.6?µg/cm² h and 23.0?µg/cm² h respectively, compared to the control with a flux of 16.2?µg/cm² h. The outcome of this research opens further scope for investigation on the transdermal penetration enhancement activity of pure compounds derived from palm oil.     

Hyaluronan-modified transfersomes based hydrogel for enhanced transdermal delivery of indomethacin

Hyaluronic acid (HA), as a hygroscopic and biocompatible molecule, has displayed unique permeation enhancement in transdermal delivery systems. Hence, indomethacin (IND) was encapsulated in HA-modified transfersomes (IND-HTs) to enhance transdermal IND delivery to reduce adverse effects in this study. The physiochemical properties of IND-HTs were characterized. Results showed that the prepared IND-HTs were spherical and revealed good entrapment efficiency (87.88 ± 2.03%), with a nanometric particle size (221.8 ± 93.34 nm). Then, IND-HTs were further incorporated into a carbopol 940 hydrogel (IND-HTs/Gel) to prolong retention capacity on the skin. The in vitro release and skin permeation experiments of IND-HTs/Gel were carried out with the Franz diffusion cells. It was found that IND-HTs/Gel exhibited sustained drug release, as well as superior drug permeation and flux across the skin. Confocal laser scanning microscopy showed improved penetration of HTs/Gel with a wider distribution and higher fluorescence intensity. The hematoxylin–eosin stained showed that HA improved the transdermal effect by changing the microstructure of skin layers and decreasing skin barrier function. In addition, IND-HTs/Gel showed significant analgesic activity in hot plate test and no potentially hazardous skin irritation. This study indicated that the developed IND-HTs/Gel could be a promising alternative to conventional oral delivery of IND by topical administration.     

In vitro penetration properties of solid lipid nanoparticles in intact and barrier-impaired skin

Treatment of skin diseases implies application of a drug to skin with an impaired epidermal barrier, which is likely to affect the penetration profile of the drug substance as well as the carrier into the skin. To elucidate this, the effect of skin barrier damage on the penetration profile of a corticosteroid applied in solid lipid nanoparticles (SLN) composed of different lipids, varying in polarity, was studied. The studies were carried out in vitro using impaired and intact porcine ear skin, and the SLN were compared with a conventional ointment. It was shown that a significantly higher amount of corticosteroid remained in the skin, intact as well as barrier impaired, when SLN was used as a vehicle. In general, the penetration profile of the drug substance into the skin was affected by the type of lipid used in the formulation and related to lipid polarity and drug substance solubility. When formulated in SLN and applied to intact skin, the permeation of the drug substance across the skin was significantly reduced, as compared to the ointment. Altogether, in both barrier-impaired and intact skin, a higher amount of drug substance remained in the skin during application of SLN for 6, 16, and 24 h, as compared to the ointment. These results emphasize the applicability of SLN to create a drug reservoir in skin, with the drug localized distinctively in the stratum corneum.     

Nanoemulsion gel-based topical delivery of an antifungal drug: in vitro activity and in vivo evaluation

Abstract

Objective: In this study, attempt has been focused to prepare a nanoemulsion (NE) gel for topical delivery of amphotericin B (AmB) for enhanced as well as sustained skin permeation, in vitro antifungal activity and in vivo toxicity assessment.

Materials and methods: A series of NE were prepared using sefsol-218 oil, Tween 80 and Transcutol-P by slow spontaneous titration method. Carbopol gel (0.5%?w/w) was prepared containing 0.1%?w/w AmB. Furthermore, NE gel (AmB-NE gel) was characterized for size, charge, pH, rheological behavior, drug release profile, skin permeability, hemolytic studies and ex vivo rat skin interaction with rat skin using differential scanning calorimeter. The drug permeability and skin irritation ability were examined with confocal laser scanning microscopy and Draize test, respectively. The in vitro antifungal activity was investigated against three fungal strains using the well agar diffusion method. Histopathological assessment was performed in rats to investigate their toxicological potential.

Results and discussion: The AmB-NE gel (18.09?±?0.6?µg/cm²/h) and NE (15.74?±?0.4?µg/cm²/h) demonstrated the highest skin percutaneous permeation flux rate as compared to drug solution (4.59?±?0.01?µg/cm²/h) suggesting better alternative to painful and nephrotoxic intravenous administration. Hemolytic and histopathological results revealed safe delivery of the drug. Based on combined results, NE and AmB-NE gel could be considered as an efficient, stable and safe carrier for enhanced and sustained topical delivery for AmB in local skin fungal infection.

Conclusion: Topical delivery of AmB is suitable delivery system in NE gel carrier for skin fungal infection.     

Nanostructured Lipid Carriers (NLC)-Based Gel for the Topical Delivery of Aceclofenac: Preparation, Characterization, and In Vivo Evaluation

The aim of this study was to prepare nanostructured lipid carriers (NLC)-based topical gel of aceclofenac for the treatment of inflammation and allied conditions. Stearic acid as the solid lipid, oleic acid as the liquid lipid, pluronic F68 as the surfactant, and phospholipon 90G as the co-surfactant were used. NLCs were prepared by melt-emulsification, low-temperature solidification, and high-speed homogenization methods. Characterization of the NLC dispersion was carried out through particle size analysis, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and an in vitro release study. The anti-inflammatory effect of the NLC gel was assessed by the rat paw edema technique and compared to marketed aceclofenac gel. The NLC dispersions exhibited d_90% between 233 nm and 286 nm. All of the NLC showed high entrapment efficiency ranging from 67% to 82%. The particle size of NLC was further confirmed by the SEM study. The result of DSC showed that aceclofenac was dispersed in NLC in an amorphous state. Both the entrapment and release rate were affected by the percentage of oleic acid, but the method of preparation affected only the entrapment efficiency. The nanoparticulate dispersion was suitably gelled and assessed for in vitro permeation. Finally, NLC-based gels were found to possess superior (almost double) the anti-inflammatory activity compared to the marketed product. The anti-inflammatory activity of NLC gel showed a rapid onset of action, as well as a prolonged duration of action as compared with the marketed gel.     

Nanostructured lipid carrier (NLC) based gel of celecoxib

Nanostructured lipid carriers (NLC) based topical gel of celecoxib was formulated for the treatment of inflammation and allied conditions. NLC prepared by the microemulsion template technique were characterized by photon correlation spectroscopy for size and scanning electron micrograph (SEM) studies. Drug encapsulation efficiency was determined using Nanosep centrifugal device. The nanoparticulate dispersion was suitably gelled and assessed for in vitro release and in vitro skin permeation using rat skin. Efficacy of the NLC gel was established using a pharmacodynamic study, i.e., aerosol-induced rat paw edema model. The skin permeation and rat paw edema pharmacodynamic studies were carried out in comparison with a micellar gel which had the same composition as that of the NLC gel except for the solid lipid and oil. The NLC based gel described in this study showed faster onset and elicited prolonged activity until 24h.     

Influence of various lipid core on characteristics of SLNs designed for topical delivery of fluconazole against cutaneous candidiasis

Dermal delivery of fluconazole (FLZ) is still a major limitation due to problems relating to control drug release and achieving therapeutic efficacy. Recently, solid lipid nanoparticles (SLNs) were explored for their potential of topical delivery, possible skin compartments targeting and controlled release in the skin strata. The retention and accumulation of drug in skin is affected by composition of SLNs. Hence, the aim of this study was to develop FLZ nanoparticles consisted of various lipid cores in order to optimize the drug retention in skin. SLNs were prepared by solvent diffusion method and characterized for various in vitro and in vivo parameters. The results indicate that the SLNs composed of compritol 888 ATO (CA) have highest drug encapsulation efficiency (75.7?±?4.94%) with lower particle size (178.9?±?3.8?nm). The in vitro release and skin permeation data suggest that drug release followed sustained fashion over 24?h. The antifungal activity shows that SLNs made up of CA lipid could noticeably improve the dermal localization. In conclusion, CA lipid based SLNs are represents a promising carrier means for the topical treatment of skin fungal infection as an alternative to the systemic delivery of FLZ.     

Polymeric microparticles-based formulation for the eradication of cutaneous candidiasis: development and characterization

Abstract

Cutaneous candidiasis is a common topical fungal infection which may be more prominent in patients associated with AIDS. It is usually treated by conventional formulations such as cream, gel, which show various adverse effects on skin along with systemic absorption. To overcome these drawbacks, various novel drug delivery systems have been explored. Poly(lactic-co-glycolic acid) (PLGA)-based microparticulate systems have shown good dermal penetration after topical application. Therefore, in the present study clotrimazole-loaded PLGA microspheres were prepared for targeted dermal delivery. Microspheres were prepared by using a single emulsification (oil-in-water, O/W) evaporation technique and characterized for different parameters. Prepared microparticulate systems were dispersed in Carbopol 934® gel and antifungal activity was carried out on experimentally induced cutaneous candidiasis in immunosuppressed guinea pigs. Particle size of optimized formulation was 2.9?µm along with 74.85% entrapment of drug. Skin retention studies revealed that drug accumulation in the skin was higher with microspheres gel as compared to marketed gel. Confocal microscopy of skin further confirmed penetration of microspheres up to 50?µm into the dermal region. In-vivo antifungal activity studies demonstrated that microsphere gel showed better therapeutic activity, lowest number of cfu/ml was recorded, as compared to marketed gel after 96?h of application. Based on the results of the study, it can be concluded that PLGA microparticles may be promising carriers to deliver clotrimazole intradermally for the treatment of invasive fungal infections.     

Design of solid lipid nanoparticles for caffeine topical administration

Context: Solid lipid nanoparticles (SLN) are drug carriers possessing numerous features useful for topical application. A copious scientific literature outlined their ability as potential delivery systems for lipophilic drugs, while the entrapment of a hydrophilic drug inside the hydrophobic matrix of SLN is often difficult to obtain.

Objective: To develop SLN intended for loading caffeine (SLN-CAF) and to evaluate the permeation profile of this substance through the skin once released from the lipid nanocarriers. Caffeine is an interesting compound showing anticancer and protective effects upon topical administration, although its penetration through the skin is compromised by its hydrophilicity.

Materials and methods: SLN-CAF were formulated by using a modification of the quasi-emulsion solvent diffusion technique (QESD) and characterized by PCS and DSC analyses. In vitro percutaneous absorption studies were effected using excised human skin membranes (i.e. Stratum Corneum Epidermis or SCE).

Results: SLN-CAF were in a nanometric range (182.6?±?8.4?nm) and showed an interesting payload value (75%?±?1.1). DSC studies suggest the presence of a well-defined system and the successful drug incorporation. Furthermore, SLN-CAF generated a significantly faster permeation than a control formulation over 24?h of monitoring.

Discussion and conclusions: SLN-CAF were characterized by valid dimensions and a good encapsulation efficiency, although the active to incorporate showed a hydrophilic character. This result confirms the suitability of the formulation strategy employed in the present work. Furthermore, the in vitro evidence outline the key role of lipid nanoparticles in enhancing caffeine permeation through the skin.     

Mechanistic insight into the dermal delivery from nanoparticle-coated submicron O/W emulsions

The influence of silica nanoparticle coating of negatively and positively charged submicron emulsion oil droplets on the dermal delivery of a lipophilic fluorescent probe, acridine orange 10-nonyl bromide (AONB) using an ex vivo porcine skin model is reported. The skin retention and depth of the penetration of AONB significantly increased (p ≤ 0.05) up to a skin depth of ～265 µm by nanoparticle coating of negative lecithin-stabilised emulsion oil droplets especially when nanoparticles were added from the water phase. The extent and depth of penetration of AONB incorporated into positively charged silica-coated oleylamine-stabilised emulsions significantly increased up to the upper dermis (～290 µm) with more pronounced effect by nanoparticle incorporation from the water phase of the control oleylamine emulsion. The permeation of AONB through full-thickness porcine skin was negligible (<0.12% of the topically applied dose). The skin penetration profile of AONB was well correlated to the more facilitated transport of the electrostatically bond silica–AONB complex compared to free AONB as one of the potential mechanisms of the improved delivery. The skin permeation of silica nanoparticles was negligible (<1 µg mL^?1 after a 6-h exposure time) which demonstrated the potential of nanoparticle-coated emulsions for topical targeting. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:890–904, 2010