Nanocosmetics and Nanomedicines
Ruy Beck, Silvia Guterres, and Adriana Pohlmann (Eds.)
Nanocosmetics and Nanomedicines New Approaches for Skin Care
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Editors Ruy Beck Federal University of Rio Grande do Sul Faculdade de Farmácia Dept. de Produção e Controle de Medicame Av. Ipiranga 2752 90610-000 Porto Alegre Brazil E-mail:
[email protected] Adriana Pohlmann Federal University of Rio Grande do Sul Institut of Chemistry Departamento de Química Orgânica Av. Bento Gonçalves 9500 91501-970 Porto Alegre Brazil Email:
[email protected] Silvia Guterres Federal University of Rio Grande do Sul Faculty of Pharmacy Dept. de Produção e Controle de Medicame Av. Ipiranga 2752 90610-000 Porto Alegre Brazil E-mail:
[email protected] ISBN 978-3-642-19791-8
e-ISBN 978-3-642-19792-5
DOI 10.1007/978-3-642-19792-5 Library of Congress Control Number: 2011923550 c 2011 Springer-Verlag Berlin Heidelberg This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilm or in any other way, and storage in data banks. Duplication of this publication or parts thereof is permitted only under the provisions of the German Copyright Law of September 9, 1965, in its current version, and permission for use must always be obtained from Springer. Violations are liable to prosecution under the German Copyright Law. The use of general descriptive names, registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. Typesetting: Scientific Publishing Services Pvt. Ltd., Chennai, India. Cover Design: eStudio Calamar S.L. Printed on acid-free paper 987654321 springer.com
Forward
The interaction of particles with biological systems unravels a series of new mechanisms not found for molecules: altered bio-distribution, chemically reactive interfaces, and the combination of solid-state properties and mobility. The tremendous progress and recent advances of nanotechnology has not been accompanied by sufficient studies of nanomaterial toxicity even though they possess unique, completely new properties. One certainty: the toxicity of nanomaterials can neither be extrapolated from the toxicity of bulk materials nor from the toxicity of their constituents in molecular/ionic form. Therefore the research on nanotoxicity is of extremely high scientific, social, and economic value in particular for human applications. As nanomaterial-based products enter the market, there is an urgent need for related research in order to prevent dramatic consequences of any healthoriented issues caused by nanotechnology-driven products. Indeed, the results of research on nanotoxicity have profound significance because the design of nanomaterials used in industry and consumer products should be based on the outcome of such work. This is more urgent in view of the infancy of these studies and that many of the data available on the biological effects of nanomaterials do not always come from studies that can be considered reliable. The responsibilities are enormous not only in social terms but also this research has multi-billion dollar significance for industry and an even greater value for consumers and health care. Therefore one of key questions is to understand the behavior of nanoparticles in biological systems that will certainly opens up new directions for medical treatments and is essential for the development of safe nanotechnology. The widespread use of untested nanomaterials can cause an enormous cost of care for health problems for the word population. In particular, in Brazil the applications and uses of “bio” stands among the most productive and successful area of the Brazilian “nano” initiative in both academia and industry. Indeed, not only in terms of the number and impact of the papers (more than a half of the Brazilian scientific papers in “nano” are from the nano bio area) but also the numbers of commercial products that are already cases of success. With this in mind Pohlmann, Beck and Guterres have ingeniously collected a series of state of the art contributions on an important and hot area on the use of nanomaterials on the use of nanocosmetics and nanomedicines for skin care. The book NANOCOSMETICS AND NANOMEDICINES: New approaches for skin care will certainly stands as the landmark and part of the classical literature on nanomaterials and skin care. Jairton Dupont, Tarragona, 30th January 2011.
Contents
Part I: Fundamentals of Skin Delivery Chapter 1: Transport of Substances and Nanoparticles across the Skin and in Vitro Models to Evaluate Skin Permeation and/or Penetration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Renata V. Contri, Luana A. Fiel, Adriana R. Pohlmann, S´ılvia S. Guterres, Ruy C.R. Beck
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Chapter 2: Rheological Behavior of Semisolid Formulations Containing Nanostructured Systems . . . . . . . . . . . . . . . . . . . . . . . . . Marta P. Alves, Renata P. Raffin, Solange B. Fagan
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Part II: Nanocarriers for Skin Care and Dermatological Treatments Chapter 3: Polymeric Nanocapsules: Concepts and Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fernanda S. Poletto, Ruy C.R. Beck, S´ılvia S. Guterres, Adriana R. Pohlmann Chapter 4: Topical Application of Nanostructures: Solid Lipid, Polymeric and Metallic Nanoparticles . . . . . . . . . . . . . . . . . Nelson Dur´ an, Zaine Teixeira, Priscyla D. Marcato
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Chapter 5: Lipid Nanoparticles as Carriers for Cosmetic Ingredients: The First (SLN) and the Second Generation (NLC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 Kleber L. Guimar˜ aes, Maria Inˆes R´e Chapter 6: Industrial Production of Polymeric Nanoparticles: Alternatives and Economic Analysis . . . . . . . . . . 123 Luciane F. Trierweiler, Jorge O. Trierweiler
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Contents
Chapter 7: Elastic Liposomes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 Maria Helena A. Santana, Beatriz Zanchetta Chapter 8: Chitosan as Stabilizer and Carrier of Natural Based Nanostructures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163 Maria I.Z. Lionzo, Aline C. Dressler, Omar Mertins, Adriana R. Pohlmann, N´ adya P. da Silveira
Part III: Applications of Nanocosmetics and Nanomedicines for Skin Treatments Chapter 9: Performance of Elastic Liposomes for Topical Treatment of Cutaneous Leishmaniasis . . . . . . . . . . . . . . . . . . . . . . 181 Bartira Rossi-Bergmann, Camila A.B. Falc˜ ao, Beatriz Zanchetta, Maria Vit´ oria L. Badra Bentley, Maria Helena Andrade Santana Chapter 10: Druggable Targets for Skin Photoaging: Potential Application of Nanocosmetics and Nanomedicine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197 Giselle Z. Justo, S´ılvia M. Shishido, Daisy Machado, Rodrigo A. da Silva, Carmen V. Ferreira Chapter 11: Nanomedicine: Potential Killing of Cancercells Using Nanoparticles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229 Patricia da Silva Melo, Priscyla D. Marcato, Nelson Dur´ an Chapter 12: Zebrafish as a Suitable Model for Evaluating Nanocosmetics and Nanomedicines . . . . . . . . . . . . . . . . . . . . . . . . . . 239 Carmen V. Ferreira, Maria A. Sartori-da-Silva, Giselle Z. Justo Chapter 13: Nitric Oxide-Releasing Nanomaterials and Skin Care . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253 Amedea B. Seabra Chapter 14: Nanocarriers and Cancer Therapy: Approaches to Topical and Transdermal Delivery . . . . . . . . . . . . . . . . . . . . . . . . 269 Juliana M. Marchetti, Marina C. de Souza, Samantha S. Marotta-Oliveira Chapter 15: Nanocarriers to Deliver Photosensitizers in Topical Photodynamic Therapy and Photodiagnostics . . . . . . . 287 Wanessa S.G. Medina, Fab´ıola S.G. Pra¸ca, Aline R.H. Carollo, Maria Vit´ oria L. Badra Bentley
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Chapter 16: Production of Nanofibers by Electrospinning Technology: Overview and Application in Cosmetics . . . . . . . . . 311 Maria Helena A. Zanin, Natalia N.P. Cerize, Adriano M. de Oliveira Chapter 17: Nanosized and Nanoencapsulated Sunscreens . . . 333 C´ assia B. Detoni, Karina Paese, Ruy C.R. Beck, Adriana R. Pohlmann, S´ılvia S. Guterres About the Editors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363 Subject Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 365 Author Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369
Part I
Fundamentals of Skin Delivery
Chapter 1
Transport of Substances and Nanoparticles across the Skin and in Vitro Models to Evaluate Skin Permeation and/or Penetration Renata V. Contri1, Luana A. Fiel1, Adriana R. Pohlmann2, Sílvia S. Guterres1, and Ruy C.R. Beck1 1
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Universidade Federal do Rio Grande do Sul, Faculdade de Farmácia, Av. Ipiranga, 2752, 90610-000, Porto Alegre, RS, Brazil
[email protected] Universidade Federal do Rio Grande do Sul, Departamento de Química Orgânica, Av. Bento Gonçalves, CP 15003, 91501-970, Porto Alegre, RS, Brazil
Abstract. Nanotechnology can be used to modify the drug permeation/penetration of encapsulated substances, through the manipulation of many different factors, including direct contact with the skin surface and controlled release. In general, nanoparticles cannot cross the skin barrier, which can be explained by the cell cohesion and lipids of the stratum corneum, the outermost skin layer. The device most commonly used to study the transport of substances and nanoparticles across the skin is the Franz vertical diffusion cell, followed by the substance quantification in the receptor fluid or determination of the amount retained in the skin. Microscopy techniques have also been applied in skin penetration or permeation experiments. This chapter will present the fundamental considerations regarding the transport of encapsulated substances and/or nanoparticles across the skin, the experimental models applied in these studies and a review of the main studies reported in the literature in order to allow the reader to gain insight into the current knowledge available in this area.
1.1 Introduction The skin is the largest organ of the human body, presenting a total area of close to 2 m2. It acts as a barrier between the organism and the external environment [1]. Important skin functions include protection against UV radiation, physical and chemical damage and microbiological attack, maintenance of the body temperature and sensorial functions such as pain and temperature [2]. The skin is mainly composed of two layers (epidermis and dermis) besides the subcutaneous tissue [3]. It is composed of a variety of different cells, being considered more complex than the brain regarding this aspect [1]. The epidermis is composed of several lipids including phospholipids, phosphatidylcholine, cholesterol and triglycerides [4]. The main cell types found in the epidermis are keratinocytes, melanocytes, Langerhans cells, and Merkel cells [3]. The epidermis is
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divided into several layers and its outermost layer, the stratum corneum, is responsible for the barrier function of the skin due to its lipophilicity and high cohesion between cells [5, 6]. The stratum corneum is composed of keratinized corneocytes embedded in lipid bilayers [2]. Ceramides, cholesterol and free fatty acids comprise its extracellular lipid compartment [7]. The dermis is the layer next to the subcutaneous tissue and it is composed of collagen, elastin, glycosaminoglycans, and fibroblasts. This layer is highly vascularized besides containing the appendices (sweat glands and pilosebaceous units) and leucocytes, adipocytes and mast cells [3]. Considering the skin anatomy and physiology, some active substances will not provide the desired activity after their cutaneous administration. Nanotechnology can be used to modify the drug permeation/penetration by controlling the release of active substances and increasing the period of permanence on the skin [8, 9] besides ensuring a direct contact with the stratum corneum [10] and skin appendices [11, 12] and protecting the drug against chemical or physical instability [13, 14, 15, 16]. Also, depending on their sizes and structures, some nanostructures can also penetrate across the skin [17]. The aim of this chapter is to discuss the permeation and penetration of nanoencapsulated substances and nanoparticles through the skin. The transport across the skin and the in vitro models and membranes used to evaluate the skin permeation and/or penetration are also reviewed.
1.2 Transport across the Skin Despite the efficient barrier property of the skin, some substances can penetrate across its different layers [18]. The stratum corneum, known as a coherent and compact membrane, is the limiting layer for the penetration process, acting as a passive diffusion barrier [2, 19]. The permeability of some substances through the full-thickness of skin is at least 14 times lower than that of the same substances through the dermis [18]. The integrity of the stratum corneum and the concentration of the applied drug are important aspects that influence the drug penetration profile [19]. The lipids of the stratum corneum, especially ceramides, are important components in terms of its barrier function [2, 20]. There are some passive routes by which a molecule can cross the stratum corneum (Fig. 1.1): intercellular (through solubilization in the extracellular lipids arranged into structured bilayers), transcellular (through the corneocytes and the lipid bilayers) and appendageal (through either the sweat glands or hair follicles) [1]. However, the contribution of the latter route is considered small since the skin appendices occupy 0.1% of the skin surface [21]. The sweat glands are not a common pathway for drugs to pass through the skin due to the tortuous pathway and the ascendant sweat. The hair follicles, on the other hand, are common mechanism of transport for some ions, polyfunctional polar compounds and high molecular weight molecules [5, 22]. It has been verified that the hair follicles, despite their smaller superficial area, play an important role in the permeation of nanoencapsulated substances, since they serve as nanoparticle depots [11, 23]. The impermeability of skin can be a drawback when this route is desirable for the delivery of active substances. Only a small percentage of a substance reaches
1 Transport of Substances and Nanoparticles across the Skin and in Vitro Models
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its target when topically applied [1]. The stratum corneum is slightly permeable to both hydrophilic and lipophilic compounds. Thus, the transcellular and intercellular routes are the most important pathways across the skin [19]. The partition coefficient of a substance between the epidermis and its pharmaceutical form is a determining factor in its penetration into the epidermis, which is the determining step of its diffusion rate across the skin [18].
Fig. 1.1 Mechanisms of transport across the skin. (a) intercellular, (b) transcellular and (c) hair-follicles.
1.3 In Vitro Models and Membranes Used to Evaluate Skin Permeation and/or Penetration 1.3.1 In Vitro Diffusion Models The guidelines for dermal absorption of the World Health Organization (WHO) [24] differentiate between the processes of skin permeation and penetration. Penetration is the entry of a substance into a particular layer or structure, whereas permeation is the transport from one layer into a second layer, these being associated with different functions and structures.
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The diffusion cells are the systems normally used to evaluate the drug permeation through the skin [21]. There are vertical or horizontal cells, associated with the drug diffusion, and static or flow-through cells, considering the receptor fluid [24]. Thus, it is important to select a model where the transport is limited only by the skin and not by a stagnated diffusion, which can occur particularly in the case of highly lipophilic substances [5]. Franz (1975) [25] developed a static vertical diffusion cell and verified a good relation between the in vivo and in vitro data for organic substances. The Franz diffusion cell is the most common type of diffusion cell, mainly because of its low cost [2, 5, 26]. Furthermore, it is useful for studying semisolid formulations and is ideal for simulating in vivo performance [24]. In the Franz technique, a membrane (skin) is placed between the diffusion compartments of the cell. The dermis, when present, is turned toward the receptor compartment, which is usually filled with an isotonic saline solution or phosphate buffer containing surfactants or cosolvents in the case of lipophilic substances in order to maintain the sink conditions. The system is maintained under continuous magnetic stirring (Fig. 1.2) [21, 26]. The sample is deposited in the donor compartment on the epidermis. The diffusion rate of the active substance to the receptor compartment is determined by an appropriate and validated analytical method, such as chromatographic or spectroscopic techniques, liquid scintillation counting or other suitable methods [27, 28]. A flow-through cell was developed by Bronaugh and Steward (1985) [29] to automate the collecting of samples from a two-compartment cell. Moreover, this cell facilitates the maintenance of the system viability because the receptor fluid is continuously replaced. The flow-through cell mimics the blood flow through the removal of hydrophobic substances from the skin. However, the amount of substance absorbed and the period necessary for its removal are similar for both the flow-through cell and Franz diffusion cell [26]. Several guidelines [24, 27] recommend static Franz diffusion cells or flowthrough cells for permeation studies. The choice of the cell type must be based on the experimental aims and the substance characteristics, such as theoretical absorption properties. According to the Scientific Committee on Consumer Products guidelines (SCCP, 2006), the static diffusion cell presents the advantage of easy quantification, since the receptor fluid is not replaced continuously, only when the sampling takes place. Recently, the development of equipment based on static permeation cells has presented the possibility of automatic sampling from the receptor fluid, which facilitates the collection and replacement of the medium without the formation of air bubbles. Horizontal diffusion cells, which are also called side-by-side cells, are less common. Here, the cell also comprises two compartments, and the donor and the receptor (usually containing equal volumes) are separated by a membrane [30]. This kind of system is useful for studying mechanisms of diffusion through the skin, such as permeation from one stirred solution into another stirred solution through a membrane [24]. Besides the assay of the active substance in the receptor compartment, the amount of the substance retained on the skin or penetrated into different skin layers is also commonly evaluated using diffusion cells. In order to determine this
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profile, the skin is cleaned after the permeation experiment to remove the excess of formulation. The stratum corneum layers are usually removed by the tape stripping technique where adhesive tapes are placed on the skin surface and the layers are taken by applying constant pressure [21, 31]. In addition, the epidermis and dermis can be separated by heat and force [32, 33]. The amount of substance remaining in each layer is extracted using an appropriate solvent and assayed by a validated analytical method. Studies on the penetration of active substances into different skin layers can also be performed using the alternative Saarbrücken diffusion model [9, 34, 35]. In this system, the skin is placed onto a filter paper wetted with Ringer solution, which is placed into the hole of a Teflon block. The Teflon block with the sample is fitted into the cavity of a Teflon punch and applied to the skin surface. A standard weight is placed on the top of the punch for 2 min to increase the contact between the skin and the formulation. The gap between the two Teflon pieces is then sealed to avoid the loss of water from the skin and the system is placed into a plastic box at 32 ± 1°C. The skin is removed at different time intervals and tape stripping is carried out. After this procedure, the skin is separated into parallel sections using a cryomicrotome and extraction techniques are performed for the quantification of the drug [36].
Fig. 1.2 (a) Horizontal diffusion cell, (b) Vertical diffusion cell and (c) Saarbrucken model.
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1.3.2 Microscopy Techniques Microscopy techniques are interesting tools to visualize the location of the particles or of the active ingredient in the skin tissue after in vitro or in vivo skin permeation or penetration studies. These studies provide information on the penetration pathway or permeation route of substances or particles across the skin [17, 37, 38]. Scanning Electron Microscopy (SEM), Confocal Laser Scanning Microscopy (CLSM), Transmission Electron Microscopy (TEM) and Scanning Transmission Ion Microscopy (STIM) are the microscopic techniques most commonly employed in this type of study [38, 39, 40, 41]. Figure 1.3 shows microscopy images obtained using these different techniques.
Fig. 1.3 (a)* Confocal scanning microscopy images showing fullerene penetration through the skin. All scale bars represent 50 μm. (b)* Transmission electron microscopy image showing that fullerenes are present within the intercellular space of the stratum granulosum cell layer. The scale bar represents 300 nm. (c)** Scanning electron microscopy of Zinc oxide nanoparticles distribution into different areas of in vitro human epidermis. * Reprinted (Adapted) with permission from Rouse et al., 2007. Copyright 2007. American Chemical Society. ** Reprinted (Adapted) with permission from Roberts et al., 2008. Copyright 2008. WILEY-VCH Copyright & Licenses.
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1.3.3 Membranes 1.3.3.1 Types of Membranes Since the skin is an organ with multiple layers, it can be used during in vitro skin permeation/penetration studies with its two basic layers, epidermis and dermis (full-thickness skin) or it can be submitted to treatments that separate its layers supplying different types of membranes (split-thickness skin) to be used for in vitro studies [26, 42, 43]. The choice of the membrane is related to the focus of the study (permeation or penetration). In the full-thickness skin membranes only the subcutaneous tissue is removed [26, 42, 43]. On the other hand, split-thickness skin can be obtained in several ways [26, 42, 43] and the isolation of one specific layer of a skin sample with a controlled thickness can be made using heat and force (heat-separated epidermis), dermatome (dermatomed skin) or enzymatic processes (trypsin-isolated stratum corneum) [44, 45]. Epidermis and stratum corneum membranes are more fragile and some mass balance techniques, such as tape stripping, cannot be applied [27]. Divergences can be found in the literature concerning the effect that these processes can have on the skin characteristics. Some studies have demonstrated that the skin barrier is reestablished with the hydration of these membranes [46, 47]. On the other hand, some reports have claimed that the viability of the skin and the flow through the epidermis can be disturbed by these processes [26, 48, 49]. 1.3.3.2 Sources of Membranes Membranes obtained from diverse sources, such as synthetic [43, 50, 51], vegetable [52], human [53, 33, 43], animal [43, 54] and reconstructed tissues [43, 45, 47] can be evaluated as candidates to predict the transport of substances across the skin and used during in vitro experiments. The advantages and disadvantages of these membrane models need to be investigated regarding their effectiveness to determine the transport of substances across the skin [26]. There is no consensus regarding the standardization of these sources in this type of study. In general, only human, animal or reconstituted skin models should be used as sources of membranes to evaluate the transport of substances across the skin [26, 27]. On the other hand, synthetic membranes are usually recommended and used to study the in vitro release of substances from semisolid or liquid pharmaceutical or cosmetic formulations [43, 55, 56, 57]. 1.3.3.2.1 Human Skin Human skin offers a greater possibility for in vitro-in vivo correlations compared with the other sources of membranes [33, 43, 58, 59, 60]. The samples can be obtained from portions remaining from surgical procedures (plastic surgery or amputation) or autopsies. The most commonly used anatomical regions are abdomen, breast and legs. In the case of skin membranes from a human source, dermatomed skin (200-500 μm) is recommended [27]. To minimize the variability in the results due to differences in the permeation properties of different anatomical regions and volunteers, the anatomical region as well as the sex, race and age of the donors
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should be standardized [90, 92]. However, the availability of human skin sources is limited due to the need to acquire the consent of the volunteer [26]. 1.3.3.2.2 Animal Skin Skin samples obtained from animals allow easily obtainment and standardization of the anatomical region, sex and age of the animal. Thus, the skin of several animal species is frequently used as an alternative to human skin to evaluate the in vitro transport of substances [43]. The use of monkey, rodent, pig and snake skin is reported in the literature. In the evolutionary chain, monkeys represent the species closest to humans. Comparative in vitro-in vivo studies demonstrate that the transport of substances across monkey skin is similar to that across human skin [62, 63, 64]. However, few studies have been carried out using monkey skin for ethical reasons. Studies using rodent skin as a membrane model are more common for the evaluation of the in vitro transport of substances. As sources of membranes, the use of rat, mouse, guinea pig and rabbit skin has been reported. Although it is known that rat skin is around 10 times more permeable than the human skin [27, 64, 65] its use for in vitro experiments is still common in toxicity studies, making in vitro-in vivo correlations possible [64, 66]. Furthermore, a correlation between the skin diffusion coefficients for nortriptyline was observed on comparing Wistar rat skin and human heat-separated epidermis [67]. Considering mouse skin, only full-thickness skin membranes should be used since this type of skin presents a very low thickness [26]. Snake skin has been studied and recommended as a model for the stratum corneum membrane to evaluate in vitro penetration [68, 69]. The stratum corneum membrane is commonly employed to verify the barrier function of the skin, considering it as the main obstacle in the skin penetration of substances [45, 47]. Anatomically, pig skin presents the greatest similarity to human skin [43]. Thus, it is frequently used as a membrane to evaluate the transport of substances through the skin in in vitro studies [43]. Generally, the samples come from the ears or from the abdominal or dorsal regions. Some particularities, such as size and density of hair follicles and the stratum corneum thickness, are indicated as reason for divergences in the results obtained from pig and human skin [34]. The evaluation of the relative permeability of some drugs through membranes obtained from different sources suggests differences in the following order: human < pig < rat < rabbit < mouse [70]. 1.3.3.2.3 Regenerated Skin The extrapolation of results obtained from skin permeation/penetration experiments carried out with animal membranes to the human skin is always questionable given the influence of the inter-species variability. Moreover, there are ethical questions regarding the use of animal skin [71]. The Organization for Economic Cooperation and Development has affirmed that the regenerated human skin models can be used to evaluate the in vitro transport of substances across the skin if there is equivalence [72]. However, this use requires validation of its applicability, which is still under evaluation [73]. The models of regenerated human skin commercially available are: Apligraf®, Epiderm®, SkinEthic® and EpiSkin®. Apligraf®/Graftskin® (Organogénese Incorporation) [74, 75]
1 Transport of Substances and Nanoparticles across the Skin and in Vitro Models
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and EpiSkin® (L‘Oréal) are models of two live layers. SkinEthic® (SkinEthic) and Epiderm® (MatTek) [71] are epidermis models. Despite attempts to investigate the appropriateness of using regenerated membranes in in vitro studies on the transport of substances across the skin [45, 73, 76], to date no study has verified that they can act as substitutes for human or animal skin models. These models do not provide a barrier to the transport of substances through the skin [45, 47, 77]. However, regenerated human epidermis models could provide an adequate tool for routine tests, such as the quality control of cosmetic products [73].
1.4 Transport of Nanoparticles and Encapsulated Substances across the Skin The delivery of therapeutic agents without the need for chemical enhancers is desirable to maintain the normal skin barrier function. Treatment with chemical enhancers, such as surfactants and organic solvents, can cause not only a reduction in the barrier function of the skin, but also irritation and damage to the skin [17, 78, 79]. Drug-release nanocarriers, such as liposomes, micelles, polymeric and solid lipid nanoparticles as well as inorganic nanoparticles and sub-micrometric emulsions, have been used as alternatives to chemical enhancers to reduce the damage and increase the permeation of therapeutic agents through the skin [17, 78, 79]. Additionally, controlling the release of therapeutic agents can be achieved with reduced systemic absorption [17, 78, 79]. The transport of nanoparticles and nanoencapsulated substances through the skin is related to the nature and physicochemical properties of the nanoparticles and vehicles, the nature of the substance and the conditions of the skin [78, 79]. Most studies related to inorganic particles are recent (Fig. 1.4) while permeation/penetration studies applying organic (polymeric and lipid) particles have been published since 1999.
Fig. 1.4 Articles which studied the skin penetration/permeation of encapsulated substances or nanoparticles.
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1.4.1 Nanoparticles Based on Organic Compounds Nanoparticles based on organic compounds can be either polymeric or lipid systems, and either vesicular or matrix structures. Such nanoparticles have been proposed for enhancing or controlling the cutaneous penetration of hydrophilic and lipophilic substances. They can be built using a bottom-up or top-down approach. 1.4.1.1 Polymeric Systems Polymer-based nanoparticles are of interest for skin administration due to the controlled release of encapsulated active ingredients, which have to diffuse through the polymeric matrix to permeate the skin. Nanocapsules (See Chapter 3) and nanospheres (See Chapter 4) are the most common types of polymeric nanoparticles studied in terms of their skin permeation (Table 1.1). Polymeric vesicles [80] and dendritic core-multishell nanotransporters [81] have also been reported. Table 1.1 shows an overall view of the reports in the literature on skin permeation/penetration studies employing polymeric nanoparticles. All studies shown in the table are discussed in the following text. In general, polymeric nanoparticles are very stable due to their rigid matrix, and they are able to maintain their structures for long periods of time when topically applied [82, 11]. The contact of the drug with the skin surface is limited by the drug diffusion rate from the nanocarrier [83]. In fact, some reports have shown that polymeric nanoparticles can retard the permeation of encapsulated substances to the receptor compartment or to deep skin layers [9, 54, 84, 85] and increase the amount of drug retained in the stratum corneum in comparison to other skin layers [32, 86]. The amount of drug retained in deep skin layers might increase some time after application [9]. On comparing vesicular and matrical polymeric systems, very similar profiles for the drug penetration into the stratum corneum were observed [33]. Interestingly, an increase in the permeation of active substances through the skin and/or penetration into a specific skin layer following encapsulation in polymeric nanoparticles has also been reported. This has been attributed to the direct contact of the nanoparticles with the stratum corneum due to their high total surface area [31], high thermodynamic activity due to their nanometer scale structure [31, 37], the possibility for their deposition into the hair follicles [31], the surface characteristics [87, 88, 89] and the affinity of the nanoparticle components for certain skin layers [88]. The passive targeting of polymeric nanoparticles to the hair follicles has been reported [11, 83, 90] and the ideal particle size for penetration into the hair follicles was estimated at between 320 and 750 nm [91], although smaller particles also show affinity for the hair follicles [26, 61]. The storage reservoir capacity of the hair follicles is 10 times higher than the storage reservoir capacity of the stratum corneum [23]. Polymeric particles of 320 nm (polydispersion index = 0.06) can be retained in the hair follicles for up to 10 days, being expelled due to sebum production without reaching living cells [11]. Skin furrows may also be the target of polymeric nanoparticles on the skin surface [80, 90, 93].
Poly( -caprolactone), Labrafac hydrophile WL 1219
Poly n-butylcyanoacrylate, benzyl benzoate Polystyrene
Poly( -caprolactone)
Poly(lactic-co-glycolic acid) (PLGA), polystyrene
Poly( -caprolactone) Poly(lactideco-glycolide)
Poly( -caprolactone)
Poly(vinyl alcohol), fatty acids
Poly( -caprolactone)-block-poly(ethylene glycol)
Nanocapsules
Nanoparticles
Nanocapsules
Nanoparticles
Nanocapsules
Nanospheres
Nanocapsules
Nanoparticles
Nanoparticles
Main Components
Nanocapsules
Type*
Minoxidil
Benzophenone-3
Chlorhexidine
Trimethylpsoralen
Octyl methoxycinnamate
-
Octyl methoxycinnamate
-
Indomethacin
Clorhexidine
Active Ingredient
In vitro, full-thickness guinea pig, hairless guinea pig, hairless mouse skin,
In vitro, full-thickness pig skin, Franz diffusion cell,
In vitro, full-thickness and stripped hairless rat skin, Franz diffusion cell
In vitro, full-thickness human skin, Franz diffusion cell
In vitro, full-thickness pig skin, Franz diffusion cell
In vitro, epidermal sheets from mouse skin, confocal laser microscopy
In vitro, full-thickness porcine skin, Franz diffusion cell, confocal microscopy
In vitro, full-thickness porcine skin, Franz diffusion cell, confocal microscopy
In vitro, rat skin, Franz diffusion cell, confocal microscopy
In vitro, full-thickness porcine skin, diffusion cell
Study Type
Table 1.1. Overview of permeation and/or penetration studies applying nanoparticles based on polymeric compounds.
[12]
[85]
[82]
[84]
[32]
[97]
[31]
[90]
[87]
[89]
Reference
1 Transport of Substances and Nanoparticles across the Skin and in Vitro Models 13
Latex, polystyrene
Poly(lactideco-glycolide) Poly(lactideco-glycolide)
Nanoparticles
Nanoparticles
Nanoparticles
Nanocapsules
Poly( -caprolactone) and octyl salicylate
Poly( -caprolactone), triglycerides
Poly(lactic-co-glycolic acid)
Nanoparticles
Nanocapsules and nanospheres
Poly(lactide- co -glycolide)
Nanoparticles
Table 1.1 (continued)
In vitro, full-thickness pig skin, laser scanning microscopy In vivo, human skin, tape stripping technique
-
Hinokitiol
In vitro, hairless full-thickness mouse skin, Franz diffusion-cells, confocal microscopy
In vitro, full-thickness and heatseparated human skin, Franz diffusion cell
In vivo, human skin, tape stripping technique, laser scanning microscopy
-
Nimesulide
In vitro, full-thickness human skin, fluorescence microscopy and laser scan microscopy
In vitro, full-thickness human skin, multiphoton microscopy and confocal laser scanning microscopy
In vitro, full-thickness human skin, Saarbrücken penetration model In vitro, heat-separated epidermis, Franz diffusion cell, multiphoton fluorescence imaging
-
-
Flufenamic acid
Franz diffusion cell, confocal microscopy
[37]
[33]
[11]
[23]
[96]
[94]
[9]
14 R.V. Contri et al.
-
Polystyrene and hexadecane
Microcapsules
Poly( -caprolactone)
Nanocapsules
* cited according to the original reference
Poly(lactide)
Nanoparticles
Dendritic core-multishell (CMS) nanotransporters and solid lipid nanoparticles (SLN)
Polyglycerolamine, 1-(2,5dioxopyrrolidin-1-yl)-18-methoxypoly(ethylene glycol)yl octadecanedioate (CMS) and Compritol 888 ATO (SLN)
-
Poly( -caprolactone)–poly(ethylene glycol)-poly( -caprolactone) co-polymer
Polymerosomes
Octylmethoxycinnamate
Octylmethoxycinnamate
In vitro, full-thickness pig skin, Franz diffusion cell
[54]
[86]
[81] In vitro, full-thickness pig skin, Franz diffusion cells, normal and fluorescence light microscopy In vitro, full-thickness pig skin, Franz diffusion cell
[83]
[80]
[92]
[93]
[88]
[98]
In vitro, dermatomed porcine skin, confocal microscopy
In vitro, heat-separated epidermis, Franz diffusion cells, confocal laser microscopy
In vitro, full-thickness porcine skin, Franz diffusion cell, confocal microscopy
Polystyrene and poly-(2 hydroxyethyl methacrylate
Nanoparticles
-
Polystyrene and poly(methyl methacrylate)
Nanoparticles
In vitro, full-thickness pig skin, Franz diffusion cell In vitro, dermatomed porcine skin, Franz diffusion cells, confocal microscopy
Clobetasol propionate
Chitosan and lecithin
Nanoparticles
In vitro, dermatomed pig skin, Franz diffusion cells, scanning and laser electron microscopy
-
-
Dendritic core-multishell (CMS) nanotransporters and solid lipid nanoparticles (SLN)
Polyglycerolamine, 1-(2,5dioxopyrrolidin-1-yl)-18-methoxypoly(ethylene glycol)yl octadecanedioate (CMS) and Compritol 888 ATO (SLN)
Table 1.1 (continued)
1 Transport of Substances and Nanoparticles across the Skin and in Vitro Models 15
16
R.V. Contri et al.
The penetration of polymeric nanoparticles into skin layers does not commonly occur under normal skin conditions [37, 83, 90; 94], probably due to the small size of the intercellular space [95]. However, the penetration of poly(nbutylcyanoacrylate) nanocapsules (188 nm) into the epidermis and dermis of full-thickness rat skin has been observed by confocal laser microscopy after cryosectioning of the skin, which also increased the permeation of the encapsulated substance [87]. The type of skin used could have influenced this result since rat skin is more permeable than human skin, as previously mentioned (section 1.3.3.2.2). Hydrophilic vesicles (122 nm) composed of poly(caprolactone)–poly(ethylene glycol)– poly(caprolactone) co-polymer were able to penetrate the epidermis using human epidermis sheets [80]. Accumulation of the vesicles was observed by confocal microscopy in the epidermal layers. The particle sizes mentioned are mean values and the presence of smaller particles due to the polydispersity should be taken into account. In fact, smaller polymeric particles (close to 40 nm) penetrated the full-thickness skin of human [96] and rodent [12] sources, predominantly via the follicular route. Permeation enhancers such as Plurol® (polyglyceryl-6 dioleate), Transcutol® (diethyleneglycol monoethyl ether) and Labrasol® (PEG-8 caprylic/capric glycerides) can promote the nanoparticle penetration across the stratum corneum of mouse skin due to the disruption of the ordered lipid structure [97]. 1.4.1.2 Lipid Systems Nanoparticles based on lipid systems are the most common type of nanoparticles studied for topical application. Solid lipid nanoparticles, nanoemulsions and nanostructured lipid carriers are the main types of matrix nanoparticles while liposomes are the main type of vesicular particles evaluated in permeation studies. Other types cited in the literature include niosomes [99], cubosomes [100, 101], bicellar systems [102], vesicles [103, 104] and nanodispersions [105]. As in the previous table, Table 1.2 provides details of the studies which are discussed herein, regarding the skin permeation/penetration studies performed with lipid nanoparticles. In contrast to the polymeric nanoparticles, they are less stable when applied on the skin surface. After topical application, solid lipid nanoparticles were observed to lose their shape and melt after a period of 2 h [98] due to the interaction between the particle components and skin lipids [81, 98]. This occurrence can reduce the skin barrier function and occlude the skin surface [106, 107], favoring the skin penetration process. Thus, an increase in the permeation to the receptor medium [99, 108, 109, 110, 111, 112, 113, 114] or in the penetration into the skin layers [104, 105, 115, 116, 117, 118, 119] of the active substance is commonly observed when it is encapsulated in different lipid-based nanoparticles, either matrical or vesicular. The lipid components [98, 100, 120] or the surfactant components of nanoparticles can interact with the skin [109, 121]. Moreover, the addition of other components such as ethanol [110, 122] and magnetic nanoparticles [123] to lipid nanoparticles can even enhance the permeation. Besides the enhancement of the permeation/penetration due to encapsulation of substances in lipid nanoparticles, the opposite result has also been reported. This can probably be attributed to an increase in the rigidity of the nanoparticles due to
Tristearin glyceride, stearic acid
Sucrose laurate ester, octaoxyethylene laurate ester
Solid lipid nanoparticles
Elastic and rigid vesicles
Indomethacin
-
Cyclosporin A Indomethacin
Compritol®, Precirol®, Oleic acid, Miglyol® 812
Monoolein, oleic acid
Compritol® 888 ATO, Miglyol®
Solid lipid nanoparticles, nanostructured lipid nanocarrier and nanoemulsion
Hexagonal phase nanodispersion
Nanostructured lipid car-
Octyl methoxycinnamate
Ketorolac
Triptolide
Monooleine
Cubosomes
Octyl methoxycinnamate
Cetyl palmitate, Tego Care 450®
Solid lipid nanoparticles
Nanoemulsion
Vitamin A
Compritol® 888 ATO
Solid lipid nanoparticles Oxybenzone
Vitamin A or E
Lipid nanospheres
Active Ingredient
Main Components
Lecinol, soybean oil
Type*
In vitro, human skin, Franz-type diffusion
In vitro, full-thickness porcine skin, Franz diffusion cell
In vitro, full-thickness pig skin, Franz diffusion cell, fluorescence microscopy
In vitro, human epidermal membranes, Franz diffusion cell In vivo, human skin, tape stripping technique
In vivo, Human skin, tape-stripping technique
In vivo, human skin, tape stripping technique, infrared spectroscopy
In vitro, full-thickness rat skin, Franz diffusion cell
In vivo, human skin, tape stripping technique
In vitro, full-thickness pig skin, Franz diffusion cell
In vitro, full-thickness rat skin, Franz diffusion cell
Study Type
Table 1.2. Overview of permeation and/or penetration studies applying nanoparticles based on lipid compounds.
[59]
[105]
[117]
[100]
[132]
[103]
[112]
[127]
[10]
[121]
Reference
1 Transport of Substances and Nanoparticles across the Skin and in Vitro Models 17
Vitamin A palmitate
Compritol® 888 ATO
Solid lipid nanoparticle
Artemisia arborescens essential oil
Triglycerides
Compritol® 888 ATO
Nanoemulsion
Stearic acid
Soya phosphatidylcholine,
Lipid nanoparticles
Ethanolic liposomes
Solid lipid nanoparticles
Nimesulide
Soybean oil
Nanoemulsion
Melatonin
Hinokitiol
Nabumetone
Compritol 888 ATO, Miglyol 812
Nanostructured lipid carriers
Ketorolac
Podophyllotoxin
Tripalmitin
Solid lipid nanoparticles
®
RU58841-myristate
Compritol®, Precirol®
Solid lipid nanoparticles
®
Triptolide
Tristearin glyceride, stearic acid
Solid lipid nanoparticles
In vitro, dermatomed human skin, Franz diffusion cell, confocal microscopy and FT-IR analysis.
In vitro, full-thickness hairless mouse skin, Franz diffusion cell
In vitro, full-thickness pig skin, Franz diffusion cell
In vitro, full-thickness pig skin, Franz diffusion cell
In vitro, full-thickness rat skin, Franz diffusion cell
In vitro, epidermal human membranes, Franz-type diffusion cell
In vitro, full-thickness human skin, Keshary Chien cells
In vitro, full-thickness porcine skin, Franz diffusion cell
In vitro, reconstructed epidermis (SkinEthic), Franz diffusion cell, Fluorescence microscopy
In vitro, full-thickness rat skin, Franz diffusion cell
cell Ascorbyl palmitate
In vitro, full-thickness human skin, Franz diffusion cell
®
812
®
Witepsol E85, Mygliol 812
Solid lipid nanoparticles, nanostructured lipid carriers
riers
Table 1.2 (continued)
[110]
[113]
[129]
[33]
[109]
[126]
[115]
[116]
[134]
[108]
[125]
18 R.V. Contri et al.
Miconazole nitrate -
Compritol® 888 ATO
Soybean phosphatidylcholine
Solid lipid nanoparticle
Ethosomes
Tretinoin
Ketoprofen and naproxen
Compritol® 888 ATO, Miglyol® 812
Lipid nanoparticles
Fruit kernel fats
Corticosterone
Medium-chain triglycerides, tripalmitate, cholesteryl myristate, cholesteryl nonanoate, glycerol monooleate
Lipid nanoparticles
Solid lipid nanoparticles
In vitro, human epidermis, Franz diffusion cell, spectrofluorometry
-
1,2-Dipalmitoyl-sn-glycero-3phosphocholine, 1,2-dioleoylsn-glycero-3-phosphocholine,
Lipossomes
In vitro, human skin scar, confocal microscopy
In vitro, full-thickness human skin, Franz diffusion cell
In vitro, full-thickness rat skin, Franz diffusion cell
In vitro, human epidermal membranes, Franz diffusion cell
In vitro, human heat-separated epidermis trypsin isolated stratum corneum, Franz diffusion cell, Fluorescence light microscopy
In vitro, full-thickness human skin, Franz diffusion cells, confocal microscopy
-
Sabowax CP®, Miglyol® 821
Nanostructured lipid carriers
In vitro, human SC and epidermis, Franz diffusion cell
Ammonium glycyrrhizinate
In vitro, dermatomed human skin, Franz diffusion cell
In vitro, full-thickness rat skin, Franz diffusion cell
In vitro, dermatomed human skin, Franz diffusion cell, confocal microscopy and FT-IR analysis
, -Hexadecyl-bis-(1-aza-18crown-6) (Bolasurfactant)
Tetracaine
Isotretinoin
Precirol® ATO 5
Hexadecane
Methotrexate
Soya phosphatidylcholine,
Niossomes
Nanoemulsions
Solid lipid nanoparticles
Ethanolic liposomes
Table 1.2 (continued)
[122]
[118]
[124]
[128]
[120]
[135]
[107]
[99]
[133]
[119]
[111]
1 Transport of Substances and Nanoparticles across the Skin and in Vitro Models 19
* cited according to the original reference
Coenzyme Q10
Precifac® ATO, Miglyol® 812
Nanostructured lipid carrier and nanoemulsion
In vitro, human heat-separated epidermis, Franz diffusion cells
In vitro, dermatomed pig skin, Franz diffusion cells.
Diclofenac diethylamine
Dimyristoyl phosphatidylcholine, dipalmitoyl phosphatidylcholine and dihexanoyl phosphatidylcholine
In vitro, hairless mice skin, Franz diffusion cells
In vitro, mouse skin, Franz diffusion cell
In vitro, mouse skin, diffusion cell
In vitro, porcine epidermal membrane, Franz diffusion cell
Berberis koreana extract
Oregonin
Minoxidil
Econazole nitrate
Bicellar systems
Monoolein
Soybean phosphatidylcholine
Elastic liposomes
Cubosomes
Distearyldimethylammonium chloride
Precirol® ATO 5
Cationic vesicles
Solid lipid nanoparticles
Table 1.2 (continued)
[106]
[102]
[101]
[114]
[104]
[131]
20 R.V. Contri et al.
1 Transport of Substances and Nanoparticles across the Skin and in Vitro Models
21
the type of lipid used as the raw material in the matrical particles [10, 124, 125] and the association of the drug with the vesicular particles [102]. Interactions between the active substance and the nanoparticle components [59, 126], film forming due to water evaporation [127] and a possible significant adherence to the stratum corneum observed for matrical lipid systems [128, 129] could reduce the release rate and the permeation of encapsulated substances. The particle size seems to play an important role in the permeation of the encapsulated active ingredient. Smaller particles seem to enhance the permeation to a greater extent than larger particles [130, 131, 132]. However, this conclusion is contradictory since it has already been shown that for the same kind of nanoemulsion there was no influence of the emulsion droplet size on the skin penetration of the encapsulated substance when applied to dermatomed human skin [133]. In comparison to nanocapsules, the nanoemulsions present a higher capacity to penetrate and/or permeate the skin, probably due to their flexibility [132] and lack of polymer which has an affinity with the stratum corneum [33]. As in the case of polymeric nanoparticles, an accumulation of lipid nanoparticles in the hair follicles can occur. Solid lipid nanoparticles of around 200 nm were detected in the hair follicles after 24 h of topical application [134]. The penetration of intact particles is not common, since the lipid nanoparticles tend to lose their shape when topically applied [98]. Depending on the nature and size of the particle, it seems possible for the vesicular lipid nanoparticles to penetrate/permeate the skin. The permeation of liposomes of 50, 100 and 200 nm through human epidermal membranes has been demonstrated, although there was a continuous increase in the average particle size in the receptor compartment, probably due to the particle agglomeration [135]. The rigidity of liposomes seems to be related with the skin permeation capacity, especially for larger vesicles [135]. Also, the penetration of elastic vesicles obtained from sucrose laurate ester and octaoxyethylene laurate ester into the deeper stratum corneum layers (close to the junction with the viable epidermis) was observed by means of the human tape stripping technique [103]. It was demonstrated that rigid vesicles, without octaoxyethylene laurate ester, could not penetrate as deeply into the stratum corneum as the elastic vesicles.
1.4.2 Nanoparticles Based on Inorganic Compounds Inorganic nanoparticles are considered nanosized materials. Nanosized materials are built from a top-down approach the nanoparticles being constructed from larger entities. According to their composition and physicochemical properties, these particles have been studied in the biomedical field as nanocarrier systems for targeting and controlling the delivery of active ingredients as well as an imaging device for diagnostic techniques [79]. Nanosized particles of zinc oxide and titanium dioxide, other metallic compounds and fullerenes are the main particles used for these purposes. Considering the cutaneous administration route, inorganic materials are used in a nanostructure form to increase the transport of the active ingredient through the skin, to increase its permanence in the skin or even to improve the cosmetic aspect
22
R.V. Contri et al.
[79, 136]. Regardless of the desired application (transdermal or topical), the transport characteristics of the nanocarrier are related to its dimensions (hydrodynamic diameter and shape - spherical, elliptical, nail-shaped) [78, 136]. Table 1.3 provides an overview of the methodologies used in skin permeation studies which are discussed in this topic. These studies investigated the penetration or permeation capacity and the possible penetration or permeation pathway of nanoparticles based on inorganic compounds proposed for cutaneous application as nanocosmetics or nanomedicines. As can be observed in Table 1.3 there are still few reports in the literature concerning these inorganic nanoparticles compared to organic nanoparticles. These studies have been carried out since 2004. 1.4.2.1 Titanium Dioxide or Zinc Oxide Nanoparticles Titanium dioxide (TiO2) and zinc oxide (ZnO)-based nanoparticles have been studied with a view to their inclusion in sunscreen preparations to reduce the visual opaque effect after the cutaneous application of such preparations compared to the use of bulk forms of these materials (see Chapter 17) [136]. As TiO2 or ZnO are intended to act as physical sunscreens, these materials have to be available on the skin surface to scatter the light. Therefore, the ZnO or TiO2 nanoparticles should not permeate rapidly through the skin. Thus, studies on the permeation capacity, penetration and/or permeation pathways and the location of these particles after topical application have been frequently performed. Several in vitro permeation studies carried out with ZnO or TiO2 nanoparticles showed, despite the size, no permeation of the particles through the skin. According to these results, the particles penetrate the stratum corneum and remain retained in the outermost corneocyte layers [38, 41, 138, 140, 142]. Permeation of the solubilized zinc form seems to be reduced in these studies. Thus, nanoparticle formation is suggested to avoid the presence of zinc in the solubilized form and consequently its permeation [138]. However, a size-dependent permeation was observed when TiO2 nanoparticles were administered in vivo for a long period of time [142]. Particles of 4 nm reached deeper epidermal layers compared to particles of 60 nm, but they did not reach the viable epidermis and dermis. Additionally, these particles were able to permeate through hairless mouse skin in vivo and reach several tissues [142]. However, it is important to consider the source of skin used. As reported in the section 1.3.3, mouse skin seems to be much more permeable than human skin. The main pathways proposed for the penetration of ZnO and TiO2-based nanoparticles are the intercellular route and the hair-follicles [41, 136, 137, 139, 140]. Although one report considered only the passage via the intercellular space as the penetration route for such particles [137], the hair-follicle seems to be an important pathway for particle transport [41, 139]. Another study found 400 μm particles deep in the follicle [139]. Nevertheless, TiO2-based nanoparticles were not found in vital tissue [41, 139]. More details on the use of nanosized materials as sunscreens are given and discussed in Chapter 17.
TiO2
TiO2
TiO2
Titanium dioxide (TiO2) nanoparticles
TiO2 nanoparticles
Rutile titanium dioxide (TiO2) nanoparticles
Gold
Silver
C60
C60
Gold nanoparticles
Silver nanoparticles
Fullerenes
Fullerenes
Fe2O3 or Fe
ZnO
ZnO nanoparticles
Iron oxide (Fe2O3) and iron (Fe) nanoparticles
TiO2
TiO2
TiO2 nanoparticles
ZnO
ZnO nanoparticles
TiO2 nanoparticles
TiO2
Main component
TiO2 nanoparticles
Type
Tape stripping in vivo, pig skin, In vitro, stratum corneum isolated from pig skin. Flow-through diffusion cell. High Performance/Pressure Liquid Chromatography.
In vitro, dermatomed porcine skin. Flow-through diffusion cell. CLSM.
In vitro, intact and damaged human skin. Franz-diffusion cell. Electro thermal atomic absorption spectroscopy (ETAAS). TEM
In vitro, rat skin. Franz-diffusion cell. UV-Vis and X-ray spectroscopy (EDS) and TEM.
In vitro, human full-thickness skin. Vertical cell. ICP-optical emission spectrometry
[145]
[39]
[144]
[40]
[143]
[41]
[142]
In vitro, porcine full-thickness skin. Modified Franz equipment. Flame atomic absorption spectrometry. TEM. In vitro, intact, stripped, and hair-removed skin of Yucatan micropigs. Franzdiffusion cell. ICP-MS.
[141]
[38]
[140].
In vitro, porcine skin, healthy human skin, human skin grafted. TEM and SEM
In vitro, human skin. SEM with X-ray photoelectron spectroscopy. Zinc oxide photoluminescence In vivo
In vitro, healthy and psoriatic skin condition. Particle induced X-ray emission.
[139]
[138]
In vitro, human heat-separated epidermis membranes. Franz-diffusion cell. Inductively coupled plasma-mass spectrometry (ICP-MS). TEM. In vitro, porcine and human skin. Autoradiography.
[137]
Reference
In vivo, pig skin. Ion beam analysis methods.
Study type
Table 1.3 Overview of the methodologies used in permeation and/or penetration studies applying nanoparticles based on inorganic compounds.
1 Transport of Substances and Nanoparticles across the Skin and in Vitro Models 23
24
R.V. Contri et al.
1.4.2.2 Metallic Nanoparticles Gold, silver, iron and iron oxide nanoparticles have attracted attention in different biomedical segments [78]. Gold nanoparticles [146, 147] as well as iron [148, 149] and iron oxide [148, 150] nanoparticles are interesting photo-thermal agents in hyperthermia and as a tumor imaging device. Silver nanoparticles are widely used in topical formulations due to their antiseptic effect [151]. As nanosized structures, these particles could cross the skin resulting in systemic absorption. Thus, some studies have been carried out, especially in the past 10 years, to determine the penetration capacity of these systems. Gold nanoparticles (mean sizes of 15, 102 and 198 nm) have been shown to permeate through and accumulate in rat skin, and the permeation was found to be size-dependent. Smaller particles demonstrated faster permeation. Additionally, on increasing the particle size, the lag time to particle penetration increases. These findings are related to factors such as the partitioning kinetics, volume fraction in the receiver phase and membrane volume [40]. An increase in the particle diameter increased the amount of metal that permeated through the skin, which could be related to the higher metal loading of the larger particles [40]. An in vitro study demonstrated the capacity of metallic nanoparticles, such as iron and iron oxide nanoparticles, with mean size smaller than 10 nm, to penetrate the skin [143]. This penetration occurs through the hair follicle orifices and the stratum corneum lipid matrix. Although such particles have occasionally been found in viable epidermis, spectroscopy analysis has suggested that these metallic nanoparticles are unable to permeate the skin. The permeation observed was attributed to the particles having extremely small dimensions [143]. In the same way, silver nanoparticles (25 nm) appear to have a low absorption through skin [144]. Silver particles seem to penetrate the stratum corneum reaching, less often, the uppermost layers of the viable epidermis. Since particles with diameters ranging between 7 and 20 nm were mostly found in the infundibulum of the hair follicle and below, the dimensions of nanoparticles can be considered an important parameter in terms of their skin permeation. The low absorption of silver observed in some studies may suggest particle dissolution allowing elemental silver to diffuse through the skin [144]. Therefore, in general, in the case of metallic nanoparticles the penetration into and permeation through the skin is directly related to their mean particle size, smaller particles permeating deeper. This permeation seems to occur mainly through hair orifices and the stratum corneum lipid matrix. 1.4.2.3 Carbon-Based Nanoparticles Carbon nanotubes and fullerenes are carbon-based nanoparticles. These particles are formed of the third most stable form of carbon and differ according their shape [78]. Carbon nanotubes are multi-walled or single-walled hollow tubes while fullerenes are spherical, both with extremely small mean diameters (
