JOURNAL OF COSMETIC SCIENCE 360 equipment that most R&D labs do not possess. Among the applications illustrated in this chapter are lipid and protein com- position in stratum corneum, the confor- mational order of lipids, and the effect of water exposure on a sunscreen-containing fi lm. Several color images are presented to provide a feel for the type of information that is available from the technique. Part II of the book, “Skin Delivery from Emulsions,” begins with a chapter by Wiechers and Watkinson that describes many formulation effects on skin delivery. The physicochemical properties favoring skin penetration are summarized and in- clude such items as favorable octanol–water partition coeffi cient, low molecular weight, lack of molecular charge, and low melting point. The authors describe a detailed study of four pharmaceutical actives in fi ve for- mulations and analyze the results in terms of transdermal (through the skin) and der- mal (in the skin) absorption. They conclude that formulation effects are relatively mi- nor, while the properties of the active are of greatest importance in determining skin delivery. In contrast to this conclusion, Chapter 6, by Wiechers, shows that formu- lation optimization can improve product effi ciency and reduce the amount of an ac- tive needed to provide the desired effect. He describes a technique (formulating for effi ciency) designed to maximize thermo- dynamic activity of an active for maximum delivery. Chapter 7, by Wiechers et al., describes a study of the effect of dimethyl isosorbide and diethylene glycol monoethyl ether on skin penetration by hydroquinone and oc- tadecenedioic acid. The result (a relative lack of overall effect) illustrates how a given additive can infl uence the delivery process in opposite ways. In Chapter 8, Wiechers et al. explore the effect of several emulsifi er systems on the effectiveness of certain moisturizer compo- sitions and the skin delivery of two actives, octadecenedioic acid (lipophilic) and propagermanium (hydrophilic). Formula- tions containing emulsifi ers capable of forming liquid crystals outperformed cor- responding formulations whose emulsifi ers lacked this capability in clinical studies of moisturizer effectiveness. In vitro studies also demonstrated that liquid crystal for- mation led to increased delivery of the ac- tives. The ability of liquid crystal-forming emulsifi ers to improve emulsion stability has been known for some time this study gives additional reasons for utilizing liquid crystals in emulsion systems. In view of the importance of liquid crys- tals in cosmetic systems, Suzuki’s review of liquid crystalline emulsions (Chapter 9) is a welcome addition to the book. Sections of this chapter explore self-assembly of am- phiphilic molecules and the types of struc- ture they form, their characterization, and methods of detection. A detailed descrip- tion of the formation of fi ne three-phase emulsions is provided. Other systems that receive detailed treatment are an emulsion containing ceramide substitutes, clear gel- like emulsions, and a lamellar liquid crys- tal gel. Cosmetic applications of the various systems are also described. The relationship between emulsion droplet size and skin delivery is probed by Izquierdo in Chapter 10. A thorough lit- erature review leads to the conclusion that there is little evidence in support of a par- ticle size effect. In most cases reported in the literature, formulations varied in com- position as well as particle size, making it diffi cult to come to a defi nitive conclusion. The author refers to his own work on tetra- caine formulations, which showed a lack of infl uence of emulsion particle size on skin penetration. I should add that in our labo- ratory, we processed a sunscreen formula- tion using different techniques that resulted in two very different emulsion droplet sizes. Delivery to the skin of the dissolved sunscreen agent was the same from both variations, illustrating the lack of effect of droplet size.

BOOK REVIEWS 361 New techniques for characterizing and studying delivery systems are always wel- come. Chapter 11, by Fairhurst and Dukhin, describes the application of acoustic atten- uation spectroscopy to the stability and structure of semisolids. The technique uti- lizes a newly introduced instrument to study semisolid characteristics without re- quiring dilution or other preparative steps. The chapter provides preliminary results and suggests the value of additional inves- tigation. Part III deals with various encapsulation techniques. In Chapter 12, Honeywell- Nguyen and Bouwstra differentiate rigid (traditional) vesicles, such as liposomes, from elastic vesicles, such as Transfer- somes®, which consist of phospholipids and an edge activator, usually sodium cholate. Elastic vesicles are more effective than rigid vesicles as carriers, provided that the active is encapsulated within the vesicle. They enter the stratum corneum rapidly and pen- etrate into its inner areas. Some of the same types of delivery sys- tems are discussed by Blume in Chapter 15, who adds ethanol-containing vesicles (etho- somes). Both chapters, taken together, pro- vide a comprehensive review of the area and indicate where further research is needed. Souto and Müller describe the applica- tion of nanoparticles to cosmetics in Chap- ter 13. It is now generally agreed that the “nano” designation should be limited to particles no more than 100 nm in diameter. The authors describe the structure and preparation of various solid–liquid nano- particles (SLN) and nanostructured lipid carriers (NLC), give indications of their ap- plication, and describe several commercial applications. The principles of manufacture of micro- encapsulated actives are summarized in Chapter 14 by Poncelet. This chapter should be read in conjunction with Chap- ter 17 by Fairhurst and Loxley, who describe the melt-emulsify-chill (MEC) method of encapsulation and its applications in some detail. An example given in the latter chap- ter is of a remarkable increase in SPF by encapsulating and organic sunscreen. In Chapter 16, Grobler et al. describe pheroids, which are unique in that nitrous oxide is one of the components. Prelimi- nary studies of the effects of pheroids are described and an optimistic assessment of their potential in cosmetics is given. In Chapter 18, Nacht focuses on three polymeric entrapment systems with open structures (no surface membrane). These technologies are microsponge, polytrap, and polypore. Microsponge technology in particular has been successfully applied in commercial products to improve accep- tance of irritating actives without exces- sively compromising effi cacy. The fi nal chapter in Part III, Chapter 19, deals with an application of cyclodex- trins, stabilization of linoleic acid to oxida- tion. A 4:1 α–cyclodextrin:linoleic acid complex showed adequate stability over a 12-month period and suggests other ap- plications for labile lipophilic compounds in aqueous media. Part IV, entitled “Alternate Ways to En- hance Skin Delivery,” begins with an intro- duction to sonophoresis and iontophoresis by Fernandes that appears to be addressed primarily to skin care therapists. These methods are alternates in the sense that they go beyond chemical (i.e., formulation- based) means of increasing delivery. More details on electrophoresis appear in Chap- ter 21 by Han and Shim. The fi nal chapter in this part, by Benson and Caccetta, de- scribes electroporation, “the application of short high-voltage electrical pulses to the skin.” As the name implies, these pulses open temporary pores in the stratum cor- neum, which allows molecules to penetrate transdermally. While the technique has been shown to increase skin penetration of relatively small molecules, such as those of vitamin C, an exciting potential appli- cation is the delivery of proteins and pep- tides. Most applications will involve drug