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

JOURNAL OF COSMETIC SCIENCE 362 therapy nevertheless, careful reading of the three chapters in Part IV indicates real- ized and potential cosmetic applications along with important limitations. Part V, “Special Delivery Routes,” be- gins with a chapter by Wiechers describing studies of nicotinate delivery from a sham- poo, evaluating such variables as contact time, drug concentration, and body site. The results suggest that highly permeable molecules could be delivered from a rinse- off product, though with much greater dif- fi culty than from a leave-on product. The next two chapters, Chapter 24 by Grams et al. and Chapter 25 by Cross, describe the current state of knowledge of follicular delivery and methods for its mea- surement. Not only is this important for situations where the target is within the follicles (e.g., acne) but a knowledge of the relative contribution of the various path- ways, including the follicles, is fundamen- tal to our understanding of the permeation process. Most of what we know today about the importance of the follicular route comes from in vitro experiments, which neglect the continuous outward sebum fl ow. Some exciting experiments utilizing nano- and microparticles have been performed, but a great deal of work remains to be done on formulating to target the follicles. The book’s fi nal part, Part VI, is entitled “Future Perspectives.” It begins with a chapter by Schneider on legal aspects of de- livery systems. After providing a list of questions to answer when introducing a new delivery system, the author goes on to describe several test methods for irritation and sensitization and several classes of ac- tives, before getting into a discussion of de- livery systems that includes the importance of safety testing and making proper claims. This is followed by a brief discussion of the regulatory status of nanosized particles. In Chapter 27, Newman discusses as- pects of marketing skin care products, noting that the delivery systems must do more than controlling the release and in- creasing the performance of actives the benefi ts to consumers must be evident. Though we often focus on the properties of the active, delivery systems may add their own benefi ts—for example, in providing miniaturization. In such cases, the delivery system may be more important than the nominal active in producing a benefi cial re- sult. Newman recommends considering the active and delivery system as a unit rather than focusing marketing efforts on the “gee-whiz” value of the delivery system. The fi nal chapter is an overview, “Clini- cal Relevance of Topical Delivery Systems for Active Cosmetic Ingredients” by Thong and Maibach. The focus of this chapter does not match the title, nor does it pro- vide much in the way of a perspective for the future. The authors expound on the importance of in vitro skin penetration studies and the need for better correlation with in vivo data. Table 28.1 lists ten steps in the in vivo percutaneous absorption pro- cess. Table 28.2 lists several penetration- enhancement techniques and Table 28.2 is a non-critical listing of penetration- enhancing chemicals. This book is a comprehensive summary of the current state of the art, although two areas that receive insuffi cient attention are penetration enhancers and tape/patch de- livery systems. As is common with multi- authored volumes, there is some overlap in coverage, but the amount is minimal and does not detract from the book’s message. This book is highly recommended for scientist working on skin care products and OTC drugs. It should be part of the library of every company involved in these areas. —JOEL L. ZATZ—Rutgers University.