Biomaterids16 (1995)1117-1118 0 1995 Elsevier Science Limited

Printed in Great Britain. All rights reserved 014%9612/95/$10.00

BOOKREVIEWS

Biomedical Polymers-Designed to Degrade Systems

Shalaby W. Shalaby Hanser Publishers, Munich, 1994, pp. 263

This book comprises nine chapters written by different authors dealing with .the theme of degradable polymers intended for biomedical applications. The editor has posed the question in the preface ‘can one, syntheti- cally or biologically, design to produce chain molecules with controlled degradation profiles?‘. The book purports to provide the answer by dealing with a range of polymeric materials: poly(orthoester)s, polyan- hydrides, poly(ester-amide)s, polyphosphazenes, bacterial polyesters and variability in synthesis, polysaccharides and chemically modified proteins and polysaccharides.

The first chapter provides a review of the body of work on synthetic absorbable polymers and covers lactone-based polyeslers and oxalate-based polymers. This is a useful survey supported by a bibliography of literature and patents. It makes reference to the worldwide literature on the subjects and would be considered valuable to anyone wanting to obtain an up-to-date understand!ing. It is helped by a short discus- sion of some of the issues and trends in this field. The authors caution against drawing potentially damaging conclusions on clinical effectiveness and safety, and point the way to further studies. In view of the question put at the (outset by the editor (one of the authors of this chapter), it would have been useful to have an overall discussion at the conclusion of the chapter as to where we are in this field and whether we have begun to answer his question.

The book then turns to the important area of poly(orthoester)s, produced in response to the need for degradation products which would be benign regard- ing toxic reactions and would make it possible to control degradation and mechanical properties. Surface erosion is the hallmark of these polymer systems. The chapter deals with the chemistry and applications of different groups of polymers. This is followed by a chapter on polyanhydrides as drug carriers, which deals with synthesis, polymer structures and applications. Since the main part of the chapter is concerned with the applications, there is not much detail relating to synthesis and structure which would assist the future researcher to decide on directions for investigation. These materials are useful for surface erosion degradation and consequent release of drugs, and the relation between surface erosion and monomer compositio:n has been studied. Since it is only the drug in the surface layer which is released, that in the bulk of the polymer is afforded protection

from the environment. This chapter gives a very useful review of current progress and concludes with a look at toxicity aspects.

Chapter 4 covers bioabsorbable poly(ester-amide)s and has a comprehensive survey of synthetic methods. Much of the research has centred on the fibre-forming properties of the materials, since polyesters and polyamides are the main polymers in this class of materials. The materials are still in the developmental stage but some in vivo studies are reported which appear to show acceptable degradation and tissue reactions with no toxicity demonstrated. The next chapter considers poly(amino acid)s and concentrates on work done since 1985. The early work did not produce useful synthetic materials and they were considered, at best, protein analogues for laboratory study. They are expensive, hard to dissolve and have undesirable features in other regards. Interest as sutures led to a further examination, and the replace- ment of the peptide link by ester, carbonate or urethane has reduced the cost. Work on preparative methods for precisely arranged sequential poly(amino acid)s has helped to show the range of mechanical and related properties that can be achieved. Adhesives, ion-selective membranes, miniature motors and drug delivery systems are included among the potential uses. One of the most interesting aspects of this work is the development of polymers which involve bonds other than peptides, the so-called pseudopeptides. Backbone modification offers a whole range of materi- als applications not possible with the poly(amino acid)s themselves. This chapter gives a very interesting and timely review of the subject.

Polyphosphazenes are dealt with next and after a very brief introduction to synthesis and properties the biomedical applications are covered. Chapter 7 moves on to a consideration of polyesters obtained from microorganisms. Poly(hydroxybutyrate) is a typical and well-studied example of this type. As an introduc- tion to the subject and a review of the methods of bacterial synthesis, this chapter is useful. It does not refer to any applications of the materials. Following a similar theme the next chapter reviews bacterial polysaccharides, chitosan, pullulan, elsinian and levan, giving synthesis and applications for each one. These polymers all show good film-forming capability. As well as biomedical uses, these polymers are of value in the food and agrochemical industries.

The final chapter surveys methods for chemical

1117 Biomaterials 1995, Vol. 16 No. 14

1118 Book reviews

modification of proteins and polysaccharides and the effect this has on enzyme-catalysed degradation. Synthesis of each one is first dealt with and then the degradation aspects are given. Comprehensive coverage of the chemical methods for modification is given and then enzyme processes are introduced. There is scope in this chapter for the exercise of lateral thinking to extend the chemistry to other systems.

This book does make a serious attempt to answer the

editor’s question about influencing degradation behaviour. There is much useful and usable informa- tion and it is interesting not only to the biomaterials scientist, but also to those interested in polymer processes and applications, and for the development of our understanding of polymer structure-property relationships.

G. W. Hastings

Biomechanics and Cells

F. Lyall and A.J. El Haj Cambridge University Press, Cambridge, UK, 1994, pp. 275, ISBN 0521454549, f45.00

This book is a recent addition to the series of seminars from the Society of Experimental Biology. In this seminar the topic addressed was the response of cells to mechanical stimuli. The book is presented in two parts, the first considers the response of cells in soft tissues and the second that in hard tissues. Within each section the chapters reflect the contributions of each author. There is no doubt that this book should be of interest to research workers in both academia and industry working on the effects of mechanical environment on cell activity.

In the soft tissue section the contributors consider signal transduction pathways in vascular cells, the effects of pressure overload on vascular smooth muscle cells and the effects of flow on the release of vasoactive substances. These contributions are followed by a slightly more diverse series on the effects of stretch and overload on gene expression in striated muscle, sensitivity in stretch receptor neurones, mechanical interactions with plant cells, mechanical tensing of cells and chromosome arrangement, and alterations in gene expression induced by low-frequency, low- intensity electromagnetic fields.

The second section is said to relate to hard tissues and is largely concerned with bone cells but includes contributions on the effect of stretch on actin polymer- ization in fibroblasts of the periodontium and modula- tion of cartilage extracellular matrix turnover by pulsed electromagnetic fields. Chapters on bone cells include cellular modelling of mechanical interactions with the skeleton, regional differences in remodelling in tivo resulting from mechanical and hormonal

influences, mechanically sensitive cells in bone, mechanical stress and bone development, application of defined homogenous strains to cell cultures and the role of arachidonate in load transduction in bone cells.

In general, each chapter provides background information together with more recent data which should be of value to both established scientists and also more junior workers. As the book is a collection of individual contributions, the style and level of detail is somewhat variable between contributions. Neither of the two sections contained a general indication of the specific theme or objective of the two-part format.

The book would have a far greater impact if there had been an introductory chapter relating the overall objectives to the individual contributions. Also a general concluding chapter, to review common cellular responses and signal transduction pathways related to mechanical stimulation and highlighting recent advances and future research, would have assisted in maximizing the value of this text. The omission of these general chapters probably detracts from the potential value of the book to research students and those periph- eral to the field of cell biology.

Although this is really the proceedings of a seminar rather than a more conventional text, it would be a worthwhile purchase for scientists with specific or general interests in the response of cells to changes in physical environment.

Allen E. Goodship

Biomaterials 1995, Vol. 16 No. 14