Preface to the Second Edition

All natural systems depend on signal communication from sensing components, which leads to specific actions. In man-made artificial systems the development of suitable sensors has reached an impressive accomplishment and complexity, but sensors alone always require extra action and devices to reach goals like regulation. Chemoresponsive polymers combine sensing and action within the same material, without the need for external devices. This is the essential feature that distinguishes the present book from the multitude of recent books that are restricted to sensors. Major advances occurred in particular with biosensors, which now reach, for example, virus detection with immobilized antibodies. Aptasensors can be used for selective recognition of nucleic acids and natural tissues are applicable for example for measuring enzyme levels. Field-effect transistors (FET), originally in the form of metal-oxide-semiconductor FETs or MOSFETs have been extended to a large range of biological analytes (BioFETs). All these sensing techniques can in principle also contribute to the development of materials that implement actions upon signal sensing.

Chemoresponsive materials have already reached a considerable level of sophistication in a large diversity of fields. In the about six years that have passed since the first edition of the book, materials that respond to chemical or biological signals have found an enormously increased interest. Even fields that have been established for longer, such as those where smart membranes appear in the title or abstract of a paper, have increased by about 1500 publications within the past five years, from about 1000 up to 2014; others, such as smart graphenes, have, with about 3000 publications, virtually all appeared within the last five years. The materials discussed in the present volume cover from polymers, often gels in large or nanoscale dimensions, such as films, brushes, capsules, vesicles, to membranes. Others are based on gelators, which exhibit solubility changes or sol–gel phase transitions as a function of different chemical components. An important extension are particles such as silica microspheres with pores, which can open or close in response to their environment. All these materials can be designed to respond selectively to a chemical input, which ranges from changes in pH, to redox conditions, to specific substances, including biomolecules.

The possible applications of chemically responsive materials span from artificial muscles, actuators for process control, molecular machines, tissue engineering, self-healing surfaces and electronics, to targeted drug delivery as the most frequent aim. The large variety of the different chemoresponsive materials and the many possible applications have made a comprehensive representation difficult; some planned chapters did not materialize, but can be found in the first edition, some new were added. The chapters of the present monograph illustrate on the basis of different chemically stimulated materials their great promise. Each chapter was written by experts in their field; the editor is most grateful to all of them for their indefatigable cooperation, but takes responsibility for possible shortcomings. The indispensable support by the staff of the Royal Society of Chemistry is also gratefully acknowledged. It is hoped that this book will stimulate experienced and young scientists to explore the intriguing and virtually endless possibilities of smart materials for applications in many new technologies, particularly in biomedical fields.

Hans-Jörg Schneider

Saarbrücken, Germany