Introduction

Although there are over 80 minerals present in biological systems, the most important are hydroxyapatite (HAP) (mammals and fishes), calcium carbonates (shells, arthropods, corals), and silica (diatoms, sponges). These minerals seem to have evolved from approximately 560 million years ago.

Minerals are essential for providing compressive strength to biological systems, whereas biopolymers are primarily responsible for tensile strength. The combination of minerals and biopolymers leads to the formation of biological materials with mechanical properties tailored in terms of hardness, toughness, and anisotropy. The formation of minerals involves nucleation and growth, both mediated by biological components. The organic matrix mediates nucleation in many ways: by providing nucleation sites and by controlling the polymorphs. The growth is also mediated by organic compounds, and illustrative examples are given in Chapters 6 and 7. For instance, the rapid direction of growth for aragonite is the c-direction, and long needles are formed. In nacre, this growth is regulated by the periodic deposition of organic layers. In bone, the HAP crystals nucleate in the interstices of collagen fibrils and growth is also regulated: they reach sizes on the order of nanometers: 40–60 nm long, 20–30 nm wide, and platelets of a few nanometers thickness are formed in such a fashion.

The field of materials science and engineering (MSE) has undergone a tremendous development since it was defined for the first time in the 1950s. Materials science and engineering has supplanted traditional curricula centered on metallurgy, ceramics, and polymers. In the USA alone, there are over 50 MSE academic university departments. Materials science and engineering has initially merged metals, polymers, ceramics, and composites into a broad and unified treatment. Whereas the twentieth century was marked by revolutionary discoveries in physics and chemistry, the twenty-first century has been prognosticated to be dominated by biology. Indeed, medical and biological discoveries are bound to have a profound effect on our future. Consistent with the increasing demands of engineering students to acquire basic working tools in this domain, many engineering curricula are adding appropriate courses or modifying existing courses to address biological aspects. Within MSE, the nascent field of biological materials science encompasses three areas.

• Biological (or natural) materials: materials that comprise cells, extracellular materials, tissues, organs, and organisms.

• Biomaterials: synthetic materials used to correct, repair, or supplement natural functions in organisms.

• Biomimetics: this area encompasses the materials and structures inspired in biological systems and/or functions.

This book focuses on these three areas in a balanced manner. This is a necessity of space, and many curricula offer separate biomaterials courses. The book has 13 chapters, and the contents can be covered comfortably in one semester (one chapter per week).

In the previous chapter we showed how the amplitudes of the tidal waves generated in the deep oceans increase when they spread onto the shallow surrounding continental shelves. In this chapter we consider the further and more extreme distortions that occur as the tidal waves propagate into the even shallower coastal waters and rivers. The behaviour of these distorted tides is very important for near-shore human activities such as recreational pursuits and coastal navigation. The distortions are also important for geological and biological processes in the coastal zone.

Introduction: some observations

Sea-level records from shallow-water locations normally show that the interval from low to high water is shorter than the interval from high to low water: the rise time is more rapid than the fall. Offshore the flood currents are stronger than the ebb currents. High waters occur earlier than simple predictions, and low waters are later.

Preface

We spend much of our time studying sea-level science, a wide-ranging and constantly fascinating subject. We analyse data, read and write papers, and present findings at conferences where there are people in the same sea-level community as us. However, every so often we get to meet other people who have been exposed to this subject in a more personal way: someone who lost relatives in the 1953 North Sea storm surge, another who lost everything more than once in Bangladesh floods, a colleague who survived the 2004 Sumatra tsunami.

We remember at a conference of sea-level experts in the Maldives some years ago a small boy holding a homemade poster declaring ‘Down with sea-level rise’, as he feared for the future of his country. Concern about possible global warming and sea-level rise has rarely been expressed as simply or as effectively. These examples remind us that the results of our work are important, not just for the scientific papers that are produced, but also for many practical reasons, which somehow we find reassuring.