In the previous chapter, a series of examples was given to illustrate a range of material responses that stem from impact or explosion and result from a transient loading pulse within the material. These drivers propel waves travelling through solids, liquids and gases and place the material they have swept through into a state of compression, tension or shear. This chapter will describe these disturbances in more detail and attempt to give simple mathematical descriptions of the phenomena and the material's response. This basic approach is really a development of solid (a branch of continuum) mechanics to embrace additional features of loading at higher speeds and amplitudes; there are many, more complete texts available on the basics of solid mechanics that the reader may consult. The strategy here is to keep the derivations as simple as possible; again there are texts that derive relations with more generality than here but it is vital that the reader realises the assumptions, and more importantly their limits, in what follows. Particularly, it should be noted that solid mechanics assumes material behaviour based upon observations made in ambient states. Electronic bonding itself changes nature at around 300 GPa, so it is unrealistic to expect theory extended from the elastic state to apply in these regimes. Thus assumptions made and their limitations in the loading states the reader wishes to consider must be fully understood before using the formulae below. The basic laws of conservation of mass, momentum and energy, and classical mechanics will drive the descriptions of the thermodynamic states. To that will be added the concepts of elastic and inelastic (in metals, plastic) deformation bounded by a yield surface. To focus on material response, it is generally the simplest loading that is applied experimentally. Thus these states will be mentioned below to highlight particular relations to which the text will return.

Akrology

Extremes

The dynamic processes operating around us are often treated as transients that are not important when compared with the fixed states they precede. However, an ever-increasing knowledge base has illuminated this view of the operating physics and confirmed that extreme regimes can be accessed for engineering materials and structures. Matter is ever-changing, its form developing in a series of nested processes which complete on the timescales on which mechanisms operate; processes that occur on ever smaller timescales as length scales decrease. This book is concerned with the response that occurs when loads exceed the elastic limit. This affects behaviour in the regime beyond yield which encompasses a range of amplitudes and responses. However, it concerns condensed materials and loading, eventually taking them to a state where they bond in a different manner such that strength is not defined; this limit represents the highest amplitude of loading considered here. Nonetheless the driving forces are vast and awe-inspiring, while the different rates of change observed in operating processes are on scales that span many orders of magnitude. The following pages will highlight prime examples from the physical world and then provide a set of tools that classify mechanisms in order to analyse significant effects of these processes on the materials involved. The wide range of observations and applications create simple but powerful principles that are outlined in what follows.

Materials are central to the technologies required for future needs. Such platforms will place increasing demands on component performance in a range of extremes: stress, strain, temperature, pressure, chemical reactivity, photon or radiation flux, and electric or magnetic fields. For example, future vehicles will demand lighter-weight parts with increased strength and damage tolerance and next-generation fission reactors will require materials capable of withstanding higher temperatures and radiation fluxes. To counter security threats, defence agencies must protect their populations against terrorist attack and design critical facilities and buildings against atmospheric extremes.

The scientific method

The present chapter gives an overview of experimental platforms showing how they may be used to populate models for materials behaviour. The condensed phase defines the pressure and temperature range of interest, which may be approximately fixed at less than 1 TPa and below 10000 K. Indeed pressure has one of the largest ranges of all physical parameters in the universe (the pressure in a neutron star is c. 1033 Pa), so that most of the materials in nature are under conditions very different from those on Earth. The goal of shock experiments is to track response and mechanisms across the realms of stress and volume that are experienced by condensed-phase matter across the universe. At the highest pressures and temperatures, materials move from the solid to the liquid and then to plasma states as new correlations and bonding are formed. These high-density states have been termed warm dense matter (WDM) and lie beyond the finis extremis – outside the regime of extreme behaviour considered here. A summary of the phase space occupied by matter in these regions is shown in Figure 3.1.

The goal of experimental work is to provide adequate knowledge of the response of matter over the operating regimes of the relevant plasticity mechanisms. By this means, analytical descriptions can be constructed to try and capture the fundamental relationships between the independent variables – stress and stress state, strain and strain rate, and temperature – that determine the constitutive, damage and failure behaviour of materials. A shock impulse provides a pump to drive materials deformation and control of that impulse also allows a window into the operative mechanisms that lead to plasticity and damage evolution. This includes determining dynamic strength as a function of pressure as well as determining equation of state over the range of interest for particular applications.

Materiomics is growing. In this book, we have discussed and reviewed how one side of the materiomics coin, the screening of libraries of biomaterials, is developing, but the future of screening will go hand in hand with the other side of the coin – modelling. Materiomics is growing and is, one could say, still in its infancy. Currently, most materiomics research is performed by academic research groups, although a small but increasing number of companies are active in this area. It will be helpful to understand how fast this field will grow, and how it might develop.

To sketch a potential scenario perhaps it is worth looking at recent developments in the field of molecular biology. In the mid-1990s, there were specialized machines in the lab to produce oligonucleotides, so-called primers, used in the polymerase chain reaction, a specialist job which gave the lab a scientific head start. These days, however, a primer can be ordered online and be at your bench in days, for the cost of a few dozen Euros. By the late 1990s, we saw cDNAs arrayed on nitrocellulose, which allowed simultaneous quantification of expression for dozens to hundreds of genes. No more tedious northern blotting one gene at a time! Driven by these early successes, many institutes started investing in arraying equipment and software development, as DNA microarray analysis became increasingly popular. But the real breakthrough in the use of this technology came when companies such as Affymetrix invested not only in standardization and professionalization of the technology, but importantly also in the work flow of a DNA microarray experiment. These companies provided a full package with not only arrays but also the incubators, washing, data analysis, detailed work protocols, image analysis software and a customer service platform. In both cases, the new technological possibilities of oligonucleotide synthesis and DNA microarray production paved the way for breakthroughs in science. We think that this will also be possible for materiomics.

Scope

This chapter deals with an overview of basic microfabrication techniques. The goal is to explain to the reader how such techniques can be utilized in the field of materiomics. The basic processes used in microfabrication including photolithography, etching, electron beam lithography and micromoulding are explained. Some classic examples of these techniques as applied to materiomics are also shown. Furthermore, possible uses of such techniques, and the development and application of hybrid techniques to be able to answer fundamental questions about biological behaviour of materials, are also suggested.

Basic principles of microfabrication

Introduction

Techniques used to fabricate structures or devices smaller than 100 µm are commonly referred to as microfabrication techniques. Initially meant for the electronics industry, they have found a wide range of applications in diverse fields such as chemical engineering and the life sciences. Since the early 1990s, the application of microfabrication technologies in the area of chemical and biological analysis has been termed ‘micro total analysis systems’ (µTAS) (1). Microfabricated devices meant for µTAS initially offered the advantage of sample analysis on the microscale, but over the years, the evolution of these technologies has led to the facilitation of sample preparation, fluid handling, separation systems, cell handling and cell culturing in an integrated manner (1). The application of microtechnologies for the fabrication of devices or systems to study material properties benefits from cost efficiency, high performance, precision-based design flexibility, miniaturization and automated analysis. Miniaturization involves the convergence of multiple disciplines, such as fluid dynamics, material sciences, engineering and the life sciences, that need to join expertise in order to design functional systems. Moreover, these devices can be used to evaluate biological behaviour in vitro and can help us to test thousands of different biomaterials and surface properties without the complexity related to in vivo assays.

Scope

Given the demographic challenges of an ageing population combined with rising patient expectation and the growing emphasis placed on cost containment by healthcare providers, economic regenerative medicine approaches for regeneration of damaged and diseased organs and tissues are a major clinical and socio-economic need. The scope of this chapter is to use skeletal regeneration as the exemplar to discuss classical and high-throughput screening approaches to biomaterials development for regenerative medicine, including choice and design of materials based on clinical need, biological assessment and regulatory issues.

Basic principles: development of materials for regenerative medicine

The increase in an ageing population in developed countries is accompanied by a growing need for replacement and repair of damaged organs and tissues. Transplantation of the patient’s own tissue is still considered the gold standard in many applications, but limited availability, and complications associated with harvesting of the so-called autograft, are becoming an important drawback. Tissues and organs from human or animal donors present issues of disease transmission and functional failure. Alternative strategies, based on biological growth factors, cell therapy and tissue-engineered constructs, are being explored as alternatives to the patient’s own tissue, but their use is hampered by biological instability and high costs. These issues demonstrate the need for strategies based on biomaterials, which are often synthetic, and thus less prone to instability problems. In addition, the fact that (synthetic) biomaterials can often be produced in large quantities and thus be available off-the-shelf is an important advantage when coping with an increasing need for regenerative approaches.