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Multiscale mechanics of hierarchical materials plays a crucial role in understanding and engineering biological and bioinspired materials and systems. The mechanical science of hierarchical tissues and cells in biological systems has recently emerged as an exciting area of research and provides enormous opportunities for innovative basic research and technological advancement. Such advances could enable us to provide engineered materials and structure with properties that resemble those of biological systems, in particular the ability to self-assemble, to self-repair, to adapt and evolve, and to provide multiple functions that can be controlled through external cues. This book presents material from leading researchers in the field of mechanical sciences of biological materials and structure, with the aim to introduce methods and applications to a wider range of engineers.




The field of multiscale mechanics has witnessed an exciting development over the past decades, culminating in recent years in breakthrough discoveries that have blurred the boundaries between living and synthetic materials, and have enabled the first wave of high-impact applications of new materials and structures in biomedical, energy and structural engineering applications. Multiscale modeling offers promise for facilitating the creation of engineered materials and structures with properties that resemble those of biological systems, in particular the ability to self-assemble, to self-repair, to adapt and evolve, and to provide multiple functions that can be controlled through external cues. In addition to their potential for enabling the realization of advanced technological applications, the challenges posed by the complex behavior of hierarchical tissues and cells in biological systems represent terrific opportunities to open new chapters in the development of the mechanical sciences. It is remarkable how the mechanics practiced by da Vinci, Galileo, Newton and other great scientists has evolved to a point where now it interconnects intimately with the life sciences, and that it could ultimately contribute to the solutions of critical problems encountered in such disparate fields as medicine and the aging infrastructure.
Roberto Ballarini, Markus Buehler

Multi-scale modeling of biomaterials and tissues

Computer simulation has emerged as a powerful tool to investigate and design materials without ever making them. Predicting the properties and behavior of materials by computer simulation from the bottom-up perspective has long been a vision of computational materials scientists and, as computational power increases, modeling and simulation tools are becoming crucial to the investigation of material systems. The key to achieving this goal is using hierarchies of paradigms that seamlessly connect quantum mechanics to macroscopic systems. Particular progress has been made in relating molecular-scale chemistry to mesoscopic and macroscopic material properties essential to define the materiome. This chapter reviews large-scale atomistic and coarse-grain modeling methods commonly implemented to investigate the properties and behavior of natural and biological materials with nanostructured hierarchies. We present basic concepts of hierarchical multiscale modeling capable of providing a bottom-up description of chemically complex materials and some example applications related to the study of collagen material at different hierarchical levels.
Alfonso Gautieri, Markus J. Buehler

Microelectromechanical systems (MEMS) platforms for testing the mechanical properties of collagen fibrils

To determine how the hierarchical structures of tissues such as skin, tendon and bone confer mechanical properties to those tissues a better understanding is required of the properties of the individual components and their interactions. The architecture of bone, for example, contains six distinct features shown in Figure 1 (Rho et al. (1998)). The building blocks are collagen molecules and mineral crystals. The figure illustrates how the feature at a particular scale is assembled from those at the lower scales. The ultimate goal of computational and theoretical multiscale models is the accurate description of the properties and mechanical behavior of such complex structures. The development of robust models will undoubtedly rely on experimental data that (1) will provide some of the required input parameters; (2) could be used to assess the validity of the model’s predictions; and (3) will offer insights on how they could be improved. The mechanical testing of biological tissues at relatively large scales enjoys a long and rich history.
Roberto Ballarini, Harold Kahn

Multiscale modeling of diffusion phenomena in polymers

In the present Chapter we will present two examples where the molecular description of diffusion is used to obtain mesoscale behavior of a given bulk polymer. In the first example a large molecule (benzene) is considered as permeant molecule within a bulk polymer (Poly vinyl alcohol), in this case the problem to be overcome was to reach the normal diffusion regime, hence a complete random motion of the diffusive molecules within the polymer. In the second example the diffusing molecules are water and the polymer is poly lattic acid, in this case the problem was to model properly the degradation in time observed when this polymer is exposed to water.
Alberto Redaelli, Simone Vesentini, Alfonso Gautieri, Paolo Zunino

Advances in Experimental Cell Biology and Cell-Material Interactions

Recent advances in the physical sciences and engineering have made it possible to measure and manipulate the mechanical and binding properties of cells in new ways. In this chapter, we will introduce this field by discussing two different experimental approaches at the interface of biology and engineering: 1) ways to measure the different types of forces generated by the actin cytoskeleton and 2) how we can probe the interactions between cells and their environment using nanostructured surfaces.
Claire M. Cobley, Seraphine V. Wegner, Martin Streichfuss, Joachim P. Spatz

Microfluidic Platforms for Human Disease Cell Mechanics Studies

Microfluidics is an interdisciplinary field at the interface of chemistry, engineering, and biology; and has experienced rapid growth over the past decades due to advantages associated with miniaturization, integration and faster sample processing and analysis time (Gervais et al., 2011; Hou et al., 2011; Bhagat et al., 2010). Recently, several microfluidic platforms have been developed for the study of human disease cell biomechanics at the cellular and molecular levels so as to gain better insights into various human diseases such as cancer (Bhagat et al., 2010), pneumonia (Kim et al., 2009b), sepsis (Mach and Di Carlo, 2010) and malaria (Hou et al., 2010). In this section, we will elaborate on recent advances in cellular biomechanics using microfluidic approaches. In particular, we will look at various techniques in probing cellular mechanical properties with some novel applications in cancer and malaria such as the identification and enrichments of these diseased cells from their normal counter parts. We will also provide insights into the challenges associated with current microfluidic approaches and provide future perspectives for the next-generation platforms.
Ebrahimi Warkiani Majid, Chwee Teck Lim

Continuum analyses of structures containing cracks

The previous chapters of this book have demonstrated how multi-scale models and experiments at very small scales have improved and offer promise for furthering our understanding of the mechanical behavior and physical properties of biological materials and structures. This chapter illustrates how valuable insights can be gained using simplified continuum mechanics models that gloss over the complexities that can be handled by the multi-scale models, such as numerous distinct nano and micro scale features that comprise the structures, material inhomogeneity, biological and chemical processes, the precise geometrical description, and the presence of flaws. This as long as the simplified treatments capture the essential features controlling the mechanical response. The reward for sacrificing the details is that the simplified models are amenable to analytical treatment. The discussion is limited to linear elastic structures containing cracks.
Roberto Ballarini
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