Opportunities for materials science: From molecules to neural networks
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Introduction Biomaterials have long been an important part of materials science and engineering. Constructions and objects made of wood, bone, and cotton for thousands of years were augmented and replaced with metals, on an industrial scale, in the past 150 years, and with synthetic polymers and silicon fairly recently. Today, we may be standing at the threshold of a new era in materials science and technology, with engineered biomaterials augmenting and replacing plastic and electronic devices, and driving innovation. Previous revolutions in materials science came at the cost, we now know, of local and global ecological disasters— from the copper mines of Chile to plastic in the oceans. Engineered biomaterials have the potential of evolving into an eco-friendly sector of the economy outputting biodegradable products. Specifically, the combination of biomaterials and molecular-scale manufacturing—artificial life minus selfreproduction—could drive new engineering directions, especially in the general area of devices.1 Examples include smart tissue implants, miniaturized mechanochemical actuators (such as artificial muscles), and in general active materials which react to changes in their physical or chemical environments. As with nanoscience in general, the direction that eventual large-scale applications will take is difficult to foresee. What is clear even now is the capability of the field for generating
new science. In a general sense, the problems being addressed encompass more than one field of physics, with a focus on those fields we understand least. In keywords, these are farfrom-equilibrium, nonlinear, complex systems. As an example, the working of an enzyme, which is one big catalyst molecule, results from mechanochemical coupling within the material, in an environment with out-of-equilibrium concentrations of reactants. Nonequilibrium is of the essence, similar in this respect to a driven turbulent flow, and different from situations such as currents in conductors, where the material is locally in equilibrium. Similarly, the active gel that forms the cytoskeleton (the polymer network that provides the structural support to the cell) is fundamentally maintained by nonequilibrium processes such as treadmilling (the process by which an actin filament, for example, displaces itself by polymerizing at one end while depolymerizing at the opposite end).2 When we consider biomaterials from the point of view of the nonequilibrium processes that maintain them and the nonlinearities that underlie their functions, we see new opportunities for materials science at different scales, from the molecular to the macroscopic.
Big molecules as materials A typical monomeric enzyme is a composite solid-like nanoparticle about 4 nm in size, consisting of ∼104 atoms. Its bond
Giovanni Zocchi, Department of Physics, University of California, Los Angeles, USA; [email protected] doi:10.1557/mrs.2019.23
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• VOLUME 44 • FEBRUARY Tulane 2019 • www.mrs.org/bulletin 2019 Materials Downloaded MRS fromBULLETIN https://www.cam
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