Supported membranes represent an elegant route to designing well-defined fluid interfaces which mimic many physical-chemical properties of biological membranes. Recent years have witnessed rapid growth in the applications of physical and materials science approaches in understanding and controlling lipid membranes. Applying these approaches is enabling the determination of their structure-dynamics-function relations and allowing the design of membrane-mimetic devices. The collection of articles presented in this issue of MRS Bulletin illustrates the breadth of activity in this growing partnership between materials science and biophysics. Together, these articles highlight some of the key challenges of cellular membranes and exemplify their utility in fundamental biophysical studies and technological applications. The topics covered also confirm the importance of lipid membranes as an exciting example of soft condensed matter. We hope that this issue will serve readers by highlighting the intellectual scope and emerging opportunities in this highly interdisciplinary area of materials research.

The functional modification of solid surfaces with plasma membrane models has been drawing increasing attention as a straightforward strategy to bridge soft biological materials and hard inorganic materials. Planar model membranes can be deposited either directly on solid substrates (solid-supported membranes), or on ultrathin polymer supports (polymer-supported membranes) that mimic the generic role of the extracellular matrix and the cell surface. The first part of this review provides an overview of advances in the fabrication of polymer-supported membranes. The middle section describes how such thin polymer interlayers can physically modulate the membrane–substrate contact. The last section introduces several methods to localize membranes and membrane proteins. Finally, some ideas are presented on combining supported membrane concepts with semiconductor technology toward applications in materials science.

Lipid membranes are generally thought of as flat or spherical structures, much as we would view the plasma membrane of a cell. Within the cell, however, there exists a wide variety of stacked, folded, and other forms of bent structures that support and enable such functions as photosynthesis, light-sensing, protein synthesis, molecular shuttling, chemical uptake and release, and cell division. These functions benefit from the high asymmetry of the membrane. Stacked or folded structures provide a highly concentrated and ordered assembly for facile energy and molecular transport, while bent structures facilitate budding, division, and fusion events. In this article, we survey the progress made in understanding the formation of these membrane architectures, the development of synthetic forms of stacked and folded assemblies, and the unique materials issues they present.

Planar-supported phospholipid bilayers are responsive surfaces that reconstruct when macromolecules adsorb. This review outlines the phenomenon of lipid diffusion “slaved” to or significantly controlled by that of macromolecular adsorbates. To elucidate such systems, we discuss the value of spatially resolved experiments at the few-molecule level, lipid diffusion compared in outer and inner leaflets of the supported bilayer, and a simple method to minimize defects by the strategy of “electrostatic stitching.”

An intact cell membrane serves as a permeable barrier, regulating the influx and efflux of ions and small molecules. When the integrity of the membrane is compromised, its barrier function is also disrupted, threatening the survival of the cell. Triblock copolymer surfactants of the form poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) have been shown to help seal structurally damaged membranes, arresting the leakage of intracellular materials.

In order to understand how this particular family of triblock copolymers helps seal damaged membranes, model lipid monolayer and bilayer systems have been used to unravel the nature of the lipid/copolymer interaction. The copolymer surfactant is found to selectively insert into structurally compromised membranes, thus localizing its sealing effect on the damaged regions. The inserted polymer is “squeezed out” when the lipid packing density is increased, suggesting a mechanism for the cell to be rid of the polymer when the membrane integrity is restored.

Solid-supported lipid bilayers hold strong promise as bioanalytical sensor platforms because they readily mimic the same multivalent ligand-receptor interactions that occur in real cells. Such devices might be used to monitor air and water quality under real-world conditions. At present, however, supported membranes are considered too fragile to survive the harsh environments typically required for non-laboratory use. Specifically, they lack the resiliency to withstand air exposure and the thermal and mechanical stresses associated with device transport, storage, and continuous use over long periods of time. Several successful strategies are now emerging to make supported membranes tougher. These strategies incorporate mimics of the cytoskeleton and glycocalyx of real cell membranes. The promise of these more robust lipid bilayer architectures indicates that future materials should be designed to more fully resemble the actual structure of cell membranes.

Molecules in the cell membrane are key targets for therapeutic intervention. Technologies that enable the preservation of membrane-bound targets in their biomimetic and pharmacologically active states for screening of potential drug compounds are of great interest to bio-pharmaceutical companies. This review discusses emerging biomembrane technologies with a focus on biomembrane microarrays that enable the parallel analysis of multiple membrane-bound targets.

The following article is an edited transcript based on the David Turnbull Lecture given by Eugene E. Haller (University of California, Berkeley) at the 2005 Materials Research Society Fall Meeting in Boston on November 29, 2005. The David Turnbull Lectureship is awarded to recognize the career of a scientist who has made outstanding contributions to understanding materials phenomena and properties through research, writing, and lecturing, as exemplified by the life work of David Turnbull. Haller was named the 2005 David Turnbull Lecturer for his “pioneering achievements and leadership in establishing the field of isotopically engineered semiconductors; for outstanding contributions to materials growth, doping and diffusion; and for excellence in lecturing, writing, and fostering international collaborations.”

The scientific interest, increased availability, and technological promise of highly enriched isotopes have led to a sharp rise in the number of experimental and theoretical studies of isotopically controlled semiconductor crystals. This article reviews results obtained with isotopically controlled semiconductor bulk and thin–film heterostructures. Isotopic composition affects several properties, such as phonon energies, band structure, and lattice constant, in subtle, yet—for their physical understanding–significant ways. Large isotope-related effects are observed for thermal conductivity in local vibrational modes of impurities and after neutron transmutation doping. Spectacularly sharp photo-luminescence lines have been observed in ultrapure, isotopically enriched silicon crystals. Isotope multilayer structures are especially well suited for studies of simultaneous self-and dopant-diffusion. The absence of any chemical, mechanical, or electrical driving forces makes possible the study of an ideal random-walk problem, in which moving atoms go in random directions at random intervals. Isotopically controlled semiconductors may find applications in quantum computing, nanoscience, and spintronics.