The following is an edited transcript of the plenary lecture presented by Robert Langer at the 1995 MRS Spring Meeting on April 17, 1995 in San Francisco.

Over the last 21 years I have been involved in examining and studying, and in some cases synthesizing new polymers and biomaterials, looking at how they might be able to solve two problems. One set of problems involves drug delivery; a second involves creating new tissues.

Controlled drug release is a relatively young field that has involved a fundamental change in the way drugs are delivered. Transdermal drug delivery, for example, uses five layers of polymers, yet the whole system is 0.2 mm thick. One such polymer contains nitroglycerine, which is slowly released for one day from a patch through the skin into the blood circulation. This process provided a novel way to treat angina for patients with chest pains. First introduced in 1982, such drug-delivery systems saw a usage rate of over 500 million last year.

Norplant systems, which are silicone capsules placed under the forearm, slowly release a birth-control drug for over 2,000 days, or five years, from what are actually six small implants about the size of match sticks. These two examples illustrate that drugs can be made to slowly diffuse through polymers over a long period of time.

The following is an edited transcript of the presentation given by A. Paul Alivisatos, recipient of the Outstanding Young Investigator Award, at the 1995 MRS Spring Meeting in San Francisco.

The work I will describe on semiconductor nanocrystals started with the realization that it is possible to precipitate a semiconductor out of an organic liquid. We can precipitate out a semiconductor as a colloid—a very small-sized semiconductor with reduced dimensionality—that will show large, quantum size effects. A dream at that time was to make an electronic material by such a process in a liquid beaker, by starting with an organic fluid and somehow injecting something into the fluid to make very small particles, which we could use in electronics. The materials we use in electronics today have perfect crystalline order. We are able to put in dopants very specifically, or control precisely their arrangements in space in enormously complicated ways. The level of purity of electronic materials is so high that making an electronic material in a wet chemistry approach seems almost impossible. If, in addition, we specify that the size must be controlled precisely, we recognize the project is a problem for basic research, yet not one ready for applications. Many fundamental problems arise if we try to make semiconductor particles, in a liquid, of such high quality that they can be used as electronic materials.

More than 25 years have passed since Intermetallic Compounds, edited by Westbrook, was published. Since that time, enormous advances have been made in the understanding and usage of intermetallic compounds. It is known that intermetallic compounds are generally brittle. Thus, alloys that contain intermetallics may also be brittle. However, many intermetallic compounds are known to have extraordinary functions and characteristics that are not observed in ordinary metals and alloys. Thus, they function as magnetic materials, superconductors, semiconductors, hydrogen absorbing alloys, shape memory alloys, and so on.

Many high-strength structural alloys like maraging steels and duralumins are strengthened by fine precipitates of intermetallic phases. Nickel-based superalloys, which are used for airplane-engine parts, contain 60-70% of Ni3Al-based intermetallics by volume fraction and exhibit high strength at high temperatures. Hard metals, which are used for cutting tools, are composed of a large amount of hard but brittle intermetallics like WC and a small amount of ductile cobalt. Intermetallic compounds like TiAl are also investigated for their applications as structural materials where high strength at high temperatures is required.

In a strict sense, intermetallic compounds are composed of two or more metallic elements. In a wider sense, they are composed of metallic and/or semimetallic elements. Each is characterized by an ordered arrangement of two or more kinds of atoms, that is, the formation of a superlattice, and have various kinds of interatomic bonding, ranging from metallic to covalent or ionic bonding. The ordering of atoms and the strong interatomic bonding result in many attractive properties for intermetallic compounds.

Over the past 30 years we have seen a strong but uncoordinated effort to both increase the availability of numeric materials-property data in electronic media and to make the resultant mass of data more readily accessible and searchable for the end-user engineer. The end user is best able to formulate the question and to judge the utility of the answer for numeric property data inquiries, in contrast to textual or bibliographic data for which information specialists can expeditiously carry out searches.

Despite the best efforts of several major programs, there remains a shortfall with respect to comprehensiveness and a gap between the goal of easy access to all the world's numeric databases and what can presently be achieved. The task has proven thornier and therefore much more costly than anyone envisioned, and computer access to data for materials scientists and engineers is still inadequate compared, for example, to the situation for molecular biologists or astronomers. However, progress has been made. More than 100 materials databases are listed and categorized by Wawrousek et al. that address several types of applications including: fundamental research, materials selection, component design, process control, materials identification and equivalency, expert systems, and education. Standardization is improving and access has been made more easy.

In the discussion that follows, we will examine several characteristics of available information and delivery systems to assess their impact on the successes and limitations of the available products. The discussion will include the types and uses of the data, issues around data reliability and quality, the various formats in which data need to be accessed, and the various media available for delivery. Then we will focus on the state of the art by giving examples of the three major media through which broad electronic access to numeric properties has emerged: on-line systems, workstations, and disks, both floppy and CD-ROM. We will also cite some resources of where to look for numeric property data.

Try to imagine a world without incandescent lamps. We light our homes with 20-200-watt lamps, which are routinely purchased in local stores. These lamps are made at the rate of millions per week and their manufacture represents a large global industry. The consumer expects them to last approximately 1,000 hours and to be energy efficient and inexpensive.

Many types of incandescent lamps exist. Figure 1 shows several examples. The most common types are A-line (the general household lamp), automotive lamps, and reflector lamps for floodlight or projector applications. We also have many thousands of specialty lamps, which have a broad range of applications, such as audio-visual projectors, fiberoptic systems, video-camera lights, airport-runway markers, photoprinters, medical/scientific instruments, and stage/studio systems. They can have power ratings from a few watts to several thousand watts, but they all have at least one feature in common. They contain a filament made of tungsten wire. The diameter of the wire will vary, depending on the power rating and application of the lamp, but for most common household lamps it is less than 100 μm.