Perfect Insulin Crystals

Perfection is elusive both in nature and in the laboratory, but researchers at the University of Houston have found that crystals of insulin often grow in a perfect fashion. It is a discovery that may lead to improvements in future microelectronics, as well as higher quality medicines, chemicals, or devices that can benefit from improved crystal-growing methods. The researchers (Peter Vekilov, 713-743-4315) found that as insulin proteins crystallize around a screw dislocation defect in an existing insulin crystal, they form spiraling hillocks of perfect crystalline insulin (see image). (Screw dislocations are a common type of crystal defect that results when there is a slight angular misalignment between crystal layers.) In most crystals, interactions between stepped layers that make up the edges of a growing crystal cause the steps to bunch up, which in turn leads to striated crystals. In addition, competition for dissolved material carried in the surrounding solution can also cause step bunching. Insulin, however, is unusual in that there is there is little interaction between steps. Although the researchers say that it is not clear whether such perfection is possible in many other substances, by coming to understand the factors that lead to perfect growth of insulin crystals we may soon learn how to tweak growing conditions to improve dramatically other crystals. For example, by properly stirring a solution, it may be possible to reduce step bunching that results from competition for dissolved material between different crystal regions. Alternatively, manufacturers may choose to introduce screw dislocations to induce crystal growth, rather than allowing crystals to form around other types of defects that tend to generate imperfect structures. Microelectronics is one field that could benefit from better crystal growing techniques. In particular, microchips built of gallium arsenide are frequently much faster that ones built of silicon, but it is currently very difficult to grow the perfect gallium arsenide crystals necessary for chip manufacturing. Lessons learned from studying factors that lead to perfect insulin crystals may help solve the problem. (O. Gliko et al., Physical Review Letters, 6 June 2003)