A biological polymer assembly with a biological polymer that contains at least 90 percent of tubulin and a positively charged segment. The positively charged segment has a molecular weight of at least about 5,000 Daltons, a bulk electrical conductivity of at least about 10.sup.-7 ohms.sup.-1 meter.sup.-1 Siemens, a concentration of elemental charges per cubic centimeter of from about 10.sup.12 to about 10.sup.25, and a length of at least about 2 nanometers.