Temperature sensitive polymer hydrogels are being extensively studied because of their potential applications in the biomedical, robotics, and chemical industries. However, major hurdles in their development have been their slow response, low efficiency (swelling/deswelling ratios), and poor mechanical properties due to difficulty in processing them into mechanically strong and fine structures. Fibers made from such polymers would be highly desirable. A temperature sensitive random linear copolymer of N-tert-butylacrylamide (NTBA) and acrylamide (Am) was synthesized by the solution polymerization method, using regulated dosing of comonomers. Using a novel approach, a high molecular weight poly(N-tert-butylacrylamide-ran-acrylamide::27:73) has been converted to insoluble strong fibers with fineness of 30-50 microns by solution spinning, drawing, and subsequent crosslinking. Fibers were solution spun in acetone using a 14% copolymer solution in acetic acid with polycarboxylic acid as a crosslinker and sodium hypophosphite as a catalyst. The crosslinks were formed, subsequent to drawing, between reactive amide side groups of the acrylamide moiety of the polymer and the carboxylic acid group of the crosslinker by thermal treatment at 160degreesC. The transition temperatures of the crosslinked fibers were found to shift towards the lower temperature from 37degreesC (in linear copolymer) to 22-25degreesC. These engineered fibers display sharp temperature sensitivity, extremely high reversible change in dimensions (1000% in diameter and similar to 70% in length), and extremely fast response time ( < 20 s for expansion and < 2 s for contraction). (C) 2004 Wiley Periodicals, Inc.