Photopatterning of thermally sensitive hydrogels useful for microactuators

• Published in: Sensors and actuators. A. Physical. 1999-10, Vol.77 (2), p.139-144
• Main Authors: Hoffmann, Jan, Plötner, Matthias, Kuckling, Dirk, Fischer, Wolf-Joachim
• Format: Article
• Language: English
• Subjects: Hydrogel; Microactuator; Photocrosslinking; PNIPAAm
• ISSN: 0924-4247; 1873-3069
• DOI: 10.1016/S0924-4247(99)00080-1

Hydrogels based on PNIPAAm [poly-( N-isopropylacrylamide)] are an attractive working material for microactuators because of their swelling with thermally induced phase transitions leading to a very high volume expansion. By the employment of co-polymerization with a chromophore, a specially designed polymer has been developed that can be photocrosslinked to a gel and by this photopatterned. The focal point of this work is the preparation and characterization of mircopatterns using this co-polymer. The efficiency of the photochemical reaction is quite good and patterning results down to 20 μm spaces have been achieved. The swelling of dot-like patterned hydrogel films on Si/SiO 2 substrates in water occurs with similar temperature dependency and a swelling ratio of 3 to 3.5 in the same order of magnitude compared to bulk PNIPAAm-based gels, but the transition time of 2 to 8 s measured at the gelous dots is much shorter than that of macroscopic objects, making the material interesting for microactuator performance. The transition temperature decreases from 32 to 34°C at pure PNIPAAm to 18 to 20°C at the photopatterned gels of the copolymer.