Thermoresponsive Cell Culture Substrates Based onPNIPAM Brushes Functionalized with Adhesion Peptides: TheoreticalConsiderations of Mechanism and Design.

Thermoresponsive tissue culture substratesbased on PNIPAM brushesare used to harvest confluent cell sheets for tissue engineering.The prospect of clinical use imposes the utilization of culture mediumfree of bovine serum, thus suggesting conjugation with adhesion peptidescontaining the RGD minimal recognition sequence. The optimum positionof the RGD along the chain should ensure both cell adhesion at 37°C and cell detachment at TLbelowthe lower critical solution temperature of PNIPAM. Design guidelinesare formulated from considerations of brush confinement by the cells:(i) Cell adhesion at 37 °C is controlled by the RGDs accessiblewithout brush compression. (ii) Cell detachment at TLis driven by a disjoining force due to confinement ofthe swollen brush by cells retaining integrin–RGD bonds formedat 37 °C. These suggest placing the RGDs at the grafting surfaceor its vicinity. Randomly placed RGDs do not enable efficient detachmentbecause a large fraction of the integrin–RGD bonds are notsufficiently tensioned at TL, in linewith experimental observations (Ebara, M.; Yamato, M.; Aoyagi, T.;Kikuchi, A.; Sakai, K.; Okano, T. Immobilization of celladhesive peptidesto temperature-responsive surfaces facilitates both serum-free celladhesion and noninvasive cell harvest. Tissue Eng.2004, 10, 1125–1135). The theoryframework enables analysis of culture media based on polymer brushesconjugated with adhesion peptides in general. [ABSTRACT FROM AUTHOR]