Effect of the Hydrophobic Basal Layer of Thermoresponsive Block Co-Polymer Brushes on Thermally-Induced Cell Sheet Harvest

Abstract

Thermoresponsive poly(benzyl methacrylate)-b-poly(N-isopropylacrylamide) (PBzMA-b-PIPAAm) block co-polymer brush surfaces were prepared by surface-initiated two-step reversible addition-fragmentation chain transfer radical (RAFT) polymerization. PBzMA brushes were fabricated on azoinitiator-immobilized glass substrates in the presence of dithiobenzoate (DTB) compound as a RAFT agent. The amount of grafted polymer was regulated by initial monomer concentrations. The second thermoresponsive blocks were added to the RAFT-related DTB groups located at PBzMA termini through the propagation of PIPAAm chains, resulting in formation of PBzMA-b-PIPAAm brushes. Surface characteristics of the block co-polymer brushes and its influence on thermally regulated cellular behavior were investigated using bovine carotid artery endothelial cells (BAECs), compared with PIPAAm brush surfaces. Cell adhesion/detachment behavior on thermoresponsive polymer brush surfaces significantly depended on their individual polymer architectures and chemical compositions of grafted polymers. Low-temperature treatment at 20°C, below the phase-transition temperature of PIPAAm, induced the spontaneous detachment of adhering cells from the PBzMA-b-PIPAAm brush surfaces with a higher rate than that from PIPAAm brush surfaces. In addition, the cell-repellent effect of the hydrophobic basal layer successfully accelerated for harvesting BAEC sheets from the block co-polymer brush surfaces. Unique features of thermoresponsive block co-polymer brush architectures can be applied to control cell-adhesion strength for enhancing cell adhesion or accelerating cell detachment.

Keywords:

• Poly(N-isopropylacrylamide)
• RAFT polymerization
• block co-polymer
• polymer brush
• thermoresponse

Acknowledgements

This work was partially supported by Formation of Innovation Center for Fusion of Advanced Technologies in the Special Coordination Funds for Promoting Science and Technology ‘Cell Sheet Tissue Engineering Center (CSTEC)’ and Grant-in-Aid for Scientific Research (B) (20300169) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.

Notes

aInitial feed of IPAAm, CPDTB and V-501 was 1 M, 0.25 and 1 mM, respectively.

bDetermined by ATR/FT-IR, mean ± SD (n = 3).

cDetermined by GPC using DMF with 50 mM LiCl.

aInitial feed of IPAAm, CPDTB and V-501was 1 M, 0.25 and 1 mM, respectively.

bDetermined by captive bubble method in water, mean ± SD (n = 3)