Photo-polymerization of monomer crystals producing thermo-responsive micropatterns to direct cell growth and cell selective harvest

Abstract

Creating patterns of biomolecules and cells through precise surface engineering has offered the potentials for cancer-related studies, cellular bioassays, and drug screening because of the regulated cellular functions via the cell-substrate interactions. It is desirable in the basic laboratories with limited facilities to make the patterned surfaces by a template-free, low-cost, and high-throughput patterning technique. Here, thermo-responsive micropatterned surface was fabricated by solid photopolymerization of N-isopropylacrylamide (NIPAAm) crystals in the presence of photoinitiator and crosslinking reagent. A series of analytical tools were used to characterize the micropatterned surface for thorough understanding the pattern formation. The patterned NIPAAm crystals were created by inducing divergently needle-like monomer crystal growth from saturated monomer solution triggered by single or multiple seed crystals. Since NIPAAm crystals might have densely packed crystalline structure and effectively suppress oxygen diffusion from the environment, semicrystalline PNIPAAm films were easily obtained under UV irradiation in air without inert atmosphere protection. Subsequently, water immersion at room temperature for hours allowed the semicrystalline PNIPAAm film to form amorphous hydrogel with microscale features for cell morphology studies and heterotypic cell-substrate interactions. Microscopic visualization of human mesenchymal stem cells (hMSCs) cultured on the micropatterned PNIPAAm film exhibited significant elongation of hMSCs and nucleus along with the micropatterned features. The immunocytochemistry assay for heterotypic cancer cells on the micropatterned film not only provided the experimental evidence of cell harvesting by local heating/cooling treatment, but also demonstrated the identification of the specific cell type within heterotypic cell populations.