Modification of Poly(methyl methacrylate) Surfaces with Azobenzene Groups to Develop a Photoresponsive Surface
Photoswitchable surfaces can be used to reversibly control surface wettability, adsorptivity, and protein adhesion to influence cell interactions at the surface. Control over protein adsorption and cell adhesion is useful in many applications, from cell culture scaffolds to drug delivery devices and improving the cell response to materials in vivo. Switchable properties can be attained by polymerizing light-responsive monomers or by modifying existing materials. This project investigates surface modification as a method of developing light-responsive poly(methyl methacrylate) (PMMA) surfaces and coatings of a copolymer of methyl methacrylate (MMA) and 2-aminoethyl methacrylate (AEM) (termed MMAcoAEM). In this work, PMMA surfaces were functionalized with amine or carboxyl groups for azobenzene modification and cell-material interaction studies. PMMA was functionalized with hexamethylenediamine (HMD) or O,O'-bis(2-aminopropyl) propylene glycol-block-polyethylene glycol-block-polypropylene glycol (PPG-PEG-PPG) groups via aminolysis or functionalized with carboxyl groups via hydrolysis. Aminated PMMA was then modified with 4-(phenylazo)benzoic acid using a carbodiimide reaction. Surfaces were characterized using ninhydrin assays, titration, contact angle measurements, x-ray photoelectron spectroscopy (XPS), ultraviolet-visible (UV-VIS) spectroscopy and nuclear magnetic resonance spectroscopy (NMR). The aminolysis reaction conditions from literature1 were revised to improve the graft density, with up to 36.4 ± 7.0 nmol/cm2 of HMD or 20.3 ± 2.9 nmol/cm2 of PPG-PEG-PPG groups functionalized to PMMA. The copolymer MMAcoAEM contained 44.0 ± 2.2 nmol/cm2 of amine groups as a surface coating. Amine-functionalized PMMA or MMAcoAEM surfaces were modified with 20.5 ± 0.4 nmol/cm2 (HMD), 11.2 ± 2.6 nmol/cm2 (PPG-PEG-PPG), or 24.8 ± 4.4 nmol/cm2 (MMAcoAEM) of 4-(phenylazo)benzoic acid. UV-VIS spectroscopy was used to confirm that azobenzene grafted to materials retained the ability to photoisomerize and interact with β-cyclodextrin (β-CD). Functionalized PMMA was also used to study cell-material interactions with neutrophil-like HL-60 human promyelocytic leukemia cells activated with phorbol 12-myristate 13-acetate (PMA) to induce cell adhesion. AlamarBlue® assays and live/dead deoxyribonucleic acid (DNA) staining indicated that amine-modified surfaces contained the highest amount of extracellular DNA after incubation with HL-60s, believed to be extracellular traps (ETs). Future research aims to study the cell-material interactions with azobenzene-modified surfaces and further modify the surface using biomolecules conjugated to β-CD.