Photoresponsive Polymer Films with Directly Micropatternable Surfaces Based on the Change in Free Volume by Photo‐Crosslinking

Abstract

micropatterns are generated by selectively exposing photoreactive or photoresponsive polymer films to ultraviolet (UV) light in a photo-crosslinking or photodecomposition process and subsequently dissolving the selected areas of the film surfaces using an appropriate solvent. Photo lithography is widely employed as a high-resolution technique because it is suitable for large-area surface patterning with good alignment. However, it is not cost-effective because of the requirement of some complicated processes. In nanoimprint lithography based on pattern transfer processes, the patterning of polymers is fabricated by trapping a solid-state pattern by either cooling the molded material or UV-photocuring the polymer precursor after a mold is pressed against a softened thermoplastic polymer or a liquid polymer precursor. The softened thermoplastic polymer and liquid polymer precursor are driven into recessed portions of the mold by applying pressure, adhesion, or capillarity. Polymers to be patterned can be spin-cast, dispensed as droplets, or allowed to fill the space between the mold and substrate by capillary forces. [3,8,9] Recently, azopolymers with phototunable physical and chemical properties were also used in nanoimprint lithography for directional photo-manipulation of nanopatterns and micro-photo-actuators. [10,11] Nanoimprint lithography is the simplest way for producing large-area nanostructures in a low-cost and high-resolution patterning technique. However, it commonly requires high pressure, which increases the possibility of damage to the mold and substrate. Further, in nanoimprint lithography, mold fabrication using the conventional lithographic process and reactive ion etching facilities is indispensable. Simplified micropatterning techniques are necessary for surface patterning with polymers to achieve costeffective nano-and micropatterning with multiple shapes and scales. In particular, simple and cost-effective microfabrication technologies are required in developing low-cost devices and disposable chips for diagnosing diseases even though their resolution is not very high.Stimuli-responsive polymers undergo abrupt changes in their structures and properties in response to external stimuli, [12][13][14][15] such as pH, [16] temperature, [17][18][19][20] electric field, [21,22] and light. [23] According to previous studies, the stimuli-responsive behavior of the polymers is based on drastic changes in their affinity for solvents or in the osmotic pressure induced by Photoresponsive polymers, whose structures or properties change when exposed to ultraviolet (UV) light, have been studied for the fabrication of micro-and nano-devices for various applications. Herein, photoresponsive polymer films are investigated with directly micropatternable surfaces formed by only UV exposure without the development process using solvents. The photoresponsive polymer films are designed based on the decrease in free volume induced by the photodimerization of cinnamoyl groups. The photoresponsive polymers are synthesi...

Cell patterning on photocrosslinkable polymer films with micropatternable surfaces

“…The synthesis of 2-cinnamoyloxyethyl methacrylate (CEMA) and PCEMA-g-PDMS has been described in detail in a previous paper as shown in Scheme S1. [37] Successful synthesis was confirmed via proton nuclear magnetic resonance ( 1 H NMR, Figure S1). 1 H NMR spectra were recorded on a GSX-400 NMR instrument (JEOL) operating at 400 MHz with deuterated chloroform (CDCl 3 -d) as the solvent and tetramethylsilane as the internal standard.…”

“…In our previous study, X-ray photoelectron spectroscopy (XPS) and contact angle measurements revealed that the surface of PCEMA-g-PDMS films underwent no change in chemical properties, such as surface composition and hydrophilicity, upon UV exposure. [37] Therefore, fibronectin may recognize changes in the chemical properties of PCEMA-g-PDMS films due to UV exposure, which are too small to be detected via XPS and water contact angle measurements. However, more cells generally tend to adhere to surfaces on which more fibronectin is adsorbed.…”

“…However, in our previous paper, we suggested that crosslinking could induce changes in the volume of polymer films despite the absence of a solvent. [37] Our facile fabrication technique enabled the formation of micropatterns using only ultraviolet (UV) light exposure through a photomask without development using solvents, which is based on decrease in the free volume of poly (dimethylsiloxane) (PDMS) induced by photocrosslinking. This strategy uses the large free volume of PDMS films with the photocrosslinking of photodimerizable groups via UV exposure.…”

UV-assisted nanoimprint lithography: the impact of the loading effect in silicon on nanoscale patterns of metalens

“…On the other hand, quartz molds, while also utilized in nanoimprint lithography, may exhibit fragility and reduced durability compared to silicon molds. 5,10,32 This can affect their longevity and cost-effectiveness for industrial use. Nonetheless, the choice between silicon and quartz molds oen boils down to a trade-off between initial cost and the long-term benets of durability and precision.…”

Photoresponsive Gelation of Four-Armed Poly(ethylene glycol) with Photodimerizable Groups

“…Photodimerization occurs when a photodimerizable molecule in its ground state, such as cinnamoyl [ 38 , 39 ], maleimide [ 40 , 41 ], coumarin [ 42 ], and anthracene [ 43 ], is excited by light to form a dimer. We fabricated photoresponsive polymer films by introducing cinnamoyl groups into polydimethylsiloxane with a large free volume and photo-crosslinking only the UV-irradiated regions [ 44 ]. Photodimerization has also been utilized for forming PEG-based hydrogels for cell culture [ 45 , 46 ].…”