Tunable and Magnetic Thiol–ene Micropillar Arrays

Abstract

like tunable non-wettability and responsive properties, which ultimately can lead to new avenues in applications and functionalities in microfluidic devices and cell handling.Thiol-ene chemistry has emerged recently as a viable route toward polymer microfabrication due to its compatibility with existing microfabrication techniques and minimal requirement for investment. [2] Thiol-ene refers to the UV-initiated click chemistry reaction that occurs between thiol and allyl groups in a mixture containing two chemical components in its simplest form, one with thiol groups and the other with allyl groups mixed together in liquid form at stoichiometric or offstoichiometric ratio. It offers remarkable properties like fast curing where 2 mm thick thiol-ene layer is fully cured by UV dose of approximately 100 J m −2[3] and the ability to tune the mechanical properties of the material from low Young's modulus value of less than 11 MPa [4] to high Young's modulus value of 1750 MPa [2a] by controlling the crosslinking density. Furthermore, rapid and direct surface modification for adjusting the surface energy can be achieved with simple post-functionalization of hydrophobic groups. [2] Thiol-ene is therefore a promising material for polymer-based functional materials including micropatterned responsive surfaces.Magnetically responsive micropatterned surfaces actuated by external non-invasive stimuli allow instantaneous tuning of surface properties such as adhesion, [5] structural coloration, [6] and surface wettability. [7] Notable applications of magnetic pillars that have been reported include tactile force sensing, [8] liquid flow sensing, [9] mixing in microfluidic devices, [10] mixing of droplets, [11] switchable adhesive surfaces, [5a] cell analysis, [12] directional wetting, [13] real-time manipulation of light, [6] micromanipulation of beads, [14] and droplet transport. [15] The fabrication schemes in the reported cases involve either magnetic particle self-assembly under magnetic field or replica molding with polydimethylsiloxane (PDMS) as the common soft elastomeric material. Thiol-ene based materials have not been explored yet for responsive superhydrophobic surfaces.Here, we develop magnetic thiol-ene micropillar arrays that demonstrate fast responsiveness, suitable for droplet transport applications. The advantage of using thiol-ene is the tunability of elastic and surface properties. The elastic properties of the thiol-ene pillars are tuned by controlling the crosslinking Tunable and responsive surfaces offer routes to multiple functionalities ranging from superhydrophobic surfaces to controlled adhesion. Inspired by cilia structure in the respiratory pathway, magnetically responsive periodic arrays of flexible and magnetic thiol-ene micropillars are fabricated. Omnidirectional collective bending of the pillar array in magnetic field is shown. Local non-contact actuation of a single pillar is achieved using an electromagnetic needle to probe the responsiveness and the elastic properties of the pillars by comp...

Off-Stoichiometry Thiol–Enes Polymers Containing Silane Groups for Advanced Packaging Technologies

“…Composite materials have also been developed based on OSTE polymers. The addition of superparamagnetic carbonyl iron particles to OSTE made it possible to obtain tunable and magnetic micropillar arrays [ 24 ]. Encapsulation of an organometal hybrid perovskite nanocrystal in an OSTE polymer reduces photodegradation [ 25 ] and increases the photoluminescence bandwidth [ 26 ].…”

Core–Shell Magnetic Micropillars for Reprogrammable Actuation

“…These advanced controls with little requirement on the actuation setup enable a spectrum of unusual functionalities and potential applications for the magnetic micropillar array, as demonstrated here for the rewritable paper and recyclable display at the micrometer scale. The simultaneously programmable and reprogrammable actuation capabilities of the core–shell micropillars have not been realized using traditional magnetic micropillars or any other types of stimuli-responsive microstructures, ,− ,,− ,,,,,− where the actuated configurations are usually fixed and cannot be easily readapted.…”

“…Among the different actuation strategies to trigger the mechanical deformations of the responsive structures, the use of a magnetic field has been one of the most common due to its rapid response, remote and untethered control, and low cost. ,− ,− ,,− ,,,,,− ,,,− For the fabrication of a magnetic-responsive micro/nanostructure, the magnetic media for actuating (usually dispersed magnetic nanoparticles or nanowires) are often premixed in a flexible polymer solvent matrix (most often elastomers) and then cured and solidified together once the desired shapes/patterns of the nanocomposites are formed. − ,,− ,,,,,− In this way, the spatial distribution and magnetization profile of the magnetic media inside the cured matrix are determined permanently, and thus the obtained structures can present only one single actuation mode upon applying a specific external magnetic field. ,− ,,,− Although the deformations of the responsive structures can be adjusted by varying the actuation conditions such as the intensity and direction of the actuation field, such adjustments are only limited to the extent and direction of the deformations, and an advanced control over the actuated and reactuated shapes and/or patterns of the whole structure remains thus far inaccessible. ,− ,,,− Considering that the magnetic media can be easily and dynamically modulated when dispersed in a liquid environment, − and the actuation of the responsive micro/nanostructures would be more controllable and configurable if the magnetic mixture is in a liquid state, instead of a cured solid state, this model is adopted for actuating the deformations of the structures.…”

Microfluidic Applications of Artificial Cilia: Recent Progress, Demonstration, and Future Perspectives

“…The properties can be achieved by various methods such as lubricating, characterizations, and topography modifications by physical and chemical methods. Both permanent and switchable options were encoded [ 39 , 170 , 171 , 172 , 173 ]. The unidirectional wetting properties of the artificial cilia are shown in Figure 6 C.…”