Inkjet Printing of High Aspect Ratio Superparamagnetic SU-8 Microstructures with Preferential Magnetic Directions

Abstract

Structuring SU-8 based superparamagnetic polymer composite (SPMPC) containing Fe 3 O 4 nanoparticles by photolithography is limited in thickness due to light absorption by the nanoparticles. Hence, obtaining thicker structures requires alternative processing techniques. This paper presents a method based on inkjet printing and thermal curing for the fabrication of much thicker hemispherical microstructures of SPMPC. The OPEN ACCESSMicromachines 2014, 5 584 microstructures are fabricated by inkjet printing the nanoparticle-doped SU-8 onto flat substrates functionalized to reduce the surface energy and thus the wetting. The thickness and the aspect ratio of the printed structures are further increased by printing the composite onto substrates with confinement pedestals. Fully crosslinked microstructures with a thickness up to 88.8 μm and edge angle of 112° ± 4° are obtained. Manipulation of the microstructures by an external field is enabled by creating lines of densely aggregated nanoparticles inside the composite. To this end, the printed microstructures are placed within an external magnetic field directly before crosslinking inducing the aggregation of dense Fe 3 O 4 nanoparticle lines with in-plane and out-of-plane directions.

Self-assembly of micro/nanosystems across scales and interfaces

“…Hemispheres, easily fabricated by IJP on pedestals, are geometrically well conducive to pair-wise assembly [19]. Additionally, IJP of SU-8 doped with superparamagnetic Fe3O4 nanoparticles within a uniform magnetic field allowed the fabrication of high aspect ratio hemicapsules with anisotropic magnetization profile, which allowed to stir the motion and aggregation of the hemicapsules under external magnetic fields [38]. Subsequently, we showed in-liquid selective pair-wise assembly of full capsules driven by hydrophobic interactions among half-capsules [39].…”

Organic-inorganic-hybrid-polymer microlens arrays with tailored optical characteristics and multi-focal properties

“…hemispherical or higher (ν ≥ 90°); meaning lenses with high numerical apertures (NA). For such lenses, the diameter of the lens is larger than the diameter of the platforms, such as clearly shown in [23] which obviously imposes higher platform spacing. Secondly, the precision and accuracy of the printing position and the one of the motion stages imposes a minimum platform diameter slightly under 40 µm and a maximum value of the filling factor which depends on the lens profile targeted [31].…”

“…This confinement is possible either chemically based on local surface energy modification, such as by micro-contact printing [21] or topographically based on pre-patterned substrates [22]. Based on IJP dispensing, the minimum rim height of protrusive platforms with vertical side walls allowing liquid confinement has been demonstrated to be slightly lower than 1 µm [23]. This principle has been successfully applied for the fabrication of arrays of plano-convex lens-like structures with controlled spherical profiles [22,24].…”

Direct Laser Writing of Magneto-Photonic Sub-Microstructures for Prospective Applications in Biomedical Engineering

“…A number of synthesis and fabrication methods have been proposed to obtain desired magnetic structures, for instance, self-assembly [14,15], bio-templating [16], inkjet-printing [17], and stop-flow lithography [18]. However, these methods are complicated, expensive, and usually refer to large-scale structures.…”