ABSTRACT
PolyJet™ 3D printers have been widely used for the fabrication of microfluidic molds to replicate castable resins due to the ease to create microstructures with smooth surfaces. However, the microstructures fabricated by PolyJet printers do not accurately match with those defined by the computer-aided design (CAD) drawing. While the reflow and spreading of the resin before photopolymerization are known to increase the lateral dimension (width) of the printed structures, the influence of resin spreading on the vertical dimension (height) has not been fully investigated. In this work, we characterized the deviations in both lateral and vertical dimensions of the microstructures printed by PolyJet printers. The width of the printed structures was always larger than the designed width due to the spreading of resin. Importantly, the microstructures designed with narrow widths failed to reproduce the intended heights of the structures. Our study revealed that there existed a threshold width (wd') required to achieve the designed height, and the layer thickness (a parameter set by the printer) influenced the threshold width. The thresholds width to achieve the designed height was found to be 300, 300, and 500 µm for the print layer thicknesses of 16, 28, and 36 µm, respectively. We further developed two general mathematical models for the regions above and below this threshold width. Our models represented the experimental data with an accuracy of more than 96% for the two different regions. We validated our models against the experimental data and the maximum deviation was found to be <4.5%. Our experimental findings and model framework should be useful for the design and fabrication of microstructures using PolyJet printers, which can be replicated to form microfluidic devices.
ABSTRACT
Replica obtained from micromolds patterned by simple photolithography has features with uniform heights, and attainable microchannels are thus quasi-two-dimensional. Recent progress in three-dimensional (3D) printing has enabled facile desktop fabrication of molds to replicate microchannels with varying heights. We investigated the replica obtained from four common techniques of 3D printing-fused deposition modeling, selective laser sintering, photo-polymer inkjet printing (PJ), and stereolithography (SL)-for the suitability to form microchannels in terms of the surface roughness inherent to the mechanism of 3D printing. There have been limited quantitative studies that focused on the surface roughness of a 3D-printed mold with different methods of 3D printing. We discussed that the surface roughness of the molds affected (1) transparency of the replica and (2) delamination pressure of poly(dimethylsiloxane) replica bonded to flat glass substrates. Thereafter, we quantified the accuracy of replication from 3D-printed molds by comparing the dimensions of the replicated parts to the designed dimensions and tested the ability to fabricate closely spaced microchannels. This study suggested that molds printed by PJ and SL printers were suitable for replica molding to fabricate microchannels with varying heights. The insight from this study shall be useful to fabricate 3D microchannels with controlled 3D patterns of flows guided by the geometry of the microchannels.
ABSTRACT
We developed a rapid and simple method to fabricate microfluidic non-planar axisymmetric droplet generators using 3D printed fittings and commercially available components. 3D printing allows facile fabrication of microchannels albeit with limitations in the repeatability at low resolutions. In this work, we used 3D printed fitting to arrange the flow in the axisymmetric configuration, while the commercially available needles formed a flow-focusing nozzle as small as 60 µm in diameter. We assembled 3D printed fitting, needle, and soft tubes as different modules to make a single droplet generator. The design of our device allowed for reconfiguration of the modules after fabrication to achieve customized generation of droplets. We produced droplets of varying diameters by switching the standard needles and the minimum diameter of droplet obtained was 332 ± 10 µm for 34 G (ID = 60 µm). Our method allowed for generating complex emulsions (i.e. double emulsions and compartmented emulsions) by adding 3D printed sub-units with the fluidic connections. Our approach offered characteristics complementary to existing methods to fabricate flow-focusing generators. The standardized needles serving as a module offered well-defined dimensions of the channels not attainable in desktop 3D printers, while the 3D printed components, in turn, offered a facile route to reconfigure and extend the flow pattern in the device. Fabrication can be completed in a plug-and-play manner. Overall, the technology we developed here will provide a standard approachable route to generate customized microfluidic emulsions for specific applications in chemical and biological sciences.
ABSTRACT
Topically administered ocular drug delivery systems typically face severe bioavailability challenges because of the natural protective mechanisms of eyes. The rational design of drug delivery systems that are able to persist on corneal surfaces for sustained drug release is critical to tackle this problem. In this study, we fabricated monodisperse chitosan-coated PLGA microparticles with tailored diameters from 5 to 120 µm by capillary microfluidic techniques and conducted detailed investigations of their mucoadhesion to artificial mucin-coated substrates. AFM force spectroscopy revealed strong instant adhesion to mucins, whereas the adhesion force, rupture length, and adhesion energy were positively correlated to the particle diameter and contact time. Particle detachment tests under shear flow in a microfluidic mucin-coated flow cell were in accord with the AFM measurements and revealed that microparticles smaller than 25 µm exhibited strong persistence in the flow cell, withstanding high shear rates up to 28,750 s-1 which are equivalent to the harshest in vivo ocular conditions. A simple scaling analysis connects the AFM and detachment tests, and reveals the existence of a threshold diameter below which mucoadhesion performance essentially saturates-an important insight in managing the opposing design criteria of enhanced mucoadhesion and slow, sustained drug delivery. Our findings thus pave the way for the rational design of mucoadhesive microparticulate ocular drug delivery systems that are capable of enhancing the bioavailability of topically applied drugs to eyes, as well as to other tissues whose epithelial surfaces contain mucosae.
