Surface modification of PDMS microchips with poly(ethylene glycol) derivatives for μTAS applications

Amphiphilic, thixotropic additives for extrusion-based 3D printing of silica-reinforced silicone

The ability to utilize extrusion-based, direct ink write (DIW) 3D printing to create silica-reinforced silicones with complex structures could expand their utility in industrial and biomedical applications. Sylgard 184, a common Pt-cure silicone, lacks the thixotropic behavior necessary for effective printing and its hydrophobicity renders cured structures susceptible to biofouling. Herein, we evaluated the efficacy of various PEO-silane amphiphiles (PEO-SAs) as thixotropic and surface modifying additives in Sylgard 184. Eight amphiphilic PEO-SAs of varying architecture (e.g. linear, star, and graft), crosslinkability, and PEO content were evaluated. Modified formulations were also prepared with additional amounts of silica filler, both hexamethyldisilazane (HMDS)-treated and dimethyldichlorosilane (DiMeDi)-treated types. Numerous PEO-SA modified silicone formulations demonstrated effective water-driven surface hydrophilicity that was generally diminished with the addition of HMDS-treated silica filler. While increased yield stress was observed for PEO-SA modified silicones with added HMDS-treated filler, none achieved the initial target for 3D printing (>1000 Pa). Only the formulations containing the DiMeDi-treated filler (17.3 wt%) were able to surpass this value. These formulations were then tested for their thixotropic properties and all surpassed the targets for recovered storage modulus (G') (>1000 Pa) and loss factor (<0.8). In particular, the triblock linear PEO-SA produced exceptionally high recovered G', low loss factor, and substantial water-driven restructuring to form a hydrophilic surface. Combined, these results demonstrate the potential of silicones modified with PEO-SA surface-modifying additives (SMAs) for extrusion-based, DIW 3D printing applications.

Characterization of Off-Stoichiometry Microfluidic Devices for Bioanalytical Applications

In this paper, we further investigate the properties of off-stoichiometry thiol-ene polymers (OSTE) aiming its application in microchip electrophoresis for bioanalytical applications. The proportion of 1.3:1 (allyl:thiol) and 1:2.5 (allyl:thiol) presented the best results in terms of sealing. Raman imaging mapping of the polymers surfaces revealed an outstanding homogeneity. Water contact angle were measured as 68° ± 6° and 71° ± 5° for 1.3:1 allyl and 1:2.5 thiol, respectively. Substrates prepared with OSTE demonstrated to be less prone to sorption of nonpolar compounds. The electroosmotic flow measured for this OSTE composition was 3.8 ± 0.3·10^-4 cm² s^-1 V^-1, 1.5 times higher than the one found for polydimethylsiloxane microchips under the same conditions. As a proof-of-concept for the applicability of OSTE microchips in bioanalysis the immobilization of α-amylase on the polymer surface and the implementation of a Saccharomyces cerevisiae cell counter using contactless conductivity detection are demonstrated.

A review of microdialysis coupled to microchip electrophoresis for monitoring biological events

Microdialysis is a powerful sampling technique that enables monitoring of dynamic processes in vitro and in vivo. The combination of microdialysis with chromatographic or electrophoretic methods with selective detection yields a "separation-based sensor" capable of monitoring multiple analytes in near real time. For monitoring biological events, analysis of microdialysis samples often requires techniques that are fast (<1 min), have low volume requirements (nL-pL), and, ideally, can be employed on-line. Microchip electrophoresis fulfills these requirements and also permits the possibility of integrating sample preparation and manipulation with detection strategies directly on-chip. Microdialysis coupled to microchip electrophoresis has been employed for monitoring biological events in vivo and in vitro. This review discusses technical considerations for coupling microdialysis sampling and microchip electrophoresis, including various interface designs, and current applications in the field.