In-plane silicon microneedles with open capillary microfluidic networks by deep reactive ion etching and sacrificial layer based sharpening.

• The deep reactive ion etching (DRIE) of in-plane silicon microneedles is presented. • A needle sharpening process is developed using sacrificial layers (remaining unetched silicon). • The wedge-shaped needle is sharpened to conical structure tapering from the base to the apex. • The sharp microneedles have been demonstrated to be sufficiently robust for skin penetration. The deep reactive ion etching (DRIE) of in-plane silicon microneedles with open capillary microfluidic network is presented. The in-plane needle design allows easy fabrication of long needles for accessing abundant dermal fluids and improves the correlation with blood biomarkers. However, the anisotropic DRIE yields wedge-shaped (not sharp) needle tip. We developed a sharpening process using the sacrificial layers (remaining unetched silicon layer below the needle shaft) to facilitate the buildup of the concentration gradient of the etching species during the wet etching sharpening process, resulting in the relatively fast etching rate at shaft top than the bottom. As a result, the wedge-shaped structure is sharpened to conical structure, tapering smoothly from the base to the apex. Such sharp microneedles have been demonstrated to be sufficiently robust to penetrate porcine skins, with needles being intact after repetitive penetrations. The fabricated silicon devices are treated with oxygen plasma for making the surface hydrophilic, such that the capillary fluid is introduced within the open microfluidic network. [ABSTRACT FROM AUTHOR]