Glassy carbon microneedles—new transdermal drug delivery device derived from a scalable C-MEMS process

Abstract

Because carbon is the basic element of all life forms and has been successfully applied as a material for medical applications, it is desirable to investigate carbon for drug delivery applications, as well. In this work, we report the fabrication of a hollow carbon microneedle array with flow channels using a conventional carbon-microelectromechanical system (C-MEMS) process. This process utilizes the scalable and irreversible step of pyrolysis, where prepatterned SU-8 microneedles (precursor) are converted to glassy carbon structures in an inert atmosphere at high temperature (900 °C) while retaining their original shape upon shrinkage. Once converted to glassy carbon, the microneedles inherit the unique properties of hardness, biocompatibility, and thermal and chemical resistance associated with this material. A comparative study of hardness and Young’s modulus for carbon microneedles and SU-8 microneedles was performed to evaluate the increased strength of the microneedles induced by the C-MEMS process steps. Structural shrinkage of the carbon microneedles upon pyrolysis was observed and estimated. Material characterizations including energy-dispersive X-ray spectroscopy (EDX) and Raman spectroscopy were carried out to estimate the atomic percentage of carbon in the microneedle structure and its crystalline nature, respectively. Our investigations confirm that the microneedles are glassy in nature. Compression and bending tests were also performed to determine the maximum forces that the carbon microneedles can withstand, and it was found that these forces were approximately two orders of magnitude higher than the resistive forces presented by skin. A microneedle array was inserted into mouse skin multiple times and was successfully removed without the breakage of any microneedles.

Biocompatibility of SU-8 and Its Biomedical Device Applications

“…Figure 11 shows the SEM image of one the fabricated SU-8 microneedle arrays using SU-8 itself as microneedle structural material. Mishra et al’s work started with the fabrication of high-aspect-ratio SU-8 hollow structures [ 65 ]. The hollow SU-8 structures were then subsequently pyrolyzed in an inert atmosphere at 900 °C to convert the SU-8 structures into glassy carbon structures.…”

“…( f , g ) Magnified images of the CMNs and the underlying flow channel. Reprinted from Mishra et al [ 65 ] with permission from Springer Nature.…”

Recent Advances in Micro-Electro-Mechanical Devices for Controlled Drug Release Applications

“…This study mainly analyzed MNs flexibility and concluded that this feature could be tuned depending on the required application. Another relevant studies, reported the design, fabrication and characterization of a hollow glassy carbon MN array (Pramanick et al, 2016) with flow channel integration (Mishra et al, 2018). The strategy was based on the direct laser writing patterning of photoresist as precursor and conversion of these structures into glassy carbon by pyrolysis retaining their tubular MN shape.…”

“…(C) a: Etched microfluidic conduit in silicon through which the drug flows from the drug reservoir to the glassy carbon microneedles; b: SU-8 microneedles fabricated on a microfluidic conduit backside of the image shown in a; c: glassy carbon microneedles array formed after pyrolysis; d: magnified view of a glassy carbon microneedles; e: optimized glassy carbon microneedles aligned on etched microfluidic ports on a silicon wafer. Adapted fromMishra et al (2018) with permission from Springer Nature (http://creativecommons.org/licenses/by/4.0/).…”

Modelling of Stem Cells Microenvironment Using Carbon-Based Scaffold for Tissue Engineering Application—A Review

“…The biocompatibility of scaffolds is first influenced by the types of materials used. Recently, various materials were investigated, including metal, ceramic, natural, and synthetic [ 6 , 7 , 8 , 9 , 10 ].…”