Fabrication of Biocompatible Hollow Microneedles Using the C-MEMS Process for Transdermal Drug Delivery

Abstract

Microneedles are important component for the local delivery of drug with precise dose in controlled release to overcome the over dosage problem and decrease side-effects in drugs. These have been identified as a transformative technology for a painless, self-administered alternative to hypodermic injection and solid microneedles have been marketed for a many applications including scar treatment and improving skin permeability of topical drug formulations. Hollow microneedles have the potential to offer a large advantage in performance over these solid microneedle architectures. The architecture of hollow microneedle is more flexible and allows for delivery of larger drug molecules and volumes than other microneedle architectures. By integrating the hollow microneedles with micropumps, these can facilitate active control over the drug delivery profile to allow for continuous drug release for the applications such as insulin delivery. However the complications in the fabrication process are limiting towards future development of hollow microneedle platforms. A variety of microfabrication technologies have been developed for microneedles. The primary approaches for fabricating hollow microneedles have motivated on top-down approaches using the materials such as silicon, metal, or glass. However, the requirement to fabricate a hollow microneedle creates a substantial fabrication challenge for top-down approaches. We present here a novel method for fabricating hollow microneedles using Carbon-MEMS (C-MEMS) process. C-MEMS process is getting more attention since last 15 years for its low cost, reliability and simplicity in the process. The high aspect ratio carbon hollow microneedle structures are fabricated in two steps: fabrication of SU8 microneedles in one step photolithography and conversion of polymer structures to carbon in pyrolysis process. The ease of fabrication of high aspect ratio SU8 structure makes it a suitable candidate for microneedle application. We report here for the very first time the hollow microneedle with glassy-carbon nature which is biocompatible. The percentage of shrinkage of SU8 structures after pyrolysis is also reported in this work. The outer diameter shrinkage is around 42% for 200µm tall needle where the inner and outer diameter ratios are 1/5, 1/3, 1/2 and it is 34.92% for solid needle structure. The inner diameter is also shrunk for all the cases. However, the outer diameter is shrunk only around 15% when the ratio of inner and outer diameter is 2/3 and the inner diameter is expanded in this case. The integration of these needle structures with drug delivery system (micropump) is our ongoing work. Figure 1