Microfabricated microneedle with porous tip for drug delivery

This paper presents a novel approach to fabrication of a silicon microneedle array with porous tips. Dry etching technology with SF6/O2 gas by STS's inductively coupled plasma (ICP) etch tool was used to achieve the pyramidal needle structure. A thin silicon nitride layer was deposited after a thick photoresist layer was coated and reflowed at 120 °C. The silicon nitride layer and residual photoresist on the tips of the pyramidal structures were removed using reactive ion etching (RIE). Electrochemical etching in MeCN/HF was carried out to generate porous silicon on the tips of the microneedles. The fabricated microneedle array has potential applications in drug delivery, since the porous tips can be loaded with a high molecular weight drug. Analytic solutions to the critical loadings of the fabricated microneedle structure are also presented. The variations of the square cross-section were expressed as a function of the axial coordinate to analyze the bending normal stress and critical buckling loading. This analytic method can also be used for other microneedle structures with different cross-sections.

[1]  Martin A. Schmidt,et al.  Influence of Coil Power on the Etching Characteristics in a High Density Plasma Etcher , 1999 .

[2]  Morphology of macro-pores formed by electrochemical etching of p-type Si , 2004 .

[3]  K. Wise,et al.  A multichannel neural probe for selective chemical delivery at the cellular level , 1997, IEEE Transactions on Biomedical Engineering.

[4]  Mark G. Allen,et al.  Microfabricated needles for transdermal delivery of macromolecules and nanoparticles: Fabrication methods and transport studies , 2003, Proceedings of the National Academy of Sciences of the United States of America.

[5]  Wijaya Martanto,et al.  Transdermal Delivery of Insulin Using Microneedles in Vivo , 2004, Pharmaceutical Research.

[6]  S. Ossicini,et al.  Porous silicon: a quantum sponge structure for silicon based optoelectronics , 2000 .

[7]  M. Allen,et al.  Microfabricated microneedles: a novel approach to transdermal drug delivery. , 1998, Journal of pharmaceutical sciences.

[8]  Mark R Prausnitz,et al.  Microneedles for transdermal drug delivery. , 2004, Advanced drug delivery reviews.

[9]  Mark R Prausnitz,et al.  Insertion of microneedles into skin: measurement and prediction of insertion force and needle fracture force. , 2004, Journal of biomechanics.

[10]  Dorian Liepmann,et al.  Fluid injection through out-of-plane microneedles , 2000, 1st Annual International IEEE-EMBS Special Topic Conference on Microtechnologies in Medicine and Biology. Proceedings (Cat. No.00EX451).

[11]  C. J. Mogab,et al.  Plasma etching of Si and SiO2—The effect of oxygen additions to CF4 plasmas , 1978 .

[12]  Philippe M. Fauchet,et al.  Microhardness of porous silicon films and composites , 1997 .

[13]  Paul A. Kohl,et al.  The Electrochemical Oxidation of Silicon and Formation of Porous Silicon in Acetonitrile , 1994 .

[14]  S. L. Buckberry,et al.  A material for melding humans and machines , 1999 .

[15]  J. Matriano,et al.  Macroflux® Microprojection Array Patch Technology: A New and Efficient Approach for Intracutaneous Immunization , 2004, Pharmaceutical Research.

[16]  S. Mitragotri,et al.  Current status and future potential of transdermal drug delivery , 2004, Nature Reviews Drug Discovery.

[17]  R Langer,et al.  New methods of drug delivery. , 1990, Science.

[18]  Serrita A. McAuley,et al.  Silicon micromachining using a high-density plasma source , 2001 .

[19]  Marc Christophersen,et al.  Crystal orientation and electrolyte dependence for macropore nucleation and stable growth on p-type Si , 2000 .

[20]  Chong H. Ahn,et al.  A tapered hollow metallic microneedle array using backside exposure of SU-8 , 2004 .

[21]  M. Cormier,et al.  Transdermal Delivery of Antisense Oligonucleotides with Microprojection Patch (macroflux®) Technology , 2001, Pharmaceutical Research.

[22]  A. Vincent,et al.  NANOINDENTATION INVESTIGATION OF THE YOUNG'S MODULUS OF POROUS SILICON , 1996 .

[23]  W. Smith.  Analytic solutions for tapered column buckling , 1988 .