Coated Microstructures and Methods of Manufacture Thereof

Abstract

Coated microneedle devices and methods of making such devices are provided. In one aspect, a method for coating includes providing a microstructure having at least one surface in need of coating; and applying a coating liquid, which comprises at least one drug, to the at least one surface of the microstructure, wherein the surface energy of the coating liquid is less than the surface energy of the surface of the microstructure. The coating liquid may include a viscosity enhancer and surfactant. Microneedles having heterogeneous coatings, pockets, or both are also provided.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]This application claims benefit of U.S. Provisional Application No. 60 / 691,857, filed Jun. 17, 2005, and U.S. Provisional Application No. 60 / 732,267, filed Nov. 11, 2005. Those applications are incorporated herein by reference in their entirety.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT[0002]This invention was made with U.S. government support under Contract No. 8 RO1 EB00260-03 awarded by the National Institute of Health. The U.S. government has certain rights in the invention.BACKGROUND OF THE INVENTION[0003]This invention is generally in the field of microneedles useful in medical applications, and more particularly to coated microneedles for drug delivery and sensing, such as transdermally.[0004]Biopharmaceuticals, such as peptides, proteins, and future uses of DNA and RNA, represent a rapidly growing segment of pharmaceutical therapies (Walsh, Trends Biotechnol 23:553-58 (2005)). These drugs are delivered almost ...

AI Technical Summary

Benefits of technology

[0019]In another aspect, a microneedle device is provided for insertion of a drug into a biological tissue, which includes at least one microneedle having a base, a tip end, and a shaft portion therebetween; and a coating on at least a portion of the surface of the at least one microneedle, the coating comprising at least one drug, wherein the coating has a heterogeneous composition. The coating may include discrete particles, two or more discrete layers, two different phases, or a combination thereof.

[0020]In another aspect, a microneedle device for insertion of a drug into a biological tissue is provided which includes at least one microneedle having a base, a tip end, and a shaft portion therebetween; and a coating on at least a portion of the surface of the at least one microneedle, the coating comprising at least one drug, wherein the shaft portion of the at least one microneedle comprises one or more pockets therein. The coating may be located substantially only in the one or more pockets. The one or more pockets may contain at least a portion of the coating where the coating is in the form of a liquid, gel, microparticles, or a combination thereof.

[0021]

Problems solved by technology

These drugs are delivered almost exclusively by the parenteral route, as the oral route is generally unavailable due to poor absorption, drug degradation, and low bioavailability.

However, conventional parenteral administration with hypodermic needles undesirably requires expertise for delivery, can lead to accidental needle sticks, and causes pain, which results in reduced patient compliance.

The tough barrier posed by the skin's outer layer of stratum corneum has limited the applicability of this method to drugs that are hydrophobic, low molecular weight, and potent, as the stratum corneum's barrier properties severely limit passive delivery of most drugs, especially macromolecules and microparticles.

While the microneedle itself can be fabricated by adapting the tools of the microelectronics industry for inexpensive, mass production (Reed & Lye, Proc IEEE 92:56-75 (2004)), precise coating of microneedles presents technical challenges.

However, such dip coating to coat microneedles by simply dipping and withdrawing them from an aqueous solution of a compound (e.g., calcein, sulforhodamine or vitamin B) results in non-uniform coatings with frequent spreading of the solution to the substrate from which the microneedles extend.

Moreover, predictions of dip-coating theory to produce uniform coatings from different coating solutions mostly apply to static equilibrium systems; dynamic systems as in the case of dip coating are more complex.

In addition, because surface tension-driven phenomena often take place on the micron scale, conventional dip-coating methods have difficulty coating specified sections of micron-dimensioned structures, especially when those structures are closely spaced.

For instance, bridging of liquid coating material between closely spaced microneedles is problematic.

Usefulness of the process would appear to be limited due to the tendency of ripple formation in the film while dipping microprojections.

The method also would appear be restricted to certain dip lengths and to certain microprojection spacings, given that wicking of liquid up between closely spaced microprojections and onto the base of the device would still be expected to be a problem.

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