Methods for conformal coating and sealing microchip reservoir devices

#This invention is generally in the field of implantable miniaturized devices that provide controlled delivery or exposure of molecules or smaller devices. More specifically, the invention relates to implantable microchip devices.

#When an implanted medical device such as a pacemaker is placed in the body, one needs to consider both the impact of the body on the device and the impact of the device on the body. The environment is electrically conductive and relatively corrosive, which can compromise the integrity and performance of the device electrically or mechanically. The presence of a foreign object in the body triggers the body's defense mechanisms, which can impair the functioning of the body and/or the device. One commonly used method to enhance the body's acceptance of the implanted device is coat the device with a biocompatible coating material.

#Pinhole-free, conformal coatings are designed to seal devices from liquids and gases, while protecting and electrically insulating the device. Such coatings are typically used to conform to the surface contours of an assembled printed circuit board and electronic components. They protect the circuitry from the environment, prevent damage, provide mechanical strength, and increase dielectric strength between components. Examples of conformal coatings include silicone, urethane, acrylic, and epoxy. Typical methods for depositing these coatings include dipping, spraying, spin coating, and ultraviolet (UV) curing. U.S. Pat. No. 5,510,138 discloses a method of applying such coatings using hot melt dispensing equipment. Although these conformal coatings and processes are adequate for coating electronics and circuits, they may be inappropriate for microchip chemical delivery devices, such as described in U.S. Pat. Nos. 5,797,898 and 6,123,861 to Santini, Jr. et al. and in Nature, 397:335–38 (1999) and Angewandte Chemie, 39:2396–407 (2000). Most of the typical coatings require a high temperature or UV cure. Some are also solvent-based coatings, which could adversely react with the reservoir contents (e.g., drug molecules or a device) in the microchip device. These types of coatings also may be unacceptable due to trapped air bubbles and uneven coating.

#FIG. 1 depicts the chemical structures of Parylene C, Parylene N, and Parylene D.

#FIG. 2 is a process flow diagram illustrating one embodiment of a parylene conformal coating process.

#FIG. 3 illustrates, in cross-sectional views, one embodiment of a process for fabricated a conformally coated microchip device, wherein tape masking is used to pattern a parylene conformal coating.

#Microchip devices having a conformal coating are provided that store and protect molecules and smaller devices from the environment for a period of time until controlled release or exposure of the molecules or smaller devices to the environment is desired. The microchip device includes (1) a substrate having a plurality of reservoirs; (2) reservoir contents comprising molecules, a secondary device, or both, located in the reservoirs; (3) reservoir caps covering the reservoirs contents to isolate said contents from one or more environmental components outside the reservoirs, wherein the reservoir caps can be selectively disintegrated or permeabilized to expose the reservoir contents within selected reservoirs to the one or more environmental components; and (4) a conformal coating over the outer surface of at least a portion of the substrate other than the reservoir caps. As used herein, the term “one or more environmental components” simply refers to constituents of the environment external the reservoirs, including, but not limited to, biological tissues and fluids at the site of implantation, air, fluids and particulates present during storage or in vitro use of the microchip devices.

#The conformal coating preferably provides an inert and biocompatible surface for implantation of the microchip device, mitigating adverse responses by the body following implantation. The coating process desirably is one that avoids the need for solvents, heat, or chemical techniques that could degrade or damage the drug and/or device. For example, parylene can be deposited from a vapor preferably at room temperature and at a vacuum of approximately 0.1 torr. This is particularly advantageous for temperature sensitive drug molecules, which otherwise may be degraded by high temperature sealing or coating processes. The coating methods provide a means for containing and sealing a drug or other material in a microchip device, electrically insulating the electrical connections to the microchip, and at the same time provide an inert biocompatible coating suitable for implantation in the human body.

#The microchip devices include a substrate having a plurality of reservoirs that contain the molecules or devices (i.e. the reservoir contents). The reservoirs can be individually filled and addressed, enabling the time and rate of release of multiple chemicals to be controlled. The reservoirs are closed at a first surface of the substrate by a reservoir cap or other membrane. Release or exposure of reservoir contents is from this first surface. The reservoirs also are closed at a second surface of the substrate distal the first surface. The reservoir opening at the second surface is sealed following filling of the reservoir with the reservoir contents. The conformal coating is applied either following or as part of the sealing process.