Implantable Variable Permeability Drug Infusion Techniques

1. Field of the Invention

This invention relates to implantable drug delivery techniques, and more particularly to such techniques in which fluid from a body is used to provide a force which delivers a treatment agent.

2. Description of Related Art

Drug delivery systems based on osmotic pumps are known and are described, for example, in U.S. Pat. No. 4,624,847 (Ayers et al.), issued Nov. 25, 1986. When using such an osmotic pump, it is impossible to control the rate of hydration of the osmotic medium. In known osmotic pumps, a porous membrane separates a hygroscopic media from body fluids. As the membrane passes water from the body into the pump due to osmosis, the media swells and forces the infusate out of a reservoir. Such an osmotic pump is a passive device that has a fixed infusion rate and no on/off control. This invention addresses the fixed infusion rate problem of known osmotic pumps which limits their therapeutic value.

The invention useful for dispensing a treatment agent, such as a drug, to a body including a body fluid. A preferred form of dispensing device useful in such an environment includes a first chamber for holding the treatment agent. A conduit is located between the first chamber and the body for delivering the treatment agent to the body. A second chamber holds a hygroscopic media. There is a means for applying pressure to the first chamber due to an increase in volume of the hygroscopic media in the second chamber so that the treatment agent is delivered through the conduit to the body. A variable permeability membrane responds to changes in an electromagnetic parameter for controlling the rate at which the volume of the hygroscopic media is increased. Means also are provided for controlling the value of the electromagnetic parameter, whereby the rate of delivery of the treatment agent is controlled. By using the foregoing techniques, the rate at which a treatment agent can be delivered from an implantable device is made controllable, thereby increasing the therapeutic value of the treatment agent.

These and other advantages and features will become apparent upon reading the following detailed description and referring to the accompanying drawings in which like numbers refer to like parts throughout and in which:

FIG. 1 is a diagrammatic and partially cross-sectional view of a preferred form of implantable dispensing device made in accordance with a preferred practice of the invention; and

FIG. 2 is a top plan view the device shown in FIG. 1.

Referring to FIGS. 1 and 2, a preferred form of implantable device made in accordance with the invention is adapted to be implanted in a body that includes body fluid BF. Device 10 includes a chamber 12 that holds a treatment agent TA, such as a drug, intended to be infused into the body for therapeutic treatment. A conduit 14 enables the delivery of treatment agent TA from reservoir 12 to the body in the direction of arrow B. The conduit comprises a hollow, cylindrical 21 gauge stainless steel tube having an outer end 15 in contact with the body and an inner end 16 in contact with the treatment agent in chamber 12.

Device 10 also includes a chamber 20 for holding a hygroscopic media HM. Such media include a solution of sodium chloride and water or a hydrophilic polymer (e.g., hydrogel) having a composition such that as hydration occurs, the media swells due to osmosis, creating a displacement force that exerts pressure on chamber 12.

Chamber 12 is separated from chamber 20 by a plastic synthetic elastomer impermeable sheet 22 that is deformable due to the increase volume of hygroscopic media HM. When the volume of the hygroscopic media increases, sheet 22 deforms, thereby applying pressure to chamber 12 so that treatment agent TA is delivered from chamber 12 through conduit 14 to the body in the direction of arrow B.

Device 10 also includes a variable permeability membrane 24 that has a generally cylindrical shape. One such membrane suitable for use with the present invention is described in U.S. Pat. No. 4,513,034 (Sparer et al, issued Apr. 23, 1985, "the '034 Patent"). As described in the '034 Patent, membrane 24 comprises a liquid crystalline membrane with a porous structure containing a polymeric liquid crystal which can undergo a phase change. The phase change can be controlled by various electromagnetic parameters, including an electrical field and a magnetic field. The '034 Patent is incorporated by reference.

Referring to FIG. 1, device I 0 includes a control module which is held in a sealed chamber 32 defined by a dome structure 34 and circular disk-shaped flange 36 which seals chamber 32 from chambers 12 and 20. Control module 30 includes a power supply 40 which applies a voltage to membrane 24 through conductors 42 and 43. The voltage supplied by the conductors changes the electric field of membrane 24 in order to adjust the permeability or pore size of the membrane, thereby controlling the rate at which the hygroscopic media HM increase its volume. The rate at which the hygroscopic media increases its volume controls the rate at which treatment agent TA is infused from chamber 12 to the body. Alternatively, the power supply could vary the magnetic field applied to membrane 24. If the pore size of membrane 24 is increased, body fluid BF diffuses from the body to chamber 20 at an increased rate, thereby increasing the rate at which the volume of the hygroscopic media increases.

The value of the voltage applied to conductors 42 and 43 by power supply 40 is determined by the value of a signal transported over a conductor 48 from a control circuit 46. The control circuit receives radio frequency power signals through an antenna lead 52 from a antenna 50 located as shown in control module 30. Antenna 50 receives radio frequency signals from a conventional transmitting antenna located outside the body. Apparatus for transmitting electrical power and data signals to an implanted device are well known, and are described, for example, in U.S. Pat. Nos. 5,314,458 (Najafi, issued May. 24, 1994) and 5,370,672 (Fowler et al., issued Dec. 6, 1994). In a well-known manner, control circuit 46 receives data from the radio frequency signals received by antenna 50 and processes the data in order to determine the proper value of control signal to be transmitted to power supply 40 in order to control the voltage applied to membrane 24.

Device 10 also may include a conventional semi-permeable membrane 60 of the type normally supplied with existing osmotic pumps.

Control circuit 46 may be programmed so that membrane 24 operates as an on/off switch to control the delivery of treatment agent TA. In this mode of operation, when a bias is placed on membrane 24, it causes the membrane to open its pores which allows body fluid BF to be passed into the hygroscopic media HM. The influx of body fluid results in infusion of treatment agent TA into the body. Removal of the bias results in a closure of the pores of membrane 24 and a cessation of infusion. Preferably, membrane 24 is bistable, i.e., the membrane requires energy only in order to change the state of its pores from open to closed. However, membrane 24 also may be of the type which requires a continuous bias and offers a continuously variable pore size.

Power for supplying an appropriate electromagnetic parameter to membrane 24 may be supplied from a battery held within power supply 40, or antenna 50 may continuously receive electrical power signals which provide the energy for biasing membrane 24.

Those skilled in the art will recognize that the preferred embodiments may be altered or amended without departing from the true spirit and scope of the invention, as defined in the accompanying claims.