Controlled gas generation for gas-driven infusion devices

Gas is generated at a controlled rate from a liquid and solid phase combination that generated gas upon contact, by using diffusive transport of the liquid toward the solid phase surface to prolong the rate of gas generation, with a variety of alternatives for controlling the rate of diffusive transport. This system is useful in infusion devices for delivering medications or other beneficial liquids from a retaining pouch at controlled rates over a prolonged period of time.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention resides in the field of controlled liquid delivery devices, 
such as those used in the administration of medicaments. This invention 
also relates to the chemistry of gas generation used as the driving force 
in controlled liquid delivery devices, and the types of materials used as 
sources of the gas. 
2. Description of the Prior Art 
Infusion pumps are devices that eject liquid materials at continuous and 
prolonged rates by generating gas in a contained enclosure that forces the 
liquid material out of a bladder or reservoir retained within the 
enclosure. Pumps of this type are useful for the controlled delivery of 
drugs and other medications to patients, eliminating the need for periodic 
injections or other modes of administration, and avoiding the usual 
profile of a high initial concentration of the drug in the bloodstream 
followed by a gradual decline. 
Numerous patents have issued on inventions relating to infusion pump 
design. Representative examples are U.S. Pat. Nos. 3,023,750 (Baron, Mar. 
6, 1962), 4,379,453 (Baron, Apr. 12, 1983), 3,718,236 (Reyner et al., Feb. 
27, 1973), 5,398,850 (Sancoff et al., River Medical, Inc., Mar. 21, 1995), 
5,398,851 (Sancoff et al., River Medical, Inc., Mar. 21, 1995), 5,588,556 
(Sancoff et al., River Medical, Inc., Dec. 31, 1996), 5,578,005 (Sancoff 
et al., River Medical, Inc., Nov. 26, 1996), 5,558,255 (Sancoff et al., 
River Medical, Inc., Sep. 24, 1996), and 5,106,374 (Apperson et al., 
Abbott Laboratories, Apr. 21, 1992), all of which disclose various devices 
that generate pressurized gas to expel a liquid from a liquid delivery 
device, utilizing chemically reactive sets or combinations of 
gas-generating chemicals. 
The Baron and Reyner et al. patents disclose liquid delivery systems 
powered by the generation of carbon dioxide gas by reactive chemical 
combinations, but they lack means to control the reaction rate or the 
resulting liquid flow. The Reyner et al. patent discloses a system that 
produces a series of sequential chemical reactions that release gas in a 
series of discrete releases over a period of time. 
The systems disclosed in the Sancoff et al. patents achieve controlled 
delivery primarily by extending the reaction time of the reactants. This 
is achieved by adding a rate-limiting moiety to a solid tablet consisting 
of an alkaline metal carbonate, and then submerging the tablet in a bath 
of aqueous acid media. The Sancoff et al. patents specify separate storage 
of the chemical reactants prior to use, with no premixing. The reaction 
rate upon initial contact of the chemicals is very high, and drops off 
rapidly with time as the reactants are consumed. The rate of reaction is a 
function of the concentration of remaining chemicals, and as the liquid 
acid reactant concentration decreases significantly over time, the 
reaction rate and hence the rate of carbon dioxide generation are reduced. 
While the exposed surface area of solid reactant increases with time, this 
does not fully compensate for the decreased liquid reactant concentration. 
Accordingly, a very large portion of the generated gas is wastefully 
vented through a pressure relief valve during the early part of the 
infusion process. 
The Sancoff et al. patents disclose the use of two separately disposed 
chemical reactants, one liquid and one solid. Both reactants are dangerous 
to handle, and can pose a health risk to patients and health care workers 
in the event of a leak. To initiate the reaction in the device, a barrier 
membrane is ruptured and the solid alkaline tablet is manually pushed into 
the acid solution. This is accomplished by pressing against a portion of 
the exterior wall of the device, the wall portion being of reduced 
thickness. Unfortunately, this reduced thickness portion is a prone to 
leakage. Also, the pressing of the tablet through the barrier membrane 
must be done rapidly. Otherwise, back pressure from the resulting gas can 
arrest the movement of the tablet through the membrane when the tablet is 
only part way through. A tablet resting part of the way through the 
membrane can cause failure of the device. 
The Apperson et al. patent discloses an infusion device which releases 
compressed gas from a storage cylinder at a controlled rate to power an 
infusion device. Gas pressure in this device is maintained by use of a 
pressure relief valve. In order to store the required amount of gas to 
power the device, it is necessary to store either a large volume of gas 
under low pressure or a small volume under high pressure. Neither is 
desirable since low pressure storage is subject to space limitations and 
high pressure gas entails excess weight and cost, as well as the risk of 
damage and injury. High pressure gas also requires a relatively high 
pressure gas regulator or relief valve, both of which are expensive. 
Further disclosures of potential relevance to the present invention include 
U.S. Pat. Nos. 3,888,998 (Sampson et al., The Procter & Gamble Company, 
Jun. 10, 1975), 3,992,493 (Whyte et al., The Procter & Gamble Company, 
Nov. 16, 1976), 4,007,134 (Liepa et al., The Procter & Gamble Company, 
Feb. 8, 1977), and 4,025,655 (Whyte et al., The Procter & Gamble Company, 
May 24, 1977). These patents disclose the use of carbon dioxide loaded 
(adsorbed) onto molecular sieve materials, with subsequent desorption for 
the purpose of carbonating water for use in carbonated beverages. These 
systems are designed to rapidly desorb carbon dioxide into water over a 
period of about one to five minutes only, and for the sole purpose of 
carbonating water. The molecular sieves can be formed into various shapes 
and loaded with adsorbed carbon dioxide, then immersed into water, a 
portion of which is adsorbed in preference to the previously adsorbed 
carbon dioxide, producing carbon dioxide gas bubbles which carbonate the 
water for use in beverages. The entire gas release process generally takes 
place in less than about five minutes, and no attempt is made to capture 
work from the released gas. 
SUMMARY OF THE INVENTION 
It has now been discovered that gas can be generated by desorption, 
chemical reaction, or other means resulting from the contact between 
liquid and solid phases in a prolonged and controlled manner by diffusing 
the liquid to the surface of the solid at a controlled difflusion rate. 
Various means of limiting and controlling the diffusion rate are 
disclosed, including the use of wicks and wicking methods, as well as the 
use of additives mixed in with the liquid to lower its concentration or to 
vary certain properties of the liquid that affect its difflusion rate. 
Included among the structures disclosed are those in which the liquid and 
solid substances are physically separated by barriers, with a wick serving 
as the sole means of communication, as well as those in which the solid 
substance is porous with the liquid occupying the pores but permitted only 
limited diffusion within the pores by the additives, examples of which are 
diluents and viscosity-increasing solutes. Gas generation in each of the 
various configurations of the invention is provided by any of a variety of 
mechanisms, including gas-generating chemical reactions and the release of 
adsorbed gases. 
This discovery is applicable to any device that can benefit from a 
controlled release of gas. Prominent among such devices are infusion 
pumps, in which the released gas provides the driving force for the 
pressurized expulsion of liquid medicament or other beneficial liquid to 
an environment where the liquid has a beneficial effect. In these devices, 
the beneficial liquid is held in a bladder that contains at least one 
(preferably only one) opening, the bladder retained in a housing of 
material that is gas-impermeable or very low in gas permeability. The 
housing material is also substantially non-extensible, i.e., extensible by 
no more than about 5%, and preferably by no more than about 1%, along a 
linear dimension upon exposure to the pressures typically encountered 
during use according to this invention. In addition, the housing material 
is preferably flexible. The housing further contains the solid and liquid 
substances that generate the driving gas upon contact. 
A further discovery made in connection with this invention is the choice of 
a laminate as the wall material for the housing and the effectiveness of 
the laminate in providing optimal flexibility while still serving as an 
effective barrier to gas permeation. A still further discovery is a novel 
design for a pressure relief valve, including structure within the valve 
to permit adjustment of the relief pressure and materials used in the 
valve to prevent blocking of the valve. 
Still further discoveries in connection with this invention are chemical 
systems that are particularly adaptable for generating gas in a controlled 
manner for infusion devices, and that avoid the risks of hazardous 
discharge or air/gas separation devices, which are expensive and subject 
to blockages and clogging. One such system is a molecular sieve material 
bearing an adsorbed gas as the solid phase, in combination with an aqueous 
liquid as the liquid phase. As the water in the aqueous liquid contacts 
the molecular sieve at a controlled and prolonged rate, the adsorbed gas 
is released. Another such system is a liquid solution of hydrogen peroxide 
or a superoxide compound as the liquid phase and an immobilized catalyst 
or enzyme as the solid phase, the catalyst or enzyme promoting the 
decomposition of the peroxide or superoxide to release oxygen gas. A 
controlled rate of contact and hence a controlled release of gas in either 
system is enhanced by the use of the controlled diffusion methods 
described above. 
These and other discoveries, features and embodiments of the invention will 
be understood in more detail from the descriptions that follow.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS 
The present invention is susceptible to a wide range of implementations and 
embodiments, and certain aspects of the invention as a whole will be best 
understood by the detailed explanation of specific examples. This portion 
of the specification will begin by examining the chemical aspects of the 
invention, and will then proceed with explanations of the structural 
features by specific examples. 
Wicking Materials and Methods 
In certain embodiments of this invention, as indicated above, controlled 
diffusive transport of the liquid phase to the solid phase is achieved by 
the use of a wick joining the liquid reservoir to the solid phase. The 
rate of gas desorption or generation from the tablet is roughly 
proportional to the rate of liquid flow through the wick into the solid 
phase. The rate of flow through the wick can be varied by a number of 
techniques, including varying the cross sectional area of the wick, 
varying the amount of the wick immersed in the liquid reservoir, or by 
selection of the wicking material, such as a crosslinked polyvinyl alcohol 
for highly efficient transport. The rate of flow through the wick can be 
lowered by decreasing the cross sectional area of the wick, increasing the 
viscosity of the liquid, shortening the wick, pinching or crimping the 
wick, or adding a restriction to the wick. 
A wide variety of wick materials can be used; the particular material is 
not critical to the invention. Examples of wick materials are polyvinyl 
alcohol (preferably crosslinked), polyvinyl acetate (preferably 
crosslinked), combinations of polyvinyl alcohol and polyvinyl acetate 
(preferably both crosslinked), crosslinked hydrogels, felts, open-cell 
sponge materials, and porous plastics. Preferred wick materials for 
certain embodiments of the invention are polyvinyl alcohol or combinations 
of polyvinyl alcohol and polyvinyl acetate. These materials are available 
commercially from Merocel Corporation (Mystic, Conn. USA), Kanebo Ltd. 
(Osaka, Japan), and other suppliers. A most preferred wicking material is 
Kanebo Type E(A), with an average pore size of 130 microns and apparent 
density of about 0.11 g/cm.sup.3. A description of one type of wick useful 
in this invention is found in U.S. Pat. No. 4,098,728 (Rosenblatt, Jul. 4, 
1978, incorporated herein by reference), and available from Merocel 
Corporation. The Rosenblatt wick is naturally hydrophilic, and can be made 
dense enough to prevent a rapid flow of water into the molecular sieve 
tablet, even with significant head pressures applied. The Rosenblatt wick 
material can be obtained in flat sheets and die cut to the desired final 
dimensions. A currently preferred wick cross section is 2 mm.times.2 mm. 
To achieve a very slow gas evolution rate, a slow wicking material can be 
used. For systems using water as the liquid phase, crosslinked hydrogels 
serve as slow wicking materials. One example is a cross-linked hydrogel 
containing about 4% very high molecular weight polyethylene oxide and 
about 96% water (both percents on a weight basis). A significant advantage 
of a crosslinked hydrogel wick is its ability to prevent the free flow of 
water to the solid phase, particularly to a porous solid phase such as a 
molecular sieve tablet, even when the source of water is above the tablet 
and exerts a head pressure on the wick. The reason is that diffusion 
rather than head pressure is the primary controlling factor for the water 
delivery rate through the wick. 
Some wicks are more sensitive to head pressure effects. Accordingly, when 
the water source is above the tablet, the hydrostatic pressure of the 
water will add significantly to the driving force for the water flow rate. 
Examples of this type of wick include certain felt products, large 
open-cell sponge materials, such as viscose sponge materials, and porous 
plastic structures such as those made by Porex Technologies, Fairburn, 
Ga., USA. An example of a suitable felt material is SIF Felt type 6-900Z 
made by Foamex International, Inc., Eddystone, Pa., USA. An advantage to 
the use of felt wicks is that very fast flow rates can be obtained in 
certain orientations. 
Other factors affecting the flow rate of water or other liquid into or 
toward the solid phase are the surface area of contact between the wick 
and the solid phase, the surface area of the wick exposed to the liquid 
reservoir, the liquid level in the liquid reservoir, the absorbent 
potential of the solid phase, and density of the solid phase. The greater 
the contact area between the wick and the solid phase, the faster the flow 
of water into the solid phase, although the relationship is not directly 
proportional. The cross sectional area of the wick has a large effect on 
flow rates, with larger cross sectional wicks having an enhanced ability 
to cause liquid to flow through them. If the liquid and solid phases are 
isolated in separate compartments, a pressure differential may develop 
between the compartments, causing a pressure gradient along the wick. This 
can reduce or arrest the flow of liquid through the wick. This effect can 
be eliminated by venting gas between the two compartments. Alternatively, 
the pressure differential can be used as a further means of controlling 
the wicking rate, by controlling the size or number of holes serving as 
the gas vent. 
Another means of controlling the wicking rate is the addition to the 
wicking liquid of materials that raise the viscosity of the liquid. 
Examples of such materials are hydroxy ethyl cellulose, hydrogel forming 
polymers, and polyethylene glycol polymers, particularly for aqueous 
liquid phases. Additionally, hydrophilic and hydrophobic surfactants can 
be added to the wick, the liquid phase or both, to affect the flow rate. 
For aqueous liquids, hydrophilic surfactants will decrease the wicking 
rate by lowering the surface tension. A similar effect can be achieved by 
incorporating a viscosity increasing substance in the solid phase. 
The wicking effect can also be achieved by wicking media rather than a 
discrete wick. An example of a nondiscrete wick is compacted 
superabsorbent polymer particles held together by a retaining structure. 
Superabsorbent polymer hydrates upon contact with water, and a hydrated 
superabsorbent polymer particle then hydrates other superabsorbent polymer 
particles in contact with it. Alternatively, the solid phase material 
itself can be used as a wicking material. When the solid phase is a 
molecular sieve tablet, for example, the tablet can be formed with a leg 
rather than a through hole for insertion of a discrete wick. The leg is 
thus made of compressed tablet material and acts as a wick. 
Using a tablet again as an example, the tablet itself can serve as a wick, 
and placed in direct contact with the liquid phase. With the phases thus 
in direct contact, control over the wicking rate and gas release can be 
achieved by various means. As one example, the viscosity of the liquid 
phase can be increased by the inclusion of a suitable additive. One 
example of such an additive is hydroxyethylcellulose. Further description 
of this method appears below. 
For aqueous liquids, unless the solid phase is directly immersed in the 
liquid, wicking does not require the use of a hydrophobic membrane to 
separate gas from liquid, since only gas is emitted from the solid phase. 
Excess liquid can be retained in the solid phase. Certain prior art 
devices require the use of a gas-liquid separation membrane for effective 
operation, since the evolution of gas bubbles occurs in the presence of 
free flowing liquid. Therefore, by its ability to function effectively 
with the liquid phase retained inside the solid phase, this invention 
represents a significant improvement over the use of hydrophobic 
membranes. When the solid phase is a molecular sieve tablet, the liquid 
phase is retained in the interstitial spaces between the molecular sieve 
particles that comprise the tablet. When the solid phase is a chemical 
species or combination of species that produce a solid residue when 
reacting with the incoming liquid to produce the gas, the reactants are 
replaced by the solid residue which retains the shape of the tablet. This 
ensures that the structure of the tablet is never fully compromised, 
allowing it to retain excess water. An alternative means of retaining the 
tablet shape as gas generation proceeds is by the inclusion of tableting 
agents, which can provide a stable insoluble framework. 
In preferred embodiments of the invention, the solid phase is constructed 
and formulated to prevent liquid phase from flowing out of the solid phase 
after having entered it. If a peroxide/catalyst system as described below 
is used, the tablet consists in part of absorbent media, which prevents 
excess water from flowing out of the tablet. Similarly, once the absorbent 
media in a peroxide/superoxide tablet is fully hydrated, there is no 
longer a driving force to allow for further wicking of water solution. 
With molecular sieve tablets and chemical couplets, once the tablet is 
saturated with water, there is no longer a driving force available to 
continue the wicking effect. This self limiting action prevents any free 
liquid from entering into other parts of the infusion device. 
Immersion Methods 
As an alternative to the use of a wick to control the diffusive transport 
of the liquid phase toward the solid phase, control can also be achieved 
with the solid phase immersed in the liquid phase. 
Gas adsorbed on molecular sieves, for example, can be desorbed at a 
controlled rate under certain conditions. If an untreated carbon dioxide 
loaded molecular sieve is submerged into pure water, the carbon dioxide is 
released over a period of about one to five mninutes. If a modified water 
bath is used rather than water itself, the desorption rate can be 
significantly decreased. Methods of modification include adding an inert 
solute to the water to serve as a diluent of the water, increasing the 
viscosity of the water, or both. Examples of inert solutes are 
polyalkylene glycols, particularly polyethylene glycol, preferably of a 
weight averaged molecular weight of from about 400 or to about 600 (PEG 
400 and PEG 600). Any amount of PEG 400 or PEG 600 can affect the 
desorption rate, with concentrations over about 1% and less than 100%. 
Preferred concentration ranges are about 1% to about 90%, and about 20% to 
about 60%, all by weight. 
The viscosity of water can be increased by the addition of a high-viscosity 
solute. Examples of such solutes are cellulose and cellulose derivatives. 
A specific example is hydroxyethylcellulose (HEC). A small amount (from 
about 0.1% to about 5% by weight) of HEC significantly increases the 
viscosity of water, and dramatically decreases the rate of desorption of 
carbon dioxide from a molecular sieve. With solutes of this type, the time 
required to release all carbon dioxide adsorbed on a molecular sieve 
tablet can be extended to 24 hours or more. This is useful in liquid 
infusion pumps in which long liquid infusion times are desirable. 
When an uncoated molecular sieve tablet bearing adsorbed CO.sub.2 is 
immersed in a solution of thickened or modified water, its flow rate 
starts high and gradually drops. This is due in part to the diffusion path 
of the water containing liquid into the tablet. Immediately after 
immersion, the entire outside surface area of the tablet is exposed to the 
solution, and this large surface area releases gas at an initially high 
rate. As the water diffuses deeper into the tablet, the effective surface 
area of contact, i.e., the area where incoming water contacts adsorbed 
gas, is reduced and the flow rate decreases. It is possible to achieve a 
more constant diffusion rate by coating a portion of the molecular sieve 
tablet with a water-repellent or water-impermeable coating. For tablets 
containing a central hole, a preferred method is to coat the entire 
surface of the tablet except for the central hole, and optionally the 
peripheral edge. The viscosity-modified water solution will then enter the 
central hole, migrate directly into the center of the tablet, and travel 
radially outward over time, producing a substantially constant gas 
desorption rate. This will produce a more level flow rate curve, while the 
tablet remains intact. Examples of water-impermeable coatings are hot melt 
adhesive, BLACK MAX.TM. sealant (Loctite Corporation, Newington, Conn., 
USA), synthetic rubber, and polyurethane. 
When using immersion methods as described in this section, the inclusion of 
a hydrophobic porous membrane is often desirable to separate the evolved 
gas from the liquid. The evolved gas can then be used to drive the liquid 
infusion device without regard to orientation of the device. Various 
hydrophobic membranes capable of serving this function are known to those 
skilled in the art. 
Sorbent Materials 
In certain embodiments of the invention, gas is generated by the desorption 
of gas from sorbent materials on which the gas is adsorbed. Carbon dioxide 
and other gases can be loaded (adsorbed) onto various sorbents, examples 
of which are zeolite molecular sieves (both naturally occurring and 
synthetic), carbon molecular sieves, silica gel, activated carbon. Zeolite 
molecular sieves and mixtures of zeolite molecular sieves are preferred. 
Linde type 13X, Linde type Y, Linde type 4A and Linde type 5A zeolite 
molecular sieve materials (UOP, Tarrytown, N.Y., USA) are examples of 
adsorbents that can be used in the practice of this invention. These 
adsorbents and their manufacture are disclosed in U.S. Pat. Nos. 2,882,244 
(for zeolite type X molecular sieves), 2,882,243 (for zeolite type A 
molecular sieves), and 3,130,007 (for zeolite type Y molecular sieves). 
Methods for forming these materials into bodies such as tablets, beads or 
pellets are disclosed in U.S. Pat. Nos. 3,888,998, 3,992,493, and 
4,007,134. 
Zeolite molecular sieve sorbents can be loaded with carbon dioxide gas up 
to a maximum of about 25% by weight carbon dioxide, based upon the initial 
unloaded weight of the molecular sieve. Zeolite type 13X typically holds 
the most carbon dioxide. Zeolite type 4A can hold about 60% to 70% of the 
carbon dioxide loading of Zeolite type 13X, but is capable of desorbing 
the gas at a significantly slower rate than 13X, which is useful in 
certain cases. Zeolite type Y is similar to type 13X in its capacity for 
carbon dioxide. 
Zeolite molecular sieves materials should be very dry, preferably with a 
water content below about 2% by weight prior to adsorbing gas thereto. The 
zeolite molecular sieves as received from manufacturers generally meet 
this requirement. If drying (activating) the molecular sieve is desired or 
necessary, this can be accomplished by methods disclosed in U.S. Pat. Nos. 
3,888,998, 3,992,493, and 4,007,134. These materials can also be dried by 
exposure to reduced pressure at low temperatures. Microwave energy can 
also be used to accelerate the rate of drying. Dry zeolite molecular sieve 
is loaded with carbon dioxide gas by means of placing the molecular sieve 
in a pressure vessel with carbon dioxide gas. Alternately, carbon dioxide 
gas can be passed through a packed column of the molecular sieve. Methods 
of charging the molecular sieves with carbon dioxide are disclosed in the 
above-mentioned patents, and are well known to those skilled in the art. 
Once gas is adsorbed onto the molecular sieve, it will remain adsorbed 
during storage, provided that the molecular sieve is contained in a 
barrier container to protect it from environmental gases, moisture or 
water. 
Molecular sieves are available in various physical forms, including 
pellets, beads, and powders. The preferred form of zeolite molecular 
sieves for the purposes of this invention is the powdered form. A 
preferred sorbent for use with this invention is a mixture of Linde 
Zeolite type 13X molecular sieve (about 0% to 100% of the molecular sieve 
content by weight, preferably about 55% if needed), Linde Zeolite type 4A 
molecular sieve (about 0% to about 100% of the molecular sieve content by 
weight, preferably about 45% if needed), short hydrophobic fibers, such as 
polypropylene or polyester fibers (about 1 to 10% by weight), and a tablet 
lubricant, such as magnesium stearate (about 1% to about 8% by weight). 
These materials are mixed, then formed into tablets by compression. In a 
presently preferred practice, the components are pressed into a tablet 
about 1.375 inches (3.5 cm) in diameter and about 0.76 inch (1.9 cm) 
thick, preferably with a small hole (about 0.0625 inch, 0.16 cm, in 
diameter) in the center of the tablet. The cylindrical hole in the tablet 
serves to hold a wick in place. 
Various gases can be used as alternatives to carbon dioxide. Refrigerant 
gases, for example, can be used, such as 1,1,2-trifluoroethane. The weight 
of adsorbed gas required to achieve a given volume of evolved gas is 
proportionate to the molecular weight of the gas. Unfortunately, most low 
molecular weight gasses, such as helium, oxygen, argon, and nitrogen, 
adsorb in quantities that are too small at room temperature to be useful. 
Flammable gases can also be used, although their flammability may be 
objectionable in many applications. Ammonia gas is a further alternative, 
offering a lower molecular weight than carbon dioxide and a high level of 
adsorption to the molecular sieve. In some applications, however, the 
ammonia odor may be objectionable. 
Tablets made from molecular sieve and other sorbent materials can be 
regenerated after having been depleted of adsorbed gas. It is only 
necessary to dry out (activate) the depleted sorbent and reload it with 
fresh gas to prepare the sorbent for a subsequent use. If activation is 
achieved by the use of a reduced pressure and modest temperatures, the 
sorbent can be regenerated while still in an infusion device. 
In this specification and the appended claims, the term "solid phase" 
includes solid materials as well as solid materials with gas molecules 
adsorbed onto the surface of the solid. 
Gas Generating Compositions 
Various compositions can be used to generate gas in accordance with this 
invention. One class of compositions is the combination of a base and an 
acid to produce carbon dioxide. The acid and base are combined in dry form 
and rendered reactive only when codissolved in water. Examples of suitable 
bases are water-soluble carbonate and bicarbonate salts, nonlimiting 
examples of which are sodium bicarbonate, heat treated sodium bicarbonate, 
sodium carbonate, magnesium carbonate, potassium carbonate, and ammonium 
carbonate. Nonlimiting examples of suitable acids are citric acid, 
tartaric acid, acetic acid, and fumaric acid. One presently preferred 
composition is a dry mixture of sodium bicarbonate and fumaric acid. 
Compositions containing more than one acid component or base component can 
also be used. 
The rate of gas generation can be controlled by the solubility of one or 
both of the chemicals in water. In wick and tablet systems, the available 
water as delivered by the wick to the tablet dissolves only a limited 
amount of the reactants and resulting reaction product(s). The reaction is 
thus limited by the solubility of the chemicals in the limited amount of 
available water. The rate of water delivery thereby controls the reaction 
rate. Some examples of the solubility of suitable reaction chemicals per 
100 grams of water are as follows: sodium bicarbonate, about 10 g; citric 
acid, about 200 g; tartaric acid, about 20 g; and fumaric acid, about 0.7 
g. The limited solubility and limited water delivery rate through the wick 
make it unnecessary to keep the acid and base separated either before or 
during use of the infusion device. 
As a manufacturing aid, it may be desirable to add inert agent(s) to the 
reactant composition to aid in the tableting process and to keep the 
tablet intact during and after use. Examples of suitable tableting aids 
are polyvinyl pyrrolidone and anhydrous dibasic calcium phosphate, sold by 
Edward Medell Co. (Patterson, N.J., USA) as EMCOMPRESS.RTM.. Tableting 
aids can be eliminated for certain compositions with no loss of 
performance. one such composition is the mixture of sodium bicarbonate and 
fumaric acid. 
Chemical compositions that produce oxygen or other gases can also be used. 
A composition to generate oxygen in the presence of water is disclosed in 
U.S. Pat. No. 4,405,486. The controlled rate of wicking water into such a 
tablet, and the limited solubility of the constituents can control the 
rate of oxygen release in a manner similar to that of carbon dioxide in 
the systems described above. 
Peroxide and Superoxide Chemical Systems 
In certain embodiments of this invention, gas is generated by drawing an 
aqueous solution of a peroxide or superoxide into an absorbent tablet that 
contains an enzyme or catalyst which promotes the decomposition of the 
peroxide or superoxide to decomposition products including oxygen gas. 
Alternatively, a solid peroxide or superoxide can be incorporated into the 
tablet, with oxygen generation being initiated by contact of the peroxide 
or superoxide with water. Hydrogen peroxide, for example, decomposes into 
water and oxygen, providing no hazardous reaction products after infusion 
of the liquid has been completed. Metal peroxides, such as lithium 
peroxide, sodium peroxide, magnesium peroxide, calcium peroxide, and zinc 
peroxide, react with water to produce the metal hydroxide and hydrogen 
peroxide, which then decomposes into water and oxygen. Superoxides, such 
as sodium superoxide, potassium superoxide, rubidium superoxide, cesium 
superoxide, calcium superoxide, and tetramethylammonium superoxide, react 
with water to produce the metal hydroxide and oxygen gas directly. 
Hydrogen peroxide itself is particularly preferred. 
A suitable tablet contains a water absorbent material to facilitate the 
wicking action, and the enzyme or catalyst in systems where enzymes or 
catalysts are used. Examples of water absorbents useful for this purpose 
are superabsorbent polymers, reconstituted cellulosic materials and 
compressed zeolite powder (Types 13X and 4A, both unactivated). 
One example of a suitable enzyme is catalase, with lyophilized catalases 
preferred. Catalysts effective for the decomposition include metals 
deposited on high surface area substrates such as alumina or activated 
carbon. Examples of suitable catalysts are platinum, palladium, and 
silver. 
Chemical reactants can also be used rather than enzymes or catalysts to 
decompose hydrogen peroxide. Examples of such reactants are potassium 
permanganate and sodium hydroxide. These are often less preferred, 
however, due to safety concerns. 
Among enzymes and catalysts, enzymes provide a cost benefit for single-use 
systems. For reusable systems, however, catalysts are preferred. A 
significant advantage to the use of a hydrogen peroxide system with a 
catalyst is the ability to regenerate the system. This is done by drying 
out the tablet and adding more hydrogen peroxide solution to the water 
reservoir. Regeneration in this system is thus easier than regeneration of 
a sorbent tablet for a system that requires adsorbed gas. 
Formation of a Tablet 
Tablets for use in the present invention can be prepared by conventional 
techniques. A preferred method is one in which the tablet components are 
placed in a die, then pressed to form a shaped tablet. This method is 
known as direct compaction and the procedures are well known to those 
skilled in the art. To prepare a tablet with a central hole to receive a 
wick, the hole can be formed during the pressing operation, or drilled 
into the tablet after the tablet is formed. 
The specific gravity of the pure Type 13X molecular sieve is about 2.0 
g/cm.sup.3. The density of a pressed tablet made from this material is 
about 1.5 g/cm.sup.3. The difference is attributable to porosity in the 
tablet, in the form of microscopic cavities or interstitial spaces between 
the molecular sieve particles. This porosity permits capillary diffusion 
of water or other liquid throughout the tablet. The pressure at which the 
tablet is pressed determines the relative porosity of the tablet. To 
achieve a density of about 1.5 g/cm.sup.3, about 40,000 pounds of force 
(1.8.times.10.sup.5 newtons) are needed. A density of about 1.5 g/cm.sup.3 
is preferred for molecular sieves in order to maximize the amount of gas 
adsorbed to the molecular sieve. 
For tablets containing a combination of reactant materials, the ingredients 
are mixed together and then tableted in a similar manner to that stated 
above. The amount of pressure applied during tablet formation effects the 
density, which in turn affects the water ingression rate from the wick. 
For the hydrogen peroxide system, the tablet need only contain the enzyme 
and absorptive tableting filler. The same tableting technique can be used 
to create this type of tablet as well. 
Structure of the Infusion Device 
Certain structural features of the infusion device affect its performance, 
and can be optimized by the use of preferred materials and methods of 
construction. 
The beneficial liquid to be dispensed by the infusion device is retained in 
a bladder, which term is used herein to denote any liquid-impermeable 
pouch or enclosure that is sufficiently flexible to be compressed, 
preferably to an extent sufficient to substantially eliminate its internal 
volume. 
The pressure containment pouch, or housing of substantially gas-impermeable 
wall material that surrounds the bladder that contains the beneficial 
liquid to be dispensed, is preferably flexible yet substantially 
nonextensible. A preferred construction is one consisting of a seamless 
extrusion of soft, flexible plastic, such as plasticized polyvinyl 
chloride, to form an inner lining, laminated to an outer flexible, but 
substantially nonextensible plastic such as oriented polyester. Examples 
of oriented polyester are MYLAR.RTM. Type A and Type D (E.I. Du Pont de 
Nemours Co., Wilmington, Del., USA). The MYLAR can be applied over the 
vinyl tubing on a mandril, and bonded to the vinyl by application of use 
of a pressure-sensitive adhesive and the application of pressure. 
Alternatively, the two layers can be flexible and rigid polyvinyl 
chloride, respectively. Laminated tubes can also be formed by 
co-extrusion, or from flat, multi-layer film or sheeting by adding a seam. 
The advantage of a laminated tube is that both flexibility and avoidance 
of distension due to internal pressure can be achieved with a thin total 
wall thickness. Although the thickness can vary, a preferred range for the 
inner lamina thickness is from about 0.01 cm to about 0.05 cm, and a 
preferred range for the outer lamina thickness is from about 0.001 cm to 
about 0.005 cm. in a presently preferred embodiment, the inner lamina is a 
polyvinyl chloride tube 0.010 inch (0.0254 cm) in thickness (LAYFLAT, 
Solvay Draka B.V., Enkhuizen, The Netherlands), and the outer lamina is 
MYLAR Type D polyester 0.001 inch (0.00254 cm) in thickness or an oriented 
polyester with pre-applied pressure sensitive adhesive (PROTEKT.TM. 
Overlaminating Film, Item 14, Madico Incorporated, Woburn, Mass., USA, 
about 0.001 inch (0.00254 cm) in thickness). 
An advantage of a flexible pressure containment pouch for retaining 
pressure is its ability to be stored in a folded and/or collapsed 
configuration to save space. Also, this type of composite structure can be 
made of optically clear material, which is advantageous for the purpose of 
monitoring the amount of liquid remaining to be infused, and to permit 
inspection of the pouch to detect the presence of impurities. 
The avoidance of excessive pressure within the pressure containment pouch 
and the maintenance of a steady flow rate of liquid from the infusion 
device is achieved by a pressure relief valve. Typical running pressures 
of pressure infusion devices are in the range of about 7 PSIG to about 10 
PSIG (4.8.times.10.sup.4 to 6.9.times.10.sup.4 pascals). Either a 
fixed-pressure or a variable-pressure relief valve can be used. In devices 
containing a single-pressure relief valve, a valve that relieves pressure 
at approximately 10 PSIG is preferred. A variable-pressure relief valve 
which ranges from, for example, 5 PSIG to 15 PSIG (3.4.times.10.sup.4 to 
1.0.times.10.sup.5), will accommodate wide range of flow rates with a 
single infusion set, since flow is directly proportional to the pressure 
in the device. Accordingly, a variable-pressure relief valve with such a 
range will be particularly usefull in this invention. 
One method of producing a pressure relief valve is to stretch a section of 
elastomeric tubing or sleeve over a protruding lug or stem in sealing 
relationship, the sleeve and stem constructed in such a manner that the 
pressurized gas region of the pressure containment pouch is in 
communication with the contacting surface between the sleeve and stem. The 
sleeve will then be separable from the stem when the pressure in the pouch 
exceeds a threshold gas pressure. To permit adjustment of the cracking 
(relief) and reseat pressure of the valve to a desired value, the stem can 
be slightly tapered. The elastomeric sleeve can then be moved along the 
taper of the tube to increase or decrease the hoop stress in the 
elastomeric sleeve, which will in turn increase or decrease the cracking 
pressure. A preferred sleeve material is a low tensile-set elastomeric 
material. Synthetic silicone rubbers are preferred, with poly(methyl vinyl 
siloxane) the most preferred, although other materials can also be used. 
The use of a lubricant which also functions as an antiblocking agent 
further enhances the adjustability of the device. The lubricant can be 
applied to the contacting surfaces of sleeve and stem to avoid a high 
initial cracking pressure due to blocking over time. Examples of 
lubricants suitable for this purpose are white petrolatum (VASELINE.RTM. 
Petroleum Jelly, Chesebrough-Ponds, Inc., Greenwich, Conn., USA), 
fluorinated silicone oils, mineral oil, fumed silica, and mixtures 
containing one or more of these constituents. 
A pressure relief valve of this construction and including an anti-blocking 
lubricant provides close control of cracking and reseat pressures, and 
produces cracking and reseat pressures that are close to each other in 
value to achieve a substantially constant pressure within the device. 
A further feature preferably included in infusion devices in accordance 
with this invention is a starting mechanism to permit safe storage of the 
infusion device without gas evolution for an extended period of time, and 
to provide a convenient means of starting the gas evolution when desired. 
These results can be accomplished by using a wick that is preinserted into 
a central hole in the solid phase tablet, while the free end of the wick 
is placed in a movable shroud within a chamber of the infusion device that 
contains the liquid phase. When the start of gas evolution is desired, the 
shroud can be pulled back, exposing the dry end of the wick to the liquid 
phase and starting the wicking action and hence the liquid flow. 
An alternative is to encase the wick in a frangible shroud which can be 
shattered immediately prior to use of the device, exposing the wick to the 
liquid phase. In a further alternative, the liquid phase is injected 
through a port immediately prior to use of the device. A still further 
alternative is to encapsulate the liquid phase in one or more frangible 
containers. Upon rupture of these containers, a liquid reservoir in the 
device is filled with the liquid which is then free to contact the wick. A 
still further alternative is to place a flexible tubular barrier film with 
integral tear strip(s) over the wick. The tear strips are pulled to expose 
the wick to the liquid phase. Other methods of starting and equivalents of 
these methods will be readily apparent to those skilled in the art. 
Examples of infusion devices in accordance with this invention and their 
component parts are shown in the attached Figures. 
FIG. 1 illustrates an infusion device 11 constructed of a housing 12 or 
pressure containment pouch of flexible, substantially nonextensible (i.e., 
substantially nondistendable) tubing material, sealed at one end by a 
rigid compartmented base assembly 13 formed from three pieces 14, 15, 16 
of a material such as rigid polyvinyl chloride (PVC) welded together by 
conventional means, such as ultrasonic welding. The housing 12 is sealed 
at the other end by a cap 17 that contains a fitting 18 for passage of the 
liquid that is being dispensed, and a pressure relief valve 19. Inside the 
housing 12, between the base assembly 13 and the cap 17 is a cavity 20 in 
which the bladder 21 containing the beneficial liquid resides. 
The bladder is fully closed except for a single opening 22, and is joined 
to the housing 12 around this opening in a sealing engagement. The bladder 
is thus free to compress within the cavity 20 as the gas pressure in the 
housing 12 rises, whereupon the contents of the bladder will be expelled 
through the opening 22 and out of the housing through the fitting 18. The 
bladder may be constructed with internal ribs to ensure an open passageway 
at all times for the beneficial liquid to flow through and out of the 
bladder. The capacity of the bladder 21 is not critical to the invention, 
and can vary. In one presently preferred embodiment, the bladder has a 
capacity of 100 mL when filly expanded to fill the cavity 20. The fitting 
18 can be a LUER-LOK.RTM. (Becton-Dickinson Corporation, Franklin Lakes, 
N.J., USA) type fitting, which preferably contains a syringe-activated 
check valve. 
The base assembly 13 forms two compartments 31, 32, one 31 to house the 
solid phase 33 and the other 32 the liquid phase 34. The wall section 35 
separating the two compartments contains a single hole 36 that 
communicates the interiors of the two compartments, and a wick 37 passes 
through the hole 36, joining the solid and liquid phases. The solid phase 
33 is represented in this Figure by a tablet with an axial hole through 
which the wick 37 is inserted. A typical tablet is a composite consisting 
of about 7.4 g of zeolite molecular sieve Type 13X, about 9 g of zeolite 
molecular sieve Type 4A, about 0.34 g of natural polyester fibers, and 
about 0.17 g of magnesium stearate. A typical wick is made of crosslinked 
(acetalized) polyvinyl alcohol. 
The wall section 41 separating the tablet compartment 31 from the bladder 
cavity 20 has a gas outlet hole 42 passing through its center to permit 
the gas evolved from the tablet to pass into the region of the cavity 20 
surrounding the bladder. In this particular construction, the gas outlet 
hole 42 is about 0.25 inch (0.6 cm) in diameter and is covered with a 
metallized barrier tape 43 held in place by a low-tack adhesive to render 
the tape easily removable. This protective tape serves as a barrier 
protecting the sorbent tablet from atmospheric moisture in the bladder 
cavity 20, and also prevents premature gas desorption from the sorbent 
tablet during storage (in embodiments where gas is generated by 
desorption). Upon initiation of use of the device, the barrier tape 43 is 
separated from the wall by the initial gas pressure generated in the base 
assembly. 
Premature contact between the liquid and solid phases is prevented by 
various structural devices. One such device is a shroud 51 shown in FIG. 
1, surrounding the portion of the wick 37 that extends into the liquid 
phase chamber 32. The shroud 51 is a length of rigid tubing, such as a 
molded PVC or high-density polyethylene tube, closed at one end and held 
in place by a pair of O-ring seals 52, 53. The closed end of the shroud 
has an integral eyelet 54 to which a pull string 55 (such as looped nylon) 
is attached. To place the wick 37 in contact with the liquid phase, the 
pull string 55 is pulled to draw the shroud back, thereby allowing the 
surrounding liquid to contact the wick. 
An alternative structural device and mechanism for withholding contact of 
the wick with the liquid phase until the desired point in time is shown in 
FIG. 2. Here, the liquid phase compartment 56 is empty when the infusion 
device is not in use, with only the solid phase tablet 57 contained within 
the device. A syringe-activated check valve 58 is incorporated in the 
outer wall of the liquid phase compartment 56, and at the appropriate 
time, liquid is injected into the compartment by syringe. 
A third alternative is shown in FIG. 3, where the portion of the wick 
extending into the liquid phase chamber is surrounded by a frangible glass 
shell 61. The outer wall of the liquid phase compartment 62 contains a 
protruding section 63 of flexible material such as silicone. Contact of 
the liquid phase with the wick is initiated by squeezing the flexible 
protrusion 63 to break the glass shell 61. 
The pressure relief valve 19 is shown in exploded side cross section in 
FIG. 4 and in assembled side cross section in FIG. 5. The valve is 
constructed in three parts--a valve housing 71, a valve stem 72, and a 
sleeve 73. The valve housing 71 contains an inlet passage 74 that 
communicates with the region surrounding the bladder in the pressure 
containment housing 12 (FIG. 1) of the infusion device, and an internal 
pin 75. The valve stem 72 has a well 76 that fits tightly over the pin 75 
in a secure manner that will not hold the stem in a fixed position through 
any pressures exerted inside the pressure containment housing. The sleeve 
73 fits inside the valve housing 71 between the internal wall of the valve 
housing and the outer surface 77 of the stem. Pressure from the pressure 
containment housing is thus contained in the small enclosed volume 78 
between the housing 71, stem 72 and sleeve 73. Lateral slits 79, 80 in the 
valve housing permit the sleeve to expand outward in response to high 
pressure, and thus to separate from the outer surface 77 of the valve stem 
72 to relieve pressure. The outer surface 77 of the valve stem is tapered 
so that the contact force between the valve stem and the sleeve, and hence 
the cracking or relief pressure of the valve, can be varied by either 
moving the sleeve axially relative to the valve stem or moving the valve 
stem axially relative to the sleeve. 
The following examples are offered solely for purposes of illustration. 
EXAMPLE 1 
Preparation of Composite Zeolite Molecular Sieve Tablet 
This example illustrates the formation of rigid composite tablets with a 
density of about 1 g/cm.sup.3. 
12 grams of Sodium Aluminosilicate (Zeolite) Molecular Sieve Type 13X, 0.25 
grams polyester fibers 0.040-0.060" length by 0.0025 inch diameter (type 
9001 natural, Cellusuede Products Inc., Rockford, Ill., USA) and 0.12 
grams of magnesium stearate are intensely mixed. This mixture is placed in 
a 1.375-inch diameter cylindrical tableting die. A punch placed in the dye 
is pressed against the powder using a hand-operated 20-ton Central 
Hydraulics hydraulic press. The mixture is compacted in the dye until a 
tablet height of approximately 0.6" is obtained. The newly formed tablet 
is removed from the die. Using a 1/8" diameter drill bit, a small hole is 
drilled into the center of the tablet. The tablet is then placed into a 
sealed container to protect it from atmospheric moisture. 
EXAMPLE 2 
Activating and Charging a Molecular Sieve Tablet 
This example illustrates the method for loading the composite tablet of 
Example 1 with carbon dioxide. 
Composite tablets are sealed inside a stainless steel pressure vessel from 
Pope Scientific. The pressure vessel is connected to a Marvac single stage 
high vacuum pump (Marvac Scientific Manufacturing Co., Concord, Calif., 
USA) and placed inside an air convection oven (Blue M STABILTHERM.RTM., 
Blue M Electric, Watertown, Wis., USA). The vacuum pump remains outside of 
the oven. Tablets are then heated to 120-130 C. and exposed to a vacuum of 
about 29 inches of mercury. These conditions are maintained for 1.5 hours 
to dehydrate the tablets. The dehydrated tablets were then allowed to cool 
to room temperature while remaining under a vacuum. The hydrated tablets 
remained in the pressure vessel for 1.5 hours while carbon dioxide was 
introduced at a pressure of about 3-4 PSIG. After 1.5 hours, the vessel 
was sealed and the carbon dioxide-containing tablets were maintained under 
a carbon dioxide atmosphere for storage. Analysis of the carbon 
dioxide-containing tablets shows that they contain approximately 20% by 
weight carbon dioxide based on the change in weight of the type 13X 
zeolite molecular sieve. 
EXAMPLE 3 
Gas Desorption Using Polyvinyl Acetate Wick 
This example illustrates the gas desorption process using a discrete 
polyvinyl acetate wick. 
A tablet of the type described in Example 2 was used with a reservoir of 
distilled water. One end of a 70 mm.times.3 mm crosslinked polyvinyl 
acetate (PVAc) wick with a square cross section (Type CF120, Merocel 
Corporation, Mystic, Conn., USA) was inserted in the center hole of the 
tablet with one end of the wick flush with the upper surface of the 
tablet. The other end of the wick was placed in a reservoir containing 20 
mL of distilled water. The resulting release of carbon dioxide was 
measured with an Aalborg Instruments rotameter (Aalborg Instruments & 
Controls Inc., Monsey, N.Y., USA). The resulting gas desorption rates are 
shown in Table 1 below. 
TABLE 1 
______________________________________ 
Rate of Desorption 
Outward Flow of Desorbed 
Time (minutes) CO.sub.2 (mL/min) 
______________________________________ 
2 59 
5 4.6 
11 1.6 
20 1.1 
30 1.0 
40 1.0 
50 1.0 
60 1.0 
______________________________________ 
The data in Table 1 indicates that without any type of rate modifying 
techniques, the tablet will desorb the carbon dioxide in a very short 
period of time. 
EXAMPLE 4 
Gas Desorption Using Slower Wicks 
This example illustrates the effect of using different types of wick 
materials on the desorption rate of gas from the tablet. 
Composite tablets prepared using the process described in Examples 1 and 2 
underwent gas desorption using the method described in Example 3, each 
with different wick material. The wicks employed were a hydrogel (2ND 
SKIN.RTM. Non-stick Moist Burn Pads, Spenco Medical Corporation, Haywards 
Heath, United Kingdom) and an acetalized polyvinyl alcohol wick, type D-2 
from Kanebo Ltd., Osaka, Japan (PVA-D-2). The flow of carbon dioxide out 
of each tablet was measured over time and the results are shown in Table 
2. 
TABLE 2 
______________________________________ 
Rate of Desorption 
OutwardFlow of Desorbed CO.sub.2 
(mL/min) 
Time (minutes) 
Hydrogel PVA-D-2 
______________________________________ 
1 6.74 104 
5 2.47 92 
10 1.51 65 
20 1.36 20 
30 1.47 13 
40 1.70 7 
50 1.95 6 
60 2.10 6 
______________________________________ 
Both wick materials provide transport of the water, but the PVA-D-2 
produces a higher rate of gas release which indicates that it transports 
water at a higher rate. 
EXAMPLE 5 
Use of Infusion Device With CO.sub.2 -Loaded Zeolite 
This example illustrates the method of using a composite zeolite tablet 
loaded with carbon dioxide to generate gas to run an infusion device. 
Twelve (12) grams of zeolite molecular sieve type 13X (from UOP, Tarrytown, 
N.Y., USA) was mixed with 0.12 grams of magnesium stearate and 0.25 grams 
polyester fibers 0.040-0.060 inch in length by 0.0025 inch in diameter 
(type 9001 natural, CellCellusuede Products Inc., Rockford, Ill., USA) and 
prepared into a tablet using the procedures of Example 1. The tablet was 
then placed in a device of the construction shown in FIG. 2. 
To start the device, a 25-cc syringe was used to inject 12 grams of 
distilled water into the wicking liquid reservoir of the device. The 
infusion device utilized a 0.078".times.0.078".times.1.6" crosslinked 
polyvinyl acetate wick (PF120 of Merocel Corporation, Mystic Conn., USA). 
Immediately after the injection of the distilled water, the water started 
to enter the tablet. 
The carbon dioxide desorbed from the tablet pressurized the rigid housing 
of the infusion device, causing the water in the medication pouch to flow. 
The pressure relief valve of this device was set to release excess gas at 
a pressure of 10 PSIG. 
The pressure and volumetric flow rates were monitored over time using a 
pressure gauge and graduated cylinder and were recorded in Table 3 below: 
TABLE 3 
______________________________________ 
Infusion Pressure and Liquid Delivery Rate 
Time Infusion Pressure 
Cumulative Delivered 
(minutes) (PSIG) Liquid Volume (mL) 
______________________________________ 
1 3 &lt;10 
2 9 &lt;10 
3 10 &lt;10 
5 10 12 
7 10 14 
9 10 17 
10 10 19 
12 10 22 
14 10 26 
15 10 28 
19 9.5 36 
22 9.5 42 
25 8 48 
26 8 49 
27 8 51 
28 7.5 53 
29 7.5 54 
30 7 55 
35 6 62 
40 6 69 
45 5 76 
50 5 80 
55 4 86 
60 4 90 
______________________________________ 
The data in Table 3 demonstrate that an infusion device can be run using a 
wick combined with a composite zeolite tablet loaded with carbon dioxide. 
EXAMPLE 6 
Use of a Wick to Transport H.sub.2 O.sub.2 Solution to a 
Catalyst-Impregnated Tablet 
This example illustrates the use of a wick to transport hydrogen peroxide 
solution to a tablet with an impregnated catalyst to generate gas to run 
an infusion device. 
Five (5) grams of 20.times.50 mesh activated high surface area carbon 
coated with 3% by weight palladium catalyst was mixed with 0.05 grams of 
magnesium stearate, 0.10 polyester fibers 0.040-0.060" in length by 0.0025 
inch in diameter (type 9001 natural, Cellusuede Products Inc., Rockford, 
Ill., USA), 3.4 grams of zeolite molecular sieve type 4A and 1.4 grams of 
zeolite molecular sieve type 13X. This mix was formed into a tablet using 
the tablet pressing procedures described in Example 1. The zeolite 
materials were not activated or loaded with gas in this example, and were 
present only for the purpose of creating a tablet to hold the catalyst. 
An 8% (by weight) hydrogen peroxide solution was then prepared by diluting 
a 35% hydrogen peroxide solution with distilled water. This solution was 
injected into the wicking reservoir of the infusion device using a 25-cc 
syringe. The device contained a 0.078".times.0.078".times.1.6" acetalized 
polyvinyl alcohol grade E-2 wick from Kanebo Corporation. The hydrogen 
peroxide solution was drawn into the tablet over a period of time, 
initiating the release of oxygen gas. 
In this case the gas was generated within a rigid PVC power pack assembly, 
and transported by a tubing connection to a 250-mL rigid infusion device 
which has a gas side and a liquid side separated by a dual membrane 
system, in a rolling diaphragm configuration. As the gas side of the 
device expands, the diaphragm rolls into the liquid side of the device, 
expelling the liquid contents. Distilled water was used as the infusion 
liquid. The oxygen generated from the decomposition of the hydrogen 
peroxide pressurized the gas side of the infusion device, causing the 
distilled water to flow out of the device. A pressure relief valve was 
used to vent gas from the gas portion of the device when the internal 
pressure of the device exceeded about 10 PSIG. An infusion tubing set 
calibrated for 5% dextrose solution, viscosity expected to be 10-15% 
greater than test solution, to deliver 100 mL/h of liquid at 10 PSIG was 
connected to the device. 
The gas pressure and volumetric flow rates were monitored over time using a 
standard laboratory pressure gauge and graduated cylinder and are shown in 
Table 4. 
TABLE 4 
______________________________________ 
Infusion Pressure and Liquid Delivery Rate 
Infusion Pressure 
Cumulative Delivered 
Time (min) (PSIG) Liquid Volume (mL) 
______________________________________ 
1 2.5 &lt;10 
2 4.5 &lt;10 
3 6 &lt;10 
4 7.6 6 
5 9 7 
10 10.3 17 
15 10.3 28 
20 9.1 38 
25 8 no reading 
30 7.5 53 
35 8.5 62 
40 8.1 71 
45 7.9 77 
50 7.5 84 
55 7.9 89 
60 7 95 
______________________________________ 
The data in Table 4 demonstrates that an infusion device can be powered by 
wicking a peroxide-containing liquid into a tablet which is impregnated 
with a catalyst. 
EXAMPLE 7 
Use of Acetalized PVA Wick to Transport Water to Sodium Carbonate/Citric 
Acid Tablet 
This example illustrates the method of using an acetalized polyvinyl 
alcohol wick to transport a limited amount of water to a tablet containing 
sodium bicarbonate and citric acid for the purpose of generating carbon 
dioxide gas in a controlled manner. 
Sodium bicarbonate (8.6 g) was mixed with citric acid (5.7 g), fumed silica 
(1 g, AEROSIL.RTM. 200 from Degussa Corp., Ridgefield Park, N.J., USA), 
polyvinyl pyrrolidone (0.75 g, Type K-90 from ISP Technologies, Inc., 
Wayne, N.J., USA) and natural polyester fibers (0.75 g), 0.040-0.060 inch 
in length by 0.0025 inch in diameter (Type 9001 natural, Cellusuede 
Products Inc.). This mix was formed into a tablet using the tablet forming 
procedures of Example 1. 
Through the tablet was placed a 0.078".times.0.078".times.1.6" acetalized 
polyvinyl alcohol wick (Grade E from Kanebo). The tablet was placed in a 
rigid PVC infusion device assembly. The wick was extended into a water 
reservoir in the assembly filled with distilled water. The rigid PVC 
assembly also contained a pressure relief valve set to vent gas at 
pressures above about 10 PSIG. The carbon dioxide gas generated from the 
controlled reaction of the citric acid and sodium bicarbonate was then 
used to power an infusion device as described in Example 6, with liquid 
being delivered through a 100 mL/h administration set calibrated for a 5% 
dextrose solution, viscosity expected to be 10-15% greater than the test 
solution. 
The pressure and volumetric flow rates were monitored over time and were 
recorded in Table 5. 
TABLE 5 
______________________________________ 
Infusion Pressure and Liquid Delivery Rate 
Cumulative Cumulative 
Infusion Delivered Infusion Delivered 
Time Pressure Liquid Time Pressure Liquid 
(min) (PSIG) Volume (mL) (min) (PSIG) Volume (mL) 
______________________________________ 
1 1.5 2 70 9.3 100 
2 7 3 75 9.5 106 
3 10 5 80 9.5 111 
4 10.2 6 85 9.5 116 
5 10 7 90 9.5 119 
10 9.5 17 100 n/a* n/a 
15 9 25 110 9.5 131 
20 8.5 32 120 9.5 138 
25 8 40 130 9.3 155 
30 8 47 140 9.1 174 
35 8 53 150 9.1 192 
40 8.8 60 160 9.3 210 
45 9 68 170 9.3 229 
50 9 76 180 9.5 243 
55 9 n/a 190 9.5 256 
60 9.1 88 200 n/a n/a 
65 9.1 94 
______________________________________ 
*"n/a": data not recorded 
The results of this example demonstrate that an infusion device can be 
powered for an extended period of time by the controlled generation of 
carbon dioxide gas by wicking a limited amount of water into a tablet 
containing a mixture of sodium bicarbonate and citric acid. 
EXAMPLE 8 
Use of Acetalized PVA Wick to Transport Citric Acid Solution to Solid 
Sodium Carbonate 
This example illustrates the use of a wick made of acetalized polyvinyl 
alcohol to transport a citric acid solution into a sodium 
bicarbonate-containing tablet for the purpose of generating carbon dioxide 
gas in a controlled manner to power an infusion device. 
Sodium bicarbonate (10 g) was mixed with polyvinyl pyrrolidone (1 g, Type 
K-90 from ISP Technologies) and polyester fibers (1 g) 0.040-0.060 inch in 
length by 0.0025 inch in diameter (Type 9001 natural, Cellusuede Products 
Inc.). This mix was formed into a tablet using the general procedures of 
Example 1. 
A 2.6 molar solution of citric acid solution was prepared by dissolving 
citric acid into distilled water. A 12-mL portion of this solution was 
placed into the wicking liquid reservoir of a PVC assembly. A 
0.078".times.0.078".times.1.6" acetalized polyvinyl alcohol wick (Grade E 
from Kanebo) was placed through the hole in the tablet. The citric acid 
wicking solution was allowed to wick into the tablet by placing the free 
end of the wick into the water reservoir. The carbon dioxide generated by 
the controlled reaction of the citric acid and sodium bicarbonate was used 
to power a 100-mL capacity infusion device, with liquid being infused 
through a 100 mL/h set calibrated for a 5% dextrose solution, viscosity 
expected to be 10-15% greater than the test solution. The infusion device 
was similar in construction to that described in Example 7. Again, a 
pressure relief valve with a setting of about 10 PSIG was used to vent 
excess gas from the system. 
The pressure and volumetric flow rates were monitored over time and were 
recorded in Table 6: 
TABLE 6 
______________________________________ 
Infusion Pressure and Liquid Delivery Rate 
Infusion Pressure 
Cumulative Delivered 
Time (min) (PSIG) Liquid Volume (mL) 
______________________________________ 
1 5 2 
2 10.5 4 
3 10.5 6 
4 10.2 8 
5 10.2 10 
10 10 20 
15 10 29 
20 10 39 
25 10 48 
30 10.2 56 
35 10.2 65 
40 11 75 
45 n/a n/a 
50 8.5 93 
55 8 100 
60 7.5 105 
______________________________________ 
EXAMPLE 9 
Use of Wick Enclosed in Frangible Shell 
This example illustrates the use of a breakable shell as an alternative 
method to start an infusion device powered by desorption of carbon dioxide 
from a composite zeolite molecular sieve tablet. 
A mixture (16.5 g) of 55% by weight zeolite type 4A and 45% by weight 
zeolite type 13X molecular sieve, was mixed with magnesium stearate (0.17 
g) and polyester fibers (0.34 g) 0.040-0.060 inch in length by 0.0025 inch 
in diameter (Type 9001 natural, Cellusuede Products Inc.). The mixture was 
formed into a carbon dioxide loaded tablet using the procedures of Example 
1 and Example 2. 
The tablet was placed in a three-piece rigid PVC assembly, as shown in FIG. 
3. One piece of the assembly served as the housing for tablet. The second 
piece served as a reservoir for wicking liquid (distilled water in this 
case). The two sections were separated by a round disk with a central hole 
for the wick to pass through. One end of an acetalized polyvinyl alcohol 
wick was placed through the tablet, and the other end through the central 
hole of the separator disk and into the water reservoir. Prior to filling 
the reservoir with water, however, the wick was enclosed in a frangible 
glass shell that extended beyond the end of the wicking reservoir. The end 
of the shell protruding beyond the water reservoir was surrounded by a 
flexible plastic sleeve. The purpose of the shell was to keep the wick dry 
prior to using the device, while the sleeve was included to contain the 
water when the shell was later compromised. The water reservoir was filled 
with distilled water. 
To begin infusion, the plastic sleeve surrounding the shell was compressed 
radially between two fingers, shattering it along its length, exposing the 
wick to the reservoir of distilled water. Once exposed, the wick 
transported water to the tablet, starting the desorption of carbon dioxide 
gas and thus beginning the infusion process. 
The remainder of the infusion device was similar to that described in 
Example 6. An administration set, calibrated at 100-mL/h for a 5% dextrose 
solution, with viscosity expected to be 10-15% greater than the test 
solution, was clamped shut for the first five minutes following the 
crushing of the glass shroud. The pressure and volumetric flow rates were 
monitored over time using a pressure gauge and graduated cylinder and the 
results are listed in Table 7. 
TABLE 7 
______________________________________ 
Infusion Pressure and Liquid Delivery Rate 
Infusion Pressure 
Cumulative Delivered 
Time (min) (PSIG) Liquid Volume (mL) 
______________________________________ 
0 2 Set Clamped Shut 
1 3.1 Set Clamped Shut 
2 6.8 Set Clamped Shut 
3 8.5 Set Clamped Shut 
4 9.8 Set Clamped Shut 
5 10.2 0 
10 10.3 11 
30 10.3 42 
45 10.2 65 
70 10.2 120 
90 10.2 170 
110 10 188 
120 10 207 
140 10 242 
160 9.9 268 
______________________________________ 
The above data clearly demonstrates that an infusion device can be started 
via the breakage of a crushable glass-enclosed ampule. 
EXAMPLE 10 
Use of a Retractable Shell 
The basic steps of Example 9 were repeated, except the crushable glass 
shell shrouded in flexible plastic was replaced with a rigid retractable 
plastic shell with a pull string at one end, as shown in FIG. 1. To expose 
the wick to water, the pull string is pulled outward until the shell abuts 
a stop in the water reservoir. Once the shell is retracted in this manner, 
the wick is exposed and infusion begins. 
The pressure and volumetric flow rates were monitored over time using a 
standard lab pressure gauge and graduated cylinder and were recorded in 
Table 8. In generating this data, the device was clamped shut for the 
first five minutes after wick exposure was initiated to allow the pressure 
to build to 10 PSIG. 
TABLE 8 
______________________________________ 
Infusion Pressure and Liquid Delivery Rate 
Infusion Pressure 
Cumulative Delivered 
Time (min) (PSIG) Liquid Volume (mL) 
______________________________________ 
0 3 -- 
1 7 -- 
2 9.8 -- 
3 10 -- 
4 10.5 -- 
5 10.5 0 
15 10.7 21 
30 10 50 
45 10 76 
60 10 104 
75 10 133 
90 10 160 
120 10 215 
150 10 262 
160 9.8 274 
______________________________________ 
The above data demonstrates that an infusion device can be started by 
retraction of a protective shell. 
EXAMPLE 11 
Further Use of Infusion Device With CO.sub.2 -Loaded Zeolite 
This example is as further illustration of the use of an infusion device 
powered with carbon dioxide desorbed from a composite zeolite tablet. 
A tablet was formed from 16.5 g of a mixture of 55% by weight zeolite type 
4A and 45% by weight zeolite type 13X molecular sieve, mixed with 
magnesium stearate (0.17 g) and polyester fibers (0.34 g) 0.040-0.060 inch 
in length by 0.0025 inch in diameter (Type 9001 natural, Cellusuede 
Products Inc.), using the procedures of Examples 1 and 2. 
A flexible device comprising a 100-mL pillow-shaped medication pouch 
constructed of flexible polyvinyl chloride film was sealingly contained 
within a flexible, yet nonextensible, oriented 0.001-inch thick polyester 
film adhesively laminated to flexible polyvinyl chloride LAYFLAT tube of 
about 0.008 inch in thickness. The diameter of the tube was about 1.7 
inches. This laminated tube was in fluid communication with a source of 
gas as described in Example 9. When carbon dioxide gas desorbed from the 
tablet, the gas entered the tube and pressured the inside of the 
gas-containing tube to about 10 PSIG. Excess gas pressure was relieved via 
an elastomeric pressure relief valve as shown in FIGS. 4 and 5 set to 
about 10 PSIG. This pressurized gas exerted pneumatic pressure on all 
sides of the medication pouch, forcing medication through an attached 50 
mL/h infusion set. The infusion set was clamped for the first 5 minutes of 
gas generation to allow enough gas pressure to build prior to the start of 
infusion. 
The pressure and volumetric flow rates were monitored over time using a 
pressure gauge and graduated cylinder and were recorded in Table 9. In 
generating this data, the device was clamped shut for the first five 
minutes after wick exposure was initiated to allow the pressure to build 
to 10 PSIG. 
TABLE 9 
______________________________________ 
Infusion Pressure and Liquid Delivery Rate 
Infusion Pressure 
Cumulative Delivered 
Time (min) (PSIG) Liquid Volume (mL) 
______________________________________ 
0 2.2 -- 
1 5.8 -- 
2 8.5 -- 
3 9.8 -- 
4 10.5 -- 
5 10.5 0 
10 10.2 6 
15 10.2 11 
30 10.2 27 
45 10.2 41 
60 10 49 
75 10 63 
85 9.8 72 
100 10 81 
120 10 92 
130 9.7 97 
140 9.7 101 
150 9.6 104 
160 9.7 108 
______________________________________ 
The above data demonstrates that a flexible pouch within a pouch can 
readily be employed as an infusion device. 
EXAMPLE 12 
Variation in Ratio of Types of Molecular Sieve 
This example illustrates the use of composite zeolite tablets with varying 
proportions of zeolite molecular sieve types 4A and 13X to ran an infusion 
device and varying flow characteristics. 
A 17-g molecular sieve mixture containing 50% by weight 4A zeolite 
molecular sieve and 50% by weight 13X zeolite molecular sieve was mixed 
with magnesium stearate (0.175 g) and polyester fibers (0.35 g) 
0.040-0.060 inch in length by 0.0025 inch in diameter (Type 9001 natural, 
Cellusuede Products Inc.), and formed into a carbon dioxide loaded tablet 
using the general procedures of Examples 1 and 2. 
An infusion device as described in Example 6 was used. The infusion device 
contained 100 mL of liquid to be delivered, with an administration set 
calibrated at 50 mL/hr for a 5% dextrose solution, viscosity expected to 
be 10-15% greater than the test solution. 
The pressure and volumetric flow rates were monitored over time using a 
standard lab pressure gauge and graduated cylinder and were recorded in 
Table 10. 
TABLE 10 
______________________________________ 
Infusion Pressure and Liquid Delivery Rate 
Infusion Pressure 
Cumulative Delivered 
Time (min) (PSIG) Liquid Volume (mL) 
______________________________________ 
1 4.2 &lt;10 
2 8.2 &lt;10 
3 10.5 &lt;10 
4 10.7 &lt;10 
5 10.9 &lt;10 
10 10.9 10 
30 10.9 27 
40 10.9 36 
70 10.8 60 
90 10.5 76 
110 10.4 87 
120 9.8 95 
130 7.5 103 
140 6.6 108 
______________________________________ 
The above data demonstrates that the gas flow rates of an infusion device 
can be altered by varying the proportions of molecular sieve types used to 
construct the tablets. 
EXAMPLE 13 
A Further Variation on the Molecular Sieve Composition 
This example illustrates the use of a second small layer comprising of a 
high percentage of zeolite molecular sieve type 13X to provide a rapid 
pressure build up of within an infusion device. 
A mixture of 12 g of 60% zeolite molecular sieve type 4A and 40% zeolite 
molecular sieve type 13X, was mixed with magnesium stearate (0.12 g) and 
polyester fibers (0.24 g) 0.040-0.060 inch in length by 0.0025 inch in 
diameter (Type 9001 natural, Cellusuede Products Inc.) and formed into a 
carbon dioxide-loaded tablet using the general procedures of Examples 1 
and 2. In addition to this main tablet, type 13X zeolite molecular sieve 
(1.8 g) was mixed with of the same type of polyester fibers (0.20 g), and 
prepared into a tablet using the general procedures of Examples 1 and 2. 
The second tablet (consisting primarily of type 13X zeolite molecular 
sieve) was placed beneath the first tablet, and then inserted with a 
common wick and placed into an infusion device as described in Example 6. 
In this case, the 100-mL infusion device was connected to an 
administration set calibrated at 50 mL/h for a 5% dextrose solution, 
viscosity expected to be 10-15% greater than the test solution. 
The pressure and volumetric flow rates were monitored over time using a 
pressure gauge and graduated cylinder and are shown in Table 11. 
TABLE 11 
______________________________________ 
Infusion Pressure and Liquid Delivery Rate 
Infusion Pressure 
Cumulative Delivered 
Time (min) (PSIG) Liquid Volume (mL) 
______________________________________ 
1 3.5 &lt;10 
2 5.5 &lt;10 
3 7 &lt;10 
4 8.4 &lt;10 
5 9.5 &lt;10 
10 9.5 8 
15 9.5 13 
20 9.5 17 
25 9.5 21 
30 9.5 26 
35 9.3 30 
40 9.3 34 
45 9.3 38 
50 9.3 42 
55 9.3 46 
60 9.3 50 
65 9.3 54 
70 9.3 59 
75 9.3 63 
80 9.3 67 
85 9.3 71 
90 9.3 74.5 
100 9.3 82 
110 9.3 90 
120 9.5 98 
130 9.5 105 
140 9.5 114 
150 9.5 124 
______________________________________ 
The above data demonstrates that this type of combination tablet can 
expedite the rate of initial pressurization of an infusion device. 
EXAMPLE 14 
Use of Crosslinked Acetalized PVA to Transport Water to Sodium 
Carbonate/Citric Acid Tablet 
This example illustrates the use a crosslinked acetalized polyvinyl alcohol 
wick (Kanebo type E-2) to provide water necessary to mediate the reaction 
between sodium bicarbonate and citric acid. The reaction is mediated by 
providing a controlled rate of water delivery to control the quantity and 
concentration of reactants in solution at any given time. 
Sodium bicarbonate (14.7 g) was mixed with citric acid (9.8 g), and 
anhydrous calcium phosphate (0.25 g, EMCOMPRESS.RTM. from Mendell Co.). 
This mix was formed into a tablet using the general procedure of Example 
1. Through the tablet was placed a 0.078".times.0.078".times.1.6" 
acetalized polyvinyl alcohol wick (Kanebo type E-2). The tablet and wick 
were then sealed off inside a rigid PVC assembly, controlled by an 
elastomeric pressure relief valve set to approximately 10 PSIG. The wick 
was then exposed to distilled water, allowing the water to wick into the 
tablet, as in Example 3. The gas generated from this system was used to 
power a 250-mL infusion device similar to that described in Example 6, 
with liquid being infused through a 100 mL/h administration set calibrated 
for a 5% dextrose solution, viscosity expected to be 10-15% greater than 
the test solution. 
The pressure and volumetric flow rates were monitored over time and are 
shown in Table 12. 
TABLE 12 
______________________________________ 
Infusion Pressure and Liquid Delivery Rate 
Infusion Pressure 
Cumulative Delivered 
Time (min) (PSIG) Liquid Volume (mL) 
______________________________________ 
1 3.5 &lt;5 
2 11 &lt;5 
3 10.8 5 
4 10.8 7 
5 10.2 8 
10 10 18 
20 9.5 35 
30 9.5 50 
40 9.5 66 
70 9.9 120 
90 10 156 
110 9 194 
140 8.4 231 
160 8.4 270 
180 9.6 all liquid delivered 
______________________________________ 
EXAMPLE 15 
Use of a Solid Phase Enzyme 
This example illustrates the use of hydrogen peroxide solution and a tablet 
containing an enzyme capable of decomposing hydrogen peroxide to run an 
infusion device. 
Thirty-six OXYSEPT.RTM. 2 neutralizing enzyme tablets (Allergan Inc., 
Irvine, Calif., USA) (3.2 g) were crushed into a fine powder and mixed 
with polyvinyl pyrrolidone (1 g, ISP Technologies K-25). This mixture was 
then formed into a tablet using the general procedures of Example 1. 
An aqueous solution of 8% hydrogen peroxide was then drawn into the tablet 
through an acetalized polyvinyl alcohol (Kanebo type E-2) wick as 
described in Example 3. The resulting oxygen which was generated from the 
enzymatic decomposition of hydrogen peroxide was used to power a 250-mL 
device as described in Example 6, with liquid being delivered through an 
administration set calibrated at 100 mL/h for a 5% dextrose solution, 
viscosity expected to be 10-15% greater than the test solution. 
The pressure and volumetric flow rates were monitored for 10 minutes, until 
the peroxide was completely exhausted. The data was recorded in Table 13. 
TABLE 13 
______________________________________ 
Infusion Pressure and Liquid Delivery Rate 
Infusion Pressure 
Cumulative Delivered 
Time (min) (PSIG) Liquid Volume (mL) 
______________________________________ 
1 6 1 
2 11.2 3 
3 10.8 5 
4 10.6 7 
5 10.6 9 
6 10.4 12 
7 10.2 14 
8 10.2 16 
9 10 18 
10 9.5 20 
______________________________________ 
EXAMPLE 16 
Driving Infusion Device without Use of a Discrete Wick 
This example illustrates the desorption of gas from a sorbent material to 
power an infusion device without the use of a discrete wick. In this 
example, zeolite molecular sieve type 13X (5.4 g) was mixed with magnesium 
stearate (0.53 g) and prepared into a 1-inch diameter, solid cylindrical 
tablet using the compaction method described in Example 1. Unlike the 
tablets in preceding examples, this tablet contained no center hole. Once 
formed, the tablet was activated and loaded with carbon dioxide using the 
methods of Example 2. 
A 35-g solution containing 70% by weight polyethylene glycol 600 (J. T. 
Baker, Phillipsburg, N.J., USA) and 30% by weight distilled water was 
prepared and placed inside a small pressure vessel. To begin the 
desorption process, the sorbent tablet was then dropped onto the solution. 
Upon contact with the solution the sorbent tablet desorbed carbon dioxide 
gas in a controlled manner. 
The volume of carbon dioxide gas desorbed from the tablet was recorded and 
is listed in Table 14. 
TABLE 14 
______________________________________ 
Gas Desorption Rate 
Cumulative Desorbed CO.sub.2 
Time Volume 
(min) (mL) 
______________________________________ 
.5 40 
1 48 
2 58 
3 66 
4 73 
5 80 
6 87 
7 92 
8 97 
9 103 
10 107 
11 114 
______________________________________ 
While this experiment did not include the use of an infusion device, the 
data demonstrates that an infusion device can be run using only a loaded 
molecular sieve sorbent tablet and an aqueous solution to affect a 
controlled desorbing of gas without the use of a discrete wick. 
EXAMPLE 17 
Use of a Hydrogel 
This example illustrates the desorption of gas from a sorbent material to 
power an infusion device using a bed of hydrogel. 
Zeolite molecular sieve type 13X (2 g) was mixed with magnesium stearate 
(0.5 g) and formed into a 0.5-inch diameter, solid cylindrical tablet 
using the compaction method of tableting similar to that described in 
Example 1. No center hole was formed in the tablet. The sorbent tablet was 
activated and loaded with carbon dioxide using the general procedures of 
Example 2. 
A sheet of hydrogel (2".times.2".times. about 1/16" thick, 2ND SKIN.RTM. 
Non-stick Moist Burn Pads, Spenco Medical Corporation, Haywards Heath, 
United Kingdom) was placed on the bottom surface of a small pressure 
vessel. To begin gas desorbing, the loaded sorbent tablet was placed on 
top of the hydrogel sheet. This placement allowed the tablet to adsorb 
water at a slow rate from the hydrogel, and in turn desorb the adsorbed 
gas. 
The volume of carbon dioxide desorbed from the tablet over time is shown in 
Table 15. 
TABLE 15 
______________________________________ 
Gas Desorption Rate 
Cumulative Desorbed CO.sub.2 
Time Volume 
(min) (mL) 
______________________________________ 
0 54 
1 72 
2 80 
3 88 
4 92 
5 96 
6 99 
7 102 
8 104 
9 107 
10 108 
11 110 
12 112 
13 113 
14 114 
15 116 
16 118 
17 118 
18 120 
19 121 
20 122 
25 127 
30 132 
35 137 
______________________________________ 
The above data demonstrates that an infusion device can be run using only a 
sorbent tablet and a hydrogel bed upon which it is placed. It also shows 
that liquid water or water containing solution is not absolutely necessary 
for desorption of gas from a sorbent loaded tablet. 
The foregoing is offered primarily for purposes of illustration. It will be 
readily apparent to those skilled in the art that the component shapes and 
dimensions, materials, operating conditions, procedural steps and other 
parameters of the inventions described herein may be further modified or 
substituted in various ways without departing from the spirit and scope of 
the inventions.