Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND OF THE INVENTION
Patents 3,854,874 and 3,954,361 describe a process
for sterilizing a web of packaging material by dip coating
the we~ in a concentrated solution (1~% to 40%) of hydrogen
peroxide and then quickly evaporating the liquid film within
20 seconds as it travels through a hot chamber at tempera-
tures of 80 C to 120 C where some hydrogen peroxide gas is
generated for contact with the web.
Submersion of the web in concentrated liquid
hydrogen peroxide solution would cause a "shock" effect on
microorganisms making them easier to kill in the hot chamber
Also at 80 C heat alone starts to become sporicidal and its
sporicidal activity increases with temperature. It is noted
that steam sterilization is carried out at 120 C to 125 C.
Although hydrogen peroxide gas is generated for contact with
the packaging web, it is believed that sterilization occurs
primarily because of the combined liquid and heat treatment.
Temperatures below 80 ~ are generally considered
nonsporicidal and a "cold" sterilizing process would operate
in this range. The conventional ethylene oxide gas sterili-
zation process is considered a "cold" process and typically
operates at about 55 C.
The processes shown in the above two patents
reduce viable bacterial spore population ~y only 5 log
orders. The Food and Drug Administration (FDA) is currently
recommending that all medical and surgical products be
sterili~ed to a probability of survival for spores, which
are the most resistant of cells to kill, of 10 or ~etter.
-2-
This means that the sporicidal activity of a sterilizing
process must be so reliable as to assure the probability of
less than 1 organism out of 1,000,000 will survive a ster-
ilization cycle.
A "cold" hydrogen peroxide gas sterilizing process
that produces survival probability sufficient for sterile
medical and surgical products has been described by others
in a co-owned, co-pending Moore and Perkinson application,
S.N. 836,667, filed September 26, 1977 (Continuation-in-part
of S.N. 638,966, filed December 11, 1975 and now abandoned).
The Moore and Perkinson application describes a process that
operates below 80 C without requiring submersion in a
concentrated hydrogen peroxide solution. Nothing is dis-
closed in their process relating to the space sterilized or
the concentration of hydrogen peroxide in the gas phase.
The conventional ethylene oxide process is run at approxi-
mately 55 C with a gas phase concentration of 630 mg/L.
SUMMARY OF TNE INVENTION
Our invention is an improvement on the basic
"cold" sterilization process of Moore and Perkinson and
involves the unexpected discovery that evaporation of large
quantities of liquid hydrogen peroxide is not needed for
sterilization. The present invention involved the discovery
that extremely low concentrations of hydrogen peroxide in
the gas phase, (such as 0.5 mg/L) can accomplish the same
order of magnitude of sterilization as ethylene oxide at 630
mg/L in the ~ phase as in current commercial use.
z~
With '~his discovery, there is recognized a tremen-
dous economic advantage over ethylene oxide gas steriliza-
tion as equivalent molecular amounts of hydrogen peroxide
and ethylene oxide currently cost approximately the same.
In addition, the low concentration of hydrogen peroxide gas
is easy to dissipate from the sterilized product and does
not require the extensive time necessary to eliminate
ethylene oxide residues from the sterile product. A device
for sterilizing contact lenses is shown using the "cold"
hydrogen peroxide gas sterilization process. The device has
structure for circulating hot tap water and for manual
evacuation.
THE DRAWINGS
Figure 1 is a side elevational view of a contact
lens sterilization receptacle connected to an evacuating
hypodermic syringe; and
Figure 2 is an enlarged view of the contact lens
receptacle o~ Figure 1 schematically showing a conduit for
directing hot water through the receptacle.
DETAI~ED DESCRIPTION
The following laboratory tests were run at the
following hydrogen peroxide concentration in the gas phase.
E_ample 1
Thirty silk sutures and 30 porcelain penicylinder
carriers each inoculated with approximately 10 mature
ili24ZO
spores of Bacillus subtilis var. niger were placed in a
vessel under 25 in Hg negative pressure and an atmosphere of
1.1 mg H2O2/L was generated. After a 4 hour exposure at 55
C, testing of the carriers indicated them to be sterile.
Example 2
Ten silk sutures and lO porcelain penicylinder
carriers each inoculated with approximately 10 mature
spores of Bacillus subtilis var. niger were placed in a
vessel under 25 in Hg negative pressure and an atmosphere of
0.6 mg H2O2/L was generated. After a 2 hour exposure at
60 C, testing of the carriers indicated them to be sterile.
Example 3
Same procedure as in Example 2, except that l.l mg
H2O /L and 0.5 hours exposure at 55 were used. All carriers
were rendered sterile.
Example 4
Same procedure as in Example 1 with the substitu-
tion of approximately 10 mature spores of Clostridium
sporo~enes per carrier. All carriers were rendered sterile.
Example 5
Approximately 10 mature spores of Bacillus
subtilis var~ ni~er on spore strips were placed in a vessel
under 25 in Hg negative pressure and 1.4 mg H2O2/L was
generated~ After 1 hour exposure at 22 C, testing of the
:~1;Z42i)
carriers indicated them to be sterile.
Example 6
Same procedure as in Example 5 but without vacuum.
After 24 hours exposure at 22 C, testing of the carriers
indicated them to be sterile. Sterility was not achieved
within 6 hours exposure.
While the variables of time, temperature, and H2O2
vapor concentration can be varied, the ranges of operation
are .1 to 75 mg H2O2 vapor/L with a preferred range of .1 to
1~ 50 mg/L; 20 - 80 C; and 60 seconds to 24 hours time. In
commercial use, the temperature might be in the range of
45 - 65 C and the time 10 minutes to 2 hours. The negative
pressure applied is preferably greater than 15 inches of Hg.
The precise mechanism of why the hydrogen peroxide
sterilizes at such extremely low concentrations is not fully
understood. When a tiny amount of liquid hydrogen peroxide
is introduced into a very large confined space, the water
ha~ing a greater partial pressure in the vapor phase than
the hydrogen peroxide evaporates quicker than the hydrogen
2~ peroxide. Thus, as the liquid phase ~ecomes reduced in
volume, it becomes more concentrated in hydrogen peroxide.
As evaporation continues toward the end of the evaporative
cyclel a ~reater hydrogen peroxide to water ratio is entering
the gaSeQUS phase. This might have an effect on ~he unex-
pected sporicidal activity of the low hydrogen peroxide gasconcentration.
~1242i)
Experiments of Examples 5 and 6 relative to vacuum
show that a vacuum can increase the killing rate several-
fold. For instance, when 1.4 mg of H2O2 was added per liter
of sterilizable space, the Bacillus subtilis spores were
killed within 6-24 hours. When a vacuum of 24 inches of Hg
was applied to a closed container, the time of kill decreased
to 1 hour.
Throughout the specification hydrogen peroxide has
been referred to relative to its concentration in its gaseous
phase. Since this is a "cold" gas sterilization process
similar to that of ethylene oxide, as opposed to a heat or
liquid contact sterilization process, it is immaterial how
the gaseous hydrogen peroxide concentration is obtained. A
very small amount of liquid hydrogen peroxide could be
placed inside of a package containing a product to be steri-
lized or inside of a sterilizer tank and then evaporated
inside such package or tank to generate the desired concen-
tration of hydrogen peroxide in gaseous phase. Alterna-
tively, the vaporization process could be carried on outside
of the package or sterilizing tank and gaseous hydrogen
peroxide of the required concentration injected into the
package or tank. If desired, a product to be sterilized
could be packaged in a pac~age that is pervious to hydrogen
peroxide gas, but impervious to microbial passage.
It is recommended that a stabilized form of hy-
drogen peroxide be used. One such hydrogen pexoxide that
includes a stabilizer to prevent substantial catalytic
decomposition caused by ions of aluminum, iron, copper,
manganese, and chromium is marketed by F.M.C. Corporation of
New York under the name Super D. Their technical bulletin
~24~
No. 42 explains that a 6% solution retains 98% of its
original acti~e oxygen after ~eing subjected to 100 C for
24 hours. This is a more stringent temperature exposure
than is utilized in the moderate temperatures of the present
invention. A typical stabilizer for hydrogen peroxide might
be sodium stannate as explained in the book entitled "Hy-
drogen Peroxide," by W. C. Schumb et al, Reinhold, 1955,
pages 535-547.
An apparatus for sterilizing contact lenses using
either the basic "cold" hydrogen peroxide sterilization
process of Moore and Perkinson previously described, or the
present improvement to that process is shown in the attached
drawings. Figure 1 schematically shows a receptacle 1 with
a pair of joined compartments 2 and 3 respectively for
holding each of a pair of contact lenses. The gas tight
closure 4 screws on to the receptacle. This general con-
struction of a contact lens receptacle that separates the
two lenses to keep them from abrading against each other is
conventional. What is not conventional is a vacuum port and
adapter 5 that can connect to a piston type hypodermic
syringe 6 for manually evacuating the contact lens recep-
tacle.
Figure 2 is an enlarged view of the receptacle
showing separate supporting surfaces 7 and 8 for the two
contact lenses 9 and 10. Such lenses could ~e o~ the "soft"
flexible plastic lenses that require frequent disinfection
or sterilization to control growth of microorganisms on the
lenses. Although not shown, it is understood that chambers
containing lenses 9 and 10 are interconnected so hydrogen
peroxide gas can freely circulate and contact both lenses.
42~)
In addition to evacuating the contact lens recep-
tacle with syringe 6, it is preferred to elevate the recep-
tacle's temperature in the range of 20 C to less than 80
C, such as to 55 C. This can be done by circulating hot
tap water through a conduit within the chamber shown sche-
matically as 11. It is understood that other conduit struc-
ture could be used.
As shown in Figure 2, the small droplet 12 of
liquid hydrogen peroxide is in the receptacle. This droplet
can be placed in the receptacle by the user and then evapor-
ated to generate the necessary hydrogen peroxide gas.
Alternatively, other means for generating the gas and in-
troducing it into the receptacle could be used. After the
lenses are sterilized, the receptacle is opened to vent the
sterilizing gas and the lenses removed.
In the above described contPct lens sterilization
apparatus, the "cold" hydrogen peroxide gas sterilization
process is preferably used to cause sporicidal kills of the
magnitude recommended by the FDA for medical and surgical
products, i.e. to a probability of survival of 1 x 10 or
better. The "cold" hydrogen peroxide gas sterilization
pr~cess is very well suited for contact lenses because it is
so convenient and fast. Depending on such factors as degree
of vacuum applied, hydrogen peroxide gas concentration, and
temperature, gas contact time can be in the range of 60
seconds to 1 hour. As shown in Example 3 above, a 1.1 mg~L
concentration in the gas phase at 55 C sterilizes in only
30 minutes. ~rom calculations it is estimated that ster-
ility occurs substantially sooner than this and there is a
time safety factor in Example 3.
It is recognized that contact lenses are required
to be sterile when sold. However, once in the hands of the
user, the manufacturers of contact lenses are recommending
periodic treatment by the user that merely disinfects the
lenses. A liquid hydrogen peroxide solution is often
recommended. A disinfectant is generally recognized as
killing only vegetative cells, ~ut not spores.
The reason manufacturers have not recommended full
sterility of the magnitude recommended by the FDA for
medical and surgical products, such as scalpels, sutures,
hypodermic syringes, etc. is that there has been no con-
venient, economical and easily understandable device for use
by the millions of people who now wear contact lenses. The
present invention provides a simple economical device that a
wearer can use to periodically sterilize rather than merely
disinfect his contact lenses.
In the foregoing specification, specific examples
have been use~ to describe this invention. However, those
skilled in the art will understand how to make changes to
these examples, without departing from the spirit and scope
of the invention.
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