Medical instrument sterilization container

A medical instruments sterilization container (10) which includes a housing (12) and a removable lid (14). A removable tray (16) is adapted to hold various medical instruments to be sterilized. The container is formed of a polymer of relatively low thermal conductivity, with a material having a relatively high thermal conductivity being added thereto in order to substantially increase the overall thermal conductivity of the container to absorb radiant heat and rapidly conduct that heat throughout the container to reduce condensate within the container.

TECHNICAL FIELD OF THE INVENTION 
This invention relates to sterile containers and more particularly relates 
to a medical instrument sterilization container with high thermal 
conductivity. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, a medical instrument 
sterilization container comprises a housing dimensioned to receive medical 
instruments for sterilization by gas or steam. A removable lid for the 
housing enables access to the housing and seals with the housing to 
maintain the sterility of the housing interior. The housing is formed from 
a polymer of relatively low thermal conductivity and also includes 
material having relatively high thermal conductivity in order that the 
housing absorbs radiant heat to reduce condensate within the container. 
The high thermal conductivity material may be mixed in the polymer or may 
be painted or coated on the container. 
In accordance with another aspect of the invention, a medical instrument 
sterilization container includes a housing having a bottom and side walls 
for receiving medical instruments for sterilization. A removable lid 
sealingly fits over the housing. A housing bottom slopes to at least one 
location to bring condensate to the one location. A filter is disposed in 
the housing bottom at the one location. The filter passes air therethrough 
but prevents passage of contaminants into the housing. 
In accordance with yet another aspect of the invention a medical instrument 
sterilization container includes a housing for receiving medical 
instruments for sterilization. A removable lid sealingly fits over the 
housing. A tray is removably disposed within the housing for supporting 
the medical instruments. Apertures are formed through the bottom of the 
tray to drain condensate therefrom. The tray has domed portions between 
the apertures in order to facilitate draining of condensate. 
BACKGROUND OF THE INVENTION 
It is necessary in hospital and other medical environments to sterilize 
medical instruments with steam or ethylene oxide. Various types of 
sterilization containers for such medical instruments have heretofore 
comprised muslin wraps, various paper wraps and sterilization containers. 
When using the various types of wraps, medical instruments are placed in a 
tray, wrapped by a recommended procedure, taped, labeled and placed in a 
steam or ethylene oxide sterilizer. The steam or ethylene oxide penetrates 
the wrap and kills the bacteria. Disadvantages in the use of the 
sterilization wraps include the repeated expenses of the disposable wraps, 
potential punctures of wrapping materials thereby causing contamination, 
limited shelf life of the wrapped instruments and the fact that the wraps 
are not stackable. 
Various sterilization containers have been heretofore proposed which 
provide a hermetically sealed container with various filters which provide 
a relatively long shelf life, which cannot be easily punctured, which 
enable improved organization of the medical instruments and which are 
stackable. Sterilization containers made of metal such as stainless steel 
and aluminum have been used, but are relatively expensive. These devices 
are generally also opaque, thereby preventing a visual inventory of the 
container interiors. Consequently, sterilization containers made of 
plastics have been developed which can withstand the harsh environments of 
the sterilization chamber and which are clear such that inventories of the 
containers can be seen. Examples of such previously developed plastic 
sterilization containers are the Sterile-Case system manufactured and sold 
by Bemis Corporation and the Steri-Stor system manufactured and sold by 
Research Surgical Systems of Santa Ana, Calif. 
Prior plastic sterilization containers have, however, suffered from the 
problem of condensate accumulation of the internal and external surfaces 
after sterilization. Although bacteria inside the container should be 
substantially eliminated through the sterilization process, medical 
technicians are trained to regard moisture as a breeding place for 
bacteria and thus condensate tends to cause technician acceptance 
problems, as well as providing an actual possible breeding ground for 
bacteria. In addition, the condensate increases the possibility for 
rusting and other deterioration of the metal instruments in the container. 
Steam Sterilization units, whether they be gravity steam, pulsating 
pressure steam or alternating vacuum and pressure or the like, all 
normally have a drying cycle. During the drying cycle, steam is applied to 
the jacket of the autoclave to create a hot environment and normally some 
vacuum is applied to the chamber in order to lower the boiling point of 
the moisture. The drying cycle is utilized to evaporate the moisture in 
the sterilization container wrap or the like. However, clear or 
translucent plastic sterilization containers have a relatively low thermal 
conductivity and thus do not allow the residual moisture to be evaporated 
within an economical time frame. The heat reaching the sterilization 
container within the sterilization unit comprises both conductive and 
radiated heat. The conductive heat tends to heat the container relatively 
slowly, in turn heating the moisture in the container and creating slow 
evaporation. The radiated heat emanates from the jacket of the autoclave, 
but such radiant heat is not able to be utilized in evaporation of clear 
or translucent plastic containers because the majority of the radiative 
heat passes through the clear surface of the plastic containers. The need 
has thus arisen for a plastic sterilization container which enables the 
sterilization of medical instruments and which also tends to prevent or 
eliminate from being formed on the interior surfaces thereof within an 
economical time frame.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIG. 1, the present sterilization container is identified 
generally by the numeral 10 and may be seen to include the housing 12 and 
a removable lid 14. A removable tray 16 is received within the housing 12 
and is adapted to receive various medical instruments such as knives, 
scissors and the like. 
A filter 18 is disposed through the lid 14 in order to allow the package of 
heated sterile air therethrough while preventing the passage of bacteria 
or other contaminants into the interior of the container. Two additional 
filters, to be subsequently described, are disposed in the bottom of the 
housing 12. The tray 16 includes removable metal handles 20 and 22 to 
enable easy withdrawal of the tray 16 from the housing 12. Apertures 24 
are disposed through the tray 16 to allow the passage of steam and 
condensate therethrough. Metal clamps 26 are attached on both sides of the 
housing 12 and are manually movable in order to clamp against the side of 
the lid 14 in order to lock the lid to the housing. Suitable sealingly 
surfaces are provided between the housing 12 and the lid 14 in order to 
provide an essentially airtight container when the lid is clamped to the 
housing. Handles 28 are provided on opposite ends of container 12 to 
facilitate handling. 
FIG. 2 illustrates a partially sectioned view of the sterilization 
container of the present invention. 
The filter 18 may be seen to include apertures 30 which communicate with 
the atmosphere. A removable filter 32 is clamped into place by a twistable 
cap 34. A sealing portion 36 is illustrated between the housing 12 and the 
lid 14. The clamp 26 may be seen to comprise a stationery portion 38 which 
is mounted by pivot 40 to a pivotal clamp portion 42. Manual depression 
upon a lip 44 causes clamp 42 to be moved outwardly in order to accept the 
lid 14. When the lid 14 is in place, the movable clamp member 42 is moved 
by spring pressure to clamp against the lid in order to sealingly affix it 
to the housing. 
FIG. 2 further illustrates pedestals 46 which elevate the bottom of the 
housing 12. Also disposed on the bottom of the housing 12 are two 
additional filters 48 and 50 which are constructed in a similar manner as 
filter 18. Apertures 52 are disposed through the bottom of the housing 12 
in the filter area. The removable filter 54 is held tightly in place by a 
twistable cap 56. A handle 58 is provided on the cap 56 to enable twisting 
into place. Catch members 60 inwardly extend from the bottom of the 
housing 12 for abutting with portions of the cap 56 in order to maintain 
the filter 54 securely in place. 
An important aspect of the present invention is that the bottom of housing 
12 slopes downwardly toward both filter 48 and filter 50. Specifically, 
the bottom walls 62 and 64 each slope toward the location of filter 48 in 
different directions. Thus, condensate or moisture in the left-hand side 
of the tray of the housing 12 will move by gravity to the filter 48. 
Likewise, moisture and condensate in the right-hand side of the housing 12 
will move by gravity along similarly sloping housing bottom wall to filter 
50. 
Referring again to FIG. 2, tray 16 includes apertures 24 as previously 
noted. An important aspect of the present invention is that the tray 
bottom is domed at locations 66 between each aperture 24. This domed 
configuration causes condensate, steam and the like to run into the 
apertures 24 and prevents the accumulation of droplets of condensate or 
liquid on the bottom of the tray 16. 
Referring to FIG. 3, which illustrates a section of one corner of a tray 
taken along section lines 3--3 in FIG. 2, the domed portions 66 are shown 
from a top view. It may be seen that each one of the domed portions 
comprises a rectangle with an aperture 24 located at the corner thereof. 
The domes 66 are formed such that they slope at the corners thereof to an 
aperture 24. Channels 68 are formed between adjacent apertures 24 to 
further assist in draining condensate or liquid through the apertures 24. 
FIG. 4 illustrates in greater detail the construction of each of the 
filters 18, 48 and 50. A twistable cap 56 includes four locking flanges 
70. The filter 54 is circular in shape and includes a plastic member 
having plastic cross-members 72 which support the filter media 74. The 
filter media may be any suitable type of commercially available filter 
which allows the passage of air therethrough but which prevents the 
passage of contaminants such as bacteria. A tab 76 extends from the filter 
to enable manual insertion and removal of the filter. Filter 54 is 
disposable such that the filters may be periodically replaced. Four 
locking members 60 are formed around the recessed area for receiving the 
filter 54 and the twistable cap 56. Apertures 52 extend through the bottom 
to enable steam or condensate to pass therethrough. 
In operation, the filter 54 is placed within the recessed area and the cap 
56 is twisted such that the locking flanges 70 are tightly held within the 
locking members 60. The cap 56 thus very tightly presses the filter 54 
against the side walls of the housing to seal the filter and prevent the 
passage of air past the edges thereof. 
In the preferred embodiment, the present container is formed from a 
suitable plastic or polymer. As previously noted, clear or translucent 
plastic has a low thermal conductivity and cannot thus absorb enough 
radiant heat to eliminate condensate within the housing during the drying 
cycle of a sterilizer system in an economical time frame. Subsequently, 
the present invention contemplates the use of additional high thermal 
conductivity materials in conjunction with clear plastic or polymer in 
order to cause the absorption of sufficient radiant heat and rapidly 
radiant that heat through the container to eliminate condensate in an 
economical time frame such as within twenty (20) minutes. In the preferred 
embodiment, the present invention contemplates the mixture of high thermal 
conductivity materials 78, shown in FIG. 5, within the clear or 
translucent plastic. Alternatively, the invention contemplates the 
addition of a coating of high thermal conductivity materials to the clear 
or translucent plastic. It will be understood that various types of high 
thermal conductivity materials may be utilized to accomplish the object of 
the present invention. The following are examples which have been found to 
work well in practice and which provide a sterilization container having a 
resultant high thermal conductivity which tends to eliminate the formation 
of condensate therein when used in an autoclave. 
EXAMPLE 1 
A plastic is formed for use in a conventional plastic forming maching to 
provide the present container by charging a non-fluxing type high 
intensity mixer with polypropylene copolymer, calcium carbonate and low 
molecular weight polyethylene and mixing to 105.degree. C. Aluminum flakes 
are then added and mixed for 15 to 20 seconds. The mixture is then fed to 
a single screw compounding extruder and is melt mixed at a temperature of 
190.degree. to 205.degree. C. The resulting polymer is then pelletized as 
it comes out of the extruder. The resulting copolymer pellets may be 
utilized in a conventional forming machine to form the present container. 
The formula for use with this example is listed below as a percentage by 
weight: 
______________________________________ 
Polypropylene Copolymer 
55-65% approximately 
Aluminum Flake 35-50% approximately 
Low Molecular Weight 
1-5% approximately 
Polyethylene 
Calcium Carbonate (CaCO.sub.3) 
0-15% approximately 
______________________________________ 
The polypropylene copolymer may comprise, for example, the copolymer 
manufactured by Eastman Company and noted as Tenite. Aluminum flakes may 
comprise the aluminum flakes manufactured by Transmet Corporation and 
identified as K-151. Suitable low molecular weight polyethylene is 
manufactured by Allied Fibers and Plastics Company as AC-9. A suitable 
source of calcium carbonate is Thompson, Wyman and Company under the trade 
name Atomite. 
EXAMPLE 2 
A non-fluxing type high intensity mixture is charged with polysulfone, EBS, 
CaCO.sub.3 and titanate and is mixed to 150.degree. C. Aluminum flakes are 
then added and mixed for 15 to 20 seconds. The mixture is then fed to a 
single screw compounding extruder and is melt mixed to a stock temperature 
of 250.degree. to 260.degree. C. The formula for this mixture is listed 
below as a percentage by weight: 
______________________________________ 
Polysulfone 50-60% approximately 
Aluminum Flake w/silane 
25-40% approximately 
surface treatment 
(EBS) Ethylenebisstearamide 
1-5% approximately 
Neoalkoxy Titanate .01-.1% approximately 
Calcium Carbonate (CaCO.sub.3) 
0-15% approximately 
______________________________________ 
The polysulfone may comprise, for example, polysulfone manufactured by 
Union Carbide as Udell T-1700. A suitable neoalkoxy titanate is 
manufactured by Kenrich Petrochemicals under the trade name Capow 38/M. 
EXAMPLE 3 
A non-fluxing type high intensity mixture is charged with Polysulfone, 
titanate and EBS and mixed to 150.degree. C. Carbon fiber 80, shown in 
FIG. 6, is added and the mixture is mixed to 160.degree. C. The mixture is 
then fed to a single screw compounding extruder and is melt mixed at a 
stock temperature of 250.degree. to 260.degree. C. 
The formula for this mixture is set forth below as a percentage by weight: 
______________________________________ 
Polysulfone 90% approximately 
Carbon Fiber 10% approximately 
Neoalkoxy Titanate .01-.1% approximately 
(EBS) Ethylenebisstearamide 
1-5% approximately 
______________________________________ 
The carbon fiber may comprise, for example, the fiber manufactured by Union 
Carbide Specialty Polymers and denoted as Thornel (VMD). 
EXAMPLE 4 
A clear or translucent plastic container is formed by one of the mixtures 
noted above such as polypropylene, calcium carbonate and low molecular 
weight polyethylene. A container is formed by conventional forming 
techniques and the interior of the housing and lid is then coated 82, 
shown in FIG. 7, with semi-opaque high thermal conductivity material such 
as a heat resistant paint or the like which contains carbon or the like. 
The container may be coated by painting, dipping or other well-known 
coating techniques. The clear plastic container may alternatively be 
impregnated with carbon pigments under pressure. 
Sterilization containers formed by any of the above examples will have a 
relatively high thermal conductivity. For example, the thermal 
conductivity of polysulfone plastic is approximately 1.7 BTU/HR/F.sup.2 
/.degree.F/IN, while the thermal conductivity of aluminum is 10.8 and 
carbon fibers 60 BTU/HR/F.sup.2 /.degree.F/IN. Plastic containers formed 
in accordance with the present invention absorb substantially more heat 
through conduction and radiation and, therefore, heat faster and are more 
effective in moisture evaporation as well as more effective in killing 
bacteria in marginally operating steam sterilizers. The present container 
also enables the heat to more rapidly be transmitted to the entire 
interior, including the tray 16, thereby more effectively treating 
moisture or bacteria. The present construction of the container with the 
sloping bottom walls and domed portion of the removable tray also assist 
in preventing the accumulation of moisture and condensation. It will thus 
be seen that the present container provides a very efficient technique for 
sterilizing medical instrument and yet may be made in an economical 
manner. 
Whereas the present embodiment has been described in detail, it should be 
understood that various changes, alterations and substitutions can be made 
therein without departing from the spirit and scope of the invention as 
defined by the appended claims.