Cleaning and liquid contact with solids – Processes – Using solid work treating agents
Reexamination Certificate
1999-12-17
2002-09-24
Gulakowski, Randy (Department: 1746)
Cleaning and liquid contact with solids
Processes
Using solid work treating agents
C134S022120, C134S022140, C422S028000
Reexamination Certificate
active
06454871
ABSTRACT:
This invention relates to a method for removing biofilm, debris, contaminants and the like from the surfaces of passageways, including passageways which have irregular or complex shapes or whose walls are permeable, using a mixed-phase cleaning solution.
BACKGROUND OF THE INVENTION
Interior surfaces of passageways such as small-bore tubing, pipes, ducts and the like, which may carry fluids such as liquids, gases, slurries or aerosols, are very difficult to clean and to maintain in a clean condition. When the flow path is long and narrow, or hard to reach, it is difficult to clean the surfaces by conventional liquid phase flushing because such a long, narrow passageway limits liquid flow velocities by creating a high resistance to flow. As a result, shear stresses which could aid in the removal of contaminants from such surfaces are limited. Low flow velocities also limit the usefulness of solvents for the same reasons.
Cleaning of small diameter passageways is also difficult because of the nature of certain types of residues. Fluid passageways which supply water, even purified water, develop bacterial and fungal growth from the water on their interior surfaces, as is well known. Bacteria present in the water strongly adhere to tubing surfaces and then grow laterally, forming what is known as biofilm. Biofilm is apparent to the touch as a slimy film and is composed of both organic residues and the multiplying microorganisms. The bacteria deposit an underlying structural matrix comprising polysaccharides with some peptide moieties, calcium carbonate and other materials which adhere to the surfaces of the passageways. An illustrative example is dental unit water line tubing, which carries rinse water to the mouth of a dental patient. It has been determined that, in the absence of any special precautions, this water exiting from such tubing can include as much as one million (1×10
6
) colony-forming units of bacteria per milliliter of water (CFU/ml). The source has been shown to be the surface biofilm which sheds bacteria into the flowing water. The American Dental Association has recommended reduction of the level of bacteria present in dental water delivery systems to below 200 CFU/ml to be adopted by the year 2000. Thus, these water lines and tubing must be periodically disinfected or cleaned to ensure the deactivation of viable bacteria and the removal of this biofilm from the walls of the tubing in order to prevent infection in dental patients. Removal of biofilm from passageways is also necessary for other applications, including medical, industrial and food service applications, because such biofilms are the main cause of high bacterial counts and high levels of endotoxins.
However, removing biofilm from fluid passageways is quite difficult, which makes disinfecting the surface more difficult as well. The biofilm is strongly adherent to passageway surfaces, whether the surface is made from natural materials, such as rubber or metals, or synthetic polymeric materials, such as polyvinylchloride, polyethylene, polytetrafluoroethylene and the like. Treatment with chemical agents, such as disinfectant and biocidal agents, can kill the exposed surface bacteria and so reduce the contribution of the biofilm to the total bacterial count. However, these agents do not readily diffuse into the entire thickness of the biofilm. The biofilm protects the remaining viable bacteria which then rapidly multiply. If it happens that all of the bacteria are killed, the biofilm structure remains an ideal host for new bacteria to colonize and grow. Thus these treatments are generally only partially effective, and the original levels of viable bacteria return quite rapidly. In order to remove biofilm from a surface, in addition to chemical treatment, some mechanical action is necessary to produce shear stress or sufficient impact at the surface.
In dentistry, there are applications for cleaning and disinfecting both tubing and the dental handpiece. The handpiece, which contains an air-driven turbine or other method of driving a drill and other parts, is about six inches long and is detachable. The tubing and other passageways inside the handpiece have a ratio of length to inside diameter of about 100. At present the most common sterilization procedure is steam autoclaving. However, in addition to the fact that autoclaving does not actually remove debris from the handpiece, this autoclaving procedure can be damaging to the turbine and various seals in the handpiece. For example, the operating rotational speed of a dental drill has been found to decrease with the number of sterilizations performed.
The old method of cleaning dental handpieces is to flush them with water or a cleaning solution. While this may flush nonadherent biofilm and debris from passageways, it can be shown that it provides little or no removal of adherent biofilm and debris such as blood, mucous and the like. In order to obtain more force behind the liquid flushing, Littrell, U.S. Pat. No. 3,625,231, describes a device utilizing compressed air to force a quantity of a cleaning and conditioning fluid through the passageways of the handpiece. This device primarily uses single-phase liquid flow as evidenced by the requirement to observe the clarity of the fluid being expelled from the handpiece as a criterion for cleaning. This method is only slightly more effective than flushing with water but may be significantly better than flushing with a hand-operated syringe. However, complete removal of adherent biofilm, debris and contaminants will not occur.
Cleaning of instruments, handpieces and the like by spraying with water or cleaning solutions is also well known. The spray may be generated by an aerosol can or an atomizing device. While this is a useful method of distributing a cleaning solution, it does not ensure complete cleaning of adherent debris. Complete cleaning only occurs when the adhesion of the debris is overcome by shear stress. Additionally, an effective cleaning method may act to weaken the adhesive bond between the debris and the surface to which it adheres to reduce the required stress. The adhesive strength must be overcome by a significant margin to ensure complete cleaning. Total coverage of all surfaces by shear stress is required and sufficient mass transfer must be provided to prevent loosened debris from shielding unloosened debris. Simple spraying does not ensure that these conditions are met.
It can be estimated that prior art techniques which use a total of only a drop or two of liquid would not provide enough liquid for the surface area of a dental handpiece tube to achieve significant re-formation of droplets. One or two drops equals tenths of a milliliter. The present method uses a continuous flow for a period of time such that the amount of liquid used for the same purpose would be tens of milliliters, some two orders of magnitude higher.
In addition to biofilm, passageways of various medical devices may contain food particles, particles of various bodily tissues, mucous, saliva, unclotted or clotted blood or blood components, pathogens, macromolecules and the like, which are referred to hereinafter as “debris”. It is also necessary to remove this debris from the passageways in which it exists. Such debris may even need to be cleaned from passageways which are not fluid-carrying passageways in the normal use of the device, such as where a cable slides inside a sheath or conduit in an endoscope or biopsy device. Infections arising from the use of endoscopic devices have been reported and traced to the inefficient cleaning and debris removal by conventional methods.
Endoscopes may contain a passageway for use of a biopsy device, as well as passageways for other purposes. Both the internal passageways and the exterior of the endoscope must be cleaned after each use. The biopsy device itself also has interior and exterior surfaces which must be kept clean. Guidelines for cleaning gastrointestinal and other flexible endoscopy units promulgated by the American Society for Gastrointestinal Endoscopy and
Labib Mohamed Emam
Lai Ching-Yue
Mahon Geoffrey Lawrence
Materna Peter A.
Chaudhry Saeed
Princeton Trade & Technology, Inc.
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