System and method for electrical control of bacteria
11590247 · 2023-02-28
Assignee
Inventors
- Martin L. Yarmush (Boston, MA, US)
- William G. Austen (Weston, MA)
- Alexander Goldberg (Boston, MA, US)
- Saiqa I. Khan (Agawam, MA, US)
Cpc classification
A61L2202/24
HUMAN NECESSITIES
A61B18/00
HUMAN NECESSITIES
C12N13/00
CHEMISTRY; METALLURGY
International classification
A61L2/00
HUMAN NECESSITIES
A61B18/00
HUMAN NECESSITIES
A61N1/30
HUMAN NECESSITIES
A61M1/00
HUMAN NECESSITIES
C25B5/00
CHEMISTRY; METALLURGY
C12N13/00
CHEMISTRY; METALLURGY
Abstract
A system and method for controlling microbial growth on and in medical devices and implants, especially biofilm infections, involves using pulsed electric fields (PEF). To eradicate at least a portion of a biofilm on a medical implant, for example, 1500 volts can be applied through an electrode system, with pulse duration of 50 μs and pulse delivery frequency of 2 Hz. In the clinical setting, systemic microbial therapy can be combined with PEF to achieve a synergistic effect leading to improved eradication of infections.
Claims
1. A method for disinfecting a medical device using pulsed electric fields, the method including the steps of: a. identifying one or more characteristics of a microbial biofilm to be eradicated, the biofilm being located on or in a medical device; b. selecting a suitable protocol for the pulsed electric field to be applied, the selected protocol defining: 1) a voltage; and 2) a pulse frequency; c. positioning an electrode system at a medical device to be disinfected; d. applying a pulsed electric field to the microbial biofilm to eradicate at least a portion of the microbes in the biofilm, the pulsed electric field having: 1) A voltage of at least 1000 volts; 2) An electric field strength of at least 150 V/mm; and 3) a pulse frequency of at least 1 Hz.
2. The method of claim 1, wherein the medical device is a synthetic mesh, the method further including the step of diagnosing a mesh infection.
3. The method of claim 1, further including the step of using a systemic antimicrobial in combination with the pulsed electric field.
4. The method of claim 1, further including the steps of inserting the electrode system in a patient and positioning the electrode system at an implanted medical device to be disinfected.
5. The method of claim 1, wherein the selected protocol further defines: 1) A number of pulses; and 2) a pulse duration.
6. The method of claim 5, wherein the number of pulses is at least 150 pulses and wherein the pulse duration is at least 25 μs.
7. The method of claim 1, wherein selecting a suitable protocol for the pulsed electric field to be applied further comprises: selecting a suitable protocol for the pulsed electric field to be applied based on the one or more characteristics of the microbial biofilm, and wherein applying a pulsed electric field to the microbial biofilm to eradicate at least a portion of the microbes in the biofilm further comprises: applying a pulsed electric field to the microbial biofilm to eradicate at least a portion of the microbes in the biofilm based on the selected protocol.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1)
(2)
(3)
(4)
(5)
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DETAILED DESCRIPTION
(7) The following discussion is presented to enable a person skilled in the art to make and use embodiments of the invention. Various modifications to the illustrated embodiments will be readily apparent to those skilled in the art, and the generic principles herein can be applied to other embodiments and applications without departing from embodiments of the invention. Thus, embodiments of the invention are not intended to be limited to embodiments shown, but are to be accorded the widest scope consistent with the principles and features disclosed herein. The following detailed description is to be read with reference to the figures. The figures depict selected embodiments and are not intended to limit the scope of embodiments of the invention. Skilled artisans will recognize the examples provided herein have many useful alternatives that fall within the scope of embodiments of the invention.
(8) The invention may be described herein in terms of functional and/or logical block components and various processing steps. It should be appreciated that such block components may be realized by any number of hardware, software, and/or firmware components configured to perform the specified functions. For example, an embodiment may employ various integrated circuit components, e.g., memory elements, digital signal processing elements, logic elements, diodes, look-up tables, etc., which may carry out a variety of functions under the control of one or more microprocessors or other control devices. Other embodiments may employ program code, or code in combination with other circuit components. It should also be appreciated that certain components and functions may be shared and/or shuffled between blocks and among blocks in different embodiments of the invention, as deemed suitable. For example, the role of a processing unit may range from giving a command to a generator to generate pulses according to a self-directed protocol, without coordination of the generation by the processing unit, or it may take a more active role in the steps involved in implementing a particular generation protocol.
(9) Referring to
(10) An electrode system 170 may be provided for disinfecting devices that are not easily transported to the system 100 for placement in the receptacle 150, such as devices implanted in a patient. The system 100 may have both the ability to apply pulsed electric fields externally via an extendible electrode system 170, as well as “internally” via the device receptacle 150, which may be an enclosure with one or more of its own electrodes for applying pulsed electric fields to devices placed in the receptacle 150. An exemplary electrode system may include a ring electrode concentric with a needle electrode, the two secured to each other via a non-conducting material, or an array of needles arranged to apply pulsed electric fields as desired. The needles in such an array can be arranged linearly or non-linearly, and the electrodes (rings, needles, etc.) may be sized and spaced so as to accommodate (for example) the sizes and shapes of devices to be disinfected, the magnitude of the pulses to be applied, the area to be disinfected, and/or the surroundings of the device (such as location in the body and the size of openings through which the electrode system must pass). Once a device is positioned in the receptacle 150, the electrodes may be moved into place relative to the device by, for example, a sliding or pivoting motion. To accommodate devices with different shapes and sizes, the electrode positions may be further adjustable to allow for fine-tuning after they have slid or pivoted into place. A slidable/pivotable cover may also be provided to help contain the device in the receptacle 150 and keep contaminants out during disinfection. The electrodes may be secured to the cover, such that “closing” the receptacle concurrently or automatically slides/pivots the electrodes into position with respect to the device.
(11) The processing unit 120 includes a processor, one or more memory modules, and instructions in the form of software (which can be loaded into the memory), firmware, hardware, or any combination thereof. The components of the processing unit 120 are involved in coordination and implementation of the functionality of the system 100 by, for example, interfacing with the pulse generator 110 to control the generation of pulsed electric fields, the user interface 130 to receive inputs, the display 140 to provide outputs, and the scope 160 to receive images. The processing unit 120 may also serve as an intermediary between, for example, the pulse generator 110 and the electrode 170 (to, e.g., initiate application of pulsed electric fields), the scope 160 and the display 140 (to, e.g., process images to be displayed), and the user interface and the device receptacle 150 (to, e.g., initiate disinfection).
(12) Referring to
(13) An exemplary process 300 for determining which protocol is to be applied is represented in
(14) In a less “automated” alternative process, once the biofilm has been characterized/identified 310, the user may review from among a set of predetermined/preselected protocols 320 suitable for multiple microbes/biofilms and select one of the predetermined/preselected protocols. The parameters for such predetermined protocols could be set such that they are suitable in multiple situations (e.g., expected to be effective for a set of devices and/or a group of microbes) based on prior experiments and experiences. Once a predetermined/preselected profile has been selected, the user may optionally wish to customize or otherwise adjust a subset of the parameters of the predetermined/preselected protocol, and such adjustments may be input 360 into the system 100 via user interface 130. The user may then be asked to confirm the modified protocol 370, if required, before initiating pulsation 380. It is noted that the process 300 may also begin by review and selection of predetermined/preselected protocols 320, without characterization and/or identification of the biofilm 310. The protocol may be adjusted/customized if desired 360 before initiating pulsation 380. In yet another alternative implementation of the process 300, the user may begin by manually entering the parameters of the protocol to be applied 340. Once the parameters have been confirmed 370, pulsation may begin 380.
(15) Selection of an effective protocol—whether based on a recommendation of the disinfection system 100 (following characterization/identification 310), selection from among predetermined/preselected protocols, or a user-defined protocol—is influenced by such factors as the microbe (e.g., class, type, species, strain), infected area, etc. For example, disinfecting a nonabsorbable synthetic prolene mesh that is infected with the pathogenic Gram-negative bacterium Pseudomonas aeruginosa has been found to respond to certain electric field pulses when applied via concentric ring electroporation, which delivers a centrifugal gradient of disinfection from the center outwards to the periphery. The center of the mesh, where the needle is in direct contact (see
(16)
where V1 is the voltage delivered through the central needle, V2 is the voltage at the external ring, r is the radial distance of each point inside the treatment area from the center, R1 is the radius of the needle, and R2 is the external ring radius (see
(17) In one experiment, a sterile, nonabsorbable synthetic prolene mesh (Ethicon, Calif.) was infected with the pathogenic Gram-negative bacterium Pseudomonas aeruginosa that had been rendered bioluminescent. The P. aeruginosa strain employed was ATCC 19660 (strain 180). It can cause septicemia by intraperitoneal injection, and is pathogenic in mice with infected cutaneous burns. The bioluminescent variant (strain Xen 05) carried the integrated bacterial lux operon into its chromosomes for stable bacterial luciferase expression, which allowed them to be used for bioluminescent imaging. A colony of bioluminescent Pseudomonas aeruginosa was then placed in a 50 mL falcon tube with prolene mesh and 30 mL of brain heart infusion broth (BHI). This was agitated on a shaker at 180 rpm for 30 minutes at room temperature and then moved to a C24 Incubator Shaker (Brunswick Scientific) at 37° C. with agitation at 100 rpm for three days. After three days, the infected mesh was placed on sterile agar plates and incubated overnight at 37° C., 5% CO.sub.2.
(18) Referring to
(19) Referring to
(20) As further evaluation and confirmation of the disruption of biofilms, sterile uninfected mesh, untreated infected mesh, and treated infected mesh were processed for Scanning Electron Microscopy (SEM). Samples were placed in one-half (½) strength Karnovsky's fixative immediately after treatment and imaging. Samples remained in fixative for twenty-four hours prior to embedding. After fixing the samples for twenty-four hours, they were dehydrated in a series of graded ethanol concentrations. A Tousimis Samdri semi automatic Critical Point Dryer was used to completely dehydrate the samples. The mesh was then mounted on aluminum stubs and coated with Chromium with a GATAN 610 Ion Beam Coater. Samples were then viewed in the SEM at a voltage of 5 kV. For image scanning a JEOL 7401F Field Emission Scanning Electron Microscope was used. Magnification of images ranged from 25× to 10000×. One to three fields were obtained at each magnification.
(21) For data analysis, a method of determining critical electroporation parameters was used. A set of images before and after the treatment were used to derive the parameters. First, the luminescence intensity was normalized to the correct value to compensate for the difference in the microscope settings before and after the scanning. Following the normalization, the pixels were converted to distances, where each pixel length was 5 mm. The intensity as a function of radius r, for each exposure time t, I.sub.t(r) was obtained by calculating the average intensity of a cluster of bacteria according to the following:
(22)
where r=√{square root over ((x−x.sub.ct).sup.2+(y−y.sub.ct).sup.2)} represents the spherical radius from the center of the plate (x.sub.ct, y.sub.ct); (x, y) are the coordinates of the plate; δ is the length of the cluster in mm, and N.sub.r is the normalization factor, which refers to the number of pixels in the cluster in the spherical radius. The intensity over different distances, I.sub.t(r), was converted to intensity over electrical field strength using Equation (1).
(23) The relationship between the survival fraction and the treatment time (for a predetermined pulse energy) is commonly described by a mathematical model based on the Weibull distribution:
(24)
where S is the survival fraction of bacteria after the treatment, E is the local electric field, and b and n are the field normalization and field exponent factors that can be estimated from fitting the empirical data for each pulse rate. The fitting used to estimate these parameters was least-squares nonlinear curve-fitting. The Weibull distribution depicts the dependence of bacterial survival on electric field intensity. A medium-scale Quasi-Newton line search for the fitting algorithm was used.
(25) To quantify the effect of pulse number using 100, 150, and 300 pulses, where the voltage, pulse length duration, and frequency remained unchanged (1500V, 50 μs, and 2 Hz, respectively), the images before and after treatment with concentric ring electrodes were analyzed. The effect of treatment was measured as a function of the radius of central clearing as seen in the bioluminescent images of the mesh. In images of the mesh before and after treatment with concentric ring electrodes, it was seen that in all treatments with 150 and 300 pulses there was an effect that resulted in lower intensity in the images after treatment. To quantify the treatment effect, areas with over 80% eradication were deemed to be effective eradicated areas. According to this criterion, the critical electrical field strength was 121±14 V/mm when 300 pulses were applied, 235±6.1 V/mm when 150 pulses were applied, with related eradication area of 50.5±9.9 mm.sup.2 for 300 pulses and 13.4±0.65 mm.sup.2 for 150 pulses (see Table 1, showing bacterial eradication results for number of pulses delivered, in which V1=1500, V2=0, 50 μs pulse length duration, and 2 Hz).
(26) TABLE-US-00001 TABLE 1 E.sub.cr for 80% Area Eradicated Treatment Eradication (V/mm) over 80% (mm.sup.2) 100 pulses none none 150 pulses 121 ± 14 50.5 ± 9.9 300 pulses 235 ± 6.1 13.4 ± 0.65
(27) This indicates that the treatment efficacy increases as the number of pulses increases. A clear increase in treatment efficacy is appreciated at the center of the mesh, which was the area that received the strongest electric field delivery even at 100 pulses. A thick biofilm matrix (see
(28) Survival rate is defined as the ratio of bacterial survival (measured as RLU) compared to the initial value, and is depicted in a logarithmic scale.
(29) In comparing the treatment efficacy to a theoretical model, the model fitting to the theoretical Weibull distribution in Equation (3) is very high with a correlation coefficient R2 of 0.9563, 0.9943, and 0.9956, for the 100, 150, and 300 pulses, respectively. The model fitting is more accurate in the case of higher pulses, where the treatment effect is more significant. The model fitting parameters used, and their corresponding R2, are depicted in Table 2.
(30) TABLE-US-00002 TABLE 2 Treatment (b, n) R.sup.2 100 pulses −0.49, 0.074 0.9563 150 pulses 5.4650, 0.3379 0.9943 300 pulses 0.0001, 0.0828 0.9956
(31) These experiments demonstrated that pulsed electric fields can eradicate bacteria and disrupt biofilms in mesh implants without damaging the mesh. The results demonstrate the effectiveness of PEF treatment of biofilm-infected mesh, showing increased bacterial eradication with increased number of pulses, and with increased electrical field strength. Additionally, the area of complete eradication of bacteria increases as the number of pulses increases (p=0.000056). This indicates that increased efficacy of treatment is due to increased number of pulses delivered. Additionally, the p-value between the conditions of 150 and 300 pulses was 0.101, which indicates a marginal significance between 150 and 300 pulses. This indicates that the effect of number of pulses between 150 and 300 pulses is considerably small compared to lower pulse numbers (50), where the effect on survival rate is less. This suggests that protocols with fewer than 300 pulses may be suitable, without significant impact on treatment efficiency. Suitable protocols for other biofilms, devices, and applications can be determined and evaluated using techniques similar to those used for synthetic mesh infected with Pseudomonas aeruginosa, or using other techniques and approaches where appropriate.
(32) The protocols selected—i.e., the depth of PEF treatment—can be controlled in order to avoid damage to surrounding tissue and/or organs if clinically applied in a patient with infected mesh. The treated area in the clinical scenario will be predefined by the configuration of the electrodes and the applied PEF parameters. In order for the effect of PEF treatment to be maximized, it would work synergistically with the human immune system and intravenous (IV) antibiotics. PEF could be used to stimulate the immune system by recruiting inflammatory cytokines and mediators to the site of treatment, and it has the potential to eradicate the biofilm synergistically with antibiotics. Disruption of bacteria in the biofilm could decrease the concentration of secreted molecules such as eDNA in the biofilm, therefore enabling more efficient drug delivery to the treated area.
(33) PEF treatment mitigates the problem of antibiotic resistance. Additionally, PEF does not involve enzymatic removal, chemical treatments, metallic nanoparticles, chelating agents, or other methods previously applied to biofilms. Moreover, PEF is a non-thermal treatment that is not expected to destroy the integrity of medical devices (such as the mesh, which is not damaged), while sparing surrounding tissue from injury. Combining antibiotic therapy with PEF could effectively eradicate biofilms, therefore avoiding mesh removal and/or life-long high dose antibiotic therapy. The disinfection system 100 could be customized with an array of needles at various distances apart from each other to treat any given infected device in a patient.
(34) The present invention has been described in terms of one or more preferred embodiments, and it should be appreciated that many equivalents, alternatives, variations, additions, and modifications, aside from those expressly stated, and apart from combining the different features of the foregoing versions in varying ways, can be made and are within the scope of the invention. It should be appreciated that the invention is applicable to other procedures and to achieve other objectives as well. Following are additional examples. These examples are not to be construed as describing the only additions and modifications to the invention. It is expressly contemplated that any of the processes or steps described herein may be combined, eliminated, or reordered. Accordingly, this description is meant to be taken only by way of example, and not to otherwise limit the scope of this invention. The patentable scope of the invention is defined by the claims and may include other examples that occur to those skilled in the art.
(35) For example, although protocols were discussed with respect to eradiation of an infection on a mesh, the features and advantages that arise due to the invention are well suited to other implants as well as other devices generally (medical or otherwise). Additionally, it should be appreciated that the above systems and methods can be implemented using hardware, software, single integrated devices, multiple devices in wired or wireless communication, or any combination thereof.