Patent Application
20190046670
The present invention relates to the treatment of biofilms forming on medical implants and, more particularly, to a system and method for treating biofilms that form on cochlear implants.
A cochlear implant is an electronic device that is implanted in a patient with deafness to enhance hearing. A cochlear implant usually has a polysilicon housing that contains antenna coils, a receiver/stimulator modulus, a magnet, and electrode arrays that connect to the vestibulocochlear nerve system. As is the case with other implanted devices, a cochlear implant is prone to bacterial colonization and subsequent infections. The infections can lead to ulcers, or even inflammation of brain tissue, thereby requiring surgical intervention such as implant relocation, fixation, and even explanation.
Bacterial biofilms play an important role in recalcitrant cochlear implant infections. The major causative agents of cochlear implant infections include Staphylococcus aureus, Pseudomonas aeruginosa and Streptococcus species. S. aureus is a common strain isolated from lesions of cochlear implant infection and usually leads to ulcer and swelling, while P. aeruginosa is more related to chronic infections. Recently, Streptococcus species, especially S. pneumonia, have attracted attention due to an associated high risk of meningitis among children with cochlear implant implants.
Direct current (DC) when applied for relatively long periods (from several hours to days) has been shown to have bactericidal effects in treatment including biofilms. DC has also been shown to have a synergy with antibiotics in bacterial killing. However, conventional approaches for applying DC all require a direct connection between the requisite electrodes and a power source. As a result, conventional approaches for treating cochlear implants with DC would require piercing the skin of the patient with the wiring needed to provide current for treatment. Accordingly, there is a need in the art for a non-invasive approach for applying DC to cochlear implant to treat bacterial infections.
The present invention provides infection control for medical implants using DC, by inducing DC wirelessly using a magnetic field. Implantable biomedical devices, such as pacemakers, deep brain stimulators, and cochlear implants, are provided an inductive coil located on the internal sides of the human body, respectively, for the delivery of electrical power by electromagnetic induction. Electromagnetic inductive coupling powers the implant devices wirelessly without any piercing of the skin. The delivered electrical power is used to power a circuit that applies an effective amount of DC to the medical implant to treat biofilm infections.
Wirelessly derived DC was found to have a strong effect in killing P. aeruginosa and S. aureus planktonic and biofilm cells, and the levels of effective DC are within the range that is known to be safe to human. The present invention demonstrates that biofilm cells can be effectively killed by using electromagnetic induction to deliver DC wirelessly from a power source. After treatment with 5-50 μA/cm2 of wirelessly delivered DC over 6 hours, the viability of biofilm cells was reduced by approximately 4 logs and 2 logs for P. aeruginosa and S. aureus, respectively. The coupling induction technology is applicable to implanted medical devices since it can deliver power and signals wirelessly without skin piecing wiring, and overcome the infection problems as well as lifetime limitation if a battery was used to power.
The present invention will be more fully understood and appreciated by reading the following Detailed Description in conjunction with the accompanying drawings, in which:
Referring to the figures, wherein like numerals refer to like parts throughout, there is seen in
Materials and Methods
Bacteria Strains and Growth Media
P. aeruginosa PAO1 was obtained from Department of Genome Sciences, University of Washington and S. aureus ALC2085 (strain RN6390 containing pALC2084) was obtained from the Sauer lab at Binghamton University. Both strains were cultured in Luria-Bertani (LB) medium (Niepa, et al. 2012b) containing 10 g/L tryptone, 5 g/L Yeast extract and 10 g/L NaCl. Both strains were routinely cultured overnight at 37° C. with shaking at 200 rpm.
Biofilm Formation
Biofilms were formed on polydimethylsiloxane (PDMS) blocks (1 cm×0.5 cm). Briefly, 25 μL overnight culture of planktonic cells was used to inoculate a petri dish containing 25 mL of LB medium and PDMS blocks. The culture was incubated at 37° C. for 24 h without shaking. Then the PDMS blocks with biofilms were removed from the petri dish and washed gently with 0.85% NaCl solution for DC treatment.
DC Treatment of Planktonic Cells
The P. aeruginosa PAO1 or S. aureus ALC2085 overnight cultures were washed with 0.85% NaCl solution, and then resuspended in 3 ml 0.85% NaCl solution to approximately 1×108 cells/ml. After being transferred to a petri dish, the cells were treated with DC for varying duration (2, 4 or 6 hours). The untreated samples were used as controls. After treatment, the number of viable cells was quantified by counting colony forming units (CFUs) in the solution.
DC Treatment of Biofilms
The DC treatment of biofilm was carried out in 3 mL 0.85% NaCl solution. A PDMS block with P. aeruginosa PAO1 or S. aureus ALC2085 biofilm was placed between two electrodes. The biofilm was treated with DC for 2, 4 or 6 h. The untreated samples were used as controls. After treatment, each PDMS block was transferred to a 10 mL tube containing 2 mL 0.85% NaCl solution. The biofilm cells were removed from the surface by gentle sonication for 1 min. The number of viable cells detached from PDMS blocks was quantified by counting CFU in the solution.
Tobramycin (Tob) also used to evaluate the synergy with low level DC. PDMS blocks with P. aeruginosa PAO1 biofilm were treated with 5 μA/cm2 DC and 4.5 μg/mL Tob for 2 or 6 h. The number of viable biofilm cells was quantified by counting CFU.
Power calculation
The electric power consumption of DC treatment can be calculated using the equation below:
Power=I2×ρ×d
where I is current level; ρ is average resistivity (e. g. soft tissue between electrodes); and d is the distance between two electrodes.
Results
Effects of DC on P. aeruginosa Planktonic Cells
As shown in
Effects of DC on P. aeruginosa and S. aureus Biofilms
The biofilm of P. aeruginosa was more tolerant to DC treatment than its planktonic cells. The maximum killing effect (approximately 3.9 logs) on P. aeruginosa biofilms was observed under the condition of 50 μA/cm2 DC for 6 h treatment, which was reduced to 2 logs when the DC treatment was shortened to 2 h (
Similar killing effects were also observed for S. aureus biofilms under the same treatment conditions. For example, the number of viable S. aureus biofilm cells was reduced by 1.6 and 2 logs after treatment with 50 μA/cm2 DC for 2 and 6 h, respectively. The 25 μA/cm2 DC showed similar killing activities on S. aureus biofilms (1.6 and 1.7 log for 2 and 6 h treatment, respectively); and 5 μA/cm2 DC only exhibited significant killing effect (1.5 log) with 6 h treatment (
Synergy Between DC and Antibiotics in Killing P. aeruginosa Biofilms
When P. aeruginosa biofilm was treated with DC and tobramycin (Tob) for 6 h, the maximum killing effect (2.5 logs) was observed under the condition of 5 μA DC/cm2 and 4.5 μg/mL tobramycin. In comparison, treatment with 5 μA/cm2 DC or 4.5 μg/mL Tob alone only showed 0.5 log and 0.9 log of killing, respectively (
Power Consumption of DC Treatment System
The power consumption for DC treatment in our system in vivo should be 0.15 (0.5 μA/cm2 DC) to 1.5 mW (50 μA/cm2 DC) by calculation.
Discussion
Different levels of direct currents (DC) and alternative currents (AC) have been demonstrated to kill biofilm cells in the presence or absence of antibiotics (Brinkman, et al. 2016; del Pozo, et al. 2009; Schmidt-Malan, et al. 2015; Voegele, et al. 2015). Our group recently found synergetic effects between low level DC and the antibiotic tobramycin in killing P. aeruginosa biofilm and persister cells (Niepa, et al. 2012a ; Niepa, et al. 2012b ; Niepa, et al. 2016). However, all those systems require physical connection between the treatment component and power source. Such setup requires skin piecing or battery if applied to implanted medical devices, which would bring problems such as limited device lifetime, pain associated with treatment, and risk of additional infection. In this study, we delivered the electric power wirelessly by induction coupling and achieved effective killing of bacteria including biofilm cells and synergy with antibiotics. Our results show that the viability of P. aeruginosa and S. aureus biofilm cells can be reduced by up to 4 logs with 6 h treatment of 5-50 μA/cm2 DC. The lower level DC (0.05-0.5 μA/cm2) also showed the killing effect on planktonic cells, but not biofilms. Synergetic effect was observed for concurrent treatment with 5 μA/cm2 DC and 4.5 μg/ml tobramycin for 6 h.
Typical power supply for cochlear implants is approximately 10 mW (Wei and Liu 2008), which is 7-70 folds higher than the power requirement of DC treatment in vivo based on our calculation. Hence, it is possible to take the original electronic units of cochlear implant and rewire the system to provide both hearing aid and infection control. Formation of biofilms can be monitored by measuring impedance and the therapeutic DC can be delivered by adding additional control modules. The maximum current density of DC that can be safely applied in human brain is 2 mA/cm2 (Murray, et al. 2015; Valic, et al. 2009; Neuroelectric's). The DC density used in this design (approximately 5-50 μA/cm2) is much lower than that and thus is expected to be safe. The published long-term DC current level of cochlear implant is approximately 0.3 μA (Clark 2006). In our system, we can reduce the viability of P. aeruginosa planktonic cells by 2 logs with only 0.05 μA/cm2 DC in 6 h, although the biofilm cells may require longer treatment time or higher DC level (still in the safe range). Based on our results, we speculated that biofilm killing can be obtained by nano-amp level DC with longer treatment, e.g. >24 h.
Referring to
As seen in
Internal unit 32 is provided with a pair of electrodes 50 mounted on an exterior surface thereof as described above. A controller 52 is interconnected to the power source 54 of internal unit 32 and electrodes 46 as well as and decoder 46 and stimulator 48. Controller 52 is programmed to perform a DC treatment function as desired, e.g., in respond to an external signal received by decoder 46, or according to a predetermined schedule. Otherwise, controller 52 is programmed to allow internal unit 32 to function as a conventional cochlear implant. Controller 52 may also be configured to sample changes in the redox properties of electrodes 50. Any attached biofilm will change the redox properties, which can be characterized by electrochemical approaches such as cyclic volumetric method. Thus, the present invention could also serve as a biofilm sensor that monitors implant system 30 for any biofilm formation on the surface of implant system 30 and then provides for DC treatment if controller 52 determines that treatment is necessary. Power source 54 may be the battery for the cochlear implant circuity, a dedicated power source, or an inductive coil that can be magnetically coupled to produce a voltage for use by controller 52 to produce the direct current via the pair of electrodes 50.
Like cochlear devices, other medical implants are also known to have biofilm infections. For example, many bone fracture patients suffered from bacterial infection after surgery. The present invention can be applied to those implants. Because they do not carry charging units as the cochlear implant, implantable receiver coils will need to be added to wirelessly deliver DC. With this modification, it is possible to not only control bacterial biofilm formation, but also achieve electric stimulation of osteoblast without skin piecing.
The present invention demonstrates that the two typical pathogenic bacteria associated with cochlear implants, P. aeruginosa and S. aureus, can be efficiently killed by low-level DC delivered with wireless coupling induction. The killing effect of low-level current was time dependent. This approach could avoid skin piercing, and can be applied to cochlear and other implants to monitor and eradicate biofilms on demand.
As described above, the present invention may be a system, a method, and/or a computer program associated therewith and is described herein with reference to flowcharts and block diagrams of methods and systems. The flowchart and block diagrams illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer programs of the present invention. It should be understood that each block of the flowcharts and block diagrams can be implemented by computer readable program instructions in software, firmware, or dedicated analog or digital circuits. These computer readable program instructions may be implemented on the processor of a general purpose computer, a special purpose computer, or other programmable data processing apparatus to produce a machine that implements a part or all of any of the blocks in the flowcharts and block diagrams. Each block in the flowchart or block diagrams may represent a module, segment, or portion of instructions, which comprises one or more executable instructions for implementing the specified logical functions. It should also be noted that each block of the block diagrams and flowchart illustrations, or combinations of blocks in the block diagrams and flowcharts, can be implemented by special purpose hardware-based systems that perform the specified functions or acts or carry out combinations of special purpose hardware and computer instructions.
The present application claims priority to U.S. Provisional Application No. 62/543570, filed on Aug. 10, 2017.
| Number | Date | Country | |
|---|---|---|---|
| 62543570 | Aug 2017 | US |
