Audible frequency vibration of puncture-access medical devices
Section snippets
Introduction and background
Numerous procedures in nearly every field of medicine require the insertion of an access device into a tissue medium along an axial path. Hypodermic needles, laparoscopic trocars, and other similar devices require an axial force to be applied by the user in order to penetrate various tissue layers. This force is determined not only by the geometry of the device itself but also by the mechanical properties of the tissue medium that it penetrates. Due to the complexity and variability of the
Concept
The concept proposed in this study is to drive a needle-like device to oscillate linearly along its longitudinal axis at audible frequencies. This concept is intended to lower the force required to insert a needle-like device by lowering both the frictional and tip forces. The device should oscillate at a frequency below a maximum value such that the insertion force is significantly lowered but there is not sufficient frictional heating for local residual tissue damage to occur. The concept is
Existing devices
The idea of applying vibration to medical instruments is highly prevalent in both patent literature and current medical practice. Ultrasonic cutting devices are common in many surgical specialties including laparoscopy and cosmetic surgery. Although ultrasonic instruments employ vibration to decrease cutting or insertion force, their function relies on frictional heating and cavitation to denature proteins and vaporize intracellular fluid [6]. Depending on the amplitude and frequency at which
Proof of concept: experimental methods
To test the analytical model and concept proposed above, three needle configurations were constructed. The “NN” configuration was a standard 3.81 cm long 16 gauge lancet-tip hypodermic needle (BD 305198). The “VN” configuration was a standard 3.81 cm long 16 gauge lancet-tip hypodermic needle that was driven to oscillate linearly along its long axis at 150 Hz. The needle was fixed to the dust cap of a Jameco 135812 5W voice coil speaker driven by a function generator and power amplifier. The
Proof of concept: results and discussion
Table 1 shows the parameter values used to construct the theoretical insertion force as a function of insertion depth for a standard 16 gauge needle inserted into ballistics gel, corresponding to the NN configuration, given by (6). All possible values of cutting coefficient B are considered.
Fig. 1 shows the axial insertion force as a function of insertion depth for all 15 test repetitions, as well as the theoretical axial insertion force as a function of insertion depth for the parameter values
Device parameters: experimental methods
Once the VN configuration was shown to require the least insertion force, an experiment to determine the effect on insertion force of varying needle diameter, vibration frequency, and peak to peak input voltage amplitude was conducted. A similar test setup to the proof of concept experiment was employed. The VN configuration was made to vibrate at a given parameter configuration. Axial force was recorded as the needle was driven into a block of ballistics gel at a rate of 0.0508 cm per second.
Device parameters: results and discussion
Table 2 shows the parameter values, as well as the measured free-vibration needle-tip peak-to-peak stroke length, for each parameter configuration. Note that as per our earlier assumption, increasing the input signal amplitude with other parameters held constant always resulted in a higher measured needle stroke amplitude. In addition, with other parameters held constant, a frequency of 150 Hz consistently produced the greatest needle-stroke amplitude. This is likely due to the needle apparatus
Frequency range effect on insertion force
In order to validate and differentiate the use of audible frequency vibration from widely available ultrasonic devices, comparative studies of insertion force and local tissue damage were conducted. To evaluate insertion force effects, the required force for a 16 gauge hypodermic needle to puncture deceased porcine skin was measured for non-vibrating, audible frequency vibration, and ultrasonic frequency vibration needle configurations. To achieve ultrasonic frequency oscillation, a needle was
Immediate local tissue effects
It is important in designing medical devices that a new method or instrument does not significantly increase risk to the patient. The immediate effect of linear oscillation of the cutting tip on local tissue damage was observed in an in vivo histology study.1 For comparison and frequency range validation, a device oscillating at ultrasonic frequency was also included. Flat surgical blades were fixed to the
Conclusions and recommendations
Applying axial vibration to a hypodermic needle, specifically within the 50–500 Hz frequency range, lowers both the frictional and tip forces experienced by the needle, and subsequently results in a lower force required to advance the needle into tissue; in addition significantly less immediate tissue damage occurs than if ultrasonic vibration were used. By reducing the force necessary to advance the needle, the probability that the needle will advance too far and cause damage or other
Funding
None.
Conflict of interest
None declared.
Ethical approval
Not required.
Acknowledgments
The authors of this paper would like to thank the MIT Precision Engineering Research Group staff; S. Gallagan and Branson Ultrasonics; Dr. E. Edelman, Dr. R. Marini, M. St-Pierre, Y. Miller, and the MIT Division of Comparative Medicine; The MIT Koch Institute Histology Core Center; Dr. R.T. Bronson; Dr. C. Hogan, Professor I. Hunter, and the MIT Bioinstrumentation Lab; and Dr. J. Bales and the MIT Edgerton Center; for their guidance and generosity in helping with the completion of this study.
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