This is the second blog from our Engineering Summer Interns on their project for Gasless Laparoscopic Surgery.
After the initial designs for the force measurement device, several prototypes were made for the two aspects of the project. We went through several iterations to improve strength and fit of the different parts that interface with each other.
PROTOTYPING
The next step in this project was to manufacture the initial prototype as a proof of concept. Our device was made using materials that were readily available to us and made use of 3D printing.
Components of the prototypes:
Two concentric pipes were cut to length, and together they house the spring. We found that the 3d printed designs shrunk slightly when printed so the dimensions had to be readjusted by hand. The spring was an off-the-shelf component that could hold a force equivalent to the retraction force applied during gasless laparoscopy. An electronic force measurement device was also incorporated into the prototype for testing during the clinical trial.
The spring was then calibrated to a simple scale to show if the force being applied to the abdominal wall was excessive. Using a colour coded scale, with green signifying a force in the appropriate range and red to show that the force is too high, we could lower the risks of damaging the equipment and causing abdominal wall trauma.
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Figure 1: Final prototype
Testing of prototype
The ability for our 3D printed attachment to withstand the load was a point of concern for us. Even though hand calculations said it was strong enough, we wanted to carry out load testing to ensure that this would be the case.
Fortunately, the part in question did not fail, but the point of attachment to the test bench did. This raised the question of whether the cadaver table would be able to hold the whole gasless laparoscopic kit during the cadaveric trial. A preliminary visit to the dissection room before the trials is planned to ensure that the test can go ahead as planned.
The bend of the arm can be observed in the photograph. However the aluminium beam that attached the device to the table failed under the moment at 14 kg of load.
Figure 2: Testing the prototype with weights
The abdominal wall box trainer
The initial prototype for the box trainer was fabricated from two pieces of perspex and two sheets of silicone rubber that come fully formed. Below the pictures demonstrate the initial prototype being used with the hook of the device.
We continued this by using the newton meter to demonstrate the cavity created when the expected surgical load of 140 N is applied. There were few problems with this model, the sheets of silicone are larger than the perspex sheets and as there is no air gap between the table and the sheets, a vacuum is formed under the sheets when lifted. This is not an accurate representation of what happens when the abdominal wall is lifted.
Figure 3: Testing the simulated abdominal wall
To improve the prototype, a custom mould of silicone rubber has been cast and is in the process of curing. The mould can be seen in the pictures below.
Figure 4: Silicone mould
Next Steps
We are working towards a cadaveric study in the next few weeks where we will be able to assess the effect that our load device has on the force applied, by surgeons, to the abdominal wall. During this trial we hope to acquire not only load data but also 3D scans of the cavity created in order to quantify the difference in volume created by gasless and conventional laparoscopic surgery.