Final Design
Design
Commercially available microsurgical clamps (Acland clamps) consists of 3 stainless steel parts that are spot welded together. Each part is designed with high precision in order to fulfill the needs of microsurgical practices. Unfortunately, high quality and high precision comes at a high cost. We learned this lesson in trying to recreate the Acland clamps.
Our first step was to design a CAD model that looked and performed similarly to the Acland clamps. After several iterations and many adjustments, we came up with the following design:
Key components:
Jaws: closes along a line to create watertight seal
Handles: lever arm for actuation
Spring: provides clamping force and stiffness
Fold Tabs: tabs to ensure folds are flush and do not unfold
Rizzuti Forceps Tabs: compatibility with Rizzuti Forceps
Other features:
Filleted/Smooth edges to prevent punctures and cuts
1 body design for ease of manufacturability/assembly
Can be manually assembled
Angled Jaws
At the neutral position, the clamp jaws are slightly angled to adjust for the blood vessel thickness of approximately 0.01". As a result, when the jaws are clamped onto a blood vessel they close along a line and the jaws are parallel as seen in the closed position. This design decision ensures the jaws close along a line and create a watertight seal.
Neutral Position
(Not clamped)
Closed Position
(Clamped onto vessel)
Small and Medium Size
2 Sizes
We designed 2 sizes, one medium and one small. The small size is intended for smaller vein-like blood vessels whereas the medium size is intended for larger blood vessels, such as arteries.
Material Selection
Once we had a 3D render of our prototype, we needed an inexpensive material that was strong yet springy. We researched and tested all kinds of materials from plastics to springy metal to heat treated metal.
3D Printed Resin
3D Printed Carbon Fiber
18-8 Stainless Steel
Heat Treated 1075 Steel
Each material had its strengths and weaknesses, but the 18-8 Stainless had the ideal material properties. The 18-8 Stainless Steel had a high yield strength, high modulus of elasticity, metallic feel, and low cost.
Fablight Metal Laser Cutter
Manufacturing Method
With a design and material in mind, we needed a method to manufacture these clamps at a large scale. We explored EDM Machining, CNC Machining, 3D Printing, Injection Molding, Laser Cutting, and even Precision Folding. The simplest and most inexpensive option was a combination of Laser Cutting and Precision Folding. This method seemed to be the most straightforward, affordable way to put training clamps in the hands of microsurgical students in underserved regions.
First the design is laser cut from a 0.007" thick 18-8 stainless steel sheet metal. The 2D cut-outs are then folded into the 3D clamp shape. This process is relatively inexpensive and straightforward compared to other manufacturing methods.
Folding Procedure
Below are the folding procedure steps and a demonstration of the steps.
Bending Aids
While manual assembly ensures these clamps are more affordable and accessible, it introduces performance variability in each individual clamp. Consequently, we utilized bending aids to reduce the variability and standardize the performance of each clamp.
Needle Nose Pliers
Required for steps 1, 3, 4, and 5.
Crimper Tool with Custom Die
Required for step 2.
The Custom Die
The custom die on the crimper tool ensures consistent and precise folding for step 2, which is the spring fold. This is the most critical fold of the process as the fold angle dictates the springiness of the spring.
Negative Die
Positive Die
Die with Cut-out
Performance Overview
We evaluated our small and medium sized clamps with two tests. The first test utilized a Uneo GD05 Force Sensitive Resistor (FSR) to measure the clamping force of our clamps relative to the Acland clamp and competitor clamps. The FSR outputs a voltage reading that is dependent upon how much pressure is applied to the FSR. We extract the pressure ratings in grams-force from the voltage readings by characterizing the data with small weights.
Uneo GD05 Force Sensitive Resistor
Arduino FSR Circuit Setup
Medium Foldable Clamp on FSR
Small Weights on FSR
FSR Characterization
Characterization Function
Average Error: 2.97 g-f
This two term exponential function enables us to obtain force values from the voltage readings of the FSR.
FSR Test Results
Below are the FSR test results of the small and medium sized foldable clamps. The green lines denote our clamps, while the red lines depict the Acland model. The other lines represent competitor clamps and the current training clamps (Sponsor Set).
Small Clamp Specs:
Size: 3 x 4.5 x 11.5 mm
Force: 75.8 ± 25.4 g-f
Pressure: 200 mm-Hg
Medium Clamp Specs:
Size: 3.25 x 6.9 x 15.7 mm
Force: 35.0 ± 9.9 g-f
Pressure: 146 mm-Hg
The test results show that we have reached our goals for the medium sized foldable clamp. It exerts a similar pressure and metallic feel to the Acland Clamps at a much lower cost. The small sized foldable clamp exerts a significantly higher pressure than the Acland Clamps. Unfortunately, time constraints have limited our ability to redesign the small sized clamp.
Blood Flow Simulation
Another test we conducted to evaluate the performance of our clamps was a blood flow simulation test that employs Bernoulli's Principle. The setup utilizes a bucket of water held at a specific height. The height of the bucket dictates the water pressure exerted through the micro-vessel. We then apply the clamps at the micro-vessel to see if water leaks through the clamp. Our target height was 5' 6", which exerts the same pressure of standard blood pressure: 120 mm-Hg.
Blood Flow Simulation Diagram
Blood Flow Simulation Setup
Blood Flow Simulation Results
The results tell the same story as in the FSR testing. Our medium foldable clamps are able to stop pressure up to 120 mm-Hg, which current training clamps are not able to accomplish. The results of our small foldable clamps reiterate the need for design changes as it was not able to stop the flow of water when the bucket was at a height of 4 ft or greater. Due to time constraints, we were not able to redesign our small sized clamp to address these issues.
Cost
We've achieved a 99% cost reduction! Below is a table detailing the price comparison and assembly time of our clamps.
Conclusion
In conclusion, our design, manufacturing method, and performance tests have showcased the remarkable improvements offered by our clamps over existing design solutions. Not only are our clamps easier to manufacture and more cost-effective, but they also exhibit a similar performance to current training clamps. We fervently aspire that our innovation will contribute to enhancing healthcare training!
Clamp Comparison Chart
Feel free to contact us with any questions or concerns!