Biocompatible Cable Development & Evaluation

Introduction

• The Vicarious Surgical Camera System is a cable driven system that is able to achieve full, 360 degree visualization within a patient's abdominal cavity.

• In order to provide this level of control to our surgeons, the camera system is comprised of a number of cable ‘pulleys’ that are, when rotated, able to drive the camera through three degrees of freedom

  • Namely; roll, pitch and yaw

• Certain use cases of the camera see the surgeon directly surveying the patient’s abdomen to identify the target anatomy. Conversely, others see the camera automatically following a location central to the tips of the instruments. This allows the surgeon to find their target and then focus on the task at hand as they can forget about the need to position the camera. 

• In order to maintain imaging of the always-moving instrument tips, the camera needs to be able to very accurately track inputs from the surgeon. 

• The cable design used in the Vicarious Surgical robotic system has significant implications towards aspects such as shelf life, sterilizability, procedure duration and even the strength of the instruments.

Design and Development

• The primary motive for kicking off this project was the need to implement purpose-built cables that are made of a biocompatible (‘medical grade’) material and are manufactured in a certified clean environment.

• The implications of this project were fairly significant. Prototypes up to this point had been built using tough, OTS cable that was readily available in a number of sizes during the R&D phase of the camera. This provided flexibility in the design process that allowed us to test a number of different materials, sizes and braid types against a number of criteria.

• After evaluating a number of vendors based on cost, lead times, prototype capabilities, etc., we selected the best option and began development.

• Working with both the needs of the camera and instrument cable proved beneficial. Learnings from one project could be directly ported over to the other. 

Testing & Evaluation

• The most important aspect of this project was ensuring cables designs were being properly evaluated. Each design was made using a variety of different materials, thread patterns, deniers, and post processing methods to name a few of the factors. 

• The most important quantitative metrics of the cables are ultimate tensile strength (UTS), stiffness, lubricity, diameter & roundness and possibly the most important is abrasion resistance. There also exist qualitative metrics such as resistance to fraying when cut or even available color options to aid in assembly. 

• I created a number of fixtures intended to evaluate these metrics which employed Instrons, Mark-10s, machined components and prototype camera parts. 

• Data was recorded for numerous cable samples over the course of numerous different tests. Furthermore, cable designs were presented to assembly teams for a qualitative evaluation of how easy or difficult they may be to work with. 

• Eventually, a braid construction was settled on and we were able to progress with refining the post processing method to achieve an optimal cable. 

Conclusion

• Cable development was an enjoyable project given the objective nature of the task. There is little room for opinion when designs are being evaluated on what is effectively a strictly quantitative basis. 

• I learned about the importance of consistency between tests and how small differences in startup conditions can have a significant impact on the results of certain trials. In tasks such as these, diligence and attention to detail are crucial to achieve results that are reliable.

• The current cable design is both cost-effective and provides a high level of performance in all aspects. This is extremely important to the success of the Vicarious Surgical system.