6 steps bring a new surgical retractor to life

The team at LINK partnered with Advanced Surgical Retractor Systems Inc. (ASR Systems), a medical device manufacturer led by a military trauma surgeon and a veteran medical device entrepreneur, to design a novel surgical retractor to be used in invasive abdominal surgeries, called laparotomies. The team at ASR Systems had identified a need to improve upon outdated abdominal retractor technology for a variety of surgical disciplines and deliver a tool that that would be specifically designed to meet the needs of trauma and military field surgeons.

Existing abdominal retractor technology had not changed in decades with most surgeons using the industry standard Balfour and Bookwalter retractors. Neither retractor had been redesigned for many years and had several drawbacks. In early discussions with the end users – the surgeons themselves – they liked the Balfour’s ease of use, but the most common complaint was an insufficient field-of-view, and that it could not be used to retract organs and tissues beyond the incision itself. The Bookwalter, though robust and versatile, was criticized for taking excessive time to set-up and reposition, and particularly for field surgeons, that it is heavy, complicated, and ultimately unusable in the field due to limited OR equipment.

Our team moved through the following six steps to design, develop and manufacture the TITAN CSR, collaborating with our clients at ASR Systems and partners every step of the way. Below, we detail our process for delivering this new medical device to market and include key takeaways or best practices after years of working with entrepreneurs, doctors, and their teams on new product development.

1. SWOT, research, and specifications
From our initial background research and market analysis, we verified a need for a retractor as simple and fast as a Balfour with the range of functionality of the Bookwalter. With these specific needs, in addition to other surgical equipment considerations, we arrived at a list of requirements for the product.

• Lightweight
• Intuitive to use
• Deployable in less than 90 seconds (including assembly)
• Sterilizable
• Compatible with existing modular retractors, like the Bookwalter
• Sized to fit standard laparotomy incisions
• Provide field of view comparable to Bookwalter
• Not jam or bind during use
• Robust enough to withstand forces exerted by surgeons during high-stress procedures
• Durable enough to be functional for a minimum of 10 years
• Cannot be assemble-able incorrectly

Key takeaway: In the initial stages of the product development process, conducting background research and doing a market analysis are critical steps in identifying a market and viability of a new concept. We often work with clients in the early stages of a project to research competitors or similar products and have discussions with end users. A Strengths, Weaknesses, Opportunities and Threats (SWOT) analysis should be performed humbly and without preconceptions, which is why we prefer to lead our clients through this exercise. In medical device manufacturing, for example, surgeons, nurses, operating room technicians, and hospital purchasing teams can all lend an enormous amount of feedback into the use and needs for the products, as do the manufacturers, assemblers on the factory floor, and service technicians charged with the ongoing maintenance of the product. This research and analysis help inform the design process, establish requirements for the product and ultimately develop a list of collaborative specifications so the design team and other stakeholders can begin to visualize concepts and identify how the product will solve a want and need in the marketplace.

2. Brainstorming to lead industrial design
Our clients had a rudimentary prototype of an initial vision but found that it has serious functional issues. The priorities were to reduce weight, increase strength, increase reliability (eliminate racking and binding that occur during expansion and collapse), and to improve ease of use and assembly. With these requests, and our preliminary requirements set, we began to brainstorm. How could we reduce weight? Perhaps make it out an exotic material. How could we reduce the occurrence and severity of binding? Maybe self-lubricating plastics could be used. Why have the retractor expand linearly? Why not make it a scissor or spiral configuration? As concepts from initial brainstorming were eliminated due to cost, complexity, or feasibility, we began to converge on a system architecture using material to reduce weight and increase strength, a unidirectional ratchet mechanism to expand and lock retractor, reduction of degrees of freedom to prevent racking and binding, and indicators and poka-yokes to eliminate mis assembly or misuse.

Key takeaway: Although many of our clients have partisan notions of how their products will look and function, we do not. This allows us to “think outside the box” and take our research and data from the analysis and information gathering phase and apply it to initial concepts. Our initial brainstorming process is often facilitated on on-line, virtual whiteboards to allow our team and clients to collaborate and begin with a blank slate, and concepts are ranked and distilled using tools such as a Pugh matrix. Using these tools allows us to easily receive real-time feedback on sketches from miles away. It is here, with our creative juices flowing, we begin to sketch our ideas, ask additional questions, and find reference products to tear down. This process of brainstorming and concept iteration allows us to converge on a high-level system architecture and to identify high-risk elements to address during prototyping.

3. Sketch models and initial prototyping
From sketches, we moved into computer aided design (CAD), creating 3D virtual representations of our rough concepts to better visualize fit, function, and complexity, to run stress analyses to assess strength, and to create manufacturable files for rapid prototyping. Because we found binding during expansion and collapse to be the most difficult mechanical problem to solve, we focused here first. Hundreds of CAD models and dozens of 3D-printed prototypes allowed us to evaluate ergonomics, assembly, and mechanism function. Without needing to build an entire retractor, we were able to evaluate the function of each mechanism, as well as ceremony of use and ergonomics. We asked questions such as ‘Can one surgeon operate the device?’ ‘Can both right and left-handed surgeons actuate these two buttons simultaneously?’ ‘Does the design encourage the user to interact with the product correctly?’ With each iteration, physical prototypes were shipped to our clients to ensure that preferences and expertise were informing every design change.

Key takeaway: Many design firms create sketches and prototypes, but few create “sketch models” which are fast and often crude mock-ups in three-dimensional form. These sketch models are actual, physical representations of brainstormed ideas, created to rapidly mitigate risk and answer questions that the concepts might have spawned. Our main intent in this phase is to iterate quickly to prove viability of concept ideas before proceeding to (often expensive and time-consuming) like-material prototyping. In many cases, we create scores of rudimentary CAD models and dozens of clay, cardboard, laser cut wood, LEGO, hand-moldable plastic, or 3D printed prototypes allowing us to evaluate ergonomics, assembly and mechanism function.

© LINK Product Development/
Advanced Surgical Retractor Systems
https://www.linkpd.com; https://www.asrsystemsinc.com

4. Engineering CAD and final prototyping
After learning and de-risking as much as we could from plastic parts, we refined our CAD models for the retractor and completed detail engineering, integrating design for manufacturing (DfM) and design for assembly (DfA) best practices in preparation for final machined metal prototypes. We first evaluated stainless steel prototypes – though we did not expect this to be the production material – as it allowed for quicker and less expensive prototype iterations as we evaluated the design. With validation from steel prototypes, we progressed to final titanium prototypes; this was selected as our desired production material due to its lack of magnetism and chemical reactivity, its low density, and its high strength. Press-fit dowel pins fastened these prototypes in place of production welds, which allowed us to re-use prototype parts, swapping out springs and variations of machined parts quickly and easily.

Key takeaway: Before we begin detailed design, we identify specific manufacturers that are a best fit for the product’s cost and volume and establish a relationship with those manufacturers to understand their strengths and weaknesses. The same goes for creating prototypes. We are fortunate to have built our own prototyping facility in-house, but there is always a time when outside help is needed. We share prototypes with clients at each iteration to gather feedback to inform a test plan for final production units. Most often, our competitors or lesser experienced clients create too few prototypes. We find any prototype invaluable no matter how refined or developed.

5. Real-world testing and refinement
One of the fundamental difficulties in prototype validation was how to simulate human tissues, to ensure that our prototype tests were representative of the forces seen during surgery, and that the retractor performed well under these conditions. This testing process was iterative as well. We began by evaluating the retractors using elastic bands as resistance, and eventually worked our way to realistic evaluations in a series of cadaver labs. One of our clients brought in his surgeon colleagues, both civilian and military, as well as expert OR technicians from whom we solicited feedback about performance, sizing, ease of use, ease of assembly, and ease of cleaning. Each lab allowed us to evaluate the prototype’s performance in a realistic use case, and our findings drove changes made to the subsequent prototype iteration. We received the following feedback from users testing the device in a real-world medical setting.

“The TITAN CSR provided increased flexibility and allowed me to manipulate retraction instantaneously, without needing to readjust clamps which can take time in urgent and emergent cases. Very impressed!"? - Trauma Surgeon, Level 1 Trauma Center

“The TITAN was very efficient and easy to use. There was little to no set-up time with separate retractors or table mount allowing for a quicker evaluation for intraabdominal injuries compared to historical retractors. I would highly recommend this piece of equipment to be in every trauma OR.      - Trauma/General Surgeon, Level 1 Trauma Center

Key takeaway: Lab simulations, test trials and direct feedback from end users using final prototypes allows us to feel confident in the size, strength, and function of the devices we design. These physical tests, along with real time input from users in a clinical setting, are invaluable to help guide final designs prior to production and manufacturing.

6. Overseeing manufacturing
During the final iterations of prototype fabrication, we began the process of production manufacturer selection. Due to International Traffic in Arms Regulations (ITAR) constraints, and the preference of our client, our manufacturer selection was limited to domestic factories. The production manufacturer needed to be ISO 13485 certified, and an expert in machining and welding titanium. These requirements created a short list of qualified manufacturers. After in-depth design reviews (both virtual and in-person), site visits, and quote reviews, we selected a local Colorado high-end machine shop to be our production manufacturing partner. With decades of experience making high-precision components for medical and aerospace clients, they had the capabilities, capacity, and expertise to deliver a precise, robust, and beautiful product for our client.

Bring-up to production began with in-depth reviews of the current state of CAD, dimensioned drawings, and physical prototypes. We worked with our vendor to specify precise manufacturing processes (TIG vs laser welding, surface finishing, labeling and serialization) and assembly procedure. These design reviews resulted in minor design changes to optimize our design to fit their machining capabilities. After a formal engineering change order to release all files to production, the manufacturer began to fabricate production retractors. Our team provided on-site manufacturing support frequently throughout the process, working closely with their programmers, machinists, and quality engineers to ensure that our design spec was clear and complete.

The first article off the production line was subjected to 100% dimensional inspection and was taken through a thorough first article testing evaluation, as specified in the product requirement established at the project’s inception. When it was found to pass all inspection criteria and physical tests, the design was released for mass production. The next six units off the production line were submitted for full cleaning, disinfection and sterilization validation, a process which took three months to complete.

During the subsequent production runs, small design changes were made to improve the retractor’s functionality, as well as to optimize the manufacturer’s machining and assembly process. After two production revisions, the first units were taken for clinical trials at partner hospitals in San Antonio, Texas.

Key takeaway: During the final iterations of prototype fabrication, we complete the process of production manufacturer selection. We work with our selected manufacturer on in-depth reviews of dimensioned drawings and physical prototypes, and to specify precise manufacturing processes and assembly procedure. These design reviews often result in minor design changes to optimize our design to fit the manufacturers machining capabilities before the product is delivered to market, but the story doesn’t end here. Transitioning to manufacturing cannot be a “throw it over the wall” relationship, and even after tooling is made and first articles received, the collaborative work is still not complete. Only when high-volume quantities are being produced consistently can your guard be dropped. A good product development partner will be your eyes and ears during the first year of production, at least.

Conclusion
While no one product development process is the same, our process for designing medical devices is detailed yet efficient, collaborative, and creative, while mitigating as many risks as possible. One major contributor to the success of these steps is partnering with an experienced team of designers, problem solvers, and manufacturers. This advice, and following the steps outlined above with our key takeaways, will greatly increase a successful development venture, improve industry standards, and contribute to the greater good of the medical profession.

Marc Hanchak is the founder of Denver-based LINK Product Development and Alice Mayfield is a mechanical engineer and team member at LINK. ASR Systems is a medical device manufacturer based in San Antonio, Texas.