Reverse Engineering A Guidewire Assembly

At Modern Grinding we often get inquiries to help medical device designers reverse engineer a guidewire assembly so that we can manufacture something similar for their device or for their distribution business. It seems like a simple enough request. Modern Grinding is in the guidewire assembly business, how difficult can it be to slap a coil, safety ribbon and core wire together? It actually isn’t too difficult (for us), but we need to know the exact design. Here are some of the hiccups that occur when reverse engineering a guidewire assembly.

Guidewire Assembly Formed Core Wires
Guidewire Assembly Formed Core Wires

Guidewire Use Case

The most important part of a guidewire is how it is used. At Modern Grinding, we are contract manufacturers, we aren’t doctors. When someone comes to us and asks us to “copy” a guidewire, we don’t always know that exact guidewires use case. If we were to get something wrong, that can affect how the guidewire performs in surgery. Often foreign distributors will try to gloss over that fact, and say just give us something close (to another product in the market). At Modern Grinding, we take a deep concern for how our guidewires perform and we won’t accept “close”.

Guidewire Concerns

There are many small pieces of the puzzle which affect how a guidewire performs. How is the core wire connected to the coil? Is it welded or glued or fused? What tensile strength is the core wire? This can affect it’s flexibility and propensity to return to its original shape. Was the core wire heat treated? This again can affect the shape of the core wire and how it returns to its original form. What dimensions does the core wire have and what dimensions do the coils have? How much of the coil is coated? What is the tip coated with? How is the handle connected? Are all forms of PTFE the same? Are all hydrophilic  and hydrophobic coatings the same? While these all seem like little details, when you combine them all, you can lead to vastly different guidewires that appear the same.

New Guidewire Designs from Doctors

When doctors reach out for help, I feel bad if we can’t help. Often doctors come to us with a problem that they recognize with a pre-existing device. They are in the perfect position to come up with a new guidewire design that could better serve patients and help other doctors as well. The problem is that doctors don’t realize how difficult it can be to reverse engineer a product and then make a fairly similar guidewire assembly. We can do it, but we need to be able to nail down all of the key characteristics (see concerns section above) before we can start to make alterations on the wire. It takes a lot of engineering time to reverse engineer a complex product which is used in surgical applications.

This post wasn’t meant to scare anyone, just to let you know what goes into reverse engineering a guidewire assembly. We can do it, but it typically takes a couple days in engineering time, we aren’t able to just “copy” an existing wire without going through a very refined process.

Medical Device Assembly Process

As Modern Grinding grows and starts to develop manufacturing processes for a variety of products, we are getting into more and more multi-step medical device assembly processes. Our capabilities now include wire forming, wire grinding, coiling, microcoiling, welding, electropolishing and metal stamping.

Multi-Filar machine part of medical device assembly
Multi-Filar machine part of medical device assembly

One major product that we manufacture and assemble is guidewires. Many guidewires include a ground core wire (also referred to as mandrel), a coil (or microcoil) and a safety ribbon. These multiple parts typically are formed and welded together. While it would seem like this is a simple medical device assembly process, during the prototype phase it can be very time consuming to nail down the correct process. For one, your machines open up at different times. If you are trying figure out the correct process to form your ground core wires, you might need to try several different core wire designs. Once you have manufactured your core wires, you might realize that you need a different design once you get to the forming stage. This is fine if your grinding machine is always, open but ours rarely is, so you need to wait until machines open up to start over.

We recently started to pick and choose components of the six sigma process program to create a more robust project management process for medical device assembly. In the past, we did this type of project management in our heads, but as our production capabilities became more complex we realized the need for this type of system. Along with the principles of six sigma, we relied on the lean software principles of starting with a minimal design for project management and working with the main customers to create a product that everyone could use.

The main goals for me were to make sure that when we get a medical device assembly job, we get buy in from all of the departments we will be working with and we get confirmation from each department that they can accomplish the job within a given time frame. In the past, managers would take responsibility for department that they didn’t run and when a project started to get hard, the buck would get passed.

Here are a few tips from our medical device assembly project management experience:

  • Have a manager responsible for each step in the process
  • Think about alternative process routes while developing your process
  • Put your process on paper, from step 1 to shipment

Does anyone use simple project management tools for medical device assembly? We would love to hear about your trials and successes.

 

Coronary Guidewires

Many of the guidewires we manufacture at Modern Grinding are Coronary Guidewires. We are a contract manufacturer, we don’t have any of our own products. For our own knowledge base and hopefully for medical device designers, this will help provide a better understanding of coronary guidewires and the different designs. Below are the common guidewires and design considerations:

Some examples of standard guidewires include the BMW (Abbott Vascular), Cougar (Medtronic), IQ (Boston Scientific) and Stabilizer (Cordis).

Depending on the type of surgery you would like to perform, the following guidewire traits must be considered:

Guidewire Torque

Is an ability to apply rotational force at a proximal end of a guidewire and have that force transmitted efficiently to achieve proper control at the distal end

Guidewire Tracking

Is an ability of a wire to follow the wire tip around curves and bends without bucking or kinking, to navigate anatomy of vasculature

Guidewire Steerability

Is an ability of a guidewire tip to be delivered to the desired position in a vessel

Guidewire Flexibility

Is an ability to bend with direct pressure

Guidewire Prolapse Tendency

Tendency of the body of a wire not to follow the tip around bends

Guidewire Radiopacity

Is an ability to visualise a guidewire or guidewire tip under fluoroscopy.

Guidewire Tactile feedback

Is tactile sensation on a proximal end of a guidewire that physician has that tells him what the distal end of the guidewire is doing

Guidewire Crossing

Is an ability of a guidewire to cross lesion with little or no resistance

Guidewire Support

Is an ability of a guidewire to support a passage of another device or system over it

Taper Wire

For this edition of The Wire we thought it was fitting to demystify taper wire both from a manufacturing standpoint and a medical standpoint.

Taper Manufacturing

To my knowledge, the best way to taper wire is still though the OD (outside diameter) grinding process. There may by 3d printers which can build tapers through an additive process but for small precision medical wires, the best way to taper is by grinding off material around the radius of the wire. From a cost standpoint, having a guidewire with a taper is going to be more expensive than just having a straight wire since there is an added manufacturing component to the product. Calling out specific dimensions on your taper drawing can be difficult for your manufacturer to achieve. Most often the tapers that we achieve have generalized specifications such as when the taper begins and when it ends. If you are trying to achieve specific taper angles, make sure to talk through these angles with your manufacturer in advance to make sure that there are not extra costs and time constraints to doing so.

Tapers in Medical Devices

The use of mandrel tapers, guidewire tapers and stylet tapers has grown more prevalent as precision manufacturing process has evolved. From a medical maneuverability stand point, doctors may have an easier time using taper wire. Tapering wire enables the wire to have different characteristics such as flexibility and firmness. As an example, we have manufactured wire from from .024″ down to .001″ in diameter. Taper wire can be more atraumatic than the alternative since if you are putting inside of a vessel a smaller tip may be easier to fit in than the full radius of the wire.

If you have questions about tapering your next guidewire, stylet or mandrel don’t hesitate to reach out, we can help. We have manufactured flexible guidewires, superstiff guidewires, stiff guidewires, taper wire, taper coil and any other type of wire you can imagine.

Safety Ribbon or Safety Wire in Guidewires

The following is to help medical device designers better understand safety ribbons in guidewire design.

In the unlikely event stretching or fracturing occurs in the guidewire, a safety ribbon is welded to both ends of the wire to help the wire remain intact. A safety ribbon runs thru the length of the Guide wire and is welded at each end to contain the coil of the spring.

There is a good explanation of a patented safety ribbon here – http://www.google.com/patents/US5299580

A safety ribbon or core wire is commonly included on the distal end of a medical guidewire or a fixed wire catheter insertable intravascularly into a patient. Such a medical guidewire or catheter has a relatively flexible distal end usually comprising a coiled member for facilitating navigation within the patient’s vascular system. A distal end tip, which can be formed by a suitable welding process, for example, is often formed or disposed on the distal end of the coiled member.

Modern Grinding has the capability to manufacture safety ribbon as well as grind core wires, form coils and perform wire welding on the finished product.

Exchange Guidewires

At Modern Grinding, we often here about exchange guidewires, exchange wires, guidewire exchange catheters and rapid exchange guidewires and we wanted to do some explaining about what it is and why it is used.

A guidewire is typically used to find a specific spot internally though a minimally invasive process. A guidewire is introduced through the skin and then identified in the body through some form of imaging or sensing of body location. Once the correct spot is found internally, this location is marked and the the introducing guidewire is pulled out through a catheter. A new guidewire is then put into the body to perform a certain function. The new guidewire may have a stent or may perform coil embolization or some function like these. The use of separate guidewires is what necessitates the exchange of wires.

Modern Grinding has the capabilities to manufacture a wide variety of guidewires in house, please contact us for details.

This information comes from a non-medical professional and is intended to demystify this process for a non-technical audience, not provide medical advice. If you find information about exchange guidewires above to be incorrect, please correct us – info@moderngrinding.com.