INTRODUCING OUR NEW AUTOMATED DIP COATING MACHINE

We're proud to announce the launch of our new Single-Device Dip Coating Machine. The Coating Machine was developed in partnership with ISurTec and is designed to work with their Hydrophilic Medical Device Coatings and any other UV curable coating. Now you can coat your devices on your schedule, in your lab. No more minimum lot sizes or waiting for days. In fact you can buy this machine and ISurTec coatings faster than you can get a lot coated!

The Coating Machine is designed to precisely apply coatings on medical devices. It features two dipping stations, one for a primer coat and one for a top coat, allowing for a fully automated coating process. Devices are dipped and retracted at controlled speeds, with the ability to set two distinct retraction speeds along the device length for optimal coating thickness. After retraction, the coating goes through a controlled drying process with heated forced convection. It's then cured with UVC LEDs in the curing chamber. An iris mechanism minimizes UV radiation exposure by sealing the chamber during curing. The entire process is fully automatic and programmable, with the option to lock settings to prevent unauthorized changes.

Technical Specifications:

Coating Length: up to 100 cm

Device Length: up to 125 cm

Device Diameter: up to 27 fr

LED Wavelength: 275nm

User-programmable Recipes: 25

Power Input: 110 - 240 VAC 400W         

Learn more about the new Pilot Line Dip Coating Machine

Learn more about the ISurTec Hydrophilic Medical Device Coating

Coiled Catheter OD Calculation for Designers

Want to save time when ordering extrusions for your next catheter project? This article will help you calculate the diameter of your next coiled catheter.

Background

Many neuro and peripheral catheters are made by a process of reflowing or laminating polymers and reinforcement materials over a mandrel. The reinforcement material we'll consider in this article is a coil. A coil winder is used to wind a wire over a catheter mandrel. Then a polymer jacket is sized to slide over the coil during assembly. Heat shrink tubing is then slid over the jacket. During the catheter reflow process, the jacket melts and is compressed by the heat-shrink. This causes the jacket to reduce in diameter and increase in wall thickness.

Conservation of Area

For starters, let's think of the cross section of a reflowed catheter without a coil. There's a mandrel, liner, and polymer jacket. During the catheter reflow process the jacket melts and is compressed by the heat shrink tubing. This reduces inner and outer diameter of the jacket. Since no material is lost during the catheter reflowing process, the cross-sectional area of the jacket must be the same before and after reflowing. We can use this to calculate the relationship between the pre and post reflowed jacket diameters.

Keep in mind that the final ID of the jacket would be the liner OD, or the diameter of the mandrel plus twice the liner thickness.

Enter the coil

Now let's add a coil. The conservation of

area method is invalidated because the coil is not a uniform tube. In fact, the jacket is no longer a uniform tube.

The reflowed jacket has a helical void in it because of the space the coil takes up inside of it. Instead of thinking of a conservation of area, we can use a conservation of volume to equate the pre and post lamination conditions. Again, we assume that we're not losing any material during catheter reflow. Let's cut a section of coiled catheter into a unit length and work out the volumes of each component. We'll use 1 inch for the length unit and use inches for all the diameter and volume calculations too.

Finding the volume of the jacket is straightforward. We just multiply the cross-sectional area of the jacket (first equation) by the length. Since the length is 1, it's unchanged. For the coil volume it's the same plan. We'll multiply the area of the coil wire by the length of the coil wire in a unit length of catheter. Visualize un-wrapping the coil wire along the coiled length. The result forms a right triangle.

The height of the triangle (a) is 1 unit (the same unit as the rest of your calculations). For the base of the triangle (b), think of how many times the cylinder would turn if you unwrapped the coil. The number of turns can be represented by the length of the cylinder (1 unit) divided by the pitch of the coil. We multiply the number of turns by the coil mean diameter and Pi to find this leg of the triangle.

Great, we have the length of each leg, now we just apply the Pythagorean theorem to get the wire length. Note that this number expresses how much coil wire is required per length of catheter. So, if you wanted to know how much total wire a catheter would take, you just multiply this number by the length of the catheter.

To find the volume of coil wire in a unit length, we now multiply the cross-sectional area of the wire by the length of the wire. If using a round wire you'd use the equation for the area of a circle. If you're using flat wire, you'd multiply the wire width by the thickness. Add the volume of the coil to the volume of the jacket and that gets us the total volume before and after reflowing! Let's remember the equation for the area of a pipe and assume that the area is equal to the volume since the length is 1. Solving for OD we get:

Conclusion

Using this method, you can calculate the OD and wall thickness of polymer jackets for reflow. It should save you a few prototype iterations when designing a new catheter. Additionally, you can fine-tune the OD of the device by varying the coil pitch. If reflowing a braided shaft, the volume of the braid can be calculated similarly based on the braid angle, number of wires, and cross section of the wire. Of course, these calculations should only be used as a starting point. Fine-tune your catheter OD with prototypes and testing. Good luck!

The Essential Guide to 3D Printing Carbon Fiber filled Nylon

Dry box with Carbon Fiber Nylon Filament

You've probably heard that 3D printing carbon fiber-filled nylon is difficult. You may have heard it requires special hardware. Well that's half true. You will need a few essential components to be successful at it, but it's not that difficult. And this filament is worth the effort. Nylon is tough and has excellent layer adhesion. The addition of carbon fiber (CF) to the filament makes it stiffer and reduces the material's tendency to shrink during cooling. This means you can print it at room temperature and get amazing prints. The finished parts are strong, tough, and temperature resistant! Here are a few tips that will ensure success.

---

If at first you don't succeed, DRY DRY DRY!

This may as well be the title of the blog post. I can't emphasize enough how important this is. Nylon is hygroscopic, meaning that it readily absorbs moisture from the air. When printing, this moisture turns to steam and expands inside the filament as it's extruded. This causes several issues including a rough surface, blobs, and stringing. So how do you ensure your filament is dry?

Dry in a convection oven at 90° C for 4+ hours

There are several filament dryers on the market. They range from re-branded food dehydrators to purpose-built devices. But these units have a limited temperature range. We dry our nylon filament in a convection oven with a tightly controlled PID temperature controller at 90 C for 4 to 8 hours. Weigh your spool first on a gram scale. Write the value on the spool before it goes into the oven and then repeat when it comes out. You may be surprised to see it lose several grams of water. Don't forget to dry your desiccant material at the same time and weigh it too. Understanding the weight loss will help you understand your drying process.

Dry that brand new spool too

Just because you opened up a fresh spool of filament doesn't mean you can skip this step. We typically extract about 10 grams of water from new 1Kg spools (that's 1% by weight!). The image below shows a part printed with two spools of carbon fiber filled nylon from the same brand. The lower part was printed with dried filament and the upper 2 mm with a spool of fresh filament straight out of a vacuum sealed bag. You can clearly see a color change and blobs of material on the upper 2mm of the part. The same spool lost 1% of moisture after drying.

Old dry filament vs new un-dired filament (top 2mm)

Print out of a dry box

This may seem overkill if you're used to printing the same spool of PLA for weeks with no conditioning. But nylon filament will absorb enough moisture to ruin your print if it lasts more than a couple of hours (not to mention needing to be dried again for your next print). The solution is to store and use the filament in a sealed, dry box.

The filament should exit the box through a tube that runs directly into the extruder to minimize moist air contact. What else should you keep in your dry box? Dried desiccant and a digital hydrometer. You can find hydrometers on Amazon and other online vendors. If the relative humidity rises above 10%, you should re-dry the filament and the desiccant. Please note that cheaper hydrometers don't display values below 10%. This is the range that you are most interested in.

Turn up the heat, Turn off the cooling fan

You know that nylon needs to be printed hotter than PLA or ABS. The exact temperature will vary by material and printer setup. We run between 280°C and 295°C. This will require an all-metal hotend.

Not all hotends are created equally

Now that your all-metal hotend can reach a searing 300°C, you may start to find new problems. One new thing to consider is the efficiency of the hotend's heat break. The heat break is the part between the hot nozzle, and the cold tube leading to it, usually surrounded by a heat sink. When the nozzle is running hotter, more heat will be transferred through the heat break, into the cold end of the hotened. If the filament melts in this zone, it will get stuck and be quite difficult to remove. You may want to add a bigger fan or better ducting to the heat sink (as I did). Instead, consider buying a better hotened that performs better at higher temperature.

Speaking of fans

You might think that printing at such high temperatures means you need to run the part cooling fan. But nylon does not need part cooling. In fact, you will lose layer adhesion strength if you do. Running the fan slowly over bridges only is acceptable, but leave it off for the print. If small islands are being printed, you can experiment with slowing down the print speed. You can then add minimal fan speed if needed. But for general printing, it should be off.

Should I buy a super-hard, diamond-tipped nozzle?

No. But you do need something harder than brass. The reason is that carbon fiber filled nylon will erode the nozzle. The carbon filler is abrasive and will destroy a brass nozzle in a short time. Hardened steel nozzles from quality vendors are an excellent alternative. But heat transfer through the steel into the filament is worse. Increase the print temperatures and slow down the maximum speeds a bit when using steel. Another option would be to use a ruby-tipped brass nozzle. You'd get the heat transfer of the brass, and the abrasion resistance of a ruby.

A CF-filled Nylon part being made

What about build surfaces, heated chambers, etc?

Build surface and adhesion

When it comes to build surface, the secret sauce is PVA glue or regular glue stick. PEX is a favorite build surface at Pilot Line but garolite works well too. Either surface has to be coated with glue stick. The first layer parameters must also be correct (speed, height, etc).

Chamber Temperature

For chamber temperature, you're in luck. Carbon fiber filled nylon doesn't require a heated chamber. Room temperature or higher will work well. The carbon fiber helps reduce shrinking and warping in the nylon which helps stabilize it.

Build plate Temperature

The build surface does not have to be heated. We run a PEX build surface at 45°C out of tradition. Markforged printers do very well with an unheated garolite bed (and glue stick).

Print settings

Are you wondering how much retraction nylon needs to avoid oozing and stringing? Scroll back up and read the section on drying the filament. Seriously, there are no special settings needed to print nylon. Of course you'll have to experiment with the usual print settings to see what works best. If you find yourself running twice the normal retraction to avoid oozing, the problem is moisture in the filament. Dry it and try again.

Why are my nylon parts getting softer over time?

Remember that nylon is hygroscopic? Well your super-dry freshly 3D printed part is now absorbing moisture from the air. This moisture acts as a plasticizer. A plasticizer is something that is added to a thermoplastic to make it softer. This softening of the material after it's exposed to real-world conditions is something that must be considered when designing a nylon part. If you need a very stiff part, try PLA. If you want something amazingly tough with some decent stiffness that can take some heat, it's hard to beat CF nylon.

---

I hope this guide helps clarify the topic of 3D printing CF filled nylon. It might be your new favorite filament. Let us know what your experience is like, or if you have other tips for printing nylon. Good luck!