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How do I maintain and change bellows for the ViVitro Labs HiCycle?

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The Bellows Change Procedure describes the method for maintaining and changing bellows for the ViVitro Labs HiCycle. This method helps optimize durability testing by preventing and minimizing equipment downtime. If the recommendations in the wear prevention section are adhered to, the latest generation of bellows has been shown to last over 200 million cycles. This means the act of replacing bellows will be seldom conducted.

ViVitro Labs offers service agreements and contract routine onsite maintenance services. However, if you prefer to perform this and other regular maintenance on your HiCycle internally, the Bellows Change Procedure describes the best methods to do so. (more…)

10 ways ViVitro Pulse Duplicator and HiCycle compare to equipment built in-house

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People often ask, “Why buy a ViVitro Pulse Duplicator or HiCycle when I could build something myself?  How do they compare to equipment built in-house ?” My initial reaction is always similar to that of Dominik Obrist, Chair University of Bern, ARTORG Center for Biomedical Engineering Research, Cardiovascular Engineering: “It’s more complicated than you think.”  Dominik speaks from experience.

“Complicated” is actually short hand for “takes time, requires expertise, and ends up costing more.”  Here is my top 10 list of reasons why you should outsource the purchase of Pulse Duplicator and Durability testing equipment instead of doing it yourself:

  1. Ease of Use – First of all ViVitro Pulse Duplicator or HiCycle equipment will hands down be more user friendly and easier to use than any in-house system. This is especially important if you are trying to get fast, repeatable, and consistent results from technicians or students. Simplicity is an inherent design criteria from the device mounting, to the data acquisition system, and software.
  2. Reliability – When you need results in a hurry you can depend on our equipment.  Our Pulse Duplicator and HiCycle products work day in day out in countries around the world and have a proven track record of reliability. If in the unlikely event you manage to damage the equipment, see my next point…
  3. Repairs- When ViVitro Pulse Duplicator or HiCycle equipment breaks you can immediately call on extra resources to get the issue resolved right away.  For example, we inventory parts that can be easily dropped in if anything fails.  Will a homemade Pulse Duplicator or Durability Tester system give you that peace of mind? Download our Maintenance Brochure
  4. Reputation – When you report results from a ViVitro Pulse Duplicator or HiCycle system, regulators, reviewers and academics around the world know exactly what that means and how it was measured. If you do the same with your own system you will likely receive a plethora of questions trying to understand how your measurements were conducted.  Check out our citations page for a sampling of publications that use our equipment.
  5. Qualification – Many users struggle to validate that their in-house equipment is working properly. With ViVitro you can call in expertise to make sure your installed system is working to spec. Download our Qualification Brochure
  6. Training – If you have user turnover (be it employee or student), you can call in experts or access online information to get their replacements up and running right away. We invest in a variety of user manuals and training materials which in-house systems will not have. Download our Training Brochure
  7. Cost – Researchers sometimes believe that a simple home built Pulse Duplicator or Durability Tester system could be made for less.  First, factor in the time someone will spend developing their own test equipment instead of focusing on advancing their device. Combine that with the one-off machining costs for a “prototype”, and add overhead costs (which are often neglected) like documentation, user manuals etc.  ViVitro Pulse Duplicator and HiCycle equipment quickly become a very cost effective way to accelerate your development.
  8. Flexibility – If your needs change, ViVitro Pulse Duplicator and HiCycle equipment have a variety of accessories to grow with your development. Our platform of testers makes it easy to transition your device from pulsatile testing to durability testing and back. The look and feel of ViVitro Pulse Duplicator and HiCycle equipment and software is consistent from product to product. Once you know how to use one, it is intuitive to work another.  If you grow and need more capacity it can be order by phone or email.
  9. Consistency – If you ever require independent results from an ISO 17025 accredited test lab, you can come back to ViVitro to evaluate your device with no surprises due to equipment differences.
  10. Looks- As an engineer, my opinions on esthetics are somewhat suspect, but ViVitro systems look professional and impressive to visitors and investors. Home built systems often place no emphasis on appearance and deliver limited visual credibility.

Rob Fraser
Lab Manager, MSc.
ViVitro Labs Inc

HiCycle Debubbling Tips

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The ViVitro Labs HiCycle durability tester is an accelerated wear tester intended for use with cardiovascular devices. The HiCycle has six sample chambers which subject test devices to accelerated pulsatile loading conditions by moving them through a blood analog fluid. When air infiltrates the sample chambers, bubbles can cloud the visibility of your sample, change the system compliance, and cause noise in pressure readings. This article and its associated video explain how air gets into the HiCycle chambers, prevention through regular equipment maintenance, and how to remove air bubbles when they form.

Air bubbles can enter the system at any seal or interface between the test fluid and atmosphere.

1. Why do bubbles occur?

  • When a static head feeding fluid into the system runs dry, air will be sucked in.
  • Attaching syringes to remove air bubbles from pressure transducers can introduce more bubbles.
  • Accidentally opening a stop-cock to air while the HiCycle is running will allow air to be sucked into the chamber.
  • When first filling the HiCycle with fluid, small air pockets can become trapped in the chambers and released on start-up.
  • If chamber windows are not sealing properly, air can enter. Possible causes leading to a bad window seal include a worn window o-ring, salt crusted on the seal, or improperly tightened window fasteners.
  • Pressure/drain ports can come loose and allow the entrance of air.
  • The scan valve may be leaking, allowing air to enter.
  • The static head may not be high enough.
  • When the bellows start to wear, air can penetrate small cracks in the silicone.

Fortunately, air infiltration can be minimized by regular equipment maintenance and proper set-up.

2. How to prevent bubbles?

Sealing & Leaks

  • Check for salt built up around sealing edges like chamber windows, pressure/drain ports, and the scan valve. If there is salt build-up, it means fluid is leaking. If fluid can get out, air can get in!
  • Change window o-rings as needed – if you notice fluid leaking around the window edges or salt build-up, change the o-ring. When you are putting the window back on, wipe any salt and fluid from the edges of the window and o-ring, as well as the window sealing surface.
  • Check that all of the drain ports and stopcocks are tightened daily. If these come loose, they can allow air into the system.
  • If there is salt built up around the scan valve seal or fluid leaking out, the scan valve tension likely needs to be adjusted to improve the seal.
  • Attaching a static head to the system helps feed fluid into the chambers if any fluid is leaking. The fluid level in the static head should be monitored and topped up daily. If there is a substantial leak or the static head fluid level is not topped up regularly, the static head can run dry and feed air into the system.
  • Make sure the static head is open when the HiCycle is running. If you forget to open the static head when you start the HiCycle running, air can be sucked in.

System Set-up

  • Locate the static head as high as possible to help keep bubbles out of the system.
  • Use syringes with flexible tips, so you can encourage extracted air bubbles to the back of the syringe, instead of accidentally introducing more air bubbles.
  • When first filling the HiCycle chambers with test fluid and fixing devices to the pistons, air can get trapped in small pockets. It is important to run the HiCycle at low amplitude before tuning a system, to dislodge any trapped air bubbles before testing begins.
  • The HiCycle bellows experience stress over time and will fail if they are not regularly changed. We recommend changing the bellows every 200 million cycles to prevent bellows failure during HiCycle operation. When the bellows start to fail, they get tiny cracks and holes that may allow some fluid to leak out and let air into the chambers. Usually air bubbles due to bellows failure are very fine bubbles that make the fluid appear clouded. If you start to see fine bubbles clouding your test chambers, check when the bellows were last changed. The bellows should be replaced if they were last changed more than 200 million cycles ago. See our FAQ: HOW DO I MAINTAIN AND CHANGE BELLOWS FOR THE VIVITRO LABS HICYCLE?

When bubbles do accumulate in the HiCycle chambers, there are a number of ways to extract them.

3. How to get rid of bubbles when you get them?

Large bubbles

  • When it comes to larger bubbles, you can sometimes just remove them with a syringe while the HiCycle is running. If not, put the HiCycle in standby.
  • When the HiCycle is in standby, larger bubbles tend to accumulate near the upper drain port; this air can be removed with a syringe or bled out using the pressure of the static head.
  • Air sometimes accumulates in the bellows and releases when the HiCycle is stopped and started again. Put the HiCycle in standby to extract air from the chambers and check the bellows for air bubbles. If there is air accumulated in the bellows, stop and start the HiCycle a couple times to release the trapped air before extracting.
  • With any of these extraction techniques, always be careful not to let the static head run dry!

 Small bubbles

Smaller bubbles, which cloud the test fluid, can be harder to extract than large bubbles. They get caught on the chamber windows instead of accumulating at the drain port. Use a squeegee to remove them from the window. There are multiple ways to do this. Essentially you create a bigger air bubble at the top of the chamber, then refill the chamber with fluid to remove small bubbles. There are three techniques we recommend trying:

  • Injecting air: With the static head open, use a syringe to inject air at the top drain port until only air is in contact with window. Then, either draw the fluid back with the syringe or detach the syringe to let the static head fill the chamber. Be careful the static head isn’t too full, or injecting the air will cause an overflow. Do not let the static head run dry either.
  • Draining & refilling: With the static head closed, open the top drain port, then the bottom drain port to drain enough fluid so only air is in contact with the window. Then close the bottom drain port and open the static head to allow fluid to refill the chamber. You will need to add fluid to the static head as the level drops to fill the chamber.
  • Fluid extraction & refilling with syringe: With the static head closed, attach a syringe with a little bit of fluid in it to the bottom drain port and open the top drain port. Extract fluid with the syringe and allow the top of the chamber to fill with air until only air is touching the window. Re-inject the fluid in the bottom drain port until all the air is pushed out the top drain port. Be careful not to re-inject air. Close both drain ports and re-open the static head.

If none of these methods work, please view the video or  contact technical support. We’ll be happy to discuss the issue with you.

What spare parts should I have on hand for my HiCycle?

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Quantity Code Description
6 HCM046 Chamber Window
6 HCM045 O-Ring Dash 036
2 06146 HiCycle Pressure Transducer Assembly
2 HCM031 U-Cup Teflon Seal 3.441”
2 HCM032 U-Cup Teflon Seal 3.286”
2 HCM054 Teflon O-Ring – modified
12 HCM060 O-Ring Dash 060
6 HCM105 O-Ring Dash 225
18 HCM021 O-Ring Dash 009
6 HCM075 O-Ring Dash 110
1 05842 Tubing
12 HCM108 Bellows
We recommend this list of parts be stocked by a lab using the ViVitro HiCycle: