drperry.org

My Open Heart Surgery

kenperry — Thu, 18 Feb 2010 02:20:30 +0000

That’s me in the photo on the left during open heart surgery to replace my native aortic valve.

Years ago I was diagnosed with an “organic murmur” and after following it closely with my cardiologist we decided it was a good time to have a replacement of my aortic valve. I was able to plan for [...]

High Speed Testing of Medical Devices and Materials

kenperry — Wed, 17 Feb 2010 06:25:07 +0000

An important input to FEA is material characterization and limit information. In our laboratory we use a Bose 3230 test system for achieving test speeds up to 200Hz. Depending on the project, we may test complete devices, sub-components, coupon samples and/or simple material characterization samples. Many times, we will test more than one [...]

FEA and the FDA

kenperry — Wed, 03 Jun 2009 23:59:52 +0000

I just returned from a workshop sponsored by the FDA (and the NHLBI and NSF) on Computer Methods for Cardiovascular Devices. It was an excellent workshop providing an audience of regulatory, academic and industrial interests a chance to get caught up on the state-of-the-art, trends and, in general, to exchange ideas on the issues of [...]

Identifying Worst Case Device Sizes

kenperry — Wed, 06 May 2009 06:52:00 +0000

For medical devices, rarely does “one size fit all”. The human body is extremely variable and patient populations, especially those with disease present a wide range of differences that the medical device design engineer must consider.

Identifying the worst case size for a product family is an important part of the validation process for implantable [...]

FEA of NIKE AIR

kenperry — Thu, 30 Apr 2009 01:41:09 +0000

My first job out of graduate school and post-doctorate work was with the footwear company, NIKE. I was fortunate to hire into the heart of the most advanced footwear technology department in the world and I could not have had a more exciting job description. I began by learning how to design NIKE AIR cushioning [...]

Contact Interaction for Medical Implants

kenperry — Sat, 25 Apr 2009 07:05:11 +0000

There are many circumstances when it is necessary to model contact and contact interactions when analyzing medical implants. Such circumstances arise when devices interact with tooling, catheters, vessels and when self-contact occurs. This latter situation arises for example when a stent is crimped down tightly to catheter dimensions.

ABAQUS/Standard provides a range of methods for defining [...]

Interpreting FEA Results: Integration Point Data

kenperry — Wed, 15 Apr 2009 23:50:56 +0000

Finite Element Analysis (FEA) can produce an enormous amount of data as output. Solution variables such as stress and strain are computed throughout an analysis for each increment and at each location within the model. These solution variables are computed at what are called “integration points”. These locations ARE NOT the same as the nodes [...]

Evaluating Design Instabilities with FEA

kenperry — Fri, 10 Apr 2009 16:41:07 +0000

Finite Element Analysis is routinely used to evaluate the performance and durability of medical devices. When using an implicit method such as ABAQUS/Standard, FEA can also be used to evaluate the geometric stability of a proposed design. Such issues could arise for example when designing stents for large vessels, such as the aorta, [...]

FEA Geometry and Edge Detail

kenperry — Mon, 06 Apr 2009 22:32:47 +0000

A typical process for making stents is electropolishing to remove material and processing defects and to impart a smooth finish with rounded corners. It is well known that a polished part will have superior fatigue resistance, but how much does the rounding of edges affect the stress and strain in the stent when loaded?

We studied [...]

Finite Element Optimization of Medical Implants

kenperry — Fri, 27 Mar 2009 09:05:14 +0000

Finite Element Analysis is an excellent engineering tool for optimizing medical implants. It provides a fast and reliable method for evaluating both the performance and safety issues associated with any given product. A variety of design concepts can be evaluated and relative safety factors determined for the full size range of an intended product.

Parametric studies [...]