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Class II Design Problem Solved with Simulation

Many articles generalize design controls, but few provide direct application. Here, I introduce a series of articles with specific application to orthopaedic engineering in an FDA-regulated environment from a design engineer’s perspective. This first article provides a broad overview for engineers and your managers to highlight the milestones of a design process from design request to purchase order using Finite Element Analysis (FEA). —The author


Exhibit 1: The Napkin Sketch

    Exh 1 Napkin Sketch web

When developing medical devices that are subject to special controls per 21 CFR Part 820.30, Design Controls, we must be aware of paving the path to documented compliance. Let’s walk through a particular design problem received from the marketing team. The design problem is illustrated by the clinicians and/or marketing team as was shown in Exhibit 1. 

The marketing team found that when a k-wire is retained in silicone brackets within a sterilization tray, the wires could become dislodged and potentially damaged during transport. The conversational solution entails, 1) contain the wires in a tube with sterilization ports that don’t allow extrusion, 2) hold the larger diameter tube more substantially in a bracket, and 3) consider that the lids can easily be removed and reattached.

Since a sterilization container is a Class II device per FDA Product Code KCT, or the container is device–specific, making it a Class II device, we’ll apply and document conformance to design control requirements.

820.30(a): General
The device is classified as Class II, requiring both GMP and Special Controls.

820.30(b): Design and Development Planning
Competent resources have been allocated to the project, and particular milestones have been set.

820.30(c) Design Inputs
The project reached the phase wherein FDA requires us to approve User Needs and Design Inputs. The Project Manager and Marketing Manager provided the details as shown in Exhibit 2 (focusing only on the snap-fit portion of the design inputs):

Exhibit 2: Design Traceability Matrix

User Needs

Design Input

Design Output

Design Verification

Design Validation

Removable Lid
Provides Access
to K-Wires

6-15N Force

10-Caddy Rev. A

Test Report #56

Test Report #78

Exhibit 3: Design Concept

  Exh 3 Full Tube web

Let’s begin our work.

The marketing manager did a good job of identifying a practical user’s need, and the project manager converted that into a measurable design input with range of attachment forces. This project has been identified as being time-sensitive (as usual), and we’re after that big promotion, so doing a round of prototypes will leave the management team dissatisfied.

To reduce the timeline, we’re committing to a production order on the first try without prototypes. We spend the morning designing in our CAD system, and present the team with the design shown in Exhibit 3.

Everybody seems to be happy with the general concept of the simple tube with caps. The last risk to the design (other than passing sterilization to SAL-6 and a dry time validation) is the attachment performance of the end caps. The tube is anodized 6061 aluminum, and the caps are made from medical grade Radel®. Exhibit 4 (on the next page) lends a closer look at particular elements of construction.




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