Design Freeze is a significant milestone in MedTech. It's the point when you're ready to start the Verification & Validation (V&V) process. It implies maturity of your technical design and also your design control, including design requirements, risk management, and design outputs.

With this milestone being so significant, it's not uncommon for MedTech teams to sprint to "Design Freeze" in hopes of raising the next round of funding, bumping up valuation, or capitalizing on market opportunities. The problem is that pushing through "Design Freeze" before being ready can result in the exact opposite -- losing investor confidence and inserting major delays before market launch. 

But good process fixes most execution problems in MedTech. If you integrate these 5 checks before hit the 'freeze' button, you'll improve your process and be a few steps closer to Design Freeze readiness.

1. Trace Matrix

The Trace Matrix ties the critical parts of your design history file together. It's a tabular document that is often created in Excel or an eQMS. When designed well, it creates linkages between the following:

• User Needs and Design Inputs - There's a lot of art around drafting User Needs (UNs) and Design Inputs (DI). We are firm believers that UNs should drive DIs, and DIs shouldn't exist without a corresponding UN 'parent'. (Here is an article we wrote on this topic.) The Trace Matrix makes these connections explicit and prevents 'dangling' DIs.
• User Needs and Validation - Every UN just be validated through a controlled process. Validations may include lab tests (i.e. biocompatibility), human factors tests (i.e. summative studies), pre-clinical studies (i.e. GLP animal studies), or clinical studies. Listing these validations in your trace matrix doesn't mean they are complete at this time -- it just specifies that you know how each of your UNs will be validated.
• Design Inputs and Verification - Just as every UN must be validated, every DI must be verified. Verification tests may include inspections (i.e. critical geometry), mechanical testing (i.e. pull tests, torque tests), electrical safety testing (i.e. IEC 60601 testing), and software verification (i.e. unit testing). 

2. EVT

Engineering Verification Testing (EVT) is the testing process to ensure that your design achieves the critical performance criteria. It's the pre-check to make sure that you're not going to hit many big surprises once you get into the V&V stage. (Here's another article we wrote on this 'pre-check' process.) Below are some of the considerations for EVT:

• Production Materials & Processes - It's best to be using production materials and processes for EVT. Performance of 3D printed parts and injection molded parts can be vastly different. Similarly, you'll want to free yourself of Arduino PCBs and other electronics that won't be part of your production design.
• Draft Protocols - For the critical tests, you'll want to be following the protocols that will be used during the V&V process. So, it often makes sense to get your V&V protocols written before Design Freeze.
• Finding Failure Thresholds - In V&V, you'll be focused on passing the minimum bar established in your UNs and DIs. However, when running EVT, you'll want to push your devices to their maximum limits to understand the thresholds of performance. You're goal should be to see how and where your devices will fail. For instance, if you are doing drop testing, don't stop at the minimum drop. Keep dropping the devices until you get a failure to understand where and how that occurs. Think similarly for fluid ingress, ambient conditions (temperature, pressure), etc. Find the failure thresholds during EVT.

3. Tech Review

Part of the 'Design Review' you'll need to complete before 'Freeze' will be assessing the technical design. Some key considerations during the Tech Review:

• Computational Simulations - If your design involves mechanisms, fluids, thermals, electronics, software -- you'll want to run simulations under extreme conditions. These simulations may include finite element analysis (FEA), computational fluid dynamics (CFD), dynamic motion studies for mechanisms, and the like. Of course, when running any kind of simulation, it's critical to run some baseline testing to ensure accuracy in the simulation methods.
• Tolerance Analyses - There's no such thing as +/- 0 when producing parts. There will be variations in controlled dimensions, concentricity, flatness, and other elements that will affect your device's performance. Identify the critical tolerance stack-ups prior to Design Freeze and assess the design under Min/Max and RSS conditions to evaluate fit and function issues that may arise during V&V and later production.
• Design for Manufacturability (DFM) - Are your molded parts designed with the right draft angles, parting lines, ejector pin locations, gate locations in-mind? You'll need to think through all these details with the molder. Similar constraints may arise with metal part fabricators, PCBA manufacturers, wire harness assemblers, and more.
• Design for Assembly (DFA) - Who is putting this device together? You should have a set of work instructions produced based on your recommended process of assembly. However, you should also be open to the final manufacturer's input on steps, processes, jigs, etc. that may alter your original work instructions. Before 'Design Freeze' it's critical that you think through every single assembly process, from ultrasonic welds to heat stakes, snap fits, adhesive joints, and screw assemblies.

4. Design Control Review

When most engineers say "Design Review" they think about spinning CAD and reviewing circuits and code. That's the technical design, and of course that needs to be thoroughly vetted. But the other critical part of your your 'Design Review' is assessing all of your Design Control documentation created to date. This includes the following: 

• DHF Review - Your Design History File (DHF) is a living document, which needs to be reviewed and approved at key checkpoints throughout the design process. Design Freeze is definitely one of these checkpoints. Prior to Design Freeze, you'll need to complete a thorough review of all documentation from requirements to design development plan, risk management plan, risk analysis, failure modes & effects analysis, usability studies, and more. For compliance with ISO 13485 and QMSR, you'll need the right parties to sign-off on your DHF documentation before hitting the "Design Freeze" button.  
• DMR Review - Your Device Master Record (DMR) compiles all of your design outputs. This includes 2D drawings of components, work instructions, packaging specifications, labeling specifications, and more. This is effectively all the documentation that a manufacturer will need to reliably produce your design. Ensure that the eventual manufacturer has conducted a thorough review on the DMR and you have integrated their feedback to ensure a smooth transfer into production.
• DHR Plan - Your Device History Record (DHR) is something that will be produced during the V&V and commercial stages. The DHR is the set of documents that correspond to a particular lot that is being produced. This includes inspection reports, travelers, test reports, etc. You don't need to develop a DHR for your EVT units, but it's best practice to put the process in-place so that you (and/or your contract manufacturing organization) will have thought through these key details before Freezing the design.

5. Independent Review

With changes from QSR to QMSR the independent reviewer requirement is no longer required. However, it's still a pretty darn good idea to get a fresh set of eyes on all the items listed above. A design team that has been in the weeds working through the details of the design may miss big picture details that could come from an independent reviewer.

To Sum it Up..

It's a lot of work getting to Design Freeze. But it's a lot MORE work to correct the mistakes if you rush through Design Freeze before you're ready. If you deploy these 5 steps above, you'll be a lot closer to ensuring a smooth and streamlined process through V&V.