Given my background in both medical device design and manufacturing AND 3D printing, I have been approached by a number of groups asking about 3D printing medical products to address some of the extreme shortages that have occurred in response to the COVID-19 virus.
While I firmly believe that every effort should be made to use products being produced by regulated manufacturers, I also understand that there are front-line workers dealing with horrible conditions for which on-site production is their only real option.
As such, I've created a quick list of key information to support groups in these situations. I will be adding more detailed information, regulatory guidance and specific files and designs next week .
WARNING: This information is NOT for sold product. Product sold within the US is under strict regulation by the FDA. This information is for volunteers, non-profits, clinicians and care centers trying to supplement their supplies until regulated product can be obtained. This is NOT comprehensive information, merely a "hot list" of risks and best methods to address a very specific context. All information is used at your own risk. Dyad Engineering is not responsible for the results of any actions taken in response to this information.
Match the product with the method
3D printing works best to replace small to medium, complex plastic molded parts.
Things that are NOT good for 3D printing
Flexible Tubing (but you can 3D print adapter to connect tubes)
Filters (but you can print parts to hold filter material)
Anything currently made with fabric
Understand the Functional Requirements of your Product
Virus Barriers
Must seal tightly and prevent the passage of contaminated gas or fluids, other than through a filter
Air Flow
When creating masks and shields, you must allow for CO2 to escape and oxygen to pass through
Cleaning Cycles
How many times will this product be used and cleaned before it is discarded?
Product should handle the heat, humidity and/or chemicals used in cleaning, as well as handle the repeat bending, scrubbing and rough handling.
Stress Conditions
Products should have a “safety factor”. Fasteners and fastener locations, hinges, and sealing surfaces should all be able to handle 2-3 times the stress you would expect in typical use.
Ergonomics & Usability
Designs should function for a wide range of anatomy sizes and shapes. This can be done by adding adjustable features, or break designs down into different sized product (small, medium, large)
Snaps, buttons, fasteners should be easy to use, even while wearing gloves.
Understand the Risks
Skin Contact
Some materials can cause reactions to sensitive skin, or even regular skin with long contact under pressure.
Use materials considered safe for 30 day contact if at all possible.
Particulates
Treat products through which breathing will occur with extra care. Use an ultrasonic cleaner to agitate any particulates that may be left in the part, and/or flush the pathway heavily with a sterile fluid.
Cleanliness & Clean-ability
Check your materials for chemical, heat and humidity limits.
Run your product through multiple scrubbing/sterilizing cycles to check for degradation.
Use materials that can handle autoclaving if at possible. If not, identify an alternative sterilization method available to health providers and include re-sterilization instructions. Add warning labels that the product can NOT be autoclaved.
Minimize small holes, cracks and other features that can shelter pathogens. Keep geometry as simple and smooth as possible.
Choking/Strangulation
For any products that include covering the mouth, nose or wrapping around the throat, include a breakaway fail-safe.
Highly agitated patients have strangled health care workers by grabbing non-breakaway lanyards.
Validate Your Functional Requirements
Test Apparatus
Air sealing and air flow can be checked with a custom test apparatus (more to come)
Certification
Use filter materials rated for filtering something the size of a virus
Use materials with approvals for long term skin contact, or at least check the MSDS (Material Safety Data Sheet, available from most suppliers) for any mention of avoiding skin contact.
Dimensional Checks
Check that parts fit the range of faces, hand sizes, etc.
Connector Fit check
Check that designed components fit with existing parts. Can they be pressed on, threaded together, snapped in without damaging either component? Do this multiple times to see if there is a cycle limit.
Manufacturing
Update a 3D model per the design guides of your material AND machine
Each 3D printing process and material have slightly different design limitations
A design may have been created by someone with a very different 3D printer or material, so can not necessarily be printed “as is”.
Check requirements for wall thickness, minimum feature size in each axis, overhang angles, tolerances, and max print volume dimensions.
Update the file meet all these requirements.
Orient to optimize surface finish and tolerances on critical surfaces
For masks, this is the surface that seals to the face and interfaces with the filter inserts
For fasteners and adapters, these are the surfaces that screw or insert into other pieces
For most machines, the X and Y tolerances are much tighter than the Z axis. Avoid the edges of the printing volume. The precision of some machines degrades at the extremes of the positioning mechanism.
Calibrate your equipment
Most machines have their own calibration cycles, run this every time you move the machine, turn it on and off, reload new raw material, or experience a failed build.
Check your build surface or vat for contaminants. Always keep this surface covered and isolated when the machine is not in use.
Run a test file with known dimensions in X,Y,Z (a cube is fine), then measure the resulting piece.
How closely does it match the design file?
Materials frequently shrink after they are printed, sometimes by different percentages in different dimensions. This amount of shrinkage in each dimension will be unique to a specific design.
If there is a major difference along one dimension, even after calibration, use a scaling tool on a CAD program to shrink or expand the design along that axis to compensate.
The distorted design file will compensate for the manufacturing off-set.
Include an easily measured test piece in each build as a regular process check
Run a test piece
Always run a single part first. As tempting as it is to fill a large print bed, it is highly likely that you will need to print 3-6 versions of the part before you have something ready for “production”
Include a way to track lots and batches
Add a lot number (date with the number of the lot that was produced that day, ie 2020-03-27-01). You can also add a site name if coordinate multiple printing centers.
This can be added to the CAD file before printing. Make numbers and letters at least 5mm high and extrude them 1 mm OUT. Use a san serif font to avoid complexity.
Keep a log at the printer with who ran the printer, confirming the calibration worked and what version of the product was produced for each lot produced on each day.
As you get input from “the field”, you can match problems to specific lots and identify process or training errors.
If a lot starts failing, the lot numbers help clinical workers identify other units from a failed batch and isolate them.
Post-processing
Remove all support materials and sand/polish smooth any surfaces that contact skin or require a smooth surface.
Clean parts in an ultrasonic cleaner (if possible) to remove particulates and any uncured material.
If the 3D printer uses light to cure material, expose parts to a UV light, or direct sunlight, for at least 1 hour to ensure all material has been cured.
Sterilize/Clean product as needed and seal into a clean plastic bag. Label bag as “Clean”. Do not label as “sterile” unless they have been placed in a sealed package and sterilized via validated methods.
Separate batches into different spaces as they are in process (i.e. clean and unclean product should be isolated from each other, with clear labeling).
Shipping
When sending materials to a particular group, add which lots were sent to them and when. This will help you track how long some of these products have been in use, and to remind clinicians when it is time to dispose of older product.