This is a project I’ve been collaborating with Proteus on. A non-newtonian fluid is one which in which the viscosity changes according to the amount of shear applied. There are a number of types. We’re interested in the shear thickening type. Basically, you have a fluid which is relatively thin in viscosity until force is applied. Then the material thickens to the point that it’s almost a solid. The first material we trialed was made up of corn starch and water. We found that even a half inch thick bag of this mixture formed around the fist allowed us to punch a metal 90 degree edge at full power without suffering injury.
With these early trials we recognized two improvements we needed to make. We needed a more effective shear thickening agent and more importantly we needed a vessel that could survive the forces we were applying while still being biocompatible.
The shear thickening material we choose is called D30. D30 is available in a number of different forms. Unfortunately, the company only sells to manufacturers. We used a motorcycle pad for the implant. The D30 is in a foam form. It’s likely that a truly liquid formulation of D30 would be even more effective but we haven’t been able to source it as of yet.
The D30 is contained in PharMed BPT thermoplastic tubing. This tubing meets ISO 10993 standards for biocompatibility. We found it can be heat welded at moderate temperatures. After filling the tubes we melted plugs of the PharMed BPT into the ends and sanded the units perfectly smooth. We torture tested many of these until we figured out a method to get a great seal on the ends. These tubes were able to withstand 75 strikes with a big ass mallet and survive. We also tested for permeability through the tube material using baking soda and vinegar. It isn’t complicated but it works.
Once we had a unit we felt ok with, it was cleaned and autoclaved. An incision was made in Proteus’ arm and blunt dissection was performed creating a space for the unit. The unit was placed and the incision was sutured.
I wasn’t entirely happy with the procedure. For one, an implement was used to push the implant into place. The implement pushed into the tubing a bit which gave rise to concerns that it may have been punctured. Also, the distance from final placement and the incision wasn’t as far as I would have liked. This resulted in some tension on incision which can lead to poor healing.
The implant was left in place for 4 days without any apparent negative result. On day 4, the incision was reopened and the unit was removed for analysis. The depth of the pocket was increased for better placement and a new unit was implanted. The incision was closed and the unit remains implanted at this time. The intent is to keep the unit for a month time and then to remove it for analysis. Inspection of unit one showed that no puncture had occurred. No tissue adhesion was observed and the wound appeared healthy and normal .