RUG/Pennsylvania/State College/Printers/BioFab@Home/Research

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Complete Setup 1.jpg
FAB@HOME LOGOPrototype.png
BioFab@Home
Color: Acrylic
Extruder: Syringe
Temperature: -
Design: Fab@Home
Electronics: RAMPS
Firmware: Marlin


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6/24/2014

After looking at yesterday's prints, it looks like a higher extrusion rate is the way to go. I realized that it is unlikely that the entire volume extruded is going to be cross linked into the actual structure of the print. Therefore, we need a way to measure the ratio of alginate extruded to alginate cross linked to make adjustments to the extrusion multiplier (without just guessing). Initially, I attempted to extrude 5 ml of alginate into some calcium/gelatin slurry, where I would then separate the alginate and measure its volume after a short period of time. It proved to be difficult to separate the alginate from the slurry and it seems we would have very inaccurate results if the ratio were to be calculated from this data.

Next, we tried to print a spiral cylinder with the standard extrusion multiplier for volume measurement. Since Repetier outputs an approximate volume, we figured we could compare to this value and see if a proper comparison can be made from it. It is difficult to measure the volume of the printed part to such a high degree of accuracy with a small volume, however we may try larger prints once the multiplier is around where we need it to begin to refine the value.

6/23/2014

This morning, we checked on the prints from Friday. The top layer of gelatin seemed to solidify, but the rest (mostly) retained the apple sauce consistency desired. The prints on the other hand were very hard to separate, as they broke apart into small strands. Also, no real structure was visible besides the occasional spiral strand.

Today, We are testing gelatin concentrations with 8.125, 8.75, and 9.375 percent w/v solutions. After about 4 hours or so of sitting in our ~60 degree room, they began to solidify. A little stirring and adding some water to the higher concentrated solutions seemed to bring them back to a good consistency. Unfortunately stirring and adding water introduces lots of air bubbles into the gelatin. It doesn't seem that this changes its physical properties, however it looks more like foam after stirring.

We decided to run a few test prints (it is important to note that the consistency of the three solutions was almost equal at this point) to see if these solutions could support a print. We first tried with basic, 2 or 3 perimeter cylinders. These dragged the print around as usual, making a large blob of weak alginate in the center. We then tried a continuous, spiral cylinder with one perimeter and a larger, 16 gauge tapered nozzle instead of a needle tip. This seemed promising, however, upon removal, the print broke up into a bunch of coils of alginate, indicating no real layer adhesion. We then conducted an identical test to leave overnight, and two more with a typical 21 gauge syringe needle tip coated in spray on water proof coating (used for shoes and fabrics - it was worth a shot to try to reduce the globing of alginate on the tip). These created the same, dragged prints as usual, but there was no alginate stuck to the tip after these prints. Therefore, I think that it is the print settings (e.g. not a high enough extrusion rate), that is causing the dragging instead of the print, not the globbed tip. I do think that it contributed to the dragging, so it will be beneficial to continue to apply some sort of hydrophobic coating to the needles. Further investigation will have to be conducted to find more bio-compatible solutions to this problem.

- John -

6/20/2014

Today, we made a two gelatin slurries, one with store-bought Knox gelatin, and the other with Sigma Aldrich, 300-bloom gelatin. Both 40ml slurries had .2g of NaCl added along with the standard 100 mM CaCl2. Salt apparently slows the solidification of the gel, which is what we currently struggle to prevent. However the Knox brand solidified as usual, yet the Sigma brand maintained a medium viscosity for long enough for us to print. The Sigma brand gelatin slurry was also much clearer. We are unsure if it is the bloom value of the Sigma brand that could be creating this difference in behavior (the Knox brand is about 225 bloom), or manufacturing differences between food-grade gelatin and 'scientific' grade gelatin. Either way, we plan to use Sigma Aldrich gelatin from this point forward, as it seems to produce much more consistent results.

We printed two cylinders into the Sigma gelatin. The initial cylinder had 10 perimeters, which ended up globing up the nozzle tip and prevented any real precise extrusion. The other cylinder had 2 perimeters and seemed to hold its shape pretty well.

The prints are remaining in the gelatin until Monday (to ensure good cross-linking), where we will attempt to investigate the prints.

Next week we will likely be refining the recipe for the gelatin slurries in hopes to find one that is supporting of the gel.

- John -