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

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


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Blog Entries

6/25/2014

Print testing trials began with a single perimeter, non-spiraled cylinder and a black, flat tip, 22 gauge needle. They were let to sit for about 15 minutes before attempting removal from the gelatin. The single walled cylinder looked very nice at a 4.25 e.m.. We then started printing two walled cylinders. At slow speeds the slurry was being dragged and therefore deformed the print. Doubling the speed seems to help this a lot. Also, we began heating the slurries before printing. This eliminates the need to add water (diluting the solution)and helps keep the slurries very uniform. It does cross link soon after it heats, so it should be printed in soon. A two-perimeter print at 4.5 was very sturdy, however it was almost twice the desired height.

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 cross-linked alginate will have the same volume as the volume of dissolved alginate printed. 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. 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. After printing a .6ml, 3x extrusion multiplier spiral cylinder, we recorded an approximate actual volume of .4ml. Tomorrow we will try a 4.5 e.m., even though it is less than the 5 e.m. that seemed to still be a little bit low. We will continue to print solids until we can obtain stable results that do not drag in solution.

On another note, we set up a heated bed off of the RAMPS board to use as a heater that should serve as a hot plate to melt gelatin. It should be a good addition to have when it comes time to print more delicate structures that cant necessarily be separated by hand. Also, we believe that the gelatin slurry mix is less crucial as we initially thought.

- John -

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 -

6/16/2014 - 6/19/2014

6/9/2014 - 6/13/2014

6/2/2014 - 6/6/2014

5/27/2014 - 5/30/2014

This is the beginning of 8 weeks of work on the bioprinter. I am starting by exploring the use of custom G-Code for the bioprinter. Slic3r seems as though it may be too complicated for the first few prints that we will attempt. It also allows the user to set the start point easily and precisely, which is advantageous when we may be printing into containers in specific places on the bed.

Also, I printed a small stand to hold the jello-shot cups (which serve as print containers).

Testing has begun using white pudding extruded into green Jello-brand jello prepared with the instructions on the box. The tests help refine the extrusion rates where I found that .125mm E per 10mm travel was a pretty good value. Currently, the printer is not very accurate due to the axis tilting upon the change of direction. I hope to change the axis to linear bearings.

- John -