Materials research vol. 1

A project log for Printing bones on a DIY powder bed 3d printer

This project focuses on using building a budget powder bed 3d printer capable of printing bones, and creating the needed ink and powder.

JureJure 04/27/2017 at 16:120 Comments

One of the things that has a lot of impact on print quality is material, that one is using. This is why it is very important to put a lot of mind and effort in creation of material.

Desired parameters

3DP printers use powders, that solidify in presence of some specific liquid. First thing i have decided upon is what liquid to use to cure powder. I have decided on using distilled water. I have also made a decision that liquid can have some isopropyl alcochol or ethanol in it, so i could use thermal printheads as well. I also had to decide on how my desired material should be while and after printing. This way my material would have to equally absorb water, but at the same time water shouldnt spread too much. After the print the material should be hard enough so it can withstand cleaning process and handling. This means that my desired material wouldn't be hard enough for most applications, but this is still ok as it should be sintered in the end. With all of this in mind, I have set off to create the needed powders.

Plain hydroxyapatite

First I have tested plain hydroxyapatite. It was not reliably absorbing water. After drying it just fell apart. I have also tried sintering it on 1300°C for 10h of rising temperature 2h of constant temperature and 12h of slow cooling. The results showed, that strength of sintered object depends mostly on pressure with which it was compresed before printing.

Hydroxyapatite and aditives

Based on results of using plain hydroxyapatite I thought of using aditives. I have selected tested three and am planning on trying to use one aditive more (PVA plastic) and one method (ligand transition). The aditives i have done some testing with are methyl cellulose, portland cement and dodecyl benzene sulfonic acid. I used these because these work differently, but still act as binders.

Methyl cellulose is a polymer. Single molecule looks like a long strand. When it is mixed with water the strand becomes more flexible and it wraps around bigger particles (in my case hydroxyapatite). When it is dried strands become more rigid.

Portland cement is a mixture of chemicals, that have a complex chain of reactions. Products of said reactions slowly form crystals that give strength to cured cement. These crystals also form around particles. This way they trap them in some sort of cavities.

Dodecyl benzene sulfonic acid is a quite common surfactant. It is not a binder, but it alows some sort of sedimentation of powder particles. It also ataches to particles with hydrophobic tails, while hydrophylic heads have some attraction betweent them acting a some sort of a very weak binder.

Tomorrow i will be talking a bit more about electronics and mechanics. I will continue talking about materials the day after.