The first aditive that I have tried to use as a binder for hydroxyapatite is methyl cellulose. It is a polymer simmilar to cellulose. It has no interaction with human body, as it can not be digested. This is one of the reasons why it seemed as a great aditive. It can also be used for making metal clays, which makes it quite commonly used in jewelery. This was also one of the reasons why I thought of using it, as it binds together particles with small forces in between them or no at all. Methyl cellulose also burns away in the process of sintering, which makes it even better.

To start off I first made samples with hydroxyapatite and 50%, 40%, 30%, 20% or 10% of its mass being methyl cellulose. I found out that below 20% mixture was not usable as it did not form any usable solids when wetted. I found out that the best one was around 40% methylcellulose. This sample also had clay like properties. Then i left the samples to dry. The samples that solidified were quite strong. After that i put them into a kiln at 1300°C for 10h to heat up, 2h to be stable and 12h to cool down. The results were quite disappointing as the sintered objects were then just a piles of slightly sintered hydroxyapatite. I think this is due to the fact that methyl cellulose burns away at lower temperatures. Because of that and the fact that methyl cellulose made the most of the volume of the sample as it has quite low density. This all led to methyl cellulose burning away and very porous object that didn't bind together as it did not melt yet.

Anyway I still have hopes for methyl cellulose as it could be used to print objects that aren't going to be sintered. These objects would probably need to be coated with something that would increase its strength (eg. ca glue). This method would probably be cool to be used with some fine ground sands made of different colored minerals. Methyl cellulsoe could also be used to print out of materials with lower melting points (eg. some metals like tin, gold, silver... maybe even aluminum). These could then be sintered. One should keep in mind how much material like this would shrink.

To conclude methy cellulose isn't usable to use with hydroxyapatite to print bones, but it is still promising as it could be used with other materials.