3D Printed Pharmacological Implants
I recently got a 3D printer, and so now I've turned into one of those goons who makes a lot of plastic tchotchkes. While researching the IR transparencies of various 3D printer filaments, I found out that you can get PCL filament (https://www.fabbaloo.com/blog/2016/6/24/the-unusual-properties-of-pcl-3d-printer-filament). PCL (polycaprolactone) is a biodegradable polyester (previously commercially available as polymorph). It melts around 60C, so it prints at a relatively low temperature.
Where this gets more interesting is that PLC degrades harmlessly in the body. It breaks into subunits of hydroxylcaproic acid, which is converted to acetyl-CoA, enters the citric acid cycle, and is excreted (https://openwetware.org/wiki/PCL_Biomaterials_by_Katie_Kwan).
There has already been some work in building implantable PrEP delivery systems (http://www.croiconference.org/sessions/long-acting-biodegradable-subcutaneous-implant-tenofovir-hiv-prep). My thinking on the matter is that a good 3D printer should be able to print an implant, either with containers inside it with the drug in them, or using filament that has been pre-mixed with the drug. Depending on the properties of the drug, either the PLC could be melted and mixed with the drug, or they could both be dissolved in e.g. chloroform and then the solvent evaporated off. By changing the shape and density of the implant, the release rate can be altered, and there ends up being no need to remove it, as it gets naturally degraded.
It could also be used to print a "sabot" for something that is an awkward shape to implant, and then gradually decay away, leaving the implant in place. In combination with titanium oxide, it can also be used to produce bioactive surfaces that promote cell attachment, particularly for bone cells. However, that work was done with electrospinning rather than 3D printing.
 Antibacterial and Bioactive Surface Modifications of Titanium Implants by PCL/TiO 2 Nanocomposite Coatings
A. Sandeep Kranthi Kiran, T.S. Sampath Kumar 1, Rutvi Sanghavi, Mukesh Doble, and Seeram Ramakrishna