Researchers at Tufts University have developed silk fibroin-based microneedles for delivery of drugs and 
other compounds directly to tissue in a controlled manner. The researchers believe that silk fibroin is an excellent biocompatible, biodegradable material that maintains the chemical properties of embedded substances. Because the process of growing these microneedles is done at standard temperature and pressure, the chemicals that are drawn into them remain perfectly preserved for delivery.
The rate at which compounds are released and the microneedle matrix biodegrades can be controlled at a later stage of the process.
More details from the announcement:
The Tufts researchers successfully demonstrated the ability of the silk microneedles to deliver a large-molecule, enzymatic model drug, horseradish peroxidase (HRP), at controlled rates while maintaining bioactivity. In addition, silk microneedles loaded with tetracycline were found to inhibit the growth of Staphylococcus aureus, demonstrating the potential of the microneedles to prevent local infections while also delivering therapeutics.
The process involves ambient pressure and temperature and aqueous processing. Aluminum microneedle molding masters were fabricated into needle arrays of about 500 µm needle height and tip radii of less than 10 µm. The elastomer polydimethylsiloxane (PDMS) was cast over the master to create a negative mold; a drug-loaded silk protein solution was then cast over the mold. When the silk was dry, the drug-impregnated silk microneedles were removed. Further processing through water vapor annealing and various temperature, mechanical and electronic exposures provided control over the diffusity of the silk microneedles and drug release kinetics.
“Changing the structure of the secondary silk protein enables us to ‘pre-program’ the properties of the microneedles with great precision,” said David L. Kaplan, Ph.D., coauthor of the study, chair of biomedical engineering at Tufts and a leading researcher on silk and other novel biomaterials. “This is a very flexible technology that can be scaled up or down, shipped and stored without refrigeration and administered as easily as a patch or bandage. We believe the potential is enormous.”
Press release: Silk Microneedles Deliver Controlled-Release Drugs Painlessly
Abstract in Advanced Functional Materials: Fabrication of Silk Microneedles for Controlled-Release Drug Delivery