Silk MicroRockets Provide Safe Drug Delivery

Microscopic swimming devices made of biodegradable silk have the potential to be used in the human body for drug delivery and location of cancer cells, claims a new study.

Developed by researchers at the University of Sheffield (United Kingdom), the silk microrockets are just 300 microns in length and 100 microns in diameter, the thickness of a single human hair, and create their own thrust by using an entrapped enzyme as a catalyst, allowing them to swim through biologic fluids. According to the researchers, the use of a biodegradable silk fibroin (SF) rocket and enzymatic fuel removes a major barrier to micro-rockets becoming a reality outside of the laboratory.

The silk microrockets are made using a three-dimensional (3D) reactive inkjet printing method that involves a liquid solution of dissolved SF mixed with an enzyme. The solution is then placed into a 3D inkjet printer, which builds up layers of ink to create the rocket. Printing methanol on the printed construct then triggers a reaction that forms a rigid shape, trapping the enzyme within a silk lattice structure. The enzyme acts as a catalyst, reacting with fuel molecules to produce bubbles that propel the rocket forward. The study describing the silk microrockets was published on June 27, 2016, in SMALL.

“By using a natural enzyme like catalase and silk which are fully biodegradable, our devices are far more biocompatible than earlier swimming devices,” said lead author Xiubo Zhao, PhD, of the department of chemical and biological engineering. “The inkjet printing technique also allows us to digitally define the shape of a rocket before it’s produced. This makes it a lot easier to optimize the shape in order to control the way the device swims.”

Reactive inkjet printing allows two different ink solutions to react together to generate a new compound or alternatively, as used by the researchers, to produce a change in polymorphic form of silk. Reactive inkjet printing also shares the advantages of conventional inkjet printing, allowing straightforward manufacture of 3D objects with well-controlled shape and size, for example, by utilizing a layer-by-layer approach.

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