Silk microneedles allow vaccines to be administered underwater to trout fry weighing 1–2 grammes

Conventional injection is difficult to use with very small trout fry weighing around 1–2 grammes; it is generally more practical once fish reach about 30 grammes. A team from the Massachusetts Institute of Technology (MIT) and the US Department of Agriculture has developed microneedles that could offer an alternative.

The system uses microneedles made from food-grade silk fibroin and coated with a thin layer of shellac. The coating acts as a moisture barrier, preventing the silk from softening before the needles can penetrate the fish’s skin.

For early vaccination, the microneedles adhere to trout fry weighing 1–2 grammes and release their contents while the fish remain underwater. Depending on the design, release can take place in about 15 minutes or continue for up to 24 hours.

The researchers tested the system with bacterial and DNA vaccines. Under dry storage conditions, the microneedles preserved part of the structure of DNA plasmids after four weeks. This stability could reduce reliance on the cold chain, although it still needs to be assessed under production conditions.

The approach is intended to reduce individual handling and make it easier to vaccinate small juveniles. However, the work is an initial demonstration of the system, and the authors say further development is needed before it can be used at commercial scale.

The research was published in ACS Nano under the title Design of Water-Resistant, Food-Grade Microneedles for Fish Injection and Underwater Cargo Delivery.

Reference: doi.org/10.1021/acsnano.6c06013