US researchers have created a novel material out of silk protein that can be preprogrammed with biological, chemical, or optical functions, such as mechanical components that change color with strain, deliver drugs, or respond to light. Using a water-based fabrication method based on protein self-assembly, the researchers generated three-dimensional bulk materials out of silk fibroin, the protein that gives silk its durability.

They manipulated the bulk materials with water-soluble molecules to create multiple solid forms, from the nano- to the micro-scale that have embedded, pre-designed functions. Researchers created a surgical pin that changes color as it nears its mechanical limits and is about to fail, functional screws that can be heated on demand in response to infrared light, and a biocompatible component that enables the sustained release of bioactive agents, such as enzymes.

The ability to embed functional elements in biopolymers, control their self-assembly, and modify their ultimate form creates significant opportunities for bio-inspired fabrication of high-performing multifunctional materials. Silk's unique crystalline structure makes it one of nature's toughest materials. Fibroin, an insoluble protein found in silk, has a remarkable ability to protect other materials while being fully biocompatible and biodegradable. The mechanical toughness of silk fibers is probably caused by embedded crystalline units acting as cross links of silk proteins in the fiber.