Hybrid Silica - A Biocompatible, Green Material
HST’s materials are based on amorphous silica, a highly versatile, thermally stable and “green” material. As a platform for nanoscale architectures, silica has attractive chemical properties: the water soluble material can be used to encapsulate both hydrophilic and hydrophobic organic substances, silica surfaces can be readily functionalized, and silica is compatible both with biological systems as well as with the silicon processing technology used in the electronics industry.
Silicon is one of the most abundant elements on earth, but it is predominantly found bonded to oxygen as silica. Silica (silicon dioxide or SiO2) is the natural oxide formed when the element silicon is exposed to oxygen. Silica exists in a number of forms. The crystalline forms include quartz and other high temperature forms, and the amorphous forms include glasses and biosilicates such as diatoms.
It takes energy and processing to covert silica into the pure crystalline form of silicon that is used in electronics and solar panels. “Silicone” is often mistakenly referred to as silicon. Silicones are generally rubbery polymers that include silicon and other elements that are frequently used in nonstick cookware and sealants.
Silica nanoparticles are present in the cell walls of various plants (including edible ones such as string beans and plants used to make beverages such as beer). Biogenic silica is amorphous in contrast to the crystalline forms, which can be dangerous if inhaled. Amorphous silica particles are added as anti-caking agents in foods, pharmaceuticals and nutraceuticals.
Our work to functionalize silica surfaces with organic compounds and to adjust the accessibility of internal interfaces is inspired by nature, particularly by diatoms, the single-cell algae occupying the bottom of the ocean’s food chain. Diatoms are characterized by siliceous cell walls, which often form beautiful patterns. Diatoms have evolved over time to extract silicic acid from seawater and to assemble the converted silica into precise structures that support the processes that sustain life. (image at right)
