Bi-curious cylinders

A team in the US has produced micrometre-wide discs and elongated rods from bi-coloured and multicoloured compartments. The researchers used fluorescent emission studies and scanning electron microscopy to characterise their products.

A simple technique for making microscopic cylinders with multiple compartments and different colours could be used in various applications. Such bi- and multi-coloured particles could be used to develop "intelligent displays" and in drug transport, tissue culture, and bundled biological tests and diagnostics.

However, Joerg Lahann of the Macromolecular Science and Engineering Program at the University of Michigan, Ann Arbor, and colleague, Srijanani Bhaskar, and Jonathon Hitt, and Sei-Won Laura Chang in the Department of Chemical Engineering, describe a more sophisticated motivation and report details of their work in the latest issue of Angewandte Chemie.

Multifunctional colloids have importance to major biomedical applications, such as drug delivery and medical imaging, the team explains. As such methods for controlling size, shape, and surface chemistry are keenly sought by researchers. The Michigan team points out that for biomedical applications it is important to endow such particles with biocompatibility, and they point out that how effectively white blood cells can devour and destroy such particles depends strongly on the size and shape of such particles.

The team has now produced their bicolour microcylinders by pumping two biodegradable polymer - poly(lactide-co-glycolide) (PLGA) from organic solvents - solutions each of a different colour through two side-by-side jets. An electrical field stretches the material as it is extruded, resulting in a bicompartmental fibre that is then "spun" into a bundle of parallel individual fibres. The researchers can then embed the 10 mm long fibre bundles in a gel, which can then be solidified.

The next step is to slice off thin sections from this composite using a microtome. They next dissolve away the gel in water and treat with ultrasound to release bundles of separated cylinders of uniform size. The length of the cylinders depends, the researchers explain, on the thickness of the microtome sections. This makes it possible to produce flat discs and long rods.

The team adds that it is possible to use more than two jets and so produce bundles of three, four, or more different components. Depending on the arrangement of the jets, different patterns can be generated. For example, it is possible to fabricate cylindrical particles that look like a three-section or four-section pie chart. If the jets are positioned next to each other, the result is a striped structure. The individual segments are always identical in size and are clearly delineated.

They can also make specially shaped components by etching away different polymers to different degrees. It is possible, for instance, to selectively dissolve one polymer from a four-component cylinder to produce a rod with a groove.

Colour is not the only property that can be ingrained in the fibres. If the team uses different chemical reagents, such as modified biotin, instead of dyes, they can add biological "anchor sites" to the bundles.

The team explains that the production technique is not only simple, but also cost-effective, reliable, and scalable. They add that the inner structure, aspect ratio, and surface chemistry of the compartmentalised components can be fine-tuned readily by tweaking the parameters of the electrodynamic co-spinning and microcutting processes they use.

"The resulting multicompartmental microcylinders with controlled surface patterns may play an important role in the development of next-generation biomaterials with precisely designable physical and chemical properties," the researchers conclude.