Chitosan — a processed form of chitin, the long-chain polymer commonly found in the exoskeleton of crustaceans — is attracting attention for aiding post-operative wound closure, thanks to its antimicrobial activity and ability to stimulate tissue regeneration. However, fixing chitosan to the target area is not always easy.

Now, Paolo Matteini and colleagues from Italy have shown that laser activation can successfully bond a composite of chitosan and gold nanorods to biological tissue (Adv. Mater. doi:10.1002/adma.201002228; 2010). Light from a near-infrared laser drives an electromagnetic resonance in the gold nanorods, providing the heat required for the bioadhesive process. The result is an efficient laser-activatable bioadhesive for tissue repair and drug delivery.

Credit: © 2010 WILEY

The researchers first doped the chitosan films with gold nanorods (∼60 nm long and 15 nm wide) in an aqueous acidic solution. Evaporation and washing out resulted in pliable films 0.8 cm in diameter and ∼40 μm thick. The gold nanorods exhibited light absorption at wavelengths of 520 nm and 800 nm, so the team chose to use fibre-coupled 810 nm AlGaAs diode lasers because a longer wavelength allows for deeper penetration.

“We used pulses in the millisecond regime to initiate the cascade of physiochemical events leading to the activation of chitosan groups and eventual adhesion with a confining matrix,” Matteini explained.

Preventing the gold nanorods from aggregating is critical for their use in medical applications. Aggregation can cause complicated plasmonic coupling, and may result in poor photothermal conversion efficiency. The team found that the dispersion of gold nanorods within the chitosan network proved to be homogeneous throughout the film when using intermediate chitosan concentrations of 3–4% and gold nanorods densities of less than 200 pM.

The team is now interested in the possibility of precisely securing hybrid nanorod–chitosan films to a variety of biological matter upon laser activation. This may lead to a range of future opportunities for such materials, including advanced tissue repair and localized drug delivery.