"Nanotechnology is an exceptionally potent area for biomedical applications," Nick Kotov of Oklahoma State told nanotechweb.org. "However, biocompatibility of the nanoparticles and their toxicological properties remains an open question."
Kotov and colleagues built up their collagen-coated films of CdTe nanoparticles by a layer-by-layer assembly process. They dipped a substrate of glass, silicon or plastic into a solution of poly(diallyldimethylammonium) chloride (PDDA) and then into a dispersion of thioglycerol-capped CdTe nanocrystals. Repeating this cycle resulted in the formation of a number of bilayers of polymer/nanoparticle composite. To add the collagen coating, the scientists dipped a multilayer film with a PDDA-primed surface into a solution of poly(acrylic acid) (PAA) and then into a solution of collagen. Again, they repeated this cycle to build up the desired number of PAA/collagen bilayers. The final film had a layer sequence (PDDA/CdTe/)nPDDA(/PAA/collagen)m.
Atomic-force microscopy revealed that the collagen layer was porous, containing channels with diameters of between 10 and 50 nm. According to the scientists, this is large enough for many important biological molecules to pass between the layer of nanoparticles and the cell culture, while minimizing direct contact.
To test the toxicity of the films, the researchers seeded two types of cells onto both (PDDA/CdTe) multilayers and the (PDDA/CdTe/)nPDDA(/PAA/collagen)m multilayers. Cells cultured onto the (PDDA/CdTe) multilayers did not survive. For one type of cell, the addition of a single PAA/collagen bilayer significantly improved survival, and with five bilayers present the cells covered the entire surface of the film. Although the addition of collagen improved survival for the other type of cell, it did not result in a smoothly attached film of cells. Kotov and colleagues believe this indicates that the biocompatibility factors must be engineered to the cell type.
"A very thin layer of collagen - only three to five bilayers with poly(acrylic) acid - can significantly reduce toxic effects from nanoparticles," said Kotov. "Another finding of importance is that neurons - one of the living cells most sensitive to heavy metals - can successfully adhere and proliferate on the nanostructured surfaces coated with collagen by layer-by-layer assembly."
Biocompatible thin films of semiconductor nanoparticles that are photo- and electroactive could be important in neuroprosthetic devices. "The next step of the research will be the evaluation of the stimulation of neurons via photo- and electroinduced processes in the nanoparticle films," said Kotov.
The scientists reported their work in Nano Letters.