It was at a conference dinner when Nico Voelcker and his colleagues from the Future Industries Institute, University of South Australia, began bouncing around ideas for a new drug delivery method. “On the one hand we had porous silicon microparticles (pSi MPs) – which can be loaded with a multitude of drugs – but they dissolve too quickly for effective delivery,” says Voelcker, Professor of Biomaterials and Nanomedicine. “On the other hand, we had a plasma reactor that is great at coating surfaces. By putting a loudspeaker into the plasma reactor and playing music to generate vibrations, we found that the particles bounced up and down, which resulted in them being coated evenly with a hydrophobic layer.”
It seemed like the perfect match. The pSi MPs store the drug and the plasma acts as a barrier, slowing diffusion and thus release. But what music should be played? AC/DC seemed an obvious (and patriotic) choice, particularly the song “Thunderstruck” as the lightening that occurs in thunderstorms is also a plasma. “Conveniently, ‘Thunderstruck’ possessed an adequate low-frequency beat to sufficiently bounce the pSi MPs in the plasma, without throwing them off and losing yield,” says Voelcker. “But any song would have worked as long as the particles bounced high enough.” After evenly coating pSi MPs with hydrophobic plasma, the researchers were able to fine tune the kinetics of a given drug by increasing or decreasing the coating time (1). “For proof-of-concept, we used the anti-cancer drug Camptothecin – and we achieved up to 100 times slower release rates for the coated pSi MPs versus the uncoated pSi MPs,” says Voelcker. “The pSi network protects the drug payloads from harsh conditions so the system could potentially be used to fabricate a delivery system that houses sensitive payloads.” Voelcker believes that the group can tune the chemistry of the pSi to hold virtually any drug or biomolecule – and they have already contemplated scale up. “pSi can be readily manufactured in high yields (gram quantities), thanks to a new etching technique we developed during the work,” says Voelcker. “Secondly, plasma chambers are used on the industrial scale, so retrofitting them with a shaking system would be a relatively minor procedure.” For the moment, however, there is still much research to be done. Next, the group will be looking to correlate coatings with various hydrophobicities and thicknesses with drug release rates in order to allow for more versatile release profiles of the preloaded drugs. The work has been widely reported by the media, but there is some confusion as to how rock music was involved. Since the group has experimented with a cancer drug, some people have wrongly formed the impression that chemotherapy will be more efficient if you listen to AC/DC while receiving it. “We do not play the music to help release the drug from the pSi MPs when they are being used for treatment; we play the music to fabricate the coated pSi MPs prior to administration,” says Voelcker. “In fact, due to the plasma reactor being run under vacuum, we can’t even hear the song playing whilst we do the coatings!”
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References
- SJ McInnes et al., “‘Thunderstruck’: plasma-polymer-coated porous silicon microparticles as a controlled drug delivery system,” ACS Appl Mater Interfaces, 8, 4467-4476 (2016).
