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Posted: Oct 30, 2017
Of glues and gases: Barnacle adhesion and nanomechanical sensors
(Nanowerk News) Among the diverse research studies being presented at this year’s 64th AVS International Symposium and Exhibition, being held Oct. 29-Nov. 2, 2017, in Tampa, Florida, are two biomaterial interfaces sessions that feature some highly unusual applications of engineering. The first describes the use of stress forces -- more commonly employed to evaluate the failure mechanisms of materials and devices made from them -- to discover how barnacles stick to surfaces. The second explores the development of two novel mechanical systems, both smaller than the eye can see, for use with gas molecules: one to detect them with ultra-high sensitivity and the other to precisely measure their molecular weights.
In the first presentation, biomedical engineer Manuel Figueroa of the College of New Jersey will discuss his research examining the effect of hydrophobicity (resistance to bonding with water) on the adhesive ability of the acorn barnacle, Amphibalanus amphitrite. This species is an abundant and widespread biofouler that is particularly troublesome for the marine shipping industry since a barnacle-encrusted ship hull creates drag on the vessel, reducing its performance and increasing fuel consumption.
To analyze barnacle adhesion in the laboratory, Figueroa allowed the arthropods to attach for two weeks to untreated glass slides representing hydrophilic surfaces as well as glass slides coated with hydrophobic self-assembled monolayers. He then removed the barnacles using a force gauge and calculated the critical shear stress needed to do the job for both sets. Finally, the quantity of glue remaining on the substrates was measured. What Figueroa discovered was that the critical shear stress was significantly higher for the hydrophobic surfaces as was the density of residual glue. The strong correlation, he said, suggests that hydrophobic surfaces may provide a protected environment for the barnacles to release their adhesive and that barnacle release only occurs when this cohesion fails. With further research, these findings may help shipbuilders and others design surfaces that exploit the nonadhesive characteristics.
In the second presentation, nanotechnology researcher Genki Yoshikawa of the National Institute for Materials Science in Japan will discuss the ongoing development and application of two nanometer-scale (billionth of a meter) mechanical devices for the detection and characterization of gas molecules. The first is the membrane-type surface stress sensor (MSS), that utilizes a circular membrane connected by cantileverlike “bridge spans” to a frame with embedded electrical resistors. Gas molecules are detected when they adsorb to the receptor layer coated on the membrane and deform it slightly, thereby perturbing the current flowing through the resistors. The MSS has great potential as a gas sensor, Yoshikawa said, because it is highly sensitive, can be designed to detect specific gases, and offers portability, ease of use and low cost. However, Yoshikawa said that adapting the MSS into a practical consumer mobile/”internet of things” sensor system requires “further optimization and integration of lots of components including receptor layers, hardware including electronics and sample handling, multidimensional data analysis, and precise calibration for high reproducibility.” This, Yoshikawa said, is the mission of an industry-academia-government consortium known as the MSS Alliance.
Yoshikawa also will talk about his group’s research and development of a second nanomechanical system that uses “aero-thermo-dynamic mass analysis” (AMA), to characterize gases by directly measuring their molecular weight in ambient conditions without the vacuum, ionization or bulky instrumentation required by mass spectral analysis. Similar to the deformation method by which MSS detects gas molecules, AMA calculates the molecular weight of a gas species by measuring the mechanical alteration of a simple elastic object placed under a constant flow of the gas. The process can be carried out at the nanoscale as well as the macroscale, allowing AMA sensors to be extremely tiny, portable and capable of being integrated into other devices such as cell phones.
Presentation BI-MoM1, “Characterization of Adult Barnacle Adhesion Upon Reattachment to Hydrophobic Surfaces” by Manuel Figueroa, is at 8:20 a.m. EDT Oct. 30, 2017, in Room 12 in the Tampa Convention Center, Tampa, Florida.
Presentation MN+BI_NS-MoM-3, “Nanomechanical Sensors (MSS, AMA) Toward IoT Olfactory Sensor System” by Genki Yoshikawa, is at 9:00 a.m. EDT Oct. 30, 2017, in Room 24 in the Tampa Convention Center, Tampa, Florida.