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Unformatted text preview: Announcements Exam #3: Tuesday evening, 4/22, 7 PM, Coors Event Center (multiple choice as usual) Monday will be a review class No class on Wednesday Prof. Schwartz extra office hours Mon 10-noon Tue noon-2 Biomimetic Adhesives The Palm Beetle's Defense Mechanism Structural Hierarchy of Palm Beetle Feet Hunker down for protection Oil Droplets Left Behind
~100,000 contact pads per beetle. 2m in diameter. Only ~2 L of oil, divided into 100,000 droplets! Sticking force of about 1 g, body mass = 0.01 g Geckos Can Hang by One Foot 1 Structural Hierarchy of Gecko Toes Additive forces from enormous numbers of tiny contacts leads to strong adhesion. Gecko Tape 2 m Gecko tape Univ. of Manchester microfabricated polyimide Clicker Question What do "Gecko Tape", a carbon nanotube forest, and abalone nacre have in common? A: they are superhydrophobic B: they are super-adhesive C: all rely on m-scale structures (or smaller) for their special properties D: they are incredibly tough Biomimetic Construction Strategies Self-Assembly Can we understand and use these principles to design and manufacture advanced materials? Self-Assembly Nanoparticles in Nature
magnetotactic bacterium Biological organisms manufacture extraordinarily tiny, but perfect, materials and devices.
1 m Some organisms contain magnetic particles that they use for navigation. Best known examples are bacteria, but there is evidence that some birds use a similar mechanism for migration. electron microscope image The materials are not created through a complicated manufacturing process; they form spontaneously when the necessary components are introduced. light microscope image This is called self-assembly or self-organization. Magetosomes (specialized organelles): natural magnetic iron oxide nanoparticles surrounded by a lipid membrane. 500 nm 2 Magnetic Nanoparticles Particles are 25100 nm in size The Ultimate in Self-Assembly
Fluid mosaic model of cell membrane
from Human Biology by Daniel Chiras How are they made? 1. A nano-container self-assembles 2. Magnetic substance forms within the nano-container. (1) the organized assembly of small molecules like lipids. (2) folding of proteins into their functional structures. Lipids are "Amphiphilic"
"head" is hydrophilic and can hydrogen bond with water "tail" region is hydrophobic oily, non-polar hydrocarbon
this is an example of a two-tailed amphiphile, one tail is also possible Synthetic Membrane Sheets Lipids spontaneously form bilayer membranes in order to keep the hydrophobic tails from being exposed to water. water hydrophilic heads water hydrophobic tails 12 nm Bilayers wrap around to make closed bags called liposomes. Clicker Question
Which of the following situations is consistent with the amphiphilic nature of the molecules? A B Liposomes Synthetic bilayer "bags" mix amphiphilic molecules with water and stir vigorously. oil water water oil interior aqueous phase Many applications in drug delivery, food, cosmetics, particle synthesis ... Biomimetic strategy: create and utilize a self-assembled nano-container. oil exterior aqueous phase 3 Liposomes Liposomes as NanoContainers Load liposomes with cadmium ions and introduce hydrogen sulfide gas. electron microscope image The gas passes through the membrane and reacts to form cadmium sulfide nanoparticles.
H2S Cd2+ Cd2+ CdS H2S 2080 nm in diameter This is a biomimetic way to control the size of nanoparticles! Stealth Liposomes Liposomes in Drug Delivery
Encapsulating a drug in a liposome permits a lower level of drug in the blood stream. Release can be triggered by heat, sound, pH, etc. Stealth liposome Coated with molecules that cause immune system to ignore it. Control of time release. Targeted liposome Coated with molecules (antibodies) that stick to tumor cells. Deliver drug to specific location. Targeted Liposomes and Tumor Cell tumor cell liposomes Creative Challenge electron microscope image of targeted liposomes bound to an ovarian tumor cell in a mouse 4 Clicker Question Clicker Question Water molecules interact with each other via _______ A: molecular recognition B: hydrogen bonds C: hybridization D: gravity A B C Which of these pictures represents a drop of water on a smooth wax surface? Clicker Question Clicker Question What do superhydrophobic surfaces have in common? A: they are made of wax B: they are made of carbon nanotubes C: they are very smooth D: they are roughly structured at sub-micron length scales Where does a superhydrophobic surface appear in nature? A: lotus leaves B: on polymers C: ear wax 5 ...
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- Spring '04