Surface Matters

A scanning electron microscope shows the micro- and nano-structures of the Hoowaki bio-grip micro-pattern.

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Tire, golf ball, moth, felt, pearl, cell. All have at least one thing in common: surface.

As a former peach farmer, I know about peach fuzz. It’s not just about the irritation imparted to the folds of one’s skin following hours of picking in the summer heat. A peach has special powers. The tiny hairs on its surface endow the peach with the ability to suspend water droplets atop the hairs so that the main surface retains airflow. That fuzzy topology sheds water and reduces the fruit’s tendency to prematurely develop brown rot fungus.

Consider the example of a bird egg. Its surface seems completely solid but it is actually covered with thousands of tiny pores that permit gas exchange for the growing chick. While great high magnification images may be found, you do not need a powerful microscope to recognize this. All have observed the gas bubbles being expressed from inside when preparing a boiled egg.

Humans have been engineering surface performance for a very long time. However, the meaning of “surface” is being continually redefined to include smaller and smaller features. Nanomaterials have been in the news for several years, such as hydrophobic surfaces, adorned with nano-scale pillars or cones. A recent report in Nature Materials explored the antifogging properties of insect eyes and self-cleaning surfaces of insect wings. Scientists thereafter produced a surface studded with nano-cones. As with prior experiments, the surface repelled water droplets. But this time, even fog droplets were expelled. The nano-features were so closely spaced that condensing water droplets were “pinched” between conical tops, and grew to become large spheres perched atop cone-like spikes, like a balloon resting on a wire brush.

A second March report in C&E News examined tooth enamel at the nanometer level. Researchers concluded that all teeth appear like a network of tall, laterally connected bristles (think wood fiber). The unique pillar-like microstructure permits the tooth to provide an extremely hard exterior while resisting fracture by absorbing and sharing energy during chewing. Chemists, armed with this understanding, have approximated an enamel structure by growing zinc oxide pillars (nanowires) that exhibit flexibility in a stiff ceramic-like structure.

Surface engineering is important in South Carolina. Many readers know that Hoowaki is the world leader in the design of micro-surfaces. Several companies have reported super slippery surfaces and super hydrophobic surfaces (the lotus leaf effect). But Hoowaki is instead focusing on developing micro-surfaces that can adhere to exceptionally slippery surfaces. Hoowaki studied mountain goat hooves to understand the physics of such remarkable frictional adhesion, and then set out to recreate bumpy micro-textures. The result is a “micro-grip” feature that may enable the secure and precise positioning of medical implants. For example, a tubular vascular stent, used to treat heart disease, is prone to shift along a vessel wall. Hoowaki aims to impart their gripping surfaces to such implanted medical devices to eliminate migration problems without a clinician resorting to other anchoring methods such as sutures.

Kiyatec was founded to provide better understanding of the influence of surfaces on cell growth (surface versus bulk effects). Prior to their entry, laboratory testing was performed on flat transparent surfaces. Traditional 2-D Petri dish cultures could not model the complex interaction of real world tissue. Matt Gevaert developed 3-D cell culture vessels to provide a better mimic of tissue growth behavior in the body. Kiyatec has advanced clinical understanding of 3-D tissue surfaces by culturing different tissue types, even biopsy-derived tumors. Living tissues can be observed along different axes, and being able to replicate a tumor in different test containers permits evaluation of multiple treatment options. This enables personalized understanding of the most effective drug options for cancer before an actual patient exposure.

Ionbond IHI in Duncan engineers surfaces against wear. Tooling has clear advantages over wear, from turbine blades to prosthetic implants. While the company hosts a range of surface modification, including laser hardening and plasma deposition, the truly interesting innovation is Ionbond’s recent development of carbon film deposition. The company can now affix tetrahedral carbon to tool surfaces. Tetrabond pyramidal coatings provide extremely hard diamond-like carbon surfaces up to 1.5 µm. Hmm, a diamond drill bit?

Whether inspecting a pearl for authenticity, protecting a car finish, or seeking traction on a slick roadway, surface is important. South Carolina has a growing ability in surface engineering. Materials science is swiftly becoming a core strength in this state.


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