What if I told you that shark skin denticles are paving the way for anti-biofouling materials? It’s true!
Biofouling is the colonization of submerged surfaces by microorganisms (i.e. bacteria) that can have devastating effects on artificial devices used in different fields. You may have heard of biofouling in regards to it impacting submerged parts of a boat or vessel like the hull, propellers, anchors, and fishing gear which can lead to drag, corrosion, and increased fuel consumption. But biofouling represents a major challenge for a variety of industries outside of the marine world including the medical, environmental biotechnology, and industrial fields. For example, biofouling can occur in medical devices such as catheters, dental implants, and biosensors which can lead to implant rejections, biosensor malfunctions, and spread infectious diseases.
Medical devices can often play a vital role in the treatment of a myriad of ailments and are meant to substitute, or restore, biological functions. But synthetic materials used for orthopedics, catheters, infusion lines, vascular stents and grafts, and sutures into an biological environment such as our bodies can trigger what is medically known as a ‘foreign body response’ or FBR. See, the human body is endowed with an uncanny ability to distinguish self from foreign and the implantation of a foreign object into our bodyactivates complex interplay of signaling which leads to the biological encapsulation of said implant; this reaction is known as the FBR. But biomedical devices are prone to surface biofouling as a result of the foreign body response, meaning the clinical lifetime of a device is limited.
Severe biofouling of medical devices is only effectively corrected by the removal and replacement of the device through costly invasive procedures. That’s… well, less than ideal. Therefore the medical community is trying to better understand biofouling and how to reduce the initial bacterial adhesion properties of a surface, since the early attachment of bacteria on material’s surface is a key driver for biofouling.
Enter the sharks. In order to design materials that can combat the negative effects associated with surface biofouling, the world of biomimetic engineering is now looking to shark skin to study the anti-biofouling properties it has. Shark skin, termed placoid scales or dermal denticles, is a rough surface made up of grooves and ridges that apparently exhibits ‘nanostructured protuberances’ that allows them swim with reduced drag and prevents microorganisms from attaching. Previous research has copied this “riblet” dermal denticle pattern, naming it Sharklet AF™ and creating it out of silicone. It turns out The Sharklet AF™ surfaces were found to effectively inhibit bacterial adhesion by 90 %–99 %, depending on the type of bacteria, and reduce biofilm coverage. But researchers wanted to understand how surface topography affects surface properties, which in turn control bacterial attachment and biofilm formation. New research set out to answer this very question.
Scientists collected skin samples from the flank and tail abdomen, pectoral fin, and caudal fin of a shortfin mako shark specimen (Isurus oxyrinchus) from the Pacific waters of Taiwan. The samples were rinsed with large amounts of deionized water and then cleaned with phosphate buffered saline (PBS) to remove any biological residues, like buffer salts. Once dried, the polymeric shark skin patterns were replicated by imprinting from polydimethylsiloxane (PDMS) molds and then gently peeled off. All samples were then gold-coated by a sputter coater before the observation.
The shortfin shark skin exhibited natural self-cleaning and anti-fouling properties. For example, the fast flowing water that passes near the shark skin may help prevent biofouling because it not only doesn’t allow time for any microorganisms to settle but it may help wash away any that do. Other answers may be the epidermal mucus of shark skin, which provides antimicrobial activities, or that shark skin microtopography deters the settlement of microorganisms. It was also found that the microscale topography of shark skin slightly promoted bacterial attachment at an early stage, but prevented bacteria from developing biofilms.
“Our results show that in some cases the early attachment of bacteria is promoted by surface roughness. However, a high roughness completely inhibited the development of biofilms. The present systematic study provides insight into the interaction between bacterial and shark skin microstructures and may support the development of effective solutions for biofilm control,” concluded the study.