Previous Sharklet-related Publications

Here are some of the earliest publications related to Sharklet, dealing with surface energy and antifouling performance.

Antifouling Performance of Cross-linked Hydrogels: Refinement of an Attachment Model (2011)

While previous studies by the team tested micropattern in various silicones, this study tried to replicate the same performance in hydrogels.

From Biofouling: The Journal of Bioadhesion and Biofilm Research:

A correlation between the attachment density of cells from two phylogenetic groups (prokaryotic Bacteria and eukaryotic Plantae), with surface roughness is reported for the first time. The results represent a paradigm shift in the understanding of cell attachment, which is a critical step in the biofouling process. The model predicts that the attachment densities of zoospores of the green alga, Ulva, and cells of the marine bacterium, Cobetia marina, scale inversely with surface roughness. The size and motility of the bacterial cells and algal spores were incorporated into the attachment model by multiplying the engineered roughness index (ERI_II), which is a representation of surface energy, by the Reynolds number (Re) of the cells. The results showed a negative linear correlation of normalized, transformed attachment density for both organisms with ERI_II · Re (R² = 0.77). These studies demonstrate for the first time that organisms respond in a uniform manner to a model, which incorporates surface energy and the Reynolds number of the organism.

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Engineered antifouling microtopographies: the role of Reynolds number in a model that predicts attachment of zoospores of Ulva and cells of Cobetia marina (2010)

While the previous zoospore study showed that micro-topographies would help prevent the adhesion of plant cells to surfaces. This study uses surface energy and Reynolds numbers to predict similar performance in bacteria.

Here’s the abstract from Biofouling: The Journal of Bioadhesion and Biofilm Research:

A correlation between the attachment density of cells from two phylogenetic groups (prokaryotic Bacteria and eukaryotic Plantae), with surface roughness is reported for the first time. The results represent a paradigm shift in the understanding of cell attachment, which is a critical step in the biofouling process. The model predicts that the attachment densities of zoospores of the green alga, Ulva, and cells of the marine bacterium, Cobetia marina, scale inversely with surface roughness. The size and motility of the bacterial cells and algal spores were incorporated into the attachment model by multiplying the engineered roughness index (ERI_II), which is a representation of surface energy, by the Reynolds number (Re) of the cells. The results showed a negative linear correlation of normalized, transformed attachment density for both organisms with ERI_II · Re (R² = 0.77). These studies demonstrate for the first time that organisms respond in a uniform manner to a model, which incorporates surface energy and the Reynolds number of the organism.

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A model that predicts the attachment behavior of Ulva linza zoospores on surface topography (2010)

Some of the earliest Sharklet related research conducted was on the micropattern itself. Dr. Brennan and his team needed to figure out what arrangements of features would be optimal to stymie bacterial growth. This study measured how well Ulva linza zoospores adhered to a micropatterned surface.

Here’s the abstract from Biofouling: The Journal of Bioadhesion and Biofilm Research:

A predictive model for the attachment of spores of the green alga Ulva on patterned topographical surfaces was developed using a constant refinement approach. This ‘attachment model’ incorporated two historical data sets and a modified version of the previously-described Engineered Roughness Index. Two sets of newly-designed surfaces were used to evaluate the effect of two components of the model on spore settlement. Spores attached in fewer numbers when the area fraction of feature tops increased or when the number of distinct features in the design increased, as predicted by the model. The model correctly predicted the spore attachment density on three previously-untested surfaces relative to a smooth surface. The two historical data sets and two new data sets showed high correlation (R² = 0.88) with the model. This model may be useful for designing new antifouling topographies.

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Systematic variation of microtopography, surface chemistry and elastic modulus and the state dependent effect on endothelial cell alignment (2008)

Systematic evaluation of how variations in elastic modulus, surface chemistry, and height/spacing of micro-ridges interact and effect endothelial cell attachment density, viability and alignment.

Here’s the abstract, from the Journal of Biomedical Materials Research:

We examined how variations in elastic modulus, surface chemistry and the height and spacing of micro-ridges interact and effect endothelial cell (EC) alignment. Specifically, we employed independent control of the surface properties in order to elucidate the relative importance of each factor. Polydimethylsiloxane elastomer (PDMSe) was fabricated with 1.5 or 5 μm tall, 5 μm spaced and 5, 10, or 20 μm wide ridge microtopographies. Elastic modulus was varied from 0.3, 1.0, 1.4, and 2.3 MPa by controlling oligomeric additives and crosslink density. Surface chemistry was left untreated, argon plasma treated, coated with fibronectin (Fn) or patterned with Fn tracks on flat PDMSe or the tops of micro-ridges. Primary porcine vascular ECs were cultured on the PDMSe substrates and nuclear form factor (NFF) was used to determine cell orientation relative to surface microtopography. Experimental results showed that microtopographical variation strongly altered EC alignment on Fn coated surfaces, but not on plasma treated surfaces. Interestingly, similar alignment was achieved with different orientation cues, either micropatterned chemistry (2D) or microtopography (3D). In total, the effect of varying one of the experimental parameters depended strongly on the state of the others, highlighting the need for multi-factor analysis of surface properties for applications where cells and tissue will contact synthetic materials.

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Engineered nanoforce gradients for inhibition of settlement (attachment) of swimming algal spores (2008)

A study on the effect of mechanical force gradients, which is a calculation of the difference between bending moments of two adjacent features; this concept is important in capturing the surface energy effects that may favor or inhibit the settlement of marine organisms. When two adjacent features have different bending moments, cells are subjected to different stress values on either side, creating a possibly difficult environment for settlement. In order to test the concept, a finite element mesh model was used to design micro-patterns with paired features of differing geometries (and different bending moment values); the Sharklet design consists of four different features, thus with three different bending moments. The Sharklet pattern had the lowest microorganism settlement of all surfaces tested.

Here’s the abstract from Langmuir 2008:

Current antifouling strategies are focused on the development of environmentally friendly coatings that protect submerged surfaces from the accumulation of colonizing organisms (i.e., biofouling). One ecofriendly approach is the manipulation of the surface topography on nontoxic materials to deter settlement of the dispersal stages of fouling organisms. The identification of effective antifouling topographies typically occurs through trial-and-error rather than predictive models. We present a model and design methodology for the identification of nontoxic, antifouling surface topographies for use in the marine environment by the creation of engineered nanoforce gradients. The design and fabrication of these gradients incorporate discrete micrometer-sized features that are associated with the species-specific surface design technique of engineered topography and the concepts of mechanotransduction. The effectiveness of designed nanoforce gradients for antifouling applications was tested by evaluating the settlement behavior of zoospores of the alga Ulva linza. The surfaces with nanoforce gradients ranging from 125 to 374 nN all significantly reduced spore settlement relative to a smooth substrate, with the highest reduction, 53%, measured on the 374 nN gradient surface. These results confirm that the designed nanoforce gradients may be an effective tool and predictive model for the design of unique nontoxic, nonfouling surfaces for marine applications as well as biomedical surfaces in the physiological environment.

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Impact of engineered surface microtopography on biofilm formation of Staphylococcus aureus (2007)

First study evaluating the effect of the Sharklet topography on bacterial colonization relevant to medical devices. During the course of 21 days in growth media, the Sharklet topography significantly inhibited the development of S. aureus biofilm compared to the unpatterned control surfaces.

Here’s the abstract, from Biointerphases 2:

The surface of an indwelling medical device can be colonized by human pathogens that can form biofilms and cause infections. In most cases, these biofilms are resistant to antimicrobial therapy and eventually necessitate removal or replacement of the device. An engineered surface microtopography based on the skin of sharks, Sharklet AF^TM, has been designed on a poly(dimethyl siloxane) elastomer (PDMSe) to disrupt the formation of bacterial biofilms without the use of bactericidal agents. The Sharklet AF^TM PDMSe was tested against smooth PDMSe for biofilm formation of Staphylococcus aureus over the course of 21 days. The smooth surface exhibited early-stage biofilm colonies at 7 days and mature biofilms at 14 days, while the topographical surface did not show evidence of early biofilm colonization until day 21. At 14 days, the mean value of percent area coverage of S. aureus on the smooth surface was 54% compared to 7% for the Sharklet AF^TMsurface (p<0.01). These results suggest that surface modification of indwelling medical devices and exposed sterile surfaces with the Sharklet AF^TM engineered topography may be an effective solution in disrupting biofilm formation of S. aureus.