Surface Microtopographies Research Articles

Heterogeneous interface engineering of spindle shaped Fe/C through optimizing impedance response for enhanced microwave absorption and thermal conductivity

Heterogeneous interface design is pivotal in creating lightweight, broadband, and high-efficiency electromagnetic wave (EMW) absorption materials. These materials enhance wave absorption by adaptively matching impedance. In this study, spindle-shaped Fe/C nanocomposites with heterogeneous interfaces and diverse surface microtopographies were synthesized by calcining iron-supported metal-organic frameworks (MOFs). During controlled pyrolysis, Fe3+ was reduced by carbon and conversely induced the graphitization of carbon, which is essential for the distribution and appearance of Fe and graphitized carbon as well as for modulating impedance matching. The porous structure of the Fe/C composites and the polarization loss and ferromagnetic resonance from the defective carbon and Fe magnetic particles synergistically enhance the wave absorption performance. The Fe/C-700 nanocomposite achieves a reflection loss (RL) of −55.9 dB at 12.48 GHz with an effective absorption bandwidth (EAB, RL ≤ −10 dB) of 3.9 GHz at 1.8 mm. The Fe/C-900 nanocomposite demonstrates a significant RL of −63.5 dB at 15.8 GHz with an EAB of 4.4 GHz between 13.6 GHz and 18 GHz at 1.5 mm, and an EAB of 5.5 GHz at 1.63 mm. These improvements are attributed to the impedance matching facilitated by the introduction of Fe magnetic particles and graphitized carbon. Additionally, the thermal conduction pathway formed among the Fe/C nanocomposites significantly enhances the thermal conductivity to 0.502 W m−1 K−1. Thus, this work offers a novel approach to the design of advanced wave-absorbing and thermal conductive materials by optimizing impedance through heterogeneous interfaces.

Substrate microtopographies induce cellular alignment and affect nuclear force transduction

Cellular physiology has been mainly studied by using two-dimensional cell culture substrates which lack in vivo-mimicking extracellular environment and interactions. Thus, there is a growing need for more complex model systems in life sciences. Micro-engineered scaffolds have been proven to be a promising tool in understanding the role of physical cues in the co-regulation of cellular functions. These tools allow, for example, probing cell morphology and migration in response to changes in chemo-physical properties of their microenvironment. In order to understand how microtopographical features, what cells encounter in vivo, affect cytoskeletal organization and nuclear mechanics, we used direct laser writing via two-photon polymerization (TPP) to fabricate substrates which contain different surface microtopographies. By combining with advanced high-resolution spectral imaging, we describe how the constructed grid and vertical line microtopographies influence cellular alignment, nuclear morphology and mechanics. Specifically, we found that growing cells on grids larger than 10 × 20 μm2 and on vertical lines increased 3D actin cytoskeleton orientation along the walls of microtopographies and abolished basal actin stress fibers. In concert, the nuclei of these cells were also more aligned, elongated, deformed and less flattened, indicating changes in nuclear force transduction. Importantly, by using fluorescence lifetime imaging microscopy for measuring Förster resonance energy transfer for a genetically encoded nesprin-2 molecular tension sensor, we show that growing cells on these microtopographic substrates induce lower mechanical tension at the nuclear envelope. To conclude, here used substrate microtopographies modulated the cellular mechanics, and affected actin organization and nuclear force transduction.

Surface microtopography construction and osteogenic properties evaluation of bulk polylactic acid implants

In this study, polylactic acid (PLA) microspheres were used as the raw material to construct bulk implants with surface microtopography through hot pressing and heat treatment, and the microtopographical structures were regulated through the sizes of the PLA microspheres. The surface microtopographies of PLA implants were successfully constructed using micron-sized bulges, which showed a wave-like structure. The ridge width of bulges ranged from 1.64 ± 0.16 µm to 82.52 ± 14.38 µm and the valley depth ranged from 0.49 ± 0.07 µm to 37.35 ± 6.78 µm according to the sizes of microspheres. The nanoindentation tests showed that the modulus and hardness of PLA implants were gradually increased with the decrease in microsphere sizes. The surface microtopography resulted in a slight increase in the hydrophobicity of the PLA implants, but no significant differences were observed. Cells cultured on the implant surface with microtopography exhibited varying morphological responses, and significantly increased osteogenic activity was observed relative to a PLA flat film. This study demonstrated that the surface microtopography derived from PLA microspheres could regulate cellular response and activate osteogenic properties of PLA implants.

Spatial analysis of eroding surface micro-topographies

Analysis of the spatial variability in erosion rates at the micro-scale has the potential to improve our understanding of how shore platforms erode. Comparing the erosion rate of a single measurement reading with the erosion rate of other increasingly distant readings would indicate whether average variation in erosion rate is homogeneous and at what spatial scale. Little variation in erosion rate from one measurement reading as distance increased would indicate that an area is eroding homogeneously and that the surface measured is responding as a single spatial unit. An increase or decrease in the variation in erosion rate difference with increasing distance from one reading would suggest that the area was not acting as a single spatial unit and that surface responses differ with scale. This study used a two-year dataset of traversing micro-erosion meter (TMEM) readings, collected from two limestone shore platforms on the north of Malta, at Ponta tal-Qammieħ and Blata l-Bajda, in order to explore the relationship between difference in erosion rate and distance from TMEM readings. A Microsoft Excel macro was developed and applied to calculate and analyse the average variation in erosion rate difference between all possible pairs of measurement readings over a set of fixed distances. The resultant analysis suggests that there are some consistent patterns between measurement periods and locations on a platform in terms of how erosion rate difference varies with distance between readings. These are not simple relationships to either characterise or explain but nevertheless, they suggest variations in how the same surface responds to erosional forces. These findings are significant for erosion research as they imply that spatial scales to erosion within even small areas may impact upon the representativeness of an average erosional loss for the platform site. It raises issues about how representative rates really are and contributes to the discussion about the wider understanding of erosion rates across spatial scale.

Laser structuring with DLIP technology of tungsten carbide with different binder content

In machining, tool wear is one of the main influence factors for the resulting quality of the product. Several wear mechanisms have to be addressed to prevent unwanted deterioration of the tool integrity. For aluminium alloys, adhesion of the workpiece material on the cutting tool is one of the most challenging wear mechanisms. Engineering surface microtopographies has been proved as a convenient strategy to tackle this issue. Particularly, the direct laser interference patterning (DLIP) technique enables the integration of periodic structures on the micrometer or sub-micrometer scale. In this study the structuring of tungsten carbide with different cobalt content is presented. The interference of two laser beams leads to periodic line-like structures with a spatial period of 5.5 µm. A maximum structure depth of 2.2 µm is reached by controlling the processing parameters. Moreover, the wettability of the structured samples was analyzed by contact angle measurements with selected cooling lubricants, revealing a hydrophilic behavior with a decreased contact angle of 10°. This work gives an insight into the possibilities of structuring tungsten carbide materials with a picosecond laser source in combination with an innovative beam shaping setup from the point of view of an analysis to explore the formation of structured surfaces and their wetting behavior with cooling lubricants.

Tribocorrosion investigation of 316L stainless steel: the synergistic effect between chloride ion and sulfate ion

Tribocorrosion is a failure phenomenon which involves synergistic effect of electrochemical corrosion and mechanical wear. It usually results into early failure of mechanical components than simple wear and corrosion. Chloride (Cl−) and sulfate ions are often found together in corrosive media. In this study, the synergistic effect of Cl− and on tribocorrosion of 316L stainless steel was studied by changing the ratio of /Cl− in corrosive solution from 0.31 M : 0 to 0 : 0.62 M. The stainless steel was worn against with a ZrO2 sphere. The coefficient of friction (COF), material loss volume, surface micro-topographies and surface chemical composition in different solutions were compared to explore the synergism between and Cl−. The results indicated that the mix of Cl− and reduced material loss volume by a quarter when compared with that in pure Na2SO4 or NaCl solution. More than half of material loss was caused by the synergism between wear and corrosion in mixing solutions. The synergistic effect between and Cl− could promote the transmission of metal into oxides. This had two effects on tribocorrosion. First, the existence of oxides would cause abrasion which accelerated wear-affected corrosion and enhanced mechanical wear (corrosion-affected wear). On the other side, the transmission of metal into oxides benefited for the formation of tribo-film. The flexible stainless steel needed to coordinate deformation with the tribo-film which had relatively low deformability. This aggravated deformation of stainless steel and promoted surface work-hardening effect. It was helpful for stainless steel to resist wear, thus, the corrosion-affected wear was decreased.

Shape anisotropy-governed locomotion of surface microrollers on vessel-like microtopographies against physiological flows

Surface microrollers are promising microrobotic systems for controlled navigation in the circulatory system thanks to their fast speeds and decreased flow velocities at the vessel walls. While surface propulsion on the vessel walls helps minimize the effect of strong fluidic forces, three-dimensional (3D) surface microtopography, comparable to the size scale of a microrobot, due to cellular morphology and organization emerges as a major challenge. Here, we show that microroller shape anisotropy determines the surface locomotion capability of microrollers on vessel-like 3D surface microtopographies against physiological flow conditions. The isotropic (single, 8.5 µm diameter spherical particle) and anisotropic (doublet, two 4 µm diameter spherical particle chain) magnetic microrollers generated similar translational velocities on flat surfaces, whereas the isotropic microrollers failed to translate on most of the 3D-printed vessel-like microtopographies. The computational fluid dynamics analyses revealed larger flow fields generated around isotropic microrollers causing larger resistive forces near the microtopographies, in comparison to anisotropic microrollers, and impairing their translation. The superior surface-rolling capability of the anisotropic doublet microrollers on microtopographical surfaces against the fluid flow was further validated in a vessel-on-a-chip system mimicking microvasculature. The findings reported here establish the design principles of surface microrollers for robust locomotion on vessel walls against physiological flows.

Geckos cling best to, and prefer to use, rough surfaces

BackgroundFitness is strongly related to locomotor performance, which can determine success in foraging, mating, and other critical activities. Locomotor performance on different substrates is likely to require different abilities, so we expect alignment between species’ locomotor performance and the habitats they use in nature. In addition, we expect behaviour to enhance performance, such that animals will use substrates on which they perform well.MethodsWe examined the associations between habitat selection and performance in three species of Oedura geckos, including two specialists, (one arboreal, and one saxicolous), and one generalist species, which used both rocks and trees. First, we described their microhabitat use in nature (tree and rock type) for these species, examined the surface roughnesses they encountered, and selected materials with comparable surface microtopographies (roughness measured as peak-to-valley heights) to use as substrates in lab experiments quantifying behavioural substrate preferences and clinging performance.ResultsThe three Oedura species occupied different ecological niches and used different microhabitats in nature, and the two specialist species used a narrower range of surface roughnesses compared to the generalist. In the lab, Oedura geckos preferred substrates (coarse sandpaper) with roughness characteristics similar to substrates they use in nature. Further, all three species exhibited greater clinging performance on preferred (coarse sandpaper) substrates, although the generalist used fine substrates in nature and had good performance capabilities on fine substrates as well.ConclusionWe found a relationship between habitat use and performance, such that geckos selected microhabitats on which their performance was high. In addition, our findings highlight the extensive variation in surface roughnesses that occur in nature, both among and within microhabitats.

Dynamic characteristics of gear system under different micro-topographies with the same roughness on tooth surface

The topography of gear meshing interfaces is one of the key factors affecting the dynamic characteristics of the gear transmission system. In order to obtain the contact characteristics of meshing gear pair with different surface micro-topographies, an interface feature model and a tribo-dynamics coupling model for the gear system are proposed in this paper. The effects of the gear tooth surface micro-topography on the oil film distribution, contact damping and friction are considered. The time-varying meshing stiffness and the static transmission error are included in the abovementioned models. An exemplary gear pair is analyzed using the proposed models to investigate the influence of the surface micro-topography on the dynamic characteristics of gear system under different micro-topographies and input torque conditions. Simulation results show that the effects of gear tooth micro-topography on the gear dynamic responses (including the friction and the vicious damping at the gear meshing interface and the vibration in the direction of offline of action) are highly dependent on the regularity of tooth surface. The vibration and noise can be significantly controlled by manufacturing a regular gear tooth profiles instead of random profiles.

Feasibility investigation on ductile machining of single-crystal silicon for deep micro-structures by ultra-precision fly cutting

Single-crystal silicon is a widely used brittle material in infrared optics and optoelectronics industries. However, due to its extremely low fracture toughness, it is difficult to obtain deep micro-structures on single-crystal silicon with ultra-smooth surface quality using previous ductile machining models based on plunge cutting, diamond milling and grinding. Current methods to enhance the machinability of silicon include laser-assisted machining, ion implantation modification and vibration-assisted machining. However, the increase of the ductile machining depth using these methods is still very small in the fabrication of deep micro-structures with a depth over tens of micrometers on silicon. This paper proposes a novel ductile machining model for ultra-precision fly cutting (UPFC) to efficiently fabricate deep micro-structures on silicon. The modeling results show that through configuring a large swing radius, much deeper ductile machining depth can be reached by UPFC. To confirm this proposed model, micro-grooves with different depths were machined, and the surface micro-topographies, form error, tool wear patterns and material phase transformation were analyzed and compared with that acquired by diamond sculpturing method. The experimental results demonstrated that much deeper micro-grooves (over tens of micrometers) with better surface quality were acquired by UPFC. Moreover, compared with the sculpturing method, UPFC prolonged the tool life, and generated less amorphous silicon on the machined surface.

Aging effects of ultraviolet lights with same dominant wavelength and different wavelength ranges on a hydrocarbon-based polymer (asphalt)

To investigate the effects of different wavelength ranges of UV lights on chemical compositions and macro-properties of asphalt, three UV lights were used to conduct the aging test of asphalt for 1–288 h. The elemental analysis and Fourier transform infrared spectroscopy (FTIR) were performed to analyze the chemical changes of asphalt, the surface micro-topographies of asphalt before and after UV aging were studied by atomic force microscopy (AFM). In addition, the physical performance, viscosity and rheological performance of asphalt was studied with softening point test and dynamic shear rheometer (DSR), respectively. The chemical compositions and structures analyses show that the oxidation mechanism exists during the UV aging of asphalt binder. The numbers of bee-like structures in AFM height figures decrease obviously after UV aging, meanwhile the sizes of which increase. The relationships of RCC, RCS and SPI values with UV expose time follow a power function model in the first 24 h, while follows a liner model after 24 h. UV lights with different wavelength ranges have significantly different effects on the chemical compositions and macro-properties of asphalt. The UV 350–370 nm has the most obvious aging effect on asphalt binder, second is the UV 340–380 nm, the UV 200–400 nm has the lightest aging effect.

Effect of tillage on soil erosion before and after rill development

AbstractTillage has a large effect on soil surface microtopography and consequently on soil erosion. Here, we measured soil and water loss from soil prepared by contour tillage (CT) and reservoir tillage (RT), and to analyse why tilled slopes produce more sediment run‐off. Rainfall experiments (90 mm/hr) were carried out to simulate the overland and rill flow erosion processes. Soil type is silt clay loam. Results showed that CT and RT reduced surface run‐off by 60% compared with a smooth slope during overland flow, whereas only a small reduction in run‐off occurred during rill flow. Sediment erosion from CT was reduced by about 30–60% compared with a smooth slope for both overland and rill flow erosion processes. Although RT also resulted in reduced sediment erosion during overland flow, sediment erosion increased by 25% during rill flow, leading to an overall increase in sediment flow on the RT‐treated slope. For slopes with CT, sediment production depends on the ridges, but furrows limit sediment transport. For slopes with RT, sediment production depends on the depressions, but once the depressions fill with sediment, rainwater outflowing from the depressions cause rill flow erosion and greater sediment loss compared with CT. Our results suggest that sediment and run‐off differences for different surface microtopographies induced by tillage are significant, especially during the rill flow erosion process. Future studies should address rill erosion on tilled sloped land with different microtopographies to better determine how rills are triggered and change during rainfall.

Analysis of volume ratio of castor/soybean oil mixture on minimum quantity lubrication grinding performance and microstructure evaluation by fractal dimension

As a non-edible, degradable, and environment-friendly crop product, castor oil can be used as lubricating oil in material processing. However, its high viscosity results in poor flowability, thereby limiting its industrial applications. Although experiments have revealed the excellent lubrication performance of castor/soybean oil mixture, the volume ratio of castor oil and soybean oil can significantly influence their minimum quantity lubrication (MQL) grinding performance. In the current study, seven castor/soybean oil mixtures under different volume ratios ranging between 1:0.5 and 1:4 were prepared for MQL grinding of Ni-based alloy. The mixed oils were compared with pure castor oil (1:0) in terms of viscosity and tribological behaviors. The grinding experiment involved the evaluation of specific grinding force, surface roughness, surface microtopography, and grinding debris, conluding that the preferred castor/soybean volume ratios were found to be 1:0.5, 1:1, 1:1.5, and 1:2. The surface microtopographies of selected workpieces were analyzed further in terms of their fractal dimension and scale coefficient, finding that the maximum fractal dimension (D=1.31) and minimum scale coefficient (G=0.30) are achieved when the volume ratio is 1:2. Hence, the optimal volume ratio is determined.

Sensing of micropillars by osteoblasts involves complex intracellular signaling

Topographical material surface features are sensed by cells and provoke a large range of cellular responses. We recognized earlier, that at micropillar topographies in the range of 5 µm, the osteoblasts attempt to phagocytize the pillars resulted in increased energy requirements and reduced osteoblast marker expression, e.g., collagen type I and osteocalcin. However, the precise cellular signaling transducing the topographic information into the cell and evoking phagocytic processes remained unknown. Here, we could show that the RhoA/ROCK signaling is involved in the transduction of the topography-mediated cellular reactions. After inhibition of ROCK-2 with Y27632 for 24 h, no caveolae-mediated micropillar assembly of the cell membrane domain component caveolin-1 (Cav-1) was found. ROCK inhibition was also able to attenuate the pillar-induced decrease in β-actin. Interestingly, phosphatidylinositol 3-kinase (PI3K) inhibition with LY294002 for 24 h did not influence the Cav-1 clustering on micropillars. Our results illustrate the importance of the integrin down-stream signaling of RhoA/ROCK in the recognition of and adaption to surface microtopographies by osteoblasts and extend our understanding about the complex mechanism of action inside the cells.Graphical abstract

Micro-Topographies Promote Late Chondrogenic Differentiation Markers in the ATDC5 Cell Line

Chemical and mechanical cues are well-established influencers of in vitro chondrogenic differentiation of ATDC5 cells. Here, we investigate the role of topographical cues in this differentiation process, a study not been explored before. Previously, using a library of surface micro-topographies we found some distinct patterns that induced alkaline phosphatase (ALP) production in human mesenchymal stromal cells. ALP is also a marker for hypertrophy, the end stage of chondrogenic differentiation preceding bone formation. Thus, we hypothesized that these patterns could influence end-stage chondrogenic differentiation of ATDC5 cells. In this study, we randomly selected seven topographies among the ALP influencing hits. Cells grown on these surfaces displayed varying nuclear shape and actin filament structure. When stimulated with insulin-transferrin-selenium (ITS) medium, nodule formation occurred and in some cases showed alignment to the topographical patterns. Gene expression analysis of cells growing on topographical surfaces in the presence of ITS medium revealed a downregulation of early markers and upregulation of late markers of chondrogenic differentiation compared to cells grown on a flat surface. In conclusion, we demonstrated that surface topography in addition to other cues can promote hypertrophic differentiation suitable for bone tissue engineering.

Engineering microdent structures of bone implant surfaces to enhance osteogenic activity in MSCs

Problems persist with the integration of hip and dental implants with host bone tissues, which may result in long-term implant failure. Previous studies have found that implants bearing irregular surfaces can facilitate osseointegration. An improvement to this approach would use implant surfaces harboring a well-defined surface microstructure to decrease variability in implant surfaces. In this study, we tested whether well-defined surfaces with arrays of microdents (each with depth approximately 3µm) significantly affected the morphology, proliferation, and osteogenic activity of mesenchymal stem cells (MSCs). Arrays of microdents tested had diameters of 9µm, 12µm, and 18µm, while spacing between arrays ranged from 8µm to 34µm. Effects on MSC morphology (cell spreading area) and proliferation were also quantified, with both significantly decreasing on micropatterned surfaces (p<0.05) on smaller and denser microdents. In contrast, MSCs were found to deposit more calcified matrix on smaller and denser arrays of microdents. MSCs on a pattern with arrays of microdents with a diameter of 9µm and a spacing 8µm deposited 3–4 times more calcified matrix than on a smooth surface (p<0.05). These findings show that well-defined surface microtopographies promote osteogenic activity, which can be used on implant surfaces to improve integration with the host bone tissue.

The Use of Focus-Variation Microscopy for the Assessment of Active Surfaces of a New Generation of Coated Abrasive Tools

Abstract In this paper, the selected results of measurements and analysis of the active surfaces of a new generation of coated abrasive tools obtained by the use of focus-variation microscopy (FVM) are presented and discussed. The origin of this technique, as well as its general metrological characteristics is briefly described. Additionally, information regarding the focus variation microscope used in the experiments - InfiniteFocus® IF G4 produced by Alicona Imaging, is also given. The measurements were carried out on microfinishing films (IMFF), abrasive portable belts with Cubitron™ II grains, and single-layer abrasive discs with Trizact™ grains. The obtained results were processed and analyzed employing TalyMap 4.0 software in the form of maps and profiles, surface microtopographies, Abbott- Firestone curves, and calculated values of selected areal parameters. This allowed us to describe the active surfaces of the coated abrasive tools, as well as to assess the possibility of applying the FVM technique in such kinds of measurements.

Engineering bio-inspired surface microstructures to control bacterial adhesion and biofilm growth

Event Abstract Back to Event Engineering bio-inspired surface microstructures to control bacterial adhesion and biofilm growth Dalal Asker1, 2, Nicolas Lavielle1 and Benjamin Hatton1 1 University of Toronto, Materials Science and Engineering, Canada 2 Alexandria University, Food Science & Technology Department, Egypt Introduction: Bacteria are highly effective at populating living or inanimate surfaces, which causes significant problems in the healthcare industry, such as hospital-acquired infections, and persistent biofilm infection of medical devices. There is much to learn on the roles of surface topology at nano and micro scales, wettability and local adhesion forces on bacterial attachment and growth. This talk will present recent results on non-wetting materials engineered to prevent bacterial attachment, based on superhydrophobic surface microtopographies[1]. Further, we have designed a novel class of ultra low-adhesion surfaces that incorporate a micron-scale thick lubricant layer immobilized at a surface, inspired by the Nepenthes pitcher plant[2],[3]. Materials and Methods: Herein we demonstrate the role for superhydrophobic non-wetting surfaces to control (short-term) cell attachment, and the role of surface feature size on cellular attachment. Micropost arrays were molded in polyurethane (PU) with increasing diameter, from 300 nm to 20 µm, from Si masters etched by photolithography. Samples were exposed to P. aeruginosa and E. coli for 5 min contact time, and compared to flat PU and commercial medical gloves. Silicone-based ‘slips’ samples were exposed to continuous flow culture of P. aeruginosa for up to 30 days. Results and Discussion: We have modelled bacterial cell attachment as particles acting under a balance of local surface tension forces[1]. Superhydrophobic surfaces, also bio-inspired based on non-wetting natural surfaces, were found to be highly effective to prevent bacterial cell attachment (reduced from 104 to 100 cells/mm2), when the micropost diameter was smaller than the cell size (1.5 µm or less), which points to a new paradigm of antimicrobial surface design. Silicone-based ‘slips’ surfaces were also found to effectively prevent bacterial cell adhesion (3 log to 4 log reduction in CFU), due to the inert, stabilized surface liquid interface (Fig 1)[4]. Conclusions: Engineering non-wetting microstructured surfaces can effectively prevent bacterial attachment by physical mechanisms, and can be effective for a broad range of cell types. As a result, these are not biologically-specific and are not susceptible to resistance. Figure 1. Suppression of bacterial cells attachment and biofilm formation by SLIPS under continuous flow conditions for up to 30 days. (A) Fluorescence imaging of P. aeruginosa overproducing Psl biofilm attached to the micro-structured PDMS control (a-e), and micro-structured PDMS SLIPS (f-l) surfaces, respectively.

Biomimicking micropatterned surfaces and their effect on marine biofouling.

When synthetic materials are submerged in marine environments, dissolved matter and marine organisms attach to their surfaces by a process known as marine fouling. This phenomenon may lead to diminished material performance with detrimental consequences. Bioinspired surface patterning and chemical surface modifications present promising approaches to the design of novel functional surfaces that can prevent biofouling phenomena. In this study, we report the synergistic effects of surface patterns, inspired by the marine decapod crab Myomenippe hardwickii in combination with chemical surface modifications toward suppressing marine fouling. M. hardwickii is known to maintain a relatively clean carapace although the species occurs in biofouling communities of tropical shallow subtidal coastal waters. Following the surface analysis of selected specimens, we designed hierarchical surface microtopographies that replicate the critical features observed on the crustacean surface. The micropatterned surfaces were modified with zwitterionic polymer brushes or with layer-by-layer deposited polyelectrolyte multilayers to enhance their antifouling and/or fouling-release potential. Chemically modified and unmodified micropatterned surfaces were subjected to extensive fouling tests, including laboratory assays against barnacle settlement and algae adhesion, and field static immersion tests. The results show a statistically significant reduction in settlement on the micropatterned surfaces as well as a synergistic effect when the microtopographies are combined with grafted polymer chains.

Mineralization and bone regeneration using a bioactive elastin-like recombinamer membrane

The search for alternative therapies to improve bone regeneration continues to be a major challenge for the medical community. Here we report on the enhanced mineralization, osteogenesis, and in vivo bone regeneration properties of a bioactive elastin-like recombinamer (ELR) membrane. Three bioactive ELRs exhibiting epitopes designed to promote mesenchymal stem cell adhesion (RGDS), mineralization (DDDEEKFLRRIGRFG), and both cell adhesion and mineralization were synthesized using standard recombinant protein techniques. The ELR materials were then used to fabricate membranes comprising either a smooth surface (Smooth) or channel microtopographies (Channels). Mineralization and osteoblastic differentiation of primary rat mesenchymal stem cells (rMSCs) were analyzed in both static and dynamic (uniaxial strain of 8% at 1 Hz frequency) conditions. Smooth mineralization membranes in static condition exhibited the highest quantity of calcium phosphate (Ca/P of 1.78) deposition with and without the presence of cells, the highest Young's modulus, and the highest production of alkaline phosphatase on day 10 in the presence of cells growing in non-osteogenic differentiation medium. These membranes were tested in a 5 mm-diameter critical-size rat calvarial defect model and analyzed for bone formation on day 36 after implantation. Animals treated with the mineralization membranes exhibited the highest bone volume within the defect as measured by micro-computed tomography and histology with no significant increase in inflammation. This study demonstrates the possibility of using bioactive ELR membranes for bone regeneration applications.