This 6 minute long MP4-video presents some key results of the European research project "BioCombs4Nanofibers" to the broader public. Inspired by nature, some concepts of certain types of spiders are transferred to technology in order to develop bacteria-repellent surfaces through laser surface nanostructuring. Funding notice: This study was funded by the European Union's research and innovation program under the FET Open grant agreement No. 862016 (BioCombs4Nanofibers, http://biocombs4nanofibers.eu ). This video is published under the Creative Commons - CC BY - Attribution 4.0 International license, https://nbn-resolving.org/urn:nbn:de:kobv:b43-549394 A video stream can be found at https://download.jku.at/org/7kM/xyU/BioCombs4Nanofibers/D5.6_video%20for%20the%20broader%20public_23.03.2022.mp4
Nanofibers are drawing the attention of engineers and scientists because their large surface-to-volume ratio is favorable for applications in medicine, filter technology, textile industry, use in lithium-air batteries and in optical sensors. However, when transferring nanofibers to a technical product in the form of a random network of fibers, referred to as non-woven fabric, the stickiness of the freshly produced and thus fragile nanofiber non-woven remains a problem. This is mainly because nanofibers strongly adhere to any surface because of van der Waals forces. In nature, there are animals that are actually able to efficiently produce, process, and handle nanofibers: cribellate spiders. For that, the spiders use the calamistrum, a comb-like structure of modified setae on the metatarsus of the hindmost (fourth) legs, to which the 10 – 30 nm thick silk nanofibers do not stick due to a special fingerprint-like surface nanostructure. In this work, we present a theoretical model of the interaction of linear nanofibers with a sinusoidal corrugated surface. This model allows a prediction of the adhesive interaction and, thus, the design of a suitable surface structure to prevent sticking of an artificially non-woven of nanofibers. According to the theoretical prediction, a technical analogon of the nanoripples was produced by ultrashort pulse laser processing on different technically relevant metal surfaces in the form of so-called laser-induced periodic surface structures (LIPSS). Subsequently, by means of a newly established peel-off test, the adhesion of an electrospun polyamide fiber-based non-woven was quantified on such LIPSS-covered titanium-alloy and steel samples, as well as on polished (flat) control samples as reference. The latter revealed that the adhesion of electrospun nanofiber non-woven is significantly lowered on the nanostructured surfaces than on the polished surfaces.
We present a novel approach for tailoring the laser induced surface topography upon femtosecond (fs) pulsed laser irra-diation. The method employs spatially controlled double fs laser pulses to actively regulate the hydrodynamic microfluid-ic motion of the melted layer that gives rise to the structures formation. The pulse train used, in particular, consists of apreviously unexplored spatiotemporal intensity combination including one pulse with Gaussian and another with periodic-ally modulated intensity distribution created by Direct Laser Interference Patterning (DLIP). The interpulse delay is appro-priately chosen to reveal the contribution of the microfluidic melt flow, while it is found that the sequence of the Gaussianand DLIP pulses remarkably influences the surface profile attained. Results also demonstrate that both the spatial intens-ity of the double pulse and the effective number of pulses per irradiation spot can further be modulated to control theformation of complex surface morphologies. The underlying physical processes behind the complex patterns’ generationwere interpreted in terms of a multiscale model combining electron excitation with melt hydrodynamics. We believe thatthis work can constitute a significant step forward towards producing laser induced surface structures on demand by tail-oring the melt microfluidic phenomena. ].
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The fabrication of complex, reproducible, and accurate micro-and nanostructured interfaces that impede the interaction between material’s surface and different cell types represents an important objective in the development of medical devices. This can be achieved by topographical means such as dual-scale structures, mainly represented by microstructures with surface nanopatterning. Fabrication via laser irradiation of materials seems promising. However, laser-assisted fabrication of dual-scale structures, i.e., ripples relies on stochastic processes deriving from laser–matter interaction, limiting the control over the structures’ topography. In this paper, we report on laser fabrication of cell-repellent dual-scale 3D structures with fully reproducible and high spatial accuracy topographies. Structures were designed as micrometric “mushrooms” decorated with fingerprint-like nanometric features with heights and periodicities close to those of the calamistrum, i.e., 200–300 nm. They were fabricated by Laser Direct Writing via Two-Photon Polymerization of IP-Dip photoresist. Design and laser writing parameters were optimized for conferring cell-repellent properties to the structures, even for high cellular densities in the culture medium. The structures were most efficient in repelling the cells when the fingerprint-like features had periodicities and heights of @200 nm, fairly close to the repellent surfaces of the calamistrum. Laser power was the most important parameter for the optimization protocol.
The efficiency of light coupling to surface plasmon polariton (SPP) represents a very important issue in plasmonics and laser fabrication of topographies in various solids. To illustrate the role of pre-patterned surfaces and impact of laser polarisation in the excitation of electromagnetic modes and periodic pattern formation, Nickel surfaces are irradiated with femtosecond laser pulses of polarisation perpendicular or parallel to the orientation of the pre-pattern ridges. Experimental results indicate that for polarisation parallel to the ridges, laser induced periodic surface structures (LIPSS) are formed perpendicularly to the pre-pattern with a frequency that is independent of the distance between the ridges and periodicities close to the wavelength of the excited SPP. By contrast, for polarisation perpendicular to the pre-pattern, the periodicities of the LIPSS are closely correlated to the distance between the ridges for pre-pattern distance larger than the laser wavelength. The experimental observations are interpreted through a multi-scale physical model in which the impact of the interference of the electromagnetic modes is revealed.
Femtosecond laser induced changes on the topography of stainless steel with double pulses is investigated to reveal the role of parameters such as the fluence, the energy dose and the interpulse delay on the features of the produced patterns. Our results indicate that short pulse separation (Δτ = 5 ps) favors the formation of 2D Low Spatially Frequency Laser Induced Periodic Surface Structures (LSFL) while longer interpulse delays (Δτ = 20 ps) lead to 2D High Spatially Frequency LIPSS (HSFL). The detailed investigation is complemented with an analysis of the produced surface patterns and characterization of their wetting and cell-adhesion properties. A correlation between the surface roughness and the contact angle is presented which confirms that topographies of variable roughness and complexity exhibit different wetting properties. Furthermore, our analysis indicates that patterns with different spatial characteristics demonstrate variable cell adhesion response which suggests that the methodology can be used as a strategy towards the fabrication of tailored surfaces for the development of functional implants.
Due to their uniquely high surface-to-volume ratio, nanofibers are a desired material for various technical applications. However, this surface-to-volume ratio also makes processing difficult as van der Waals forces cause nanofibers to adhere to virtually any surface. The cribellate spider Uloborus plumipes represents a biomimetic paragon for this problem: these spiders integrate thousands of nanofibers into their adhesive capture threads. A comb on their hindmost legs, termed calamistrum, enables the spiders to process the nanofibers without adhering to them. This anti-adhesion is due to a rippled nanotopography on the calamistrum. Via laser-induced periodic surface structures (LIPSS), these nanostructures can be recreated on artificial surfaces, mimicking the non-stickiness of the calamistrum. In order to advance the technical implementation of these biomimetic structured foils, we investigated how climatic conditions influence the anti-adhesive performance of our surfaces. Although anti-adhesion worked well at low and high humidity, technical implementations should nevertheless be air-conditioned to regulate temperature: we observed no pronounced anti-adhesive effect at temperatures above 30 • C. This alteration between anti-adhesion and adhesion could be deployed as a temperature-sensitive switch, allowing to swap between sticking and not sticking to nanofibers. This would make handling even easier.
Bacterial adhesion and biofilm formation on surfaces are associated with persistent microbial contamination, biofouling, and the emergence of resistance, thus, calling for new strategies to impede bacterial surface colonization. Using ns-UV laser treatment (wavelength 248 nm and a pulse duration of 20 ns), laser-induced periodic surface structures (LIPSS) featuring different sub-micrometric periods ranging from ~210 to ~610 nm were processed on commercial poly(ethylene terephthalate) (PET) foils. Bacterial adhesion tests revealed that these nanorippled surfaces exhibit a repellence for E. coli that decisively depends on the spatial periods of the LIPSS with the strongest reduction (~91%) in cell adhesion observed for LIPSS periods of 214 nm. Although chemical and structural analyses indicated a moderate laser-induced surface oxidation, a significant influence on the bacterial adhesion was ruled out. Scanning electron microscopy and additional biofilm studies using a pili-deficient E. coli TG1 strain revealed the role of extracellular appendages in the bacterial repellence observed here.
A deep dive into the methods used for the production of our in-chip direct laser written nozzles (see https://doi.org/10.1002/adhm.202100898). Placement and alignment of structures to existing features for printing with the Nanoscribe was automated to speed up the in-chip DLW process.
Laser setups Using UV-laser sources, multi-scaled μm/nm-structured polycarbonate polymer surfaces were produced. The developed strategy includes the utilization of Direct Laser Interference Patterning (DLIP) to create gratings and pillar-like geometries on the μm-scale as well as Laser-induced Periodic Surface Structures (LIPSS) with features sizes of a few nm. An important parameter controlling the morphology of the periodic features was the direction of the laser beam polarization with respect to the DLIP treated surfaces. Fig.1 SEM micrpgraphs of (a) ridge-like DLIP structure with a period of 10μm. (b-g) Evolution of surface morphologies on top of the DLIP structure with increasing peak fluence levels and a laser polarization ⟂ perpendicular to the DLIP ridges. a) Fig.4 FDTD simulation of intensity distribution of a 6.7 ps laser pulse with λ=343 nm with a polarization (a) perpendicular and (b) parallel to the orientation of DLIP-ridges with a period of 1.5 μm. The arrows in the upper right corners indicate the direction of the laser polarization. Fig.3 ATR-FTIR spectra of unprocessed samples (black curves) and samples processed homogeneously with LIPSS (type LSFL-II, red curves in (a-c), ridge-like (blue curves) or pillar-like (red curves) DLIP structures with 1.5 μm period (d-f) and ridge-like (blue curves) or pillar-like (red curves) DLIP structures with 10 μm period (g-i).
Besides the well-known dragline silk, spiders produce many other types of silk with different chemical and mechanical properties. By interweaving a combination of these silks, even complex structures such as webs, attachment discs or capture threads can be built. The capture threads of cribellate spiders, e.g., consist of a complex multi-fibre system with thousands of individual fibres and up to seven different silk types - including nanofibres. The silk types involved thus form a fibre composite, in which each fibre is most likely assigned a specific mechanical task. For analysing the properties of the individual silk types, they would ideally have to be separated from their interconnected system. However, this is either not possible at all, or only by introducing mechanical stress, which would significantly influence their material properties. We present here a structural analysis of the threads of three different cribellate spiders (Badumna longinqua, Deinopis subrufa, Uloborus plumipes) by using different preparation and imaging techniques. In previous studies, the assignment of different fibre types was primarily based on varying diameters only. However, differences in light refraction effects, fluorescence and stainability revealed that fibres from different species - previously assigned to the same silk type - must actually feature different material components. Considering the individual function of the fibres within a cribellate capture thread, this could also have an impact on the mechanical properties and imply that there are more functional types of fibre than previously recognised.
Using nanofiber-like cell appendages, secreted proteins and sugars, bacteria can establish initial surface contact followed by irreversible adhesion and the formation of multicellular biofilms, often with enhanced resistance towards antimicrobial treatment and established cleaning procedures. On e.g. medical implants, in water supply networks or food-processing industry, biofilms can be a fertile source of bacterial pathogens and are repeatedly associated with persisting, nosocomial and foodborne infections. Nowadays, the emergence of resistances because of extensive usage of antibiotics and biocides in medicine, agriculture and private households have become one of the most important medical challenges with considerable economic consequences. In addition, aggravated biofilm eradication and prolonged cell-surface interaction can lead to increased biodeterioration and undesired modification of industrial and medical surface materials. Various strategies are currently developed, tested, and improved to realize anti-bacterial surface properties through surface functionalization steps avoiding antibiotics. In this study, contact-less and aseptic large-area short or ultrashort laser processing is employed to generate different surface structures in the nanometer- to micrometer-scale on technical materials such as titanium-alloy and polyethylene terephthalate (PET). The laser processed surfaces were subjected to bacterial colonization studies with Escherichia coli test strains and analyzed with reflected-light and epi-fluorescence microscopy. Depending on the investigated surfaces, different bacterial adhesion patterns were found, ranging from bacterial-repellent to bacterial-attractant effects. The results suggest an influence of size, shape and cell appendages of the bacteria and – above all – the laser-processed nanostructure of the surface itself, emphasizing the potential of laser-processing as a versatile tool to control bacterial surface adhesion.
For successful material deployment in tissue engineering, the material itself, its mechanical properties, and the microscopic geometry of the product are of particular interest. While silk is a widely applied protein‐based tissue engineering material with strong mechanical properties, the size and shape of artificially spun silk fibers are limited by existing processes. This study adjusts a microfluidic spinneret to manufacture micron‐sized wet‐spun fibers with three different materials enabling diverse geometries for tissue engineering applications. The spinneret is direct laser written (DLW) inside a microfluidic polydimethylsiloxane (PDMS) chip using two‐photon lithography, applying a novel surface treatment that enables a tight print‐channel sealing. Alginate, polyacrylonitrile, and silk fibers with diameters down to 1 µm are spun, while the spinneret geometry controls the shape of the silk fiber, and the spinning process tailors the mechanical property. Cell‐cultivation experiments affirm bio‐compatibility and showcase an interplay between the cell‐sized fibers and cells. The presented spinning process pushes the boundaries of fiber fabrication toward smaller diameters and more complex shapes with increased surface‐to‐volume ratio and will substantially contribute to future tailored tissue engineering materials for healthcare applications. A 3D‐printed microfluidic wet‐spinning platform is developed to fabricate silk fibers with diameters down to 1 µm as tissue for cell culture. The fibers shape is tailored by the nozzle‐geometry and the mechanical fiber properties are controlled by the spinning process parameters.
Background: During the coronavirus disease 2019 (COVID-19) pandemic face masks grew in importance as their use by the general population was recommended by health officials in order to minimize the risk of infection and prevent further spread of the virus. To ensure health protection of medical personal and other system relevant staff, it is of considerable interest to quickly test if a certain lot of filtering facepiece masks meets the requirements or if the penetration changes under different conditions. As certified penetrometers are rather expensive and were difficult to obtain during the COVID-19 pandemic, we describe two quite simple and cheap methods to quickly test the filter penetration based on an electronic cigarette. Methods: The first method uses a precision scale, the second method uses a light scattering detector to measure the filter penetration. To make sure these two methods yield reliable results, both were tested with freshly cut filter samples covering the range of approx. 2 % to 60 % filter penetration and compared to the results of a certified penetrometer. Results: The comparison of the two methods with the certified penetrometer showed a good correlation and therefore allow a quick and rather reliable estimation of the penetration. Conclusions: Several examples about the use of faulty masks and the resulting health risks show that simple, fast, cheap and broadly available methods for filter characterization might be useful in these days.
Inter-pulse accumulation of heat could affect the chemical and morphological properties of the laser processed material surface. Hence, the laser pulse repetition rate may restrict the processing parameters for specific laser-induced surface structures. In this study, the evolution of various types of laser-induced micro- and nanostructures at various laser fluence levels, effective number of pulses and at different pulse repetition rates (1 – 400 kHz) are studied for common metals/alloys (e.g. steel or titanium alloy) irradiated by near-infrared ultrashort laser pulses (925 fs, 1030 nm) in air environment. The processed surfaces were characterized by optical and scanning electron microscopy (OM, SEM), energy dispersive X-ray spectroscopy (EDX) as well as time of flight secondary ion mass spectrometry (TOF-SIMS). The results show that not only the surface morphology could change at different laser pulse repetition rates and comparable laser fluence levels and effective number of pulses, but also the surface chemistry is altered. Consequences for medical applications are outlined.
Bacterial biofilms are multicellular communities adhering to surfaces and embedded in a self-produced extracellular matrix. Due to physiological adaptations and the protective biofilm matrix itself, biofilm cells show enhanced resistance towards antimicrobial treatment. In medical and industrial settings, biofilms on e.g. for implants or for surfaces in food-processing industry can be a fertile source of bacterial pathogens and are repeatedly associated with persisting, nosocomial and foodborne infections. As extensive usage of antibiotics and biocides can lead to the emergence of resistances, various strategies are currently developed, tested and improved to realize anti-bacterial surface properties through surface functionalization steps avoiding antibiotics. In this study, contact-less and aseptic large-area ultrashort laser scan processing is employed to generate different surface structures in the nanometer- to micrometer-scale on technical materials, i.e. titanium-alloy, steel, and polymer. The processed surfaces were characterized by optical and scanning electron microscopy and subjected to bacterial colonization studies with Escherichia coli test strains. For each material, biofilm results of the fs-laser treated surfaces are compared to that obtained on polished (non-irradiated) surfaces as a reference. Depending on the investigated surfaces, different bacterial adhesion patterns were found, suggesting an influence of geometrical size, shape and cell appendages of the bacteria and – above all – the laser-processed nanostructure of the surface itself.
Some true bug species use droplet-shaped, open-capillary structures for passive, unidirectional fluid transport on their body surface in order to spread a defensive fluid to protect themselves against enemies. In this paper we investigated if the shape of the structures found on bugs (bug-structure) could be optimised with regard to better performance in unidirectional fluid transportation. Furthermore, to use this kind of surface structure in technical applications where fluid surface interaction occurs, it is necessary to adapt the structure geometry to the contact angle between fluid and surface. Based on the principal of operation of the droplet-shaped structures, we optimised the structure shape for better performance in targeted fluid flow and increase in flexibility in design of the structure geometry. To adapt the structure geometry and the structure spacing to the contact angle, we implemented an equilibrium simulation of the, the structure surrounding , fluid. In order to verify the functionality of the optimised structure, we designed and manufactured a prototype. By testing this prototype with pure water used as fluid, the functionality of the optimised structure and the simulation could be proved. This kind of structure may be used on technical surfaces where targeted fluid transport is needed, e.g. evacuation of condensate in order to prevent the surface from mold growth, microfluidics, lab-on-a-chip applications and on microneedles for efficient drug/vaccine coating.
Direct laser interference patterning (DLIP) with ultrashort laser pulses (ULPs) represents a precise and fast technique to produce tailored periodic submicrometer structures on various materials. In this work, an experimental and theoretical approach is presented to investigate the fundamental mechanisms for the formation of unprecedented laser-induced topographies on stainless steel following proper combinations of DLIP with ULPs. The combined spatial and temporal shaping of the pulse increases the level of control over the structure while it brings insights into the structure formation process. The aim of DLIP is to determine the initial conditions of the laser-matter interaction by defining an ablated region while double ULPs are used to control the reorganization of the self-assembled laser-induced submicrometer sized structures by exploiting the interplay of different absorption and excitation levels coupled with the melt hydrodynamics induced by the first of the double pulses. A multiscale physical model is presented to correlate the interference period, polarization orientation, and number of incident pulses with the induced morphologies. Special emphasis is given to electron excitation, relaxation processes, and hydrodynamical effects that are crucial to the production of complex morphologies. Results are expected to derive knowledge of laser-matter interaction in combined DLIP and ULP conditions and enable enhanced fabrication capabilities of complex hierarchical submicrometer sized structures for a variety of applications.
Spider silk attracts researchers from the most diverse fields, such as material science or medicine. However, still little is known about silk aside from its molecular structure and material strength. Spiders produce many different silks and even join several silk types to one functional unit. In cribellate spiders, a complex multi-fibre system with up to six different silks affects the adherence to the prey. The assembly of these cribellate capture threads influences the mechanical properties as each fibre type absorbs forces specifically. For the interplay of fibres, spinnerets have to move spatially and come into contact with each other at specific points in time. However, spinneret kinematics are not well described though highly sophisticated movements are performed which are in no way inferior to the movements of other flexible appendages. We describe here the kinematics for the spinnerets involved in the cribellate spinning process of the grey house spider, Badumna longinqua , as an example of spinneret kinematics in general. With this information, we set a basis for understanding spinneret kinematics in other spinning processes of spiders and additionally provide inspiration for biomimetic multiple fibre spinning.
Predictive modelling represents an emerging field that combines existing and novel methodologies aimed to rapidly understand physical mechanisms and concurrently develop new materials, processes and structures. In the current study, previously-unexplored predictive modelling in a key-enabled technology, the laser-based manufacturing, aims to automate and forecast the effect of laser processing on material structures. The focus is centred on the performance of representative statistical and machine learning algorithms in predicting the outcome of laser processing on a range of materials. Results on experimental data showed that predictive models were able to satisfactorily learn the mapping between the laser input variables and the observed material structure. These results are further integrated with simulation data aiming to elucidate the multiscale physical processes upon laser-material interaction. As a consequence, we augmented the adjusted simulated data to the experimental and substantially improved the predictive performance, due to the availability of increased number of sampling points. In parallel, a metric to identify and quantify the regions with high predictive uncertainty, is presented, revealing that high uncertainty occurs around the transition boundaries. Our results can set the basis for a systematic methodology towards reducing material design, testing and production cost via the replacement of expensive trial-and-error based manufacturing procedure with a precise pre-fabrication predictive tool.
Nanotechnology and lasers are among the most successful and active fields of research and technology that have boomed during the past two decades. Many improvements are based on the controlled manufacturing of nanostructures that enable tailored material functionalization for a wide range of industrial applications, electronics, medicine, etc., and have already found entry into our daily life. One appealing approach for manufacturing such nanostructures in a flexible, robust, rapid, and contactless one-step process is based on the generation of laser-induced periodic surface structures (LIPSS). This Perspectives article analyzes the footprint of the research area of LIPSS on the basis of a detailed literature search, provides a brief overview on its current trends, describes the European funding strategies within the Horizon 2020 programme, and outlines promising future directions.
Biofilm formation in industrial or medical settings is usually unwanted and leads to serious health problems and high costs. Inhibition of initial bacterial adhesion prevents biofilm formation and is, therefore, a major mechanism of antimicrobial action of surfaces. Surface topography largely influences the interaction between bacteria and surfaces which makes topography an ideal base for antifouling strategies and eco-friendly alternatives to chemical surface modifications. Femtosecond laser-processing was used to fabricate sub-micrometric surface structures on silicon and stainless steel for the development of antifouling topographies on technical materials.
The exciting properties of micro- and nano-patterned surfaces found in natural species hide a virtually endless potential of technological ideas, opening new opportunities for innovation and exploitation in materials science and engineering. Due to the diversity of biomimetic surface functionalities, inspirations from natural surfaces are interesting for a broad range of applications in engineering, including phenomena of adhesion, friction, wear, lubrication, wetting phenomena, self-cleaning, antifouling, antibacterial phenomena, thermoregulation and optics. Lasers are increasingly proving to be promising tools for the precise and controlled structuring of materials at micro- and nano-scales. When ultrashort-pulsed lasers are used, the optimal interplay between laser and material parameters enables structuring down to the nanometer scale. Besides this, a unique aspect of laser processing technology is the possibility for material modifications at multiple (hierarchical) length scales, leading to the complex biomimetic micro- and nano-scale patterns, while adding a new dimension to structure optimization. This article reviews the current state of the art of laser processing methodologies, which are being used for the fabrication of bioinspired artificial surfaces to realize extraordinary wetting, optical, mechanical, and biological-active properties for numerous applications. The innovative aspect of laser functionalized biomimetic surfaces for a wide variety of current and future applications is particularly demonstrated and discussed. The article concludes with illustrating the wealth of arising possibilities and the number of new laser micro/nano fabrication approaches for obtaining complex high-resolution features, which prescribe a future where control of structures and subsequent functionalities are beyond our current imagination.
Hierarchical micro/-nanostructures were produced on polycarbonate polymer surfaces by employing a two-step UV-laser processing strategy based on the combination of Direct Laser Interference Patterning (DLIP) of gratings and pillars on the microscale (3 ns, 266 nm, 2 kHz) and subsequently superimposing Laser-induced Periodic Surface Structures (LIPSS; 7-10 ps, 350 nm, 100 kHz) which adds nanoscale surface features. Particular emphasis was laid on the influence of the direction of the laser beam polarization on the morphology of resulting hierarchical surfaces. Scanning electron and atomic force microscopy methods were used for the characterization of the hybrid surface structures. Finite-difference time-domain (FDTD) calculations of the laser intensity distribution on the DLIP structures allowed to address the specific polarization dependence of the LIPSS formation observed in the second processing step. Complementary chemical analyzes by micro-Raman spectroscopy and attenuated total reflection Fourier-transform infrared spectroscopy provided in-depth information on the chemical and structural material modifications and material degradation imposed by the laser processing. It was found that when the linear laser polarization was set perpendicular to the DLIP ridges, LIPSS could be formed on top of various DLIP structures. FDTD calculations showed enhanced optical intensity at the topographic maxima, which can explain the dependency of the morphology of LIPSS on the polarization with respect to the orientation of the DLIP structures. It was also found that the degradation of the polymer was enhanced for increasing accumulated fluence levels.