Surface micro- and nano-texturing of stainless steel by femtosecond laser for the control of cell migration

The Impact of Ultrashort Pulse Laser Structuring of Metals on In-Vitro Cell Adhesion of Keratinocytes

Besides the need for biomaterial surface modification to improve cellular attachment, laser-structuring is favorable for designing a new surface topography for external bone fixator pins or implants. The principle of this study was to observe how bioinspired (deer antler) laser-induced nano-microstructures influenced the adhesion and growth of skin cells. The goal was to create pins that allow the skin to attach to the biomaterial surface in a bacteria-proof manner. Therefore, typical fixator metals, steel, and titanium alloy were structured using ultrashort laser pulses, which resulted in periodical nano- and microstructures. Surface characteristics were investigated using a laser scanning microscope and static water contact angle measurements. In vitro studies with human HaCaT keratinocytes focused on cell adhesion, morphology, actin formation, and growth within 7 days. The study showed that surface functionalization influenced cell attachment, spreading, and proliferation. Micro-dimple clusters on polished bulk metals (DC20) will not hinder viability. Still, they will not promote the initial adhesion and spreading of HaCaTs. In contrast, additional nanostructuring with laser-induced periodic surface structures (LIPSS) promotes cell behavior. DC20 + LIPSS induced enhanced cell attachment with well-spread cell morphology. Thus, the bioinspired structures exhibited a benefit in initial cell adhesion. Laser surface functionalization opens up new possibilities for structuring, and is relevant to developing bioactive implants in regenerative medicine.

Parametric investigation of ultrashort pulsed laser surface texturing on aluminium alloy 7075 for hydrophobicity enhancement

Hydrophobicity plays a pivotal role in mitigating surface fouling, corrosion, and icing in critical marine and aerospace environments. By employing ultrafast laser texturing, the characteristic properties of a material's surface can be modified. This work investigates the potential of an advanced ultrafast laser texturing manufacturing process to enhance the hydrophobicity of aluminium alloy 7075. The surface properties were characterized using goniometry, 3D profilometry, SEM, and XPS analysis. The findings from this study show that the laser process parameters play a crucial role in the manufacturing of the required surface structures. Numerical optimization with response surface optimization was conducted to maximize the contact angle on these surfaces. The maximum water contact angle achieved was 142º, with an average height roughness (Sa) of 0.87 ± 0.075 µm, maximum height roughness (Sz) of 19.4 ± 2.12 µm, and texture aspect ratio of 0.042. This sample was manufactured with the process parameters of 3W laser power, 0.08 mm hatch distance, and a 3 mm/s scan speed. This study highlights the importance of laser process parameters in the manufacturing of the required surface structures and presents a parametric modeling approach that can be used to optimize the laser process parameters to obtain a specific surface morphology and hydrophobicity.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00170-024-12971-8.

LASER as a tool for surface modification of dental biomaterials: A review

In recent years, the application of lasers for modifying the surface topography of dental biomaterials has received increased attention. This review paper aims to provide an overview of the current status on the utilization of lasers as a potential tool for surface modification of dental biomaterials such as implants, ceramics, and other materials used for restorative purposes. A literature search was done for articles related to the use of lasers for surface modification of dental biomaterials in English language published between October 2000 and March 2023 in Scopus, Pubmed and web of science, and relevant articles were reviewed. Lasers have been mainly used for surface modification of implant materials (71%), especially titanium and its alloys, to promote osseointegration. In recent years, laser texturing has also emerged as a promising technique to reduce bacterial adhesion on titanium implant surfaces. Currently, lasers are being widely used for surface modifications to improve osseointegration and reduce peri-implant inflammation of ceramic implants and to enhance the retention of ceramic restorations to the tooth. The studies considered in this review seem to suggest laser texturing to be more proficient than the conventional methods of surface modification. Lasers can alter the surface characteristics of dental biomaterials by creating innovative surface patterns without significantly affecting their bulk properties. With advances in laser technology and availability of newer wavelengths and modes, laser as a tool for surface modification of dental biomaterials is a promising field, with excellent potential for future research.

Wettability and biological responses of titanium surface's biomimetic hexagonal microstructure

In this research, an experiment was conducted on how the surface wettability and biocompatibility of staplers' titanium nails impact the healing of gastrointestinal tissue. Firstly, the bionic hexagonal structure was prepared on the surface of Ti metal by laser processing technology, and the laser textured titanium samples were observed by scanning electron microscope. Then, the liquid-solid contact angle-measuring instrument was used to characterize the wettability of titanium samples. Finally, cells were cultured on the surface of different titanium samples, CCK8 assay and qRT-PCR were carried out to investigate cell adhesion and collagen secretion on the surface of different samples. The results showed that the bionic hexagonal surface increased the surface roughness, reduced the liquid-solid contact angle, and promoted the adhesion and collagen secretion of fibroblasts. The increased wettability provided a better growth environment for cell growth. Microtexture is an important factor affecting the behavior of cells and its size parameters regulate cell gene expression, which is worthy of further study.

Effect of microtopography on osseointegration of implantable biomaterials and its modification strategies

Orthopedic implants are widely used for the treatment of bone defects caused by injury, infection, tumor and congenital diseases. However, poor osseointegration and implant failures still occur frequently due to the lack of direct contact between the implant and the bone. In order to improve the biointegration of implants with the host bone, surface modification is of particular interest and requirement in the development of implant materials. Implant surfaces that mimic the inherent surface roughness and hydrophilicity of native bone have been shown to provide osteogenic cells with topographic cues to promote tissue regeneration and new bone formation. A growing number of studies have shown that cell attachment, proliferation and differentiation are sensitive to these implant surface microtopography. This review is to provide a summary of the latest science of surface modified bone implants, focusing on how surface microtopography modulates osteoblast differentiation in vitro and osseointegration in vivo, signaling pathways in the process and types of surface modifications. The aim is to systematically provide comprehensive reference information for better fabrication of orthopedic implants.

Biocompatibility of micro/nano structures on the surface of Ti6Al4V and Ti-based bulk metallic glasses induced by femtosecond laser

Femtosecond laser surface modification has been proved to be a versatile technology to create various functional materials by modifying solid surface properties. An interesting experimental phenomenon is found by exposing a Ti6Al4V alloy and Ti-based metallic glass to femtosecond laser irradiation. The research results show that the femtosecond laser induces different micro-nano structures on the surfaces of Ti6Al4V alloy and Ti-based metallic glass. Spherical structure and LIPSS (Laser-induced periodic surface structures) can be formed on the surface of Ti6Al4V alloy after femtosecond laser irradiation. On the surface of Ti-based metallic glass, LIPSS, SWPSS (Super-wavelength periodic surface structure) and neatly arranged microholes structures can be found. Under the same laser parameters, the micro-nano structures showed different evolution trends on the Ti6Al4V alloy and Ti-based metallic glass surfaces. The difference in surface structure between Ti6Al4V alloy and Ti-based metallic glass is since amorphous materials have no crystal lattice and a fixed melting temperature. In addition, there are differences in the biocompatibility of different surface structures. The size and distance of the micro-pits on the surface of different structures determine the ability of cells to adhesion, proliferate and differentiate. This conclusion has important significance for the application of Ti6Al4V alloy and Ti-based metallic glass in the field of biomedicine.

Fabrication of Biomimetic 2D Nanostructures through Irradiation of Stainless Steel Surfaces with Double Femtosecond Pulses

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.

Effect of Controlled Microtopography on Osteogenic Differentiation of Mesenchymal Stem Cells

Various kinds of controlled microtopographies can promote osteogenic differentiation of mesenchymal stem cells (MSCs), such as microgrooves, micropillars, and micropits. However, the optimal shape, size, and mechanism remain unclear. In this review, we summarize the relationship between the parameters of different microtopographies and the behavior of MSCs. Then, we try to reveal the potential mechanism between them. The results showed that the microgrooves with a width of 4–60 μm and ridge width <10 μm, micropillars with parameters less than 10 μm, and square micropits had the full potential to promote osteogenic differentiation of MSCs, while the micromorphology of the same size could induce larger focal adhesions (FAs), well-organized cytoskeleton, and superior cell areas. Therefore, such events are possibly mediated by microtopography-induced mechanotransduction pathways.

Surface engineering and the application of laser-based processes to stents - A review of the latest development

Late in-stent thrombus and restenosis still represent two major challenges in stents’ design. Surface treatment of stent is attracting attention due to the increasing importance of stenting intervention for coronary artery diseases. Several surface engineering techniques have been utilised to improve the biological response in vivo on a wide range of biomedical devices. As a tailorable, precise, and ultra-fast process, laser surface engineering offers the potential to treat stent materials and fabricate various 3D textures, including grooves, pillars, nanowires, porous and freeform structures, while also modifying surface chemistry through nitridation, oxidation and coatings. Laser-based processes can reduce the biodegradable materials' degradation rate, offering many advantages to improve stents’ performance, such as increased endothelialisation rate, prohibition of SMC proliferation, reduced platelet adhesion and controlled corrosion and degradation. Nowadays, adequate research has been conducted on laser surface texturing and surface chemistry modification. Laser texturing on commercial stents has been also investigated and a promotion of performance of laser-textured stents has been proved.

In this critical review, the influence of surface texture and surface chemistry on stents performance is firstly reviewed to understand the surface characteristics of stents required to facilitate cellular response. This is followed by the explicit illustration of laser surface engineering of stents and/or related materials. Laser induced periodic surface structure (LIPSS) on stent materials is then explored, and finally the application of laser surface modification techniques on latest generation of stent devices is highlighted to provide future trends and research direction on laser surface engineering of stents.

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Compared conventional surface engineering with laser-based methods for biomedical devices.

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Explained the influence of texture geometry and surface chemistry on stents biological response.

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Reviewed state of the art in laser surface engineering of stents for improved biological response.

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Reviewed state of the art in laser surface engineering to control degradation of bioresorbable stents.

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Highlighted novel laser surface engineering designs for improved stents'performance.

Synthesis of Micro-Spikes and Herringbones Structures by Femtosecond Laser Pulses on a Titanium Plate-A New Material for Water Organic Pollutants Degradation

(1) Background: The shrinkage of water resources, as well as the deterioration of its quality as a result of industrial human activities, requires a comprehensive approach relative to its protection. Advanced oxidation processes show high potential for the degradation of organic pollutants in water and wastewater. TiO₂ is the most popular photocatalyst because of its oxidizing ability, chemical stability and low cost. The major drawback of using it in powdered form is the difficulty of separation from the reaction mixture. The solution to this problem may be immobilization on a support (glass beads, molecular sieves, etc.). In order to avoid these difficulties, the authors propose to prepare a catalyst as a titanium plate covered with an oxide layer obtained with laser treatment. (2) Methods: In the present work, we generated titanium oxide structures using a cheap and fast method based on femtosecond laser pulses. The structurized plates were tested in the reaction of methylene blue (MB) degradation under UVA irradiation (365 nm). The photocatalytic activity and kinetic properties for the degradation of MB are provided. (3) Results: Studies of X-ray diffraction (XRD) and scanning electron microscopy (SEM) confirm a titanium oxide layer with laser-induced generated structures that are called “spikes” and “herringbones”. The structurized plates were effective photocatalysts, and their activity depends on the structure of the oxide layer (spike and herringbone). (4) Conclusions: The immobilization of the catalyst on a solid support can be performed in a fast and reproducible manner by using the technique of laser ablation. The layers obtained with this method have been shown to have catalytic properties.

Biomimetic Hierarchical Structuring of PLA by Ultra-Short Laser Pulses for Processing of Tissue Engineered Matrices: Study of Cellular and Antibacterial Behavior

The influence of ultra-short laser modification on the surface morphology and possible chemical alteration of poly-lactic acid (PLA) matrix in respect to the optimization of cellular and antibacterial behavior were investigated in this study. Scanning electron microscopy (SEM) morphological examination of the processed PLA surface showed the formation of diverse hierarchical surface microstructures, generated by irradiation with a range of laser fluences (F) and scanning velocities (V) values. By controlling the laser parameters, diverse surface roughness can be achieved, thus influencing cellular dynamics. This surface feedback can be applied to finely tune and control diverse biomaterial surface properties like wettability, reflectivity, and biomimetics. The triggering of thermal effects, leading to the ejection of material with subsequent solidification and formation of raised rims and 3D-like hollow structures along the processed zones, demonstrated a direct correlation to the wettability of the PLA. A transition from superhydrophobic (θ > 150°) to super hydrophilic (θ < 20°) surfaces can be achieved by the creation of grooves with V = 0.6 mm/s, F = 1.7 J/cm2. The achieved hierarchical architecture affected morphology and thickness of the processed samples which were linked to the nature of ultra-short laser-material interaction effects, namely the precipitation of temperature distribution during material processing can be strongly minimized with ultrashort pulses leading to non-thermal and spatially localized effects that can facilitate volume ablation without collateral thermal damage The obtained modification zones were analyzed employing Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), Energy dispersive X-ray analysis (EDX), and optical profilometer. The modification of the PLA surface resulted in an increased roughness value for treatment with lower velocities (V = 0.6 mm/s). Thus, the substrate gains a 3D-like architecture and forms a natural matrix by microprocessing with V = 0.6 mm/s, F = 1.7 J/cm2, and V = 3.8 mm/s, F = 0.8 J/cm2. The tests performed with Mesenchymal stem cells (MSCs) demonstrated that the ultra-short laser surface modification altered the cell orientation and promoted cell growth. The topographical design was tested also for the effectiveness of bacterial attachment concerning chosen parameters for the creation of an array with defined geometrical patterns.

Manufacture of Binary Nanofeatured Polymeric Films Using Nanosphere Lithography and Ultraviolet Roller Imprinting

This paper describes the manufacture of binary nanostructured films utilizing nanosphere lithography and ultraviolet (UV) roller imprinting. To manufacture the binary nanofeatured template, polystyrene nanocolloids of two distinct dimensions (900 and 300 nm) were primarily self-assembly spun coated on a silicon substrate. A roller imprinting facility equipped with polydimethylsiloxane molds and ultraviolet radiation was employed. During the imprinting procedure, the roller was steered by a motor and compressed the ultraviolet-curable polymeric layer against the glass substrate, where the nanofeatured layer was cured by the UV light source. Binary nanofeatured films were thus obtained. The influence of distinct processing variables on the imprinting of nanofeatured films was investigated. The empirical data suggested that with appropriate processing conditions, binary nanofeatured plastic films can be satisfactorily manufactured. It also demonstrated that roller imprinting combined with ultraviolet radiation can offer an easy yet effective method to prepare binary nanofeatured films, with a miniatured processing time and enhanced part quality.

In vitro contact guidance of glioblastoma cells on metallic biomaterials

Cancer cells' ability to sense their microenvironment and interpret these signals for the regulation of directional adhesion plays crucial role in cancer invasion. Furthermore, given the established influence of mechanical properties of the substrate on cell behavior, the present study aims to elucidate the relationship between the contact guidance of glioblastoma cell (GBM) and evolution of microstructural and mechanical properties of the implants. SEM analyses of the specimens subjected to 5 and 25% of plastic strains revealed directional groove-like structures in micro and submicro-sizes, respectively. Microscale cytoplasmic protrusions of GBMs showed elongation favored along the grooves created via deformation markings on 5% deformed sample. Whereas filopodia, submicro-sized protrusions facilitating cancer invasion, elongated in the direction perpendicular to the deformation markings on the 25% deformed sample, which might lead to easy and rapid retraction. Furthermore, number of cell attachment was 1.7-fold greater on 25% deformed sample, where these cells showed the greatest cellular aspect ratio. The directional attachment and contact guidance of GBMs was reported for the first time on metallic implants and these findings propose the idea that GBM response could be regulated by controlling the spacing of the deformation markings, namely the degree of plastic deformation. These findings can be applied in the design of cell-instructive implants for therapeutic purposes to suppress cancer dissemination.

Response of NIH 3T3 Fibroblast Cells on Laser-Induced Periodic Surface Structures on a 15×(Ti/Zr)/Si Multilayer System

Ultrafast laser processing with the formation of periodic surface nanostructures on the 15×(Ti/Zr)/Si multilayers is studied in order to the improve cell response. A novel nanocomposite structure in the form of 15x(Ti/Zr)/Si multilayer thin films, with satisfying mechanical properties and moderate biocompatibility, was deposited by ion sputtering on an Si substrate. The multilayer 15×(Ti/Zr)/Si thin films were modified by femtosecond laser pulses in air to induce the following modifications: (i) mixing of components inside of the multilayer structures, (ii) the formation of an ultrathin oxide layer at the surfaces, and (iii) surface nano-texturing with the creation of laser-induced periodic surface structure (LIPSS). The focus of this study was an examination of the novel Ti/Zr multilayer thin films in order to create a surface texture with suitable composition and structure for cell integration. Using the SEM and confocal microscopies of the laser-modified Ti/Zr surfaces with seeded cell culture (NIH 3T3 fibroblasts), it was found that cell adhesion and growth depend on the surface composition and morphological patterns. These results indicated a good proliferation of cells after two and four days with some tendency of the cell orientation along the LIPSSs.

Bioinspired Superhydrophobic Surfaces via Laser-Structuring

Bioinspired superhydrophobic surfaces are an artificial functional surface that mainly extracts morphological designs from natural organisms. In both laboratory research and industry, there is a need to develop ways of giving large-area surfaces water repellence. Currently, surface modification methods are subject to many challenging requirements such as a need for chemical-free treatment or high surface roughness. Laser micro-nanofabrications are a potential way of addressing these challenges, as they involve non-contact processing and outstanding patterning ability. This review briefly discusses multiple laser patterning methods, which could be used for surface structuring toward creating superhydrophobic surfaces.

Femtosecond laser induced nano-textured micropatterning to regulate cell functions on implanted biomaterials

Posterior capsular opacification (PCO) is the most common complication of cataract surgery. PCO is due to the proliferation, migration, and epithelial-to-mesenchymal transition of the residual lens epithelial cells (LECs) within the lens capsule. As surface topography influences cellular response, we investigated the effect of modulating the dimensions of periodic nano-textured patterns on the surface of an intraocular lens material to regulate lens epithelial cell functions such as cell adhesion, migration, orientation, and proliferation. Patterned poly(HEMA) samples were prepared by a femtosecond laser microfabrication, and the behaviors of human B-3 LECs were observed on groove/ridge patterns with widths varying from 5 to 40 µm. In the presence of ridge and groove patterns, the adherent cells elongated along the direction of the patterns, and f-actin of the cells was spread to a lesser extent on the nano-textured groove surfaces. Both single and collective cell migrations were significantly inhibited in the perpendicular direction of the patterns on the nano-textured micro-patterned samples. We also fabricated the patterns on the curved surface of a commercially available intraocular lens for in vivo evaluation. In vivo results showed that a patterned IOL could help suppress the progression of PCO by inhibiting cell migration from the edge to the center of the IOL. Our reports demonstrate that nano- and microscale topographical patterns on a biomaterial surface can regulate cellular behavior when it is implanted into animals.

Anti-Biofouling Properties of Femtosecond Laser-Induced Submicron Topographies on Elastomeric Surfaces

Antibacterial coatings are often employed to elastomer surfaces to inhibit bacterial attachment. However, such approaches could lead to increased antibiotic resistance. Surface micro-/nanotexturing is gaining significant attention recently, as it is a passive approach to reduce bacterial adhesion to surfaces. To this end, this work aims to assess the anti-biofouling functionality of femtosecond laser-induced submicron topographies on biomedical elastomer surfaces. Femtosecond laser processing was employed to produce two types of topographies on stainless-steel substrates. The first one was highly regular and single scale submicron laser-induced periodic surface structures (LIPSS) while the second one was multiscale structures (MSs) containing both submicron- and micron-scale features. Subsequently, these topographies were replicated on polydimethylsiloxane (PDMS) and polyurethane (PU) elastomers to evaluate their bacterial retention characteristics. The submicron textured PDMS and PU surfaces exhibited long-term hydrophobic durability up to 100 h under immersed conditions. Both LIPSS and MS topographies on PDMS and PU elastomeric surfaces were shown to substantially reduce (>89%) the adhesion of Gram-negative Escherichia coli bacteria. At the same time, the anti-biofouling performance of LIPSS and MS topographies was found to be comparable with that of lubricant-impregnated surfaces. The influence of physical defects on textured surfaces on the adhesion behavior of bacteria was also elucidated. The results presented here are significant because the polymeric biomedical components that can be produced by replication cost effectively, while their biocompatibility can be improved through femtosecond surface modification of the respective replication masters.

Laser-Induced Microgrooves Improve the Mechanical Responses of Cemented Implant Systems

The impact of a laser-induced microgroove (LIM) architecture on mechanical responses of two cemented implant systems was evaluated. One system consisted of two aluminum alloy rods bonded end-to-end by polymethylmethacrylate cement. The second system consisted of a custom-made, aluminum tibial tray (TT) cemented in an artificial canine tibia. Control specimens for each system were polished smooth at the cement interface. For LIM samples in the rod system, microgrooves were engraved (100 µm depth, 200 µm width, 500 µm spacing) on the apposing surface of one of the two rods. For TT system testing, LIM engraving (100 µm spacing) was confined to the underside and keel of the tray. Morphological analysis of processed implant surfaces revealed success in laser microgrooving procedures. For cemented rods tested under static tension, load to failure was greater for LIM samples (279.0 ± 14.9 N vs. 126.5 ± 4.5 N). Neither non-grooved nor grooved TT samples failed under cyclic compression testing (100,000 cycles at 1 Hz). Compared with control specimens, LIM TT constructs exhibited higher load to failure under static compression and higher strain at the bone interface under cyclic compression. Laser-induced microgrooving has the potential to improve the performance of cemented orthopedic implants.

Improving the Mechanical Strength of Dental Applications and Lattice Structures SLM Processed

To manufacture custom medical parts or scaffolds with reduced defects and high mechanical characteristics, new research on optimizing the selective laser melting (SLM) parameters are needed. In this work, a biocompatible powder, 316L stainless steel, is characterized to understand the particle size, distribution, shape and flowability. Examination revealed that the 316L particles are smooth, nearly spherical, their mean diameter is 39.09 μm and just 10% of them hold a diameter less than 21.18 μm. SLM parameters under consideration include laser power up to 200 W, 250-1500 mm/s scanning speed, 80 μm hatch spacing, 35 μm layer thickness and a preheated platform. The effect of these on processability is evaluated. More than 100 samples are SLM-manufactured with different process parameters. The tensile results show that is possible to raise the ultimate tensile strength up to 840 MPa, adapting the SLM parameters for a stable processability, avoiding the technological defects caused by residual stress. Correlating with other recent studies on SLM technology, the tensile strength is 20% improved. To validate the SLM parameters and conditions established, complex bioengineering applications such as dental bridges and macro-porous grafts are SLM-processed, demonstrating the potential to manufacture medical products with increased mechanical resistance made of 316L.

Understanding the Effect of Surface Machining on the YSZ/Ti6Al4V Joint via Image Based Modelling

A method to improve the brazing between YSZ and Ti6Al4V by femtosecond laser surface machining is introduced. The highest strength of ~150 MPa (which is 95.2% higher than that of the flat YSZ/Ti6Al4V joint) is achieved when the processing speed is 200 μm/s. To understand the strengthen mechanism of the surface machining on the joint strength, image based models, based on the observed microstructure, have been used to probe the stress distribution in the joint. It is found that through surface machining on the ceramic, the residual stress distribution in ceramic becomes nonlinear. Upon shear testing, for the joint with a flat interface, the failure happens in the reaction layer and the out of plane stress in this layer is found to be tensile, which acts as the driving force for the crack generation and propagation. But for the joint with a rumpled interface, the compressive out of plane stress at the boundary of the grooves in the reaction layer could inhibit the propagation of the cracks. Finally, by surface machining on the ceramic, the maximum shear stress in the reaction layer is decreased, which could also help to improve the reliability of the joint.

Femtosecond Laser-Induced, Nanoparticle-Embedded Periodic Surface Structures on Crystalline Silicon for Reproducible and Multi-utility SERS Platforms

Fabrication of reproducible and versatile surface-enhanced Raman scattering (SERS) substrates is crucial for real-time applications such as explosive detection for human safety and biological imaging for cancer diagnosis. However, it still remains a challenging task, even after several methodologies were developed by various research groups, primarily due to (a) a lack of consistency in detection of a variety of molecules (b) cost-effectiveness of the SERS substrates prepared, and (c) byzantine preparation procedures, etc. Herein, we establish a procedure for preparing reproducible SERS-active substrates comprised of laser-induced nanoparticle-embedded periodic surface structures (LINEPSS) and metallization of silicon (Si) LINEPSS. LINEPSS were fabricated using the technique of femtosecond laser ablation of Si in acetone. The versatile SERS-active substrates were then achieved by two ways, including the drop casting of silver (Ag)/gold (Au) nanoparticles (NPs) on Si LINEPSS and Ag plating on the Si LINEPSS structures. By controlling the LINEPSS grating periodicity, the effect of plasmonic nanoparticles/plasmonic plating on the Si NPs embedded periodic surface structures enormously improved the SPR strength, resulting in the consistent and superior Raman enhancements. The reproducible SERS signals were achieved by detecting the molecules of Methylene Blue (MB), 2,4-dinitrotoluene (DNT), and 5-amino-3-nitro-l,2,4-triazole (ANTA). The SERS signal strength is determined by the grating periodicity, which, in turn, is determined by the input laser fluence. The SERS-active platform with grating periodicity of 130 ± 10 nm and 150 ± 5 nm exhibited strong Raman enhancements of ∼10⁸ for MB and ∼10⁷ for ANTA molecules, respectively, and these platforms are demonstrated to be capable, even for multiple usages.

Tailoring diamond's optical properties via direct femtosecond laser nanostructuring

We demonstrate a rapid, accurate, and convenient method for tailoring the optical properties of diamond surfaces by employing laser induced periodic surface structuring (LIPSSs). The characteristics of the fabricated photonic surfaces were adjusted by tuning the laser wavelength, number of impinging pulses, angle of incidence and polarization state. Using Finite Difference Time Domain (FDTD) modeling, the optical transmissivity and bandwidth was calculated for each fabricated LIPSSs morphology. The highest transmission of ~99.5% was obtained in the near-IR for LIPSSs structures with aspect ratios of the order of ~0.65. The present technique enabled us to identify the main laser parameters involved in the machining process, and to control it with a high degree of accuracy in terms of structure periodicity, morphology and aspect ratio. We also demonstrate and study the conditions for fabricating spatially coherent nanostructures over large areas maintaining a high degree of nanostructure repeatability and optical performance. While our experimental demonstrations have been mainly focused on diamond anti-reflection coatings and gratings, the technique can be easily extended to other materials and applications, such as integrated photonic devices, high power diamond optics, or the construction of photonic surfaces with tailored characteristics in general.

Fabrication of ordered hierarchical structures on stainless steel by picosecond laser for modified wettability applications

Ordered hierarchical structures were fabricated on a stainless steel surface using a single picosecond laser for highly controllable dimensions. Picosecond laser induced periodic structures were firstly used to create large-scale nano-structures with a period of ~450 nm. Subsequently, laser direct writing, by simply changing process parameters was employed to create micro squared structures with 19 μm width, 19 μm interval and 3-7.5 μm depth on the previously created nano-structures. As a result, micro squared structures covered by uniform nano-structures, similar to examples present in nature, were successfully fabricated. Additionally, the wettability of the created hierarchical structures was analyzed. The results demonstrated that the combination of both micro- and nano-structures allowed to tune the wetting behavior, presenting a great potential for wettability applications.

Multifunctional Hierarchical Surface Structures by Femtosecond Laser Processing

Hierarchical surface structures were fabricated on fused silica by using a fs-laser with a pulse duration τ = 300 fs and a wavelength λ = 512 nm. The resulting surface structures were characterized by scanning electron microscopy, atomic force microscopy and white light interference microscopy. The optical properties were analyzed by transmittance measurements using an integrating sphere and the wettability was evaluated by measuring the water contact angle θ. The silanization of structured fused silica surfaces with trichloro(1H,1H,2H,2H-perfluorooctyl)silane allows to switch the wettability from superhydrophilic (θ = 0°) to superhydrophobic behavior with θ exceeding 150°. It was shown that the structured silica surfaces are a suitable master for negative replica casting and that the hierarchical structures can be transferred to polystyrene. The transmittance of structured fused silica surfaces decreases only slightly when compared to unstructured surfaces, which results in high transparency of the structured samples. Our findings facilitate the fabrication of transparent glass samples with tailored wettability. This might be of particular interest for applications in the fields of optics, microfluidics, and biomaterials.

Surface Texture-Based Surface Treatments on Ti6Al4V Titanium Alloys for Tribological and Biological Applications: A Mini Review

Surface texture (ST) has been confirmed as an effective and economical surface treatment technique that can be applied to a great range of materials and presents growing interests in various engineering fields. Ti6Al4V which is the most frequently and successfully used titanium alloy has long been restricted in tribological-related operations due to the shortcomings of low surface hardness, high friction coefficient, and poor abrasive wear resistance. Ti6Al4V has benefited from surface texture-based surface treatments over the last decade. This review begins with a brief introduction, analysis approaches, and processing methods of surface texture. The specific applications of the surface texture-based surface treatments for improving surface performance of Ti6Al4V are thoroughly reviewed from the point of view of tribology and biology.

Reliable laser fabrication: the quest for responsive biomaterials surface

This review presents current efforts in laser fabrication, focusing on the surface features of biomaterials and their biological responses; this provides insight into the engineering of bio-responsive surfaces for future medical devices.

Fundamentals of Laser-Based Hydrogel Degradation and Applications in Cell and Tissue Engineering

The cell and tissue engineering fields have profited immensely through the implementation of highly structured biomaterials. The development and implementation of advanced biofabrication techniques have established new avenues for generating biomimetic scaffolds for a multitude of cell and tissue engineering applications. Among these, laser-based degradation of biomaterials is implemented to achieve user-directed features and functionalities within biomimetic scaffolds. This review offers an overview of the physical mechanisms that govern laser-material interactions and specifically, laser-hydrogel interactions. The influences of both laser and material properties on efficient, high-resolution hydrogel degradation are discussed and the current application space in cell and tissue engineering is reviewed. This review aims to acquaint readers with the capability and uses of laser-based degradation of biomaterials, so that it may be easily and widely adopted.

Formation and Properties of Laser-Induced Periodic Surface Structures on Different Glasses

The formation and properties of laser-induced periodic surface structures (LIPSS) was investigated on different technically relevant glasses including fused silica, borosilicate glass, and soda-lime-silicate glass under irradiation of fs-laser pulses characterized by a pulse duration τ = 300 fs and a laser wavelength λ = 1025 nm. For this purpose, LIPSS were fabricated in an air environment at normal incidence with different laser peak fluence, pulse number, and repetition frequency. The generated structures were characterized by using optical microscopy, scanning electron microscopy, focused ion beam preparation and Fast-Fourier transformation. The results reveal the formation of LIPSS on all investigated glasses. LIPSS formation on soda-lime-silicate glass is determined by remarkable melt-formation as an intra-pulse effect. Differences between the different glasses concerning the appearing structures, their spatial period and their morphology were discussed based on the non-linear absorption behavior and the temperature-dependent viscosity. The findings facilitate the fabrication of tailored LIPSS-based surface structures on different technically relevant glasses that could be of particular interest for various applications.

Functionalization of titanium dioxide nanotubes with biomolecules for biomedical applications

Titanium (Ti) and its alloys are extensively used in the manufacture of implants because they have biocompatibility. The production of a nanostructured surface can be achieved by means of titanium dioxide nanotubes (TNTs) which can have dimensions equivalent to the nanometric components of human bone, in addition to increasing the efficiency of such implants. The search is ongoing for ways to improve the performance of these TNTs in terms of their functionalization through coating these nanotubular matrices with biomolecules. The biocompatibility of the functionalized TNTs can be improved by promoting rapid osseointegration, by preventing the adhesion of bacteria on such surfaces and/or by promoting a more sustained local release of drugs that are loaded into such TNTs. In addition to the implants, these nanotubular matrices have been used in the manufacture of high-performance biosensors capable of immobilizing principally enzymes on their surfaces, which has possible use in disease diagnosis. The objective of this review is to show the main techniques of immobilization of biomolecules in TNTs, evidencing the most recent applications of bioactive molecules that have been functionalized in the nanotubular matrices for use in implants and biosensors. This surveillance also proposes a new class of biomolecules that can be used to functionalize these nanostructured surfaces, lectins.