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A special issue of Molecules (ISSN 1420-3049).

Deadline for manuscript submissions: closed (30 September 2019) | Viewed by 55109

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Dr. Guillaume Delaittre

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Karlsruhe Institute of Technology, Institute of Toxicology and Genetics + Institute for Chemical Technology and Polymer Chemistry, Karlsruhe, Germany
Interests: macromolecular chemistry; polymeric nanostructures; photochemistry; (surface) biofunctionalization; biocatalysis; nanomedicines

Special Issue Information

Dear Colleagues,

While materials were initially employed for their bulk properties and have led to an overwhelming wealth of new products for structural uses in the past century, advancing applications have now shifted focus to gaining control over materials surface properties. For instance, low-friction and wear-resistant treatments are sought after to maximize tools lifetime or to produce self-cleaning surfaces. On the other side of the spectrum, methods for specific adhesion are developed. Surfaces of implant biomaterials are designed to provide a superior compatibility with the receiving organism, while governing stability/degradability features. Further, surfaces that can change their properties depending on the environmental conditions allow for a dynamic and adaptable behavior. In addition to the specific properties of a surface, particular attention is devoted to specifically manipulate these in space through the formation of patterns possessing domains with antagonistic features, such as in array production.

The present Special Issue on “Chemical Surface Modification” is meant to host a variety of topics related to the aforementioned aspects. Therefore, reports dealing chemical procedures to modify the surface properties of any material, be it inorganic or organic, and patterning methods are expected. Contributions on simple coatings obtained by non-reactive deposition of a substance will not be considered, except if the coating itself is used for further modification. Not only is it important to develop new chemical methodologies for surface modification, but also means to assess them. Therefore, contributions dealing with advanced surface characterization techniques are also encouraged. Please refer to the non-exhaustive list of keywords for further hints.

Reviews, full papers, and short communications are welcome.

Dr. Guillaume Delaittre
Guest Editor

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Keywords

metallic substrates
silicon-based materials
polymeric materials
polymer brushes
reactive coatings
nanoparticles
fibers
scaffolds
interface
grafting
patterning
lithography
photochemistry
characterization
friction
wetting
self-cleaning
superhydrophobic
superhydrophilic
biofouling
cell adhesion

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Published Papers (11 papers)

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Research

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22 pages, 3913 KiB

Open AccessArticle

Bifunctional Bioactive Polymer Surfaces with Micrometer and Submicrometer-sized Structure: The Effects of Structure Spacing and Elastic Modulus on Bioactivity

by Sarah M. Elsayed, Vania Tanda Widyaya, Yasir Shafi, Alice Eickenscheidt and Karen Lienkamp

Molecules 2019, 24(18), 3371; https://doi.org/10.3390/molecules24183371 - 16 Sep 2019

Cited by 6 | Viewed by 3019

Abstract

This study presents a comparison of two types of bifunctional structured surface that were made from the same polymer –– an antimicrobial polycation (a synthetic mimic of an antimicrobial peptide, SMAMP) and a protein-repellent polyzwitterion (poly(sulfobetaines), PSB). The first type of bifunctional surface was fabricated by a colloidal lithography (CL) based process where the two polymers were immobilized sequentially onto pre-structured surfaces with a chemical contrast (gold on silicon). This enabled site-selective covalent attachment. The CL materials had a spacing ranging from 200 nm to 2 µm. The second type of structured surface (spacing: 1 – 8.5 µm) was fabricated using a microcontact printing (µCP) process where SMAMP patches were printed onto a PSB network, so that 3D surface features were obtained. The thus obtained materials were studied by quantitative nanomechanical measurements using atomic force microscopy (QNM-AFM). The different architectures led to different local elastic moduli at the polymer-air interface, where the CL surfaces were much stiffer (Derjaguin-Muller-Toporov (DMT) modulus = 20 ± 0.8 GPa) compared to the structured 3D networks obtained by µCP (DMT modulus = 42 ± 1.1 MPa). The effects of the surface topology and stiffness on the antimicrobial activity against Escherichia coli, the protein repellency (using fibrinogen), and the compatibility with human gingival mucosal keratinocytes were investigated. The softer 3D µCP surfaces had simultaneous antimicrobial activity, protein repellency, and cell compatibility at all spacings. For the stiffer CL surfaces, quantitative simultaneous antimicrobial activity and protein repellency was not obtained. However, the cell compatibility could be maintained at all spacings. The optimum spacing for the CL materials was in the range of 500 nm–1 µm, with significantly reduced antimicrobial activity at 2 µm spacing. Thus, the soft polymer network obtained by µCP could be more easily optimized than the stiff CL surface, and had a broader topology range of optimal or near-optimal bioactivity. Full article

(This article belongs to the Special Issue Chemical Surface Functionalization)

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23 pages, 14574 KiB

Open AccessArticle

A Green Water-Soluble Cyclophosphazene as a Flame Retardant Finish for Textiles

by Thomas Mayer-Gall, Dennis Plohl, Leonie Derksen, Dana Lauer, Pia Neldner, Wael Ali, Sabine Fuchs, Jochen S. Gutmann and Klaus Opwis

Molecules 2019, 24(17), 3100; https://doi.org/10.3390/molecules24173100 - 26 Aug 2019

Cited by 32 | Viewed by 5474

Abstract

Poly- and cyclophosphazenes are excellent flame retardants but currently, are not used as textile finishing agents because water-soluble and permanent washing systems are missing. Here, we demonstrate for the first time, the successful usage of a water-soluble cyclotriphosphazene derivative for textile finishing for cotton, different cotton/polyester, and cotton/polyamide blend fabrics. A durable finish was achieved using a photoinduced grafting reaction. The flame retardant properties of the various fabrics were improved with a higher limiting oxygen index, a reduced heat release rate, and an exhibition of intumescent. Furthermore, the finished textiles passed several standardized flammability tests. Full article

(This article belongs to the Special Issue Chemical Surface Functionalization)

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15 pages, 2348 KiB

Open AccessArticle

Biotin-Avidin-Mediated Capture of Microspheres on Polymer Fibers

by Lucas Ahrens, Daniel Vonwil, Neha Arya, Aurelien Forget and V. Prasad Shastri

Molecules 2019, 24(11), 2036; https://doi.org/10.3390/molecules24112036 - 28 May 2019

Cited by 1 | Viewed by 3623

Abstract

Systems for efficient and selective capture of micro-scale objects and structures have application in many areas and are of particular relevance for selective isolation of mammalian cells. Systems for the latter should also not interfere with the biology of the cells. This study demonstrates the capture of microspheres through orthogonal coupling using biotin (ligand) and (strept)avidin (receptor). Fibrous poly(ethylene terephthalate) (PET) meshes were hydrolyzed under controlled alkaline conditions to obtain activated surfaces with COOH groups allowing for the functionalization of the PET with biotin of various spacer length. The system capture efficiency was optimized by varying the length of spacer presenting the biotin against streptavidin. In a proof of concept experiment, avidin-functionalized microspheres were used as surrogates for cells, and their capture under dynamic conditions including virous mixing and high-flow rate perfusion is demonstrated. Functionalization of PET meshes with biotin conjugated to longest spacer yielded the most efficient capture of microspheres. These preliminary results lay the foundation for the development of biosystems for capture of specific cells under physiologically relevant conditions, using biorthogonal avidin-biotin interactions. Full article

(This article belongs to the Special Issue Chemical Surface Functionalization)

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18 pages, 3062 KiB

Open AccessArticle

Surface Structuring Combined with Chemical Surface Functionalization: An Effective Tool to Manipulate Cell Adhesion

by Sarah M. Elsayed, Stefan Paschke, Sibylle J. Rau and Karen Lienkamp

Molecules 2019, 24(5), 909; https://doi.org/10.3390/molecules24050909 - 5 Mar 2019

Cited by 5 | Viewed by 3155

Abstract

In this study, we investigate how a surface structure underneath a surface-attached polymer coating affects the bioactivity of the resulting material. To that end, structured surfaces were fabricated using colloidal lithography (lateral dimensions: 200 nm to 1 µm, height ~15 to 50 nm). The surface structures were further functionalized either with antimicrobial, cell-adhesive polycations or with protein-repellent polyzwitterions. The materials thus obtained were compared to non-functionalized structured surfaces and unstructured polymer monolayers. Their physical properties were studied by contact-angle measurements and atomic force microscopy (AFM). Protein adhesion was studied by surface plasmon resonance spectroscopy, and the antimicrobial activity against Escherichia coli bacteria was tested. The growth of human mucosal gingiva keratinocytes on the materials was analyzed using the Alamar blue assay, optical microscopy, and live-dead staining. The data shows that the underlying surface structure itself reduced protein adhesion and also bacterial adhesion, as evidenced by increased antimicrobial activity. It also enhanced cell adhesion to the surfaces. Particularly in combination with the adhesive polycations, the surfaces increased the cell growth compared to the unstructured reference materials. Thus, functionalizing structured surfaces with adhesive polymer could be a valuable tool for improved tissue integration. Full article

(This article belongs to the Special Issue Chemical Surface Functionalization)

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12 pages, 3298 KiB

Open AccessArticle

Heparinized Polyurethane Surface Via a One-Step Photografting Method

by Zhangshuan Liu, Liming Fang, Guillaume Delaittre, Yu Ke and Gang Wu

Molecules 2019, 24(4), 758; https://doi.org/10.3390/molecules24040758 - 20 Feb 2019

Cited by 6 | Viewed by 4514

Abstract

Traditional methods using coupling chemistry for surface grafting of heparin onto polyurethane (PU) are disadvantageous due to their generally low efficiency. In order to overcome this problem, a quick one-step photografting method is proposed here. Three heparin derivatives incorporating 0.21, 0.58, and 0.88 wt% pendant aryl azide groups were immobilized onto PU surfaces, leading to similar grafting densities of 1.07, 1.17, and 1.13 μg/cm², respectively, yet with increasing densities of anchoring points. The most negatively charged surface and the maximum binding ability towards antithrombin III were found for the heparinized PU with the lowest amount of aryl azide/anchor sites. Furthermore, decreasing the density of anchoring points was found to inhibit platelet adhesion to a larger extent and to prolong plasma recalcification time, prothrombin time, thrombin time, and activated partial thromboplastin time to a larger extent. This was also found to enhance the bioactivity of immobilized heparin from 22.9% for raw heparin to 36.9%. This could be explained by the enhanced molecular mobility of immobilized heparin when it is more loosely anchored to the PU surface, as well as a higher surface charge. Full article

(This article belongs to the Special Issue Chemical Surface Functionalization)

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17 pages, 4274 KiB

Open AccessArticle

Micrometric Wrinkled Patterns Spontaneously Formed on Hydrogel Thin Films via Argon Plasma Exposure

by Carmen M. González-Henríquez, Diego F. Veliz-Silva, Mauricio A. Sarabia-Vallejos, Adolfo del Campo-García and Juan Rodríguez-Hernández

Molecules 2019, 24(4), 751; https://doi.org/10.3390/molecules24040751 - 19 Feb 2019

Cited by 11 | Viewed by 3375

Abstract

The generation of microstructured patterns on the surface of a specific polymeric material could radically improve their performance in a particular application. Most of the interactions with the environment occur at the material interface; therefore, increasing the exposed active surface considerably improves their range of application. In this article, a simple and reliable protocol to form spontaneous wrinkled patterns using a hydrogel layer is reported. For this purpose, we took advantage of the doctor blade technique in order to generate homogenous films over solid substrates with controlled thickness and large coverage. The hydrogel wrinkle formation involves a prepolymerization step which produces oligomers leading to a solution with increased viscosity, enough for doctor blade deposition. Subsequently, the material was exposed to vacuum and plasma to trigger wrinkled pattern formation. Finally, a UV-polymerization treatment was applied to fix the undulations on top. Interestingly, the experimental parameters allowed us to finely tune the wrinkle characteristics (period, amplitude, and orientation). For this study, two main aspects were explored. The first one is related to the role of the substrate functionalization on the wrinkle formation. The second study correlates the deswelling time and its relationship with the dimensions and distribution of the wrinkle pattern. In the first batch, four different 3-(trimethoxysilyl)propyl methacrylate (TSM) concentrations were used to functionalize the substrate in order to enhance the adhesion between hydrogel film and the substrate. The wrinkles formed were characterized in terms of wrinkle amplitude, wavelength, pattern roughness, and surface Young modulus, by using AFM in imaging and force spectroscopy modes. Moreover, the chemical composition of the hydrogel film cross-section and the effect of the plasma treatment were analyzed with confocal Raman spectroscopy. These results demonstrated that an oxidized layer was formed on top of the hydrogel films due to the exposure to an argon plasma. Full article

(This article belongs to the Special Issue Chemical Surface Functionalization)

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17 pages, 2392 KiB

Open AccessArticle

Effect of Surface Cleaning Regimen on Glass Ceramic Bond Strength

by Barbara Lapinska, Jacek Rogowski, Joanna Nowak, Joseph Nissan, Jerzy Sokolowski and Monika Lukomska-Szymanska

Molecules 2019, 24(3), 389; https://doi.org/10.3390/molecules24030389 - 22 Jan 2019

Cited by 19 | Viewed by 4268

Abstract

This study investigated the effect of saliva contamination on chemical changes of ceramic surface as well as the influence of saliva cleaning methods on ceramic-resin bond strength. Saliva was used to contaminate leucite (LGC) and lithium disilicate (LDGC) glass ceramic surfaces. The following cleaning methods were tested: water spray, cleaning with orthophosphoric acid, universal cleaning paste, ultrasonic cleaning with water, re-etching with hydrofluoric acid. Non-contaminated ceramic sample served as control. Chemical analysis of ceramic surfaces was performed using time-of-flight secondary ion mass spectrometry (TOF-SIMS). Shear bond strength (SBS) of ceramics to resin material was tested after 24-hour water storage and after thermocycling. The most effective cleaning method of saliva-contaminated ceramic surface was cleaning LGC surface with orthophosphoric acid or re-etching the LDGC surface with hydrofluoric acid. The application of the following methods resulted in obtaining reliable bond strength. Full article

(This article belongs to the Special Issue Chemical Surface Functionalization)

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14 pages, 7718 KiB

Open AccessArticle

Multi-Layer Application of Self-Etch and Universal Adhesives and the Effect on Dentin Bond Strength

by Anna Zecin-Deren, Jerzy Sokolowski, Agata Szczesio-Wlodarczyk, Ireneusz Piwonski, Monika Lukomska-Szymanska and Barbara Lapinska

Molecules 2019, 24(2), 345; https://doi.org/10.3390/molecules24020345 - 18 Jan 2019

Cited by 35 | Viewed by 6952

Abstract

Contemporary self-etch and multi-mode adhesives were introduced to ensure a fast and reliable bonding procedure. Yet, in terms of bond strength and stability they failed to perform as well as two-bottle, etch-and-rinse adhesives, which remain the gold standard in terms of durability. The purpose of this study was to assess the shear bond strength (SBS) of dental adhesives to dentin with different application protocols. Two self-etch (Adper Easy One and Xeno V) and two multi-mode adhesives (Single Bond Universal and Prime&Bond One Select) were used in the study. The highest SBS was obtained for Single Bond Universal applied in three layers, while the lowest, for Xeno V applied in one layer. Other tested adhesives obtained the highest SBS when applied in three layers. For all tested adhesives, multi-layer application resulted in an increase in adhesive layer thickness, as observed in SEM. The increased thickness of the adhesive layer produced by triple application of unfilled adhesives corresponded with higher SBS values. The present study showed that using triple adhesive layers with simplified adhesive systems can be recommended to improve their performance. Due to differences in the composition of self-etch and universal adhesives, the exact application protocol is product dependent. Full article

(This article belongs to the Special Issue Chemical Surface Functionalization)

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12 pages, 5818 KiB

Open AccessArticle

XPS Analysis of 2- and 3-Aminothiophenol Grafted on Silicon (111) Hydride Surfaces

by Chieh-Hua Lee, Wan-Cian Chen and Yit Lung Khung

Molecules 2018, 23(10), 2712; https://doi.org/10.3390/molecules23102712 - 21 Oct 2018

Cited by 19 | Viewed by 6835

Abstract

Following on from our previous study on the resonance/inductive structures of ethynylaniline, this report examines similar effects arising from resonance structures with aromatic aminothiophenol with dual electron-donating substituents. In brief, 2- and 3-aminothiophenol were thermally grafted on silicon (111) hydride substrate at 130 °C under nonpolar aprotic mesitylene. From the examination of high resolution XPS Si2p, N1s, and S2p spectrum, it was noticed that there was a strong preference of NH₂ over SH to form Si–N linkage on the silicon hydride surface for 2-aminothiophenol. However, for 3-aminothiophenol, there was a switch in reactivity of the silicon hydride toward SH group. This was attributed to the antagonistic and cooperative resonance effects for 2- and 3-aminothiophenol, respectively. The data strongly suggested that the net resonance of the benzylic-based compound could have played an important role in the net distribution of negative charge along the benzylic framework and subsequently influenced the outcome of the surface reaction. To the best of the authors’ knowledge, this correlation between dual electron-donating substituents and the outcome of the nucleophilic addition toward silicon hydride surfaces has not been described before in literature. Full article

(This article belongs to the Special Issue Chemical Surface Functionalization)

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11 pages, 3839 KiB

Open AccessArticle

Pomelo Peel Modified with Citrate as a Sustainable Adsorbent for Removal of Methylene Blue from Aqueous Solution

by Yimei Ren, Chang Cui and Pengjie Wang

Molecules 2018, 23(6), 1342; https://doi.org/10.3390/molecules23061342 - 3 Jun 2018

Cited by 40 | Viewed by 6112

Abstract

An anionic adsorbent was prepared by grafting citrate onto pomelo peel (PPL) to remove methylene blue (MB) from aqueous solution. The PPL and modified pomelo peel (MPPL) were analyzed by Fourier transform infrared spectroscopy (FTIR) and observed by scanning electron microscopy (SEM). The effects of dye concentration, contact time, and pH on adsorption were studied. The FTIR results confirmed that the carboxyl groups were successfully bound to cellulose molecules in PPL via modification with citrate. SEM indicated that the surface of PPL became clean and the porous structure was well maintained after modification. The adsorption capacities of MB onto PPL and MPPL were 81.7 mg/g and 199.2 mg/g, respectively, thus indicating that the addition of anionic groups significantly improved the adsorption performance. The increase in the initial dye concentration and pH of the dye solution promoted the adsorption process. The adsorption equilibrium on MPPL required approximately 3 h. The adsorption of MB on MPPL was well described by a pseudo-second order kinetic model and Langmuir isotherm model. The thermodynamic parameters indicated spontaneous and exothermic adsorption. This study suggests that PPL modified with citrate can be used as a sustainable adsorbent in wastewater purification. Full article

(This article belongs to the Special Issue Chemical Surface Functionalization)

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Review

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13 pages, 1569 KiB

Open AccessReview

Micro-/Nano-Scales Direct Cell Behavior on Biomaterial Surfaces

by Shuo Wang, Jingan Li, Zixiao Zhou, Sheng Zhou and Zhenqing Hu

Molecules 2019, 24(1), 75; https://doi.org/10.3390/molecules24010075 - 26 Dec 2018

Cited by 61 | Viewed by 6665

Abstract

Cells are the smallest living units of a human body’s structure and function, and their behaviors should not be ignored in human physiological and pathological metabolic activities. Each cell has a different scale, and presents distinct responses to specific scales: Vascular endothelial cells may obtain a normal function when regulated by the 25 µm strips, but de-function if the scale is removed; stem cells can rapidly proliferate on the 30 nm scales nanotubes surface, but stop proliferating when the scale is changed to 100 nm. Therefore, micro and nano scales play a crucial role in directing cell behaviors on biomaterials surface. In recent years, a series of biomaterials surface with micro and/or nano scales, such as micro-patterns, nanotubes and nanoparticles, have been developed to control the target cell behavior, and further enhance the surface biocompatibility. This contribution will introduce the related research, and review the advances in the micro/nano scales for biomaterials surface functionalization. Full article

(This article belongs to the Special Issue Chemical Surface Functionalization)

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