AFM imaging and analysis of local mechanical properties for detection of surface pattern of functional groups

Experimental extraction of Young's modulus of gastric tissue with development of spherical, cylindrical, and crowned rollers contact theories

Nanotechnology has been considered with the aim of recognizing the structural and mechanical properties as well as improving the treatment and diagnostic process in the field of medicine. The process of nanomanipulation by examining healthy and cancerous tissues in nanoscale is one of the processes used in this field. Therefore, in this article, considering the importance of recognizing the properties of cancerous and healthy tissues in improving the treatment and diagnosis process, one of the most common types of cancer has been studied. Young modulus has been used as a parameter in the diagnosis of cancerous tissue and its value has been calculated for gastric cancerous tissue. To achieve this goal, atomic force microscopy (AFM) was used during the manipulation process. This tool with the ability to study cancerous tissues in different environments and with the least amount of damage to the target tissue, is one of the effective tools in the field of nanomanipulation. The parameter studied in this study is the geometry of gastric cancer tissue. Therefore, the simulations have been performed by considering contact models with spherical, cylindrical and crowned rollers geometries. The force-indentation depth diagram for gastric tissue is plotted experimentally and compared with theoretical results. According to the experimental work done after reviewing the recorded topographic images, the approximate range of the Young's modulus value for gastric tissue has been calculated according to different geometries. Since the geometry of the crowned rollers is closer to the geometry of the gastric tissue, it has a higher accuracy and the values of the Young's modulus have been calculated according to this geometry in the range of 316-310 KPa.

Kelvin probe force microscopy of the nanoscale electrical surface potential barrier of metal/semiconductor interfaces in ambient atmosphere

This study deals with the preparation and characterization of metallic nanoinclusions on the surface of semiconducting Bi₂Se₃ that could be used for an enhancement of the efficiency of thermoelectric materials. We used Au forming a 1D alloy through diffusion (point nanoinclusion) and Mo forming thermodynamically stable layered MoSe₂ nanosheets through the reaction with the Bi₂Se₃. The Schottky barrier formed by the 1D and 2D nanoinclusions was characterized by means of atomic force microscopy (AFM). We used Kelvin probe force microscopy (KPFM) in ambient atmosphere at the nanoscale and compared the results to those of ultraviolet photoelectron spectroscopy (UPS) in UHV at the macroscale. The existence of the Schottky barrier was demonstrated at +120 meV for the Mo layer and -80 meV for the Au layer reflecting the formation of MoSe₂ and Au/Bi₂Se₃ alloy, respectively. The results of both methods (KPFM and UPS) were in good agreement. We revealed that long-time exposure (tens of seconds) to the electrical field leads to deep oxidation and the formation of perturbations greater than 1 µm in height, which hinder the I-V measurements.

Aligned nanofibres made of poly(3-hydroxybutyrate) grafted to hyaluronan for potential healthcare applications

In this work, a hybrid copolymer consisting of poly(3-hydroxybutyrate) grafted to hyaluronic acid (HA) was synthesised and characterised. Once formed, the P(3HB)-g-HA copolymer was soluble in water allowing a green electrospinning process. The diameters of nanofibres can be tailored by simply varying the M_w of polymer. The optimization of the process allowed to produce fibres of average diameter in the range of 100-150 nm and low polydispersity. The hydrophobic modification has not only increased the fibre diameter, but also the obtained layers were homogenous. At the nanoscale, the hybrid copolymer exhibited an unusual hairy topography. Moreover, the hardness and tensile properties of the hybrid were found to be superior compared to fibres made of unmodified HA. Particularly, this reinforcement was achieved at the longitudinal direction. Additionally, this work reports the use in the composition of a water-soluble copolymer containing photo cross-linkable moieties to produce insoluble materials post-electrospinning. The derivatives as well as their nanofibrous mats retain the biocompatibility of the natural polymers used for the fabrication.

Influence of scanning rate on quality of AFM image: Study of surface statistical metrics

The purpose of this work is to study the dependence of AFM-data reliability on scanning rate. The three-dimensional (3D) surface topography of the samples with different micro-motifs is investigated. The analysis of surface metrics for estimation of artifacts from inappropriate scanning rate is presented. Fractal analysis was done by cube counting method and evaluation of statistical metrics was carrying out on the basis of AFM-data. Combination of quantitate parameters is also presented in graphs for every measurement. The results indicate that the sensitivity to scanning rate growths with fractal dimension of the sample. This approach allows describing the distortion of the images against scanning rate and could be applied for dependences on the other measurement parameters. The article explains the relevance and comparison of fractal and statistical surface parameters for characterization of data distortion caused by inappropriate choice of scanning rate.

Polymer brushes based on PLLA-b-PEO colloids for the preparation of protein resistant PLA surfaces

Deposition of PLLA-b-PEO colloidal nanoparticles from selective solvents onto a polylactide surface resulting in an anti-fouling and cell repulsive surface.

Nano-colloid printing of functionalized PLA-b-PEO copolymers: tailoring the surface pattern of adhesive motif and its effect on cell attachment

In this study, we investigate the preparation of surface pattern of functional groups on poly(lactide) (PLA) surfaces through the controlled deposition of core-shell self-assemblies based on functionalized PLA-b-PEO amphiphilic block copolymers from selective solvents. Through grafting RGDS peptide onto the functionalized copolymer surface, the presented approach enables to prepare PLA surfaces with random and clustered spatial distribution of adhesive motifs. The proposed topography of the adhesion motif was proved by atomic force microscopy techniques using biotin-tagged RGDS peptide grafted on the surface and streptavidin-modified gold nanospheres which bind the tagged RGDS peptides as a contrast agent. The cell culture study under static and dynamic conditions with MG63 osteosarcoma cell line showed that the clustered distribution of RGDS peptides provided more efficient initial cell attachment and spreading, and resistance to cell detachment under dynamic culture compared to randomly distributed RGDS motif when with the same average RGDS peptide concentration.

Investigation of the influence of UV irradiation on collagen thin films by AFM imaging

Collagen is the major fibrous extracellular matrix protein and due to its unique properties, it has been widely used as biomaterial, scaffold and cell-substrate. The aim of the paper was to use Atomic Force Microscopy (AFM) in order to investigate well-characterized collagen thin films after ultraviolet light (UV) irradiation. The films were also used as in vitro culturing substrates in order to investigate the UV-induced alterations to fibroblasts. A special attention was given in the alteration on collagen D-periodicity. For short irradiation times, spectroscopy (fluorescence/absorption) studies demonstrated that photodegradation took place and AFM imaging showed alterations in surface roughness. Also, it was highlighted that UV-irradiation had different effects when it was applied on collagen solution than on films. Concerning fibroblast culturing, it was shown that fibroblast behavior was affected after UV irradiation of both collagen solution and films. Furthermore, after a long irradiation time, collagen fibrils were deformed revealing that collagen fibrils are consisting of multiple shells and D-periodicity occurred on both outer and inner shells. The clarification of the effects of UV light on collagen and the induced modifications of cell behavior on UV-irradiated collagen-based surfaces will contribute to the better understanding of cell-matrix interactions in the nanoscale and will assist in the appropriate use of UV light for sterilizing and photo-cross-linking applications.

A novel coating of type IV collagen and hyaluronic acid on stent material-titanium for promoting smooth muscle cell contractile phenotype

The method of stent implantation is currently considered an effective means of treating atherosclerosis. However, implanting of cardiovascular stent often leads to intimal breakage and hyperplasia. The phenomenon that vascular smooth muscle cells (SMCs) transform from contractile to synthetic phenotype becomes a serious obstacle to intimal recovery. To improve how SMCs transform from a synthetic to contractile phenotype, a technique of coimmobilization was used to form type IV collagen (CoIV) and hyaluronic acid (HA) coating on the widely used stent material, titanium (Ti). In this work, several bio-functional coatings made of CoIV/HA mixtures in different ratios were fabricated on the Ti surface. The quantitative characterization of CoIV showed that introducing HA could enhance the amount of the immobilized CoIV on the alkali activated Ti (TiOH) surface. The immunofluorescence staining results of myosin heavy chain (MHC) and DAPI showed that the coating of CoIV/HA in ratios of 200 μg/ml (M200) and 500 μg/ml (M500) also could promote SMCs expressing more contractile phenotype compared with TiOH/CoIV control samples, while the AO/PI staining results indicated that SMCs on the M200 and M500 samples showed less apoptosis ratio. Thus, we hope that this study can provide more helpful exploration and application for promoting the SMC contractile phenotype on the cardiovascular stents.