Nanomechanical Characterization Research Articles

Utilizing collagen-coated hydrogels with defined stiffness as calibration standards for AFM experiments on soft biological materials: the case of lung cells and tissue

Abstract Atomic Force Microscopy (AFM) is crucial in mechanobiology for high-resolution imaging and nanomechanical measurements of biological samples, providing insights into their mechanical properties. However, AFM faces challenges such as tip damage and cantilever selection errors, impacting measurement accuracy. This study proposes a methodology using collagen-coated hydrogels with predefined stiffness for calibrating AFM measurements on soft biological materials. By facilitating appropriate cantilever selection, assessing systematic errors, and evaluating tip damage, this approach ensures reliable Young’s modulus measurements. The proof of concept with human lung cells and tissue specimens demonstrates improved accuracy and reliability of AFM-based nanomechanical characterizations, essential for understanding cellular mechanics and disease progression.

New Insights in the Nanomechanical Study of Carbon-Containing Nanocomposite Materials Based on High-Density Polyethylene

The investigation of new composite materials possessing low weight but not at the expense of their mechanical performance is of great interest in terms of reducing energy consumption in many industrial applications. This study is focused on the nanomechanical characterization of high-density polyethylene (HDPE)-based composite specimens modified with equal loadings of graphene nanoplatelets (GNPs) and/or multiwall carbon nanotubes (MWCNTs). Quasi-static nanoindentation analysis revealed the impact of the carbon nanofillers on the receiving of nanocomposites with higher nanohardness and reduced modulus of elasticity, reaching values of 0.146 GPa and 3.57 GPa, respectively. The role of the indentation size effect in elastic polymer matrix was assessed by applying three distinct peak forces. Nanoscratch experiments depicted the tribological behavior of the composite samples and inferred the influence of the carbon nanofillers on the values of the coefficient of friction (COF). It seems that the incorporation of 4 wt% GNPs in the polymer structure improves the scratch resistance of the material, resulting in a higher value of the exerted lateral force and therefore leading to the detection of a higher coefficient of friction at scratch of 0.401. A considerable pile-up response of the scratched polymer specimens was observed by means of in-situ SPM imaging of the tested surface sample area. The sway of the carbon nanoparticles on the composite pile-up behavior and the effect of the pile-up on the measured friction coefficients have been explored.

Nanomechanical characterization of hemp fiber with atomic force microscopy

Nanomechanical characterization of hemp fiber with atomic force microscopy

Nanomechanical characterization of carbon nanotube-based composite interfaces tailored by electrophoretic deposition

Carbon nanotube (CNT) addition to composite materials can offer both nanoscale reinforcement and a multifunctional element due to their extraordinary mechanical, thermal and electrical properties. Electrophoretic deposition (EPD) offers a scalable processing technique to incorporate CNTs into conventional fiber-reinforced polymer composites (FRPCs), facilitating the production of unique nanoscale structures in the critical interphase region. In this study, CNTs functionalized with polyethyleneimine (CNT-PEI) were deposited onto a planar substrate via EPD followed by the infusion of epoxy matrix in order to replicate the nanocomposite interphase region present in nanomodified FRPCs. The nanocomposite films have thicknesses ranging from several hundred nanometers to a few microns to represent different fiber-matrix interphase regions found in FRPCs. The morphology and mechanical performance of CNT-PEI/epoxy nanocomposites are examined using atomic force microscopy (AFM) in both tapping and nanoindentation modes. The EPD creates a homogeneously distributed porous CNT network bridged by PEI, forming the pathway of epoxy resin infusion through interconnected pores with diameters less than 100 nm. CNT-PEI/epoxy nanocomposites exhibited significant improvements in stiffness, hardness, and creep resistance compared to constituent porous CNT-PEI films and neat epoxy. The improvement was directly related to the ability of the load bearing CNTs chemically bonded with the epoxy matrix through the grafted PEI, providing an efficient load transfer mechanism. The chemical bond between the porous CNT-PEI and epoxy also produced far greater fracture surface in nanoscale scratch tests compared to unmodified epoxy, indicating the CNT-PEI/epoxy nanocomposite is capable of distributing load and absorbing more energy prior to fracture.

Dynamic nanomechanical characterization of cells in exosome therapy

Exosomes derived from mesenchymal stem cells (MSCs) have been confirmed to enhance cell proliferation and improve tissue repair. Exosomes release their contents into the cytoplasmic solution of the recipient cell to mediate cell expression, which is the main pathway through which exosomes exert therapeutic effects. The corresponding process of exosome internalization mainly occurs in the early stage of treatment. However, the therapeutic effect of exosomes in the early stage remains to be further studied. We report that the three-dimensional cell traction force can intuitively reflect the ability of exosomes to enhance the cytoskeleton and cell contractility of recipient cells, serving as an effective method to characterize the therapeutic effect of exosomes. Compared with traditional biochemical methods, we can visualize the early therapeutic effect of exosomes in real time without damage by quantifying the cell traction force. Through quantitative analysis of traction forces, we found that endometrial stromal cells exhibit short-term cell roundness accompanied by greater traction force during the early stage of exosome therapy. Further experiments revealed that exosomes enhance the traction force and cytoskeleton by regulating the Rac1/RhoA signaling pathway, thereby promoting cell proliferation. This work provides an effective method for rapidly quantifying the therapeutic effects of exosomes and studying the underlying mechanisms involved.

Instrumented indentation of PMMA/ZnO nanocomposites films

Piezoelectric nanocomposite films comprise zinc oxide (ZnO) nanoparticles as reinforcement and poly-methyl methacrylate (PMMA) as the matrix. These films can potentially be used as structural and functional components of microdevices that can harvest energy from ambient mechanical vibrations. The design of such energy-scavenging micro/nano-systems will require knowledge of the process-microstructure-property relationships of nanocomposite films. This study synthesized PMMA/ZnO nanocomposite films using ultrasonic probe sonication and solution-casting. The nanomechanical characterization of the nanocomposite films was conducted using a nanoindenter via quasi-static mode. Quasi-static nanoindentation revealed that the indentation modulus ranged from 3.49 ± 0.03 GPa for PMMA to 4.71 ± 0.07 GPa for PMMA/ZnO 5 wt% nanocomposite film. However, the indentation modulus of 10 wt% ZnO nanocomposites decreases, i.e. 4.22 ± 0.60 GPa. The indentation hardness varied from 311.97 ± 6 MPa for PMMA thermoplastic polymer to 432.94 ± 83.81 MPa for PMMA/ZnO 10 wt% nanocomposites film. In addition, the properties of the nanocomposite film vary, as supported by scanning electron micrographs.

Nanomechanical characterization of BiFeO3 ferroelectric ceramics

Ferroelectric perovskites are pivotal in diverse technological applications; however, a gap persists in our comprehension of their mechanical properties, emphasizing the need for additional exploration. In the present study, we report on the nanomechanical behavior of BiFeO3 ceramics in the force range between 200 μN and 2 mN, including the evolution of the hardness and the reduced Young’s modulus from (9.9 ± 0.4) GPa and (113.7 ± 6.9) GPa, respectively, with increasing force. A sequence of plastic-deformation mechanisms under the cube-corner probe was revealed through a first pop-in analysis in combination with a variety of electron microscopy techniques, starting with a homogeneous dislocation nucleation, multiplication and rearrangement leading to sub-grain formation, a phenomenon observed in metals but not in ceramics.

Microstructure and nanomechanical characterization of tectonic coal based on SEM, AFM, XRD and DSI

The microstructure and mechanical properties of tectonic coal are the key to the efficient development of tectonic coal reservoir coalbed methane. The microstructure and mechanical properties of coal samples were studied and analyzed by SEM-EDS-PCAS, AFM, XRD and DSI experiments. The results show that the fractal dimension (D) of WJB, QL, and FR coal samples of pores is 2.356, 1.946, and 1.721 respectively. The fractal dimension (Ds) of PSD is 2.26, 2.25, and 2.23 respectively. The porosity (φ) values are 2.64 %, 2.76 %, and 3.98 % respectively. and porosity (Ф) values are 2.55 %, 2.67 %, and 3.16 % respectively. With the enhancement of tectonic action, the number of pores in coal increases, the fractal dimension of pores increases, and the surface morphology and pore structure become more complex. The depth and residual depth of nanoindentation increase with the increase of load. The hardness (Hx), fracture toughness (Kc) and creep stress exponent (n) of coal are negatively correlated with the aromatic interlayer spacing d002, and positively correlated with the degree of graphitization (Gd), while the elastic modulus (Ex) has no obvious relationship with it. The linear correlation between Hx and Ex is less than that between Kc and Ex. The relationship between Ex and Hx of coal samples and different peak loads is not obvious, but the Kc and n of coal samples increase with the increase of peak load. Under a certain load, the plastic energy, fracture energy and elastic energy increase with the increase of load. The tectonic coal with high metamorphic degree is prone to elastic deformation, while the coal with low coal quality is prone to plastic deformation. The research results can provide theoretical guidance for coalbed methane mining in tectonic coal reservoirs.

Quantitative investigation on the Young's modulus of ultrathin amorphous PS films attached to different substrates

AbstractIn this work, a method combining nanomechanical characterization and finite element analysis (FEA) was applied to reveal the influence mechanism and quantify the effects of the substrate on the mechanical properties of the ultrathin polystyrene (PS) film. SiOx, polylactic acid (PLA), and polydimethylsiloxane (PDMS), respectively, were chosen as the substrate. Results show that PS film exhibits a Young's modulus that is completely different from that of the bulk when the thickness is lower than the end‐to‐end distance of PS, and the value is directly related to the substrate to which the film is attached. The equivalent Young's moduli of the 20 nm PS films attached to SiOx, PLA, and PDMS substrates are 4.9, 3.4, and 1.0 GPa, respectively, which is positively correlated with the Young's modulus of the substrates. It suggests that the substrate has non‐negligible and important influences on the mechanical properties of supported polymer ultrathin films. The results provide new insight into the unique physical properties of polymer ultrathin films and favor the design of polymer‐based nanodevices.

Azithromycin-loaded liposomes and niosomes for the treatment of skin infections: Influence of excipients and preparative methods on the functional properties

The aim of this study was to develop azithromycin (AZT)-loaded liposomes (LP) and niosomes (NS) useful for the treatment of bacterial skin infections and acne. LP based on phosphatidylcholine from egg yolk (EPC) or from soybean lecithin (SPC), and NS composed of sorbitan monopalmitate (Span 40) or sorbitan monostearate (Span 60) were prepared through the thin film hydration (TFH) and the ethanol injection (EI) methods. The formulations were subsequently characterized for their physico-chemical and functional properties. Vesicles prepared through TFH showed higher average sizes than the corresponding formulations obtained by EI. All the vesicles presented adequate encapsulation efficiency and a negative ζ potential, which assured good stability during the storage period (except for LP-SPC). Formulations prepared with TFH showed a more prolonged AZT release than those prepared through EI, due to their lower surface area and multilamellar structure, as confirmed by atomic force microscopy nanomechanical characterization. Finally, among all the formulations, NS-Span 40-TFH and LP-EPC-TFH allowed the highest drug accumulation in the skin, retained the antimicrobial activity and did not alter fibroblast metabolism and viability. Overall, they could ensure to minimize the dosing and the administration frequency, thus representing promising candidates for the treatment of bacterial skin infections and acne.

Publisher Correction: Nanomechanical characterization

Publisher Correction: Nanomechanical characterization

Light-induced modulation of viscoelastic properties in azobenzene polymers.

Photo-induced isomerization of azobenzene molecules drives mass migrations in azopolymer samples. The resulting macroscopic directional photo-deformation of the material morphology has found many applications in literature, although the fundamental mechanisms behind this mass transfer are still under debate. Hence, it is of paramount importance to find quantitative observables that could drive the community toward a better understanding of this phenomenon. In this regard, azopolymer mechanical properties have been intensively studied, but the lack of a nanoscale technique capable of quantitative viscoelastic measurements has delayed the progress in the field. Here, we use bimodal atomic force microscopy (AFM) as a powerful technique for nanomechanical characterizations of azopolymers. With this multifrequency AFM approach, we map the azopolymer local elasticity and viscosity, with high resolution, after irradiation. We find that, while in the (previously) illuminated region, a general photo-softening is measured; locally, the Young modulus and the viscosity depend upon the inner structuring of the illuminating light spot. We then propose a possible interpretation based on a light-induced expansion plus a local alignment of the polymer chains (directional hole-burning effect), which explains the experimental observations. The possibility to access, in a reliable and quantitative way, both Young modulus and viscosity could trigger new theoretical-numerical investigations on the azopolymer mass migration dynamics since, as we show, both parameters can be considered measurable. Furthermore, our results provide a route for engineering the nanomechanical properties of azopolymers, which could find interesting applications in cell mechanobiology research.

Nanomechanical characterization of nanostructured Lu2SiO5 environmental barrier coatings by nano-indentation

Nanostructured rare-earth silicates are widely considered as environmental barrier coatings for the new generation of silicon-based composites. In current work, the nanostructured Lu2SiO5 coatings were deposited successfully using nanostructured Lu2SiO5 feedstocks by atmospheric plasma spraying (APS). Moreover, the nanomechanical properties of Lu2SiO5 coatings were characterized systematically by nano-indentation. Results indicate that the grain growth of Lu2SiO5 coatings is not obvious compared to Lu2SiO5 feedstocks. The nanostructured Lu2SiO5 coatings exhibit bi-modal nanomechanical properties. The elastic modulus and nanohardness of Lu2SiO5 coatings are 148.84 ± 28.00 GPa and 8.51 ± 4.12 GPa, respectively. In addition, the elastic work and plastic work of Lu2SiO5 coatings are 10.387 ± 1.283 nJ and 18.437 ± 6.823 nJ, respectively. The proportion of consumption of energy of Lu2SiO5 coatings is 0.636 ± 0.099 during indentation, which means that nanostructured Lu2SiO5 coatings process an excellent wear resistance.

Nanomechanical, mechanical and microstructural characterization of electron beam welded Al2219-T6 tempered aerospace grade alloy: A comprehensive study

As compared to traditional fusion welding processes, electron beam welding (EBW) is known to produce structurally robust microstructures and narrow heat-affected zone (HAZ) in metals. The process becomes more significant for the tempered alloys vulnerable to heat exposure. In the present investigation, Al 2219-T6 alloy was joined using the EBW process. The microstructural, mechanical, and nanomechanical characteristics of the resulting joint were investigated. EBW resulted in a narrow HAZ (22 μm) with a 430 mm fusion zone (FZ). A dendritic structure was observed in the FZ zone, while second-phase particles were absent indicating their dissolution during welding and interesting formation of Al2Cu mixture around the dendrites. The limited content of Cu in the base metal (BM) resulted in the formation of a solid solution in the FZ, along with the presence of fine equiaxed grains in the HAZ and equiaxed dendritic grains in the FZ zone. The X-ray diffraction analysis confirmed the absence of peaks corresponding to incoherent phases in the FZ. Compared to the BM, micro-hardness measurements revealed a 12.7 % increase in the hardness in the HAZ, while a significant decrease of approximately 19 % was observed in the FZ. The joint exhibited reduced tensile strength, ultimate strength by 42.2 %, and yield strength by 47.3 % when compared to the BM. The fracture analysis indicated a ductile failure mode with the presence of microvoids. Nano-indentation tests at various loads demonstrated a decrease in the nanohardness from the BM to the HAZ and FZ regions. Atomic force microscopy (AFM) analysis revealed significant pile-ups in the FZ, indicating the occurrence of plastic deformation during the welding process. The presented findings are valuable for the joint and structure design of Al −2219T6 alloy in particular and other Al alloys in general.

Insights into nanomechanical and nanotribological characterization of cross-linked polymer nanocomposites via molecular dynamics simulation

Polymer nanocomposites (PNCs) representing the cutting-edge domain of research have been exploited through indentation with experimentation and simulation. However, comprehending the underlying deformation mechanism via indentation in PNCs is still an open question. The present study emphasis on the influence of incorporating different sizes of nanoparticles (NPs) with varied volume fraction to regulate and improve mechanical and tribological properties of PNCs through molecular dynamics (MD) simulations. The coarse-grained MD simulations for nanoindentation and nanoscratching of crosslinked polymer network without and with NPs are performed. The identification of static and dynamic properties reveals the domains of dispersion and agglomeration with structural conformations in the PNCs. The NPs act as promising reinforcements that significantly strengthen the polymer system through improvement in mechanical and tribological properties. Further the analysis of curing percentage and bond breakage play vital role in locating stress induced sites during indentation. From MD simulations, the prominent improvement in deformation resistance is shown with particles exhibiting least radius of 1.5σ and 2.5σ which enhances with increase in volume fraction of NPs. The observations evoke the fact that presence of NPs reduce coefficient of friction (cof) and diminishes the resistance against scratch which generates higher shear strain in polymer chains. The main aim of this study is to provide design rule for incorporation of NPs coordinated towards tuning mechanical and tribological performance of PNCs. Additionally, insights into the deformation and nanoscratching mechanisms are highlighted providing directions to confer multi-functionalities to advanced PNCs.

Mussel‐Inspired Adhesive Hydrogels: Chemistry and Biomedical Applications†

Comprehensive SummaryAdhesive hydrogels are an emerging class of hydrogels that combine three‐dimensional hydrated networks with adhesive properties. These properties facilitate intimate tissue‐material contact in diverse biomedical applications, enhancing tissue joining, drug transport, and signal transmission. Inspired by the universal adhesiveness of mussel foot proteins, 3,4‐dihydroxyphenyl‐L‐alanine (DOPA) and its analogs have been extensively exploited for the fabrication of adhesive hydrogels, within which the DOPA moieties can not only serve as cross‐linking mediators but also participate in various intermolecular and surface interactions to mediate wet adhesion. This mini‐review highlights recent achievements in the development of mussel‐inspired adhesive hydrogels, focusing on: (1) elucidating DOPA‐mediated adhesion mechanisms through nanomechanical characterizations, (2) designing injectable adhesive hydrogels toward applications in drug delivery, hemostasis, and wound closure, which includes in situ gelling liquids and shear‐thinning preformed hydrogels, and (3) fabricating tough adhesive hydrogels with enhanced mechanical properties for use in tissue regeneration, biosensing, and bioimaging, with typical examples of nanocomposite and double‐network hydrogels. The challenges and prospects in this rapidly developing field are also discussed.

In Situ Nanomechanical Characterization Techniques for Soft Bioelectronic Interfaces and Their Building Blocks

AbstractSoft bioelectronic interfaces constitute a paradigm shift for biomedical devices. High‐resolution monitoring and stimulation of physiological processes in vivo are becoming possible with minimally invasive devices operated without inflicting tissue damage or discomfort over prolonged timescales. However, the development and commercialization of such interfaces still must address significant challenges. Biological tissue is subjected to continuous motion and the related device deformations can easily trigger fracture or delamination of the device components, putting long‐term durability of soft implants at risk. In this review, an overview of experimental techniques for testing mechanical properties and failure mechanisms of soft bioelectronic devices at the nanoscale while the deformation takes place (in situ) is provided. Through the tensile test, bending test, nanoindentation, and micropillar compression test, precise measurements of the mechanical properties of individual building blocks and the interfaces themselves can be obtained. Such parameters are crucial to design, model, and optimize the device's performance. Then, recent examples of how this information guides design and optimization of soft bioelectronic interfaces and devices for healthcare, robotics, and human–machine interfaces is provided. Last of all, future research that is needed to fully achieve long‐term soft bioelectronic interfaces for integration with the human body is discussed.

Overcoming Challenges and Limitations Regarding the Atomic Force Microscopy Imaging and Mechanical Characterization of Nanofibers

Atomic force microscopy (AFM) is a powerful tool that enables imaging and nanomechanical properties characterization of biological materials. Nanofibers are the structural units of many biological systems and their role in the development of advanced biomaterials is crucial. AFM methods have proven to be effective towards the characterization of fibers with respect to biological and bioengineering applications at the nanoscale. However, both the topographical and mechanical properties’ nanocharacterizations of single fibers using AFM are challenging procedures. In particular, regarding imaging procedures, significant artifacts may arise from tip convolution effects. The geometrical characteristics of the AFM tip and the nanofibers, and the fact that they have similar magnitudes, may lead to significant errors regarding the topographical imaging. In addition, the determination of the mechanical properties of nanofibers is also challenging due to their small dimensions and heterogeneity (i.e., the elastic half-space assumption is not valid in most cases). This review elucidates the origins of errors in characterizing individual nanofibers, while also providing strategies to address limitations in experimental procedures and data processing.

Nanoscale evolution of rubber-oil modified asphalt binder after thermal and UV aging

Thermal oxidation and ultraviolet exposure cause complex micro-scale chemical changes in asphalt binders, leading to severe deterioration of pavements. The aging-induced evolution of nanoscale domains in asphalt binders was investigated using multiple nanoscale characterizations. This in turn provides insights to develop means of alleviating the aging of asphalt binders to extend pavement service life. The chemical composition, surface topography, and mechanical properties of four asphalt binders (base asphalt and modified asphalt with bio-oils and crumb rubber) are investigated by atomic force microscopy during thermal aging and UV aging and a combination thereof. It was shown that the three domains in the asphalt binder react differently to aging. Abundant carbonyl and sulfoxide compositions are observed in the aged base asphalt binder, which is mainly generated and concentrated in the para domains. The addition of rubber and bio-modified rubber reduces the formation of aging-related compositions in para domains, thereby enhancing the aging resistance of asphalt binder. Aging also significantly changes the surface roughness and domain structures of asphalt binders. Furthermore, it was shown that the domain stability during thermal aging and UV aging can be enhanced by crumb rubber and bio-oils, respectively. Nano-mechanical characterization shows the surface of asphalt binders becomes stiffer, and its adhesion is reduced after aging. Significant reduction (up to 26%) in latter aging indicators was observed with the bio-modifier used in rubberized asphalt. This paper provides insights pertaining to the aging-induced evolution of asphalt binders while examining the efficacy of bio-modification of rubberized asphalt to delay aging. It is recommended to include hybrid aging in future studies and to test bio-modified rubberized asphalt at a larger scale.

Thickness Gradient in Polymer Coating by Reactive Layer-by-Layer Assembly on Solid Substrate.

The study describes a simple yet robust methodology for forming gradients in polymer coatings with nanometer-thickness precision. The thickness gradients of 0-20 nm in the coating are obtained by a reactive layer-by-layer assembly of polyester and polyethylenimine on gold substrates. Three parameters are important in forming thickness gradients: (i) the incubation time, (ii) the incubation concentration of the polymer solutions, and (iii) the tilt angle of the gold substrate during the dipping process. After examining these parameters, the characterization of the anisotropic surface obtained under the best conditions is presented in the manuscript. The thickness profile and nanomechanical characterization of the polymer gradients are characterized by atomic force microscopy. The roughness analysis has demonstrated that the coating exhibited decreasing roughness with increasing thickness. On the other hand, Young's moduli of the thin and thick coatings are 0.50 and 1.4 MPa, respectively, which assured an increase in mechanical stability with increasing coating thickness. Angle-dependent infrared spectroscopy reveals that the C-O-C ester groups of the polyesters exhibit a perpendicular orientation to the surface, while the C≡C groups are parallel to the surface. The surface properties of the polymer gradients are explored by fluorescence microscopy, proving that the dye's fluorescence intensity increases as the coating thickness increases. The significant benefit of the suggested methodology is that it promises thickness control of gradients in the coating as a consequence of the fast reaction kinetics between layers and the reaction time.