Novel mineralized electrospun chitosan/PVA/TiO2 nanofibrous composites for potential biomedical applications: computational and experimental insights.

Electrospun nanofibrous materials serve as potential solutions for several biomedical applications as they possess the ability of mimicking the extracellular matrix (ECM) of tissues. Herein, we report on the fabrication of novel nanostructured composite materials for potential use in biomedical applications that require a suitable environment for cellular viability. Anodized TiO2 nanotubes (TiO2 NTs) in powder form, with different concentrations, were incorporated as a filler material into a blend of chitosan (Cs) and polyvinyl alcohol (PVA) to synthesize composite polymeric electrospun nanofibrous materials. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), nanoindentation, Brunauer-Emmett-Teller (BET) analysis, and MTT assay for cell viability techniques were used to characterize the architectural, structural, mechanical, physical, and biological properties of the fabricated materials. Additionally, molecular dynamics (MD) modelling was performed to evaluate the mechanical properties of the polymeric PVA/chitosan matrix upon reinforcing the structure with TiO2 anatase nanotubes. The Young's modulus, shear and bulk moduli, Poisson's ratio, Lame's constants, and compressibility of these composites have been computed using the COMPASS molecular mechanics force fields. The MD simulations demonstrated that the inclusion of anatase TiO2 improves the mechanical properties of the composite, which is consistent with our experimental findings. The results revealed that the mineralized material improved the mechanical strength and the physical properties of the composite. Hence, the composite material has potential for use in biomedical applications.

Computational Modeling for Biomimetic Sensors.

Computational modeling has become an important tool for scientists to both predict the properties of materials and systems and to gain a better understanding of the underlying mechanisms. This chapter is a brief yet holistic introduction to computational modeling, focusing on density functional theoretical (DFT) methods. The different types of computational modeling methods, including molecular mechanics, semiempirical, and ab initio methods, as well as the different software available for computational calculations are discussed. A step-by-step guide is presented using Gaussian16 software to introduce the basics of computational modeling based on our work with biomimetic polymer beads. However, the guide presented here is not limited to this particular system; it can be applied to any computational modeling case. The computational modeling methods for the building of the structures are described, and the calculation parameters, such as basis sets and exchange-correlation functionals, are explained. The output data and results are presented and discussed. Two simulation features were the focus of this work: (1) the simulation of the Raman spectra and (2) the different solvation environments. While some researchers in the field believe that computational simulation should be performed before the lab experiments, in fact they should be done simultaneously. This is so that the output of the experimental data can be used as the input of the computational parameters, as a form of semiempirical modeling, in order to achieve more accurate results for predicting the behavior of future experiments and understanding the atomic forces and mechanisms.

Ni-free, built-in nanotubular drug eluting stents: Experimental and theoretical insights.

Stents used for cardiovascular applications are composed of three main elements; a metal, polymer coating and the specific drug component. Nickel-based metals and polymer coatings currently used in the stent market have increased the recurrence of in-stent restenosis and stent failure due to inflammation. In this study, a Ti-8Mn alloy was used to fabricate a nanostructured surface that can be used for drug eluting stents to overcome the hypersensitivity of metals that are currently used in stent making as well as introducing a new built-in nano-drug reservoir instead of polymer coatings. Two different systems were studied: titanium dioxide nanotubes (NTs) and Ti-8Mn oxides NTs. The materials were characterized using field emission electron microscope (FESEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), roughness, wettability and surface energy measurements. Nanoindentation was used to evaluate the mechanical properties of the nanotubes as well as their stability. In-vitro cytotoxicity and cell proliferation assays were used to study the effect of the nanotubes on cell viability. Computational insights were also used to test the blood compatibility using band gap model analysis, comparing the band gap of the materials under investigation with that of the fibrinogen, in order to study the possibility of charge transfer that affects the blood clotting mechanism. In addition, the drug loading capacity of the materials was studied using acetyl salicylic acid as a drug model.

First-principles descriptors of CO chemisorption on Ni and Cu surfaces.

A comprehensive analysis of low coverage CO adsorption on Ni and Cu low-index miller surfaces - (100), (110), and (111) - over all the possible adsorption sites is presented. Systems are theoretically studied within an accurate adsorption model using RPBE density functional calculations to obtain electronic and geometrical structure predictions along with their corresponding adsorption energy computations. Based on the surface- and site-dependent comparisons of the adsorption mechanisms, we were able to grasp trends that point to the factors that determine the final C-O structure upon adsorption. The resulting C-O bond length is found to be directly dependent on structural parameters, such as depth of adsorption and metal-adsorbate bonding distances, and the quantity of charge transferred from the surface to the CO molecule. Those factors are collated into a formula that defines the final C-O bond: the "C-O formula". For each adsorption site, the final C-O bond length is calculated using this formula and compared with the DFT predictions, where consistent matching results are obtained. Deeper analysis of the adsorbed C-O molecule is also presented from a molecular orbital level. Density of states (DOS) charts were exploited to investigate the perturbations in the 3σ and 1π orbitals that hold the internal C-O bond. From this analysis, a consistent link between the degree of destabilization of the orbitals and the final C-O bond length is found, obtaining a more profound understanding of the final adsorbate structure. Energetically, adsorptions on Cu and Ni surfaces are compared within the Blyholder-Nilsson and Petersson (B-NP) model. The frontier (5σ and 2π*) orbital energies relative to the d-band center of the metal surfaces are displayed, which implicitly defines the adsorption energy. The controversial repulsive nature of the σ-interaction proposed in the NP model has been tested by tracking the charge redistribution within the metallic states, including the broad sp-states. The nature of σ-interaction is, however, found to be dependent on the substrate type; repulsive σ-interaction is concluded for Ni, while for Cu, a rather dual nature is found, including both partial repulsive and attractive behavior, with a dominant and overall repulsive nature, in agreement with the NP model. The degree of σ repulsion/attraction is also found to be dependent on the metal coordination. Finally, spin-polarized DFT calculations were repeated for Ni surfaces and compared with the previous Ni results without spin-polarization. The reported results confirmed the absence of correlation between adsorption energetics and the final adsorbate structure, and verified the factors presented in the "C-O formula" as the main descriptors for the adsorbate structure.

Unveiling CO adsorption on Cu surfaces: new insights from molecular orbital principles.

CO adsorption on Cu(100), (110), and (111) surfaces has been extensively studied using Kohn-Sham density functional theory calculations. A holistic analysis of adsorption energies, charge transfer, and structural changes has been employed to highlight the variations in adsorption mechanisms upon changing the surface type and the adsorption site. Each surface, with its unique arrangement of atoms, resulted in a varying adsorbate behavior, although the same adsorption site is considered. This directly reflects the influence of the atomic arrangement on the substrate-adsorbate interactions. Site-interactions are rigorously investigated using molecular-orbital and charge transfer principles taking into account the fundamental interaction of frontier (5σ and 2π*) orbitals. Considering the effects of the surface atomic arrangement and density of metal interacting orbitals, along with the relative d-5σ and d-2π* energy spacings, the calculated adsorption preference to higher coordination sites is explained, which also revealed valuable interpretations to the well-known DFT CO adsorption puzzle. In addition, we studied the perturbations occurring upon adsorption to the 3σ and 1π orbitals, which hold the internal C-O bond. Studying 3σ and 1π orbital perturbations provided a wealth of theoretical interpretations for the varying behavior of the adsorbate molecule when similar adsorption sites are compared at different facets.