The Corrosion Control of Temporary Magnesium (AZ31 alloy) Implants Using Electrospinning Polycaprolactone-curcumin Nanofiber Coatings

A comparative study on pre- and post-production plasma treatments of PCL films and nanofibers for improved cell-material interactions

Comparison of the short and long-term degradation behaviors of as-cast pure Mg, AZ91 and WE43 alloys

Atropa belladonna is one of the herbs used to treat wounds and prevent inflammation. This study provides a scientific assessment for the wound healing potential of biodegradable nanofibers containing Ag nanoparticles encapsulated with atropa belladonna extract (eAgNPs). Ultraviolet-visible (UV-vis) spectroscopy was used to observe the localized surface plasmon resonance (LSPR) band of AgNPs synthesized from atropa belladonna extract prepared under different conditions. Polycaprolactone (PCL) nanofibers with eAgNPs were fabricated using the electrospinning technique. The distribution of AgNPs and eAgNPs and the size of nanofibers were characterized with scanning and transmission electron microscopy (SEM, TEM) before and after degradation at the end of 18 weeks. Fourier transform infrared (FTIR) spectroscopy showed the surface interactivity between AgNPs, atropa belladonna extract and PCL nanofibers and also approved the modification of PCL nanofibers with eAgNPs. X-ray diffraction analysis (XRD) defined the formation of the crystalline AgNPs and appreciated the orientation of the nanofibers. Results of tension tests revealed that modification of PCL nanofibers with pure AgNPs and eAgNPs significantly increased strength and tensile modulus. Due to the hydrophobic nature of PCL, modification with pure AgNPs and eAgNPs slightly reduced its hydrophobicity. Biodegradation tests of PCL nanofibers with eAgNPs exhibited a higher degradation rate than neat PCL nanofibers. In vitro MTT results revealed that eAgNPs doped PCL samples have better cell viability than AgNPs doped and neat PCL nanofibers. Owing to their antibacterial properties, biodegradation rates, low cytotoxicity, mechanical and surface morphologic properties of AgNPs modified PCL nanofibers containing atropa belladonna are considered to have a great potential for skin regeneration.

In situ loading of lipase onto polycaprolactone nanofibers via alternate electrospin-electrospray for enzymatic self-degradable air filtration membranes.

The use of polyelectrolytes is emerging as a fascinating strategy for the functionalization of biomedical membranes, due to their ability to enhance biological responses using the interaction effect of charged groups on multiple interface properties. Herein, two different polyelectrolytes were used to improve the antibacterial properties of polycaprolactone (PCL) nanofibers fabricated via electrospinning. First, a new cationic cellulose derivative, cellulose-bearing imidazolium tosylate (CIMD), was prepared via the nucleophilic substitution of the tosyl group using 1-methylimidazole, as confirmed by NMR analyses, and loaded into the PCL nanofibers. Secondly, sodium alginate (SA) was used to uniformly coat the fibers' surface via self-assembly, as remarked through SEM-EDX analyses. Polyelectrolyte interactions between the CIMD and the SA, initially detected using a FTIR analysis, were confirmed via Z potential measurements: the formation of a CMID/SA complex promoted a substantial charge neutralization of the fibers' surfaces with effects on the physical properties of the membrane in terms of water adsorption and in vitro degradation. Moreover, the presence of SA contributed to the in vitro response of human mesenchymal stem cells (hMSCs), as confirmed by a significant increase in the cells' viability after 7 days in the case of the PCL/CMID/SA complex with respect to the PCL and PCL/CMID membranes. Contrariwise, SA did not nullify the antibacterial effect of CMID, as confirmed by the comparable resistance exhibited by S. mutans, S. aureus, and E. coli to the PCL/CIMD and PCL/CIMD/SA membranes. All the reported results corroborate the idea that the CIMD/SA functionalization of PCL nanofibers has a great potential for the fabrication of efficient antimicrobial membranes for wound healing.

In-vitro long term and electrochemical corrosion resistance of cold deformed nitrogen containing austenitic stainless steels in simulated body fluid

Biodegradable nanofibers are extensively employed in different areas of biology and medicine, particularly in tissue engineering. The electrospun polycaprolactone (PCL) nanofibers are attracting growing interest due to their good mechanical properties and a low-cost structure similar to the extracellular matrix. However, the unmodified PCL nanofibers exhibit an inert surface, hindering cell adhesion and negatively affecting their further fate. The employment of PCL nanofibrous scaffolds for wound healing requires a certain modification of the PCL surface. In this work, the morphology of PCL nanofibers is optimized by the careful tuning of electrospinning parameters. It is shown that the modification of the PCL nanofibers with the COOH plasma polymers and the subsequent binding of NH2 groups of protein molecules is a rather simple and technologically accessible procedure allowing the adhesion, early spreading, and growth of human fibroblasts to be boosted. The behavior of fibroblasts on the modified PCL surface was found to be very different when compared to the previously studied cultivation of mesenchymal stem cells on the PCL nanofibrous meshes. It is demonstrated by X-ray photoelectron spectroscopy (XPS) that the freeze–thawed platelet-rich plasma (PRP) immobilization can be performed via covalent and non-covalent bonding and that it does not affect biological activity. The covalently bound components of PRP considerably reduce the fibroblast apoptosis and increase the cell proliferation in comparison to the unmodified PCL nanofibers or the PCL nanofibers with non-covalent bonding of PRP. The reported research findings reveal the potential of PCL matrices for application in tissue engineering, while the plasma modification with COOH groups and their subsequent covalent binding with proteins expand this potential even further. The use of such matrices with covalently immobilized PRP for wound healing leads to prolonged biological activity of the immobilized molecules and protects these biomolecules from the aggressive media of the wound.

Mussel-inspired functionalization of PEO/PCL composite coating on a biodegradable AZ31 magnesium alloy

Correlation between electrochemical impedance measurements and corrosion rates of Mg-1Ca alloy in simulated body fluid

ABSTRACTThe interdependence of solution parameters, process parameters, and environmental parameters warrants a careful optimization of them for the fabrication of polycaprolactone (PCL) nanofibers by electrospinning. A new combination of chloroform (CF)/ethyl alcohol (EtOH)/formic acid (FA) (9:1:0.1) is explored for electrospinning of PCL nanofibers for the first time. The study aims to optimize the conditions for the fabrication of PCL nanofibers for the proposed solvent mixture and develop an electrospinnability map for the first time. The fabricated PCL nanofibers were evaluated for their characteristic properties, water absorption capacity, in vitro degradation, and cytotoxicity. The PCL nanofibers were loaded with 1 wt.% tetracycline hydrochloride (TCH) (relative to the mass of PCL), and the release profile of TCH in phosphate‐buffered saline (PBS) (pH: 7.40) at 37°C was evaluated. A combination of 10 wt.% PCL, CF/EtOH/FA (9:1:0.1), 15 kV, a working distance of 15 cm, a flow rate of 1 mL/h, 27°C, and 45% relative humidity (RH) are identified as optimum conditions for the generation of uniform and continuous PCL nanofibers. The drug release profile revealed that the TCH‐loaded PCL nanofibers will be useful for drug delivery applications where a burst release of antibiotics is required, particularly for postsurgery treatments.

Biomaterials are materials used to replace parts of living systems. 316 L stainless steel has long been used as a substitute material for bone dislocation victims. This research aims to substitute 316 L stainless steel bone implant material with Cr-Ni coated ST 41 carbon steel which has been immersed with varying time-intensity with Simulated Body Fluid. Material testing uses the method of potentiodynamic polarization, electrochemical impedance spectroscopy, and Scanning Electron Microscope. The results of this study are in the form of a comparison of corrosion rate and surface characteristics between 316 L stainless steel and Cr-Ni coated ST 41 Carbon Steel. The immersion time of the material for 12 hours and 366 shows a low corrosion rate with a corrosion rate of 0.0051714 mm year−1 with and 0.001557 mm year−1 for ST41 carbon steel material with Cr-Ni coating, whereas in Stainless Steel 316 L has a corrosion rate value of 0.0029546 mm year−1 and 0.0013166 mm year−1. Surface characteristics show insignificant differences between ST41 steel with Cr-Ni coating and 316 L stainless steel. The results of the study show that Cr-Ni coated ST41 carbon steel material can substitute 316 L stainless steel as a biomaterial in bone implants because it has a low corrosion rate and different insignificant surface characteristics.

Polycaprolactone (PCL) nanofibers (PCL-NF) with uniform fibrous structure were fabricated by electrospinning. However, PCL-NF has hydrophobic surface, lacks functional groups and hence it is not a good substrate for cell adhesion. To improve the cell adhesion, PCL-NF surfaces were modified by low pressure RF discharge plasma treatment using monomer such as acrylic acid or oxygen gas. The plasma treated PCL-NFs improved the wettability and cell proliferation.

This paper reports on the corrosion of Mg alloy AZ31 in simulated body fluid (SBF) using static immersion tests and electrochemical impedance spectroscopy. A preliminary study on the effect of flowing SBF on the corrosion behaviour of AZ31 has also been carried out. Low toxicity ionic liquids (ILs) trimethyl(butyl)phosphonium diphenyl phosphate P1444DPP and trihexyl(tetradecyl)phosphonium bis-2,4,4trimethylpentyl-phosphinate [P66614][i(C8)2PO2] have been used to provide corrosion protection for AZ31 in SBF. Time dependent immersion tests indicate that under static conditions, AZ31 suffers severe localised corrosion in SBF, with pits developing predominantly beside the Al–Mn intermetallic phase in the α matrix. At longer immersion times, the corrosion product eventually precipitates and covers the entire specimen surface. When exposed to SBF under flowing conditions with a shear stress of 0·88 Pa, more uniform corrosion was observed. The optical profilometry results and electrochemical impedance spectroscopy analysis suggest that both P1444DPP and [P66614][i(C8)2PO2] pretreatments can increase the corrosion resistance of AZ31 in SBF, in particular by decreasing the number of deeper pits found on the alloy surface. Cytotoxic test shows that the presence of the ILs P1444DPP and [P66614][i(C8)2PO2] in cell culture media slightly inhibits the growth of human coronary artery endothelial cells in comparison with the good cell viability around the treated specimen. A pretreatment with IL is used in order to improve the corrosion resistance of this alloy in SBF.

Electrochemical Impedance Spectroscopy (EIS) is widely applied in Electrochemistry for studying the electrode/electrolyte interface, films, coating, and ion transport mechanisms amongst others. Most EIS measurements are based on primary modulation in frequency and amplitude of a sine wave which serves as perturbation signal – either potentiostatic or galvanostatic. Three requirements in an electrochemical system including stability, causality, and linearity are necessary for an accurate EIS measurement. This is described in detail by Macdonald, Orazem, and Tribollet et al [1-2]. Further modulation instrumentations relating to single-sine and multi-sine wave modulations with the purpose to increase the signal-to-noise ratio, measurement time [3], and obtaining additional information about the current system (e.g. corrosion rate) are discussed in this presentation. An applied signal of two superimposed sine waves with two different frequencies can act as perturbation for measuring the general corrosion rate and pitting corrosion. This technique – also referred to as Electrochemical Frequency Modulation (EFM) – was well developed and described by Bosch and Bogaerts et al [4-5]. Impedance measurements with non-linear perturbation can provide further information relating to corrosion kinetics of the Tafel slope and corrosion rate based on Taylor expansion using the traditional Butler–Volmer equation. The overpotential (η) can be expressed as follows: η = V [sin(ω 1t) + sin(ω 2t)] After rearranging the equation and substituting various parameters, a useful relationship between potential and current can be derived. Analysis of the corrosion rate using beverages cans and soda is presented in this study. EFM is compared to other techniques such as EIS, LPR (Linear Polarization Resistance), and EN (Electrochemical Noise). Instrumentation issues relating to frequency modulation and harmonics are discussed based on applications in the corrosion and fuel cell field. The second signal modulation in EIS is the variable amplitude. Noise level or impedance increases at lower frequency. Impedance data can scatter with lower signal amplitudes. Wojcik and Orazem used variable-amplitude signals in galvanostatically modulated impedance spectroscopy to assess reactivity at the corrosion potential without distorting temporal evolution of the system relating to copper in seawater [6-7]. Variable-amplitude signals can increase the signal level for a higher quality of EIS data. However, the voltage amplitude cannot follow a linear relationship when the impedance increases at lower frequencies during galvanostatic EIS. A fixed voltage (less than 10 mV) with a variable current amplitude for the sine wave can be used to achieve this goal. Instrumentation of amplitude modulation relating to noise from instruments and electrochemical system is further discussed in this presentation. The application of variable amplitude modulation is discussed based on EIS measurements of coatings and lithium-ion batteries.

Despite the excellent oxygen barrier and biodegradability of polyvinyl alcohol (PVA), its poor physical properties owing to its inherent hydrophilicity limit its application. In this paper, we report a novel surface modification technique for PVA films, involving the control of the predrying conditions (i.e., amount of residual solvent) of the coated PVA film and adjusting the electrospinning process of hydrophobic polycaprolactone (PCL) nanofibers onto the PVA films. The residual solvent of the coated PVA film was varied by changing the predrying time. A shorter predrying time increased the residual solvent content significantly (p < 0.05) and the flexibility of the coated PVA film. Moreover, scanning electron microscopy depicted the improved physical binding of hydrophobic PCL nanofibers to the hydrophilic PVA surface with increased penetration depth to the PVA film with shorter drying times. The PVA/PCL composite films with different predrying times and electrospun PCL nanofibers exhibited an apparent increase in the contact angle from 8.3° to 95.1°. The tensile strength of the pure PVA film increased significantly (p < 0.05) from 7.5 MPa to 77.4 MPa and its oxygen permeability decreased from 5.5 to 1.9 cc/m2·day. Therefore, our newly developed technique is cost-effective for modifying the surface and physical properties of hydrophilic polymers, broadening their industrial applications.