Bioactivity and Antibacterial Analysis of Plasticized PLA Electrospun Fibers Reinforced with MgO and Mg(OH)2 Nanoparticles.

In this work, we focused on the bioactivity and antibacterial behavior of PLA-based electrospun fibers, efibers, reinforced with both MgO and Mg(OH)2 nanoparticles, NPs. The evolution of PLA-based efibers was followed in terms of morphology, FTIR, XRD, and visual appearance. The bioactivity was discussed in terms of hydroxyapatite growth after 28 days, considered as T28, of immersion in simulated body fluid, SBF. In particular, the biomineralization process evidenced after immersion in SBF started at T14 in both systems. The number of precipitated crystals increased by increasing the amount of both NPs. The chemical composition of the precipitated crystals was also characterized in terms of the Ca/P molar ratio after T28 of immersion in SBF, indicating the presence of hydroxyapatite on the surface of both reinforced efibers. Moreover, a reduction in the average diameter of the PLA-based efibers was observed, reaching a maximum reduction of 46 and 60% in the average diameter of neat PLA and PLA:OLA efibers, respectively, after 28 days of immersion in SBF. The antibacterial behavior of the MgO and Mg(OH)2 NPs in the PLA-based electrospun fibers was tested against Escherichia coli, E. coli, as the Gram-negative bacteria, and Staphylococcus aureus, S. aureus, as the Gram-positive bacteria, obtaining the best antibacterial activity against the Gram-negative bacteria E. coli of 21 ± 2% and 34 ± 6% for the highest concentration of MgO and Mg(OH)2 NPs, respectively.

Innovative Anodic Treatment to Obtain Stable Metallic Silver Micropatches on TiO2 Nanotubes: Structural, Electrochemical, and Photochemical Properties.

Electrochemical modification of the Ti surface to obtain TiO2 nanotubes (NT-Ti) has been proposed to enhance osseointegration in medical applications. However, susceptibility to microbial adhesion, linked to biomaterial-associated infections, and the high TiO2 band gap energy, which allows light absorption almost exclusively in the ultraviolet (UV) region, limit its applications. Modifying the TiO2 semiconductor with metals such as Ag has been suggested both for antimicrobial purposes and for absorbing light in the visible region. The formation of NT-Ti with Ag micropatches (Ag-NT-Ti) is pursued with the objective of enhancing the stability of the deposits and preventing cytotoxic levels of Ag cellular uptake. The innovative process proposed here involves immersing NT-Ti in a AgNO3 solution as the initial step. Diverging from previously reported electrochemical methods, this process incorporates anodization within the TiO2 oxide formation region instead of cathodic reduction generally employed by other researchers. The final step encompasses an annealing treatment. The treatments result in the in situ Ag1+ reduction and formation of stable and active micropatches of metallic Ag on the NT-Ti surface. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Raman, diffuse reflectance spectroscopy (DRS), wettability assessment, and electrochemical characterizations were conducted to evaluate the modified surfaces. The well-known properties of NT-Ti surfaces were enhanced, leading to improved photocatalytic activity across both visible and UV regions, significant stability against detachment, and controlled release of Ag1+ for promising antimicrobial effects.

Metastable FeMg particles for controlling degradation rate, mechanical properties, and biocompatibility of Poly(l-lactic) acid (PLLA) for orthopedic applications.

Poly(l-lactic) acid (PLLA) is commonly used in bioabsorbable medical implants, but it suffers from slow degradation rate and rapid decline in mechanical properties for orthopedic applications. To address this drawback, recent research has explored the use of Mg as a filler for PLLA, resulting in composites with improved degradation rate and cytocompatibility compared to neat PLLA. In this study, FeMg powder particles were proposed as fillers for PLLA to investigate the potential of PLLA/FeMg composites for bioabsorbable implants. Cylinder specimens of PLLA, PLLA/Fe, PLLA/Mg and PLLA/FeMg were prepared using solvent casting followed by thermo-molding. The microstructure, thermal behavior, in vitro degradation behavior in simulated body fluid, mechanical properties and cytocompatibility of these composites were examined. The results indicate that the presence of FeMg particles prevents the deterioration of the composite mechanical properties, at least up to 14 days. Once a certain amount of degradation of the composite is reached, the degradation is faster than that of PLLA. Direct cytotoxicity assays revealed that pre-osteoblast MC3T3-E1 cells successfully adhered to and proliferated on the PLLA/FeMg surface. The inclusion of a low percentage of Mg into the Fe lattice not only accelerated the degradation rate of Fe but also improved its cytocompatibility. The enhanced degradation rate, mechanical properties, and osteoconductive properties of this composite make it a promising option for temporary orthopedic biomedical devices.

Thermal Properties and In Vitro Biodegradation of PLA-Mg Filaments for Fused Deposition Modeling.

Additive manufacturing, in particular the fused deposition method, is a quite new interesting technique used to obtain specific 3D objects by depositing layer after layer of material. Generally, commercial filaments can be used in 3D printing. However, the obtention of functional filaments is not so easy to reach. In this work, we obtain filaments based on poly(lactic acid), PLA, reinforced with different amounts of magnesium, Mg, microparticles, using a two-step extrusion process, in order to study how processing can affect the thermal degradation of the filaments; we additionally study their in vitro degradation, with a complete release of Mg microparticles after 84 days in phosphate buffer saline media. Therefore, considering that we want to obtain a functional filament for further 3D printing, the simpler the processing, the better the result in terms of a scalable approach. In our case, we obtain micro-composites via the double-extrusion process without degrading the materials, with good dispersion of the microparticles into the PLA matrix without any chemical or physical modification of the microparticles.

Thermal treatment of magnesium particles in polylactic acid polymer films elicits the expression of osteogenic differentiation markers and lipidome profile remodeling in human adipose stem cells.

The efficacy of polylactic acid (PLA)/Magnesium (Mg)-based materials for driving stem cells toward bone tissue engineering applications requires specific Mg surface properties to modulate the interface of stem cells with the film. Here, we have developed novel PLA/Mg-based composites and explored their osteogenic differentiation potential on human adipose stem cells (hASCs). Mg-particles/polymer interface was improved by two treatments: heating in oxidative atmosphere (TT) and surface modification with a compatibilizer (PEI). Different contents of Mg particles were dispersed in PLA and composite surface and bulk properties, protein adsorption, stem cell-PLA/Mg interactions, osteogenic markers expressions, and lipids composition profile were evaluated. Mg particles were uniformly distributed on the surface and in the bulk PLA polymer. Improved and modulated particle-polymer adhesion was observed in Mg particle-treated composites. After 21 days in canonical growth culture conditions, hASCs on PLA/MgTT displayed the highest expression of the general osteogenic markers, RUNX2, SSP1, and BGLAP genes, Alkaline Phosphatase, type I Collagen, Osteopontin, and Calcium deposits. Moreover, by LC/MS QTOF mass-spectrophotometry lipidomic analysis, we found in PLA/MgTT-cells, for the first time, a remodeling of the lipid classes composition associated with the osteogenic differentiation. We ascribed these results to MgTT characteristics, which improve Mg availability and composite osteoinductive performance.

Effect of the Addition of MgO Nanoparticles on the Thermally-Activated Shape Memory Behavior of Plasticized PLA Electrospun Fibers.

In this work, the thermally-activated shape memory behavior of poly(lactic acid)-based electrospun fibers (PLA-based efibers) reinforced with different amounts of magnesium oxide (MgO) nanoparticles (NPs) was studied at different temperatures. In particular, MgO NPs were added at different concentrations, such as 0.1, 0.5, 1 and 3 wt%, with respect to the PLA matrix. The glass-transition temperature of PLA-based efibers was modulated by adding a 20 wt% of oligomer lactic acid as plasticizer. Once the plasticized PLA-based efibers were obtained and basically characterized in term of morphology as well as thermal and mechanical properties, thermo-mechanical cycles were carried out at 60 °C and 45 °C in order to study their thermally-activated shape memory response, demonstrating that their crystalline nature strongly affects their shape memory behavior. Importantly, we found that the plastificant effect in the mechanical response of the reinforced plasticized PLA efibers is balanced with the reinforcing effect of the MgO NPs, obtaining the same mechanical response of neat PLA fibers. Finally, both the strain recovery and strain fixity ratios of each of the plasticized PLA-based efibers were calculated, obtaining excellent thermally-activated shape memory response at 45 °C, demonstrating that 1 wt% MgO nanoparticles was the best concentration for the plasticized system.

PLA Electrospun Fibers Reinforced with Organic and Inorganic Nanoparticles: A Comparative Study.

In this work, different poly (lactic acid) (PLA)-based nanocomposite electrospun fibers, reinforced with both organic and inorganic nanoparticles, were obtained. As organic fibers, cellulose nanocrystals, CNC, both neat and functionalized by "grafting from" reaction, chitosan and graphene were used; meanwhile, hydroxyapatite and silver nanoparticles were used as inorganic fibers. All of the nanoparticles were added at 1 wt% with respect to the PLA matrix in order to be able to compare their effect. The main aim of this work was to study the morphological, thermal and mechanical properties of the different systems, looking for differences between the effects of the addition of organic or inorganic nanoparticles. No differences were found in either the glass transition temperature or the melting temperature between the different electrospun systems. However, systems reinforced with both neat and functionalized CNC exhibited an enhanced degree of crystallinity of the electrospun fibers, by up to 12.3%. From a mechanical point of view, both organic and inorganic nanoparticles exhibited a decreased elastic modulus and tensile strength in comparison to neat electrospun PLA fibers, improving their elongation at break. Furthermore, all of the organic and inorganic reinforced systems disintegrated under composting conditions after 35 days.

In Vitro Degradation of Plasticized PLA Electrospun Fiber Mats: Morphological, Thermal and Crystalline Evolution.

In the present work, fiber mats of poly(lactic acid), PLA, plasticized by different amounts of oligomer lactic acid, OLA, were obtained by electrospinning in order to investigate their long term hydrolytic degradation. This was performed in a simulated body fluid for up to 352 days, until the complete degradation of the samples is reached. The evolution of the plasticized electrospun mats was followed in terms of morphological, thermal, chemical and crystalline changes. Mass variation and water uptake of PLA-based electrospun mats, together with pH stability of the immersion media, were also studied during the in vitro test. The results showed that the addition of OLA increases the hydrolytic degradation rate of PLA electrospun fiber mats. Moreover, by adding different amounts of OLA, the time of degradation of the electrospun fiber mats can be modulated over the course of a year. Effectively, by increasing the amount of OLA, the diameter of the electrospun fibers decreases more rapidly during degradation. On the other hand, the degree of crystallinity and the dimension of the α crystals of the electrospun fiber mats are highly affected not only by the presence but also by the amount of OLA during the whole process.

Potential Applications of Magnesium-Based Polymeric Nanocomposites Obtained by Electrospinning Technique.

In the last few decades, the development of new electrospun materials with different morphologies and advanced multifunctional properties are strongly consolidated. There are several reviews that describe the processing, use and characterization of electrospun nanocomposites, however, based on our knowledge, no review on electrospun nanocomposites reinforced with nanoparticles (NPs) based on magnesium, Mg-based NPs, are reported. Therefore, in the present review, we focus attention on the fabrication of these promising electrospun materials and their potential applications. Firstly, the electrospinning technique and its main processing window-parameters are described, as well as some post-processing methods used to obtain Mg-based materials. Then, the applications of Mg-based electrospun nanocomposites in different fields are pointed out, thus taking into account the current trend in developing inorganic-organic nanocomposites to gradually satisfy the challenges that the industry generates. Mg-based electrospun nanocomposites are becoming an attractive field of research for environmental remediation (waste-water cleaning and air filtration) as well as for novel technical textiles. However, the mayor application of Mg-based electrospun materials is in the biomedical field, as pointed out. Therefore, this review aims to clarify the tendency in using electrospinning technique and Mg-based nanoparticles to huge development at industrial level in the near future.

Impact of PLA/Mg films degradation on surface physical properties and biofilm survival.

New biocompatible and bioabsorbable materials are currently being developed for bone regeneration. These serve as scaffolding for controlled drug release and prevent bacterial infections. Films of polylactic acid (PLA) polymers that are Mg-reinforced have demonstrated they have suitable properties and bioactive behavior for promoting the osseointegration process. However little attention has been paid to studying whether the degradation process can alter the adhesive physical properties of the biodegradable film and whether this can modify the biofilm formation capacity of pathogens. Moreover, considering that the concentration of Mg and other corrosion products may not be constant during the degradation process, the question that arises is whether these changes can have negative consequences in terms of the bacterial colonization of surfaces. Bacteria are able to react differently to the same compound, depending on its concentration in the medium and can even become stronger when threatened. In this context, physical surface parameters such as hydrophobicity, surface tension and zeta potential of PLA films reinforced with 10% Mg have been determined before and after degradation, as well as the biofilm formation capacity of Staphylococcus epidermidis. The addition of Mg to the films makes them less hydrophobic and the degradation also reduces the hydrophobicity and increases the negative charge of the surface, especially over long periods of time. Early biofilm formation at 8 h is consistent with the physical properties of the films, where we can observe a reduction in the bacterial biofilm formation. However, after 24 h of incubation, the biofilm formation increases significantly on the PLA/Mg films with respect to PLA control. The explosive release of Mg ions and other corrosion products within the first hours were not enough to prevent a greater biofilm formation after this initial time. Consequently, the Mg addition to the polymer matrix had a bacteriostatic effect but not a bactericidal one. Future works should aim to optimize the design and biofunctionality of these promising bioabsorbable composites for a degradation period suitable for the intended application.

In vitro degradation of a biodegradable polylactic acid/magnesium composite as potential bone augmentation material in the presence of titanium and PEEK dental implants.

OBJECTIVE: The aim of this study was to assess the degradation behavior by measuring the H2 release of a biodegradable composite consisting of a polylactic acid matrix reinforced with 30% wt. spherical magnesium microparticles (PLA/Mg) as potential bone augmentation material in combination with dental implants of either titanium or polyetheretherketone (PEEK) in order to evaluate the potential influence of the titanium dental implants on the corrosion behavior of the Mg particles within the PLA matrix. METHODS: Three PEEK dental implants and three titanium dental implants were put into a central perforation of six PLA/Mg-discs. These samples were incubated at 37°C for 30days in McCoy's 5A modified medium and the H2 release was evaluated. RESULTS: Between day 7 and day 16 the average H2 release per cm2 of the surface of the PLA/Mg-samples in combination with the titanium implants was significantly higher than that of the sample group combined with the implants of PEEK (3.1±0.4ml vs. 2.8±0.4ml). This significant difference disappeared afterwards, whereas the H2 release was highest at day 30 and amounted 3.5±0.7ml/cm2 for the group with the titanium implants and 3.2±0.8ml/cm2 for the group with the PEEK implants. SIGNIFICANCE: Regarding the similar values of the degradation depending H2 release of the two implant material groups, the co-implantation of a PLA/Mg composite is not only possible with new metal-free implant materials such as PEEK, but also with conventional implants of titanium.