Antibacterial Aerogels-Based Membranes by Customized Colloidal Functionalization of TEMPO-Oxidized Cellulose Nanofibers Incorporating CuO.

An innovative colloidal approach is proposed here to carry out the customized functionalization of TEMPO-Oxidized Cellulose Nanofibers (CNF) incorporating non-noble inorganic nanoparticles. A heterocoagulation process is applied between the delignified CNF and as-synthetized CuO nanoparticles (CuO NPs) to formulate mixtures which are used in the preparation of aerogels with antibacterial effect, which could be used to manufacture membranes, filters, foams, etc. The involved components of formulated blending, CNF and CuO NPs, were individually obtained by using a biorefinery strategy for agricultural waste valorization, together with an optimized chemical precipitation, assisted by ultrasounds. The optimization of synthesis parameters for CuO NPs has avoided the presence of undesirable species, which usually requires later thermal treatment with associated costs. The aerogels-based structure, obtained by conventional freeze-drying, acted as 3D support for CuO NPs, providing a good dispersion within the cross-linked structure of the nanocellulose and facilitating direct contact of the antibacterial phase against undesirable microorganisms. All samples showed a positive response against Escherichia coli and Staphylococcus aureus. An increase of the antibacterial response of the aerogels, measured by agar disk diffusion test, has been observed with the increase of CuO NPs incorporated, obtaining the width of the antimicrobial "halo" (nwhalo) from 0 to 0.6 and 0.35 for S. aureus and E. coli, respectively. Furthermore, the aerogels have been able to deactivate S. aureus and E. coli in less than 5 h when the antibacterial assays have been analyzed by a broth dilution method. From CNF-50CuO samples, an overlap in the nanoparticle effect produced a decrease of the antimicrobial kinetic.

Microstructural and Mechanical Characterization of Colloidal Processed WC/(W5Vol%Ni) via Spark Plasma Sintering.

This study investigates the sintering behaviour and properties of WC-based composites in which WC was mixed with W5vol%Ni in concentrations of 10vol% and 20vol%. Colloidal processing in water and spark plasma sintering were employed to disperse the WC particles and facilitate sintering. The addition of W5vol%Ni improved the sintering process, as evident from a lower onset temperature of shrinkage determined through dilatometric studies. All samples exhibited the formation of tungsten monocarbide (W2C), with a more pronounced presence in the WC/20(W5vol%Ni) composite. Sintering reached its maximum rate at 1550 °C and was completed at 1600 °C, resulting in a final density exceeding 99.8%. X-ray diffraction analysis confirmed the detection of WC and W2C phases after sintering. The observed WC content was higher than expected, which may be attributed to carbon diffusion during the process. Macro-scale mechanical characterisations revealed that the WC/10(W5vol%Ni) composite exhibited a hardness of 18.9 GPa, while the WC/20(W5vol%Ni) composite demonstrated a hardness of 18.3 GPa. Increasing the W5vol%Ni binder content caused a decrease in mechanical properties due to the formation of W2C phases. This study provides valuable insights into the sintering behavior and properties of WC/W5vol%Ni composites, offering potential applications in extreme environments.

The Mechanical, Thermal, and Chemical Properties of PLA-Mg Filaments Produced via a Colloidal Route for Fused-Filament Fabrication.

The effect of Mg particles on the thermal, chemical, physical, and primarily mechanical properties of 3D-printed PLA/Mg composites is studied in this paper. Recently, new colloidal processing has been proposed to introduce Mg particles into the PLA matrix, which ensures good dispersion of the particles and better thermal properties, allowing for thermal processing routes such as extrusion or 3D printing via fused-filament fabrication. The thermal and physical properties are here studied in 1D single-filament-printed PLA/Mg composites with 0 to 10 wt.% of Mg particles by Differential Scanning Calorimetry (DSC); we analyse the PLA chain modifications produced, the crystallinity fraction, and the different crystalline forms of the PLA after thermal processing. Fourier Transform Infrared Spectroscopy (FTIR) is used to confirm the influence of the PLA/Mg colloidal processing after printing. The mechanical properties are measured with a universal tensile test machine on the 1D single-printed filaments via fused-filament fabrication (FFF); the filaments were naturally aged to stable conditions. Filaments with and without a notch are studied to obtain the materials' tensile strength, elastic modulus, and fracture toughness. Different analytical models to explain the results of the PLA-Mg were studied, in which the minimum values for the interface strength of the PLA-Mg composites were calculated.

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.

Natural Ageing of PLA Filaments, Can It Be Frozen?

The physical ageing of polylactic acid (PLA) is a phenomenon that changes the material's properties over time. This ageing process is highly dependent on ambient variables, such as temperature and humidity. For PLA, the ageing is noticeable even at room temperatures, a process commonly referred to as natural ageing. Stopping the ageing by freezing the material can be helpful to preserve the properties of the PLA and stabilise it at any time during its storage until it is required for testing. However, it is essential to demonstrate that the PLA's mechanical properties are not degraded after defrosting the samples. Four different methods for stopping the ageing (anti-ageing processes) are analysed in this paper-all based on freezing and defrosting the PLA samples. We determine the temperature and ambient water vapor influence during the freezing and defrosting process using desiccant and zip bags. The material form selected is PLA filaments (no bulk material or scaffold structures) printed at 190 °C with diameters between 400 and 550 µm and frozen at -24 °C in the presence or absence of a desiccant. The impact of the anti-ageing processes on PLA's ageing and mechanical integrity is studied regarding the thermal, mechanical and fractographical properties. In conclusion, an anti-ageing process is defined to successfully stop the natural ageing of the PLA for an indefinite length of time. This process does not affect the mechanical properties or the structural integrity of the PLA. As a result, large quantities of this material can be produced in a single batch and be safely stored to be later characterised under the same manufacturing and ageing conditions, which is currently a limiting factor from an experimental point of view as polymeric filament properties can show significant variety from batch to batch.

The Effect of Ca2+ and Mg2+ Ions Loaded at Degradable PLA Membranes on the Proliferation and Osteoinduction of MSCs.

Biodegradable membranes, including Polylactic acid (PLA)-based membranes, are commonly used in bone-tissue-related clinical procedures as biointerface to promote bone tissue regeneration. Calcium (Ca2+) and Magnesium (Mg2+) ions have been related to the promotion of osteogenesis, where the PLA membranes could be used as carrier and delivery substrate for them to provide osteogenic properties to this material. For this aim, a new ion delivery system based on biodegradable PLA membranes loaded with Mg and hydroxyapatite (HA) particles has been processed by the combination of tape casting and colloidal route. Materials characterization shows that the incorporation of Mg and HA particles changes the surface and hydrophobicity of the PLA membrane, and the in vitro degradation test shows Mg2+ and Ca2+ ion release and occasionally the precipitation of different ion species onto the membrane surface. Mouse and human Mesenchymal Stem Cells (MSC) were used to define the biocompatibility and bioactivity of these PLA membrane composites, and data indicated Mg2+ promotes cell proliferation and potentiates osteoinductive signals, while Ca2+ induces the expression of ALP osteogenic marker in human MSCs. Biodegradable PLA membranes loaded with Mg and HA particles is a promising new ion delivery system of Mg2+ and Ca2+ ions that provides osteogenic signals and works as functional biointerface interfaces with bone tissues.

Characterisation and Modelling of PLA Filaments and Evolution with Time.

The properties of polylactic acid (PLA) filaments have not yet been analysed in detail, and they are strongly affected by the extrusion process used in some additive manufacturing systems. Here we present the mechanical, thermal, physical, and fractographical properties of an extruded filament (not the bulk material or scaffolds), the basic building block of any PLA structure printed via material extrusion. This research aims to create a reference point for the modelisation of additively manufactured structures via extrusion processes, as the main building block is characterised in detail for a deep understanding. Furthermore, we investigated the natural ageing (up to one year), the effect of the printing (extruding) temperature (180 and 190 °C), and the effect of the crosshead speed during the tensile tests (10-1 to 102 mm/min) to provide a deeper analysis of the material. The results showed that the material extruded at 190 °C performed better than the material extruded at 180 °C. However, after one hundred days of natural ageing, both materials behaved similarly. This was related to the flow-induced molecular orientation during the extrusion. The crosshead rate produced a logarithmic increase of the mechanical properties, consistent with the Eyring model. Additionally, the ageing produced significant changes in both the elastic modulus and the yield strength: from 2.4 GPa and 40 MPa, in one-day-aged samples, up to 4 GPa and 62 MPa once entirely aged. Finally, it was observed that the glass transition and the enthalpic relaxation increased with ageing, agreeing with the Kohlraushch-William-Watts model.

Operational Variables on the Processing of Porous Titanium Bodies by Gelation of Slurries with an Expansive Porogen.

Colloidal processing techniques, based on the suspension of powders in a liquid, are very versatile techniques to fabricate porous structures. They can provide customized pores, shapes and surfaces through the control of operational parameters, being the base of the alternative additive manufacture processes. In this work disperse and stable titanium aqueous slurries has been formulated in order to process porous materials by the incorporation of methylcellulose (MC) as a gelation agent and ammonium bicarbonate as an expansive porogen. After casting the slurries and heating at mild temperatures (60-80 °C) the methylcellulose gels and traps the gas bubbles generated by the ammonium bicarbonate decomposition to finally obtain stiff porous green structures. Using an experimental design method, the influence of the temperature as well as the concentration of gelation agent and porogen on the viscosity, apparent density and pore size distribution is analyzed by a second-order polynomial function in order to identifying the influence of the operating variables in the green titanium porous compact. After sintering at 1100 °C under high vacuum, titanium sponges with 39% of open porosity and almost no close porosity were obtained.

Controlled SrR Delivery by the Incorporation of Mg Particles on Biodegradable PLA-Based Composites.

Among several ions playing a vital role in the body, Sr2+ and Mg2+ are involved in the mechanism of bone formation, making them especially useful for bone tissue engineering applications. Recently, polylactic acid (PLA)/Mg composites have emerged as a promising family of biomaterials due to their inherent biocompatibility and biodegradability properties. In these composites, polymer and bio-metal have a synergetic effect-while the PLA inhibits the Mg fast reactivity, Mg provides bioactivity to the inert polymer buffering the medium pH during degradation. Meanwhile, the typical form of administrating Sr2+ to patients is through the medication strontium ranelate (SrR), which increases the bone mineral density. Following this interesting research line, a new group of composites, which integrates Mg particles and SrR charged onto halloysite nanotubes (HNT) in a polymeric matrix, was proposed. PLA/Mg/SrR-HNT composites have been processed following a colloidal route, obtaining homogenous composites granulated and film-shaped. The drug delivery profile was evaluated in terms of in vitro lixiviation/dissolution paying special attention to the synergism of both ions release. The combination of two of the most reported ions involved in bone regeneration in the composite biomaterial may generate extra interest in bone healing applications.

Capability of core-sheath polyvinyl alcohol-polycaprolactone emulsion electrospun nanofibrous scaffolds in releasing strontium ranelate for bone regeneration.

Core-sheath nanofibrous scaffolds from polyvinyl alcohol (PVA)-strontium ranelate (SrR)-Polycaprolactone (PCL) were prepared by water in oil electrospinning method. Thus, PCL (the oil phase) was used as the shell part and a mixture of PVA and SrR (the water phase) was inserted in the core. The amounts of SrR was varied from 0 to 15 wt.% Mussel-inspired dopamine-gelatin coating was done on the nanofibrous to improve their hydrophilicity and cellular attachment. The effect of the SrR content on morphology, mechanical, physicochemical, in vitro release behaviors, and biological properties as well as in vivo bone regeneration was investigated. Morphological observations revealed that continuous nanofibers with a core/shell structure were successfully obtained and the fibers diameter increased as the SrR content rose. X-ray diffraction (XRD) analysis revealed that SrR was molecularly distributed in the nanofibers and increasing the amount of the SrR decreased the crystallinity of the nanofibers. Moreover, the SrR release was regulated through the mechanism of Fickian diffusion and it was assumed as fast as possible in the samples with higher SrR content. The mesenchymal stem cell culturing showed improved cell proliferation by adding SrR and accelerating the expression of ALP, Runx2, Col I, and OCN genes. Besides, the SrR-loaded nanofibers improved bone formation of calvarial defects in a rat model as revealed by in vivo investigations.

Effect of SrR delivery in the biomarkers of bone regeneration during the in vitro degradation of HNT/GN coatings prepared by EPD.

Among strontium-based drugs, the Strontium ranelate (SrR) is a divalent strontium salt of ranelic acid which has an overall effect over the bone microarchitecture improvement. However, some findings reveal that the SrR affects in an opposite manner to the cell proliferation and osteoblastic differentiation, based on its concentration. Consequently, its release should be controlled. The incorporation of Halloysite nanotubes (HNT) as nanocarriers of SrR, into gelatine (GN) coatings, tailors the release of this anabolic bone-forming and anti-catabolic agent to stimulate bone growth. In fact, as-prepared GN/HNT-SrR coatings release 100 % SrR in phosphate buffered saline (PBS) within 21 days, and cellular studies of the nanocomposite coatings (MTT, Alkaline Phosphatase activity (ALP) and Calcium deposition assay) confirm the valuable bio-performance of these composite coatings to enhanced bone regeneration. In the present manuscript, suspensions with HNT/GN weight ratio of 0.5 are formulated to coat AISI 316 L stainless steel foils by Electrophoretic Deposition (EPD). Zeta potential determination is used to stablish the drug loading (HNT-SrR) by electrostatic interaction, as well as to optimize the dispersion of bare HNT and HNT SrR-loaded in a GN aqueous solution. Polyethilenimnine (PEI) is used as stabilizer to buffer the suspension media, assure cargo-drug dispersion and sequential release, while the thermal gelling of the suspension controls and step up the coating formation during EPD.

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.

Rapidly growing vegetables as new sources for lignocellulose nanofibre isolation: Physicochemical, thermal and rheological characterisation.

Rapidly growing vegetables could be an abundant and cheap sources of lignocellulose biomass for lignocellulose nanofibre (LCNF) production. The aim of this work is to study the feasibility of using Chamaecytisus proliferus and Leucaena leucocephala for LCNF isolation by mechanical, enzymatic and TEMPO-mediated oxidation pre-treatments. Characterisation of the nanofibres shows that there are significant differences in the production of LCNF depending on the raw material and pre-treatment used. XRD and FTIR analysis show that homogenisation has a strong negative effect on the crystallinity index; however, the higher lignin content of tagasaste (10%) protects the fibre, causing a smaller decrease in crystallinity. The thermal stability of LCNF is also affected by the high lignin content in the case of tagasaste, which exhibited maximum degradation temperatures of 340-315°C, that were higher than those for leucaena (330-310°C). A strong shear thinning behaviour was observed in most of the LCNF, which revealed a great degree of interconnectivity in the gel like-network.