Adsorption of poly(ethylene oxide)-block-polylactide copolymers on polylactide as studied by ATR-FTIR spectroscopy

The Influence of the Gradient Infill of PLA Samples Produced with the FDM Technique on Their Mechanical Properties

Three-dimensional printing is a dynamically developing field of industry. Its main advantage is the small amount of waste, no need to use specialized tools, and easy control of the mechanical properties of the printed model. One of the most popular techniques of 3D printing is FDM. The main factor influencing the mechanical properties of 3D-printed materials is the filling density. The aim of this study was to determine the mechanical properties of porous structures with a porosity gradient of PLA samples printed using the FDM technique. The accuracy of mapping the structures by computed tomography was assessed, and then a static compression test was performed. It has been shown that the strength properties increased with the increase in the filling density. The highest value of compression strength, amounting to 41.2 MPa, was observed for samples made of PLA with an 80% filling degree, whereas the lowest value of compression strength was found in PLA-T samples with a filling degree of 10%, reaching only 0.6 MPa. It was found that not only the core filling density, but also the outer layers, influences the mechanical properties. The assessment of spatial architecture allowed for a qualitative and quantitative assessment. The obtained images from the computed tomograph showed that the designed sample models were correctly reproduced in the entire volume.

Development of Antimicrobial PLA Composites for Fused Filament Fabrication

In addition to possessing the desirable properties of being a biodegradable and biocompatible polymer fabricated from renewable resources, poly (lactic acid) (PLA) has useful mechanical and thermal attributes that has enabled it to be one of the most widely-used plastics for medicine, manufacturing, and agriculture. Yet, PLA composites have not been heavily explored for use in 3D-printing applications, and the range of feasible materials for the technology is limited, which inhibits its potential growth and industry adoption. In this study, tunable, multifunctional antimicrobial PLA composite filaments for 3D-printing have been fabricated and tested via chemical, thermal, mechanical, and antimicrobial experiments. Thermally stable antimicrobial ceramics, ZnO and TiO₂, were used as fillers up to 30 wt%, and poly (ethylene glycol) (PEG) was used as a plasticizer to tune the physical material properties. Results demonstrate that the PLA composite filaments exhibit the thermal phase behaviors and thermal stability suitable for 3D-printing. Additionally, PEG can be used to tune the mechanical properties while not affecting the antimicrobial efficacy that ZnO and TiO₂ imbue.

Photocurable Methacrylate Derivatives of Polylactide: A Two-Stage Synthesis in Supercritical Carbon Dioxide and 3D Laser Structuring

A two-stage polylactide modification was performed in the supercritical carbon dioxide medium using the urethane formation reaction. The modification resulted in the synthesis of polymerizable methacrylate derivatives of polylactide for application in the spatial 3D structuring by laser stereolithography. The use of the supercritical carbon dioxide medium allowed us to obtain for the first time polymerizable oligomer-polymer systems in the form of dry powders convenient for further application in the preparation of polymer compositions for photocuring. The photocuring of the modified polymers was performed by laser stereolithography and two-photon crosslinking. Using nanoindentation, we found that Young’s modulus of the cured compositions corresponded to the standard characteristics of implants applied in regenerative medicine. As shown by thermogravimetric analysis, the degree of crosslinking and, hence, the local stiffness of scaffolds were determined by the amount of the crosslinking agent and the photocuring regime. No cytotoxicity was observed for the structures.

Electrospinning-Derived PLA/Shellac/PLA Sandwich—Structural Membrane Sensor for Detection of Alcoholic Vapors with a Low Molecular Weight

The development of gas sensors for detecting alcoholic vapors with a low molecular weight is essential for environmental protection, industrial process control, and the monitoring of the living atmosphere in daily life to avoid health problems in human beings. Here, poly (lactic acid) (PLA)/shellac/PLA sandwich-structural membranes were fabricated via an electrospinning approach and the interaction with alcoholic vapors with a low molecular weight was investigated. It was found that the PLA/shellac/PLA sandwich-structural membrane exhibited fast response to the alcoholic vapors with low molecular weight, especially for methanol vapor. After being treated with alcohol vapor with a low molecular weight, the PLA/shellac/PLA sandwich-structural membrane could change its transmission in a short time (~5 s) and with a concentration of 10 wt% of methanol (ethanol) in water. In the meantime, the PLA/shellac/PLA sandwich-structural membrane can hopefully be potentially used again after evaporating the alcoholic vapor at an elevated temperature.

Enhancement of the Oil Absorption Capacity of Poly(Lactic Acid) Nano Porous Fibrous Membranes Derived via a Facile Electrospinning Method

Oil spilling has been a serious problem in the world for a long time, which can bring toxic substances to marine life. A large number of researchers around the world have introduced many measures to address this problem. One of the effective methods to remove oil from the oil/water mixture is to absorb oil from the mixture. Here, we prepared porous poly(lactic acid) (PLA) membranes using the electrospinning approach with different sized syringe needles, and used these membranes to absorb oil from the top of the water. It was found that the diameter of the needle has a big impact on the size and structure of the pores on the PLA fibers. The oil absorption capacity of membranes increases with a decreasing needle diameter due to the increased pore volume and specific surface area. The highest absorption capacity reached was 42.38 g/g for vacuum pump oil, 28.17 g/g for peanut oil, and 6.74 g/g for diesel oil.

Synthesis of Thermoresponsive Amphiphilic Polyurethane Gel as a New Cell Printing Material near Body Temperature

Waterborne polyurethane (PU) based on poly(ε-caprolactone) (PCL) diol and a second oligodiol containing amphiphilic blocks was synthesized in this study. The microstructure was characterized by dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), and rheological measurement of the PU dispersion. The surface hydrophilicity measurement, infrared spectroscopy, wide-angle X-ray diffraction, mechanical and thermal analyses were conducted in solid state. It was observed that the presence of a small amount of amphiphilic blocks in the soft segment resulted in significant changes in microstructure. When 90 mol % PCL diol and 10 mol % amphiphilic blocks of poly(l-lactide)-poly(ethylene oxide) (PLLA-PEO) diol were used as the soft segment, the synthesized PU had a water contact angle of ∼24° and degree of crystallinity of ∼14%. The dispersion had a low viscosity below room temperature. As the temperature was raised to body temperature (37 °C), the dispersion rapidly (∼170 s) underwent sol-gel transition with excellent gel modulus (G' ≈ 6.5 kPa) in 20 min. PU dispersions with a solid content of 25-30% could be easily mixed with cells in sol state, extruded by a 3D printer, and deposited layer by layer as a gel. Cells remained alive and proliferating in the printed hydrogel scaffold. We expect that the development of novel thermoresponsive PU system can be used as smart injectable hydrogel and applied as a new type of bio-3D printing ink.

Nano-colloid printing of functionalized PLA-b-PEO copolymers: tailoring the surface pattern of adhesive motif and its effect on cell attachment

In this study, we investigate the preparation of surface pattern of functional groups on poly(lactide) (PLA) surfaces through the controlled deposition of core-shell self-assemblies based on functionalized PLA-b-PEO amphiphilic block copolymers from selective solvents. Through grafting RGDS peptide onto the functionalized copolymer surface, the presented approach enables to prepare PLA surfaces with random and clustered spatial distribution of adhesive motifs. The proposed topography of the adhesion motif was proved by atomic force microscopy techniques using biotin-tagged RGDS peptide grafted on the surface and streptavidin-modified gold nanospheres which bind the tagged RGDS peptides as a contrast agent. The cell culture study under static and dynamic conditions with MG63 osteosarcoma cell line showed that the clustered distribution of RGDS peptides provided more efficient initial cell attachment and spreading, and resistance to cell detachment under dynamic culture compared to randomly distributed RGDS motif when with the same average RGDS peptide concentration.

Nonfouling poly(ethylene oxide) layers end-tethered to polydopamine

Nonfouling surfaces capable of reducing protein adsorption are highly desirable in a wide range of applications. Coating of surfaces with poly(ethylene oxide) (PEO), a water-soluble, nontoxic, and nonimmunogenic polymer, is most frequently used to reduce nonspecific protein adsorption. Here we show how to prepare dense PEO brushes on virtually any substrate by tethering PEO to polydopamine (PDA)-modified surfaces. The chain lengths of hetero-bifunctional PEOs were varied in the range of 45-500 oxyethylene units (M(n) = 2000-20,000). End-tethering of PEO chains was performed through amine and thiol headgroups from reactive polymer melts to minimize excluded volume effects. Surface plasmon resonance (SPR) was applied to investigate the adsorption of model protein solutions and complex biologic medium (human blood plasma) to the densely packed PEO brushes. The level of protein adsorption of human serum albumin and fibrinogen solutions was below the detection limit of the SPR measurements for all PEO chains end-tethered to PDA, thus exceeding the protein resistance of PEO layers tethered directly on gold. It was found that the surface resistance to adsorption of lysozyme and human blood plasma increased with increasing length and brush character of the PEO chains end-tethered to PDA with a similar or better resistance in comparison to PEO layers on gold. Furthermore, the chain density, thickness, swelling, and conformation of PEO layers were determined using spectroscopic ellipsometry (SE), dynamic water contact angle (DCA) measurements, infrared reflection-absorption spectroscopy (IRRAS), and vibrational sum-frequency-generation (VSFG) spectroscopy, the latter in air and water.

A combined acidification/PEO flocculation process to improve the lignin removal from the pre-hydrolysis liquor of kraft-based dissolving pulp production process

The presence of lignin impairs the utilization of the hemicelluloses dissolved in the pre-hydrolysis liquor (PHL) of the kraft-based dissolving pulp production process. In this paper, a novel process was developed by combining the acidification and poly ethylene oxide (PEO) flocculation concepts to improve the lignin removal. The results showed that the lignin removal was improved by the addition of PEO to the acidified PHL, particularly at a low pH of 1.5. The main mechanisms involved are the lignin/PEO complex formation and the bridging of the formed complexes. This hypothesis was supported by the turbidity, FTIR and particle size measurements. Interestingly, the hemicelluloses removal from the acidification/PEO flocculation was marginal, which would be beneficial for the down-stream ethanol production from the PHL. Additionally, a process flow diagram was proposed that incorporates this new concept into the existing configuration of kraft-based dissolving pulp production process.

Attenuated Total Reflection–Fourier transform infrared microspectroscopic mapping for the characterisation of paint cross-sections

Paint cross-sections have been analysed using the attenuated total reflection technique combined with FTIR mapping microspectroscopy in order to characterise the nature of the compounds present and map their localisation in the stratigraphy. The study reveals the possibilities offered by micro-ATR devices for obtaining informations about the organic substances employed in painting techniques and in particular their distribution in the different layers, showing a real improvement over traditional analytical investigations in use for the detection of organic substances. Limitations, such as the contamination of the embedding resin and the typical spectral resolution (20 microm) are presented and alternative methods were proposed to obtain better results. In particular, the use of an infrared transparent salt (KBr) as embedding material for the cross-sections is evaluated and seems to be very promising. Furthermore, ATR mapping represent a useful non-destructive analytical technique complementary to others molecular and elemental analyses to be performed afterwards such as SEM-EDX.