Physicochemical Characterization and Finite Element Analysis-Assisted Mechanical Behavior of Polylactic Acid-Montmorillonite 3D Printed Nanocomposites.

This work aims to improve the properties of poly(lactic acid) (PLA) for future biomedical applications by investigating the effect of montmorillonite (MMT) nanoclay on physicochemical and mechanical behavior. PLA nanocomposite filaments were fabricated using different amounts of MMT (1.0, 2.0, and 4.0 wt.%) and 2 wt.% Joncryl chain extenders. The 3D-printed specimens were manufactured using Fused Filament Fabrication (FFF). The composites were characterized by Gel Permeation Chromatography (GPC), Melt Flow Index (MFI), X-ray Diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR). The thermal properties were studied by means of Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA). Moreover, the hydrophilicity of the PLA/MMT nanocomposites was investigated by measuring the water contact angle. The mechanical behavior of the PLA/MMT nanocomposites was examined with nanoindentation, compression tests, and Dynamic Mechanical Analysis (DMA). The presence of Joncryl, as well as the pretreatment of MMT before filament fabrication, improved the MMT distribution in the nanocomposites. Furthermore, MMT enhanced the printability of PLA and improved the hydrophilicity of its surface. In addition, the results of nanoindentation testing coupled with Finite Element Analysis showed that as the MMT weight fraction increased, as well as an increased Young's modulus. According to the results of the mechanical analysis, the best mechanical behavior was achieved for PLA nanocomposite with 4 wt.% MMT.

Influence of age on resistance to distraction after tracheal anastomoses in dogs: An ex vivo study.

OBJECTIVE: To determine the influence of age on the ability of tracheal anastomoses to sustain distraction in dogs. STUDY DESIGN: Ex vivo study. SAMPLE POPULATION: Cadaveric canine tracheae (n = 16). METHODS: Tracheae were harvested from the cadavers of 8 immature and 8 adult dogs. Each trachea underwent end-to-end annular ligament anastomosis with a simple continuous pattern with 2-0 polypropylene on a taper cut needle. The constructs were tested to failure in distraction, with a tensiometer set at a drop head speed of 50 mm/min, as determined by preliminary testing. Failure was defined by tissue pullthrough or suture material failure. The force and elongation at failure were compared between age groups. RESULTS: The median age was 5.5 months (4-7.5 months) in immature dogs and 8.25 years in adult dogs (2-18 years) Tracheal anastomoses failed at lower forces (44.91 ± 59.03 N) but sustained more elongation (39.75 ± 5.45%) in immature dogs than in adult dogs (149.31 ± 45.36 N, P = .007 and 30.57 ± 7.19%, P = .0012, respectively). Tissue apposition was not achieved in 4 specimens each in immature and adult dogs, respectively. CONCLUSIONS: The technique used for tracheal anastomoses in this study failed at lower loads but sustained more elongation when performed in immature dogs. CLINICAL SIGNIFICANCE: Immature dogs may be able to withstand longer tracheal resection than adult dogs but reinforcement techniques seem mandatory to improve resistance to tension. Alternative anastomosis techniques should be considered to improve tissue apposition.

Preliminary Evaluation of 3D Printed Chitosan/Pectin Constructs for Biomedical Applications.

In the present study, chitosan (CS) and pectin (PEC) were utilized for the preparation of 3D printable inks through pneumatic extrusion for biomedical applications. CS is a polysaccharide with beneficial properties; however, its printing behavior is not satisfying, rendering the addition of a thickening agent necessary, i.e., PEC. The influence of PEC in the prepared inks was assessed through rheological measurements, altering the viscosity of the inks to be suitable for 3D printing. 3D printing conditions were optimized and the effect of different drying procedures, along with the presence or absence of a gelating agent on the CS-PEC printed scaffolds were assessed. The mean pore size along with the average filament diameter were measured through SEM micrographs. Interactions among the characteristic groups of the two polymers were evident through FTIR spectra. Swelling and hydrolysis measurements confirmed the influence of gelation and drying procedure on the subsequent behavior of the scaffolds. Ascribed to the beneficial pore size and swelling behavior, fibroblasts were able to survive upon exposure to the ungelated scaffolds.

Use of mesoporous cellular foam (MCF) in preparation of polymeric microspheres for long acting injectable release formulations of paliperidone antipsychotic drug.

In this study, high surface area mesoporous silica foam with cellular pore morphology (MCF) was used for injectable delivery of paliperidone, an antipsychotic drug used in patients suffering from bipolar disorder. The aim was to enhance paliperidone solubility and simultaneously to prepare long active intractable microspheres. For this reason paliperidone was first loaded in MCF silica, and the whole system was further encapsulated into PLA and PLGA 75/25w/w copolymer in the form of microspheres. It was found that paliperidone, after its adsorption into MCF, was transformed in its amorphous state, thus leading to enhanced in vitro dissolution profile. Furthermore, incorporation of the drug-loaded MCF to polymeric microparticles (PLA and PLGA) prolonged the release time of paliperidone from 10 to 15days.

Amino-Functionalized Multiwalled Carbon Nanotubes Lead to Successful Ring-Opening Polymerization of Poly(ε-caprolactone): Enhanced Interfacial Bonding and Optimized Mechanical Properties.

In this work, the synthesis, structural characteristics, interfacial bonding, and mechanical properties of poly(ε-caprolactone) (PCL) nanocomposites with small amounts (0.5, 1.0, and 2.5 wt %) of amino-functionalized multiwalled carbon nanotubes (f-MWCNTs) prepared by ring-opening polymerization (ROP) are reported. This method allows the creation of a covalent-bonding zone on the surface of nanotubes, which leads to efficient debundling and therefore satisfactory dispersion and effective load transfer in the nanocomposites. The high covalent grafting extent combined with the higher crystallinity provide the basis for a significant enhancement of the mechanical properties, which was detected in the composites with up to 1 wt % f-MWCNTs. Increasing filler concentration encourages intrinsic aggregation forces, which allow only minor grafting efficiency and poorer dispersion and hence inferior mechanical performance. f-MWCNTs also cause a significant improvement on the polymerization reaction of PCL. Indeed, the in situ polymerization kinetics studies reveal a significant decrease in the reaction temperature, by a factor of 30-40 °C, combined with accelerated the reaction kinetics during initiation and propagation and a drastically reduced effective activation energy.