Optically pure polylactides, poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA), were blended across the range of compositions with poly(-caprolactone) (PCL) to study their crystallization, morphology, and mechanical behavior. Differential scanning calorimetry and dynamic mechanical analysis (DMA) of the PLA/PCL blends showed two T g s at positions close to the pure components revealing phase separation. However, a shift in the tan ␦ peak position by DMA from 64 to 57°C suggests a partial solubility of PCL in the PLA-rich phase. Scanning electron microscopy reveals phase separation and a transition in the phase morphology from spherical to interconnected domains as the equimolar blend approaches from the outermost compositions. The spherulitic growth of both PLA and PCL in the blends was followed by polarized optical microscopy at 140 and 37°C. From tensile tests at speed of 50 mm/min Young's modulus values between 5.2 and 0.4 GPa, strength values between 56 and 12 MPa, and strain at break values between 1 and 400% were obtained varying the blend composition. The viscoelastic properties (E and tan ␦) obtained at frequency of 1 Hz by DMA are discussed and are found consistent with composition, phase separation, and crystallization behavior of the blends. POLYM. ENG. SCI., 46:1299 -1308, 2006.

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Flax and jute fibres are inexpensive and easily available bast fibres and they are extensively used as reinforcement in polymer matrix composites. However, due to their susceptibility to moisture absorption, their application is restricted to non-structural interior products. In this study, flax and jute fibre reinforced bioresin based epoxy biocomposites were fabricated using hand lay-up method and their nanoindentation and flexural properties were investigated. In order to study the effects of water absorption on the nanoindentation and flexural properties, the biocomposites were subjected to water immersion tests by immersing specimens in a de-ionised water bath at 25 oC for a period of 961 hours. The nanoindentation behaviour and flexural properties of water immersed specimens were evaluated and compared alongside with dry specimens. The percentage of moisture uptake and diffusion coefficient ()was recorded higher for jute reinforced specimens compared to flax. The flexural properties for both types of specimens were found to decrease with increase in percentage moisture uptake. Comparison of flexural strength and flexural modulus between flax dry and flax wet biocomposites showed that wet samples lost almost 40% of its strength and 69% of its modulus respectively, compared to dry flax samples. The jute wet samples lost 60% of its strength and 80% of its modulus, respectively, compared to dry samples. The nanohardness value decreased from 0.207 GPa to 0.135 GPa for dry flax sample after immersion in water. http://mc.manuscriptcentral.com/jcm

The study was conducted to evaluate the cytocompatibility and hydrolytic degradability of the new poly(lactic acid)/polyethylene glycol-polyhedral oligomeric silsesquioxane (peg-POSS/PLLA) nanocomposite as potential material for cartilage regeneration. PLLA scaffolds containing 0 to 5% of peg-POSS were fabricated by electrospinning. Human mesenchymal stem cells (hMSC's) were cultured in vitro to evaluate the cytocompatibility of the new nanocomposite material. Hydrolytic degradation studies were also carried out to analyze the mass loss rate of the nanocomposites through time. The addition of the peg-POSS to the PLLA did not affect the processability of the nanocomposite by electrospinning. It was also observed that peg-POSS did not show any relevant change in fibers morphology, concluding that it was well dispersed. However, addition of peg-POSS caused noticeable decrease in mean fiber diameter, which made the specific surface area of the scaffold to rise. hMSC's were able to attach, to proliferate, and to differentiate into chondrocytes in a similar way onto the different types of electrospun peg-POSS/PLLA and pure PLLA scaffolds, showing that the peg-POSS as nano-additive does not exhibit any cytotoxicity. The hydrolytic degradation rate of the material was lower when peg-POSS was added, showing a higher durability of the nanocomposites through time. Results demonstrate that the addition of peg-POSS to the PLLA scaffolds does not affect its cytocompatibility to obtain hyaline cartilage from hMSC's.

ObjectiveAerosol delivery holds potential to release surfactant or perfluorocarbon (PFC) to the lungs of neonates with respiratory distress syndrome with minimal airway manipulation. Nevertheless, lung deposition in neonates tends to be very low due to extremely low lung volumes, narrow airways and high respiratory rates. In the present study, the feasibility of enhancing lung deposition by intracorporeal delivery of aerosols was investigated using a physical model of neonatal conducting airways.MethodsThe main characteristics of the surfactant and PFC aerosols produced by a nebulization system, including the distal air pressure and air flow rate, liquid flow rate and mass median aerodynamic diameter (MMAD), were measured at different driving pressures (4–7 bar). Then, a three-dimensional model of the upper conducting airways of a neonate was manufactured by rapid prototyping and a deposition study was conducted.ResultsThe nebulization system produced relatively large amounts of aerosol ranging between 0.3±0.0 ml/min for surfactant at a driving pressure of 4 bar, and 2.0±0.1 ml/min for distilled water (H2Od) at 6 bar, with MMADs between 2.61±0.1 µm for PFD at 7 bar and 10.18±0.4 µm for FC-75 at 6 bar. The deposition study showed that for surfactant and H2Od aerosols, the highest percentage of the aerosolized mass (∼65%) was collected beyond the third generation of branching in the airway model. The use of this delivery system in combination with continuous positive airway pressure set at 5 cmH2O only increased total airway pressure by 1.59 cmH2O at the highest driving pressure (7 bar).ConclusionThis aerosol generating system has the potential to deliver relatively large amounts of surfactant and PFC beyond the third generation of branching in a neonatal airway model with minimal alteration of pre-set respiratory support.

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The emergence of new high-performance thermoplastics to replace thermosets in fiber-reinforced polymers puts up a new challenge: their machining. In this study, carbon fiber-reinforced poly-cyclic butylene terephthalate laminates were manufactured, drilled, and inspected. Different commercial drill geometries and machining conditions were compared. Roughness, microscopy, and non-destructive tests allowed us to determine the hole quality as well as delamination. The surface tests showed better results after working at the most common cutting speed (3000 rpm) than at high speed (15,000 rpm) with a constant feed rate. This fact can be explained based on the viscoelastic properties of the matrix that becomes fragile at high cutting speeds. The Delamination factor obtained by means of Ultrasonics and X-ray Computed Tomography also confirmed that the best results are achieved with a Twist drill bit at 3000 rpm. In contrast to carbon fiber-reinforced thermosets, the detected delamination at high cutting speeds is not as remarkable as expected. These results allow us to conclude that this new composite will certainly increase production rate without delamination damage. Chip formation takes also a special role. It can be recovered to be used as reinforcement in manufacturing processes due to the recyclability of the thermoplastic matrix.

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