3D-Printing for Analytical Ultracentrifugation

Analytical ultracentrifugation (AUC) is a classical technique of physical biochemistry providing information on size, shape, and interactions of macromolecules from the analysis of their migration in centrifugal fields while free in solution. A key mechanical element in AUC is the centerpiece, a component of the sample cell assembly that is mounted between the optical windows to allow imaging and to seal the sample solution column against high vacuum while exposed to gravitational forces in excess of 300,000 g. For sedimentation velocity it needs to be precisely sector-shaped to allow unimpeded radial macromolecular migration. During the history of AUC a great variety of centerpiece designs have been developed for different types of experiments. Here, we report that centerpieces can now be readily fabricated by 3D printing at low cost, from a variety of materials, and with customized designs. The new centerpieces can exhibit sufficient mechanical stability to withstand the gravitational forces at the highest rotor speeds and be sufficiently precise for sedimentation equilibrium and sedimentation velocity experiments. Sedimentation velocity experiments with bovine serum albumin as a reference molecule in 3D printed centerpieces with standard double-sector design result in sedimentation boundaries virtually indistinguishable from those in commercial double-sector epoxy centerpieces, with sedimentation coefficients well within the range of published values. The statistical error of the measurement is slightly above that obtained with commercial epoxy, but still below 1%. Facilitated by modern open-source design and fabrication paradigms, we believe 3D printed centerpieces and AUC accessories can spawn a variety of improvements in AUC experimental design, efficiency and resource allocation.Comment: 25 pages, 6 figure

Designing bioactive porous titanium interfaces to balance mechanical properties and in vitro cells behavior towards increased osseointegration

Titanium implant failures are mainly related to stress shielding phenomenon and the poor cell interaction with host bone tissue. The development of bioactive and biomimetic Ti scaffolds for bone regeneration remains a challenge which needs the design of Ti implants with enhanced osseointegration. In this context, 4 types of titanium samples were fabricated using conventional powder metallurgy, fully dense, dense etched, porous Ti, and porous etched Ti. Porous samples were manufactured by space holder technique, using ammonium bicarbonate particles as spacer in three different ranges of particle size (100–200 μm, 250–355 μm and 355–500 μm). Substrates were chemically etched by immersion in fluorhydric acid at different times (125 and 625 s) and subsequently, were characterized from a micro-structural, topographical and mechanical point of view. Etched surfaces showed an additional roughness preferentially located inside pores. In vitro tests showed that all substrates were biocompatible (80% of cell viability), confirming cell adhesion of premioblastic cells. Similarly, osteoblast showed similar cell proliferation rates at 4 days, however, higher cell metabolic activity was observed in fully dense and dense etched surfaces at 7 days. In contrast, a significant increase of alkaline phosphatase enzyme expression was observed in porous and porous etched samples compared to control surfaces (dense and dense etched), noticing the suitable surface modification parameters (porosity and roughness) to improve cell differentiation. Furthermore, the presence of pores and rough surfaces of porous Ti substrates remarkably decreased macrophage activation reducing the M1 phenotype polarization as well M1 cell marker expression. Thus, a successful surface modification of porous Ti scaffolds has been performed towards a reduction on stress shielding phenomenon and enhancement of bone osseointegration, achieving a biomechanical and biofunctional equilibrium.Ministry of Economy and Competitiveness of Spain grant MAT2015-71284-PJunta de Andalucía – FEDER (Spain) Project Ref. P12-TEP-140

Synthesis and characterization of liquid crystalline epoxy resins

Fiber reinforced polymer matrix composites (FRPs) have been developed for many decades and used in a wide variety of applications. However, the residual stresses caused by the mismatch in the coefficient of thermal expansion (CTE) between the polymer matrices and the fiber reinforcements during the processing of FRPs is a crucial factor affecting the performance of the composites, which can lead to a reduction of mechanical properties and loss of dimensional stability, thereby limiting the use of FRPs in high performance applications. Additionally, the relatively poor matrix properties is another factor affecting overall performance of the composites, including chemical resistance, moisture absorption, and long term durability of FRPs. A potential strategy to solve the problems mentioned above involves the development of novel polymer matrices with improved physical, thermal, and mechanical properties with low thermal expansion to ensure minimal mismatch in CTE with the fiber reinforcements, which can reduce the magnitude of residual stresses, facilitating the development of FRPs for advanced applications. Liquid crystalline epoxy resins (LCERs) are a unique class of thermosetting materials formed upon curing of low molecular weight, rigid rod epoxy monomers, resulting in the retention of a liquid crystalline (LC) phase by the three dimensional networks. LCERs exhibit a polydomain structure, thereby combining the outstanding properties of liquid crystals and thermosets. The rigid and ordered structure of LC domains is expected to reduce the CTE of the resins as well as improve the thermal and mechanical properties of the resins. In addition, liquid crystals possess properties that can be controlled by external fields, greatly improving the design flexibility. These attractive features make LCERs good candidates for polymer matrices in high performance composites. The goal of this research is to synthesize a LCER based on biphenyl mesogen, characterize the thermal, physical, and mechanical properties of the resin, and evaluate the potential use of LCERs as polymer matrices in high performance composites

Threading Through Macrocycles Enhances the Performance of Carbon Nanotubes as Polymer Fillers

In this work we study the reinforcement of polymers by mechanically interlocked derivatives of single-walled carbon nanotubes (SWNTs). We compare the mechanical properties of fibers made of polymers and of composites with pristine single-walled carbon nanotubes (SWNTs), mechanically interlocked derivatives of SWNTs (MINTs) and the corresponding supramolecular models. Improvements of both Young's modulus and tensile strength of up to 200 % were observed for the polystyrene-MINTs samples with an optimized loading of just 0.01 wt.%, while the supramolecular models with identical chemical composition and loading showed negligible or even detrimental influence. This behavior is found for three different types of SWNTs and two types of macrocycles. Molecular dynamics simulations show that the polymer adopts an elongated conformation parallel to the SWNT when interacting with MINT fillers, irrespective of the macrocycle chemical nature, whereas a more globular structure is taken upon facing with either pristine SWNTs or supramolecular models. The MINT composite architecture thus leads to a more efficient exploitation of the axial properties of the SWNTs and of the polymer chain at the interface, in agreement with experimental results. Our findings demonstrate that the mechanical bond imparts distinctive advantageous properties to SWNT derivatives as polymer fillers.Comment: 39 pages, 19 figure

Effect of Organo Montmorillonite Nanoclay on Mechanical Properties Thermal Stability and Ablative Rate of Carbon fiber Polybenzoxazine Resin Composites

Organo-Montmorillonite (o-MMT) nanoclay added polybenzoxazine resin (type I composites) were prepared with varying amounts of clay (0, 1, 2, 4 and 6 wt %). Clay dispersion, changes in curing behaviour and thermal stability were assessed in type I composites. Findings from these studies of type I composites were used to understand thermal stability, mechanical, and mass ablation rate behaviour of nanoclay added carbon fiber reinforced polybenzoxazine composites (type II). Interlaminar shear strength and flexural strength of type II composites increase by 25% and 27%, respectively at 2 wt% addition of clay. An oxy-acetylene torch test with a constant heat flux of 125 w/cm2 was used to investigate mass ablation rate of type II composites. The ablation rate has increased as the weight percentage of clay has increased. This is contradicting to type I composites with up to 6 wt% clay and type II composites with up to 4 wt% clay, which have improved thermal stability. The microstructure of the ablated composites was examined using scanning electron microscopy. Increased ablation rates are due to the reaction of charred matrix with nanoclay, which exposes bare fibers to the ablation front, resulting in higher mechanical erosion losses

Course Catalog, 1975-1976

Course Catalogs include available majors, course requirements, costs, pictures, a brief institution history, and more.https://digitalcommons.kean.edu/ua_kc_cc/1003/thumbnail.jp

The Dynamics of Liquid Drops and their Interaction with Solids of Varying Wettabilites

Microdrop impact and spreading phenomena are explored as an interface formation process using a recently developed computational framework. The accuracy of the results obtained from this framework for the simulation of high deformation free-surface flows is confirmed by a comparison with previous numerical studies for the large amplitude oscillations of free liquid drops. Our code's ability to produce high resolution benchmark calculations for dynamic wetting flows is then demonstrated by simulating microdrop impact and spreading on surfaces of greatly differing wettability. The simulations allow one to see features of the process which go beyond the resolution available to experimental analysis. Strong interfacial effects which are observed at the microfluidic scale are then harnessed by designing surfaces of varying wettability that allow new methods of flow control to be developed

Materiály kombinující vodivé polymery a drahé kovy

Polyaniline-silver composites combine the electrical properties of metals and the material properties of polymers. Polyaniline is one of the most studied conducting polymers on account of high electrical conductivity (units S cm-1 ), environmental stability, ease of preparation from common chemicals, good processibility and low cost. Silver is well known because of its highest conductivity among metals (500 000 S cm−1 ), antibacterial properties, and low price compared to other noble metals. Aniline was oxidized with silver nitrate in acidic aqueous medium to polyaniline-silver composite. The presence of different organic acids was studied. The most promising became methanesulfonic acid solution, in which most problems (such as inhomogeneity of samples and limited solubility of silver salts) got solved. The oxidation of aniline with silver nitrate is slow and takes over several months to get a reasonable yield. An addition of a small amount of p-phenylenediamine, even 1 mol. % relative to aniline, shortens the reaction time to several hours or even to tens of minutes. Small amounts of ammonium peroxydisulfate had similar effect. The content of silver in composites is fixed by the stoichiometry of reaction, and composites always contain ≈70 wt.% of silver. By using mixed oxidants, silver nitrate and...Kompozity polyanilinu se stříbrem kombinují elektrické vlastnosti kovů a materiálové vlastnosti polymerů. Polyanilin je jedním z nejvíce studovaných vodivých polymerů díky vysoké elektrické vodivosti (jednotky S cm−1 ), stabilitě, jednoduchosti přípravy z běžných chemikálií, dobré zpracovatelnosti a nízkým nákladům syntézy. Stříbro je dobře známo pro svou vodivost, nejvyšší mezi kovy (500 000 S cm−1 ), antibakteriální vlastnosti a nízkou cenu, ve srovnání s jinými drahýmy kovy. Anilin byl oxidován dusičnanem stříbrným ve vodném kyselém prostředí za vzniku kompozitu polyanilin-stříbro. Byl studován vliv různých organických kyselin a jejich koncentrace. Nejslibnější se ukázala kyselina methansulfonová, pro níž se podařilo vyřešit četné problémy, jako jsou nehomogenita vzorků a omezená rozpustnost stříbrných solí. Oxidace anilinu dusičnanem stříbrným je pomalá a trvá i několik měsíců, nežli se získá přiměřený výtěžek. Přidání malého množství p-fenylendiaminu, i jen 1 mol.% relativně vzhledem k anilinu, zkracuje reakční dobu na několik hodin nebo dokonce i desítky minut. Malé množství peroxodvojsíranu amonného má podobný účinek. Obsah stříbra v kompozitu je dán stechiometrií reakce, a kompozity vždy obsahují ≈70 hm.% stříbra. Použitím smíšených oxidantů, dusičnanu stříbrného a peroxodvojsíranu...Department of Physical and Macromolecular ChemistryKatedra fyzikální a makromol. chemieFaculty of SciencePřírodovědecká fakult