A CONTINOUS ROTARY ACTUATION MECHANISM FOR A POWERED HIP EXOSKELETON

This thesis presents a new mechanical design for an exoskeleton actuator to power the sagittal plane motion in the human hip. The device uses a DC motor to drive a Scotch yoke mechanism and series elasticity to take advantage of the cyclic nature of human gait and to reduce the maximum power and control requirements of the exoskeleton. The Scotch yoke actuator creates a position-dependent transmission that varies between 4:1 and infinity, with the peak transmission ratio aligned to the peak torque periods of the human gait cycle. Simulation results show that both the peak and average motor torque can be reduced using this mechanism, potentially allowing a less powerful motor to be used. Furthermore, the motor never needs to reverse direction even when the hip joint does. Preliminary testing shows the exoskeleton can provide an assistive torque and is capable of accurate position tracking at speeds covering the range of human walking. This thesis provides a detailed analysis of how the dynamic nature of human walking can be leveraged, how the hip actuator was designed, and shows how the exoskeleton performed during preliminary human trials

Binding of bacterial lipopolysaccharide by the cationic amphiphilic peptide WLBU2 at interfaces

Passage of blood through a sorbent device for removal of bacteria and endotoxin by specific binding with immobilized, membrane-active, bactericidal peptides holds promise for treating severe blood infections. Peptide insertion in the target membrane and stable binding is desirable, while membrane disruption and release of degradation products to the circulating blood is not desirable. Here we describe interactions between bacterial endotoxin (lipopolysaccharide, LPS) and the membrane-active, bactericidal peptides WLBU2 and polymyxin B (PmB). Analysis of the interfacial behavior of mixtures of LPS and peptide using air-water interfacial tensiometry and optical waveguide lightmode spectroscopy strongly suggested insertion and stabilization of intact LPS vesicles by WLBU2, while no such peptide-LPS interactions were evident with PmB. Analysis with dynamic light scattering showed in fact that LPS vesicles appear to undergo peptide-induced destabilization in the presence of PmB. Circular dichroism spectra confirmed that WLBU2, which shows disordered structure in aqueous solution and substantially helical structure in membrane-mimetic environments, is stably located within the LPS membrane in peptide-vesicle mixtures. Interactions between LPS and WLBU2 were also evaluated following immobilization of the peptide at uncoated and polyethylene oxide (PEO)-coated hydrophobic surfaces. PEO layers were prepared by radiolytic grafting of selected PEO-polypropylene oxide (PPO)-PEO triblock surfactants to silanized, hydrophobic surfaces. Immobilization of WLBU2 at the PEO layers was achieved by its noncovalent entrapment among the pendant PEO chains and in separate experiments, its covalent coupling to PEO chains that had been end-activated with pyridyl disulfide groups. Analysis of peptide-LPS interactions using a quartz crystal microbalance with dissipation monitoring showed that upon introduction of LPS suspension to a flow cell housing a surface presenting tethered WLBU2, LPS located at the interface in a fashion irreversible to elution. Circular dichroism spectra recorded for suspensions of LPS and (silanized) hydrophobic silica nanoparticles to which WLBU2-triblock constructs had been adsorbed, confirmed that binding of LPS by tethered WLBU2 is mediated through peptide insertion and conformational change within the LPS membrane. LPS capture by tethered WLBU2 was detected in the presence of fibrinogen as well. However, that outcome is best considered tentative, as it was associated with potentially complex interactions between fibrinogen, LPS, and WLBU2, that remain uncharacterized. In summary, the results of this study strongly suggest that presentation of tethered WLBU2 within a sorbent device will enable the capture of endotoxin from suspension without reintroduction of degradation products to the circulating stream. Thus, they provide a rationale for hypotheses to drive further development of perfusion for the treatment of severe blood infections.Keywords: OWLS, Cationic Amphiphilic Peptide, Endotoxin, Peptide antibiotics, WLBU2, Endotoxins, Hemoperfusion, Bactericides, QCM-

Functionalization of Surfaces with Nisin in a Polyethylene Oxide Brush Layer

Infections in hospitals account for over 100,000 deaths per year. These infections occur at the hospital from complications following bacterial adhesion to intravenous catheters, coronary stents and other implanted devices. Another common problem is protein adsorption to the surface of the device and subsequent blood clotting. Methods for combating these issues have been previously studied using antimicrobial coatings consisting of a tri‐block polymer with a hydrophobic base and two hydrophilic tails called Pluronic® F108 and an antimicrobial agent, nisin; however studies have not been conducted to determine how long such coatings are effective. Experiments were designed to test the long term efficacy of an F108 coated, nisin loaded surface for killing the Gram positive bacteria, Pediococcus pentosaceus. The overall experimentation, consisting of aging nisin‐coated microspheres for selected periods of time, followed by assaying bioactivity to determine nisin effectiveness, lasted 28 days, with samples taken from the microsphere suspensions once each week. These samples were plated on MRS agar plates and P. pentosaceus was allowed to grow for 48 hours, after which the colony forming units were counted for each sample. The F108‐coated, nisin loaded layers showed greater activity retention in comparison to layers prepared with nisin in the absence of F108, but only in the final week of the study

Nisin adsorption to PEO-PPO-PEO tri-block copolymer layers and its resistance to elution by fibrinogen

While hydrophobic surfaces coated with the poly[ethylene oxide]-poly[propylene oxide]-poly[ethylene oxide] (PEO-PPO-PEO) surfactant Pluronic® F108 are highly resistant to plasma protein adsorption, the antimicrobial peptide nisin has been observed to adsorb in multilayer quantities at such surfaces, and the PEO chains themselves suggested to inhibit nisin exchange by blood proteins. But this had been investigated only with F108 bound by physical association between the hydrophobic surface and its apolar PPO block. In this work, nisin adsorption at hydrophobic, silanized silica surfaces coated with F108, and in separate experiments, coated with F108 that had been end-activated with nitrilotriacetic acid groups (EGAP-NTA), was detected in situ, by zeta potential measurements. The triblocks were covalently immobilized prior to the introduction of protein in each case. Zeta potential measurements were also used to evaluate fibrinogen adsorption, and the sequential adsorption behavior of nisin and fibrinogen, at bare hydrophobic and triblock-coated surfaces. Silica microspheres (1 µm diameter) were silanized with either allyldimethylchlorosilane (ADCS) or trichlorovinylsilane (TCVS). Silanized microspheres were incubated overnight in a solution of F108 or EGAP-NTA to allow for self assembly of a PEO layer. Coated microspheres were then subjected to γ-irradiation under water or in the presence of the triblock coating solution. Layer stability was quantified by its resistance to elution by SDS. Zeta potential changes indicated that pretreatment with TCVS, and γ-irradiation performed in the presence of the triblock coating solution, produced more stable triblock layers than were produced with ADCS. For this reason silanization only with TCVS was used in protein adsorption experiments. Introduction of fibrinogen to triblock-coated microspheres showed little change in zeta potential, indicating the presence of a steric repulsive barrier to fibrinogen adsorption. Introduction of nisin to triblock-coated microspheres showed a significant increase in zeta potential, a result of adsorption of the cationic nisin. In sequential adsorption experiments, the introduction of fibrinogen to "nisin-loaded" triblock layers caused a decrease in the zeta potential, consistent with the net negative charge of fibrinogen. This decrease was substantially more pronounced for TCVS-modified silica in the absence of triblock coatings, suggesting an enhanced resistance to nisin elution owing to its location in the PEO layer

Gallus GBrowse: a unified genomic database for the chicken

Gallus GBrowse (http://birdbase.net/cgi-bin/gbrowse/gallus/) provides online access to genomic and other information about the chicken, Gallus gallus. The information provided by this resource includes predicted genes and Gene Ontology (GO) terms, links to Gallus In Situ Hybridization Analysis (GEISHA), Unigene and Reactome, the genomic positions of chicken genetic markers, SNPs and microarray probes, and mappings from turkey, condor and zebra finch DNA and EST sequences to the chicken genome. We also provide a BLAT server (http://birdbase.net/cgi-bin/webBlat) for matching user-provided sequences to the chicken genome. These tools make the Gallus GBrowse server a valuable resource for researchers seeking genomic information regarding the chicken and other avian species

Detecting Molecular Rotational Dynamics Complementing the Low-Frequency Terahertz Vibrations in a Zirconium-Based Metal-Organic Framework

We show clear experimental evidence of co-operative terahertz (THz) dynamics observed below 3 THz (~100 cm-1), for a low-symmetry Zr-based metal-organic framework (MOF) structure, termed MIL-140A [ZrO(O2C-C6H4-CO2)]. Utilizing a combination of high-resolution inelastic neutron scattering and synchrotron radiation far-infrared spectroscopy, we measured low-energy vibrations originating from the hindered rotations of organic linkers, whose energy barriers and detailed dynamics have been elucidated via ab initio density functional theory (DFT) calculations. For completeness, we obtained Raman spectra and characterized the alterations to the complex pore architecture caused by the THz rotations. We discovered an array of soft modes with trampoline-like motions, which could potentially be the source of anomalous mechanical phenomena, such as negative linear compressibility and negative thermal expansion. Our results also demonstrate coordinated shear dynamics (~2.5 THz), a mechanism which we have shown to destabilize MOF crystals, in the exact crystallographic direction of the minimum shear modulus (Gmin).Comment: 10 pages, 6 figure

Saving Bones: a direct comparison of FTIR-ATR, whole bone percent nitrogen, and NIR

89th Annual Meeting of the American-Association-of-Physical-Anthropologists (AAPA), Los Angeles, CA, APR 15-18, 202

WKB analysis of relativistic Stern-Gerlach measurements

Spin is an important quantum degree of freedom in relativistic quantum information theory. This paper provides a first-principles derivation of the observable corresponding to a Stern-Gerlach measurement with relativistic particle velocity. The specific mathematical form of the Stern-Gerlach operator is established using the transformation properties of the electromagnetic field. To confirm that this is indeed the correct operator we provide a detailed analysis of the Stern-Gerlach measurement process. We do this by applying a WKB approximation to the minimally coupled Dirac equation describing an interaction between a massive fermion and an electromagnetic field. Making use of the superposition principle we show that the +1 and -1 spin eigenstates of the proposed spin operator are split into separate packets due to the inhomogeneity of the Stern-Gerlach magnetic field. The operator we obtain is dependent on the momentum between particle and Stern-Gerlach apparatus, and is mathematically distinct from two other commonly used operators. The consequences for quantum tomography are considered.Comment: 13 pages, no figures. Comments welcom

Tracking Thermal-Induced Amorphization of a Zeolitic Imidazolate Framework via Synchrotron In Situ Far-Infrared Spectroscopy

We present the first use of in situ far-infrared spectroscopy to analyze the thermal amorphization of a zeolitic imidazolate framework material. We explain the nature of vibrational motion changes during the amorphization process and reveal new insights into the effect that temperature has on the Zn-N tetrahedra.Comment: 5 pages, 3 figures, 2 table